Abstract
A simple and in situ method, by using a high-voltage electrostatic system, for the fabrication of chi- tosan microspheres (in a form of isolatable microgels) by an extrusion process, exhibiting variable sizes and different membrane structures, was presented. The chitosan micro- spheres exhibited good sphericity and were in the range of 185.8 13.8 to 380.9 11.5 m in diameter. There were two significant factors, the pump flow rate and electrostatic field strength, that affected the chitosan microsphere size. The microsphere size decreased when the flow rate was in- creased from 0.1 to 0.4 mL/h. Also, the microsphere size decreased when the electrostatic field strength was in- creased from 5.5 to 6.5 kV/cm. However, when the electro- static field strength was raised to 7 kV/cm and higher, the microsphere size increased. For the latter case, with other parameters fixed, chitosan microsphere size can be con- trolled by adjusting the electrostatic field strength and pre- determined by a simple linear regression equation: Micro- sphere Diameter (D ,i nm) (75.48) 45.67 (Electro- static Field Strength, E, in kV/cm), at (7 (Electrostatic Field Strength) 10) (R 2 0.956, P 0.001). Following treatment with various ratios of crosslinking/gelating (Na5P3O10/NaOH) agents, the prepared chitosan micro- spheres exhibited distinct membrane structures that yielded various mechanical strengths. In the Na5P3O10/NaOH ratio of 19, the chitosan microspheres had a distinct two-layer structure. The selection of crosslinking/gelating ratio pro- vided an additional degree of freedom, permitting the si- multaneous regulation of mechanical properties and perme- ability of the microspheres, without extra manipulation, and thus, improved applicability in the biomedical field. When the chitosan microsphere extrusion process was used to encapsulate -tricalcium phosphate powder for application as bony material, we found that the ultra fine -tricalcium phosphate powder was trapped inside of the membrane very well. After appropriate collecting procedures, stored microspheres also retained good spherical shape. © 2004
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