| To improve the bioactivity of titanium alloy implants and to promote the osseointegration process, laser rapid forming (LRF) was used to coat titanium with calcium phosphate bioceramics, which integrated the good mechanical property of titanium alloys with excellent bioactivity of bioceramics. Biomechanism of osseointegration at the interface between bone and implantation in early periods was investigated using biological experiments. It was expected that the new method of bioceramics coatings can make the foundation for the LRF application in the future clinics.Methods:1. In situ bioceramics coating was prepared on commercially pure titanium substrate using LRF. The 80% CaHPO4·2H2O and 20% CaCO3 were mixed and used as raw powders. The microstructure, composition and phase components of the in situ laser coating were evaluated. DMEM fluid including fetal bovine serum was chosen as simulated body fluid to perform in vitro immersion experiment. The micro-morphology of the specimens were observed to evaluate the ability of inducing apatite deposition.2. According to the GB and YY-T standard, the specimens were tested with the in vitro cytotoxicity test, hemolytic test and oral mucous membrane irritation test, respectively.3. The osteoblasts were cultured on specimens of LRF calcium phosphate coating. The specimens of polished titanium were used as control. Cell adherence, proliferation and bone-related gene expression were investigated using MTT assay, flow cytometry, morphology analysis and real time RT-PCR.4. To evaluate the healing degree and interaction between bone and implants. The specimens of calcium phosphate coating and polished titanium were implanted into rabbit femur. After the healing period of 4 and 8 weeks, the interfaces between bone and implants in femur were selected for histomorphometric evaluation.Results:1. When the laser power was 400W, scanning speed was 100mm/min, powder feeding rate was 3.0g/min, and overlap rate was 35%, the feeding powder was 80wt% CaHPO4·2H2O and 20wt% CaCO3, the bioceramics coating was obtained by the method of in situ synthesis by laser cladding. The coating was mainly composed of Ca, P, O elements and a small amount of Ti, C elements. XRD revealed the presence ofβ-TCP (β-Ca3(PO4)2) as a predominant phase. The cross section was composed of ceramic layer, interface and titanium substrate. The microstructure changed gradually from the coating surface to the titanium substrate, which indicated metallurgical bond was formed.2. The calcium phosphate coating may have the ability of inducing the deposition of apatite, thus accelerate the nucleation and crystallization of apatite.3. The result of in vitro cytotoxicity test showed that the coating had no cytotoxicity. The result of hemolytic test showed that the hemolytic rates of all specimens were lower than 5%. The result of oral mucous irritation test showed that all specimens had no mucous membrane irritation.4. The calcium phosphate coating fabricated by LRF could accelerate the early adherence and proliferation of osteoblasts. The surface topological structure and chemical composition may be reasons for enhanced osteoblasts behaviors. The coating regulated the bone-related gene expressions and cell cycle, and accelerated the cell DNA synthesis, cell cleavage and proliferation.5. The calcium phosphate coated implants had good bioactivity and could bond tightly to bone tissues and accelerate formation and rebuild of bone tissues.Conclusions:In situ coating of calcium phosphate on titanium substrate by laser rapid forming have been successful prepared using mixed powders of CaHPO4·2H2O and CaCO3. The microstructure, chemical composition, phase structure of the coating were excellent. The coating had reliable biological safety and good cell compatibility, and could induce apatite deposition so as to accelerate formation and rebuild of bone tissue, which could shorten osseointegration periods of implants.
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