Structural Optimal Design Of Titanium Matrix Composite DIW Scaffold By Finite Element Method

Combining engineering technology with biomaterials,a kind of bone tissue scaffolds prepared by 3D printing technology,which is well matched with the defect and deformity of bone tissue,is one of the effective ways to treat such diseases at present.Based on the principles of bionics and the design requirements and objectives of bone scaffolds,it was established that the three-dimensional structure model of titanium matrix composite bone scaffold prepared by direct ink writing（DIW）method in this study.Considering the structural parameters of pore width,angle and layer height,the effects of structural parameters were studied on the mechanical properties of DIW bone scaffold using orthogonal design,finite element simulation and experimental test,which aimed to obtain the optimal scaffold structures and mechanical properties.The main research contents and results are as follows.Ti-TiC three-dimensional bone scaffold models was designed by orthogonal experiments with various structure parameters of pore widths,angles and layer heights.Thus,the uniaxial compression deformation of 16 kinds of bone scaffolds was simulated by using finite element method.The influence degree of structural parameters on the Young’s modulus of bone scaffolds was shown as pore width>layer height>angle.The pore width and layer height were inversely proportional to the Young’s modulus of the bone scaffold.That means,as the pore width and layer height increased,the Young’s modulus of the bone scaffold gradually decreased.According to the results of range analysis and variance analysis,the optimal structural parameters of the bone scaffolds were d₁θ₁h₁（pore width 550μm,layer height 150μm,angle 45°）and d₁θ₂h₂（pore width 550μm,layer height 175μm,angle 60°）,both of which had good mechanical properties.Compared with the compression test results of DIW bone scaffolds,the stress concentration position obtained by simulated during compression deformation was basically consistent with the fracture position of bone scaffolds in the test.The results showed that the compression deformation behavior of the bone scaffold can be predicted well.Based on the three-dimensional macroscopic models of the bone scaffolds,a Python subprogram with random distribution of particles and voids was compiled according to the microstructure of the actual Ti-TiC bone scaffold.The bone scaffold models were built with containing of TiC particles（diameter:5-10μm,volume fraction:5-17%）and voids（diameter:5-10μm,volume fraction:5-10%）from a mesoscopic perspective,and used to simulate its uniaxial compression deformation by finite element method.The results showed that the Young’s modulus and yield strength of the bone scaffold gradually decreased with the increase of void diameter and volume fraction,and the effect of volume fraction on the mechanical properties of the bone scaffold was greater than that of the void size.The mechanical properties of the bone scaffold were best when the diameter was 5μm and the volume fraction was 5%.Meanwhile,the stress-strain distribution in compression deformation showed that the stress and strain inside the scaffold were mainly concentrated on the surface of the voids.The Young’s modulus and yield strength of the bone scaffold increased significantly with the increase of volume fraction and the decrease of diameter of the TiC particles,and the best mechanical properties of the bone scaffold were obtained at a TiC particle diameter of 10μm and a volume fraction of 17%.In compression deformation,the surface of TiC particles was the main locations where stress concentration appeared,and the smaller the distance between particles,the more obvious the stress concentration was.