Localized Immunomodulatory Silk Macrocapsules for Islet-like Spheroid Formation and Sustained Insulin Production

Abstract

Pancreatic islet encapsulation in a 3D scaffolding matrix has achieved limited clinical success due to loss of islet function and cell death, shortly after transplantation. Also, transplant-associated inflammatory responses create an unfavorable microenvironment for islet survival. The current study delineates the development of cell-encapsulating immunomodulatory 3D silk scaffolds as bioartificial pancreas (BAP) systems for sustained insulin release. Insulin producing cells were encapsulated inside silk scaffolds with either alginate or agarose for immunoisolation to augment islet survival and function. The scaffolds were extensively characterized for pore architecture, porosity, swelling index, water uptake, and density. Further, suitability of these scaffolds was assessed through diverse in vitro tests, including cell adherence, viability, proliferation, 3D spheroid like pancreatic structures development, glucose stimulated insulin secretion, and macrophage polarization. Rat insulinoma (RIN-5) cells were metabolically active within the macroencapsulates and proliferated up to 2.5-fold over 5 weeks in culture. Cultured cells formed 3D islet-like spheroids spontaneously. Primary islets maintained their function in macroencapsulates with enhanced glucose stimulation index when compared to nonencapsulated islets, 1.2 vs 1.7. RT-qPCR and immunohistochemistry results supported the results obtained from glucose challenge assay. Controlled release profiles of anti-inflammatory cytokine interleukine-4 (IL-4) and dexamethasone evinced their prospective application in reducing local foreign body response and immunosuppression. Released IL-4 was biologically active and polarized M0 macrophages to the M2 phenotype, advocating immunosuppressive function. Reduced inflammatory responses illustrated the biocompatibility of these scaffolds. In conclusion, this novel biomaterial system was successfully used to encapsulate insulin-producing cells with enhanced cell functions. Further development of the system may have potential BAP applications.