Vascular prosthesis

Artificial blood vessels are another important type of medical textile materials, and are mainly inserted into an existing artery. As is commonly known, arteriosclerosis is the result of degenerative changes of the vessel wall, which can lead to thickening, loss of elastidly, and finally stenosis or even occlusion of the blood vessel. The stenosis of coronary arteries is a frequently encountered medical problem, and is often treated by using natural vessels (mainly veins from the leg) to make a bypass. 

Historically, the idea of using textile vascular prostheses came up in the US in 1952, when their suitability was demonstrated in experiments where the abdominal 

It is known that small-diameter coronary prostheses with diameters 6 mm are not effective, since the body s reaction to foreign material will cause an occlusion of the device in a very short time. More commonly, textile-based prostheses are used where diameters of more than 6 mm are to be replaced. The most common textile prosthesis is used for the abdominal aortic aneurysm (AAA), a bulge of the aorta close to the bifurcation into the two iliac arteries leading into the legs. AAA is caused by a dilatation of the weakened vessel wall and occurs most commonly in older men ( 60 years old). The disease is normally symptom free, but may end in a rupture of the aorta which leads to death within minutes due to internal bleeding. It is estimated that worldwide 4.5 million people are living with an AAA, and in the USA about 15,000 people die every year from AAA rupture. 

During the application of vascular prosthesis, the porosity of the textile structure would cause bleeding if the pores are not temporarily closed. Pore closure used to be achieved by soaking the artificial vessel in blood and allowing it to clot. Today, most prostheses are coated with a gel, usually gelatin. In both cases the closing material is degraded by the body over time and replaced by proteins deposited from the blood, which is called neointima or pseudointima. 

To improve their blood compatibility, the inner surfaces of prostheses are seeded with endothelial cells to reconstitute the natural inner surface structure of blood vessels. These cells prevent blood coagulation and the formation of a thrombus, but in practice it is difhcult to hold the cells on the artilicial surface for long periods. Rather than preseeding the prosthesis, a new method has been developed to attract endothelial cells from the blood stream on to the inner wall of the prosthesis. New processes have also been developed to suppress bacterial growth, because intraoperative infections are still a general problem causing persistent biofilms on implants. 

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Schiraldi et al. [64] have developed this kind of material by combining silica particles and pHEMA. pHEMA is a biocompatible hydrogel that has been widely studied in the past decades due to its chemical-physical structure and mechanical properties. It has been widely used in ophthalmic prostheses (contact or intraocular lenses), vascular prostheses, drug delivery systems and soft-tissue replacement [65]. These authors have shown that by incorporating silica nanoparticles, the resulting hybrid material is highly biocompatible and promotes bone cell adhesion and proliferation of bone cells seeded on it.1 ... 

From polytetrafluoroethylene to microporous teflon-based vascular prostheses 388... 

Last but not least requirement, artificial arterial substitutes must be able to be connected to the host s vessels using sutures, the only reliable mean surgeons trust (Fig. 2). The connections performed must be stable and blood tight for as long as the prosthesis will remain patent. This last condition has supported the interest of surgeons for vascular prostheses made of woven or non-woven and knitted synthetic fabrics. The following sections give an outline of the different steps that line the evolution of materials for the cardiovascular system, and present some prospective solutions that have been proposed and supposed to improve the performances of these materials. 

FROM POLYTETRAFLUOROETHYLENE TO MICROPOROUS TEFLON-BASED VASCULAR PROSTHESES... 

Like PET, which further became more and more popular under various trade names (Dacron in USA, Rhodergon in France, Dallon in Russia and European Eastern countries), PTFE was initially used as thread, which could be woven or knitted to obtain vascular prostheses. These resulting woven devices, in which two sets of threads, respectively called weft and warp, cross each other perpendicularly, are known to easily fray near anastomoses. For knitted devices, in... 

Another field of application of fluorinated biomaterials is connected to lesions or evolving disease pathology of blood vessels. In particular, arteries may become unable to insure an adequate transport of the blood to organs and tissues. Polytetrafluoroethylene (PTFE) and expanded e-PTFE are the preferred materials for vascular prostheses. The interactions of blood cells and blood plasma macromolecules with both natural and artificial vessel walls are discussed in terms of the mechanical properties of the vascular conduit, the morphology, and the physical and chemical characteristics of the blood contacting surface. 

