Introduction: To investigate if coating dissociated or whole islets with microporous annealed particle (MAP) gel could support cell function and viability and improve islet transplantation outcomes.

Methods: a) C57BL/6 mouse islets were mixed with MAP gel and cultured in 24 well plates at 37°C. The viability of islets was scored after Propidium Iodide-Fluorescein Diacetate (PI/FDA) staining and Glucose stimulated insulin secretion (GSIS) assay performed on Day 1, 3, 5, and 7 post-culture. The experiment was done thrice. b) Single cells from C57BL/6 mouse dissociated islets were mixed with MAP gel, and cultured in 24 well plates at 37°C. Viability of cells was scored after PI/FDA staining and GSIS assay performed 1, 24, 48, and 72 hours post-culture. c) 100 C57BL/6 mouse islets were dissociated into single cells by Trypsin, mixed with MAP gel, and transplanted into syngeneic diabetic recipients under the kidney capsule. Blood glucose (BG) was measured daily.

Results: Mouse islets protected with MAP gel displayed similar GSIS and viability scores when compared to uncoated islets. Both groups retained above 95% viability, with the stimulation index (SI) of MAP gel-protected islets 3.2 and that of uncoated islets is 2.4. Viability of dissociated islets protected with MAP gel was 84% with a SI=8.5 at 72 hours post culture. In contrast, uncoated dissociated islets were nearly dead with only 35% viability and an SI=0.38 at 72 hours post culturing. In MAP scaffold, dissociated islet cell viability was density dependent − cell viability in the 50 and 12.5 dissociated islet conditions was on average >78%, while dissociated cells from 2.5 islets demonstrated 56% viability after 72 hours. In in vivo studies, no significant difference was observed in the ability to return Streptozotocin-induced diabetic mice to normoglycemia when either MAP gel coated or uncoated whole islets (75-100 islets) were transplanted under the mouse kidney capsule. C57BL/6 mouse islets (100 islets) that were dissociated to single cells and co-transplanted with MAP gel under the kidney capsule, permanently returned transplanted mice to normoglycemia, with glucose levels below 200 mg/dL within 18 days post-transplantation (n=6). In contrast, uncoated dissociated islets failed to restore normoglycemia in tranplanted mice. Treatment efficacy continued 40 days post-transplantation (time mice were monitored). The average blood glucose measured at Day 30 was 163 ± 38.2 mg/dL. Recipient mice transplanted with cells from dissociated islets without MAP gel remained hyperglycemic (n=6/group).

Conclusion: The MAP scaffold protects delivery of dissociated islet cells, and helps promote islet transplantation outcomes. Moreover, MAP scaffold provides a possible platform for delivering stem cell-derived insulin-secreting cells.