Microstructure Design for 3D Printed Metal Prosthesis of Adjustable Modulus

In order to avoid the stress shielding caused by the difference of elastic modulus between human bone and the prosthetic implant, porous design can be effective to reduce the effectively modulus of the prostheses. However, how to optimize the microstructure geometric parameters for better matching with the bone tissue has not been solved yet. By taking the advantages of 3D printing technology on customized microstructure manufacture, a design method to adjust the modulus of the metal prosthetic for better matching with the bone tissue is proposed in this study, to obtain satisfactory and manufacturable prosthesis by 3D printing. The elastic modulus of two porous lattices along the edge direction, surface diagonal and body diagonal have been calculated individually by implementing the finite element method (FEM). Thereafter the functional relationship between the equivalent elastic modulus and the strut diameter has been established. The anisotropy characteristics of the microstructure has been analyzed along with the change of the strut diameter, and the influence of the edge diameter and the lattice size on the elastic modulus has been investigated as well. Within the limitation of manufacturing capacity of metal 3D printing, the calculated equivalent elastic modulus of the prosthesis were found to be consistent with those of the human bone by reducing the strut diameter. The body-centered cubic (BCC) is superior to reinforced body-centered cubic (RBCC) in terms of the isotropy characteristics. The BCC unit implementing successfully interface connection of adjacent and different modulus lattice can be used to construct prosthesis of adjustable modulus, and the allowable range of elastic modulus is 15.9-100 GPa. The proposed method can be applied to build prosthesis with gradient modulus gradient in order to achieve the optimized stress distribution within the joints.