Preparation and preliminary characterization of concentric multi-walled chitosan microspheres.

Chitosan was first converted into micro-droplets by using a high voltage electrostatic field system. The droplets were then dropped into a series of Na(5)P(3)O(10)/NaOH solution mixtures with volume ratio of 17:3, 19:1, 1:0 (pure aqueous Na(5)P(3)O(10)) or 0:1 (pure aqueous NaOH) in order to fabricate chitosan microspheres with different membrane structures. The microspheres exhibit distinct chemical and physical properties, including release behaviors of encapsulated drugs. These chitosan microspheres prepared by this method exhibited good sphericity within the range of (286.6 +/- 15.9) to (356 +/- 9.5) microm in diameters. SEM observations have indicated that the chitosan microspheres exhibited distinct surface structures depending on the post-treatment solutions. The mechanical strength of the chitosan microspheres significantly improved upon treatment with Na(5)P(3)O(10)/NaOH solution at ratio of 17:3 (v/v), as compared with the same but at ratio of 19:1, 1:0 (pure Na(5)P(3)O(10)) and 0:1 (pure NaOH) solutions. In addition, chitosan microspheres with unique multi-walled concentric shell membrane structures were prepared by treating with Na(5)P(3)O(10)/NaOH solution at ratio of 19:1. Release studies were carried out to evaluate the kinetic profiles of two model drugs (5-fluorouracil and cytochrome C) from these prepared chitosan microspheres. When chitosan microspheres treated with Na(5)P(3)O(10)/NaOH ratio at 17:3, the release of cytochrome C was found to be the slowest as compared to those treated by the same Na(5)P(3)O(10)/NaOH solution of other mixing ratios, after a period of 35-day "endurance" test. However, in one case, 5-fluorouracil released quite quickly in a period of 30 min (about 80% completion). The wide range of drug release results might be attributed to the unique and wide range of surface characteristics, porosities, and various structures of chitosan microspheres upon treatment with Na(5)P(3)O(10)/NaOH solutions. These results indicate that, by adjusting the Na(5)P(3)O(10)/NaOH ratios, without extra manipulation on polymer material formulation, one could obtain an additional degree of freedom in drug release profile that permits the simultaneous regulation of morphologies of surface texture and internal structure, mechanical properties, and molecular permeability of the microspheres.