(33c) Reversible Control of Hydrogel Mechanics with Irreversible Photo-Mediated Reactions

The extracellular matrix is a dynamic environment that undergoes cycles of stiffening and softening, especially during disease and development. A platform that recapitulates these dynamic changes will lead to better models that may shed light on the impact of matrix mechanics on disease mechanisms. Here, we present a strategy to reversibly control the modulus of hyaluronic-acid (HA) based hydrogels with light exposure through the use of photoresponsive crosslinkers. Hyaluronic acid polymers were functionalized with o-nitrobenzyl acrylates (14 mol%) and methacrylates (40 mol%), as well as short RGD peptides for cell adhesion (1 mol%). Hydrogels were formed with an initial elastic modulus of 14.8 kPa, as measured by AFM. These gels could be softened to 3 kPa upon exposure to 365 nm light, and subsequently re-stiffened with a photoinitator and visible light to 27.7 kPa. Because these moduli span a range of active mechanosensing for human mesenchymal stem cells (hMSCs), the cells were seeded onto the dynamic HA substrates and monitored for changes in cell morphology and YAP/TAZ nuclear localization at each stiffness condition. Reversible changes in cell spread area and YAP/TAZ nuclear localization were observed in response to the changes in substrate modulus. Due to their tunability and non-invasive stimulus, these innovative materials may be broadly useful for probing the effect of dynamic stiffness on many cell types.