A review of non-biodegradable alloys implantation induced inflammatory and immune cell responses

Metal implants are widely used in orthopedics and can improve the quality of life of injured and diseased patients. However, many metal implants activate the local host immune system and cause a persistent inflammatory response, which accounts for a proportion of hospital-acquired infections. In this review article, we focus on three commonly used alloys materials for implantation, following the development of alloy implant from stainless steel to cobalt-chromium to titanium alloys. Also, we summarize their clinical uses and their associated inflammatory responses and induced immune cell responses including T cells, B cells, macrophage, granulocyte, and natural killer cells. Finally, we discuss the use of new 3-dimensional printing technology for structural modification and coating with antibacterial agents to reduce alloy implantation-induced infection. A better understanding of the induced immune responses provides further information for clinicians and patients to consider the use of metal for surgery with alloy implantation. More importantly, the prediction of the possible inflammatory outcome after implantation can help us to redesign and modify the existing alloy materials for implantation to minimize the inflammation.