The use of artificial materials in medicine is increasing. The most important and common reason for their use is to replace tissue that has become damaged or destroyed through some pathological process, for example, destruction or degeneration of bones, joints, ocular lenses, heart valves, and arteries. Artificial materials are also indicated for medical applications that support or monitor more complex body functions, for example, cardiac pacemakers, dialysis membranes for extracorporeal gas or fluid exchange, and biosensors. The research for appropriate materials is determined by the desired function of the medical device (biofunctionality) and by the biological response to these materials o (biocompatibility).
According to different functional and biological requirements, a huge variety of different materials are currently in use. Metals and alloys-particularly stainless steel, titanium, and cobalt chromium alloys—and different ceramics, such as alumina and calcium phosphates, are used for bone and joint replacement. Different polymers, including polypropylene, poly(tetrafluoroethylene) (PTFE), polyesters, and polyurethanes, are applied for sutures, soft tissue augmentation, and vascular prostheses. Silicones and poly(methyl methacrylate) (PMMA) are used for intraocular lenses. Membranes of regenerated cellulose were the most widely used hemodialysis membranes, but in the recent decades, several attempts were made to replace cellulose with alternative polymers in order to improve blood compatibility-particularly polyacrylonitrile, polycarbonate, PMMA, and polysulfone.
However, today there remain problems of both biocompatibility and biofunctionality. Clinically, the main problems emerge from interactions between materials and the local tissue environment, as summarized in Table I. To ensure a maximum of biocompatibility and functionality, the material in vivo should not evoke any of the reactions outlined in Table I. Today, none of the classical materials fulfills this high demand.