ARTIFICIAL BLOOD VESSEL

To test this hypothesis, the Dacron graft of Fig. 6 was replaced by a coated graft similar to the one described in Section II,G, and the indium-111 platelet accretion study was repeated in the absence of the Fig. 6 infusion assembly. The half that had not been treated with NO accumulated 

5 X 10 platelets within 40-60 min of blood flow initiation but, as shown in Fig. 11, platelet deposition in the NO-releasing graft was virtually absent over the same period. Apparently, it does not take much released NO, concentrated locally at the surface of an otherwise highly thrombogenic 

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Health Safety. PET fibers pose no health risk to humans or animals. Eibers have been used extensively iu textiles with no adverse physiological effects from prolonged skin contact. PET has been approved by the U.S. Eood and Dmg Administration for food packagiug and botties. PET is considered biologically iuert and has been widely used iu medical iaserts such as vascular implants and artificial blood vessels, artificial bone, and eye sutures (19). Other polyester homopolymers including polylactide and polyglycoHde are used iu resorbable sutures (19,47). 

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). 

By varying the nature of the side chain, R, various elastomers, plastics, films, and fibers have been obtained. These materials tend to be flexible at low temperatures, and water and fire resistant. Some fluoroalkoxy-substituted polymers (R = CHXFJ are so water repellent that they do not interact with living tissues and promise to be useful in fabrication of artificial blood vessels and prosthetic devices. 

In another line of research, scientists began to look for synthetic materials from which artificial blood vessels could he manufactured. Some of the earliest materials to be tried were synthetic fibers, such as nylon, vinyon (a polymer consisting primarily of vinyl chloride), and ivalon (a polymer of vinyl alcohol). These materials were largely unsuccessful because they tended to lose their strength too quickly after implantation. 

Dacron, however, continues to he the most popular material used in the production of artificial blood vessels. When first used with experimental animals, treated Dacron appeared to induce the regeneration of interior walls of blood vessels (called neointima) in essentially the same way as the natural process. When implanted into humans, however, the same treated Dacron has a somewhat different effect, resulting instead in the formation of a thin (about 1 mm thick) layer of fibrin (or a pseudointima) on the inner lining of the blood vessel. While this thin layer of fibrin is of relatively modest concern in larger blood vessels, it can be a serious problem in vessels less than 5 mm in diameter. In such cases, fibroblasts from the blood stream attach themselves to the fibrin, and the blood vessel gradually becomes blocked. 

Scientists continue to look for new andbetter materials out of which to form artificial blood vessels. In 1990, for example, the biomedical company Organogenesis began testing a material they called living blood vessel equivalent (LBVE), whose structure mimics the three-layer structure of natural blood vessels. The three layers, consisting of en-... 

Also, in late 2002, scientists from Stanford University announced progress in the development of artificial blood vessels using only natural body cells. They made a two-layer sheet of material, one layer consisting of human fibroblast cells, which form the outer wall of blood vessels, and the other made of endothelial cells, cells that form the inner lining of blood vessels, taken from experimental animals. Researchers wrapped the two-layer sheet around a tiny cylinder to form the blood vessels, which were then implanted in rats and dogs. 

Because of the extraordinary supramolecular structure and exceptional product characteristics as high-molecular and high-crystalline cellulosics with a water content up to 99%, nanocelluloses require increasing attention. This review assembles the current knowledge in research, development, and application in the field of nanocelluloses through examples. The topics combine selected results on nanocelluloses from bacteria and wood as well as their use as technical membranes and composites with the first longtime study of cellulosics in the animal body for the development of medical devices such as artificial blood vessels, and the application of bacterial nanocellulose as animal wound dressings and cosmetic tissues. 

Our investigations on BASYC (BActerial-SYnthesized Cellulose) as artificial blood vessel and cuff for nerve suturing [65] are reviewed below. Because of... 

Heisel, M.A., Laug, W.E., Stowe, S.M., Jones, P.A. (1984). Effects of X-irradiation on artificial blood vessel wall degradation by invasive tumor cells. Cancer Res. 44 2441-5. 

PTFE CF2=CF2 Cookware coatings Goretex (W.R. Gore Co.) waterproof clothing electrical insulators medical uses such as artificial blood vessels. 

However, to date, almost all of the artificial organs (artificial hearts, blood vessels, hips and knees, etc.) have been constructed from hard and dry materials. These artificial organs, to some extent, have successfully served as substitutes for real organs, but are still far from satisfactory. For example, artificial hips and knees made of metals and ceramics, which are hard and dry materials, lack the shockabsorbing function and have a high frictional resistance against sliding motion [3]. Another example is artificial blood vessels. Blood blots occur in artificial blood vessels made of polymers due to protein adsorption at the surface of the blood vessel wall [4]. 

Controlling viability to cells and compatibility to tissues. For example, a hybrid artificial blood vessel consists of a gel vessel with its inner surface covered by endothelial cells, therefore, gels on which the endothelial cells are able to form a continuous monolayer should be developed. 

The Cl atoms in the polymers are readily replaced, and this is a route to some commercially important materials. Treatment with sodium aUcoxides, NaOR, yields linear pol5mers [NP(0R)2] which have water-resistant properties, and when R = CH2CF3, the pol5mers are inert enough for use in the construction of artificial blood vessels and organs. Many phosphazene polymers are used in fire-resistant materials (see Box 16.1). 

Biomedical materials include metals, ceramics, natural polymers (biopolymers), and synthetic polymers of simple or complex chemical and/or physical structure. This volume addresses, to a large measure, fundamental research on phenomena related to the use of synthetic polymers as blood-compatible biomaterials. Relevant research stems from major efforts to investigate clotting phenomena related to the response of blood in contact with polymeric surfaces, and to develop systems with nonthrombogenic behavior in short- and long-term applications. These systems can be used as implants or replacements, and they include artificial hearts, lung oxygenators, hemodialysis systems, artificial blood vessels, artificial pancreas, catheters, etc. 

In vascular surgery the insertion of artificial blood vessels is a common method, but limited to specific medical applications. Long-term studies have revealed that unspecific adhesion of fibrin and collagen to the implant surface leads to thrombus formation and occlusion, even though PTFE is extremely inert and hydrophobic. 

The adhesion molecules (i.e., gelatin, fibronectin, coUagen, Min3) were covalently coupled to an artificial blood vessel made from PTEE. Due to unspecific adhesion of fibrin and collagen to the implant surfaces, thrombus formation and occlusion may occur in clinical use. To overcome this problem, the concept of EC cultivation on modified implant material was developed to mimic the physiological surface of blood vessels [36]. The expiration of these ceU layers strictly depends on the cell-surface interaction, which can be improved by modifying the graft surface with adhesion molecules. 

With in vivo microdialysis (Delgado et al., 1972 Ungerstedt, 1984), the extracellular fluid sample is ftirther qualified by a small sack or loop of semipermeable dialysis membrane (Fig. 51B). Artifidal CSF is slowly circulated into and out of the dialysis r on at flow rates of 1 -5 il/min, so that recovery of small molecules across the membrane from the extracellular space is effective. In essence the probe acts as an artificial blood vessel which may be sampled externally as a function of time during basal behavioral periods, drug administration (via the probe or elsewhere), external stimuli, etc. 

Spare parts surgery also became commonplace. Technologists were encouraged to provide cardiac assist devices, such as artificial heart valves and artificial blood vessels, and the artificial heart program was launched to develop a replacement for a defective or diseased human heart. 

Figure 16.3 Photopolymerizable Liquid Crystalline Monomers bone fixation screws, and artificial blood vessels.

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