Andreas S. Bommarius, Ph.D. (Georgia Institute of Technology)

Co-advisors:

Sven H. Behrens, Ph.D. (Georgia Institute of Technology)

Yury O. Chernoff, Ph.D. (Georgia Institute of Technology)

Committee members:

Julie A. Champion, Ph.D. (Georgia Institute of Technology)

M. G. Finn, Ph.D. (Georgia Institute of Technology)

STUDIES ON AMYLOID AGGREGATION AND CROSS-SPECIES PRION TRANSMISSION

Proper folding of protein molecules into their native structure is necessary to maintain function. Misfolding of proteins can reduce functionality as well as result in the formation of amorphous aggregates or ordered aggregates like amyloids. Amorphous aggregate formation during production, transport, and storage of protein-based biologics is a cause of concern in the biopharmaceutical industry as it results in a reduction in the efficacy or activity of the active pharmaceutical ingredient. On the other hand, ordered aggregation of proteins into amyloids (and their transmissible versions, prions) has been shown to result in several neurodegenerative diseases in humans and other mammals. While the effect of co-solutes including ions has been extensively studied in the context of measuring the stability of protein formulations and formation of disordered aggregates, there is limited information available on the effect of ions on the formation of ordered amyloid aggregates. In this thesis, we have investigated in detail the effect of presence of ionic co-solutes on the aggregation of amyloids.

Here, we have studied the efficiency of cross-transmission of the NM fragment of Sup35 protein, from three closely related species of the Saccharomyces sensu stricto group, namely S. cerevisiae, S. bayanus and S. paradoxus, amongst each other. Using ions of the Hofmeister series, we discerned the relative effects of protein sequence, seed conformation, and environment on the cross-species transmission of this protein. Further, investigation of the fibrillation of Amyloid beta-42 (Aβ₄₂) and Sup35NM in the presence of anions of the Hofmeister series at pH above and below their isoelectric points uncovered interesting differences in their aggregation behavior pointing to key differences in the aggregation mechanism and the biophysical/biochemical properties of these proteins. Lastly, we developed a computational model for amyloid aggregation kinetics and used it for global fitting of Sup35NM amyloid aggregation data. In all, this thesis expands the current knowledge of ion-specific effects on aggregation of amyloid proteins as well as the mechanisms of amyloid aggregation.

J. Brandon Dixon, PhD (George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology)

Committee:

Michael J Davis, PhD (Department of Medical Pharmacology & Physiology, University of Missouri)
Hanjoong Jo, PhD (Department of Biomedical Engineering, Georgia Institute of Technology)
Levi Wood, PhD (School of Mechanical Engineering, Georgia Institute of Technology)
Stanislav Emelianov, PhD (School of Electrical and Computer Engineering, Georgia Institute of Technology)

Functional Changes in Lymphatic Physiology in Response to Oscillatory Mechanical Stimuli

Lymphedema, a debilitating disease characterized by excess interstitial fluid accumulation in the extremities of the body, is suspected to be caused by dysfunctions in the lymphatic system. Elevated transmural pressure and wall shear stress in studies on isolated lymphatic vessels have been shown to modify the lymphatic vessel function, although focus have been put on functional changes in response to constant mechanical loading. However the underpinning molecular details and the frequency limitations of the lymphatic vessel response to dynamic pressure and shear stress waveforms are unknown. Hence the present work will try to quantify the effects of oscillatory mechanical forces on the function of lymphatic vessels by 1) Ex vivo quantification of the contractility of isolated lymphatic vessels modified in response to oscillatory shear stresses, 2) In vitro quantification of the calcium dynamics in lymphatic endothelial cells in response to oscillatory shear stress and stretch and 3) In vivo quantification of the change in lymphatic pumping metrics, obtained by NIR imaging, in response to steady and oscillatory external pressure waveforms in a rat model. This work will inform studies on molecular mechanisms leading to mechanosensitivity of lymphangions and will provide experimental evidence for improved physiotherapy techniques for lymphedema.

AGENDA

12:30 - 2:30 p.m.    Poster session and reception - Petit Atrium
2:30 - 3:30 p.m.    BioE Overview - Andrés García, Ph.D.
3:30 - 3:45 p.m.    Training Grant Information Session

• Cell and Tissue Engineering (CTEng) training grant - Andrés García, Ph.D.
• BioMaterials training grant - Christine Payne, Ph.D.

3:45 - 4:15 p.m. Course Advisement - Andrés García, Ph.D.
4:15 - 4:45 p.m. BioE Student Panel

• Marcus Walker - ECE
• Seleipiri Charles - BME
• Kelly Hyland - MSE
• Michael Hunckler - ME
• Jeffrey Noble - ChBE

4:45 - 5:15 p.m.    Peer Counseling - current students discuss classes they have taken
5:30 p.m.    Meet in atrium for outing with current BioE students, 5:45 p.m. departure

EDUCATION & OUTREACH - Host visitors from local schools and organizations, coordinate educational events such as Buzz on Biotechnology. This is a super-fun, capstone Petit Institute event that requires lots of hands, so sign up to help with hands-on science demos, lab tours, and seminars for eager/curious high school scientists!
 
COMMUNICATIONS - The communications committee is responsible for disseminating information about upcoming BBUGS events via the website, Mailchimp, and maintaining the mailing list. 
 
INDUSTRY - Collaborate with established professionals to host events such as workshops and site-visits to prepare graduate students for a career in industry.
 
POLICY - Engaging and increasing the policy interests of graduate students, particularly in areas related to biomedical and bioengineering research, such as public health, healthcare access and regulation of medical devices and therapeutics.
 
PROFESSIONAL DEVELOPMENT - Seminars and panel presentations to guide individuals at different stages of their careers with topics ranging from advisor selection to interviewing and negotiating job offers.
 
RESEARCH - Help chairs organize events pertaining to research on campus, networking with clinicians and exposure to the impacts that research brings to hospitals and businesses.
 
SOCIAL - Events to build community amongst bioengineering and bioscience graduate students through social events (football tailgates, etc.)
 
SERVICE - Help with various community service activities throughout the year such as informational sessions on the GT Ideas to Serve Competition and volunteering with local groups such as MedShare.
 
...something for EVERYONE!
 

BioE Day 2017 Agenda
Petit Biotechnology Building Atrium

12:00 p.m.      Keynote Speaker Introduction - Andrés García, Ph.D. 

12:05 p.m.      Keynote Address - Sean Coyer, Ph.D.  - W.L. Gore & Associates
                      "What’s Next? Tips and Tricks to Life after Grad School"

1:00 p.m.        Lunch

                       Poster Competition - Suddath Seminar Room 1128

2:00 p.m.        Rapid Fire Competition

3:00 p.m.        Coffee break

3:15 p.m.        Faculty introduction of the BioE "Outstanding Paper Award" - Laura                                    O'Farrell, D.V.M.

3:20 p.m.        Presentation by Outstanding BioE Paper Winner - Yogi Patel (Butera Lab)

3:35 p.m.        Award Presentations

4:00 p.m.        Presentation by Outstanding BioE Advisor Winner - Ross Ethier, Ph.D.

4:30 p.m. - 6:30 p.m.   Cookout and lawn games - BioTech Quad

REGISTER HERE

Craig Forest, Ph.D.  (Mechanical Engineering) 
COMMITTEE:    

Brian Hammer, Ph. D. (Georgia Institute of Technology)

Faramarz Fekri, Ph. D. (Georgia Institute of Technology)

Mark Styczynski, Ph. D. (Georgia Institute of Technology)

Peter Hesketh, Ph. D.  (Georgia Institute of Technology)

Dynamics of molecular communication in bacteria within microfluidic environments

Biosensors exploiting communication within genetically engineered bacteria are becoming increasingly important for monitoring environmental changes. Recently these sensors have miniaturized towards microfluidics due to the greater control they provide over things such as the population density and dynamic inputs. Although great strides have been made to study a single strain of bacteria in a microfluidic device, there is still a need to be able to study two populations of bacteria communicating with one another. Currently, there are a variety of mathematical models for understanding and predicting how genetically engineered bacteria respond to molecular stimuli in bulk culture environments, but when applied to microfluidics and to complex time-varying inputs, the shortcomings of these models have become apparent. The effects of microfluidic environments such as low oxygen concentration, increased biofilm, diffusion limited molecular distribution, and higher population densities strongly affect rate constants for gene expression not accounted for in previous models. In this work we developed a microfluidic platform capable of housing two bacteria populations to study the bacterial communication with dynamic control of inputs, long-term experimentation, and no cross contamination. We also developed a mathematical model that accurately predicts the biological response of the bacteria populations communicating in the microfluidic environment. This work can serve as a valuable tool in understanding genetically engineered bacteria and improving biosensor design capabilities, opening the door for sensors that adapt to environmental dynamics and communicate with each other.

BioE Day 2016 Agenda
Petit Biotechnology Building Atrium

12:00             Andrés García, Ph.D. introduces Keynote Speaker, Bob Nerem, Ph.D.

12:05-12:55   Keynote Address - "Bioengineering: Building a New Discipline, a Personal
                      Journey” - Bob Nerem, Ph.D., 5-10 minutes of Q&A

1:00                Lunch

                       Poster Competition - Suddath Seminar Room 1128

2:00                Rapid Fire Competition

3:00                Coffee break

3:05                Wilbur Lam, M.D., Ph.D. introduces student Jordan Ciciliano

3:10-3:25        Presentation by Outstanding BioE Paper Winner (Jordan Ciciliano)

3:30-3:45        Presentation by Outstanding BioE Advisor Winner (Krishnendu Roy, Ph.D.)

3:50                Award Presentations

4 - 6:30 p.m.  Cookout and lawn games - BioTech Quad

REGISTER HERE

Committee:

Andrés García, Ph.D. (Georgia Institute of Technology)

Susan Thomas, Ph.D. (Georgia Institute of Technology)

Approaches to Improve Expression and Specificity of an Antibody Probe Against Fibronectin

Phage display is a convenient method to select proteins of interest based on binding affinity. The Barker lab recently used this technology to discover an antibody fragment (scFv), termed H5, capable of selectively binding to the integrin binding domain of fibronectin (Fn) under a strained configuration, typically due to forces exerted on the extracellular matrix (ECM) by cells.

Large scale production of H5 scFv is hindered by non-optimized codons and suspected protein toxicity, since the E. coli strain producing the protein grew poorly at normal temperatures. Moreover, the transfected vector containing H5, pIT2, appeared to be degraded in consecutively selected bacterial cultures, as suggested by the isolation of significantly shorter than expect plasmids.

After significant effort, reconstruction of the pIT2 vector sequence was accomplished from multiple colonies and cross referencing with the provided anti-ubiquitin scFv antibody fragment, and the complete DNA sequence of H5 was recovered. The sequence was codon optimized for expression in an E. coli strain engineered for high levels of scFv production. Furthermore, the H5 DNA was recombined with error prone PCR, to generate a library of random mutants, which was transformed into a stable, E. coli strain. This library will be panned on the targets again through phage display in order to find an improved version of H5, defined by more selective binding to the extended conformation of the integrin binding domain of Fn.

Susan Thomas, Ph.D. (Georgia Institute of Technology)

Committee:
Andrés García, Ph.D. (Georgia Institute of Technology)
Wilbur Lam, Ph.D. (Georgia Institute of Technology & Emory University)
John McDonald, Ph.D. (Georgia Institute of Technology)
Cheng Zhu, Ph.D. (Georgia Institute of Technology)

ELUCIDATING THE CONTRIBUTIONS OF CELLULAR AND MICROENVIRONMENT CHARACTERISTICS ON CELL ADHESION PROCESSES IN FLOW

Circulating cell recruitment is critical to a variety of physiological and pathophysiological processes and occurs amidst the high shear environment of the vasculature via a multistep rolling to firm adhesion cascade. Cells initially engage the vascular endothelium through interactions between endothelial-presented selectins and their corresponding ligands presented by circulating cells. These interactions precede firm adhesion and arrest and eventually transmigration across the endothelium for tissue infiltration. Since many cell subtypes including leukocytes and metastatic cancer cells employ this mechanism to facilitate their escape the vasculature, understanding differences in cell-subtype adhesive behavior can inform the development of targeted therapeutics that interfere with metastatic cell transport, while leaving physiologically important immune cell recruitment mechanisms intact. As such, the overall objective of this proposal is to explore how selectin-mediated adhesion 1) is regulated by the biochemical and biophysical microenvironment of the vasculature and 2) varies among different cell subtypes. Through the use of in vitro fluidic methodologies in conjunction with innovative single-cell analyses we expect to elucidate key differences in the selectin-dependent adhesive behavior of metastatic versus leukocytic cells in order to inform targeted drug development and dosing strategies for the cell-subtype selective interference of cell adhesion.

