Biomaterials: Factors Favoring Colonization and Infection

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Abstract
For more than a decade, various aspects of medical device and biomaterial infections have been studied in an effort to develop a fundamental and applied basis for infection-resistant biomaterials. This chapter presents an approach and perspectives on factors favoring biomaterial colonization and infection. Infection is a potentially serious complication with implants and devices and a major impediment to the long-term clinical success of devices like vascular grafts, artificial heart valves, and ventricular assist devices. The microorganisms most frequently identified on infected polymer implants either are present in the host flora or are nosocomial in origin, most notably the coagulasenegative staphylococci, particularly Staphylococcus epidermidis. The virulence of the commensal S. epidermidis is a result of the foreign-body implant, which acts to inhibit the normal host defense. Focal thrombosis is a common finding with cardiovascular devices such as prosthetic heart valves, vascular grafts, arteriovenous fistulas, and artificial hearts. Catastrophic failure with significant morbidity and possibly death may occur when infectious foci initiate thrombosis with subsequent septic embolization. Adhesion of bacteria to an implant surface through specific and nonspecific mechanisms is a critical initial step in the development of biomaterial-centered infection. The adhesion of S. epidermidis directly on biomaterials appears to be governed by nonspecific interactions. The GRGDS pentapeptide sequence was selected as the inhibitor, since it binds to several platelet integrin receptors, including GPIIb/IIIa. The complement system and phagocytic leukocytes, which are the primary defense mechanisms against infection, are obvious targets for the down regulation of host defenses by the biomaterial.