| A cross-cut test was employed to optimize the process parameters of depositing aCa-P layer onto the surface of NiTi shape memory alloy. Its mechanical properties andbiocompatibility before and after the process were also discussed. Surface morphology, elements and surface energy of the NiTi alloy after differentpre-treatment, i.e., different acid treatment and alkali treatment were investigated byScanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD), Energy dispersion X-ray spectroscopy(EDXS) and Dynamiccontact angle testing equipment(DCAT). The results of cross-cut test indicated that the longer the acid treatment, the lowerthe concentration and temperature of HNO3 solution, the better and quicker thegrowth of Ca-P layer; the higher the concentration of NaOH solution, the longer thealkali treatment and the lower the temperature, the better and quicker the deposition ofCa-P layer. The optimum process parameters for acid and alkali treatment were30%HNO3, 60℃,24hours and 5MNaOH, 90℃, 5hours respectively. After alkalitreatment Na2TiO3, NaTi2O4 and NaNiO2 appeared on the alloy surface and?-Ca3(PO4)2, ?-Ca2P2O7 formed after pre-calcification. Pull-out test and micro-indentation test were carried out to measure the bondingstrength between the Ca-P layer and its substrate. The results showed the bonding wasgood. As the tensile test showed, acid treatment had no effect on the mechanicalproperties of NiTi alloy. Cytotoxicity test of osteoblast showed that NiTi alloy had no effect on the growthand propagation of osteoblast cells and the alloy with Ca-P layer had betterbiocompatibility. Carboxyl was introduced onto the surface of NiTi alloy by means of electrolysis.Collagen was used in the experiment in order to deposit an organic and inorganiclayer with better biocompatibility and bone-repairing ability. A complete Ca-P layerwas prepared within 1 or 2 days using the electrolysis method but whether the layercontained collagen was left to study further.
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