Two-Way CO₂-Switchable Triblock Copolymer Hydrogels

CO 2 -responsive ABA triblock copolymer hydrogels are described. Through rational block copolymer design, these hydrogels could undergo either CO 2 -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 CO 2 . For the gel-to-sol transition, the A block was made to have a lower critical solution temperature (LCST) that can increase upon CO 2 bubbling, while for the sol-to-gel transition, the A block was designed to have a LCST that decreases with CO 2 . Repeated cycles of hydrogel formation and dissociation could be achieved by simply passing CO 2 and an inert gas alternately through the solution, at a constant temperature and without adding acids and bases for pH change. Moreover, CO 2 -induced release of an encapsulated protein was demonstrated.