(355j) Dynamic Control of Hydrogel Swelling Using Carbon Dioxide

Polymers exhibit phase behavior that can be exploited for the development of advanced materials. Certain crosslinked hydrogels exhibit a volume phase transition, which is characterized by a change from a shrunken, hydrophobic state to a swollen, hydrophilic state. This phase transition regulates the release and absorption of water via a change in temperature across the volume phase transition temperature (VPTT). In this study, we describe and characterize a crosslinked hydrogel displaying a carbon dioxide (CO₂)-switchable volume phase transition, enabling isothermal and reversible gas-triggered swelling. Specifically, we systematically assess the effects of hydrogel composition on its shift in VPTT, swelling kinetics, and swelling extent upon CO₂ exposure. Over the compositional range studied, we measured shifts in the transition temperatures in response to CO₂ of up to 8.6 °C, enabling CO₂-induced swelling with up to a five-fold increase in mass. Dynamic control of the swelling response was demonstrated by triggering repeated swell-shrink cycles via the addition and removal of CO_2, and the morphological changes occurring through this cycle were observed using SEM. The system described and characterized in this work allows for tunable and controlled swelling and may be utilized for the design of hydrogels for biomedical applications, including drug delivery and wound dressings.