Cyclodextrin-Containing Tannic Acid–Lipoic Acid Hydrogels for the Loading and Reduction-Responsive Release of Nile Red

Hydrophobic molecules are generally difficult to incorporate into aqueous hydrogels because of their poor water solubility. In this study, a cyclodextrin (CD)-containing tannic acid–lipoic acid (TA–LA) hydrogel was developed using lipoic acid-modified β-cyclodextrin (LACD). LACD retained the host–guest recognition ability of the cyclodextrin cavity after lipoic acid modification and was successfully incorporated into the TA–LA hydrogel without interfering with gel formation. Using Nile Red (NR) as a model hydrophobic molecule, the LACD-containing hydrogel showed higher NR encapsulation efficiency and greater cyclodextrin retention than the hydrogel containing unmodified β-cyclodextrin. The LACD-containing hydrogel also exhibited reduction-responsive NR release in the presence of dithiothreitol (DTT). These results show that LACD can be incorporated into the TA–LA hydrogel while retaining the host–guest recognition ability of the cyclodextrin cavity and can be used for reduction-responsive release of NR.