The molecular inclusion function and pH-sensitivity of hydrogel as a novel drug delivery system

A reactive β-cyclodextrin (β-CD) based monomer carrying vinyl carylboxic acid functional groups was synthesized by reaction of β-CD with maleic anhydride (MAH). Through graft copolymerization of the monomer with acrylic acid (AAc), a novel hydrogel, poly(β-CD-g-AAc) hydrogel with molecular inclusion function plus pH-sensitivity, was prepared by free radical polymerization using a redox system as the initiator in an aqueous solution. The structure and properties were characterized by FT-IR, 13C-NMR and elemental analysis. The equilibrium swelling ratio (ESR) was tested with different pH values. The results indicated that the ESR of the poly (β-CD-g-AAc) hydrogel presented marked variations following the change of pH values, and functioned in a transition region when pH values ranged from 4.5 to 5.5. Using drug Ketoprofen as a model molecule, the drug release from the poly (β-CD-g-AAc) hydrogel in pH 7.4 medium was higher than that in a medium with a pH 1.4. A low level of drug release from the poly (β-CD-g-AAc) hydrogels with a low content of β-CD can be obtained compared with high content of β-CD. When pH was modified across both simulated gastric and intestinal pH conditions, reversible pH-sensitive drug release behavior was observed.