Anisotropic Design And Mechanical Properties Study Of Porous Scaffold Based On Minimal Surface

A large number of scientific researches and clinical practice results have shown that the elastic modulus of metal material is much higher than that of human bone tissue,and the mismatch in mechanical properties can easily lead to loosening of the metal prosthesis and bone tissue,which is difficult to meet the expected effect.In recent years,with the development of 3D printing technology,the mechanical properties of porous materials can be controlled by designing microstructure and porosity,thereby improving the mechanical properties of implants,promoting bone growth and improving the long-term stability of implants.The porous structure based on Three Period Minimal Surface is considered to be one of the most promising orthopedic biomaterial structures.Its good surface continuity,excellent mechanical properties and manufacturing properties have attracted widespread attention.Cancellous bone is a porous composite material with obvious anisotropic mechanical behavior.However,there are few studies on the anisotropic design of structure based on TPMS,and the relationship between its geometric parameters and mechanical properties is still unclear.This study proposed an anisotropic design method for the Gyroid cellular structure(GCS),which is widely studied in structures based on TPMS,and analyzed the resulting changes in geometry and mechanical properties.In addition,the GCSs was manufactured by EBM(Electron beam melting)method,and the influence of the manufacturing method on the geometrical and mechanical deviation was studied.The result of the thesis provide theoretical support for structure and mechanical design of GCS.The content of this study mainly includes:(1)Anisotropic design of Gyroid structure and its geometric structure analysis: An anisotropic design method based on GCS was proposed.The influence of anisotropic design on the geometric continuity,surface-volume ratio and geometric shape of GCS was analyzed.The porosity of the structure has a linear relationship with the parameter t,and anisotropic design will not affect it.Keeping the porosity constant,the anisotropic design will lengthen or shorten the Gyroid unit cell.The elongated unit cell is good for geometric continuity but not good for the specific surface area,and the shortened unit cell is completely the opposite.The angle and diameter of the support strut will change with the unit cell change,and the rule in different directions is different.(2)Research on the anisotropic elastic response of GCS: Using the finite element method,the elastic response of the anisotropic GCS was analyzed,and the mathematical relationship between the geometric parameters and the elastic modulus,structural anisotropy of GCS was obtained.This study found that anisotropic design cannot increase or decrease the elastic modulus out of thin air.If the stiffness in a certain direction is increased through anisotropic design,the stiffness in the orthogonal direction will be weakened.In addition,the relationship between the anisotropy of the elastic response and the porosity,structural anisotropy and loading direction was further studied to guide the design of the elasticity and anisotropy in CGS.Within the parameters considered,the degree of anisotropy in GCS varied from 0.17 to 3.6,as compared with 0.2 to 4 for human bones;the elastic modulus of the anisotropic GCS was in the range 0.03 GPa to 5.6 GPa for titanium alloy,which included the elastic modulus range of human cancellous bone.(3)The manufacturing and mechanical deviation analysis of anisotropic GCS: The scaffold was manufactured by EBM,and the reconstruction model of scaffolds was obtained by ?CT scanning.The geometric and porosity deviation between the reconstructed model and the designed scaffold were evaluated,and the mechanical deviations of reconstruction model and the experimental model caused by the manufacturing direction and geometric discrepancy were analyzed.The results show that the anisotropic design reduced the geometric deviation,so that the deviation range of the compressive strength was within 12%,and the deviation range of the elastic modulus was reduced from 40% to 24%.In addition,the failure mode of GCS was analyzed through the evolution of surface deformation and failure during the loading process.The microscopic morphology of the fracture surface on the strut indicated that the fracture mode is a mixed mode of ductile fracture and brittle fracture.