Committee:

• Cyrus K. Aidun, Ph.D. (Georgia Institute of Technology)
• Wei Sun, Ph.D. (Georgia Institute of Technology)
• F. Levent Degertekin, Ph.D. (Georgia Institute of Technology)
• Joseph H. Gorman, M.D. (University of Pennsylvania)
• Vinod H. Thourani, M.D. (Emory University)

Wilbur Lam, M.D., Ph.D. (Georgia Institute of Technology & Emory University)

Committee:

Brandon Dixon, Ph.D. (Georgia Institute of Technology)

Todd Sulchek, Ph.D. (Georgia Institute of Technology)

Susan Thomas, Ph.D. (Georgia Institute of Technology)

Hua Wang, Ph.D. (Georgia Institute of Technology)

DEVELOPING MICROFLUIDIC SYSTEMS TO DECOUPLE BIOPHYSICAL AND BIOCHEMICAL ASPECTS OF HEMATOLOGICAL PROCESSES

Recent research has revealed that cells dynamically sense and respond to their physical microenvironments. For instance, in hematology specifically, it was shown that shear mediated red blood cell (RBC) deformation results in ATP release, and that platelets attenuate contraction force based on substrate stiffness. The objective of this proposal is thus to create microfluidic systems in which the biophysical and biochemical aspects of hematological processes can be independently investigated. More specifically, this proposal will present novel microfluidic devices: an “endothelial”-ized, T-junction to elucidate the biophysical processes that define the mechanism of action of the ferric chloride thrombosis model; a micropillar array to examine the physical effect of a geometrically relevant, non-biological matrix on platelet and RBC activity; and an electrospun fibrinogen mesh device and a micro-slit device to define the physical parameter space (shear, time of deformation, cell stiffness) that governs RBC fragmentation. Microfluidic platforms allow for real-time, microscopic evaluation of cell response (via brightfield morphology and immunostaining) and precise spatiotemporal control of system inputs and flow characteristics, including shear stress. The knowledge gained by successfully decoupling the biophysical and biological aspects of hematology can result in improved diagnostic assays for blood cell activity and new targets for therapeutics. 

J. Brandon Dixon, Ph.D. (ME/Georgia Institute of Technology)

Committee:

Andrés J. García, PhD (Georgia Institute of Technology)

C. Ross Ethier, PhD (BME/(Georgia Institute of Technology)

Michael Davis, PhD (BME/Georgia Institute of Technology & Emory University)

Mariappan Muthuchamy (Medical Physiology/Texas A&M)

Role of Mechanical Microenvironment on the Regulation of Lymphatic Function and Health

Failure of lymph fluid transport plays an important role in pathologies, such as lymphedema and lymphacele after organ donation. The lymphatic system plays a critical role in maintaining fluid homeostasis in all of the soft tissue of the body. Its ability to transport interstitial fluid is partially dependent on the intrinsic pumping capacity of lymphatic smooth muscle cells. Recently, our lab has shown that lymphatic collecting vessels near an injury never return to pre-injury levels of pumping and lymph transport, but factors that impact collecting vessel phenotype are poorly understood. The central hypothesis of this work is that the components of the extracellular matrix (ECM) and mechanics of the lymphatic microenvironment play a central role in the contractile phenotype of lymphatic muscle cells (LMCs). 

Committee: 

Wilbur A. Lam, MD, PhD (Georgia Institute of Technology & Emory University)

Todd C. McDevitt, PhD (Gladstone Institutes)

John F. McDonald, PhD (Georgia Institute of Technology)

Paula M. Vertino, PhD (Emory University)

“Cellular Stiffness as a Sorting-compatible Indicator of Stem Cell Potency”

Due to their characteristic properties of self-renewal and differentiation, stem cells hold the capacity to serve as phenotype-specific cell factories for various regenerative medicine and tissue engineering applications. However, current phenotyping techniques, which typically employ multiple surface protein-specific antibodies, are often insufficient to identify or enrich cells of a target phenotype. An improved technique that could select target cells could be used to purify starting cell populations for directed differentiation protocols or to enrich specific terminally differentiated phenotypes for tissue engineering.

The goal of this project is to investigate cellular mechanical parameters as stem cell phenotype markers to complement the currently available biomolecular markers. This objective was accomplished through 1) the establishment of cell stiffness as a single-cell marker of potency in both mesenchymal stem cells, which give rise to cells of the connective tissue, and limbal stem cells, which replenish the cornea, 2) the development of a method to compare cell mechanics and gene expression at the single-cell level, which will enable more detailed studies of the relationships between cell phenotype, mechanics, and structure, and 3) the determination that pluripotent embryonic stem cells, which are softer than their differentiated progeny, can be enriched using a cell stiffness-based microfluidic sorting device, as assessed by potency-related morphological and genetic factors. Ultimately, this project established cell stiffness as a marker of stem cell differentiation in various cell systems, with applications to label-free selection of target cell phenotypes.

Robert E. Guldberg, PhD, (School of Mechanical Engineering, Georgia Institute of Technology)

Todd C. McDevitt, PhD, Gladstone Institutes

Committee:

Johnna S. Temenoff, PhD (Department of Biomedical Engineering, Georgia Institute of Technology)

Krishnendu Roy, PhD (Department of Biomedical Engineering, Georgia Institute of Technology)

Tom Koob, PhD (MiMedx Group, Inc.)

Engineering an Improved Cartilage Repair Strategy Combining Cells and ECM-derived Materials

Osteoarthritis (OA) is the leading cause of disability in the United States and one in two people are expected to develop symptomatic knee OA by age 85. The avascularity, low cellularity, and slow proliferation of chondrocytes all limit the natural regenerative capacity of cartilage in addition to the inflammation prevalent in the joint space. Cell therapies, such as autologous chondrocyte implantation (ACI), offer promising options for treating persistent cartilage lesions, but the inability to expand chondrocytes to sufficient numbers without adversely affecting their phenotype remains a significant problem for graft success. ACI is not indicated for cartilage damage associated with osteoarthritis (OA) or other inflammatory diseases, however, and this lack of efficacy is attributed to the inflammatory environment cells are exposed to, since multiple inflammatory mediators have been shown to play a pivotal role in the initiation and perpetuation of OA. Anti-inflammatory therapies with single molecular inhibitors are unable to effectively modulate the complex inflammatory environment presented in OA. Thus, novel therapies that are capable of modulating multiple signaling pathways and cell types are an attractive alternative to address OA-associated inflammation.

Therefore, the objective of this proposal was to engineer an improved cartilage repair strategy by combining cells and ECM materials to address problems with both cartilage repair and OA-associated inflammation. We developed decellularized cartilage microcarriers that retain endogenous extracellular matrix proteins to both expand and deliver chondrocytes while retaining their phenotype. We also characterize the effects of aggregation, culture conditions, and donor variability on the ability of mesenchymal stem cell (MSC) immunomodulation of OA. To this end, we quantified MSC paracrine factor production, suppression of activated synoviocyte inflammation, and therapeutic efficacy in the rat medial meniscal transection (MMT) rat model of OA. Furthermore, we investigated the interaction between MSCs and human amniotic membrane and the influence of cell-cell and cell-ECM therein on the modulation of inflammation, both in vitro and in vivo. Overall, this work broadens current understanding of cartilage tissue engineering and immunomodulation via ECM and stem cell-based therapies, providing valuable information that can be used to develop strategies to improve efficacy of osteoarthritis treatments. 

Craig R. Forest, PhD

Georgia Institute of Technology, G. W. Woodruff School of Mechanical Engineering

Committee:

R. Clay Reid, MD

Allen Institute for Brain Science

Machelle T. Pardue, PhD

Georgia Institute of Technology, Coulter Department of Biomedical Engineering

Peter J. Yunker, PhD

Georgia Institute of Technology, School of Physics

Todd Sulchek, PhD

Georgia Institute of Technology, G. W. Woodruff School of Mechanical Engineering

Batch processing of brain tissue sections for millimeter-scale serial section transmission electron microscopy connectomics

The field of connectomics has emerged a promising approach for exploring the nature of neural circuits. A millimeter-scale connectome—a neuron-to-neuron wiring diagram of a neural circuit—potentially contains significant information regarding information processing and memory. The field is held back, however, by the difficulty in consistently and rapidly collecting neuroanatomical datasets with serial section transmission electron microscopy (ssTEM). In the cerebral cortex, for instance, a local circuit is contained in a cubic millimeter, but single sections—obtained by cutting brain samples with a diamond knife—must be “ultrathin” (< 40 nanometers), thus requiring 25,000 consecutive sections to be processed. Currently, the processing of ultrathin sections remains an unsolved problem that is necessary for the advancement of ssTEM connectomics. The goals of this proposal are: (1) design, model, and test a novel device that uses hydrodynamic forces and curvature-induced capillary interactions for the transport and trapping of ultrathin sections, (2) design, implement, and characterize batch processing of single sections to enable reliable processing of thousands of serial sections, and (3) design, test, and characterize automated batched section processing, enabling high-throughput and reliable section processing. In total, these aims comprise a novel platform for section processing for millimeter-scale ssTEM connectomics studies.

Summary: Autoimmune disorders are estimated to be among the top ten leading causes of death among women of all ages below 65, for which available treatments include systemic immunosuppressants that cause serious long-term side effects. There is hence a growing interest to engineer mechanisms of inducing target-specific immune tolerance with biomaterials particularly professional antigen presenting cells namely dendritic cells (DCs). DCs previously studied in the context of biomaterials have been discovered to elicit differential responses to biomaterials suggesting that materials on their own have the ability to stimulate specific DC phenotype. As the phenotype of DCs is a key mediator of downstream adaptive immune responses that lead to normal or aberrant immunity, there is increasing interest in delineating the underlying mechanisms of material-cell interaction. In this proposal, we initially investigate the role played by DCs in the adjuvant effect shown by certain materials such as poly lactic-co-glycolic acid (PLGA) and further exploit the differential nature of the response towards agarose compared to PLGA, to develop solely biomaterial-based methods in inducing antigen-specific immune tolerance in an in vivo mouse model. Moreover, DCs can be locally treated with specific immunomodulators rather than biomaterials to express a tolerogenic phenotype that can trigger antigen-specific immunoregulation. As a second and distinct approach, in this proposal, we examine the possibility of developing the spatiotemporally controlled delivery of immunomodulators from a single implantable biomaterial niche. The design of such a delivery device would call for not only incorporating a strategy for DC phenotype modulation but also a technique for promoting endogenous DC recruitment upon in vivo implantation; thus it would enable the localized delivery of factors while promoting systemic circulation of in situ primed DCs for effective downstream immune function, a feature commonly lacking in existing treatments of autoimmune diseases. Finally, the efficacy of this technique will be assessed in the context of an autoimmune disease model, to explore its potential use as a therapeutic cure for individuals with autoimmune disorders.

Advisor:

Julia E. Babensee, PhD

Wallace C. Coulter Department of Biomedical Engineering

Georgia Institute of Technology and Emory University

Thesis Committee:

Julie Champion, PhD

School of Chemical and Biomolecular Engineering

Georgia Institute of Technology and Emory University

Edward Botchwey, PhD

Wallace C. Coulter Department of Biomedical Engineering

Georgia Institute of Technology and Emory University

Susan Thomas, PhD

George W. Woodruff School of Mechanical Engineering

Georgia Institute of Technology and Emory University

 Krishnendu Roy, PhD

Wallace C. Coulter Department of Biomedical Engineering

Georgia Institute of Technology and Emory University

Thesis Committee Members

Advisor: Julie A. Champion, Ph.D. - School of Chemical and Biomolecular Engineering, Georgia Institute of Technology

Jennifer K. Leavey, Ph.D. - School of Biology, Georgia Institute of Technology

Krishnendu Roy, Ph.D. - Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology 

Mark R. Prausnitz, Ph.D. - School of Chemical and Biomolecular Engineering, Georgia Institute of Technology

Bao-Zhong Wang, Ph.D. - Department of Microbiology and Immunology, Emory University School of Medicine

Highly conserved pathogen proteins are essential for broadly cross-protective vaccines, but tend to be poorly immunogenic. Protein nanoparticle vaccines made from conserved influenza matrix protein 2 and hemagglutinin trigger specific, adaptive immune responses that soluble protein cannot. Without excipients or adjuvants, protein nanoparticles eliminate the possibility of off-target immune responses, and their abiotic nature makes them amenable to cold chain-independent storage and use. The mechanisms by which protein nanoparticles enhance component protein immunogenicity are still not well understood. Protein nanoparticles will be made from hen egg ovalbumin and influenza proteins to examine dendritic cell responses in vitro and adaptive immune responses in vivo. The goals of this project are two-fold: to understand the immunological basis behind protein nanoparticle adjuvancy, and to improve this adjuvancy with studies into nanoparticle stability, enhancing endosomal buffering, and molecular adjuvants as nanoparticle coatings. This project aims to assess the viability of protein nanoparticles as a vaccine delivery platform.

Robert E. Guldberg, Ph.D. (Georgia Institute of Technology)

Committee:

Rudolph L. Gleason, Ph.D. (Georgia Institute of Technology)

Manu O. Platt, Ph.D. (Georgia Institute of Technology)

Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

M. Neale Weitzmann, Ph.D. (Emory University)

HIV-1 Protein Effects on Skeletal Development and Bone Tissue Regeneration

HIV and AIDS have drastically compromised the quality of life and lifespan for millions of people worldwide. Since its inception in 1996, highly active antiretroviral therapy (HAART) has dramatically increased the life expectancy of those infected with HIV to nearly that of the general population. However, HIV-infected individuals on treatment are now faced with the premature onset of disorders traditionally associated with the natural aging process including cardiovascular disease, neurocognitive decline, and osteoporosis. It is well understood that HIV infection alone is a risk factor for osteopenia and osteoporosis and subsequently for fragility fractures. More recently, studies have established an increase in fracture prevalence in the HIV-infected population. However, the effects of HIV infection, HIV proteins, and antiretroviral drugs on bone are difficult to investigate in the clinical setting. Traditional risk factors for osteoporosis – such as vitamin D deficiency, drug use, smoking, and alcohol use – can complicate any observed effects that HIV or HAART drugs may have. Despite the increased risk for fracture and fracture prevalence in the HIV-infected population, few studies have investigated the potential for HIV infection to adversely affect fracture healing. Considering the critical role of immune cells in the fracture healing process, bone repair may be impaired or delayed with HIV infection.

The goal of this project is to determine the effects of HIV-1 proteins on skeletal development and bone tissue regeneration through the use of two HIV-1 transgenic animal models. This will be accomplished through three specific aims:

1. I.                   Investigate the longitudinal skeletal changes in the growing HIV-1 transgenic rat.
   1. II.                Determine the bone regeneration capacity in the HIV-1 transgenic rat using a BMP-2-mediated segmental bone defect repair model.
   2. III.             Characterize the skeleton of the HIV-1 transgenic mouse and the effects of HAART drug treatment.

