Electrodeposition And Characterization Of Hydroxyapatite Coatings On Magnesium Substrate Biomaterials

For the density and elastic modulus being close to human bone, magnesium andmagnesium alloy have superior mechanical properties, which makes them are morebiocompatibility for medical use than other metals, but they are easy to corrode due totheir active chemical properties. HA or HAP short for hydroxyapatite, has goodcorrosion resistance and biocompatibility. The hydroxyapatite coating on magnesiumsubstrate biomaterials has become one of the research emphases in recent years,because with HA as coating material, the metal substrate biomaterial will have strongadhesion after implanting organism in a short time, and make firmly combinationbetween the interface of material and bone, meanwhile restrain the substrate ionreleasing to organism effectively.In this article, metalloscope, X-ray diffraction analysis, scanning electronmicroscopy and other test methods were used to study the different pretreatmentimpact on the magnesium substrate surface appearance, the phase of deposition andthe weight increase. The results showed that: corrosive liquid of HNO₃+HF andH₃PO₄+HF can make great corrosion pits on the surface of the magnesium substrate,may obtain the massive spoiled etch pits in the magnesium substrate surface. The bestpretreatment is150ml/L HNO₃+25ml/L HF corrosion one minute.With high chemical activity, the magnesium is extremely easy to oxidation,meanwhile can produce hydrogen in the electrodeposition process, and ultimatelyreduce the coating’s quality. By adding some hydrogen peroxide into the electrolyte,the coating’s quality can be improved. This article discussed the different content ofhydrogen peroxide in the electrolyte influence on the electrodeposition product andthe appearance. The results indicated that: with no hydrogen peroxide in theelectrolyte, the main electrotdeposition product is Ca₃（PO₄）₂before and after alkali-heat treatment, and due to the weak bonding force, the coating is easy to strip. Withhydrogen peroxide being in the electrolyte, the electrodeposition product isCaHPO₄·2H₂O, which can transform into hydroxyapatite after the alkali-heattreatment. The better content of hydrogen peroxide is6ml.Hydroxyapatite coating on magnesium substrate biomaterial was prepared byelectrochemical deposition method, and the different electrodeposition parameters effect on the coating was studied via orthogonal experiment. The research resultsindicated that: pH is the main influencing factor on the deposition phase, the pH valueapproach neutral aren’t conducive to produce CaHPO₄·2H₂O, which is the precursorof hydroxyapatite; deposition temperature is the main influencing factor on thedeposition weight increase, and its excellent level is60℃; Well-distributed coatingdeposited on magnesium substrate surface after electrodeposition, and its morphologyshows that the coating is larger pieces organization and some smaller clusterorganization. Energy spectrum analysis showed that the molar ratio of calcium andphosphorus is slightly greater than1.5.Biomimetic liquid SBF immersion corrosion test was used to research the invitro bioactivity and the corrosion resistance of pure magnesium and magnesium/HAPcomposite in this article. The research results demonstrated that: the weight ofmagnesium/HAP composite increased greater after immersion7days, almost twicetimes of pure magnesium. The biomimetic liquid’s pH value of pure magnesium isobviously higher than the pH value of magnesium/HAP composite within24hours.Meanwhile pure magnesium immersion in biomimetic liquid produced manycorrosion cracks on the surface, and the white deposition particles on the surface haveweak bonding force with the substrate, while in SBF immersion process themagnesium/HAP composite was gradually covered with a layer compactnewbornsubstance, which significantly enhance the corrosion resistance andbioactivity of magnesium substrate.