Mechanical cues from the extracellular matrix (ECM) regulate vascular endothelial cell (EC) morphology and function. Since naturally derived ECMs are viscoelastic, cells respond to viscoelastic matrices that exhibit stress relaxation, in which a cell‐applied force results in matrix remodeling. To decouple the effects of stress relaxation rate from substrate stiffness on EC behavior, we engineered elastin‐like protein (ELP) hydrogels in which dynamic covalent chemistry (DCC) was used to crosslink hydrazine‐modified ELP (ELP‐HYD) and aldehyde/benzaldehyde‐modified polyethylene glycol (PEG‐ALD/PEG‐BZA). The reversible DCC crosslinks in ELP‐PEG hydrogels create a matrix with independently tunable stiffness and stress relaxation rate. By formulating fast‐relaxing or slow‐relaxing hydrogels with a range of stiffness (500–3300 Pa), we examined the effect of these mechanical properties on EC spreading, proliferation, vascular sprouting, and vascularization. The results show that both stress relaxation rate and stiffness modulate endothelial spreading on two‐dimensional substrates, on which ECs exhibited greater cell spreading on fast‐relaxing hydrogels up through 3 days, compared with slow‐relaxing hydrogels at the same stiffness. In three‐dimensional hydrogels encapsulating ECs and fibroblasts in coculture, the fast‐relaxing, low‐stiffness hydrogels produced the widest vascular sprouts, a measure of vessel maturity. This finding was validated in a murine subcutaneous implantation model, in which the fast‐relaxing, low‐stiffness hydrogel produced significantly more vascularization compared with the slow‐relaxing, low‐stiffness hydrogel. Together, these results suggest that both stress relaxation rate and stiffness modulate endothelial behavior, and that the fast‐relaxing, low‐stiffness hydrogels supported the highest capillary density in vivo.

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Volumetric muscle loss (VML) is associated with irreversibly impaired muscle function due to traumatic injury. Experimental approaches to treat VML include the delivery of basic fibroblast growth factor (bFGF) or rehabilitative exercise. The objective of this study was to compare the effects of spatially nanopatterned collagen scaffold implants with either bFGF delivery or in conjunction with voluntary exercise. Aligned nanofibrillar collagen scaffold bundles were adsorbed with bFGF, and the bioactivity of bFGF-laden scaffolds was examined by skeletal myoblast or endothelial cell proliferation. The therapeutic efficacy of scaffold implants with either bFGF release or exercise was examined in a murine VML model. Our results show an initial burst release of bFGF from the scaffolds, followed by a slower release over 21 days. The released bFGF induced myoblast and endothelial cell proliferation in vitro. After 3 weeks of implantation in a mouse VML model, twitch force generation was significantly higher in mice treated with bFGF-laden scaffolds compared to bFGF-laden scaffolds with exercise. However, myofiber density was not significantly improved with bFGF scaffolds or voluntary exercise. In contrast, the scaffold implant with exercise induced more re-innervation than all other groups. These results highlight the differential effects of bFGF and exercise on muscle regeneration.

Treatment strategies for peripheral artery disease (PAD) remain limited due to the many challenges of surgical intervention. Stem cell therapy offer a promising option, but barriers exist to their clinical translatability. Among these barriers include lifestyle choices like nicotine use that may influence the efficacy of stem cell therapy. The objective of this study aims to examine the efficacy of iPSC-EC therapy for treatment of PAD in mice with prior chronic exposure to nicotine. We hypothesize that chronic nicotine exposure negatively affects the therapeutic potential of implanted iPSC-ECs in a murine model of PAD. NSG mice were implanted with an osmotic pump for controlled exposed to nicotine or saline (control) for 28 days. Plasma cotinine was measured to confirm nicotine exposure. After 28 days of nicotine or saline exposure, the mice underwent induction of hindlimb ischemia and before receiving an injection of 10 6 iPSC-ECs. A second dose of cells were injected to the ischemic limb on day 7 post-surgery. All mice were monitored for blood perfusion recovery using laser Doppler spectroscopy imaging. Survival of the transplanted cells in vivo were tracked by bioluminescence imaging. The mice receiving iPSC-ECs were also imaged for cell survival using bioluminescence imaging. At day 14 post-surgery, mice were euthanized, and the gastrocnemius muscle and thigh muscle were harvested for histological analysis. The results show that the average cotinine concentration in sera was ~200 ng/mL, which is within physiological range for a tobacco user. Blood perfusion recovery at day 14 showed trends of nicotine treated groups have hindered perfusion recovery, compared to those treated with saline. Importantly, nicotine exposure trended with poorer perfusion recovery after cell therapy. Bioluminescent imaging showed iPSC-ECs persisted in vivo for all groups with a gradual decline in cell numbers over time. In conclusion, nicotine exposure was associated with poorer blood perfusion recovery after iPSC-EC therapy, compared to control saline exposure, suggesting that chronic nicotine exposure may have adverse effects on the efficacy of iPSC-EC therapy for treatment of PAD.