(93aj) Stimuli-Responsive Hydrogels Integrating Binding Protein Recognition Elements

Proteins that undergo conformational changes, such as the periplasmic proteins of bacteria, are stimuli-responsive molecular machines. The integration of a hinge motion binding protein, like calmodulin (CaM), and its ligand (in the CaM case a phenothiazine derivative) within a porous hydrogel network causes the hydrogel to undergo a phase transition in the presence of free ligand. This phase transition results in the swelling of the hydrogel network, with a magnitude that is analogous to the concentration of the free ligand. Therefore, these hydrogels can be utilized for sensing, with a selectivity that is conferred by the biological sensing element employed. In addition to sensing, the ability of these hydrogels to undergo a ligand-induced phase transition can be also utilized as an actuation mechanism. Such a mechanism can be employed to trigger an action, such as the release of molecules, either through the swollen material of higher porosity, or through the volume expansion of the hydrogel in the swollen state, which can trigger the opening of a valve. These biohybrid hydrogels are highly integrated materials, and can find numerous applications, such as in high-throughput screening and biomedical applications.