Pyrolytic Carbon Heart Valves

Carbon is an important bioceramic. It combines outstanding biocompatibility and chemical inertness. Carbon exists in many forms, some of which have been discussed in earlier chapters. The most important form of carbon 

A chemical vapor deposition (CVD) process (see Section 28.4) involving the codeposition of carbon and SiC is typically used to produce the LTI-Si alloys. Two possible reactions are 

The articles to be coated are suspended within a fluidized bed of granular particles, usually Z1O2. The reactions take place in the range of 1000-1500°C and the products coat the components as well as the Zr02 particles. 

FIGURE 35.9 LTI pyrolytic carbon-coated heart valve. 

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Goodman SL, Tweden KS, Albrecht RM (1996) Platelet interaction with pyrolytic carbon heart-valve leaflets. Journal of Biomedical Materials Research 32 249-258. 

Ceramics Carbon (pyrolytic carbon) Heart valve components Bioinert Dellsperger, and Chandran (1991)... 

Figure 12.19 A bileaflet disc heart valve, known as the St. Jude valve, which was named for the medical center at which it was developed. The surfaces of the valve are coated with pyrolytic carbon. The valve is secured to the surrounding tissue via a Dacron sewing ring. 

Biomedical. Heart-valve parts are fabricated from pyrolytic carbon, which is compatible with living tissue. Such parts are produced by high temperature pyrolysis of gases such as methane. Other potential biomedical apphcations are dental implants and other prostheses where a seal between the implant and the living biological surface is essential. Plasma and arc-wire sprayed coatings are used on prosthetic devices, eg, hip implants, to achieve better bone/tissue attachments (see Prosthetic and BiOLffiDiCALdevices). 

The deposition of pyrolytic graphite in a fluidized bed is used in the production of biomedical components such as heart valves, ] and in the coating of uranium- and thorium-carbides nuclear-fuel particles for high temperature gas-cooled reactors, for the purpose of containing the products of nuclear fission.fl" The carbon is obtained from the decomposition of propane (CgHg) or propylene (CgHg) at 1350°C, or of methane (CH4) at 1800°C. Its structure is usually isotropic (see Ch. 4). 

Ely JL, Emken MR, Accuntius JA, Wilde DS, Haubold AD, More RB, Bokros JC (1998) Pure pyrolytic carbon preparation and properties of a new material, On-X (R) carbon for mechanical heart valve prostheses. Journal of Heart Valve Disease 7 626-632. 

Even so, synthetic polymers are important in replacing parts of our essential organs. Thus, silicon balls are used in the construction of mechanical heart valves. Many of these fail after sometime and they are being replaced by a flap valve made from pyrolytic carbon or POM. 

Pyrolytic Carbon Coating Artificial Heart Valves Pyrolytic Carbon Coatings Spinal Surgery Bloactive Glass-Ceramic HA... 

FIGURE 44.6 Photographs showing pitting on pyrolytic carbon surface of a mechanical heart valve. (Courtesy of Baxter Health Care, Irvine, CA.)... 

Kafesjian, R., Howanec, M., Ward, G.D., Diep, L., Wagstaff, L.S., and Rhee, R. 1994. Cavitation damage of pyrolytic carbon in mechanical heart valves. /. Heart Valve Dis. 3 (Suppl. 1) S 2-S 7. 

Metals such as titanium, stainless steel, nitinol, cobalt-chrome alloys, etc., are used in many devices. Generally, these are metals with passive surfaces or surfaces that can be passivated. Silver has been used as a coating designed to resist infection. Glassy carbons have also been used as coatings to render surfaces thromboresistant. Pyrolytic carbon structures or coatings on graphite have been utilized in the fabrication of bileaflet heart valves. These are the most popular mechanical valves in use today. 

Ritchie, R. O., Fatigue and fracture of pyrolytic carbon A damage-tolerant approach to structural integrity and life prediction in ceramic heart valve prostheses, Journal of Heart Valve Disease 5 (Suppl. 1) S9-... 

Carbons are widely used in prosthetic heart valves, as a result of their favorable mechanical and biological properties. Pyrolytic carbons, deposited in a fluidized bed, have high strength, and high fatigue and wear resistance. Compatibility with blood and soft tissue is good. 

LTI pyrolytic carbons, since their introduction in the late 1960s, have become the material of choice for use in the fabrication of mechanical prosthetic heart valves. Over 90% of the mechanical valves implanted... 

Cardiac valves with components fabricated from low temperature isotropic carbons (pyrolytic carbon) are successfully used clinically [23]. These materials are appropriate for such applications as mechanical valves which require long-term chemical inertness, smoothness, and wear-resistance. The reasons for the marked improvement in the performance (reduced thrombosis and thromboembolic stroke rates) of these newer vs. older style heart valves are not entirely understood, but are undoubtedly multifactorial and related to improved patient management and valve design, as well as to the nature of the carbon surface. The specific benefits conferred by pyrolytic carbons with respect to blood cell and protein interactions, resulting in a very low frequency of clinical complications, remain to be defined. The use of carbon coatings has been proposed for other devices, i.e., vascular grafts, although such devices have not yet been used clinically. 

A pyrolytic, low-temperature isotropic LTt) carbon is also used by depositing it on substrates such as metals. For instance, an artificial heart valve is composed of a metal coated with LTI carbon. It has not been found out so far why this carbon has a good blood compatibility... 

The meyor applications of pyrolytic carbon deposited by fluidized bed are found in the production of biomedical components such as heart valves and in the coating of uranium carbide and thorium carbide nuclear-fuel... 

Biomedical applications require a material with good strength, fatigue-resistance, high erosion resistance, chemical inertness, and compatibility with blood and tissues. Isotropic pyrolytic carbon meets these criteria and is used extensively in biomedical devices such as heart valves and dental implants where Its performance is superiorto other forms of carbon such as pyrolytic graphite or vitreous carbon.PSJ... 

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