2024 AIChE Annual Meeting
CO2-Controlled Swelling in Hydrogels
Swelling is a key behavior exhibited in hydrogels. Despite their widespread use, few hydrogels offer control over the swelling process via application of an external stimulus. Poly(N-isopropylacrylamide) (pNIPAM) hydrogels exhibit a volume phase transition temperature (VPTT), in which the gel reversibly transitions from an unswollen, hydrophobic state to a swollen, hydrophilic state by altering the temperature. Here, pNIPAM hydrogels are engineered to respond to CO2 which imparts enhanced hydrophilicity to the gel, thus elevating its VPTT. Under isothermal conditions, CO2 is used as a trigger to increase the VPTT from below to above the swelling temperature of the gel which enables control over the onset and extent of swelling. We characterize the CO2-controlled swelling behavior by measuring the uptake of water every ten minutes for three hours. Specifically, the swelling kinetics and swelling extent are studied as a function of hydrogel composition. To further understand and predict swelling behavior, a Voigt model was fitted to the experimental swelling data for each composition to determine the maximum swelling capacity and time constant that describes the swelling behavior. Across the range of compositions tested, gels swelled up to four times their original mass when exposed to CO2. Furthermore, argon was sparged into the system to displace the CO2 and reverse the swelling. We show that this swell-deswell behavior is repeatable at least three times via cyclical sparging of CO2 and argon, and observed longer deswell times compared to swelling times. This CO2-controlled system enables easily adjustable swelling characteristics via small modifications to composition, which may lend itself to applications in the medical field particularly for wound treatment in diabetes patients where CO2 therapy is used to improve vascularization.