Silicone blood-compatible

As a preeminent biomaterial, silicones have been the most thoroughly studied polymer over the last half century. From lubrication for syringes to replacements for soft tissue, silicones have set the standard for excellent blood compatibility, low toxicity durability, and bioinertness. Many medical applications would not have been possible without this unique polymer. 

PDMS-co-PS has been proposed to have the antithrombogenicity. PDMS-PEO-heparin has been synthesized to achieve better blood compatibility. Silicone-PC copolymers are always used as blood oxygenation, dialysis, and microelectrode membranes. 

Williams RL, Wilson DJ, and Rhodes, NP. Stability of plasma-treated silicone rubber and its influence on the interfacial aspects of blood compatibility. Biomaterials, 2004, 25, 4659 673. 

The design of bioeompatible (blood compatible) potentiometric ion sensors was described in this chapter. Sensing membranes fabricated by crosslinked poly(dimethylsiloxane) (silicone rubber) and sol gel-derived materials are excellent for potentiometric ion sensors. Their sensor membrane properties are comparable to conventional plasticized-PVC membranes, and their thrombogenic properties are superior to the PVC-based membranes. Specifically, membranes modified chemically by neutral carriers and anion excluders are very promising, because the toxicity is alleviated drastically. The sensor properties are still excellent in spite of the chemical bonding of neutral carriers on membranes. 

Y. Kanda, R. Aoshinma, and A. Takada, Blood compatibility of components and materials in silicon integrated circuits. Electron. Lett. 17, 558-559 (1981). 

Scanning electron microscopy (SEM) has been used to visualize specific regions of intimate contact between the ventral sur ce of adherent cells and an underlying sur ce. Polycaibcmate and silicone wafer sur ces were coated with sulphonated polyelectrolytes (SPE) to improve their blood compatibility. Figure 5 indicates the scanning electron micrographs of the adhered platelets (fiom PRP, 1 hour) on polycarbonate and SPE modified polycarbonate. 

Zhang H, Annich GM, Miskulin J, Oster-holzer K, Merz SI, et al. 2002. Nitric oxide releasing silicone rubbers with improved blood compatibility preparation, characterization, and in vivo evaluation. Biomaterials 23 1485-94... 

Wilson, at Bishop College, and Eberhart and Elkowitz at University of Texas (27) have irradiated a silicone substrate in the presence of chloromethylstyrene monomer to produce a reactive graft polymer that can be quarternized with pyridine and reacted with sodium heparin to produce a thromboresistant heparinized product that has a higher blood compatibility than the untreated silicone. The same group has used essentially the same methods to create a heparin grafted polyethylene surface. 

Several other groups have also studied the blood compatibility of silicones with various radiation grafted copolymer constituents. Chapiro, et al (25) have grafted N-vinyl pyrroli-done using Co-60 onto silicone in both "bulk and "solution type reactions. It is interesting to note that similar work using E-beam radiation has not been as successful (26). 

This modification could be made by plasma polymerization wherein a thin, highly cross-linked and pin hole free film of filler free silicone polymer could be added onto a variety of substrate materials in order to prepare improved blood compatible surfaces (1). Alternatively, gaseous plasma could be used to add new chemical groups to a material surface which could then be used for attaching a variety of biomolecules. By anhydrous ammonia plasma, amino groups can be added to the surface of polypropylene membranes or to the surface of polypropylene beads. These amino groups can then be employed to bind albumin to polypropylene as was done in our previous work in which a quantitative measure of bound protein was... 

Implanted polymeric materials can also adsorb and absorb from the body various chemicals that could also effect the properties of the polymer. Lipids (triglycerides, fatty acids, cholesterol, etc.) could act as plasticizers for some polymers and change their physical properties. Lipid absorption has been suggested to increase the degradation of silicone rubbers in heart valves (13). but this does not appear to be a factor in nonvascular Implants. Poly(dimethylsiloxane) shows very little tensile strength loss after 17 months of implantation (16). Adsorbed proteins, or other materials, can modify the interactions of the body with the polymer this effect has been observed with various plasma proteins and with heparin in connection with blood compatibility. 

Angioflex Abiomed (Danvers, MA) Silicone-urethane copolymer MDI-PTMEG BD-Sil Good blood compatibility Difficult to make... 

Another challenge in the biomedical materials area is the search for synthetic materials with Improved blood compatibility for artificial heart devices and other organs. An early study by Wade (24) using a series of poly(organophosphazenes) showed these polymers in the unfilled state are as blocompatlble as silicon materials. More recent blood compatibility studies using radiation crossllnked PNF showed excellent hemo compatibility... 

Silicone, natural, and synthetic rubbers have been used for the fabrication of implants. Natural rubber is made mostly from the latex of the Hevea brasiliensis tree and the chemical formula is the same as that of cw-1,4 polyisoprene. Natural rubber was found to be compatible with blood in its pure form. Also, cross-linking by x-ray and organic peroxides produces rubber with superior blood compatibility compared with rubbers made by the conventional sulfur vulcanization. 

Oligo-silicone soft Biostability, blood compatibility, oxygen... 

Silicone elastomers have a long history of use in the medical field. They have been applied to cannulas, catheters, drainage tubes, balloon catheters, finger and toe joints, pacemaker lead wire insulation, components of artificial heart valves, breast implants, intraocular lenses, contraceptive devices, burn dressings and a variety of associated medical devices. A silicone reference material has been made available by the National Institutes of Health to equate the blood compatibility of different surfaces for vascular applications. This material is available as a silica-free sheet. Contact the Artificial Heart Program, NHBLI, NIH, Bethesda, Md. for further information. 

Silicone has also a long history as a biomedical polymer and has preferably been used for special catheters and shunts which require good blood compatibility. This is because the polymer exhibits an extremely high chemical stability and hydrophobicity. Poor mechanical properties can be improved by mixing with fillers, which, howeva-, decrease the blood compatibility A commercial product, Avcothane , seems to be composed largely of polyurethane and silicone... 

Polytetraftuoroetkylene (PTFE) is chemically more inert and displays a higher hydrophobicity than silicone. Expanded PTFE with its microporous structure is oftai used for vascular grafts and patches. Normally, vascular grafts made from PTFE become blood-compatible as a result of neointima ingrowth, but are also reported to exhibit relatively good antithrombogenicity if the micropores are filled with plenty of water... 

Fig. 26. Ex vivo evaluation of the blood compatibility of various surfaces. O glass siliconized glass poly(vinyl alcohol) A vinyl alcohol-ethylene copolymer A polyethylene...

Kolobow, T., Stool, E., Weathersby, P., Pierce, J., Hayano, R, Suaudeau, J. Superior blood compatibility of silicone rubber free of silica filler in the membrane lung. ASAIO Trans. 20, 269 (1974)... 

D. End-Chain Silicone-Modified Segmented Polyurethane Membrane as Blood-Compatible Ion-Selective Electrode... 

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