Swelling Behaviour of Alginate-N, O-Carboxymethyl Chitosan Gel Beads Coated by Chitosan

Swelling behaviour is one of the important properties of hydrogel-based drug delivery systems, which always affects the diffusion of solvent into and release of drugs from drug loaded microcapsules. In this study, the swelling behaviour of alginate-chitosan beads at acidic and basic conditions, to simulate gastric and intestinal media, were investigated. Spherical hydrogel beads were prepared by addition of aqueous sodium alginate and alginate-N,O-carboxymethyl chitosan (NOCC) solutions into CaCl2 solution. These hydrogel beads were then transferred into a chitosan solution to obtain chitosan coated beads. The effect of concentration of calcium chloride, residence time for ionic cross-linking, concentration of chitosan, addition of NOCC into alginate solution, coating of alginate-NOCC by chitosan as well as drying method on the swelling behaviour of the alginate-chitosan beads was studied. It was found that swelling degree of the air-dried and chitosan coated beads was lower than that for freeze-dried and uncoated beads, respectively. In addition, the presence of NOCC in the network resulted in reducing swelling of hydrogel beads. Swelling degree of hydrogels in basic media (pH 7.4) was also much higher than that in acidic media (pH 1.2). Thus, alginate-NOCC-chitosan beads are good candidate to be studied as colon-specific drug delivery systems.