Related Prostheses

Vascular and Related Prostheses.—Poly (ethylene terephthalate) and poly- 

Pizzoferrato, D. Leake, S. Michieli. A. Hanbold. and S. Freeman, Biomater. Med. Devices Artif. Organs, 1979, 7, 321. 

Christenson, E. Ginarsson. B. Ekiof, and L. Norgren, Scand. J. Thorac. Cardiovasc. Surg., 1978. 12. 121. 

The two major problems in materials behaviour in work of this type lie in the achievement of patency at the junction with natural tissue and the avoidance of unacceptable levels of thrombogenicity. In relation to the former problem, the extent to which the elastic properties of host tissue and graft are matched has previously been suggested as an important factor (i.e., this Series, Volume 1, p. 421, refs. 81 and 82). Further clinical results accumulated over a two-year period support this proposition, indicating patency success rates of over 80% in artery grafts with matched compliance and less than 45% with mismatched grafts.  

The success rate with both polyfethylene terephthalate) and polytetra-fluoroethylene in man seems to vary greatly and, although variation in site of 

The suitability of poly(ethylene terephthalate) as an arterial prosthetic material has been reviewed and collected clinical experiences of its role in the correction of transposition of the great arteries have been reported together with cases of its failure in arterial prostheses. The suitability of polytetrafluoroethylene e.g. Goretex) has been similarly considered. Vascular access for chronic haemodialysis presents particular problems associated with the need for repeated usage. 

Goldfarb, J. A. Hoube, J. R. Moore, and D. L. Gain, Trans. Amer. Soc., Artif. Intern. Organs, 1977, 23, 253. 

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A closely related challenge is the design of materials that interact with cells or living tissues to promote desired biological responses. Such responses might be cell attachment, cellular differentiation and organization into functional tissue, or promotion of in-growth of bone into an artificial prosthesis such as an artificial hip. 

The latest results of BASYC relate to long-term incorporation (1 year) in the rat. Special interest was directed to investigation of the contact region between the artificial prosthesis and the newly formed blood vessel. Therefore, longitudinal sections of the preparation were examined. 

An earlier study has Indicated the ability of parenteral prophylactic antibiotic therapy to reduce the Incidence of prosthetic mitral valve failure In dogs associated with valve related Infections. As an alternative to the above approach, we have Investigated the therapeutic efficacy of a system providing for a sustained release of gentamicin, Incorporating the antibiotic In silicone rubber which Is In the sewing rim of a mitral valve prosthesis Implanted In dogs. 

American Medical Association as much as possible amorphous material ambulate ambulatory arm muscle circumference age-related macular degeneration acute megokaryoblastic leukemia acoustic myography acute myocardial infarction acute myelogenous leukemia agnogenic myeloid metaplasia acute myelomonoblastic leukemia amniocentesis acute monoblastic leukemia amputation ampule Austin-Moore prosthesis alternating motor rates acute mountain sickness amylase assisted mechanical ventilation... 

It is also well known that regions of flow stagnation, flow separation and excessively low shear, in the immediate vicinity of the valve superstructure have been related to thrombus formation and/or excess tissue overgrowth on the prosthesis. 

The flow velocity, shear stress and pressure fields in the immediate vicinity of a given heart valve prosthesis design are directly related to the fluid dynamic characteristics of the prosthesis. Therefore, detailed in vitro fluid dynamic studies should help predict potential problems and complications that may arise in vivo with different designs of prosthetic heart valves. 

Developments related to medical implants, artificial organs, and prosthesis have improved the quality of life and increased the life expectancy of many individuals. 

In addition, oxidative degradation related to poor consolidation has been found in both in vivo and shelf-aged prostheses that were either gamma sterilized or ethylene oxide gas (EtO) sterilized (Costa et al. 2002). When oxidation related to consolidation occurs, the oxidation profile through the cups section is inhomogeneous and the maximum oxidation is observed near the center of the prosthesis. It is worth mentioning that this consolidation-related oxidation mechanism is often accompanied by whitening of the material, visible to the naked eye. 

Abstract The chapter discusses the advantages and limitations of arterial prostheses (or vascular grafts) in terms of their biocompatibility, biofunctionahty and biostabUity. Criteria for biomaterials selection and prosthesis design that have enabled patients to recover more rapidly without any device-related complications are reviewed, and developments are considered that may lead to future improvements in healing and clinical outcomes for the next generation of vascular prostheses. 

The circulatory fluid is ejected by an electropneumatically driven ventricular pump. Downstream of the pump, an aortic valve assembly is located two different models have been built in order to offer lateral or frontal view of the prosthesis movements. Suitable stent adapters allow to test prostheses of different type and size. The aorta is a variable compliance rubber tube. Through a rigid conduit the fluid is conveyed to the laminar flow assembly which controls peripheral resistances. Aortic compliance and peripheral resistances are hydropneumatically controlled. The fluid, passing through a venous reservoir open to atmospheric pressure, reaches the left atrium. This is a rigid wall chamber in which a hydropneumatic system relates cardiac output to venous return, reproducing Frank--Starling s Law. Between atrium and ventricle there is another valve test assembly which allows to test mitral valves. 

One other material that is used for its limited cell adhesion feature is expanded pol-ytetrafluoroethylene (ePTFE). Polytetrafluoroethylene (PTFE) was launched in the 1940s by Du Pont de Nemours as Teflon brand name. PTFE was used for the first time as a vascular prosthesis in 1963 by Edwards Lifescience and then in 1970s by Gore-Tex in expanded and microporous form (Fig. 13.12). Polytetrafluoroethylene is very stable chemically and has high hydrophobic grade that provides reduced throm-bogenicity compared to material such as PET. However, ePTFE-related mechanical properties are very poor with low compliance and elasticity. 

Legro MW, Reiber GD, Smith DG et al. (1998) Prosthesis evaluation questionnaire for persons with lower limb amputations assessing prosthesis-related quality of life. Arch Phys Med Rehabil 79 931-938. 

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