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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.
United States Classification
Medical devices are classified by the U.S. Food and Drug Administration (FDA) under three different classes depending on the risks that the medical device may impose on the user. Class I devices are considered to be devices that pose the least amount of risk to the user and require the least amount of control. Class I devices include simple devices such as arm slings and hand held surgical instruments. Class II devices are considered to be devices that need more regulation than Class I devices and are required to under go specific requirements before FDA approval. Class II devices include x-ray systems and physiological monitors. Class III devices are medical devices that require the most regulatory controls since the device supports or sustains human life or may not be well tested. Class III devices include replacement heart valves and implanted cerebella stimulators. Many implants typically fall under Class II and Class III devices (Syring, 2003).
Under ideal conditions, implants should initiate the desired host response. Ideally, the implant should not cause any undesired reaction from neighboring or distant tissues. However, the interaction between the implant and the tissue surrounding the implant can lead to complications (Basu, Katti, Kumar, 2009). The process of implantation of medical devices is subjected to the same complications that other invasive medical procedures can have during or post surgery along with several different complications. Common complications include infection, inflammation, and pain. Other complications that can occur include risk of rejection from implant induced coagulation and allergic foreign body response. Depending on the type of implant, the complications may vary.
When the site of an implant becomes infected during or after surgery, the surrounding tissue becomes infected by microorganisms. There are three main categories of infection that can occur post operation. Superficial immediate infections are infections that are caused by organisms that commonly grow near or on skin. The infection usually occurs at the surgical opening. Deep immediate infection is the second type of infection that occurs immediately after surgery at the site of the implant. Skin dwelling and airborne bacteria cause deep immediate infection. The skin dwelling and airborne bacteria enters the body by attaching to the implant’s surface prior to implantation. Though not common, deep immediate infections can also occur from dormant bacteria from previous infections of the tissue at the implantation site that have been activated from being disturbed during the surgery. The last type of infection is late infection. Late infection occurs months to years after the implantation of the implant. Late infections are caused by dormant blood borne bacteria that are attached to the implant prior to implantation. The blood borne bacteria colonize on the implant and eventually get released from the implant. Depending on the type of material used to make the implant, the implant may be infused with antibiotics to lower the risk of infections during surgery. However, only certain types of materials can be infused with antibiotics, the use of antibiotic infused implants runs the risk of rejection by the patient since the patient may develop a sensitivity to the antibiotic, and the antibiotic may not work on the bacteria (Black, 2006).
Inflammation is a common occurrence after any surgical procedure. Inflammation is the body’s response to tissue damage as a result of trauma, infection, intrusion of foreign materials, or local cell death. Inflammation may occur as a part of an immune response. Inflammation starts with the rapid dilation of local capillaries to supply the local tissue with blood. The inflow of blood causes the tissue to become swollen and may cause cell death. The excess blood, or edema, can activate pain receptors at the tissue. The site of the inflammation becomes warm from local disturbances of fluid flow and the increased cellular activity to repair the tissue or remove debris from the site (Black, 2006).
Implant induced coagulation is similar to the coagulation process done within the body to prevent blood loss from damaged blood vessels. However, the coagulation process is triggered from proteins that become attached to the implant surface and lose their shapes. When the proteins lose their shape, the protein chances conformation and different activation sites become exposed. From the exposure of the different protein sites, the proteins may trigger an immune system response where the body attempts to attack the implant to remove the foreign material. The trigger of the immune system response can be accompanied by inflammation. The immune system response may lead to chronic inflammation where the implant is rejected and has to be removed from the body. The immune system may encapsulate the implant as an attempt to remove the foreign material from the site of the tissue by encapsulating the implant in fibrogen and platelets. The encapsulation of the implant can lead to further complications since the thick layers of fibrous capsulation may prevent the implant from performing the desired functions. Bacteria may attack the fibrous encapsulation and become embedded into the fibers. Since the layers of fibers are thick, antibiotics may not be able to reach the bacteria and the bacteria may grow and infect the surrounding tissue. In order to remove the bacteria, the implant would have to be removed. Lastly, the immune system may accept the presence of the implant and repair and remodel the surrounding tissue. Similar responses occur when the body initiates an allergic foreign body response. In the case of an allergic foreign body response, the implant would have to be removed (Dee, Puleo, Bizios, 2002).
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.
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- D.F. Williams, Williams Dictionary of Biomaterials. Liverpool University Press, 1999 ISBN 978-0-85323-734-1; ISBN 0-85323-734-4
- Syring, G. (2003, May 6). Overview: Fda regulation of medical devices. Retrieved from http://www.qrasupport.com/FDA_MED_DEVICE.html