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A novel platform for islet transplantation using silk hydrogels

Nicolynn Davis¹, Caitlin Rugg¹, Annie Mirsoian¹, Annelise Barron², Sara Michie¹, David Kaplan³, Liese Beenken Rothkopf², Nikola Kojic³, Magali Fontaine¹

¹Pathology; ²Bioengineering, Stanford University, Stanford, CA, United States; ³Biomedical Engineering, Tufts University, Medford, MA, United States

Current biomaterials for pancreatic islet encapsulation have had limited clinical success due to mechanical and chemical instability, limited permeability, and stimulation of fibroblast overgrowth, leading to islet cell death. Silk, despite being used as a biomaterial for centuries, has not been fully investigated as an islet encapsulation material. Maintenance of islet graft function depends, in part, on stimuli from the islet microenvironment that promote revascularization, survival and proliferation of the islet cells. To reestablish the islet microenvironment during the peritransplant period, we are developing and testing in vitro a non-immunogenic silk-based hydrogel scaffold for islet encapsulation. The silk hydrogel scaffold includes extracellular matrix proteins (i.e. laminin and collagen IV) and mesenchymal stem cells (MSCs), known to have immunomodulatory properties and to enhance islet cell graft survival and function. Up to 7 days post encapsulation in silk, islets maintained greater than 95% viability in vitro, as determined by LIVE/DEAD fluorescent staining. Islet function was assessed by quantifying insulin secretion in response to high glucose stimulation in vitro. After 2 days of culture, islets encapsulated in silk with collagen IV had a 1.6 fold increase in insulin secretion compared to free islets (P<0.05). At day 7, islets encapsulated in silk with laminin had a 1.6 fold increase in insulin secretion compared to islets encapsulated in silk without extracellular matrix proteins (P<0.05). Co-encapsulation with MSCs increased islet insulin secretion in vitro by 1.4 fold. In addition, co-encapsulation with MSCs suppressed splenocyte proliferation of anti-CD3/CD28 activated- or alloreactive splenocytes by 3.3 and 4.6 fold, respectively. These results suggest that a silk hydrogel-based MSC bioconstruct may be a suitable platform for islet transplantation by enhancing beta-cell function and diminishing the immune response.

Source of funding

NIH-P41 Center Grant (D. Kaplan)

NIH- 5T32AI007290-25 –Stanford Immunology Program Training grant

BIO-X Stanford Interdisciplinary Initiatives Program (M Fontaine, A Barron, S Michie)