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Polymer gels with photoresponsive cross-links enable tunable mechanics and surface morphologies, making them promising for adaptive materials. While prior work on coumarin cross-linked gels has focused on photomediated events in dilute solution, their network-level mechanical responses remain unclear. Herein, we design PEG hydrogels with both permanent covalent and dynamic coumarin cross-links, allowing in situ modulation of cross-linking under wavelength-specific UV light. Real-time FTIR and dynamic mechanical analysis (DMA) show that postcure 365 nm irradiation drives rapid dimerization, increasing storage modulus by up to 69%, whereas cleavage of coumarin cross-links via 254 nm postcure irradiation has a more limited effect due to attenuation in bulk samples. Surface imaging reveals that dynamic cross-linking governs swelling-induced crease formation and evolution. Together, these results establish design principles for hydrogels with programmable mechanics and adaptive surface topographies, enabling light-addressable coatings, mechanically lockable soft actuators, and dynamic biomaterial interfaces.
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This content will become publicly available on March 6, 2027
Leveraging bond dissociation kinetics to tune shear-thickening behavior in dynamic covalent tetra-PEG hydrogels
Dynamic covalent cross-links impart hydrogels with viscoelastic and self-healing properties, motivating applications as biomimetic cell scaffolds and injectable materials. The long bond lifetime results in complex rheological behavior including shear thickening. We hypothesized that this behavior applies broadly across dynamic covalent hydrogels and can be engineered through reaction rate constants. Thus, we synthesized multiarm poly(ethylene glycol) (PEG) hydrogels with conjugate addition, boronate ester, or terpyridine-zinc cross-links, which tune bond dissociation kinetics and hydrogel relaxation times over four orders of magnitude. All formulations exhibited shear thickening, with the onset dictated by the relaxation time. Although multiple mechanisms may underlie this behavior, chain stretching is hypothesized to contribute to shear thickening, as the cross-linking concentration remained constant under shear and networks with more defects correlated with increased shear thickening. These molecular and structural drivers of shear thickening apply across dilute dynamic covalent tetra-PEG hydrogels, clarifying their suitability for applications under shear.
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- PAR ID:
- 10685493
- Publisher / Repository:
- American Association for the Advancement of Science
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 12
- Issue:
- 10
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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