Improved Corrosion Behavior of Biodegradable Mg-4Zn-1Mn Alloy Modified by Sr/F co-doped CaP Micro-arc Oxidation Coatings

The Sr/F co-doped CaP(Sr/F-CaP)coatings were prepared by micro-arc oxidation(MAO)under different voltages to modify the microstructure and corrosion behavior of Mg-4Zn-1Mn alloy.The surface and interface characteristics investigated using scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS)showed that the MAO coatings displayed uneven crater-like holes and tiny cracks under lower voltage,while they exhibited relatively homogeneous crater-like holes without cracks under higher voltage.The thickness of MAO coatings increased with increasing voltage.The corrosion behavior of Mg-4Zn-1Mn alloy was improved by the MAO coatings.The MAO coatings prepared under 450 V and 500 V voltages possessed the best corrosion resistance with regard to the electrochemical corrosion tests and immersion corrosion tests,respectively.The MAO coatings fabricated under 450-500 V could provide a better corrosion protection effect for the substrate.

Microstructure and mechanical and corrosion properties of hot-extruded Mg–Zn–Ca–(Mn)biodegradable alloys

Biodegradable Mg-based implants are widely used in clinical applications because they exhibit mechanical properties comparable to those of human bone and require no revision surgery for their removal.Among Mg-based alloys,Mg–Zn–Ca–(Mn)alloys have been extensively investigated for medical applications because the constituent elements of these alloys,Mg,Zn,Ca,and Mn,are present in human tissues as nutrient elements.In this study,we investigated the effect of the hot extrusion temperature on the microstructure,mechanical properties,and biodegradation rate of Mg–Zn–Ca–(Mn)alloys.The results showed that the addition of Mn and a decrease in the extrusion temperature resulted in grain refinement followed by an increase in the strength and a decrease in the elongation at fracture of the alloys.The alloys showed different mechanical properties along the directions parallel and perpendicular to the extrusion direction.The corrosion test of the alloys in the Hanks’solution revealed that the addition of Mn significantly reduced the corrosion rate of the alloys.The Mg–2 wt%Zn–0.7 wt%Ca–1 wt%Mn alloy hot-extruded at 300℃ with an ultimate tensile strength of 278MPa,an yield strength of 229MPa,an elongation at fracture of 10%,and a corrosion rate of 0.3 mm/year was found to be suitable for orthopedic implants.

Friction and wear behaviors of biodegradable Mg-6Gd-0.5Zn-0.4Zr alloy under simulated body fluid condition

The friction and wear behaviors of biodegradable Mg-6Gd-0.5Zn-0.4Zr(wt%,GZ60K)alloy were evaluated under simulated body fluid(SBF)condition using ball-on-disk configuration and compared with those under dry sliding condition.The results show that under dry sliding and SBF conditions,the friction coefficient declines with increasing applied load and keeps stable with prolonging sliding time.The friction coefficient of the alloy effectively decreases in SBF as compared to dry sliding due to lubrication caused by SBF.The real wear rates under SBF condition are lower than those under dry sliding condition for each parameter.Nevertheless,the nominal wear rates are higher in SBF which are attributed to the more mass loss caused by corrosion but not wear.Both the nominal wear rate in SBF and the dry sliding wear rate increase with increasing applied load,and they decline firstly and then keep stable with prolonging sliding time.It is concluded that the wear of the alloy is restricted by the SBF,but the corrosion of the alloy is aggravated by the wear.

Evaluation of the biodegradation product layer on Mg-1Zn alloy during dynamical strain

Magnesium(Mg)alloys are attractive biodegradable implant materials.The degradation products on Mg alloys play a critical role in the stability of the interface between implant and surrounding tissue.In the present study,the effects of dynamic deformation on the interface layer of biomedical Mg-1Zn alloy were investigated using the constant extension rate tensile tests(CERT)coupled with electrochemical impedance spectroscopy(EIS).The deformation of the Mg-1Zn alloy had an adverse influence on the impedance of the surface degradation layer formed in simulated body fluid that only containing inorganic compounds.However,the surface degradation layer with improved corrosion resistance was obtained for the strained samples tested in protein-containing simulated body fluid.The spontaneous or enhanced adsorption of protein into the degradation product led to a flexible and stable hybrid anti-corrosive layer.A relationship between the dynamic deformation of Mg alloy and the impendence of the degradation layer was established,which demonstrates the necessity for in situ characterisation of the evolution of the surface layer under dynamic condition.

Challenges and Solutions for the Additive Manufacturing of H) Biodegradable Magnesium Implants

Due to their capability of fabricating geometrically complex structures,additive manufacturing(AM)techniques have provided unprecedented opportunities to produce biodegradable metallic implants—especially using Mg alloys,which exhibit appropriate mechanical properties and outstanding biocompatibility.However,many challenges hinder the fabrication of AM-processed biodegradable Mg-based implants,such as the difficulty of Mg powder preparation,powder splash,and crack formation during the AM process.In the present work,the challenges of AM-processed Mg components are analyzed and solutions to these challenges are proposed.A novel Mg-based alloy(Mg-Nd-Zn-Zr alloy,JDBM)powder with a smooth surface and good roundness was first synthesized successfully,and the AM parameters for Mg-based alloys were optimized.Based on the optimized parameters,porous JDBM scaffolds with three different architectures(biomimetic,diamond,and gyroid)were then fabricated by selective laser melting(SLM),and their mechanical properties and degradation behavior were evaluated.Finally,the gyroid scaffolds with the best performance were selected for dicalcium phosphate dihydrate(DCPD)coating treatment,which greatly suppressed the degradation rate and increased the cytocompatibility,indicating a promising prospect for clinical application as bone tissue engineering scaffolds.