Functionally graded materials for knee and hip arthroplasty; an update on design, optimization, and manufacturing

The stress-shielding (SS) effects following orthopedic implantation can lead to implant loosening. Functionally graded materials (FGMs) and coatings (FGCs) are special heterogeneous composites with an altered gradient from one surface to the other. Using such materials in the implant structure with the ability to mimic the bone's characteristics may lead to proper consequences. This study reviewed papers to argue for two groups of studies: 1) research focusing on fabrication methods of FGM prostheses and research focusing on the design and optimization of knee and hip arthroplasty components. Manufacturing techniques with advantages and disadvantages have been classified based on solid, liquid, and gas-based processing. Moreover, 3D printing is used to fabricate arthroplasty components from FGMs. Despite the production of cement or cementless FGMs for orthopedic applications, the optimal design of implants is essential for preparing long-span products. This research highlighted FGMs and their applications in the manufacturing, design, and optimization of hip and knee arthroplasty components. While several researchers have focused on the design of implants via finite element analysis to reduce SS, further scientific studies are required in the future to prove their clinical applications. Furthermore, we suggest using 2D and 3D FGMs in the design of TKA and THA.