| Implant materials to be used as substitutes for high load-bearing bones need to possess not only bone-bonding ability but also high fracture toughness. However, neither the currently available bioactive ceramics nor biocompatible metals fulfill both these requirements. The fracture toughness of ceramics are lower than that of human cortical bone, and none of biometals can directly bonds to living bone. Coating bioactive ceramics onto a tough biometals integrates the bone-bonding ability of bioactive ceramics and the mechanical properties of the biometals. So, in this paper, we developed a new technology to prepare highly stable bioactive coating on titanium alloy. The technology of preparing Hydroxyapatite (HA) - Bioglass (BG) compound coating on a non-line-sight titanium alloy substrate was realized by electrophoretic deposition (EPD). The dense glass layer, as the inner sublayer of the compound coating, which could bond with the substrate by chemical bonding and mechanical locking, prevents the body fluid seeping into the interface between the coating and substrate. The outmost sublayer is porous HA-BG compound layer which can provide an excellent environment for bonding with a living bone.According to the requirements of coating on T16A14V alloy, the bioglass used in this experiment was designed on the basis of the Na2O-CaO-SiO2-P2O5 bioglass system. The composites of the bioglass are listed as below: Na2O-10. CaO-15, SiO248, P2O5-5, B2O3-10, TiO2-6, CaF2-6 (wt%). The thermal expansion coefficient of the bioglass is slightly higher than that of Ti6A14V alloy at high temperature (>320℃) and slightly lower at low temperature (<320℃). The melting temperature of the bioglass is lower than 700℃. Therefore, the bioglass has high chemical stability and can bond with the substrate after thermal treatment. The preparation process of EPD was carried on in the ethanol system, and the suspensions of BG and HA is stable in this system. Furthermore, the charge of BG particle was reversed through ion absorption, which made both BG and HA charged positively and realized the co-deposition of them in ethanol. The effect of concentration of ions, depositionvoltage, deposition time and solid concentration of the suspension to the EPD was also studied in this paper. Through two-step electrophoretic deposition, a BG layer and a HA-BG compound layer were successively deposited on the titanium alloy substrate. The thermal treatment of the coating employed the low-temperature-fast-firing technology.The relationship between the bonding strength of the BG coating and the thermal treatment system and that between the bonding strength of the compound coating and the amount of HA were studied in this paper. It is shown that the bonding strength of the BG coating was higher then 35 MPa. and that of the compound coating was higher then 25 MPa. The concentration of Ca2+ in ethanol solution before and after the BG was immersed by the solution was tested and the control experiment with other ions was carried out. The results presented that Ca + was absorbed onto the BG particles selectively and changed the zeta potential of BG in ethanol. The microstructure and the element distribution of the coating were analyzed by Scanning Electron Microscope (SEM), Electron Probe Micro-Analysis (EPMA) and Energy Dispersion X-ray fluorescence analysis (EDXA). The results revealed the structure of inner dense sub-layer and outmost porous sub-layer. The HA particles embedded in the bioglass could be seen from both the surface of the coating and the wall of the inner pore of the coating, which enlarged the contact area of the HA with the body fluid. The results showed that the HA-BG compound coating could be prepared by EPD in ethanol system. Integrating the mechanical, chemical stability and the bioactivity, the coating could resolve the problem of low stability in the current Ca-P bioactive coatings.
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