Heart valve

Heart, artificial Heartguard 30 Heart-lung machine Heart pacers Heart valves... 

Biomedical Applications. In the area of biomedical polymers and materials, two types of appHcations have been envisioned and explored. The first is the use of polyphosphazenes as bioinert materials for implantation in the body either as housing for medical devices or as stmctural materials for heart valves, artificial blood vessels, and catheters. A number of fluoroalkoxy-, aryloxy-, and arylamino-substituted polyphosphazenes have been tested by actual implantation ia rats and found to generate Httle tissue response (18). 

Hea.rt Va.Ives. Since the early 1960s nearly 50 different heart valves have been developed. The most commonly used valves as of the mid-1990s include mechanical prostheses and tissue valves. Nearly 75,000 of these prosthetic valves are implanted aimually worldwide, and about 30,000 in the United States alone. Caged-baH, caged disk, and til ting-disk heart valves are the types most widely used. 

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). 

In the general area of medicine uses range from spare-part surgery, such as hip joints and heart valves, through catheters, injection syringes and other sterilisable equipment, to more mundane but nevertheless desirable uses such as quietrunning curtain rails. 

Wear of medical devices and biomaterials can affect quality of life. Wear of tooth fillings, artificial joints and heart valves can be inconvenient, costly (more frequent replacement) or even life-threateiiiiig (premature breakdowns). Wear of components can also cause accidents. Worn brakes and tires can cause automobile accidents, worn electrical cords can result in electrocution and fires and worn out seals can lead to radiation leaks at nuclear power plants. 

Carbon is inactive in blood and is not rejected from the human body. It is therefore increasingly used in artificial limbs, tendons and heart valves. 

Polymers are a fundamental part of the modem world, showing up in everything from coffee cups to cars to clothing. In medicine, too, their importance is growing for purposes as diverse as cardiac pacemakers, artificial heart valves, and biodegradable sutures. 

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). 

Coatings for hip j oints, heart valves, and other prostheses DLC is biocompatible and blood compatible,... 

The major biological application of isotropic carbon is in heart valves. The material is performing well and several hundred thousand units have been produced so far. Other applications include dental implants, ear prostheses, and as a coating for in-dwelling catheters. 

There has been an increase in the use of cadaveric heart valves for patients with valvular defects. The valves are best stored by freezing but some success has been achieved by simple cold storage in an antibiotic medium made up of ingredients common to most tissue culture solutions. At a storage temperature of 4 °C there is a continual loss of viability of fibroblasts so that by three weeks there are practically no viable cells and the valves cannot be used. 

In all types of PHAs, P4HB is of the most interest because it was used in the degradable scaffold that resulted in the first successful demonstration of a tissue-engineered tri-leaflet heart valve in a sheep animal model. Its copolymers with PHB and polyhydroxyoctanoate (PHO) are also promising in tissue engineering because of their nontoxic degradation products, stability in tissue culmre media, and the potential to tailor the mechanical and degradation properties to match soft tissue. 

The growing interests in finding tissue-engineering solutions to the devastating worldwide problem of cardiovascular disease has prompted the attractions of PHAs in the heart valves and vessel patches tissue engineering. ... 

The degradation rate of P4HB is slower than that of PGA, but faster than PLEA, PCE, and some other PHAs, such as P3HB. P4HB are likely to undergo gradual changes in mechanical properties rather than the more. A remarkable improvement to develop the heart valve was achieved by... 

In order to develop a tissue-engineered heart valve, a group at Children s Hospital in Boston evaluated several synthetic absorbable polyesters as potential scaffolding materials for heart valves. Unfoitu-nately, the most synthetic polyesters proved to be too stiff to be function as flexible leaflets inside a tri-leaflet valve. " In the late 1990s, a much more flexible PHAs called poly-3-hydroxyoctanoate-co-3-hydroxyhexanoate (PHO) was used as the scaffold material for the valve leaflet, and then the entire heart valve. ... 

Sodian R, Hoerstrup SP, Sperling JS, Daebritz S, Martin DP, Moran AM, Kim BS, Schoen FJ, Vacanti JP, and Mayer JE. Early In. vivo experience with tissue-engineered trileaflet heart valves. Circulation, 2000, 102(111), 22-29. 

Hoerstrup SP, Sodian R, Sperling JS, Vacanti JP, and Mayer JE Jr. New pulsatile bioreactor for in vitro formation of tissue engineered heart valves[J]. Tissue Eng, 2000, 6(1), 75-79. 

Sodian R, Loebe M, Hein A, Martin DP, Hoerstrup SP, Potapov EV, Hausmann H, Lueth T, and Hetzer R. Application of stereolithography for scaffold fabrication for tissue engineered heart valves. ASAIO, 2002, 48, 12-16. 

Subcutaneous in vivo testing of these polymers (13,14) has shown minimal tissue response—similar, in fact, to the response to poly-(tetrafluoroethylene). These materials are candidates for use in heart valves, heart pumps, blood vessel prostheses, or as coating materials for pacemakers or other implantable devices. 

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