PREPARATION AND RELEASE PROPERTIES OF BIODEGRADABLE CHITIN MICROCAPSULES .1. PREPARATION OF 6-MERCAPTOPURINE MICROCAPSULES BY PHASE-SEPARATION METHODS

Chitin [poly-(N-acetyl-1,4-beta-D-glucopyranosamine)] microcapsules we re prepared by the simple desolvation and the non-solvent addition pha se separation methods. In the simple desolvation method, chitin drople ts were dropped into the desolvation agent (water, ethanol, or acetone ) and microcapsules soon formed. Several solvent-nonsolvent pairs: N,N -dimethylacetamide (DMAc)-water, DMAc-ethanol, DMAc-n-propanol, DMAc-n -butanol, and DMAc-acetone with different solubility parameter differe nce, (Delta delta) were chosen to prepare chitin microcapsules contain ing 6-mercaptopurine by using the nonsolvent-addition phase separation method. The results showed that the surface morphology and release be haviour of the microcapsules were greatly affected by different solven t-nonsolvent pairs. The surface of the microcapsules prepared from the system of high Delta delta was more smooth than those from the system s of low Delta delta. The drug content using the simple desolvation me thod increased with decreasing Delta delta because of the higher film formation rate of the microcapsules. On the other hand, the drug conte nt using the nonsolvent addition method was lower than that using the simple desolvation method because of the dispersion forces, applied by mechanical stirring. Microcapsules prepared by the simple desolvation method had a narrower size distribution and larger mean size than tho se prepared by the nonsolvent addition method.