Fabrication And Properties Of Biodegradable Porous Zn-Mg-β-TCP Composite Scaffolds

Bone defects are common orthopedic conditions caused by trauma,infection,tumor removal,and congenital diseases,and the market demand for bone defect repair materials will continue to expand as society ages and medical needs continue to rise.Although autologous bone graft,allogeneic bone graft,ceramic and polymer-based synthetic materials have been used for clinical bone repair,all have their own limitations.In recent years,biodegradable metals,represented by iron（Fe）-based,magnesium（Mg）-based and zinc（Zn）-based metal materials,have shown great potential for application in bone defect repair due to their good mechanical properties and degradation performance.Among them,Zn-based materials not only possess moderate degradation rates compared with Fe-based materials,which degrade too slowly,and Mg-based materials,which degrade too quickly,but also do not release gas during the degradation process,and are expected to become the next generation of bone defect repair materials for clinical use.Although the degradation rate of Zn-based materials is moderate,it is still slow compared with the bone repair rate,and the osteogenic activity needs to be further improved.How to improve the degradation rate and osteogenic activity of Zn-based bone repair materials,while maintaining their excellent mechanical properties,is the key to their clinical application.To solve the above problems,biodegradable Zn-Mg-β-TCP composites were prepared by adding both Mg andβ-tricalcium phosphate（β-TCP）to the Zn matrix through vacuum heating-press sintering method,and the pore structures were designed on this basis to finally construct biodegradable porous Zn-Mg-β-TCP composite scaffolds.In the whole research process,the objects were systematically tested and evaluated in terms of microstructure,mechanical properties,in vitro degradation,in vitro cytocompatibility and in vivo osteogenic properties according to the logical sequence of"exploration of process parameters-design of porous structure-determination of composite components-design of porous composite".The main results of the study are as follows:（1）The bulk pure Zn was prepared by vacuum heating-press sintering at different sintering pressures（40,60 and 80 MPa）,and it was found that the densities of the materials increased with increasing sintering pressure and modulated the properties of the materials:the higher the densities of the materials,the higher the mechanical strength;the samples with different densities also showed some differences in degradation behavior;it was also verified that all groups of pure Zn samples It was also verified that all pure Zn samples did not inhibit the proliferation of MC3T3-E1 cells.The feasibility of the vacuum heating-press sintering method for the preparation of biodegradable Zn-based materials was confirmed,and the relationship between sintering pressure and material properties was established,which provides a process reference for the preparation of subsequent composites and the construction of porous structures.（2）Porous pure Zn scaffolds with different porosity were prepared by vacuum heating-press sintering,and it was found that the porosity produced modulation of the material properties:the higher the porosity,the lower the mechanical strength of the material,but the degradation rate would increase dramatically;the higher the porosity,the larger the surface area of the sample to provide adhesion and spreading for MC3T3-E1 cells,thus promoting the cell proliferation.After analysis,porous pure Zn scaffolds with suitable preset porosity（40-60%）exhibited superior overall performance.In addition,porous pure Zn scaffolds were found to be subject to degradation due to the combined effects of metal corrosion and degradation product shedding.（3）Zn-1 wt.%Mg-n vol.%β-TCP（n=0,1,3,5,10）composites with differentβ-TCP contents were prepared by vacuum heating-press sintering,where Mg was present as Zn₂Mg and Zn₁₁Mg₂ in the Zn matrix andβ-TCP were diffusely distributed in the Zn matrix.The microstructure produced modulation of the material properties:the mechanical properties of the composites were improved by the combination of the second-phase strengthening mechanism and the dislocation strengthening mechanism;the formation of microelectric couples at the Zn-Mg interface and the large number of corrosion interfaces brought about byβ-TCP together accelerated the degradation of the material;the changes in ion release concentration and surface microstructure caused by the differences in corrosion behavior together modulated the MC3T3-E1 cells proliferation activity;a 24-week in vivo animal experiment showed that the Zn-Mg-β-TCP composites have better osteogenic ability than pure Zn,which was closely related to the incorporation ofβ-TCP.This elucidated the composites’compositional and microstructure-dominated performance modulation mechanism.（4）Porous Zn-1 wt.%Mg-3 vol.%β-TCP composite scaffolds were prepared by vacuum heating-press sintering,with compressive yield strengths ranging from 58.46-71.04 MPa and corrosion rates ranging from 2.73-4.28 mm/y.In vivo animal experiments over a 24-week period showed that the degradation process of the composite scaffolds occurred simultaneously with the new bone generation process.The degradation of the composite scaffold occurred simultaneously with new bone production,and the corrosion products fused with the new bone tissue over time,achieving a synergistic effect between implant degradation and bone defect repair.Overall,the porous Zn-1 wt.%Mg-3 vol.%β-TCP composite scaffolds possess great mechanical stability,degradability and in vivo osteogenic properties.In summary,the biodegradable Zn-Mg-β-TCP composites and their scaffolds were constructed in this study,and the relationships between material composition,pore structure and mechanical properties,degradation behavior and bone repair ability were established,which are important for the development and clinical application of ideal bone repair materials,especially for the repair of large segmental bone defects.