beta-Cyclodextrin hydrogels containing naphthaleneacetic acid for pH-sensitive release.

beta-Cyclodextrin (beta-CD) hydrogel was prepared in a strong alkali condition using epichlorohydrin (EPI) as a cross-linker, where the molar ratios of EPI to beta-CD were 8:1, 10:1, and 15:1. In order to endow a pH sensitivity to the hydrogel, naphthaleneacetic acid (NAA) was loaded in the hydrogel by taking advantage of its hydrophobic interaction with the cavities of beta-CD. The releases of blue dextran (a water-soluble dye) from the hydrogels were promoted, as the pHs of the media increased. When the molar ratio of EPI to beta-CD was lower, the degrees of release were higher, and the pH dependency of the release became more prominent. In fact, the swelling ratio of the hydrogels having a lower molar ratio of EPI to beta-CD was higher. The higher swelling ratio would account for the higher degree of release and the marked pH sensitivity.