Preparation And Characterization Of Zinc-based Porous Bone Tissue Engineering Scaffolds

At least 4 million bone defect replacement surgeries are performed each year,and bone tissue engineered stents are a good way to repair large bone defects.Metal bone tissue engineering scaffolds are suitable for large bone defects in load-bearing parts,but most of them are non-degradable materials.Zinc-based degradable biomaterials overcome the disadvantages of non-degradable traditional metal biomaterials(such as titanium alloy)and may have long-term clinical complications.Zn is an essential trace element for human body and has good biocompatibility.In order to prepare a zinc-based bone tissue engineering scaffold suitable for large bone defects in load-bearing parts,porous zinc-based scaffolds were fabricated by two methods:seepage casting and laser selective melting(SLM).(1)In order to optimize the composition of the alloy,Zn-Li alloys with different Li contents(Zn-0.2Li,Zn-0.4Li,Zn-0.8Li,Zn-1.2Li)were smelted by gas protection method.With the increase of Li content,the yield strength of as-cast Zn-0.8Li alloy is improved.The as-cast Zn-0.8Li alloy has excellent comprehensive properties,and its compressive yield strength reaches 312MPa.After adding 0.2wt.%Ag,the yield strength of Zn-0.8Li-0.2Ag alloy decreases to 297MPa,but the ductility increases by1.2%.After soaking in SBF for 30 days,the degradation rates of Zn-0.8Li and Zn-0.8Li-0.2Ag alloys are 41.5?m/Y and 42.3?m/Y,respectively.Zn-0.8li and Zn-0.8Li-0.2Ag alloys have sufficient mechanical strength and appropriate degradation rate,which are ideal materials for preparing porous zinc alloy scaffolds.(2)Porous zinc and zinc alloy(Zn-0.8Li,Zn-0.8Li-0.2Ag)with different pore sizes(150-350?m,350?m-550?m)and different porosity(50%-70%)were prepared by percolation casting method.The average pore size of the large sample is 285.7?m,and the average pore size of the small sample is 152.3?m.The larger pore size samples showed better pore connectivity than the smaller pore size samples,and the larger pore size samples also showed higher porosity.The mechanical properties of the porous samples decrease with the increase of porosity.The compressive yield strength of the zn-0.8Li scaffolded with large pore size and 71%porosity is 24.89MPa,and that of the Zn-0.8Li scaffolded with small pore size is 42.45MPa.Immersion experiments show that the weight loss rate is closely related to the pore size and porosity of the sample,and the small pore size and low porosity will greatly slow down the later degradation of the porous sample.(3)The chitosan coating was prepared on Zn-0.8Li scaffolds with large pore size.In vitro cell experiments showed that the activity of chitosan coated scaffold(CS-Zn-0.8Li)against MC3T3-E1 cells at 100%and 50%concentration was 32%and72%,respectively.SEM image of the scaffolds implanted for one month in vivo showed that a large number of new bone tissues were generated in the pores of both Zn-Li scaffolds and CS-Zn-0.8Li scaffolds,and Micro-CT results showed that the scaffolds coated with chitosan showed better bone growth.Von Kussa staining after two months of implantation showed more new bone tissue in the pores.These results indicate that Zn-Li scaffolds and CS-Zn-0.8Li scaffolds degrade slowly and release Zn²⁺,providing an ideal microenvironment for mesenchymal stem cell adhesion,proliferation and differentiation,and this bionic porous structure may be suitable for the growth of new bone.(4)In the method of laser selective melting(SLM)to prepare porous zinc scaffolds,0.2wt.%nano Mg O particles were added to zinc to improve the degradation of zinc scaffolds.The skeletal-Gyroid model and skeletal-IWP model porous scaffolds with different mono-size and porosity were printed.The microstructures of printed Zn and Zn-0.2Mg O were observed by backscattering,and the Mg O nanoparticles were mainly distributed in the strip defects of the matrix by EDS.The porosity of the printed porous scaffold was measured by weighing method,and the porosity of the prepared scaffold was in the range of 50%-70%.Finally,mechanical compression tests were performed on the porous Zinc scaffolds.For the porous Zn scaffolds with different measured porosity,the porosity was 53.5%,59.3%and 64.2%,and the compressive yield strength was 17.8MPa,10.6MPa and 7.3MPa,respectively.For the multiple Zn-0.2Mg O scaffolds with different measured porosity,the porosity is 50.8%,60%,61.0%,and the compressive yield strength is 17.5MPa,10.8MPa,and 8.9MPa,respectively.The skeletal-Gyroid model has a higher compression yield strength than the Skeletal-IWP model when the measured porosity is the same.Immersion experiments show that the printed porous Zn scaffold is more prone to pitting corrosion,and the pitting corrosion is the main reason affecting the weight loss rate.The printed porous Zn-0.2MGO supports are more inclined to uniform corrosion,and their corrosion loss rate is mainly related to the connectivity of pore structure and specific surface area of the sample.