Vascularized Immunoprotective Biomaterials as a Platform for β-Cell and Islet Replacement Therapy in Diabetes: Mechanisms and Translational Potential

Islet and β-cell replacement can restore physiological insulin secretion in type 1 diabetes, but donor scarcity, chronic immunosuppression, and the fragility of avascular grafts have kept the approach from becoming routine therapy. Biomaterial engineering has approached these problems from two directions historically treated as separate traditions: immunoisolation, which shields transplanted cells behind a permselective barrier, and vascularization, which restores the oxygen and nutrient supply lost when islets are stripped of their native microvasculature. This review argues that the two goals are mechanistically coupled, because the same barrier properties that exclude immune effectors also constrain the oxygen diffusion on which β-cell survival depends. We examine the biological barriers to graft survival, the determinants of islet revascularization, and the principal classes of immunoprotective biomaterials (macroencapsulation devices, microcapsules, nanothin conformal coatings, hydrogels, and decellularized matrices) with attention to the trade-offs each imposes between permeability, mechanical durability, and immune exclusion. We then synthesize emerging platforms that engineer vascularization and immunoprotection together: pro-angiogenic and oxygen-generating materials, prevascularized and device-less sites, and local immunomodulatory strategies designed to substitute for systemic immunosuppression. Evidence is graded from mechanistic and rodent studies through non-human primate and clinical data, and we discuss why encouraging preclinical results have translated unevenly into durable clinical benefit. We conclude that no single material property solves this problem in isolation; durable, immunosuppression-free β-cell replacement will likely require materials engineered simultaneously for vascular integration, immune modulation, and manufacturable reproducibility, alongside renewable stem-cell-derived cell sources.