Research On The Modification Of Chitosan Scaffold During The Preparation By In-situ Precipitation

Using the properties of amino group on the chitosan molecular, which is cationic in dilute acid and gelable in alkaline solution, our research group prepared the three-dimensioned oriented chitosan scaffold. In order to satisfy the needs of bone repair, we further researched the properties such as strength, degradation, stability and formation of hydroxyapatite. Focusing on the effect of poor solvent to the chitosan molecular, we studied the three status of chitosan in the process of preparation, which are solution, gel and scaffold.(1) First of all, we studied the rheological properties of chitosan ethanol-aqueous solution. With the ethanol content increasing, the solution was closed to the Newtonian fluid first, and then began to deviate from the Newtonian fluid. The performance of fluid index first increased, and then decreased, which was similar to the change of viscosity and gel point.(2) In this paper, we prepared the chitosan-based gel by in situ preparation, and ethanol and glycerol treatment was carried out. Surface morphology of the obtained scaffold by freeze-drying the gel, became rough, micro-pores increased, and a large number of nano-hydroxyapatite crystal (width of25-180nm, a length of50-500nm) distributed in the matrix. Compared with untreated scaffold, the pore diameter of the scaffold with ethanol treatment reduced but evenly distributed; the pore diameter of the scaffold with glycerol treatment was similar to that of the untreated scaffold, the porosity increased with the addition of hydroxyapatite, and the mechanical strength was enhanced in the wet environments. The common features of the scaffolds with ethanol or glycerol treatment were lower thermal stability, higher water absorption, slower degradation rate in vitro, and good cell growth and proliferation.(3) Using the lithium hydroxide and urea mixed solution, we successfully prepared a kind of chitosan gel solution having spontaneous tendency. As the concentration and temperature increased, this trend was more obvious, having shorter time to form the gel. Inducing the alkaline solution of chitosan to rapidly gel with6%sulfuric acid solution, we prepared the scaffold with layered structure, pore connectivity and rough surface morphology. Through the simulation of biological mineralization, the block bracket hydroxyapatite crystals formed on the surface of scaffold, which can promote adhesion rate of osteoblast on the scaffold surface and stimulate cell activity.