Mechanical Characterization of Additively Manufactured Orthopedic Cellular Implants: Case Study on Different Cell Types and Effect of Defects

A porous structure is widely used in additive manufacturing of orthopedic implants to reduce the stiffness mismatch between the implant and the bone. The development and improvement of porous structures for orthopedic implants is still a major challenge. It is essential to study mechanical properties of different porous structures and their relation to the deformation mechanism. In this paper, the relation between the deformation mechanism and the mechanical properties of Ti6Al4V triply periodic minimal surface (TPMS) structures, such as stretching-dominated IWP and bending-dominated gyroid structures, are investigated using the finite element analysis for uniform and density gradient scaffolds. The method for designing network-based and sheet-based TPMS structures is presented. The numerical results show that failure in the stretching-dominated structure (IWP) starts with buckling of the vertical struts, whereas failure in the bending-dominated structure (gyroid) occurs with the formation of the 45° shear band. The gyroid structure shows a higher shear modulus than the IWP structure. The numerical results exhibit good agreement with the previous experimental data for uniform and density gradient structures. Finally, the effect of the void defect on the elastic and shear moduli is evaluated. The results indicate that the elastic modulus of the bending-dominated structure shows a greater reduction in the presence of void defects than that of the stretching-dominated structure, and the shear modulus of the stretching-dominated structure is more sensitive to void defects than that of the bending-dominated structure.