Design of Injectable Hydrogels for Regenerative Medicine

Cell transplantation via direct cell injection at the target site is a minimally invasive strategy for treating various injuries and degenerative diseases. However, cell viability is typically only 5% in these procedures, and the therapeutic success critically hinges on the survival and subsequent maintenance of the transplanted cells. To protect these cells, we designed an injectable hydrogel that undergoes two different physical crosslinking mechanisms. The first crosslinking step occurs ex vivo through peptide-based molecular recognition to encapsulate cells within a physical hydrogel, while the second crosslinking step occurs in situ through a thermal phase transition to form a reinforcing network.  At room temperature, the physical hydrogel is shear-thinning and self-healing to facilitate gentle cell encapsulation and transplantation by syringe injection. At body temperature, the hydrogel forms a dual-network resulting in a 10-fold increase in shear modulus and significantly reduced erosion rates and prolonged retention time. Human adipose-derived stromal cells (hASCs) injected through a 28-gauge syringe needle were significantly protected from disruptive mechanical forces when encapsulated within the hydrogel compared to medium alone. In vivo subcutaneous injection of hASCs in a murine model demonstrated significantly improved cell retention when delivered in a double-network hydrogel compared to a single-network gel or medium alone. These cell-delivery materials are being further investigated for the ability to support functional tissue regeneration at sites of ischemia. In one strategy, the hydrogel mechanical properties are being tuned to enhance the secretion of pro-angiogenic growth factors by hASCs. In a second strategy, the hASCs are being co-cultured with induced pluripotent stem cell-derived endothelial cells (hiPSC-ECs) to promote tissue regeneration in a murine hindlimb ischemia model of peripheral arterial disease.