Preparation,Characterization And Properties Of Biodegradable Medical Zn-Mg/HAp Composites

Zinc possesses proper degradation rate,good biocompatibility and appropriate chemical activity,which could be a potentially degradable material.However,the mechanical performance of pure zinc is poor due to the pure zinc brittleness,which can not satisfy the clinical demand.Therefore,in order to improve the mechanical properties of pure zinc,adding alloy elements or preparing zinc matrix composites has become the current research direction and hotspot.In this paper,pure zinc was used as matrix material;Mg was chosen as alloying element to improve the mechanical properties of pure zinc,and the bioactive ceramic nano-hydroxyapatite was used as the enhancement phase.Then High energy ball milling and sparking Plasma Sintering?SPS?were employed to fabricate Zn-xMg and Zn-Mg/xhap composites.The effects of Mg content and hap content on microstructure,density,phase composition,component distribution,interfacial behavior,mechanical properties,corrosion properties and cytotoxicity of Zn-xMg and Zn-Mg/xHAp composites were studied by Zn-xMg and Zn-mg/x HAp composites.The main contents and conclusions of the study are as follows:The microstructure of the sintered Zn-xMg alloys is uniform,and the density of the alloys is high.It can be seen that are were MgZn₂ and Mg₂Zn₁₁phases in the alloys from the X-ray diffraction patterns.The micro hardness and compressive yield strength of the Zn-xMg alloys is improved significantly when alloying with Mg.The hardness and compressive yield strength raise because of the primary phases MgZn₂ and Mg₂Zn₁₁1 by the metallurgic reaction of Zn and Mg.The Zn-10Mg alloys showed the best combination of mechanical properties?hardness of 364.7 HV₃,ultimate compressive strength of 555 MPa and elastic modulus of 10.1 GPa?.And it has good biomechanical compatibility with bone.In vitro biodegradation behaviors of Zn-Mg alloys were evaluated through the immersion test in SBF.The corrosion rate of Zn-15Mg is the lowest about0.40 mm/a,and Zn-20Mg is the highest about 3.18 mm/a,corrosion intensifies because of a large Mg content in Zn-x Mg alloy.According to the above conclusion,the optimum mass fraction of magnesium was determined to be 15%.The interface of Zn-15Mg/xHAp composites sintered by SPS has good interfacial bonding and there is no obvious pore,and there is no reaction between HAp particles and Zn-Mg alloy matrix during sintering.The density of composites decreased with the increase of HAp content.The compressive strength and flexural strength of Zn-15Mg/5HAp composites are 330 MPa and 75 MPa,slightly lower than those of Zn-15Mg/10HAp composites.The compressive strength,flexural strength and modulus of Zn-15Mg/5HAp composites are closer to those of human bone,so the"masking effect"can be avoided effectively.The corrosion rate of Zn-15Mg/5HAp composites in simulated body fluid was lower than that of Zn-15Mg/10HAp composites and the corrosion rate of composites was the lowest after four days of immersion.The composite not only produces Zn?OH?₂,but also deposits Ca-P compounds in simulated body fluid immersion,then helps to slow down the corrosion of materials.The high content of HAp reduces the density of the composite,makes the bonding property of the composite worse,and thus increase the corrosion rate of the composite.The cytotoxicity ratings of both Zn-15Mg and Zn-15Mg/5HAp composites were 0¹,non-toxic.The cell morphology of Zn-15Mg and Zn-15Mg/5HAp composites was long fusiform and polygonal,and the cells grew well.The cells were cultured in the extract of Zn-15Mg/5HAp composites for 48 hours.The relative survival rate of cells exceeded 100%and the evaluation grade of cytotoxicity was 0.This indicated that the addition of HAp could promote the proliferation of cells to a certain extent.