This project will contribute to the growing body of knowledge on the effects of HIV infection on skeletal health and present initial investigations into the effects of HIV on the bone repair process. In addition, it will characterize two HIV-1 transgenic animal models as functional surrogates for studying skeletal disorders in the context of HIV.

Michelle Dawson, Ph.D.

Raphael Lee, M.D., Sc.D. (University of Chicago) 
Todd Sulchek, Ph.D.
Johnna Temenoff, Ph.D.

Directing the Migration of Mesenchymal Stem Cells and Bystander Cells using Superparamagnetic Iron Oxide Nanoparticles

 Cell migration plays an important role in numerous normal and pathological processes. The physical mechanisms of adhesion, protrusion/extension, contractions, and polarization can regulate cell migration speed, persistence time, and downstream effects in paracrine and endocrine signaling. Methods for understanding these biophysical and biochemical responses to date have been limited to the use of external forces acting on mechanotransductive receptors. Additionally, as the use of magnetic nanoparticles for cell tracking and cell manipulation studies continues to gain popularity, so does the importance of understanding the cellular response to mechanical forces caused by these magnetic systems.

This thesis work utilizes superparamagnetic iron oxide nanoparticles and static magnets to induce an endogenous magnetic force on the cell membrane. This cell manipulation model is used to better understand the mechanobiologal responses of mesenchymal stem cell to SPIO labeling and endogenous force generation. Directionally persistent motility, cytoskeletal reorganization, and altered pro-migratory cytokine secretion is reported in this thesis as a response to SPIO based cell manipulation.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology

Committee Members:

Andreas S. Bommarius, Ph.D.

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology

Michael J. Leamy, Ph.D.

The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology

Pamela Peralta-Yahya, Ph.D.

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology

Peng Qiu, Ph.D.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology

Title: Computational Inference of the Structure and Regulation of the Lignin Pathway in Panicum virgatum

Abstract: Switchgrass is a prime target for biofuel production from inedible plant parts and has been the subject of numerous investigations in recent years. Yet, one of the main obstacles to effective biofuel production remains to be the major problem of recalcitrance. Recalcitrance emerges in part from the 3-D structure of lignin as a polymer in the secondary cell wall. Lignin limits accessibility of the sugars in the cellulose and hemicellulose polymers to enzymes and ultimately decreases ethanol yield. Monolignols, the building blocks of lignin polymers, are synthesized in the cytosol and translocated to the plant cell wall, where they undergo polymerization. The biosynthetic pathway leading to monolignols in switchgrass is not completely known, and difficulties associated with in vivo measurements of these intermediates pose a challenge for a true understanding of the functioning of the pathway. The proposed work aims to apply a systems biological modeling approach to address this challenge.

Robert J. Butera, Ph.D. (Georgia Institute of Technology, School of ECE and Dept. of BME)

Thesis Committee:

Chris Rozell, Ph.D. (Georgia Institute of Technology, School of ECE)

Laura O Farrell, DVM, Ph.D. (Georgia Institute of Technology, GTRC)

Arthur English, Ph.D. (Emory University, Dept. of Cell Biology)

Thomas Burkholder, Ph.D. (Georgia Institute of Technology, School of Applied Physiology)

Neural modulation of liver function to regulate lipid and glucose metabolism

Mammalian blood glucose concentrations are maintained within well-defined biological limits despite considerable fluctuations in the rate at which glucose is obtained from food and utilized by tissues. Of all homeostatic mechanisms, maintenance of blood glucose levels is finely regulated, and one in which the liver and the central nervous system play a prominent role. The liver can add or remove glucose from circulating blood in accordance with the demands of the body, which are transmitted by both hormonal and neural messaging. The hormonal messaging system is well understood, unlike the neural messaging system. Hormonal messaging is mediated by insulin and glucagon, which have opposite effects on blood glucose levels. Studies have shown that frequency-dependent electrical stimulation of peripheral nerves innervating the liver can lead to increased output of glucose by the liver. Studies have also shown that transection of the peripheral nerves innervating the liver may lead to changes in lipid and glucose metabolism. However, the magnitude and temporal scale with which these effects can be regulated remains unclear. In addition, whether electrical stimulation of peripheral nerves can lead to a decrease in blood glucose levels also remains unclear. The goal of this proposal is to investigate (1) the extent to which activity in peripheral nerves innervating the liver can be altered via electrical stimulation to regulate lipid and glucose metabolism and (2) how blood glucose levels are encoded in peripheral nerve activity for homeostatic regulation by the central nervous system. These goals will be accomplished via three specific aims: First, I will characterize the effects of electrical stimulation in a frequency-dependent manner to excite or inhibit activity in autonomic and somatic peripheral nerves. Second, I will use electrical stimulation to excite or inhibit activity in autonomic nerves innervating the liver and quantify the effects on lipid and blood glucose metabolism. Third, I will use statistical modeling methods to decode autonomic nerve activity communicated to the central nervous system and correlate nerve activity to blood glucose levels. I hypothesize that decoding liver-specific autonomic nerve activity can be used to optimize electrical stimulation, resulting in a closed-loop approach to regulate lipid and glucose metabolism via neural messaging. Together, these experiments will explore the dynamics underlying neural control of lipid and glucose metabolism.

 Thesis Committee Members:

Julia Babensee, Ph.D.

Manu Platt, Ph.D.

Brandon Dixon, Ph.D.

Zvi Schwartz, DMD, Ph.D.

 Title: 24R,25-dihydroxyvitamin D3 based Therapy for the Treatment of Knee Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease, which according to the center for disease control (CDC), affects nearly 30 million people in the United States. The disease is characterized by joint inflammation, which leads to chondrocyte apoptosis, cartilage matrix degradation, loss of joint function, and eventually total knee replacement. Current drug therapies aim to ease pain and reduce local inflammation; however, no drug exists that effectively alleviates the disease condition without significant side effects that are typical to anti-inflammatory drugs. Therefore, an unmet medical demand exists for development of tissue-engineering strategies to promote articular cartilage repair and regeneration to treat OA. 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] is an attractive option for articular cartilage repair because of its anti-apoptotic properties in cartilage cells. The overall objective of this work was to prevent degeneration of articular cartilage through the development of a 24R,25(OH)2D3 based therapy, enhancing chondrocyte survival and cartilage repair. The central hypothesis was that 24R,25(OH)2D3 has therapeutic effects on osteoarthritic articular chondrocytes, reducing cell apoptosis and factors contributing to joint inflammation and  cartilage degradation, thus promoting articular cartilage repair and regeneration.

BioEngineering PhD Defense Presentation

March 19, 2015, 3:00 pm

Suddath Room, IBB

Advisor: Manu Platt, Ph.D.

Thesis Committee Members:

Rudy Gleason, Ph.D.

Suzanne Eskin, Ph.D.

W. Robert Taylor, Ph.D.

Roy Sutliff, Ph.D.

Title: The Role of HIV-1 Tat and Antiretrovirals on Cathepsin Mediated Arterial Remodeling

Major advances in highly active antiretroviral therapies (ARVs) have extended the lives of people living with HIV, but there still remains an increased risk of death by cardiovascular diseases (CVD). HIV proteins and ARVs have been shown to contribute to cardiovascular dysfunction with effects on the different cell types that comprise the arterial wall. In particular, HIV-1 transactivating factor, Tat, is a cationic polypeptide that binds to endothelial cells, inducing a range of responses that have been shown to contribute to vascular dysfunction. It is well established that hemodynamics also play an important role in endothelial cell mediated atherosclerotic development where upon exposure to low or oscillatory shear stress, such as that found at branches and bifurcations, endothelial cells contribute to proteolytic vascular remodeling, by upregulating cathepsins, potent elastases and collagenases. Mechanisms to understand the influence of HIV proteins on shear mediated vascular remodeling have not been fully elucidated.

The objective of this thesis is to explore the effects of pro-atherogenic shear stress, HIV proteins, and antiretroviral therapies on the vasculature using in vivo and in vitro models. The goals are to determine the effects of pro-atherogenic shear stress conditions coupled with these HIV factors on proteolytic activity  and determine downstream regulatory mechanisms using in vitro culture systems and the HIV-transgenic mouse model. 

AGENDA

Thursday, March 26th , 2015

2:30-4:30pm Optional Tour of Emory
Meet in IBB Atrium @ 2:15pm

5:00pm - BioE Social
Marlow’s Tavern
950 West Peachtree Street
*Meet there or walk from IBB lobby @ 4:45pm

Friday, March 27, 2015

9:45am - BioEngineering Overview- Andrés García, PhD

10:45am - BGA (BioEngineering Graduate Association) student panel

11:30am - Lunch and poster session

1:00pm - Faculty Interviews

5:30 - BioE Social
Ray’s New York Pizza
26 5th Street NW- Tech Square
*Meet there or walk from IBB lobby @ 5:15pm

Committee:

Brian Hammer, PhD (Georgia Institute of Technology)

Faramarz Fekri, PhD (Georgia Institute of Technology)

Mark Styczynski, PhD (Georgia Institute of Technology)

Peter Hesketh, PhD  (Georgia Institute of Technology)

Dynamics of Molecular Communication in Bacteria within Microfluidic Environments

Advisor: Rudy Gleason, Ph.D.

Thesis Committee Members:
Manu Platt, Ph.D.
W. Robert Taylor, MD, Ph.D.
Roy Sutliff, Ph.D.
Hanjoong Jo, Ph.D.
J. Brandon Dixon, Ph.D.

 
Biomechanics and Modeling Methods for Quantifying Mechanically-mediated Disease Progression in Neglected Populations

It is well known that biological tissue grows and remodels in response to changes in mechanical loading. Arteries and lymphatic vessels share many similar mechanical loads including luminal pressure, axial force, and fluid shear force on the endothelium. Diseases of vascular systems have previously been associated with deviations from a hypothesized “preferred” homeostatic mechanical environment and maladaptive growth and remodeling. Mechanically-mediated disease development affects many populations, but developing nations face challenges that are unique due to disease burdens that are region-specific. Treatment strategies for HIV have resulted in HIV-positive patients living longer lives, but these patients also suffer from non-AIDS-related comorbidities including vascular remodeling and accelerated progression of cardiovascular disease. Similarly, lymphatic filariasis often leads to lymphedema, a condition characterized by tissue swelling and fibrosis as well as remodeling of the lymphatic vasculature. Disease burden in sub-Saharan Africa is due in large part to pathologies such as these; yet, studies investigating the role of biomechanics in disease development in these populations are limited. Thus, the purpose of this dissertation is to develop novel experimental and theoretical frameworks for the study of mechanically-mediated diseases of the arterial and lymphatic vasculature that are commonly seen in developing nations with the ultimate intention of identifying key parameters that contribute to tissue growth and remodeling leading to disease progression.

     Dr. Peter Hesketh, Chair (ME)

    Dr. Alexander Alexeev (ME)

    Dr. J. Brandon Dixon (ME)

    Dr. Hang Lu (ChBE)

     Dr. Todd Sulchek (ME)

Title: Mixing and Sampling in a Microfluidic Channel Using Rotating Magnetic Microbeads

The objective of this research proposal is to create and study the use of a bed of rotating magnetic microbeads (3µm diameter) in a channel for mixing in a microfluidic channel and for capturing particles from a dilute fluid sample in a microfluidic channel. Rotation of the magnetic microbeads is created by actuating the beads via magnetized pieces of permalloy, an alloy of nickel and iron. These pieces of permalloy will be patterned onto glass wafers via microfacbrication techniques yielding features less than 10µm in size. The study will involve quantifying the effectiveness of both mixing and capturing using three different geometrical layouts of these features with multiple channel heights. For each geometry and channel height, multiple flowrates will be measured. Mixing will be characterized using two phase flow and quantified by examining the variance in fluorescent intensity. Capture will be quantified by taking real time videos of captured fluorescent particles. Capture of the fluorescent particles is performed by binding of functionalized proteins on the surface of the microbeads and fluorescent particles. This work will be used to build a higher throughput, multiplexed microfluidic device. 

Hang Lu, Ph.D. (Chemical and Biomolecular Engineering)

Committee Members:

Robert Butera, Ph.D. (Electrical and Computer Engineering)

Patrick McGrath, Ph.D. (Biology)

Lena Ting, Ph.D. (Biomedical Engineering)

Patricio Vela, Ph.D. (Electrical and Computer Engineering)

Title: All-optical white noise analysis of mechanosensory neural circuits in Caenorhabditis elegans

Project Summary:

The human brain is a system that processes sensory information from the environment to output behavioral responses. A fundamental question in neuroscience is how the neural circuitry calculates the appropriate output from a given input, or in terms of systems analysis, what are transfer functions that describe this system’s function? A key challenge in answering this question is the overwhelming complexity of this system. Another challenge is acquiring accurate output measurements while simultaneously controlling the input of the system. C. elegans serves as a useful model organism in answering this question by addressing and overcoming both of these issues. First, the C. elegans’ nervous system contains only 302 neurons, and is the only organism that has its entire connectome mapped. Second, it has easily manipulated genetics, high progeny number, and a transparent body, allowing for high-throughput calcium imaging, optogenetics, and behavior tracking experiments. In my thesis, I will develop a platform that can precisely control neuronal activity with optogenetics, while simultaneously measuring neuronal activity with calcium imaging and behavioral output with computer vision tools in order to perform white-noise analysis. This will allow for estimation of impulse responses that characterize C. elegans neural circuitry, providing accurate models of its function. This method will be applied to two mechanosensory circuits in order to compare their spatial and temporal properties. 

