Abstract Body: Introduction: Endothelial cells (ECs) can improve blood perfusion in diseased blood vessels associated with peripheral artery disease (PAD), but direct injection of therapeutic cells significantly decreases their survival and functionality for angiogenesis. To address these limitations, we employed a class of mechanically tunable protein hydrogels to enhance the survival and angiogenic behavior of human induced pluripotent stem cell-derived ECs (iPSC-ECs).
Hypothesis: We hypothesize that the optimal stress relaxing mechanical property of hydrogels will modulate iPSC-EC survival and function in a mouse model of hindlimb ischemia.
Materials & Methods: Engineered hydrogels, termed elastin-like protein (ELP)-polyethylene glycol (PEG), consists of two components of a hydrazine-modified elastin-like protein (ELP-HYD) and an aldehyde- or benzaldehyde-modified, polyethylene glycol (PEG-ALD or PEG-BZA), which interact with each other through hydrazone dynamic covalent chemistry bonds to form ELP-PEG hydrogels. By varying the use of PEG-ALD or PEG-BZA, we created hydrogels with the same stiffness but at either fast or slow stress relaxation rates. The hydrogels were assessed by dynamic oscillatory rheology. Afterwards, 10⁶ human iPSC-ECs were encapsulated within gels and injected into a mouse limb ischemia model to assess transplant cell viability and the ability to restore vascular perfusion to the ischemic limb.
Results and Discussion: Although both hydrogels had a Young’s Modulus of 500 Pa, the stress relaxation rate of the PEG-BZA was 2.5h (slow), whereas that of PEG-ALD was within minutes (fast). When the iPSC-ECs were injected into the ischemic limb within either fast or slow-relaxing hydrogels or in saline, bioluminescence imaging of the luciferase-tagged iPSC-ECs showed higher cell survival within the fast-relaxing hydrogel over the course of the first 7 days. Blood perfusion recovery by laser Doppler similarly showed higher mean perfusion ratio when cells were delivered in the fast-relaxing hydrogel.
Conclusions: ELP/PEG-ALD promotes iPSC-EC cell survival and perfusion recovery in the ischemic limb. This work highlights the therapeutic benefit of optimally tuned hydrogels as vehicles for stem cell transplantation in the setting of PAD.