Effects of Topological Parameters on the Lattice Structure for Orthopedic Applications

Abstract

Conventional solid orthopedic implants face various mechanical and biological issues when they are implanted in the human body. The most important mechanical problem being faced due to use of these implants is stress shielding effect which is caused by mismatch of mechanical properties, Young’s modulus and yield strength, between the implant and host bone. Porous orthopedic implants designed with lattice structures can overcome this problem as their mechanical properties can be tailored to match with host bone. For this purpose, it is important to understand the effects of topological parameters of lattice structure on its mechanical properties. In this work, eighteen lattice structures have been systematically modelled keeping in view the predefined porosity range for lattice structures intended to be used in orthopedic implants. Finite element analyses (FEA) have been carried out on these lattice structures modelled with IsoTruss, Diamond and Fluorite unit cell types, 0.200mm, 0.225mm and 0.250mm strut thicknesses, and 3.375mm3 and 1 mm3 of unit cell volumes where each lattice structure contains either value of these topological parameters. Young’s modulus and yield strength of each lattice structure under uniaxial compression loading are determined from the results of FEA. The material of lattice structures used in this work is 316L stainless steel. Sixteen lattice structures have been found within the predefined porosity range. Out of eighteen lattice structures, Young’s moduli and yield strengths of only nine lattice structures have been laid within the range of these properties for either trabecular or cortical bones. The trends of these properties to the change in topological parameters have been observed. The sensitivity of these properties to the change in topological parameters for various categories of lattice structures and the efficiency of each lattice structure to use its material content for increasing the mechanical properties have also been determined. Furthermore, all lattice structures having similar type of unit cell have been found in conformity with Ashby Gibson model.