Development of Functionally Graded Implant Materials in Commercial Use

Total hip replacements (THR) and total knee replacements (TKR) are the most frequently performed surgeries in the world. Some problems appeared after implantation was solved step by step in terms of prophylaxis against infection and thrombosis, but there are some major problems remain to be solved. In total hip replacement, the femoral stem is still under many investigations performed by lots of researchers. The researchers have investigated the ways of producing a femoral stem in order to improve the corrosion resistance and the mechanical properties. For instance, one of the main problems in this area is related to the resorption of the bone due to the high value of Young’s modulus of metallic part of the implant. Therefore, when the femoral stem is located in the bone, the stresses are concentrated on the down part of the implant which mainly causes pain for the patient. Another problem is related to the metallic ion releasing which causes inflammatory reaction for the body. After the implantation, the fixation of the implant inside the bone tissue is the main important issue, thus the femoral stem material needs to be biocompatible and needs to have suitable conditions for growing the bone tissue. There are several materials such as stainless steel, titanium and its alloys, cobalt-chromium based alloys suitable for producing femoral stem. Cobalt-chromium based alloys are strong, hard and also have good corrosion resistant. These alloys are used in a variety of joint replacement implants that require a long service life. Although, Co-Cr based alloys show a good background, there is still has some problems to be solved like lack of bioactivity, metallic ion releasing, aseptic loosening and high value of Young’s modulus.