(267d) Tunable Viscoelastic Synthetic Hydrogels Crosslinked through Reversible Thia-Conjugate Addition

Viscoelastic hydrogels are exciting for biological applications such as injectable hydrogels and cell culture. For example, mesenchymal stem cells have shown different differentiation based on the culture platform viscoelasticity. In addition, many viscoelastic hydrogels have also demonstrated self-healing properties, which promotes increased injectability and cellular viability post-injection. Reversible covalent crosslinks provide a useful approach for viscoelastic hydrogels due to their high mechanical stability and tunability. Using a reversible Michael-type addition between a thiol and a benzalcyanoacetamide conjugate acceptor, we have developed a dynamic PEG-based hydrogel with an easily tunable degree of viscoelasticity. Altering the substituent groups on the aromatic ring attached to the alpha-carbon of the conjugate acceptor allows tuning of the kinetic values for the reaction. We specifically synthesized a para-cyano (CBCA)-modified conjugate acceptor and an unmodified (BCA) conjugate acceptor because these variants provide a range of equilibrium values to probe the reaction effects on hydrogel mechanical properties: 5000 M^-1 and 1000 M^-1 for the CBCA and BCA, respectively. Hydrogels were formed by crosslinking a 4-arm 10 kDa PEG-thiol with a 4-arm 20 kDa PEG-conjugate acceptor. Shear rheology measurements demonstrated that the inclusion of the cyano functional group more than tripled the plateau modulus from 2300 Pa to 7700 Pa and increased the crossover point of the storage and loss moduli from 0.09 to 0.14 rad/s. The cyano functional group inclusion also decreased the half-life of stress relaxation from 7.5 seconds to 4.4 seconds. Preliminary cytotoxicity studies show promising results for the primary degradation products of the hydrogel. This reversible Michael-type addition allows for easily tunable mechanical properties that will facilitate further insight into the structure-property relationships of reversible covalent hydrogels, allowing for advanced biomaterial applications.