                  Dr. Nick Willett (BME, BioE, Department of Orthopedics) Emory University, Georgia Institute of Technology

                  Dr. Joseph Williams (Department of Surgery) Emory University

Design of Maxillofacial Implants for Cosmetic and Reconstructive Procedures           

Maxillofacial surgery can be used to help appearance and restore function.  Often there is a need to provide additional volume with soft tissue properties. This works explores the use of a new biomaterial invented at GT with soft tissue properties as possible maxillofacial implants to provide volume.  The implants are for restoring speech function in cleft palate patients presenting velopharyngeal insufficiency and providing volume to reduce the nasolabial folds in order to create a more youthful appearance. 

We have developed facial implants for the nasolabial fold and lip plumping to address low efficiency of the current methods employed for dermal fillers by providing both long-term usage as well as removability. Furthermore, an insertion method and insertion tools were developed to facilitate the implantation for the surgeons.

Regarding the reconstructive aspects of the maxillofacial implants, we have developed a pharyngeal implant aiming to reduce the gap between the pharyngeal implant and the velum (soft palate) of 20% of patients presenting a cleft palate. This implant will allow the care team to delay the palatoplasty in order to not hinder palatal growth in patients. The material used for the implants can also be used to better the current obturators by replacing the acrylic, posterior portion. The main current obturators are the nance obturator and custom acrylic obturators, deemed uncomfortable for the patients due to the hardness of the material. The design process for the implants and the novel obturator involved the optimization of material and shape, taking into consideration mechanical properties of the implants’ surrounding tissues, the anatomy of each feature being enhanced as well as potential implantation modes. 

School of Mechanical Engineering, Georgia Institute of Technology

Co-Advisor: Edward Botchwey, Ph.D. - Department of Biomedical Engineering, Georgia Institute of Technology

Committee:

Thomas Barker, Ph.D. - Department of Biomedical Engineering, Georgia Institute of Technology

Stanley Rockson, M.D. - Stanford School of Medicine

Todd Sulchek, Ph.D. - School of Mechanical Engineering, Georgia Institute of Technology

“Design and Optimization of Near-Infrared Functional Lymphatic Imaging in Health and Lymphedema”

The lymphatic vasculature is present in nearly all tissues of the body and serves three primary functions: (1) regulation of tissue fluid homeostasis through the transport of large proteins and excess interstitial fluid,  (2) immune cell trafficking, and (3) lipid transport.  When the normal function of the lymphatic system deteriorates, many complications can arise.  Loss of lymphatic pump function often leads to tissue fluid accumulation, fibrosis, and lipid deposition – a disease known as lymphedema.  Despite the critical roles that it performs, very little is known about the lymphatic vasculature in comparison to the blood vasculature.  One of the main reasons for this knowledge gap may be the lack of in vivo imaging techniques to non-invasively visualize and obtain quantifiable information regarding lymphatic function, both in health and disease.  New techniques are needed to better study lymphatic biology, elucidate the functional role of lymphatics and lymphangiogenesis in health and disease conditions, and better diagnose patients with lymphatic disease at an early stage before any resulting tissue damage is permanent.

Near-infrared (NIR) lymphatic imaging has emerged as a new technology for imaging of lymphatic architecture and quantification of vessel function.  Although the technique has shown very exciting early results, the technique remains immature and several enhancements specifically for lymphatic imaging and functional quantification remain necessary.  Therefore, we have characterized and optimized NIR imaging specifically for lymphatic vessels through a physical and physiological approach.  Furthermore, the enhanced NIR lymphatic imaging technique was performed in the context of a novel rodent model of lymphedema to evaluate and characterize the role of lymphatic vessel function in the progression of the disease.

Committee:

Patrick McGrath, Ph.D. (Georgia Institute of Technology)

Robert Butera, Ph.D. (Georgia Institute of Technology)

Mark Stycyznski, Ph.D. (Georgia Institute of Technology)

Yun Zhang, Ph.D. (Harvard University)

A High-Throughput Microfluidic Platform for High-Content

Learning Studies in C. elegans

Learning is a complex process governed by many genetic and environmental factors. C. elegans serves as a useful model organism for learning studies, as it contains a simple nervous system with only 302 neurons, and yet exhibits a large repertoire of behaviors, including learning and memory. My thesis aims to develop a platform for high-throughput learning-phenotype classification through the extraction and analysis of high-content behavioral data. The platform will consist of a microfluidic behavioral arena to provide a standardized and finely tunable closed-loop assay environment to detect preference changes due to learning. Hardware and software will enable simultaneous multiple-animal behavioral tracking as animals navigate through their environment during the learning assays. Methodologies will be developed to extract relevant behavioral features and subsequently quantify learning phenotypes based on the temporal, feature-rich behavioral data. The platform will be utilized to assess the roles, interactions, and functional effects of a putative insulin-like peptide (ILP) network on pathogenic learning in C. elegans. This platform will improve learning-phenotype classification through advancements in microenvironment standardization, presentation of dynamic spatial stimuli, and the amount of information collected. Additionally, this high-content information can be used to better infer putative biological mechanisms from observed morphologies.

Ajit P. Yoganathan, PhD- Georgia Institute of Technology, Atlanta, GA 

Committee Members:

Vasilis Babaliaros, M.D. Emory University, Atlanta, GA

Gautam Kumar, M. D.^- Atlanta VA Medical Center, Atlanta, GA.

Wei Sun, PhD ^-Georgia Institute of Technology, Atlanta, GA

Cyrus Aidun, PhD-Georgia Institute of Technology, Atlanta, GA

Title: A Parametric Investigation of Aortic Valve-in-Valve Performance

With recent advances in transcatheter aortic valve replacement (TAVR), off-label use of these devices is increasing, posing unknown risks to patients.  Clinicians who are using these devices in an off-label manner are doing so with limited basis for judgment except experience. In recent years, with an aging population of surgical aortic valve replacement (SAVR) patients, it is becoming increasingly more common to correct a failing bioprosthesis with a TAVR in a procedure known as valve-in-valve (VIV). It should be clearly noted that based on ISO Failure Mode Effect Analysis standards (5840-2,3) and FDA 201X Heart Valve guidelines, the design intent of the current generation of TAVR designs does not address VIV use. Furthermore, the Valve-in-Valve International Data Registry documents a number of hemodynamic and structural complications associated with this type of off-label use, which may compromise patient safety. Providing clinicians with an engineering basis to compliment an otherwise experience-based decision making process could lead to even more favorable patient outcomes. Based on generalized valve characteristics, this study aims to clarify what type, size, and deployment positioning of a TAVR will yield the most favorable performance evaluated by 1) hemodynamic pressures and flows, 2) flow field characterization via high-speed particle image velocimetry (PIV) and particle tracking, 3) level of sinus obstruction via trans-TAVR gradient, 4) valve dynamics via high-speed en face photogrammetry, and 5) migration risk through uniaxial pullout force measurements and elevated cardiac output conditions.  The results of this study will help better inform the VIV procedural decision-making process.

Committee Members:

Garrett B. Stanley, PhD (Georgia Institute of Technology, Biomedical Engineering)

Todd Sulchek, PhD (Georgia Institute of Technology, Mechanical Engineering)

Hongkui Zeng, PhD (Allen Institute for Brain Science)

Edward S. Boyden, PhD  (Massachusetts Institute of Technology, Biological Engineering and Brain and Cognitive Sciences)

Suhasa B. Kodandaramaiah, PhD (University of Minnesota, Mechanical Engineering)

In vivo serial patch clamp robotics for cell type identification in the mouse visual cortex

Patch-clamping, the gold standard technique for measuring trans-membrane voltages and currents in neurons, involves delicately resting a 1 μm diameter pipette against a cell to create an intimate electrical and mechanical connection between the pipette tip and the cell membrane. From there, it is possible to record essentially interference-free single-neuron “spikes” in membrane voltage. These spikes are the primary method of inter-neuronal communication in the nervous system.

 The experimental procedure to obtain these high-fidelity recordings is considered an art form performed in vivo by a small number of highly trained individuals.  Previous work has introduced mechanical and electrical automation techniques, or "autopatching," to reduce the cognitive load and the required training to obtain these recordings, but the low yield is still a major limitation and requires many attempts to obtain a single recording.  

 This work introduces additional robotic tools to completely automate serial patch clamp recording attempts.  Electrical and mechanical hardware and software algorithms have been developed to automate pipette manipulation, specifically, pneumatic control, electrical control, precise positioning, replacement, filling, wire threading, and storage.  Taken together, these tools enable the first completely autonomous, serial patch clamp recording attempts in the living brain.

 These robotic tools also enable more difficult experiments that combine patch clamp recording with other techniques such as biocytin filling for morphological reconstruction.  Progress towards a survey of 50 cells in the visual cortex will be presented to establish cell type identification schemes based on coupled electrophysiology and morphology.

Committee:

Laura O’Farrell, Ph.D. (Georgia Institute of Technology)
W. Robert Taylor, Ph.D., M.D. (Georgia Institute of Technology and Emory University)
Philip Santangelo, Ph.D. (Georgia Institute of Technology and Emory University)
Anatoliy Gashev, Ph.D., M.D., D.MSci. (Texas A&M University)

Quantifying the Role of Lymphatics in Lipid Transport and Lymphatic Filariasis Using Novel Engineering Approaches

The lymphatic system has fundamental physiological roles in maintaining fluid homeostasis, immune cell trafficking and lipid transport from the small intestine to the venous circulation. Lymphatic vessels are the main functional organ responsible for the diverse transport roles the system plays. Unlike the blood vasculature, the lymphatic system does not have a central pump, such as the heart, and relies on a variety of factors to move lymph through. It was long thought that only external factors, such as skeletal muscle contraction and lymph formation, played a role in the functional transport capacity of these vessels. With the advancement of imaging capabilities (both hardware and software), it has become clear in the past two decades or so that the main factor in driving lymph transport is the ability of these vessels to intrinsically contract whereby each vessel is comprised of a chain of `mini pumps' in series. The functional capacity of these vessels is thus now understood to be primarily determined by this pumping activity that has been shown to be regulated by various mechanical and biochemical cues. Lymphatic vessel dysfunction has been implicated in a variety of diseases including many lipid related pathologies and a neglected tropical disease known as lymphatic filariasis. While it has been possible to study the vessel function in the context of fluid drainage and immune cell trafficking, the capability to understand the role of lymphatic vessels in lipid transport has not been available due to the lack of experimental animal models and acquisition systems. As part of this thesis, we sought to develop an experimental animal model along with hardware and software tools to investigate the interplay between lymphatics and their lipid content. We report the first functional measurements of how vessels respond to elevated lipid loads. We further utilized our engineering expertise to develop an experimental platform allowing us to further understand the parasite known as B. malayi that migrates to and resides in lymphatic vessels.

Advisor: Brani Vidakovic, PhD (ISyE/BME, Georgia Tech)

Co-Advisor: Douglas Robertson, MD, PhD (BME, Georgia Tech/Emory)

Gary May, PhD (ECE, Georgia Tech)

Barbara Boyan, PhD (VCU)

Joseph Williams, MD (CHOA)

Title: Craniosynostosis developmental quantification and severity assessment

Abstract:

Quantifying disease progression is one the most difficult challenges facing physicians as they look to provide the most effective treatment customized for individual patients especially in the case of surgical intervention. In more severe cases of craniosynostosis, when the cranial sutures between the bone plates prematurely fuse causing a constriction of skull development, surgery is often pursued to correct the deformity, but the optimal timing and technique of this surgery is not well characterized as well as the cause of postoperative complications.

The goal of this project is to develop computational algorithms that provide a comprehensive analysis of individual pediatric skulls in preparation for surgery using their CT scans and provide insights into what makes specific cases more severe than others. These same analytics are then used more broadly to evaluate normal and abnormal cranial development in the different forms of craniosynostosis. Then utilizing these cranial features and clinical information from a large patient population, predictive models will be developed for the identification of risk factors and severity markers related to postoperative intracranial pressure and resynostosis of the fused suture or other sutures. These outcomes are especially important because patients with these complications frequently seek successive follow-up surgeries for additional correction.

This comprehensive analysis of the skull is proposed through characterizing the intracranial volume asymmetries and measuring the cranial sutures from preoperative CT scans for synostosis differentiation and severity. Then the bone plates, separated by their corresponding sutures, are characterized using maximum intensity projections with wavelet statistical image improvement techniques to help identify signs of high underlying intracranial pressures along with three-dimensional surface fitting and vector analysis to quantify bone thickness around the skull. These techniques combine to provide an extensive assessment of the skull for further understanding of craniosynostosis and an identification of the cases that pose the greatest risk.

 Committee:

Melissa Kemp, Ph.D. (Georgia Institute of Technology)

Dong M. Shin, M.D. (Georgia Institute of Technology, Winship Cancer Institute, Emory University)

Brani Vidakovic, Ph.D. (Georgia Institute of Technology)

Howard Weiss, Ph.D. (Georgia Institute of Technology)

Mathematical Models for Data Mining and System Dynamics to Study Head and Neck Cancer Progression and Chemoprevention

Head and neck squamous cell carcinoma (HNSCC) is the 6^th most prevalent cancer worldwide, and more than 12,000 deaths from this disease are anticipated in 2015 in the U.S. alone. The advancement of genomic, transcriptomic, and other –omic data acquisition technologies has enabled deeper exploration of the molecular-level mechanisms behind HNSCC development and progression. The insights gained through data-driven analysis can lead to earlier diagnosis and better treatment strategies, and ultimately can result in better patient outcomes. However, the volume and complexity of –omic data remain great challenges.

The goal of this research is to address several key challenges related to applying –omic data for HNSCC research. These are: (1) the lack of modeling tools and systems for discovering biomarkers at the protein and metabolite levels; (2) the lack of effective strategies for integrating heterogeneous types of –omic data for prediction; and (3) the lack of systems-level representations of biomarker knowledge for effectively predicting responses to bioactive agents. Overall, this research accelerates knowledge extraction, enables prediction using –omic data for HNSCC, and delivers a suite of mathematical modeling tools for data mining and system dynamics. 

