Carbon in medical devices

Abstract

Abstract The variability of the crystalline structure of carbon allows a correspondingly wide range of possible properties. By controlling the structure of carbon through processing, as for example in the deposition of carbon in a fluidized bed, it is possible to produce deposits with unique combinations of properties. Certain of these carbons have been found to be extremely useful in prosthetic devices. The isotropic carbons deposited at relatively low temperatures (below about 1500°C), often called LTI carbons, are blocompatible in the broadest sense. They do not induce thrombosis or hemolysis or otherwise affect either the formed or molecular element of blood. They have exceptional wear and fatique properties which are not degraded by the body environment. Accordingly, these carbons are widely used in the construction of prosthetic heart valves. The modulus of elasticity of LTI carbon is unusually low for a material of such strength and falls within the limits reported for the elasticity of bone. This property, together with its ability to interface with both soft and hard tissue without eliciting a foreign body response, makes it possible to produce orthopedic joint replacements that can attach directly to bone without using polymethylmetacrylate bone cement. Using special vacuum deposition techniques, it is possible to deposit thin, impermeable isotropic carbons that mimic the structure and properties of the LTI carbon. Materials such as polymers and fabrics can be coated with such carbons and these coatings are finding use on vascular grafts, heart valve sewing rings, percutaneous access devices, and tendon and ligament replacements. Other forms of carbons, e.g. fibers and fiber composites, are currently being used clinically in orthopedic surgery. The impact of carbon on current replacement surgery and some possibilities for future applications will be described.