Sarah Heilshorn, Postdoctoral Faculty Sponsor
Elastin-like protein hydrogels with controllable stress relaxation rate and stiffness modulate endothelial cell function.
Journal of biomedical materials research. Part A
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 (500-3300Pa), 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 3days, 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.
View details for DOI 10.1002/jbm.a.37520
View details for PubMedID 36861665
Tuning Polymer Hydrophilicity to Regulate Gel Mechanics and Encapsulated Cell Morphology.
Advanced healthcare materials
Mechanically tunable hydrogels are attractive platforms for three-dimensional cell culture, as hydrogel stiffness plays an important role in cell behavior. Traditionally, hydrogel stiffness has been controlled through altering either the polymer concentration or the stoichiometry between crosslinker reactive groups. Here, we present an alternative strategy based upon tuning the hydrophilicity of an elastin-like protein (ELP). ELPs undergo a phase transition that leads to protein aggregation at increasing temperatures. We hypothesize that increasing this transition temperature through bioconjugation with azide-containing molecules of increasing hydrophilicity will allow direct control of the resulting gel stiffness by making the crosslinking groups more accessible. These azide-modified ELPs are crosslinked into hydrogels with bicyclononyne-modified hyaluronic acid (HA-BCN) using bioorthogonal, click chemistry, resulting in hydrogels with tunable storage moduli (100-1000Pa). Human mesenchymal stromal cells, human umbilical vein endothelial cells, and human neural progenitor cells are all observed to alter their cell morphology when encapsulated within hydrogels of varying stiffness. Taken together, we demonstrate the use of protein hydrophilicity as a lever to tune hydrogel mechanical properties. These hydrogels have tunable moduli over a stiffness range relevant to soft tissues, support the viability of encapsulated cells, and modify cell spreading as a consequence of gel stiffness. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/adhm.202200011
View details for PubMedID 35373510