Andrés García, PhD  School of Mechanical Engineering
Luke Brewster,MD/ PhD, Emory University School of Medicine

Title: Delivery of Prolyl Hydroxylase inhibitors to MSC Spheroids for Enhanced Angiogenesis.

Chronic non-healing wounds are a major healthcare concern in the U.S, especially due to the growing diabetic and elderly population. Wound healing is a complex biological process that is dependent on cells at the site of injury to signal and recruit immune cells, fibroblasts, and endothelial cells in order to rebuild damaged vasculature via angiogenesis. MSCs aid in wound healing and revascularization of damaged tissue because of their ability to secrete pro-angiogenic cytokines such as VEGF and IL-6 and recruit immune cells and endothelial cells to the site of injury to form new blood vessels. Hypoxia is known to be a key regulator in the angiogenic response of many cells, including MSCs.  Small molecule drugs termed Prolyl Hydroxylase inhibitors (PHDi) are able to cause a hypoxic response in cells can enhance MSCs ability to facilitate angiogenesis. The objective of this project is to investigate and compare the effects of commercially available PHDi on pro-angiogenic factor secretion of MSCs. Additionally, since the response to the drugs is likely short-lived, a method for prolonged delivery or exposure of PHDi to MSCs will be investigated.

Robert E. Guldberg, Ph.D. (Georgia Institute of Technology)

Committee

Edward A. Botchwey, PhD. (Georgia Institute of Technology)

Andrés J. García, Ph.D. (Georgia Institute of Technology)

Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

Lisa Tran, D.D.S., M.D. (Emory University)

Biomaterial strategies for improved bone healing with bone morphogenetic protein-2 delivery

Musculoskeletal injuries account for two-thirds of all injuries that occur in the United States annually, and among these injuries, large bone defects are particularly challenging to repair. Although bone morphogenetic protein-2 (BMP-2) delivered on an absorbable collagen sponge (ACS) has shown clinical success in long bone healing, complications associated with the empirical use of supraphysiological doses of BMP-2, including heterotopic mineralization and inflammation, necessitate the development of a biomaterial carrier that localizes growth factors to the site of injury. In the development of bone tissue engineering strategies, another critical design parameter is the timing of delivery vehicle degradation, since bone regeneration may be impeded by the presence of residual biomaterials at the injury site. Further, bioactive, naturally derived extracellular matrix (ECM) products with pro-healing and immunomodulatory properties are attractive therapeutics with rapid translatability that may function to attenuate heterotopic mineralization often observed with high dose BMP-2 treatment.

The goal of this work was to investigate hybrid biomaterial systems with controlled strategies for BMP-2 delivery to promote structural and functional restoration of segmental bone defects. Using a critically sized rat segmental bone defect model, we (i) evaluated the effects of alginate hydrogel oxidation on BMP-2 release and bone regeneration, (ii) elucidated the spatiotemporal effects of high dose BMP-2 on bone healing and gene expression, and (iii) investigated the ability of amniotic membrane to attenuate heterotopic mineralization in critically sized bone defects. Modification of the delivery vehicle to modulate growth factor availability may help minimize adverse side effects associated with high dose BMP-2 delivery, while harnessing the healing efficacy of BMP-2 for bone tissue engineering applications.

Edward A. Botchwey, PhD. (Georgia Institute of Technology)

Yusuf A. Hannun, M.D. (Stony Brook Cancer Center)
Melissa L. Kemp, Ph.D. (Georgia Institute of Technology)

Mark P. Styczynski, Ph.D. (Georgia Institute of Technology)

Characterization of Sphingolipid-Based Stress Responses in the Yeast Saccharomyces cerevisiae through Reverse Engineering

 Sphingolipids regulate numerous cell functions through the activation of specific signaling cascades. Although sphingolipids have been investigated for several decades, a detailed mechanistic and systemic understanding of their biosynthesis and utilization is still lacking. As a consequence, it is still impossible to predict with reliability how cells react and adapt to external stresses and which specific roles sphingolipids play in such stress responses.  

In this thesis, I develop mathematical and computational approaches that shed light on the regulatory mechanisms with which baker’s yeast responds to two types of stresses: heat and hydroxyurea. Stresses typically mandate the transition of a cellular system from its normal steady state to a different state. Thus, in the first project, I perform a theoretical state transition analysis. Based on this theoretical foundation, I propose in the second project an optimization strategy that appropriately captures the sphingolipid dynamics under 30 minutes of heat stress. This analysis reveals novel cellular response strategies, including a switch from biosynthesis to sphingolipid retrieval from cell membranes. To address the roles of these distinct ceramide variants, which differ in their fatty acyl CoA chain lengths, I propose a model that uses the previous model as boundary conditions. The model reveals interesting patterns of ceramide dynamics that are different for variants with long and very fatty acyl groups. Finally, I analyze long-term exposure of yeast cells to hydroxyurea. This analysis permits the novel identification and characterization of subtle regulatory mechanisms that are based on the cells’ distinction between ceramides with saturated or unsaturated fatty acyl groups.    

Taken together, this dissertation work reveals novel control mechanisms with which yeast cells coordinate complex responses to external stresses. Beyond the analysis of sphingolipids, this work demonstrates how innovative techniques of dynamic modeling and optimization can assist in the extraction of detailed information from modern metabolomics data.

Zulma Gazit, Ph.D. (Cedars-Sinai Medical Center)
Todd C. McDevitt, Ph.D. (Gladstone Institutes)

Modulation of Stem Cell Delivery Strategy by Platelet Lysate Utilization and Cell Aggregation for Enhanced Bone Regeneration

Large bone defects, such as those resulting from trauma or tumor resection, are repaired using graft tissue as the current gold standard. However, limitations of this treatment approach, including limited tissue availability and poor revascularization post-grafting, have motivated the development of cell- and protein-based strategies. Although recombinant human bone morphogenetic protein 2 (rhBMP-2) is clinically utilized to promote bone repair in incidences of non-union, supra-physiologic dosing of rhBMP-2 can result in adverse effects including heterotopic bone formation and systemic inflammation. Mesenchymal stem cell (MSC)-based bone tissue engineering strategies offer several potential advantages over the use of osteoinductive protein alone. However, challenges to control delivered cell behavior remain a significant barrier to the clinical translation of MSC-based therapeutics.

Human platelet lysate (hPL) utilization and cell aggregation have each demonstrated the capacity to modulate a range of MSC outcomes, including cell number, phenotype, and secretome. The goal of this work was to investigate their potential application in MSC-based large bone defect repair. We pursued this objective through development of a bioluminescent cell tracking protocol and subsequent evaluation of these strategies for improved MSC survival and facilitated bone regeneration. Additional to engineering an efficacious MSC-based treatment for bone injury, this research aimed to relate key principles influencing cell-based tissue regeneration more globally.

Edward A. Botchwey, PhD. (Georgia Institute of Technology)

Thomas J. Burkholder, Ph.D. (Georgia Institute of Technology)
Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

Thomas H. Barker, Ph.D. (Georgia Institute of Technology)

Biofunctional Hydrogels for Skeletal Muscle Constructs

     Skeletal muscle tissue damage costs the US government hundreds of billions of dollars annually. Meanwhile, there is great potential to use skeletal muscle as a scalable actuator system, covering wide length scales, frequencies, and force regimes.  Hence, the interest in soft robotics and regenerative medicine methods to engineer skeletal muscle has increased in recent years. The challenges to generate a functional muscle strip are typical to those of tissue engineering, where common issues such as cell source, material scaffold, bioreactor method or configuration play key roles. Specifically, it is important to translate the existing body of myogenesis knowledge into engineering muscle constructs by examining the impact of the cell microenvironment on growth, alignment, fusion, and differentiation of skeletal muscle cells. 

     The main motivation behind this thesis was to generate a contractile 3D skeletal muscle construct utilizing organized biochemical and physical cues to guide muscle cell differentiation and maturation. Such a construct is expected to play an important role in medical applications and the development of soft robotics. To do this, 3D, swollen hydrogels were chosen to provide tailorable platforms that support cellular activities to similar extents as native matrices. For this work, we utilized an engineered bio-functionalized poly(ethylene glycol)-(PEG)-hydrogel with maleimide (MAL) cross-linking reaction chemistry that gels rapidly with high reaction efficiency under cytocompatible reaction conditions. PEG alone has been shown to have low protein adsorption, a minimal inflammatory profile, well established chemistry, and a long history of safety in vivo.  The PEG-MAL system in particular allows “plug-and-play” design variation, control over polymerization time, and small degradation products.

     To develop an effective soft biomaterial for the development of an aligned, functional muscle construct, we (i) screened hydrogel properties for differentiation, (ii) recreated alignment of skeletal muscle cells, (iii) determined effective generated force upon action of an external agonist. The impact of this study in generating a controllable force actuator will be significant in the construction of biological machines. Concomitantly, this study will provide a unique regenerative solution for skeletal muscle tissue repair and regeneration.

Peter Hesketh, PhD (Georgia Institute of Technology)

Committee:

Mostafa Ghiaasiaan, PhD (Georgia Institute of Technology)
Albert Frazier, PhD (Georgia Institute of Technology)
Oliver Brand, PhD (Georgia Institute of Technology)
Jean-Marie Dimanja, PhD (Spelman College)

Todd Sulchek, PhD (Georgia Institute of Technology)
   

Integration of a Micro-Gas Chromatography System for Detection of Volatile Organic Compounds

The focus of this dissertation is on the design and micro-fabrication of an all gas chromatography column with a novel two dimensional resistive heater and its integration with an ultra-low power TCD sensor for fast separation and detection of Volatile Organic Compounds (VOC). The major limitations of the current MEMS-GC column are: direct bonding of silicon to silicon, and peak band broadening due to slow temperature programming. Direct fusion bonding of silicon to silicon is not an effective technique for proper sealing of a high density micro-machined surface such as a GC column. This technique requires extremely smooth and clean surfaces, otherwise small voids and unbonded areas occur. As part of this thesis, a new gold eutectic-fusion bonding technique is developed to improve the sealing of the column. The time and power required to ramp and sustain the column’s temperature are very high for the current GC columns. To reduce the time required to separate the compounds, a new temperature gradient programming heating method was developed to generate temperature gradients along the length of the column. This novel heating method refocuses eluding bands and counteract the part of the chromatographic band spreading. At the end, a low power TCD sensor was designed and integrated for a faster and more accurate measurement of the VOC gases separated with the MEMS GC column. These features enable the MEMS-GC system to analyze live and fast detection of the VOC gases released by pathogenic species of Armellaria fungus. 

Committee:

Thomas H. Barker, PhD (Georgia Institute of Technology)

Andrew P. Kowalczyk, PhD (Emory University)

Susan N. Thomas, PhD (Georgia Institute of Technology)

Cheng Zhu, PhD (Georgia Institute of Technology)

Quantitative Analyses for Cadherin-Based Cell-Cell Adhesive Force

Cell adhesion is a critical determinant of tissue architecture and tissue organization. Cadherin proteins mediate cell-cell adhesion in a calcium-dependent manner. The functional roles for cadherin proteins early in development and in adults, as well as the multiple disease phenotypes resulting from cadherin dysregulation, underscore the importance of cadherin proteins. Quantitative assessment of cadherin interaction structure, force, and interaction dynamics is not yet completely understood because of lack of experimental platforms to study cadherin proteins as well as their often-conflicting roles in a tissue-specific manner.  Adhesive force measurements promise to meet this challenge of elucidating how cadherin complex assembly and function coheres in a spatiotemporal manner in human health and disease. The goal of this thesis was to engineer adhesive surfaces that support cadherin-based adhesion as a model system to analyze cadherin-dependent forces. We have engineered two different types of surfaces, based on self-assembly monolayers of alkanethiols on gold surfaces as well as micro-fabricated post-array detectors that present isolated and purified vascular endothelial cadherin ligands. The proposed research is significant because it focuses on creating a robust, quantitative experimental platform to study the formation of the cadherin complex in vitro and integrates a quantitative understanding of cell mechanics. Once validated, our approach will provide a strategy to understand the variables that promote the greatest adhesion strength. 

Committee Members:

Dieter Jaeger, PhD (Georgia Institute of Technology & Emory University)

Robert Liu, PhD (Georgia Institute of Technology & Emory University)

Christopher Rozell, PhD (Georgia Institute of Technology & Emory University)

Anna Roe, PhD (Vanderbilt University)

State-dependent information processing in the rat vibrissa pathway

To navigate the world, we must efficiently extract relevant information from complex sensory inputs to form perceptions and make decisions on a moment-to-moment basis. The efficient encoding of sensory information necessarily relies on the ability of the pathway to dynamically interpret the sensory input according to the context under which external stimuli are processed. Internally, this context is represented by the state of the brain, which can be modulated by bottom-up processes such as sensory adaptation, intrinsic mechanisms such as neuromodulators, and top-down processes such as arousal.

 This thesis examines the modulation of brain state induced via bottom-up sensory adaptation and the spontaneous change in brain state, the relationship between brain state and sensory-evoked activity, and the potential implications of brain state modulation for the perception of the stimulus.

 Using voltage-sensitive dye imaging in anesthetized rats and the paradigm of detection / spatial discrimination task by the ideal observer, I quantified, in the adapted state, how the cortical response to a stimulus in the vibrissa pathway was shaped and how the information for detecting and spatially discriminating the stimulus was differentially optimized. Cortical activation and detection / discrimination tradeoff were quantified in relation to the degree of adaptation, which was modulated continuously by the frequency and velocity of the adapting stimulus. I investigated the spontaneous changes in brain state reflected in the frequency content and phase of the pre-stimulus activity and how it modulated sensory evoked response. Finally, I explored the interaction between the intrinsic changes in brain state and sensory adaptation. 

