Horizontal functionally graded material coating of cementless hip prosthesis

Geometry and material property optimization represent the possible methods of using prosthesis stiffness for alignment with bone stiffness and increasing total hip replacement lifespan. Previous researchers have tried to substitute conventional materials for new materials such as composites in femoral prosthesis. The concept of functionally graded materials (FGMs) was taken from biological structures. Previous study was carried out by Hedia and Fouda [1] to design the coating of a cementless hip prosthesis as a vertical FGM. In this study a finite element analysis and optimization method have been carried out in order to design the coating of cementless hip stem using the horizontal FGM to diminish stress shielding at the medial proximal region of the femur, as well as reducing the interface shear stress between the coating and bone that affects the long term stability of the hip implant. The optimal design compared with HAP coating and with homogenous uncoated titanium stem. The optimal design showed that using a coating material consists of collagen at the inner layer adjacent to stem graded to HAP at the outer layer adjacent to bone, increase the maximum von Mises stress at the medial proximal region of the femur by 60% and 15% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral shear stress is reduced by 18% and 6%. However, the maximum medial shear stress is reduced by 35% and 8% compared to titanium stem and titanium coated with HAP, respectively.