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

骨科植入物的长期存活仍然是一个挑战，因为患者变得更年轻，更活跃。影响种植体寿命的一个因素是骨吸收，这被认为是由于应力屏蔽造成的。骨是一种活组织，并对其机械刺激作出反应。当骨被移走用人工植入物代替时，骨内的应力会发生重新分配。这种应力屏蔽现象的发生是由于金属种植体和周围骨之间的刚性差异很大。因此，骨被应力屏蔽，因此骨被吸收，其密度下降，最终导致关节置换术失败。为了减少应力屏蔽现象，需要新的材料来模拟天然骨。****如今，增材制造技术使复杂的、控制良好的多孔材料成为可能，例如具有高孔隙率（50-80%）的金属，具有适合所需的材料特性。这种新材料可用于设计降低刚度的植入物，以减少应力屏蔽。此外，它们允许孔隙内良好的骨整合（细胞通过植入物生长以获得适当的稳定性）。在中尺度上可以制造出无限的结构，从而可以设计出无限的力学性能。植入物可以通过具有高孔隙度的区域和具有较少孔隙度或无孔隙度的其他区域来进行功能分级。最后，可以制造适合每位患者的定制植入物。****这项研究计划的目的是设计和模拟使用增材制造技术获得的用于骨科应用的新型多孔金属材料。数值模拟被广泛应用于全关节置换术中植入物的力学行为预测。由于固体材料的均匀性，可以得到准确的预测。然而，对于高多孔金属材料，由于中尺度结构是由细长的支撑和空隙组成的，因此无法准确预测其力学行为。中尺度的标称尺寸约为几百微米。作为植入物的一个例子，支柱直径约为500微米，孔约为800微米。对于高多孔材料，标称尺寸和实际（制造）尺寸之间的差异变得很重要。因此，用有限元模型预测的力学行为与实验数据有很大的不同。在力学测试和临床前测试之前，有限元分析对于研究多孔材料设计植入物的整体（宏观尺度）和局部（中观尺度）力学行为至关重要。本研究计划将开发数值工具来预测多孔金属材料，并使用实验来验证数值模型。******

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.******