Cell-instructive Adhesive Materials for Regenerative Medicine
Cell-based therapies represent promising strategies for various regenerative medicine applications including myocardial infarcts, type 1 diabetes, neurological disorders, and non-healing bone defects. In all these applications, poor survival and engraftment of transplanted cells due to the lack of suitable delivery vehicles severely limits the therapeutic potential and translation of these cell-based strategies. We have engineered degradable hydrogels presenting integrin-specific adhesive ligands and growth factors that enhance transplanted cell survival, engraftment, and function, thereby improving tissue repair and regeneration. Synthetic hydrogels (highly hydrated cross-linked polymer networks) offer tremendous advantages as cell delivery vehicles in terms of delivery formulation (injectable), high cytocompatibility, low inflammatory profile, and tailorable mechanical properties and biofunctionality. We have established a new class of poly(ethelyne glycol)-based hydrogels based on maleimide cross-linking chemistry superior to other synthetic hydrogels in terms of structure, cross-linking and biofunctionalization efficiency, and degradation profile. We are exploring these hydrogels for cell delivery in various regenerative medicine applications, including transplantation of pancreatic islets into diabetic mice and human mesenchymal stem cells in segmental bone defects and myocardial infarcts. Our initial analyses indicate robust transplanted cell survival, engraftment and function, resulting in significant enhancements compared to the current clinical treatment (Fig. 5). Additionally, these protease-degradable hydrogels provide robust vehicles for controlled delivery of protein therapeutics, and we are exploring these synthetic matrices to deliver vasculogenic and osteogenic proteins for tissue repair and regeneration. For instance, we have shown that delivery of VEGF from these hydrogels promotes a stable vascular network and reperfusion in a model of hind limb ischemia, whereas bolus delivery of VEGF results in vessels that regress after 2 weeks and do not rescue ischemia. Similarly, our preliminary studies indicate that delivery of BMP-2 to bone defects via these synthetic hydrogels reduces the BMP-2 dose required for bone repair by 20-fold compared to BMP-2 delivered via collagen sponges (clinically used delivery vehicle) (Fig. 6), thereby addressing major delivery limitations of this promising therapeutic. We have also leveraged this expertise into implant coatings that enhance tissue integration and mechanical function. Future work focuses on examining the interplay of cells, bioadhesive ligands, and growth factors in relevant pre-clinical animal models, including allogenic transplant models and large animals.
Figure 5. Vasculogenic hydrogels for pancreatic islet cell engraftment and function. (A) VEGF release profile from collagenase-degrading gels or gels treated in PBS showing on-demand release of VEGF. (B) Random daily blood sugar levels in diabetic mice transplanted within syngeneic islets. Only islets delivered within hydrogels with VEGF restored normoglycemia (p<0.001). (C) Transplant site in the small bowel mesentery at day 0 and at 4 weeks demonstrating significant remodeling of the hydrogel. (D) Islet graft explants (4 weeks) with patent vascular structures stained with IV-perfused FITC-lectin (green), DAPI (blue), and immunostained for insulin (red). (E) Quantification of vascular area normalized to islet area p<0.05). Adapted from Ref. 51.
Figure 6. BMP-2 delivery from GFOGER-functionalized gels improves bone regeneration compared to collagen foams. (A) 3D µCT reconstructions of radii (left) and mineral density sagittal sections (right), scale bar 1 mm. (B) µCT measures of bone volume in radial defects.