Investigation of porous cells interface on elastic property of orthopedic implants: Numerical and experimental studies

Abstract

Application of porous cells in orthopedic implants makes it possible to better approximation of elastic property of human bones. Although the mechanical and biological properties of orthopedic porous implants are studied in many researches, the interaction between different porous unit cells from geometrical compatibility and also, considering manufacturing conditions for the ultimate goal of bone ingrowth is not thoroughly investigated. In this study, a kelvin cell is designed with 530 to 810 μm pore sizes, which is the appropriate range for bone ingrowth. Due to anatomical position of implants in the human body and the limited range of the elastic modulus of kelvin cell with different geometrical parameters, this unit cell is combined with other cells to extend the range of its elastic modulus. After selecting the appropriate combination of cells to achieve desired properties, they are fabricated with Stainless Steel 316 L using radially gradient porosity in the range of 64% to 80%, and then finite element method (FEM) is performed to evaluate the elastic modulus, stress distribution, and strain energy of the proposed structures. Gradient and uniform structures are fabricated using selective laser melting (SLM) to validate FEM results. The simulation and experimental results are close to each other with an average error of about 4.5%. The elastic modulus derived from FEM for the designed gradient structures are in the range of 7.48 to 10.49 GPa, which can be modified, and present mechanical properties close to trabecular or compact bone based on the position and conditions of the bone defect.