This thesis investigates the regulation of brain state via bottom-up sensory adaptation and spontaneous changes, providing a glimpse into a high-dimensional continuum.

1:00pm                 BioE Overview- Andrés García, PhD- Director, Interdisciplinary                  BioEngineering Graduate Program

2:00pm                 Course Advisement- Andrés García, PhD

2:30pm                 Current BioE Student Panel

                                ECE/BioE- Aaron Enten

                                BME/BioE- Olivia Burnsed

                                ChBE/BioE- Jaya Arya

                                MSE/BioE- Kirsten Paratt

                                ME/BioE- Kevin Hetzendorfer

3:00pm                 Fellowships Office

                                Center for Career Discovery & Development

3:15pm                 Training Grant Information Session

                                IGERT, Robert Nerem, PhD

                                CTEng, Andrés García, PhD

                                BioMaterials, Julie Champion, PhD

3:30pm                 Poster Session & Reception        

Oliver Brand, Ph.D., ECE, (Georgia Institute of Technology)

Peter Hesketh, Ph.D., ME, (Georgia Institute of Technology)

Wilber A. Lam, MD, Ph.D., BME, (Georgia Institute of Technology)

Hang Lu, Ph.D., ChBE, (Georgia Institute of Technology)

“Toward an Aspirating Force Probe: Microfabrication of a high sensitivity fluidic AFM probe”

This work presents significant advancements toward the development of an aspirating force probe or "AFP". The technology is an elaboration on the canonical AFM probe, targeting added capacity to physically manipulate both adhesive and nonadhesive cells by fluid pressure controlled aspiration at the cantilever terminus.  We demonstrate a low stiffness design of a fully integrated fluidic probe.  This may be combined with the dynamic loading and high spatial resolution capabilities of any AFM system, as the design requires no modification to a mounting unit.  We developed three key microfabrication techniques to achieve this: a low stiffness (k < 100 pN/nm) nano-fluidic cantilever via a thermally decomposable polynorborne sacrificial layer, fully integrated fluidic system that requires no modification to an AFM probe mount, and two micro to nano-fluidic interfaces for connecting the latter.

Committee:

M.G. Finn, Ph.D. (Georgia Institute of Technology)

Brandon Dixon, Ph.D. (Georgia Institute of Technology)

Valeria Milam, Ph.D. (Georgia Institute of Technology)

Michael Davis, Ph.D. (Georgia Institute of Technology, Emory University)

BIOMATERIALS-BASED NANOTECHNOLOGY FOR LYMPHATIC-TARGETED NITRIC OXIDE MODULATION

The lymphatics play a vital role in the regulation of tissue fluid levels and immune response. Loss of lymphatic function leads to accumulation of interstitial fluid (edema), tissue damage, loss of lipid transport, increased adipocyte differentiation (obesity), and downregulated immune function. Alleviating lymphatic dysfunction therefore represents a critical hurdle in the treatment of many pathologies. Nitric oxide (NO) is among the principal signaling molecules controlling lymphatic function when it is produced in physiological levels, and is also integral in the cytotoxic immune response of leukocytes where it is produced it high concentrations and can react with other inflammatory species. Therefore, corruption of NO signaling is associated with the initiation and/or propagation of many lymphatic pathologies. Given the importance of the lymphatics and the pronounced effect NO has on lymphatic and immune function, modulation of NO within lymphatics offers a promising means of alleviating lymphatic deficiencies that may arise from loss of function or parasitic infection, and which eventually contribute to many diseases. To date, however, clinical application of NO modulation within lymphatics has been hindered by the lack of adequate vehicles to both deliver and modulate NO levels in a controlled manner. The objective of this proposal is to develop a biomaterials-based approach to improve the efficacy of NO modulation within lymphatic tissues. 

Suman Das, Ph.D. (Georgia Institute of Technology)

Committee:

Kyriaki Kalaitzidou, Ph.D. (Georgia Institute of Technology)

Wilbur A. Lam, Ph.D. (Georgia Institute of Technology & Emory University)

David Ku, Ph.D. (Georgia Institute of Technology & Emory University)

Jeannette Yen, Ph.D. (Georgia Institute of Technology)

Additive Manufacturing of Tissue Engineering Scaffolds for Bone and Cartilage

Bone and cartilage constructs are often plagued with mechanical failure, poor nutrient transport, poor tissue ingrowth, and necrosis of embedded cells. However, advances in computer aided design (CAD) and computational modeling enable the design of scaffolds with complex internal michroarchitectures and the a priori prediction of their transport and mechanical properties, such that the design of constructs satisfying the needs of the tissue environment can be optimized. The goal of this research is to investigate the capability of additive manufacturing technologies to create designed microarchitectured tissue engineering scaffolds for bone and cartilage regeneration. This goal will be achieved by pursuing the following two objectives: (1) the manufacture of bioresorbable thermoplastic scaffolds by selective laser sintering (SLS) (2) and the manufacture of hydrogel scaffolds by large area maskless photopolymerization (LAMP). SLS is a laser based additive manufacturing method in which an object is built layer-by-layer by fusing powdered material using a computer-controlled scanning laser.  LAMP is a massively parallel ultraviolet curing-based process that can be used to create hydrogels from a photomonomer on a large-scale (558x558mm) while maintaining extremely high feature resolution (20µm). In this research, SLS is used to process polycaprolactone (PCL) and composites of PCL with hydroxyapatite (HA) for bone tissue engineering applications while LAMP is used to process polyethylene glycol diacrylate (PEGDA) which can be used for hard and soft tissue applications

Committee: 

Edward Botchwey, Ph.D. (Georgia Institute of Technology)

Krishnendu Roy, Ph.D. (Georgia Institute of Technology)

Athanassios Sambanis, Ph.D.

Edmund Waller, M.D., Ph.D. (Emory University) 

“Engineering a Platform to Harness Pluripotent Stem Cell-Derived Paracrine Factors”

The results of initial stem cell transplantation studies indicate that many of the observed functional improvements are due to transient paracrine actions of the transplanted stem cells, rather than the stem cells permanently engrafting and replacing the damaged cellular material. Thus, research on the identity and potency of paracrine factors secreted by stem cells has become an increased area of focus in the regenerative medicine field. Due to the mitogenic and morphogenic roles of embryonic stem cells (ESCs) during the early stages of development, they are an underexplored cell population which likely possess a unique and potent secretome. A potential application for the milieu of mitogens and morphogens produced by pluripotent stem cells is the restoration of the proliferative and regenerative capacity of adult stem cell populations, as these multipotent cells have a limited capacity for expansion outside the body and are also negatively regulated by dysfunctional signals in vivo which are implicated in the reduced capacity for regeneration with injury or aging.

To take advantage of the stimulatory potential of pluripotent cell-derived signals, the goal of this project was to develop a controlled means of harnessing and delivering soluble factors derived from pluripotent stem cells. This objective was accomplished through the (1) development of a microencapsulation-based culture system for ESC aggregates, (2) design of a novel upstream bioreactor for encapsulated ESC culture which enabled the concentration and delivery of stem cell secreted products, (3) characterization of the global expression profile of ESC-secreted factors, and (4) investigation of the influence of ESC-derived factors on adult stem and progenitor populations. Ultimately, this project established pluripotent stem cells as a unique source of potent growth factors and cytokines which can be regulated and concentrated using engineering design parameters to enable multiple applications in the field of regenerative medicine.

Committee:

Krishnendu Roy, Ph.D. (Georgia Institute of Technology)

Edward Botchwey, Ph.D. (Georgia Institute of Technology)

Fredrik Vannberg, Ph.D. (Georgia Institute of Technology)

Edmund Waller, M.D., Ph.D. (Emory University)

ROLE OF VASCULAR REMODELING IN THE ACCUMULATION, CLEARANCE, AND BIODISTRIBUTION OF BIOMOLECULAR FACTORS IN LOCAL INFLAMMATORY DISEASE

Local inflammation within tumors and injured joints is implicated in the systemic side effects that precipitate development of more advanced pathologies, such as metastasis and rheumatoid arthritis (RA), respectively. Soluble factors (SF) produced within the tissues of localized disease, including cytokines, exosomes, proteases, and microvesicles, mediate pathological signaling and have emerged as putative therapeutic targets. However, SF bioavailability in distributed tissues and the impact of disease course on their dissemination profiles is poorly defined. This stymies progress towards therapeutic amelioration of SF signaling activities to improve disease outcome and is the critical knowledge gap this proposal seeks to fill. The central hypothesis is that vascular remodeling within diseased tissues redirects the organism-wide signaling activity of locally secreted SF and may negatively contribute to disease burden by altering the bioavailability of molecules important to systemic disease progression. The overall objective of this proposal is to elucidate how local tissue remodeling may lead to pathological signaling within distributed tissues in order to provide insight into the potential for localized disease to exert systemic effects.

John N. Oshinski, Ph.D., Department of Biomedical Engineering, Georgia Tech

Committee:

Xiaoping Hu, Ph.D., Department of Biomedical Engineering, Georgia Tech

Michael S. Lloyd, M.D., Division of Cardiology, Department of Medicine, Emory University School of Medicine

David Ku, Ph.D., Department of Radiology and Imaging Sciences, Emory University School of Medicine

Orlando Simonetti, Ph.D., Department of Biomedical Engineering, Ohio State University

Development of a Combined Angiography and Late Gadolinium Enhancement MR Sequence

With the rapid growth of catheter-based interventional cardiology procedures, knowledge of the vasculature surrounding the heart relative to the distribution of scar tissue can provide important information for procedural planning and appropriate patient selection. Two examples of this are: (1) selecting patients for Cardiac Resynchronization Therapy (CRT), or (2) evaluating the outcome for atrial fibrillation (AF) patients who have undergone Pulmonary Vein Isolation (PVI).

CRT uses a biventricular pacemaker to restore synchronous myocardial contraction in heart failure patients with evidence of ventricular dyssynchrony. Optimal improvement from therapy necessitates that the left ventricular pacing lead, which is transvenously implanted through the coronary veins, is situated at the latest contracting site that is not predominantly myocardial scar. In order to achieve this, co-registered images of the coronary veins and myocardial scar are necessary. However, current MR imaging protocols use separate sequences to image these features, complicating co-registration. 

PVI aims to circumferentially ablate around the pulmonary veins to electrically isolate triggers from reaching the left atrium. In order to evaluate ablation effectiveness, segmentation of the atrial wall is necessary. Yet, the thin nature of the atrial wall and low contrast at the blood-atrial wall interface make segmentation a challenge. While angiography images clearly delineate the inner atrial wall, co-registration is still necessary to the scar images.

These examples benefit from co-registration between MR angiography and scar images yet use different MR sequences making image registration cumbersome, preventing a unified display. The overall goal of this project was to develop a sequence that would produce inherently co-registered angiography and scar images using a single acquisition sequence and create image processing methods for a combined display. This sequence uses a slow infusion of gadolinium with a centric-ordered k-space acquisition scheme for angiographic imaging. Central k-space will be re-acquired at the end of the sequence (~10 mins after injection) and share outer k-space from the initial angiographic k-space to create inherently co-registered scar images. This sequence will be validated by imaging porcine hearts and then tested on two patient groups: (1) patients with known previous myocardial infarct (MI), and (2) patients with AF who have undergone PVI, to use LGE to evaluate ablation effectiveness. Algorithms will be developed to combine coronary vein and myocardial scar displays to allow LV lead planning. In addition, the concept of a pulmonary vein bullseye will be created to allow quantification of the extent of circumferential ablation in post-PVI patients.

Robert E. Guldberg, Ph.D. (ME, Georgia Institute of Technology) (Advisor)

Todd C. McDevitt, Ph.D. (Gladstone Institute of Cardiovascular Disease)

Thomas J. Koob, Ph. D. (Chief Scientific Officer, MiMedx Group, Inc.)

Johnna S. Temenoff, Ph.D. (BME, Georgia Institute of Technology)

Krishnendu Roy, Ph. D. (BME, Georgia Institute of Technology)

Title: Engineering an Improved Cartilage Repair Strategy Combining Cells and ECM-derived Materials

Abstract

Cartilage has a limited capacity to heal and regenerate due to its low cellularity and avascular nature. As a result, osteoarthritis (OA) affects nearly 27 million adults in the US and there are no clinically proven disease modifying therapies, leading to nearly half a million total knee replacements annually. Autologous chondrocyte implantation is the only clinically approved cellular therapy for chondral defects in the US, but the inability to expand chondrocytes to sufficient numbers without adversely affecting their phenotype remains a significant problem. Additionally, the multiple inflammatory mediators involved in the initiation and perpetuation of OA hinder the efficacy of cellular therapies. The inherent immunomodulatory capabilities of MSCs offer a potent alternative to conventional drug treatment regimens due to their ability to regulate multiple signaling pathways and cell types of innate and adaptive immunity. The primary objective of this study is to engineer an improved cartilage repair strategy by combining cells and extracellular matrix(ECM)-derived materials. Specifically, this work will (i) develop cartilage-derived microcarriers for chondrocyte expansion (ii) determine the effect of tissue-specific ECM-derived materials on the chondrogenesis, cell expansion, and secretion of anti-inflammatory factors, and (iii) characterize the effect of MSC delivery format, via single cells, spheroids, or ECM-derived microcarriers, on OA progression in a  post-traumatic small animal model. This work will increase the scientific community's understanding of the role of ECM-derived materials in influencing cell phenotype and expansion as well as the effect of culture format and delivery on MSC-mediated immunomodulatory activity.

