Preparation And Biocompatibility Study Of Ca-P Film On Carbon/Carbon Composites

Carbon/carbon composites have excellent biocompatibility. Its major mechanical properties are closer to that of human bone compared with other widely used hard-tissue repair biomaterials. It is therefore a promising bone repair material. However, carbon/carbon composites could neither conduct nor induce the regeneration of bone tissue due to its bio-inert property. Besides, pure carbon/carbon composites implant may release carbon debris after implantation. These drawbacks have limited its potential application. Coating this material with apatite could grant its surface with bioactivity, increase the bonding strength between implant and bone tissue, and significantly decrease the release of carbon debris. In this paper, carbon/carbon composites+hydroxyapatite(C/C+HA) coating implants made through plasma spraying by our team earlier were implanted into crossed Boer Goats to evaluate its biocompatibility. Later, to overcome the drawback that plasma spraying could not make coatings on implants with complex shape, carbon/carbon composites were treated with strong oxidizing agents and soaked in stimulated body fulid to deposite Ca-P minerals. In order to accelerate deposition rate, accelerated calcification solution immersion and electrochemical deposition method were tried to make Ca-P deposition on carbon/carbon composites.In vivo biocompatibility test confirmed that, C/C+HA coating composites have good biocompatibility. Implant surgery did not induce inflammatory responses or acute toxic reactions; no serious injury to circulatory system, digestive system, respiratory system of experimental animals was caused. Histological observations indicate that both pure C/C and HA coating surfaces showed good morphology of bone tissue remodeling; but the thickness of connective tissue film on HA-coated surface were significantly smaller than those on pure C/C surface, the carbon particles peeling off from implant were also decreased significantly. These results indicated that preparation of HA coating further enhances bone tissue compatibility of carbon/carbon composites, improved bone conduction of implant surface, and greatly reduced the possibility of releasing carbon particles.Surface modification experiments and the subsequent simulated body fluid immersion test showed that C/C have weak ability to induce Ca-P deposition in simulated body fluid. After immersed in simulated body fluid for 4 days, small amount of Ca-P deposition could be observed on the surface of C/C, the amount of deposits become larger as soaking time increased. When treated with concentrated nitric acid, hydrogen peroxide, acidic potassium permanganate, ammonium persulfate and other strong oxidizing agents, oxygen-containing functional groups on C/C were increased and the ability of C/C to induce Ca-P deposition in simulated body fluid was enhanced. Gas surface modification can also increase content of oxygen-containing functional groups, the content of oxygen functional groups increased as treating temperature increased. However, the improvement of gas surface modification to the biomimetic mineralization ability of C/C is weaker than liquid-phase oxidation; and high treating temperature may weaken structural stability of materials. When gas surface modification was added after liquid phase oxidation, the biomimetic mineralization ability of C/C was not enhanced.Using accelerated calcification solution immersion or electrochemical deposition method could obtain continuous Ca-P deposits on carbon/carbon composite, but these deposits were porous.