Azopyrazole boronic ester crosslinks with long thermal half-lives for phototunable viscoelastic hydrogels
Year: 2026
Type: preprint
Abstract: Covalent adaptable networks (CANs) based on boronic acid–ester exchange undergo rapid network reconfiguration in ambient conditions, making them useful materials for biomedical applications. The combination of photoswitches and dynamic bonds imparts reversible spatiotemporal control over mechanical properties for smart and responsive materials. Here, we report azopyrazole boronic acids that undergo rapid photoisomerization to their metastable Z isomers, which have extremely long thermal half-lives (over a year at 25 °C) and a 3-fold enhancement in binding affinity for diols compared to the E isomer. When incorporated into hydrogels, these photoswitchable dynamic bonds enable reversible changes in stiffness and stress relaxation time with at least 6 cycles of visible and UV light. Despite only containing dynamic crosslinks, these hydrogels are comparable in stiffness to our previously reported hybrid materials containing dynamic azobenzene boronic ester and static bis(acrylamide) crosslinks. This work demonstrates an alternative strategy to tuning boronic acid-ester equilibria with light while maintaining strong binding in both isomers.
Source: ChemRxiv
Institution: Northwestern University
Language: English
Subfield: Molecular Medicine
Domain: Life Sciences
Open Access status: green
Funders: National Science Foundation, Northwestern University, National Institutes of Health, Materials Research Science and Engineering Center, Harvard University, International Institute for Nanotechnology, Northwestern University, National Institute of General Medical Sciences, Division of Materials Research, Division of Electrical, Communications and Cyber Systems, Division of Chemistry
Awards: G1276186940, Acquisition of a 500 MHz NMR Spectrometer for Chemical Research, G1820835029, Development of Photoreversible 4D Cell Culture Technologies, G2343375527, NSF Center for Sustainable Polymers, G2499401798, G2788453484, G3203750490, Designing Photoswitchable Dynamic Covalent Crosslinks for Photocontrolled Polymer Networks, G336680401, Northwestern University Materials Research Science and Engineering Center, G5306386714, NNCI: Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource, G6068553369, G6386240557, G7915745552, G8073314406, G8230932042, G8741441373, Chemistry of Life Processes Predoctoral Training Program
OpenAlex ID: W7213454676