MOLECULAR-WEIGHT DEPENDENCE OF THE PROPERTIES OF CHITOSAN AND CHITOSAN HYDROGEL FOR USE IN SUSTAINED-RELEASE DRUG

Chitosan was treated with NaBO3 under a homogeneous condition in which it was previously dissolved in an aqueous acetic acid solution. Different molecular weight chitosan samples were obtained, depending upon the reaction conditions, NaBO3 concentration, reaction temperature, and reaction time. The performance of chitosan hydrogel for use in a sustained-release drug was investigated while focusing on the swelling properties of chitosan coated on a drug. Theophylline was used as a model drug to be released. Theophylline tablets were coated with respective chitosan samples, and then tested for the drug release rate. Each drug release obeyed zero-order or near zero-order kinetics, due to a reservoir system comprising a saturated theophylline solution and a chitosan hydrogel wall. The release rate of theophylline decreased with increasing the amount of coated chitosan, which affects the permeability of the drug, and increased with decreasing the molecular weight of coated chitosan, which affects the degree of hydration of the gel. A lag time effect was observed when higher molecular weight chitosan was coated. These experimental results were interpreted in terms of the degree of hydration of chitosan hydrogel and Fick's law of diffusion.