Vessel implants

Substantial research has also been performed on organo compounds of the metalloids. Silicon compounds particularly have played a major role, as witness the monograph by Voronkov 270) and the articles by Fessenden and Fessenden 86) and Garson and Kirchner 107). Silicones, because of their inertness to biological processes, have been used as heart valves, blood vessels, implants, ointments, etc. 192). Other organosilicon compounds are extremely active biologically 270a). 

Recently, success was achieved in depositing pyrolitic carbon onto the surfaces of blood vessel implants made of polymers. This type of carbon is called ultra low temperature isotropic (ULTI) carbon instead of low temperature isotropic (LTI) carbon. The deposited carbon has excellent compatibility with blood and is thin enough not to interfere with the flexibility of the grafts [Park and Lakes, 1992]. 

Figure 2.6. BNC hydrogels formed in situ a) Film prepared in a polypropylene container under static conditions dimensions 25x25 cm2, thickness 200 tm b) Spheres formed by agitated cultivation with a shaking rate of 80-100 rpm diameter 2-3 mm, smooth surface c) Tubes created by a matrix technology as blood-vessel implants inner diameter 0.6-6 mm. Reprinted with permission of [13],...

Components for dialysis equipment, unbreakable sterile bottles, syringes, hoses, packaging material, inhalation masks Sewing material, catheter hoses, components for dialysis equipment, syringes, bicuspid valves, hemofiltration membranes, clothing Vessel implants, clamps... 

Microcapsules for drug delivery systems, surgical thread, dressings, vessel implants... 

Biocompatibility investigations on artificial blood vessels made from polyethylene terephthalate show good in-vivo tissue compatibility. Investigations of porous, textile blood vessel implants show that connective tissue formed within 28 days within the textile material. However, this tissue differs from normal connective tissue. With increasing implantation time, a reduction in molecular mass has been observed bursting strength was reduced to 25% after 13.5 years, which is considered sufficient for this application [988]. 

Figure 21.13 IXibes created by a matrix technology as blood-vessel implants. Reprinted from Klemm, D. Schumann, D., Udhardt, U., Marsch, S., Bacterial synthesized cellulose—artificial blood vessels for microsurgery. Prog. Polym. Set, 26, 1561-1603. Copyright (2001) with permission from Elsevier [28].

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). 

Vascular grafts are tubular devices implanted throughout the body to replace blood vessels which have become obstmcted by plaque, atherosclerosis, or otherwise weakened by an aneurysm. Grafts are used most often in peripheral bypass surgery to restore arterial blood flow in the legs. 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

Another example was done by Opitz et al. They utilized P4HB scaffolds to produce viable ovine blood vessels, and then implanted the blood vessels in the systemic circulation of sheep. Enzymatically derived vascular smooth muscle cells (vSMC) were seeded on the scaffolds both under pulsatile flow and static conditions. Mechanical properties of bioreactor-cultured blood vessels which were obtained from tissue engineering approached those of native aorta. 

They also seeded autologous vSMC and ECs obtained from ovine carotid arteries to study autologous tissue-engineering blood vessels in the descending aorta of juvenile sheep. They found that after three months implantation, grafts were fully patent, without dilatation, occlusion, or intimal thickening. A continuous luminal EC layer was formed. However, after six months ... 

The controlled release from PTA-SA 50 50 of several drugs known to inhibit the formation of new blood vessels in vivo, cortisone and heparin, is shown in Fig. 9 (15). The inhibitors of angiogenesis delivered in vivo using this polyanhydride were shown to prevent new blood vessel growth for over 3 weeks, following the implantation of the VX2 carcinoma into rabbit cornea (15). 

FIGURE 9 Influence of angiogenesis inhibitors on blood vessel growth. Several inhibitors of angiogenesis were released from PTA-SA 50 50 in vivo. The effect of these agents on the growth of blood vessels around the VX2 carcinoma implanted into rabbit corneas was then determined as described in the text. 

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. 

In contrast, implantation of four small pieces of poly(N-palmitoyl-hydroxyproline ester) into four rabbit corneas elicited no pathological response in three corneas and a very mild inflammatory response in one cornea. Histological examination of the corneas 4 weeks postimplantation showed no invading blood vessels or migrating inflammatory cells in the area around the implants. 

Glass pH electrodes are simple to use and maintain. They respond selectively to hydronium ion concentration and provide accurate measurements of pH values between about 0 and 10. They can be small enough to be implanted into blood vessels or even inserted into individual living cells. In precision work, these electrodes are calibrated before each use, because their characteristics change somewhat with time and exposure to solutions. The electrode is dipped into a buffer solution of known pH, and the meter is electronically adjusted until it reads the correct value. 

The mechanical pump approach employs miniature mechanical devices, such as implantable and portable infusion pumps and percutaneous infusion catheters, to deliver drugs into appro priate blood vessels or to a discrete site in the body. When compared with the... 

For pH sensors used in in-vivo applications, especially those in continuous pH monitor or implantable applications, hemocompatibility is a key area of importance [150], The interaction of plasma proteins with sensor surface will affect sensor functions. Thrombus formation on the device surface due to accelerated coagulation, promoted by protein adsorption, provided platelet adhesion and activation. In addition, variation in the blood flow rate due to vasoconstriction (constriction of a blood vessel) and sensor attachment to vessel walls, known as wall effect , can cause significant errors during blood pH monitoring [50, 126],... 

An important development towards the artificial kidney was achieved by Dr. Belding Scribner in 1960, who devised a U -shaped shunt implanted through the skin between an artery and vein to access the blood stream to perform routine dialysis (Ratner, 2004). Dr. Scribner made use of Teflon tubes to access the vessels and provides a nonstick surface for the transport of blood. The Scribner shunt has allowed more than one million patients to survive from kidney failure. 

Along with electronic transport improvements must come attention to substrate transport in such porous structures. As discussed above, introduction of gas-phase diffusion or liquid-phase convection of reactants is a feasible approach to enabling high-current-density operation in electrodes of thicknesses exceeding 100 jxm. Such a solution is application specific, in the sense that neither gas-phase reactants nor convection can be introduced in a subclass of applications, such as devices implanted in human, animal, or plant tissue. In the context of physiologically implanted devices, the choice becomes either milliwatt to watt scale devices implanted in a blood vessel, where velocities of up to 10 cm/s can be present, or microwatt-scale devices implanted in tissue. Ex vivo applications are more flexible, partially because gas-phase oxygen from ambient air will almost always be utilized on the cathode side, but also because pumps can be used to provide convective flow of any substrate. However, power requirements for pump operation must be minimized to prevent substantial lowering of net power output. 

Additionally, we could neither find any evidence that MSCs are able to differentiate into vascular endothelial cells nor did we find more vessels within the transplantation areas as compared to the control group. But, in contrast to normal myocardium the amount of vessels was twice as high in the injection areas. This might indicate that the injury (puncture) of the myocardium caused by the syringe needle alone can be an adequate stimulus for the induction of angiogenesis. Therefore, rather the paracrine effects of implanted MSCs than the incorporation of these cells into the vessel walls may be required for vascular growth in the adult (Kinnaird et al., 2004). 

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