Design of orthopedic implants made of porous metallic materials using additive manufacturing technologies

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Long-term survivorship of orthopedic implants remains a challenge as patients are becoming younger and more active. One factor compromising the longevity of the implant is bone resorption believed to be due to stress shielding. Bone is a living tissue and reacts to its mechanical stimuli. When bone is removed to be replaced by an artificial implant, a redistribution of the stresses within the bone occurs. This stress shielding phenomenon occurs because of the large difference in rigidity between the metallic implant and the surrounding bone. The bone is thus stress shielded, consequently the bone is resorbed and its density decreased, eventually leading to failure of the arthroplasty. New materials are needed to mimic the natural bone to reduce the stress shielding phenomenon.****Nowadays, additive manufacturing technologies make possible complex, well-controlled porous materials such as metals with high porosity (50-80%) having material properties tailored to the desired need. Such new materials can be used to design implants with reduced stiffness to diminish the stress shielding. Furthermore, they allow for good osteointegration within the porosity (cell growth through the implant for appropriate stability). Infinity of structures at the mesoscale can be fabricated, thus infinity of mechanical properties can be designed. The implant can be functionally graded by having regions of high porosity and other regions with less porosity or no porosity. Finally, customized implants adapted to each patient can be manufactured.****The aim of this research program is to design and model new porous metallic materials obtained using additive manufacturing technologies for orthopedic applications. Numerical modeling is widely used to predict the mechanical behavior of implants of total joint replacements. Accurate prediction can be obtained because of the homogeneity of the solid material. However, for highly porous metallic materials, the mechanical behavior is not predicted accurately since the structure at the mesoscale is made of slender struts and voids. The nominal dimensions at the mesoscale are of the order of hundreds of microns. As an example for an implant, strut diameters are approximately 500 microns and pores 800 microns. The discrepancy between nominal and actual (manufactured) dimensions becomes important for highly porous materials. As a result, the mechanical behavior predicted with finite element models differ importantly from experimental data. Finite element analysis is essential to study the overall (at the macroscale) and local (at the mesoscale) mechanical behavior of porous materials to design implants, before mechanical testing and pre-clinical testing. This research program will develop numerical tools to predict the porous metallic materials using experiments to validate the numerical model.******