Soft tissue implants, foreign body

The foreign body reaction occurring around soft tissue implants and thrombosis on surfaces in contact with blood are the major reactions encountered with implants. Both reactions involve the interaction of cells with the implant, especially in the later stages, and much previous study has therefore emphasized cellular events in the biocompatibility process. However, cells encounter foreign polymer implants under conditions that ensure the prior adsorption of a layer of protein to the polymer interface. The properties of the adsorbed layer are therefore important in mediating cellular response to the material. 

Foreign body reaction to soft tissue implants —Other processes such as contact lens fouling... 

It is often demanded that the surface of polymeric biomaterials should exhibit permanent tenacious adhesion to soft connective and dermal tissues. However, conventional non-porous, polymeric materials will be encapsulated by a fibrous membrane generated de novo by surrounding fibroblasts, when subcutaneously implanted into the living body in contact with soft connective tissues. This is a typical foreign body reaction of the living system to isolate foreign materials from the host inside the body. On the other hand, it should be noted that the small gap present between a percutaneously-implanted device and the surrounding tissue provides a possible route for bacterial infection because of the lack of microscopic adhesion at the interface. 

A recent review (4) considers a foreign body reaction induced in soft tissues by the presence of artificial implants to be a chronic inflammatory response it was noted specifically that denaturation of proteins at the surface of the implanted material may evoke an immunologic response. This possibility has already been examined experimentally with respect to materials in contact with blood. Stern and co-workers (5) reasoned as follows ... 

Inflammation, wound healing, foreign body response, and repair of implant sites are usually considered components of the general soft tissue response to biomaterials or medical devices. The extent or degree and temporal variations in these responses are dictated by the inherent biocompatibility characteristics of the biomaterial or medical device. Factors which may play a role in the soft tissue response include the size. 

A 49-year old woman had severe reactions to all six titanium implants that were placed in her mandible between the left and right mental foramen. Three types of implants were used, an LIBB compression implant, a cylindrical implant, and a Brdnemark-like implant. The tissue reactions were severe enough to warrant removal of all the implants and the surrounding soft tissues showed chronic inflammation with fibrosis around all the implants and foreign-body giant-cell reactions around two. She recuperated and the soft and hard tissues healed satisfactorily. 

The main classes of lipid identified in connective tissues include neutral fats, fatty adds, phospholipids and sterols, especially cholesterol. Very few investigations have been made on lipids in soft connective tissues, except for their deposition in porous foreign bodies implanted in these tissues. These experiments suggest that all four types of lipid can be synthesized by fibroblasts. 

The extent and duration of tissue reactions to polymeric implant materials is important in assessing biocompatibility. In general, the ideal foreign body reaction in soft tissue to a pol nneric implant is one in which the acute inflammatory response, marked by pol3nnorpho-nuclear leukocytes, exudation and hyperemia, resolves quickly with little or no chronic inflammatory phase, marked by lymphocytes, plasma cells or histiocytes, and increasing fibrosis and eventual encapsulation of the implant by fibrous tissue occurs (7-9). Interaction of the tissue with the polymeric implant may result in a continuation of the chronic inflammatory phase or lead to increased fibrosis. This increased fibrosis or over-development of the fibrous capsule may involve adjacent organs or tissues and lead to adverse reactions (10, 11). 

---