(57h) Design of Injectable Hydrogels to Promote Angiogenesis

Authors: 
Heilshorn, S. C., Stanford University
Cai, L., Stanford University

Human adipose-derived stem cells (hASCs) possess tremendous potential for multiple regenerative medicine therapies including neovascularization. Unfortunately, direct injection by syringe needle into ischemic tissue typically results in only 5% cell viability, in part due to mechanical membrane damage during injection. We demonstrate that pre-encapsulating cells in a weak hydrogel (G' ~ 50 Pa) provides significant protection from membrane damage during injection. However, this stiffness is much lower than that of native adipose tissue (G' ~ 2000 Pa), which we hypothesized would promote secretion of paracrine, pro-angiogenic factors. Therefore, we designed a next-generation family of injectable hydrogels that are soft ex situ (G' ~ 50 Pa) for enhanced cell transplantation and undergo double-network formation in situ to achieve a range of stiffnesses (G' ~ 100 - 2000 Pa). hASCs injected through a 28-gauge syringe needle were significantly protected from membrane damage within all hydrogel formulations compared to delivery in medium alone. Following injection, 3D cell proliferation over two weeks was significantly enhanced within stiffer hydrogels. Similarly, pro-angiogenic gene expression and vascular endothelial growth factor (VEGF) secretion were significantly upregulated from hASCs encapsulated within stiffer hydrogels. These hASC-laden hydrogels are being further investigated for their ability to support proliferation and tubule formation of surrounding endothelial cells in vitro and for functional neovascularization in a murine model of peripheral arterial disease. Together, these data suggest that hydrogel mechanical properties may need to be separately optimized for each phase of cell transplantation, with weaker gels preferred during implantation and stiffer gels favored during neovascularization.