Forbes MJ (1980) Cross-flow filtration, Transmission electron micrographic analysis and blood compatibility testing of collagen composite materials for use as vascular prostheses. M.S. Thesis, Massachusetts Institute of Technology, Cambridge, MA... 

Bonzon, N., Lefebvre, F., Ferre, N., Daculsi, G., and Rabaud, M. (1995). New bioactivation mode for vascular prostheses made of Dacron polyester. Biomaterials 16, 747-751. 

Experiments showed that coagulation increases for applied potential differences greater than +0.2 V vs. NHE below this value, clot formation is very small. The rest potential of various materials used for vascular prostheses and cardiac valves was determined. In Table 17.2 some of the materials tested are mentioned. It was concluded that metallic electrodes with a negative potential vs. NHE in the blood are anticoagulant while those with positive potential are coagulant. Unfortunately, the metals most useful for prostheses are the most easily corroded those of platinum and gold, not corroded, are unsuitable because of their positive rest potentials. Attempts to resolve the problem have utilized prostheses of plastic materials compatible in terms of their qualities of physical resistance, durability, etc. with their end use. 

Maturri L, Azzolini A, Campiglio GL, Tardito E. Are synthetic prostheses really inert Preliminary results of a study on the biocompatibility of Dacron vascular prostheses and silicone skin expanders. Int Surg 1991 76(2) 115-18. 

This phenomenon is worthy of further study because it provides an opportunity to test two or more materials in the same device, and it may be important for understanding thrombus propagation in vascular prostheses. 

Deutsch, M., Eberl, T, Fischlein, T., Meinhart, J., Minar, E., Puschmann, R., Schmid, P., Zilla, P., In vitro endotheliali-zation of ePTFE vascular prostheses in clinical use preliminary results. Vasa Suppl., 1990, 30 219-220. 

Chronic infection with C burnetii is usually manifested by infective endocarditis, which is also the most severe complication of Q fever. In addition, a report73 from France of 92 cases published in 1993 also listed hepatitis, infected vascular prostheses and aneurysms, osteomyelitis, pulmonary infection, cutaneous infection, and an asymptomatic form. In addition, 7 of the 92 patients described in this report experienced fever only. Also noted was the observation that although 81% of patients had an identifiable risk factor, only 31% lived in a rural area. In addition, some form of immunodeficiency was observed in 20% of the patients, raising the possibility that chronic Q fever occurs as a result of reactivation of latent infection.73 Inflammatory pseudotumor of the lung as a chronic complication of Q fever has also been reported.74,75... 

Endean, E. K., Kim, D. U., Ellinger, J. et al.. Effects of polypropylene s mechanical properties on histological and functional reactions to polyglactin 910/ polypropylene vascular prostheses, Surg. Forum, 38, 323,1987. 

Schwarcz, T. H., Nussbaum, M. L. et al. and Greisler, H. P, Prostaglandin content of tissue lining vascular prostheses, Curr. Surg., 44, 18, 1987. 

As we shall see in Chapter 15, polyurethane is a polymer of choice for a wide variety of biomedical applications. Polyurethane is used extensively in the construction of devices such as vascular prostheses, membranes, catheters, plastic surgery, heart valves, and artificial organs. Polyurethanes are also used in drug delivery systems such as the sustained and controlled delivery of pharmaceutical agents, for example, caffeine and prostaglandin. ... 

Greisler, H.P., 1982. Arterial regeneration over absorbable prostheses. Arch. Surg., 117 1425-1431. Greisler, H.P., 1988a. Macrophage-biomaterial interactions with bioresorbable vascular prostheses. 

In advanced stages of vascular diseases such as obstructive atherosclerosis and aneurysmal dilatation, when other treatment modalities fail, replacement of diseased segments with vascular prostheses is a common practice. Vascular prostheses can be classified as given in Table 44.4. 

Antithrombogenic Characteristics of Cathodically Polarized Vascular Prostheses... 

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