Fabrication And Characterization Of Biodegradable Zn-based Porous Scaffold For Bone Regeneration Applications

Bone tissue defect has become an important disease affecting people’s health and life.When the bone defect exceeds the critical threshold,it cannot be healed only by the repair ability of the bone tissue itself.Therefore,the bone repair scaffold materials need to be implanted into the lesion site for structural replacement,which play mechanical support and achieves other functions.In recent years,the research of a bone repair scaffold material Zn has developed rapidly,but some problems have been found:low strength,slow degradation rate and certain cytotoxicity.Alloying and compound process of pure Zn are the most common methods to obtain excellent comprehensive properties of bone repair scaffold materials.In this study,Cu and Ag were used as alloying elements to improve the mechanical properties of pure Zn,while regulating the corrosion degradation rate and giving it better antibacterial performance.Using Mg as alloying element andβ-TCP as the composite strengthening phase to improve the mechanical properties,it was explored that the the corrosion degradation rate was controlled by the content of strengthening phase,and theβ-TCP can give Zn alloy better biological activity.In addition,this study also explored the use of powder mixing,SPS sintering process to prepare porous bone repair scaffold materials,and carried out preliminary characterization and testing.The main research results and conclusions are as follows:Porous Zn,Zn-2wt%Cu and Zn-2wt%Cu-0.5wt%Ag series scaffolds and porous Zn-1wt%Mg-xvol%β-TCP(x=0,0.5,1,3)series scaffolds were prepared by the air pressure infiltration method.Connected pores were distributed homogeneously,the average pore size was about 242～259μm,and the porosity of the scaffolds was about60%.The platform stressσ_yat 3%strain and elastic modulus E of Zn-2Cu scaffold material are 16.17 MPa and 0.89 GPa.The platform stressσ_yat 3%strain and elastic modulus E of Zn-2Cu-0.5Ag scaffold material are 23.71 MPa and 1.02 GPa.The platform stressσ_yat 3%strain and elastic modulus E of Zn-1wt%Mg-xvol%β-TCP(x=0,0.5,1,3)scaffold materials are 13.22～16.89 MPa and 0.62～0.82 GPa respectively.The mechanical properties are close to cancellous bone of human body.Zn,Zn-2Cu and Zn-2Cu-0.5Ag scaffold materials can induce the deposition of Ca-P compounds on the surface of samples.The addition of Cu and Ag would accelerate the corrosion of the scaffold.Zn-1Mg-xβ-TCP(x=0,0.5,1,3)scaffolds materials induced an increase in the content of Ca-P deposition with the increase ofβ-TCP addition,showing good biological activity.The porous pure Zn scaffold had antibacterial ability against Escherichia coli and Staphylococcus aureus,and the antibacterial ability was significantly enhanced by adding Cu and Ag on the basis of pure Zn.Porous Zn,Zn-2Cu and Zn-2Cu-0.5Ag scaffold materials have certain toxic effects on mouse fibroblasts(L929)and mouse osteoblasts(MC3T3-E1).Zn-1Mg-xβ-TCP(x=0,0.5,1,3)showed little difference in antibacterial activity against Escherichia coli and Staphylococcus aureus.When the concentration of Zn-1Mg-xβ-TCP(x=0,0.5,1,3)scaffold material extract was diluted to 25%,the proliferation of mouse osteoblasts(MC3T3-E1)was promoted.The pure Zn and Zn-2Cu porous scaffolds were implanted into the femur of SD rats.Micro-CT analysis showed that there were signs of osteogenesis around the two implanted materials,and the degradation rate of Zn-2Cu scaffold was faster than that of Zn scaffold.No inflammatory reaction was found in all blood biochemical indexes.Histological analysis revealed new bone formation around the two porous implants at various time points after implantation and the bone mass increased with the increase of time.Although the vitro test was slightly toxic,but the vivo evaluation results indicated that the porous Zn-Cu(x=0,2)scaffolds have good biocompatibility and they were safe and reliable in long-term bone repair.Preparation of porous Zn-xvol%β-TCP(x=0,0.5,1,3)scaffold materials by spark plasma sintering(SPS).Compared with the melting method,β-TCP can be introduced into the composite material stably and they were more evenly distributed in grain boundaries.