| Carbon/carbon composites are characterized by excellent biocompatibility, very similar elastic modulus to human bone and fine chemical stability. Also, they possess fine mechanical properties that are suitable for artificial bone. However, carbon/carbon composites as hard tissue restoration and reconstruction materials have a few drawbacks. Firstly, carbon/carbon composites cannot form chemical bond with human bone tissue due to their bioinert property. Secondly, the surface of unprocessed carbon/carbon is hydrophobic, so if it is put into the human body for a long time, the nomadic carbon will flow with the body fluid and deposit on the skin, causing "The Black Skin Effect". Thirdly, the color difference between carbon/carbon composites and human bone is obvious. In order to avoid the decline of the mechanical properties due to the shedding of the surface carbon particles and enhance the bioactivity, people have prepared several biomedical coatings on carbon/carbon composites in different ways. Among these coatings, hydroxyapatite coatings have been broadly used as bioactive ones on artificial bone materials for their excellent biocompatibility and bioactivity. In the present work, hydroxyapatite coatings were prepared on carbon/carbon composites by plasma spraying technology. And the biological behaviors of the hydroxyapatite coated on carbon/carbon composites were studied in vitro and in vivo. By means of SEM, optical microscope, XRD and electronic tension machine, the material preparation, surface microstructure, phase transformation and coating bond strength were also investigated.The experimental results revealed that the impurity contents of PAN based carbon/carbon composites could meet the standard of artificial bone materials. What's more, the graphitation could reduce the main impurities in carbon/carbon composites significantly and this material had the similar microhardness to the human bone. The XRD's results indicated that the crystallization of the carbon/carbon composites before graphitaion was about 20%, and after 2400°C×2h of graphitaion the crystallization is above 60%. The surface microstructure observations of the sand blasted carbon/carbon composites revealed that under the condition of 5—11μm SiC sands and 0.2MPa blasting air pressure, an integrated carbon/carbon composites surface structure with enough coarseness could be got. The shear strength between the as-sprayed hydrxyapatite coating and carbon/carbon composites was 4.93 MPa.In the process of the plasma spraying, the average thickness of the hydroxyapatite coating is 76μm under the condition of the moving speed 200mm/s of a sprayer. XRD results revealed that hydroxyapatite was the main phase in the coating, followed byα-TCP andβ-TCP. The crystallination of the coating is lower, and the shape of deformed hydrxyapatite particles changed from spheres to flat plates on the substrates during the spraying process. There were many micro-cracks in the coatings because of the thermal expand coefficient difference between hydroxyapatite and carbon/carbon composites. The SEM pictures demonstrated that the as-sprayed coating was constituted by a lot of nano-sized cystal particles.When as-sprayed hydroxyapatite coatings were immerged in simulated body fluid, it began to dissolute and the nuclearation as well as the growth of the new phases occurred. By means of XRD, the as-heat treated hydroxyapatite coatings were analyzed. It was found that 600℃×10min of heat treating process was the proper recrystallization one and the cytoxicities of both hydroxyapatite coated carbon/carbon composites and the one without coating were evaluated as a grade of number one.In the 90 days after the implantation, it was found that such materials were favourable for health and no cytotoxic effects were discovered. The histological observation of osteogenic response of HA coated on C/C showed that the osteoplaque had scansorially grown along the surface of the HA coatings and the muscle tissue could bond with the material tightly. Based on these studies, the C/C+HA lumbar spinal fusion cages have been designed and produced for the larger animal testing in the near future.
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