Fabrication And Performances Study Of Zn-modified Calcium Phosphate Coating On Biomedical Magnesium Alloy

Magnesium and its alloys are regarded as the potential biodegradable orthopaedic implant materials because of their mechanical properties which are similar to natural bone, good biocompatibility and biodegradation in physiological environment. However, magnesium alloys have high chemical activity, which accordingly results in lose efficacy before the bone tissues have healed. So, it is necessary to control its corrosion rates to match the rates of bone healing by the surface modification.In this study, a degradable Zn-modified calcium phosphate coating was fabricated on Mg-Zn-Ca alloy by pulse reverse current(PRC) eletrodeposition to improve its corrosion resistance. The as-deposited coating was characterized with scanning electron microscope(SEM) equipped with energy dispersive X-ray spectroscopy(EDS), X-ray diffraction(XRD), fourier transform infrared spectroscopy(FT-IR), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS), respectively, so as to investigate its microstructure, phase composition and suggest the deposition mode. The electrochemical corrosion resistance of the Zn-modified calcium phosphate coating in Kokubo’s simulated body fluid(SBF) was investigated. The effect of Zn-modified calcium phosphate coating on degradation behavior of Mg-Zn-Ca alloy was studied through immersing in SBF, and the degradation mode was suggested. Moreover, the antibacterial capability and cytotoxicity of the Zn-modified calcium phosphate coating was also studied. This research can provide the scientific grounds for the development of biodegradable magnesium-based materials.1. The uniform non-stoichiometry Zn-modified calcium phosphate coating on Mg-Zn-Ca alloy is successfully deposited by PRC electrodeposition. The optimal fabrication parameters are fabricating for 50 min in 5% Zinc electrolyte. The coating particles are packed closely and the composition of the coating is CaZn2(PO4)2?2H2O based on the result of XRD. The molar ratios of Zn/Ca and(Zn+Ca)/P are about 2 and 1.27. The thickness of the coating is about 8.38μm. The lap shear strength between the coating and the substrate is 8.78 MPa. The coating has a better wettability.2. The deposition process of the Zn-modified calcium phosphate coating on magnesium alloy was studied carefully. The addition of zinc makes the deposition mode of the calcium phosphate coating has undergone tremendous change. From "nucleationâ†' coverageâ†' growth" change to " nucleationâ†' expansion and growthâ†' coverageâ†' destruction".3. The electrochemical tests show that compared with the substrate the corrosion potential of magnesium alloy with Zn-modified calcium phosphate coating increases 60 mV, while the corrosion current density decreases by about two orders of magnitude. The electrochemical tests also show that compared with the common calcium phosphate coating, the corrosion potential of magnesium alloy with Zn-modified calcium phosphate coating increases 20 mV, while the corrosion current density decreases by about one order of magnitude. The immersion test indicates that the coating will degrade gradually during the process of immersion.4. The tests of antibacterial effect show that the magnesium alloy with Zn-modified calcium phosphate coating exhibits a stronger antibacterial effect against colibacillus and S. aureus than the common calcium phosphate coating. The tests of cytotoxicity show that the magnesium alloy with Zn-modified calcium phosphate coating exhibits a better cytotoxicity than the common calcium phosphate coating. The Zn-modified calcium phosphate coating is a qualified potential bone implant material.