In a medical sense, the term "biocompatibility" is used to refer to the ability of materials to interact with the body without causing harm. Materials that need to be tested for biocompatibility include surgical instruments, medical implants, and materials that will come into contact with the skin. The body is extremely complex, so a single test cannot possibly cover all of the situations in which a material might be used, and thus biocompatibility testing tends to be a lengthy and involved process.
Several characteristics need to be present in biocompatible materials. The first is that they should not be toxic to cells. If a medical implant is installed and it kills the surrounding cells, this would obviously cause complications for the patient. In addition, the material must not trigger an immune response. A common problem with medical implants is rejection, where the immune system identifies the substances in the implant as foreign and attempts to fight them. This leads to inflammation and infection, and can interfere with the function of the implant.
Biocompatible materials must also not trigger chemical responses that cause injuries in the body. For instance, a stenting material used to treat narrowing arteries should be inert in blood. If it is not, the blood might start to clot or develop other problems. This could lead to complications such as obstruction of blood that leads to tissue death. Things like clots can also obstruct the device itself, causing it to stop working.
Researchers are constantly working on the development of biocompatible materials such as surgical steel and medical grade silicone that can safely be used in the body. These materials are tested in lab facilities for obvious problems that could cause them to fail in the body. New devices can be received on an experimental basis by patients who agree to be monitored for signs of incompatibility such as device rejection. Doctors are also required to submit reports when they observe reactions to medical instruments and other tools they use, so that manufacturers can identify problems with their products on the basis of reports from the field.
As researchers have learned, biocompatibility is not universal. Latex, for example, is a material that is considered biocompatible for many people and it is a standardized material for use in medical tubing, protective gloving, and other medical materials. Some people are allergic to latex, however, and can experience reactions when exposed to this supposedly biocompatible material. Likewise, people sometimes have unusual allergies to metals that cause their bodies to react to metals that have been successfully tested for biocompatibility in most patients.