| Chitosan hydrogel beads were developed by interaction of cationic chitosan with sulfate ion in solution, with subsequent characterization of the beads. The molecular weight of chondroitin sulfate, λ-carrageenan, and dextran sulfate probably created a diffusional resistance to the ionic interaction and hydrogel were not formed with chitosan. Sulfate ion and chitosan formed spherical beads that swelled in phosphate buffer without disintegration or dissolution. The loading of lipase, a model macromolecule, was 50% when the sulfate solution pH was 5.0, although pH did not affect the bead strength. Higher chitosan and sulfate concentrations increased the bead ruggedness and, when the sulfate solution pH was 4.0, the beads sustained lipase release in phosphate buffer at 65% over 8 hours. A diffusion-controlled release mechanism for lipase from the optimal formulation was predicted by release data linearization using the Higuchi equation. The optimal formulation shows promise for sustained drug delivery and in enzyme immobilization. |
