Two-Way CO2-Switchable Triblock Copolymer Hydrogels

CO2-responsive ABA triblock copolymer hydrogels are described. Through rational block copolymer design, these hydrogels could undergo either CO2-induced gel-to-sol or the reverse sol-to-gel transition. While the middle block B is water-soluble, the solubility of the two end blocks A can be switched by CO2. For the gel-to-sol transition, the A block was made to have a lower critical solution temperature (LCST) that can increase upon CO2 bubbling, while for the sol-to-gel transition, the A block was designed to have a LCST that decreases with CO2. Repeated cycles of hydrogel formation and dissociation could be achieved by simply passing CO2 and an inert gas alternately through the solution, at a constant temperature and without adding acids and bases for pH change. Moreover, CO2-induced release of an encapsulated protein was demonstrated.