An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue. The surface of implants that contact the body might be made of a biomedical material such as titanium, silicone or apatite depending on what is the most functional. In some cases implants contain electronics e.g. artificial pacemaker and cochlear implants. Some implants are bioactive, such as subcutaneous drug delivery devices in the form of implantable pills or drug-eluting stents.
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Among the most common types of medical implants are the pins, rods, screws and plates used to anchor fractured bones while they heal.
The process of implantation of medical devices is subject to the same complications as any other invasive medical procedure, including infection, inflammation, and pain. Implants also run the risk of rejection if they ellicit a reaction from the host immune system.
There have been many examples of implant failures, including rupture of silicone breast implants, hip replacement joints and artificial heart valves, such as the Bjork–Shiley valve, all of which have caused FDA intervention. The consequences of implant failure depend on the critical nature of the implant, and its position in the body. Thus heart valve failure is likely to threaten the life of the individual, while breast implant or hip joint failure is less likely to be life-threatening.