Functional Characterization of a Novel Protocol for Encapsulation of Pancreatic Islets within a Conformal Layer of Poly(Ethylene Glycol)-Based Hydrogel

Type 1 Diabetes is an autoimmune disease with no currently available therapies for a definitive reversal of the pathological phe- notype. Among available therapies, pancreatic islet transplantation is a promising strategy, although the requirement of life-long systemic immunosuppression and the limited number of islet donors reduces its widespread application. In this context, islet encapsulation is a promising strategy to create a physical barrier to prevent islet de- struction by the recipient immune system. Furthermore, the encap- sulation material can be exploited as a substrate to conjugate immunomodulatory antibodies or bioactive molecules in order to enhance the immunoprotection activity and to drive targeted im- munosuppression. In this study we developed a protocol for coating murine islets with a conformal layer of poly(ethylene glycol) (PEG)- based hydrogel by employing a photopolymerization method that leads to single islet encapsulation and provides a suitable substrate for targeted functionalization. To validate the biocompatibility of our approach, we assessed encapsulated islet viability and functionality in vitro, and we analysed possible gene expression variations. Our encapsulation protocol preserved islet viability and did not affect significantly expression of apoptotic and hypoxic marker genes. The physiological responsiveness of encapsulated islets to glucose- stimulated insulin secretion was confirmed both at mRNA and pro- tein level. Moreover, effects of the coating on islet architecture were investigated by analysing cytoskeletal morphology and expression of cell-cell and cell-matrix interaction marker genes, observing no substantial differences between encapsulated and control islets. Concluding, our encapsulation protocol provides a safe and bio- compatible approach to encapsulate pancreatic islets, thus suitable for targeted functionalization