Committee:

Jennifer Curtis, Ph.D. (Georgia Institute of Technology)

Daniel Goldman, Ph.D. (Georgia Institute of Technology)                                                   

Patrick McGrath, Ph.D. (Georgia Institute of Technology)                                                   

Le Song, Ph.D. (Georgia Institute of Technology)                                                  

Mark Styczynski, Ph.D. (Georgia Institute of Technology)               

An automated and low-cost microfluidic platform for behavioral phenotyping of Caenorhabditis elegans

            Animal behavior results from a multitude of factors, including external stimuli and internal neural state, as well as past experiences. Behavior is therefore highly variable and dependent on developmental trajectory. This plays clear roles in disease, including psychiatric disorders and diseases that span a continuum, such as autism spectrum disorder. At the same time, these disorders are partially heritable, and usually this heritability is multigenic. In order to address how genes and the environment interact to regulate variability, large-scale experiments with high repeatability are requisite. Caenorhabditis elegans, a small roundworm, significantly simplifies genetic experiments through ease of isogenic culture.  However, no technology currently exists that can provide continuous temporal monitoring and behavioral analysis of C. elegans for days-long timescales. In this thesis, a low-cost microscopy and analysis system will be developed to enable scalable implementation of a dynamically controlled microfluidic environment. A general-purpose behavior analysis system will be implemented to evaluate behavioral flexibility across biologically relevant physical and chemical environments. This same analysis technique will then be used to compare the behavior of a library of recombinant inbred C. elegans lines, with the goal to map quantitative behavioral traits to a set of genetic loci and begin addressing the complex question of gene-environment interactions in relation to behavior. This system will also be useful for other large-scale behavioral applications, including drug screening and associative learning. 

Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

Committee:

Edward A. Botchwey, Ph.D. (Georgia Institute of Technology)
Robert E. Guldberg, Ph.D. (Georgia Institute of Technology)
Todd C. McDevitt, Ph.D. (The Gladstone Institutes)
William L. Murphy, Ph.D. (University of Wisconsin-Madison)

The Development of Glycosaminoglycan Coatings for Mesenchymal Stem Cell-Based Culture Applications

Mesenchymal stem cells are multipotent cells that have the ability to differentiate down multiple lineages as well as secrete trophic and anti-inflammatory factors. These qualities make MSCs a promising cell source for cell-based therapies to treat a variety of injuries and pathologies. Biomaterials are often used to control and direct stem cell behavior by engineering a desired environment around the cells. Recent research has focused on using the naturally derived sulfated glycosaminoglycan (GAG), heparin as a biomaterial due to its negative charge and ability to sequester and bind positively charged growth factors. Engineering a heparin coating that can mimic the native heparan sulfate proteoglycan structure found at cell surfaces can be used as a novel platform to present GAGs to cells to direct cell behavior. The overall goal of this dissertation was to develop GAG-based coatings on MSC spheroids in order to study the role of heparin and its derivatives on MSC culture applications.

To investigate the role of heparin in coating form on MSC behavior, the ability of the coating to sequester positively charged growth factors was characterized. Given the role of sulfation in the negative charge density of heparin and growth factor interactions, a desulfated heparin coating was develop and used to examine how presentation of coatings with native and no sulfation levels could potentiate response to growth factors in the surrounding environment. Additionally, heparin and growth factor binding in coating presentation was explored to develop a novel platform to assemble MSC-based microtissues. Together these studies provided valuable insight into a novel approach to direct cell behavior by engineering a coating that harnesses heparin interactions with the surrounding environment.

Committee:

Thomas Barker, PhD,(BME, Georgia Tech)

Edward Botchwey, PhD (BME, Georgia Tech)

Robert Guldberg, PhD (ME, Georgia Tech)

Todd McDevitt, PhD (Gladstone Institutes)

Integrin Specificity as a Novel Strategy for Enhancing Transplanted Stem Cell Survival and Tissue Repair in Vivo

Despite the promising clinical results for the use of human mesenchymal stem cells (hMSC) in musculoskeletal defect treatment, inadequate control of cell survival, engraftment and fate limits the success of this cell-based therapy. Integrin-mediated cell adhesion plays a central role in tissue formation, maintenance, and repair by providing anchorage forces and triggering signals that regulate cell function. We hypothesize that biomaterials presenting integrin-specific adhesive motifs will direct hMSC engraftment and function to improve bone repair. The objective of this project is to engineer bioartificial hydrogels presenting integrin-specific ligands as biomimetic cell delivery vehicles for enhanced in vivo engraftment and function – an innovative strategy as it focuses on engineering specificity to integrin receptors to promote survival and cell-based repair without the use of exogenous growth factors.

We investigated the performance of a cell-mediated degradable hydrogel functionalized with integrin-specific ligands in supporting the survival of transplanted hMSC and tissue repair in a segmental bone defect. This was accomplished by incorporating the adhesive a2b1 integrin-specific GFOGER ligand, adhesive avb3 integrin-specific RGD ligand, non-adhesive RDG peptide, or non-adhesive GAOGER peptide combined with human mesenchymal stem cells in a protease-degradable PEG-maleimide hydrogel. Cell survival was tracked through transgenic luciferase expression and bone repair was monitored by microcomputer tomography. We hypothesized that hydrogel delivery vehicles that promoted cell viability in combination with the pro-osteogenic properties of the carrier would result in superior bone repair. We found that α2β1-specific GFOGER-functionalized hydrogels promoted enhanced hMSC survival and bone repair, with differential expression of vascularization and inflammation-related genes in vivo compared to RGD- or RDG-functionalized hydrogels, highlighting integrin-specificity as an important consideration in the design of cell delivery vehicles for engraftment and tissue repair. We have generated new insights into transplanted hMSC survival, engraftment and function in a bone repair model allowing for direct correlations among hydrogel formulation and integrin specificity, transplanted cell survival, and bone repair outcomes. This work is significant and innovative because improved design of cell delivery vehicles may improve efficacy of current hMSC therapies in the clinic. 

Committee:

Julie A. Champion, Ph.D. (Georgia Institute of Technology)

J. Brandon Dixon, Ph.D. (Georgia Institute of Technology)

Andrés García, Ph.D. (Georgia Institute of Technology)

Hanjoong Jo, Ph.D. (Georgia Institute of Technology)

Microfluidics for translating multifunctional nanomaterials

Cardiovascular disease (CVD) remains as one of the most impactful diseases in the western hemisphere. Atherosclerosis, the underlying pathology for CVD, is the stiffening and occlusion of arteries that may ultimately cause heart attacks or strokes. While there are many therapeutic options available to treat the pathological symptoms, there is a large unmet need for synergistic approaches that actively address the regression of atherosclerosis rather than progression preventative focuses. MicroRNAs may help to address this need as short RNA sequences that play active roles in multiple disease pathways. In particular, inhibiting the microRNA mmu-miR-712 (miR-712) in atherosclerotic mice using anti-miR-712 (am712) results in atherosclerotic plaque reduction. However, its effectiveness may benefit from the addition of a specific method of delivery to the target site. This study will screen for the in vitro effects of delivering am712 using targeted nanomaterials derived from high-density lipoproteins (HDL), which have been known to be an endogenous transporter of microRNAs through blood circulation. To do so involves the engineering of HDL-derived nanomaterials to incorporate am712 (HDL-am712), the implementation of a microfluidic device to mimic and screen HDL-am712 effects on the inflamed endothelium in vitro, and the in vivo validation of the findings with a mouse model. 

Committee:        

         Alexander Alexeev , PhD (Georgia Institute of Technology, Mechanical Engineering)

         J. Brandon Dixon, PhD (Georgia Institute of Technology, Mechanical Engineering)

         Hang Lu, PhD (Georgia Institute of Technology, Chemical and Biomolecular Engineering)

         Todd Sulchek, PhD (Georgia Institute of Technology, Mechanical Engineering)

Mixing and Sampling in a Microfluidic Channel Using Rotating Magnetic Microbeads

This work presents a novel microsystem utilizing an array of rotating magnetic beads inside a microfluidic channel. The magnetic beads are actuated via a rotating magnetic field. The work demonstrates the fabrication of this device using non-standard MEMS fabrication materials.

The physical operational limits of the device are demonstrated and quantified. The effectiveness of this system is experimentally evaluated in two separate common microfluidic operations. The first operation is the ability for these beads to mix fluids inside a microfluidic channel. This is done by measuring the mixing of two streams of fluid as they flow over the rotating array of beads. The interaction between the speed of the bulk fluid and the speed of the rotating magnetic beads is studied as well as the effect of the path of the bead. The second operation is the capacity to capture particles from the microfluidic channel. This capturing is accomplished via protein-protein bond between the surface functionalizations of the magnetic bead and the particle. In capture experiments, the interplay between density of beads per channel length, channel height and bead rotational speed are studied.

Committee:

Robert Guldberg, Ph.D. (Mechanical Engineering-Georgia Institute of Technology)

Hang Lu, Ph.D. (Chemical Engineering-Georgia Institute of Technology)

Valarie Milam, Ph.D. (Materials Science and Engineering-Georgia Institute of Technology)

Johnna Temenoff, Ph.D. (Biomedical Engineering-Georgia Institute of Technology and Emory University)

High throughput, high replicate screening of materials using flow cytometry

  Due to challenges inherent in biological research, the study of how material structure contributes to cell function is plagued by high variability and non-reproducible data, which leads to waste of time and resources. In order to bring the statistical power of a study to an acceptable level, the best solution often is to miniaturize samples while increasing replicate number. However, this introduces new organizational challenges during both experimentation and analysis, and still does not resolve the limitations of population-based analyses. Currently there is no widely accessible system for high replicate, high-throughput, non-destructive screening of material-encapsulated cells and this limits our ability to study how material structure can be engineered to control cell function.

  Flow cytometry can be used to solve this problem. The technology allows for the automated collection of a large number of unique events in a short time period, which can be combined to characterize a large population. By multiplexing microparticle shape, size, and fluorescence as variables in flow cytometry, a high-throughput, high replicate, rapid assay system will be developed. This will enable the simultaneous study of many parameters, reduce experimental variability, and provide population data with single cell resolution. Due to their history in the field of tissue engineering, polymeric hydrogels for the differentiation of bone marrow stem cells into chondrocytes were chosen as a model system. The proposed project will compare the potentials of many materials for chondrogenic differentiation and demonstrate a high-throughput materials screening platform that will be widely applicable to other areas of research.

Andrés J García, Ph.D. (Georgia Institute of Technology, Mechanical Engineering)
Susan N. Thomas, Ph.D. (Georgia Institute of Technology, Mechanical Engineering)

Committee:        

Emina H. Huang, M.D. (Cleveland Clinic,  Lerner College of Medicine of Case Western Reserve University)
Hang Lu, Ph.D. (Georgia Institute of Technology, Chemical Engineering)
Todd C. McDevitt, Ph.D. (Gladstone Institute of Cardiovascular Disease, UCSF)
 

Adhesion Signature Based Enrichment of Tumor Initiating Cells

      In spite of major therapeutic advances, cancer relapse and low rates of patient response to cancer therapeutics persist. This failure is due in part to a small subpopulation of tumor initiating cells (TICs) with stem cell-like properties that are responsible for the growth of the tumor and the progression of metastasis. These cells are capable of surviving chemotherapy, rendering them highly resistant to conventional cancer therapies. Although the question of whether TICs are stem cells remains a controversial topic in the cancer field, it has become increasingly evident that a better understanding of their biology and function is necessary to effectively treat cancer and eradicate tumors without allowing for relapse to occur.
      This project aims to develop an objective, label-free, fast, and scalable method for TIC enrichment based on the adhesion strength signature of these cells. Currently, no efficient and reliable methods to isolate TICs exist. Although many in the field rely on surface marker expression profiles, these are variable and subjective, which hinders the study of TIC biology. Our lab has developed a technology to isolate cells based on their unique adhesion binding strength to a matrix. The novel technology (micro-Stem cell High- Efficiency Adhesion based Recovery [μSHEAR]) consists of a microfluidic device that applies varying degrees of detachment shear forces to adherent cells. Using this device, human pluripotent stem cells and their progeny have been isolated with high reproducibility, yield (>97%), purity (95-99%), and survival (>95%) rates (Singh et al, Nature Methods 2013). The process is fast (<10 min), label free, and scalable. Our hypothesis is that subtypes of cancer cells will exhibit distinct ‘adhesive force signatures’ that can be exploited to selectively purify TICs with high efficiency using the μSHEAR technology. The significance of this work is the development of a novel platform for objective, reliable, and scalable TIC purification 

Andrés J. García, Ph.D. (Georgia Institute of Technology)-Chair

Edward A. Botchwey, Ph.D. (Georgia Institute of Technology)

Robert E. Guldberg, Ph.D. (Georgia Institute of Technology)

W. Robert Taylor, M.D., Ph.D. (Emory University, Georgia Institute of Technology)

Alberto Fernández-Nieves, Ph.D. (Georgia Institute of Technology)

Title: Vascularization of constructs for Improved Survival of Human Mesenchymal Stem Cells for Bone Repair

Abstract:

Repair of non-healing bone defects through tissue engineering strategies remains a challenging feat in the clinic due to the aversive microenvironment surrounding the injured tissue. The vascular damage that occurs following a bone injury causes extreme ischemia and a loss of circulating cells that contribute to regeneration. Tissue engineered constructs aimed at regenerating the injured bone suffer from complications based on the slow progression of endogenous vascular repair and often fail at bridging the bone defect. Furthermore, stem cell-based strategies aimed at regenerating the critical-size defect routinely demonstrate subpar performance due to the extreme ischemic environment causing massive loss of implanted cell viability. To that end, various strategies have been explored to increase blood vessel regeneration within defects to facilitate both tissue engineered and natural repair processes.

