BACKGROUND: There is no study on starch/polyvinyl alcohol (PVA) as guided tissue regeneration membranes. The guided tissue regeneration membrane with porous structure were prepared, which combined with the advantages of natural polymer and synthetic polymer. OBJECTIVE: To research the effects of the preparation conditions on the properties of starch/PVA membranes. METHODS: The porous membranes of guiding tissue regeneration were prepared mainly by starch and PVA through solution mixing, casting, freezing and drying. The effects of the mass ratio of PVA and starch, solution concentration, and pre-freezing temperature on the properties of the membrane were researched. The surface morphology, tensile strength, porous ratio, water absorbance and cell cytotoxicity were characterized. RESULTS AND CONCLUSION: The aperture of the membrane was 1-50 μm, the porosity was 60%-70%, and the tensile strength was 12-26 MPa. And this membrane had the excellent biocompatibility and hydrophilicity. The pores in the surface were evenly distributed with the solution concentration of 5% and the pre-freezing temperature of -30℃. The more content of starch was, and the larger of the aperture was.

BACKGROUND: The strength and elasticity of general starch can be enhanced dramatically after plastic blends. The major characters of this material are magnitude molecular weight, many enwinded points, extreme containment of small molecules,and great gelation ability. It can be used as a biodegradable replacement of alginate. Furthermore, by adding osteoinductive factors, thermoplastics starch (TP) can be used as an organic engineering material, which can provide dual functions:anti-bleeding and bone formation. TP can also be used as intraoral tissue formation membrane and burn dressings.OBJECTIVE: To evaluate the bio-safety of TP through a cytotoxicity test.DESIGN: A controlled observation.SETTING: Beijing Research Institute of Traumatology and Orthopaedics; Beijing Jishuitan Hospital; Beijing University of Chemical Technology; Peking Univesity School of Stomatology.MATERIALS: The experiment was conducted at the laboratory of Beijing Research Institute of Traumatology and Orthopaedics from April to October in 2006. TP sample was obtained by plasticization of corn starch (12 wt % water content) with glycerol in a Haake Rhenmix at 110℃ and with 80 rounds per minute for 25 minutes, elongation at break from 115.3% to 245.3%. It was prepared by Beijing Key Laboratory for Preparation and Processing of Novel Polymeric Materials, Beijing University of Chemical Technology. Mouse fibroblast L-929 cell strain was provided by the cell bank of Peking University Health Science Center.METHODS: 1 × 107 L-1 cell aqueous suspension was cultured into leaching liquor ( 50% ), serving for TP group, and routine culture medium served for negative control group. Effect of TP on relative growth rate of L-929 cell strain was quantitatively measured by MTI" assay. The cytotoxicity of TP was evaluated according to GB/T16175-1996. Morphological changes and proliferation of cells were observed after2, 4, and 7 days of culture in the medium through an inverted phase contrast microscope.MAIN OUTCOME MEASURES: Cytotoxicity, morphological changes and proliferation of cells, and cell relative growth rate.RESULTS: Cytotoxicity: After 2 and 4 days of incubation, the absorbance (A) value was lower in the TP group than in the negative control group. After 7 days of incubation, the A value was significantly higher compared to negative control group (P＜0.01). It indicated that after 2 and 4 days of incubation, the cytotoxicity in the TP group was larger than in the negative control group, while after 7 days of incubation, it was on the opposite. All the test time, TP's cytotoxicity grade ranged from 0 to 1. Morphological change and proliferation of cells: After 2 days of incubation, both groups of cells were not extended to the outside of the scope, with a majority shape of being round, triangle, and quadrangle in the TP group or fusiform cells in the negative control respectively. Four days later, there were gaps among cells in the TP group, while in the negative control group, there were hardly any distance between cells and some cells piled up. Seven days later, cells in starch medium suddenly grew up to such a degree that all the cells lapped over and presented with more bloom than the negative control. Cell relative growth rate: After 2, 4, and 7 days of incubation, relative growth rate increased with time, being 85.63%,82.22%, and 113.05%, respectively.CONCLUSION: TP has no evidence of cytotoxicity and has good bio-safety.