Julia Babensee, BME
       Julie Champion, ChBE

       Susan Safley, Emory School of Medicine

       Johnna Temenoff, BME

Abstract:

The development of a bioartificial pancreas (BAP) has the potential to substantially improve the treatment of insulin-dependent diabetes.  Composed of insulin-secreting cells encapsulated in a hydrogel material, a BAP may provide superior glycemic regulation compared with conventional exogenous insulin-delivery therapies. Towards this goal, β- cells or islets encapsulated in alginate microcapsules remain a promising approach. Due to the limited supply of human islets, alternative cell sources are under investigation for incorporation into a BAP, including porcine islets and β- cell lines. Several challenges remain to clinical implementation, including loss of islet or β- cell function and viability following transplantation and host response to the transplanted microcapsules.

The objective of this work was to evaluate strategies to improve a BAP by supporting the function and survival of encapsulated islets and β -cells.  Towards this goal, two areas were explored: 1) the provision of pro-survival and insulinotropic factors, namely, CXCL12 and GLP-1, to encapsulated islets and β-cells and 2) modification of the alginate microcapsule to confer long-term resistance to host cell adhesion.  

To achieve the first objective, methods to deliver both pro-survival and insulinotropic factors to a BAP were developed and their effects on encapsulated β-cells and islets were studied, both in vitro and in vivo. Results demonstrate that delivery of both pro-survival and insulinotropic factors are a promising strategy to prolong the survival and function of a BAP.  To reduce host cell adhesion to the microcapsule, we employed covalent conjugation of PEG to the surface of alginate-PLL capsules to replace the un-crosslinked layer of alginate used in traditional alginate-PLL-alginate (APA) microcapsules.  Results demonstrate that while PEGylation of alginate-PLL microcapsules initially reduced host cell adhesion over 2 weeks in vivo compared with APA capsules, the PEG coating did not provide long-term protection over 3 months.  Taken together, these studies represent a multipronged approach towards improving the duration of BAP function, with the ultimate goal of advancing this technology to the clinic.