Synthesis and characterization of pH-sensitive glycopolymers for oral drug delivery systems.

pH-sensitive hydrogels are suitable candidates for oral delivery of therapeutic peptides and proteins, due to their ability to respond to environmental pH changes. New pH-sensitive glycopolymers have been developed by free-radical photopolymerization of methacrylic acid and 2-methacryloxyethyl glucoside, using tetra(ethylene glycol) dimethacrylate as a cross-linking agent. To determine the suitability of these hydrogels as carriers for oral drug delivery devices, their swelling behavior was investigated as a function of the pH and copolymer compositions, and various structural parameters such as the number-average molecular weight between cross-links, Mc, the mesh size, xi, and the cross-linking density, rho(x), were calculated. The transition between the swollen and the collapsed states of these hydrogels was at a pH of 5. The swelling ratios of the hydrogels increased at pH values above 5. The mesh sizes of the hydrogels were between 18 and 35 A in the collapsed state (at pH 2.2) and between 70 and 111 A in the swollen state (at pH 7.0). Finally, as the cross-linking ratio of the copolymer increased, the swelling ratio of the hydrogels decreased at both pH 2.2 and 7.0.