Tubular blood-contacting polymeric materials were modified by plasma polymerization and evaluated in the baboon with respect to their capacity to induce both acute and chronic arterial thrombosis. Polymer surface composition was determined by electron spectroscopy for chemical analysis. Steady-state arterial thromboembolism was initiated by introducing tubular segments into chronic arteriovenous shunts. Rates of platelet destruction induced by the test materials were calculated from 111In-platelet survival measurements. Nine plasma polymers based on tetrafluoroethylene, hexafluoroethane, hexafluoroethane/H2, and methane, when deposited on silicone rubber, consumed platelets at rates ranging from 1.1-5.6 x 10(8) platelets/cm2-day. Since these values were near the lower detection limit for this test system, the plasma polymers were considered relatively nonthrombogenic. Acute thrombus formation was initiated by inserting expanded Teflon (Gore-Tex PTFE) vascular grafts into the shunt system. 111In-platelet deposition was measured by scintillation camera imaging over a 1-h exposure period. Standard PTFE grafts (10 cm x 4 mm i.d.) accumulated approximately 1 x 10(10) platelets over this interval. While modification of PTFE grafts with a plasma polymer based on hexafluoroethane/H2 did not alter graft surface morphology, platelet deposition was reduced by 87% as compared to the controls (p less than 0.001). We conclude that both the surface chemistry and texture of prosthetic materials influence thrombogenesis. The method of plasma polymerization may be useful for assessing the importance of these variables independently and, perhaps, for minimizing certain adverse blood-material interactions.
SynopsisT h e cause of the conspicuous Si content consistently o b s c n d on plasma polymers deposited on silicone ruhher was investigated in this study. Plasnia polymers of tetrafluoroethylene and of hexafluoroethme were deposited on the inside surface of Silastic tubings with and without oligomers by using a semicontinuous plasma polymerizution rcactor. This tube coating rcactor is unique in t h e sense that the only surface which interacts with the plasma is the substrate surface (i.e., inside wall of tubing) and that plasma polymeriyation occurs in a Leery small volume of 3,3-nini-l.l>. and 2-cm-long section of tuhing a t any given time. These two factors render the reactor a suitable system for the investigation of plxwria-substrate surface interaction. Silastic tubings free of oligomers were prepard by extracting the tubings x s rweivtul with distilled n-hexane for 3 h which yielded a 39 weight loss. It was found that the conspicuous Si content noted previously was not occasion& by the migration of oligomers through t h e plasma polymers hut was caused by the redeposition of plasma copolymers formd from a mixture of the feed-in monomer and t h e silicon-containing volatile coniponents evolved from the silicone rubber when exptwd t o t h e plasma. The presence of Si-containing compounds in the plasnia evidently interfered with the plasma polymerization of tctrafluormthylene and hexafluororthane. Without volatile oligomers (the extracted samples), ESCA analysis indicatd that the plasma polymers contained large amounts of CF3, CF,. w d CF moieties, just like most typical plasma polymers of these monomers deposited on nonreactive substrates. With the presence of volatile oligomers, the fluorine content decreased drastically and n significant increase of oxygen-containing and siliconcontaining moieties was observed. The influence of the volatile oligomers in the substrate on the h d w c e between ablation and polymerization in plasma polymerization m d its energy input level dependence (manifested by W/FM) were studied as well. The results were also discusscd in relation to t h e bicyclic rapid step-growth polymerization mechanism. I n the case of a polymer-forming plasma, the degradation of substrate materials is not as substantial as in the nonpolymer-forming plasma. On the other hand, the type of substrate used may affect the properties of the plasma
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