Biodegradation of chitosan-tripolyphosphate beads: in vitro and in vivo studies.

In this study, chitosan [(1 --> 4) linked 2-amino-2-deoxy-beta-D-glucopyranose] beads were prepared by interacting this polycation (> 90% deacetylated) with the tripolyphosphate (TPP) polyanion. The resulting chitosan-TPP beads (C) were modified either by coating with sodium alginate (CA) or by cross-linking with glutaraldehyde (CGA). The in vitro degradation of C beads was found to be faster than its CA and CGA counterparts. C beads degraded faster at pH 6.5, compared to pH 7.4 conditions. At pH 7.4, about 41%, 37% and 10% of dry mass loss after 12 months was determined for C, CA and CGA, respectively. At pH 6.5, the dry mass loss of CA and CGA after the same period of time was found to be 73% and 37%, respectively. However, C beads completely degraded at pH 6.5 after 8 months of in vitro incubation. The in vivo biodegradation experiments were performed on Wistar rats (n = 24) for a duration of 6 months. No sign of fibrotic capsule formation was observed around any of the implanted beads at 2 and 6 months post-transplantation. At 2 months, the in vivo-degradation was slow-going and the beads in all groups were intact; CGA beads had more tissue reaction than C and CA beads at this time point. While the C beads had almost completely degraded after 6 months, the biodegradation process in CA and CGA beads was progressing. Histomorphometric analysis revealed that the in vivo biodegradation was in the order of C (approximately 85%) > CA (approximately 50%) > CGA (approximately 25%) after 6 months. Neovascularization was observed at the vicinity of the bead implants close to major blood vessels, both at 2 and 6 months time-points.