The release behavior of brilliant blue from calcium-alginate gel beads coated by chitosan: the preparation method effect.

The aim of this study is to reveal how the release behavior of a model drug (brilliant blue, BB) from chitosan coating calcium-alginate gel beads (CCAGB) was influenced by the preparation methods. The CCAGB were prepared by dropping alginate solution into CaCl(2)/chitosan solution (method 1(a)), or into chitosan solution then gelled by CaCl(2) (method 1(b)), or into CaCl(2) solution then coated by chitosan (method 2). Scanning electron microscopy was used for morphology observation, and elemental analysis was applied to determine the chitosan content bound on calcium-alginate gel beads (CAGB). Compared to CAGB, the dried CCAGB had poorer shape and rougher surface morphology especially in methods 1(a) and (b); moreover, CCAGB was found to be more instable in 0.9% NaCl and serious burst of beads occurred when high concentration of alginate (3.0 and 5.0% w/v) was used. The influence on BB release from the beads by chitosan coating was not only related to the chitosan density on bead surface, but also preparation method and other factors. Under un-dried bead state in method 1(a), the increase of chitosan content prolonged BB release in 0.9% (w/v) NaCl; while in method 2, the increase of chitosan concentration over 0.1% (w/v) (3.0% (w/v) alginate concentration was used) resulted in more serious burst of beads and hence facilitated BB release. Furthermore, in both methods 1(a) and 2, the increase of alginate from 1.5 to 3.0 or 5.0% (w/v) usually resulted in the significant burst of beads and accelerated BB release when 0.3 or 0.5% (w/v) chitosan was used for coating. Drying process greatly influenced BB release profile due to the destroying of alginate-chitosan film. The acceleration of BB release from CCAGB by drying process was more significant in the case of method 1 than of method 2.