In vitro and in vivo degradation behavior of acetylated chitosan porous beads.

Chitosans with different degree of acetylation (DA, 10-50%) were synthesized by the acetylation reaction of deacetylated chitosan and acetic anhydride with different ratios. The porous beads (approx. 500 mum) fabricated from the acetylated chitosans were used to investigate the degradation behaviors of chitosans with different DA in vitro and in vivo. The in vitro degradation behavior of the acetylated chitosan beads was investigated in solutions of lysozyme and/or N-acetyl-beta-D-glucosaminidase (NAGase), which are enzymes for chitosan present in the human body. It was observed that the degradation rate of acetylated chitosans can be controlled by adjusting the DA value: the degradation increased with increasing DA value of the acetylated chitosans. It seemed that NAGase plays an important role for the full degradation of chitosans in the body, even though NAGase itself can not initiate the degradation of chitosans. The in vitro degradation behavior of the chitosans in the mixture solution of lysozyme and NAGase was more similar to the in vivo degradation behavior than in the single lysozyme or NAGase solution. It may be owing to the sequential degradation reaction of chitosans in the mixture solution of lysozyme and NAGase (initial degradation by lysozyme to low-molecular-weight species or oligomers and the following degradation by NAGase to monomer forms). The in vivo degradation rate of acetylated chitosan beads was faster than the in vitro degradation rate. The acetylated chitosan porous beads with different DA value (and thus different degradation time) can be widely applicable as cell carriers for tissue-engineering applications.