Background: Our study aimed to generate a functional, prevascularized endocrine construct using amniotic membrane-derived hydrogel, islets, and blood outgrowth endothelial cells (BOECs) for transplantation into diabetic hosts.

Methods: Human amniotic membranes were decellularized, lyophilized, and solubilized to obtain hydrogels. To investigate the impact of these hydrogels on islet function in vitro, both rodent and human-derived islets and human BOECs were combined within the hydrogels and cultured in vasculogenic media to promote endothelial cell assembly into tubular, vascular-like structures. To assess in vivo function, vascularized constructs containing either 500 rat islet equivalents (IEQ) or 2000 human IEQ and 2× 10^5 BOECs were implanted subcutaneously in diabetic NSG mice. Control mice were transplanted with constructs containing islets only. Graft function was evaluated by measuring non-fasting blood glucose levels and performing intraperitoneal glucose tolerance tests (IPGTT). Graft morphology and vascularization were assessed using immunohistochemistry.

Results: Engineered vascularized constructs supported islet function and facilitated the development of an abundant, well-integrated vascular network with the islets. Blood glucose levels in mice transplanted with vascularized constructs normalized within 7 days, with long-term maintenance of normoglycemia. In contrast, most mice transplanted with islets combined in hydrogels remained diabetic. Histological analysis of explanted grafts revealed healthy islet morphology and successful revascularization. Experiments using human islets produced similar results, with rapid diabetes reversal and increased human C-peptide levels following transplantation. Explanted grafts exhibited excellent islet morphology, hormone expression, and, most importantly, intense vascularization. The presence of red blood cells within capillaries in the graft area and positive alpha SMA staining indicated functional and fully matured vessels inside the graft.

Conclusions: Our findings demonstrate that amnion-derived hydrogel seeded with endocrine pancreatic tissue and endothelial cells can be utilized for bioengineering functional, prevascularized endocrine constructs.