| 1.PerfaceIn the end of 1950's, with the AO principals for treating bone fracture being accepted, internal fixation materials that are made of metal have been widely used in clinic. However, metal materials has its own limitations: (1) Because of its high strength, the stress block is occurred during the later period of fracture healing and therefore it is unfavorable to the healing of bone fracture and may cause osteoporosis; (2) The metal may produce certain electrolysis that will obstruct the healing of bone fracture; (3) The metallic internal fixation devices shall be taken out by another operation. ? Because of the above limitations of the metallic internal fixation devices, researchers begin to think about to use biodegradable material as the internal fixation devices. These materials mush have good biocompatibility and in the meantime have no toxicity. In 1969, Mr. Schmit and Mr. Polistina for the fist time used PGA for the animal experiment in rabbits and dogs, and in 1984, Mr. Tormala and Mr. Rokkanen for the first time used PGA in clinic. The screws and pins made by varied kinds of biodegradable materials, mainly including PGA, PLA and PDS, were profoundly clinical practiced in the later period of 1980's. However, biodegradable materials also have some disadvantages that limits the use of them. (1) The initial strength is rather low; (2) The rate of degradation is quick; (3) The incidence of foreign body reaction in the later period is high; (4) The cost of foreign products is high and it is difficult to be spread in domestic market. 2.ObjectiveIn order to overcame the defects of biodegradable material, we used calcium carbonate whisker and nanometer calcium carbonate to compound with PLLA by solution mixing and casting method to produce two kinds of new composites materials (nanometer calcium carbonate/PLLA composites and calcium carbonate whisker/PLLA composites) in order to enhance the initial strength of PLLA matrix and delay its degradation. 3.Methods and ResultsAt first, we tested calcium carbonate whisker, nanometer calcium carbonate and PLLA by light microscope, scanning electron microscope and transmission electron microscope. Then we comprehensively evaluate the biocompativity, mechanical properties and degradation behavior of the composites materials. A lot of clinical and experimental researches have showed that PLLA had the nature of biocompativity, no cytotoxicity, no stimulation and no mutation. However, it still should be proved by experiment to see whether calcium carbonate whisker /PLLA composites and nanometer calcium carbonate/PLLA composites has good biocompativity. In the course of NIH3T3 and L929 cells culture in vitro, we added the above new type of composites materials to investigate the proliferation of the cells by using microscope, MTT assay and used PLLA as the control group. The results showed: each group of cells grown well and the form of cell was normal. The data of statistics revealed that the culture of cells of each group had no marked difference (P>0.05), and the composites did not influence the proliferation of cells. The above proved that composites had no toxicity and side effects to cells. However, it needs more researches to understand the long term's influence to cells. Whiskers are now playing an increasingly important role in the development of new types of composite materials with high performance. Whisker as a new kind of reinforcing, toughening, heat-resisting materials is suitable for the industry of plastics, rubber and ceramics. Calcium carbonate whisker is prepared by modified carbonate process with the industrial limestone. The suitable synthesis temperature of the whisker of calcium carbonate is 80℃, simultaneously, the additions of the inoculating crystal of needle calcium carbonate and phosphate which can promote the growth of the whisker of calcium carbonate is of great of advantage to the manufacture of calcium carbonate whisker. In our experiments, the crystal type of calcium c... |
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