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Vascular grafts
Materials used in vascular grafts can be plasma surface modified to promote endothelialization, while retaining non-fouling characteristics
Expanded polytetrafluoroethylene (ePTFE) is a commonly used material for prosthetic implant applications. It’s mechanical strength, impermeability to blood and inertness to bio fouling make ePTFE ideal for such in vivo applications. Its flexibility aids in healing, and catheter tubing doesn’t kink very easily and generally has good compression resistance. For biomedical applications the ability to modify PTFE surfaces is important to promote interfacial biocompatibility. For example, the adhesion of anti-thrombogenic enzymes such as thrombomodulin, urokinase and heparin requires the PTFE surface to be first modified with chemical “anchors” such as carboxylic groups that provide covalent immobilization of these enzymes. Grafting of carboxylic groups to PTFE has also been used for the covalent immobilization of chitosan, for example, a membrane forming compound useful for the purification of biomaterials.
Epithelial cell growth can be encouraged on PTFE enabling this material to be used for blood contacting devices such as vascular grafts, stents synthetic heart valves, and other in vivo devices. The the use of biologically active collagen IV (CNIV) as a synthetic scaffold to promote the adsorption of endothelial cells to PTFE devices used for in vivo vascular implants, has been investigated. In order to couple the CNIV to PTFE, the surface must first be activated by grafting hydroxyl functionality, followed by the covalent attachment of N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide, while at the same time retaining the hydrophobic properties of the base PTFE. Retention of hydrophobic properties are important for surfaces that have intimate contact with blood since they are non-activating to platelet adsorption (leading to the adsorption of fibrin). It is possible to graft polar functional groups to PTFE by plasma activation with only a modest loss in hydrophobicity. At PVA TePla we plotted surface energies against the percentage surface –OH functionality following plasma induced alcohol copolymerization on PTFE.

We determined that the surface energy can be controlled by limiting the degree of functionalization. This is simply controlled by the amount of time the substrates are exposed to the plasma. For example, after 30 seconds plasma we obtain a surface –OH concentration of 2% while the surface energy remains less than that of polyetheretherketone (PEEK), circa 41 dynes/cm.
PTFE can be surface modified with amino functionality as a first step in the eventual covalent conjugation of peptides that promote in vivo endothelialization. This has particular relevance to arterial prosthesis.


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Plasma Surface Treatment
Plasma surface modification
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