Surface Treatment Of Mg-Zn-Zr Alloy And Study On The Degradation Behavior In Vitro And In Vivo

Magnesium alloy is a very promising clinical application as bone fixation materials dueto their proper biomechanics, biocompatible and biodegradable properties. However, It isreported that the rapid degradable rate could result Mg alloy losing their mechanical integritypotentially during implantation period. In this study, the MgF2coating, HA/MgF2coating andHA/MgF2/Col coating was fabricated on the surface of Mg-3Zn-0.8Zr alloy using HFtreatments and Ca-P chemical deposition to adjust the corrosion resistance and bio-compatibleproperties. The surface characteristics and the degradation behavior of composite coatings ofMg-3Zn-0.8Zr alloy in vivo and in vitro were studied. We get such conclusions:(1) In this work, for HF treatment, the samples were immersed in HF of concentration20%at37℃temperature for2h. An uniform and compact fluoride coating has formed, thethickness of MgF2layer is0.9μm。It was composed by small parcels which size of9-25nm.The corrosion potential of coated alloy in SBF is0.28V higher than uncoated alloy.(2) Immersed the HF treated alloy in Ca-P solution in90℃for2h. Needle-like crystalclusters formed in the surface of alloy, the Ca/P ratio of the needle-like crystal is1.46, it’sindicated the needle-like crystal is a calcium-deficient FHA, by comparison, rod-1ike HAstructure growing along the c-axis. The corrosion potential of MgF2/FHA coated alloy in SBFis-1.48V, this coating could enhance the corrosion resistance effectively.(3) In this work, we used collagen of different concentration to prepare the collagencoating, after immersed in3g/L concentration collagen, the coating is smooth and uniform.Collagen solution could promote the mineralization of FHA crystal, and further improve thecorrosion resistance of the coating.(4) After implanted the Mg-3Zn-0.8Zr alloy with different coating in rabbit bone. wefound that the degradation rate of the implant coated with MgF2coating and FHA coatingwere smaller than uncoated sample. After4weeks implanted, the sample with MgF2/FHAcoating stayed volumes at90.24%，After15weeks implanted, this sample stayed volumes at63.06%,12%higher than uncoated sample. Screw could repaired bone effectively, the screwwith MgF2coating stayed volumes at62.6%in4weeks and43%in15weeks, while theuncoated screw stayed59.6%in4weeks and33%in15weeks. Degradation rate in screwbody is higher than in cap, condyle degradation rate is higher than the canal.