Chitin-based Embolic Materials in the Renal Artery of Rabbits: Pathologic Evaluation of an Absorbable Particulate Agent

PURPOSE: To prospectively evaluate the tissue reaction to and the embolic effect and absorption of chitin and chitosan microspheres and polyvinyl alcohol (PVA) in the renal artery of rabbits. MATERIALS AND METHODS: This experiment was performed in accordance with regulations on animal care and experiments. Thirty-six New Zealand white rabbits were divided into four groups according to the materials (PVA, chitin particles, and chitosan particles, and chitosan microspheres; diameter, 150-250 microm) used for embolization of the right renal artery. A rabbit from each group was sacrificed 1 and 3 days and 1, 2, 4, 8, 16, 24, and 32 weeks after embolization. Gross and microscopic pathologic findings were examined with hematoxylin-eosin, Masson trichrome, and Victoria blue staining. RESULTS: Gross pathologic findings were examined, and swelling of embolized kidneys was observed 1 and 3 days after embolization, whereas shrinkage of the embolized kidneys was consistently seen after 2 weeks, with a hard consistency and nodular surfaces being noted. At histologic analysis, chitosan microspheres filled the lumen more compactly than did other particles. With PVA, a large amount of capillary formations occurred within the embolized arteries, whereas chitin particles and chitosan microspheres showed a lower rate of capillary formation. The shape of all embolic materials remained intact until week 8, at which time the materials gradually decreased in size and number. The chitosan particles and the chitosan microspheres were absorbed around weeks 16 and 24, respectively. CONCLUSION: Chitosan microspheres have great potential as a new embolic material since they block blood vessels more compactly with a lower rate of capillary formation. This material is biocompatible, and it is absorbed 24 weeks after embolization.