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Abstract 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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Design Parameters for Injectable Biopolymeric Hydrogels with Dynamic Covalent Chemistry Crosslinks
Abstract Dynamic covalent chemistry (DCC) crosslinks can form hydrogels with tunable mechanical properties permissive to injectability and self‐healing. However, not all hydrogels with transient crosslinks are easily extrudable. For this reason, two additional design parameters must be considered when formulating DCC‐crosslinked hydrogels: 1) degree of functionalization (DoF) and 2) polymer molecular weight (MW). To investigate these parameters, hydrogels comprised of two recombinant biopolymers: 1) a hyaluronic acid (HA) modified with benzaldehyde and 2) an elastin‐like protein (ELP) modified with hydrazine (ELP‐HYD), are formulated. Several hydrogel families are synthesized with distinct HA MW and DoF while keeping the ELP‐HYD component constant. The resulting hydrogels have a range of stiffnesses,G′ ≈ 10–1000 Pa, and extrudability, which is attributed to the combined effects of DCC crosslinks and polymer entanglements. In general, lower MW formulations require lower forces for injectability, regardless of stiffness. Higher DoF formulations exhibit more rapid self‐healing. Gel extrusion through a cannula (2 m length, 0.25 mm diameter) demonstrates the potential for minimally invasive delivery for future biomedical applications. In summary, this work highlights additional parameters that influence the injectability and network formation of DCC‐crosslinked hydrogels and aims to guide future design of injectable hydrogels.
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- Award ID(s):
- 2033302
- PAR ID:
- 10431313
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Healthcare Materials
- ISSN:
- 2192-2640
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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