ABSTRACT
Blood comes in contact with foreign materials for a short term in extracorporeal devices such as dialysers, blood oxygenators, ventricular assist devices, and catheters. Long-term vascular implants include heart valve prostheses, vascular grafts, and cardiac pacemakers among others. In this section, we will be concerned with development of biomaterials for long-term implants, specifically for heart valve prostheses, total artificial heart (TAH), and vascular grafts. The primary requirements for biomaterials for long-term implants are biocompatibility, nontoxicity, and durability. Furthermore, the material should be nonirritating to the tissue, resistant to platelet and thrombus deposition, nondegradable in the physiological environment, and neither absorb blood constituents nor release foreign substances into the blood stream [Shim and Lenker, 1988]. In addition, design considerations include that the implant should mimic the function of the organ that it replaces without interfering with the surrounding anatomical structures and must be of suitable size and weight. The biomaterials chosen must be easily available, inexpensive, easily machinable, sterilizable, and have a long storage life. The selection of material will also be dictated by the strength requirement for the implant being made. As an example, an artificial heart valve prosthesis is required to open and close on an average once every second. The biomaterial chosen must be such that
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the valve is durable and will not fail under fatigue stress after implantation in a patient. As sophisticated measurement techniques and detailed computational analyses become available with the advent of super computers, our knowledge on the complex dynamics of the functioning of the implants is increasing. Improvements in design based on such knowledge and improvements in selection and manufacture of biomaterials will minimize problems associated with blood interfacing implants and significantly improve the quality of life for patients with implants. We will discuss the development of biomaterials for the blood interfacing implants, problems associated with the same, and future directions in the development of such implants.