 This project aims to engineer biomaterials that understand and accelerate the vascularization of critical-size defects for the purposes of enhanced bone regeneration and heightened implanted stem-cell survival. We have engineered polyethylene-glycol (PEG)-based hydrogels that can be functionalized with differing cell adhesive ligands and proteins through a facile Michael-addition reaction between a maleimide moiety on the PEG macromer and a free thiol on the biological molecule. These protease-degradable hydrogels have been previously shown to have the ability to incorporate vascular endothelial growth factor (VEGF) for enhanced vascularization when implanted subcutaneously in mice. We propose to utilize this platform to investigate how integrin-specificity affects vascularization within critical-size defects and how incorporation of VEGF or small molecules to increase expression of hypxoxia inducible factor 1-alpha work in conjunction with integrin-specificity to promote vascularization. Our hypothesis is that integrin-specificity plays a role in vascularization of tissue engineered constructs. By exploiting the role integrins play in vascularization, the efficacy of other strategies such as protein or small molecule delivery can be enhanced and vasculogenesis increased. The significance of this work is the development of synthetic biomaterials that allow for increased stem cell survival and enhance the efficacy of stem cell-mediated therapies. 

Dr. Cheng Zhu (BioE, Gatech)

Committee:

Dr. Larry McIntire (BioE, Gatech)
Dr. Wilbur Lam (BioE, Gatech)
Dr. Xiaoping Du (University of Illinois at Chicago)
Dr. Renhao Li (Emory University)

“Platelet Mechanosensing via Surface Receptors GPIbα and Integrin α_IIbβ₃”

In hemostasis and thrombosis, platelet adhesion and signaling play key roles. Two platelet receptors, glycoprotein Ibα (GPIbα) and integrin α_IIbβ₃, mediate the early and mid-stages of platelet adhesion in arterial environments. GPIbα is part of the GPIbα-V-IX complex that constitutes the receptor for von Willebrand factor (VWF). Its binding to VWF A1 domain enables rolling of platelets on the sites of vascular injury. α_IIbβ₃, upon activation, allows for platelet stable adhesion to the sub-endothelial surface and facilitates the platelets aggregation by cross-linking via soluble fibrinogen, fibronectin and VWF. GPIbα and α_IIbβ₃ has been reported to trigger outside-in mechano-activating signals upon ligand engagement in a sequential fashion, but exactly how the extracellular mechano-signals are transduced and translated to intracellular chemical signals remains unknown. In my PhD thesis research, I study GPIbα and α_IIbβ₃ in the context of platelet adhesion and signal initiation. I conduct single-molecule and single-cell level experiments to investigate 1) the conformational and functional dynamics of integrin molecules under mechanical forces; and 2) the relation between mechanical signals received by GPIbα and α_IIbβ₃ and platelet activation readouts, including intraplatelet Ca²⁺ signals, β₃ integrins up-regulation, P-selectin expression and more, and decode the signaling transduction process step-by-step.

Committee:

Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

Krishnendu Roy, Ph.D. (Georgia Institute of Technology)

Greg Gibson, Ph.D. (Georgia Institute of Technology)

Steven L. Stice, Ph.D. (University of Georgia)

Patient-specific Approaches to Bone Regeneration

The first recorded bone grafting procedure was performed by Dr. Job van Meekeren in 1668, who transplanted a fragment of dog skull into the skull of a wounded soldier. Today, bone is the second-most transplanted tissue after blood with more than 1.6 million bone grafting procedures performed annually in the US at a cost of over $5 billion. Treatment of large bone defects in particular remains one of the most challenging problems faced by orthopedic surgeons. Current therapies include bone grafts and/or delivery of osteoinductive proteins such as bone morphogenetic protein 2 (BMP-2). Despite advances in surgical technique and medical care, many of these treatment options still exhibit high variability in patient outcomes, suggesting that patient-specific factors, such as age, treatment timing, and immune status, may play a much more pivotal role in long-term treatment success than previously thought. Thus, the need to account for these patient-specific factors with more sophisticated treatment strategies has become increasingly apparent.

            The main objective of this project is to use preclinical animal models to investigate how patient-specific factors influence biomaterial-mediated bone regeneration. Preliminary work suggests that better understanding of these factors will motivate a targeted immunomodulatory therapy for improving bone regeneration. The impact of age on large bone defect healing will be elucidated using an established bone injury model along with delivery of rhBMP-2 in a collagen sponge, which is the current clinical standard. These results may provide valuable insight on a controversial subject: the use of rhBMP-2 in pediatric patients. Additionally, this work will identify some of the key mechanisms that lead to nonunion, a significant clinical problem that affects up to 10% of patients with long bone injuries. Along the way, a chronic nonunion model will be developed that can potentially serve as a more rigorous and clinically relevant platform for testing new technologies and therapeutics. Finally, the issue of trauma-induced immune dysregulation will be explored and the novel approach of immunomodulation to enhance bone repair will be assessed. Collectively, these studies will advance our understanding of the factors that affect bone regeneration and represent a critical step towards improved, more personalized care and management of patients recovering from orthopedic trauma.

Committee:

Aldo Ferri, PhD (Mechanical Engineering)
Jun Ueda, PhD (Mechanical Engineering)
Maysam Ghovanloo,PhD (Electrical and Computer Engineering)
Young-Hui Chang, PhD (APPH)
Mark Greig (Industry)

Development of a Dynamic Wheelchair Model with Empirical Validation by a Robotic Testbed

For the 1.6 million wheelchair users who live in the United States, the wheelchair forms the foundation for all of their academic, vocational, and societal activities. Amongst these users, 94% own manual wheelchairs, a mobility device that relies on the occupant for propulsive force. Less mechanically efficient wheelchairs require these users to exert greater instantaneous force and total effort for accomplishing desired travel. Greater propulsion effort can lead to difficulty in achieving desired speeds, a higher probability of fatigue over long bouts of mobility, and difficulty negotiating inclines. The accumulation of this greater effort can also increase the potential for injury in the upper extremities. Regretfully, despite the risks associated with low performance wheelchairs, modern wheelchair design is hinged upon hitting arbitrary weight cutoffs that determine the amount of government medical coverage.

Systems-level dynamic wheelchair models would offer the ability to analytically investigate how different components and designs influence efficiency. To date, models have been developed by the wheelchair community, but are limited to straight-line motion, lack accurate modeling of kinetics, or do not have sufficient empirical validation. Therefore, the objective of the proposed research will be to develop a family of dynamic models that define the relationship between wheelchair properties and their respective impacts on wheelchair performance. The novelty of this modeling approach will stem from the use of a wheelchair-propelling robotic test bed for model validation, as well as custom-designed measurement tools that characterize inertial and resistive wheelchair properties for model input. The proposed approach will 1) model wheelchair kinematics to characterize and partition the system kinetic energy, 2) develop a dynamic wheelchair model to partition resistive energy losses, and 3) generate a cost of transport function for optimizing manual wheelchair design.

Specifically, these models will illustrate how mechanical design parameters impact the complex interactions between inertia and energy loss during wheelchair maneuvers. By developing accurate dynamic models for manual wheelchairs, manufacturers will be given the capacity to optimize wheelchair design based on objective performance metrics. Furthermore, users and clinicians will be better informed about selecting wheelchair configurations to best meet the needs of users.

Committee:

Michael Davis, Ph.D. (Georgia Institute of Technology & Emory University)

Charles Searles Jr., M.D. (Emory School of Medicine)                                                  

Loren Williams, Ph.D. (Georgia Institute of Technology)                                                   

Younan Xia, Ph.D. (Georgia Institute of Technology)                                                  

miR-744 Modulation by Disturbed Flow and Role in Endothelial Dysfunction and Atherosclerosis

 Atherosclerosis is the leading cause of death worldwide despite the use of cholesterol-lowering statins and anti-platelet drugs. The disease localizes to arterial regions exposed to disturbed flow due to the effect of low-magnitude and oscillating shear stress (OS) on endothelial gene expression. However, there are no treatment options to target hemodynamic-mediated mechanisms due to a lack of mechanistic understanding. The objective of this proposal is to elucidate the effects of d-flow-induced miRNAs on endothelial gene expression and the mechanisms initiating endothelial dysfunction and atherosclerosis. Recently, our lab reported that miR-663 is highly upregulated by OS in human endothelial cells and potentially induces endothelial inflammation. Interestingly, preliminary studies indicate that another miR-663 family member, miR-744, which has a common seed sequence with miR-663, is also upregulated by OS, and may also induce inflammation. Therefore, the overall hypothesis is that overexpression of miR-744 by OS causes endothelial dysfunction and atherosclerosis.  To test the hypothesis, miR-744 modulation of OS-induced endothelial dysfunction will be assessed in vitro, the therapeutic effect of miR-744 inhibition on atherosclerosis development will be assessed in vivo, and relevant direct targets will be determined. 

Advisor: David Ku, M.D., Ph.D. (Georgia Institute of Technology)

Committee:

Wilbur Lam M.D., Ph.D. (Georgia Institute of Technology, Emory University)

Julia Babensee, Ph.D. (Georgia Institute of Technology)

Lakshmi Sankar, Ph.D. (Georgia Institute of Technology)

Kevin Maher, M.D. (Emory University, Children's Healthcare of Atlanta)

Shriprasad Deshpande, M.D. (Emory University, Children's Healthcare of Atlanta)

Determination of Thrombogenicity of Materials Under Flow for Improved Device Design

Medical devices are burdened with complications of thrombosis and hemorrhage. The combined interaction of material surface, local hemodynamics (in particular shear rate), and large-scale thrombosis is poorly understood. 

First, basic science studies will attempt to deduce the relative importance of material surface and shear rate for large-scale bulk thrombus formation in an in vitro setup. Next, a model will be built from those results to predict thrombus surface coverage, growth rate, and time to occlusion. Finally, a selection of current blood-contacting devices will be modified based on these results. My goal is to demonstrate reduction in thrombogenicity in an in vitro simulation.

This approach may provide quantitative predictions of clinical thrombogenicity to allow for future systematic design of medical devices to avoid thrombogenic material and flow combinations, as well as improve risk and outcomes for current devices.

Committee:

Julie A. Champion, PhD, (ChBE, Georgia Tech)

Jonathan S. Colton, PhD, (ME, Georgia Tech)

Krishnendu Roy, PhD, (BME, Georgia Tech)

William C. Weldon, PhD, (Centers for Disease Control and Prevention)

Formulation and clinical translation of microneedles for vaccination in developing countries

Most vaccines are currently administered by healthcare personnel using a needle and syringe. This delivery method poses significant hurdles in vaccine delivery, especially in developing countries. We propose dissolving microneedle patches to be a suitable alternative to needle and syringe vaccination in developing countries. Dissolving microneedle patches contain micron sized needles made out of water-soluble biodegradable polymers that dissolve in the skin to deliver the vaccine. They offer the simplicity of patch application and the possibility to mitigate the logistical and safety challenges associated with conventional hypodermic needles.

The overall goal of this thesis was to develop dissolving microneedle patches to further clinical translation of this technology in the context of vaccinations in developing countries. We studied two specific scenarios, development of microneedle patches for rabies vaccination of dogs and assessment of dissolving microneedle patches in human subjects. Human rabies is eliminated in most developed countries by employing control measures of vaccinations in animals. However, dogs account for nearly all human rabies infections in developing countries and vaccinations are difficult to employ in animals due to the need of a needle and syringe and the cost of administration. While microneedle patches are in pre-clinical development for different vaccines, limited information is available about their use in human subjects, which will be important for clinical translation.

The central hypothesis was that rabies vaccine can be stabilized in a dissolving microneedle patch and be at least as immunogenic as conventional needle and syringe while enabling simple administration and that dissolving microneedle patches could be easily administered without the need of an applicator, be well tolerated in the skin and preferred over needle and syringe administration. This was assessed by engineering patches for veterinary rabies vaccination and evaluating immune response in dogs and determining tolerability, usability and acceptability of placebo microneedle patches in human subjects. Altogether, the results from this thesis should further clinical translation of microneedles for vaccination in developing countries.

Committee:

Ken Gall, Ph.D. (Duke University)

Johnna S. Temenoff, Ph.D. (Georgia Institute of Technology)

Nick J. Willett, Ph.D. (Georgia Institute of Technology)

Meisha L. Shofner, Ph.D. (Georgia Institute of Technology)

Fatigue and Cyclic Loading of 3D Printed Soft Polymers for Orthopedic Applications

The use of soft materials in orthopedic applications has largely been stalled due to a lack of biocompatible materials with sufficient fatigue resistance. Silicone was once touted as a potentially suitable material for the replacement of arthritic joints, however numerous studies since have documented cases of failed implants when silicone is used in hand, foot, wrist, and spinal applications. The failure of these implants is generally attributed to fracture, compressive deformation, and wear leading to inflammation, arthritis, foreign body response, and loss of function. More recently there has been a large push for polyurethanes in soft orthopedic devices, specifically polycarbonate urethane (PCU). PCU has been used in applications such as intervertebral disc replacements, acetabular cup bearing surfaces, and meniscal implants, among others. Early clinical data for these devices is promising, with some already in use overseas or in US clinical trials. However, a literature search turns up a surprising lack of fundamental knowledge pertaining to the fatigue and cyclic loading response of PCU. In a more general sense, the relationships between soft polymer structure/processing and fatigue performance are largely understudied.

With the studies proposed, we hope to provide fundamental knowledge as to the relationships between soft polymer structure and processing and fatigue performance. We will start by investigating relationships between soft polymer structure and compressive fatigue performance for an array of soft synthetic polymers, which we will compare to native soft tissue. From there, we will focus our efforts on polycarbonate urethane (PCU), which has recently shown great promise in vivo. Studies on PCU will include examining the effects of hard segment content as well as 3D printing, and a 3D printed topography, on the resulting fatigue properties. Such studies will provide fundamental knowledge useful for the use and optimization of soft polymers in fatigue prone applications.