J.P. Lens

Heparinization of gas plasma-modified polystyrene surfaces and the interactions of these surfaces with proteins studied with surface plasmon resonance

Polystyrene surfaces obtained by spin-coating a solution of polystyrene in toluene on a gold layer were functionalized with carboxylic acid groups by preadsorption of the sodium salt of undecylenic acid, followed by an argon plasma treatment. A conjugate of albumin and heparin (alb-hep) was covalently immobilized onto the functionalized surface via preactivation of carboxylic acid groups with a water-soluble carbodiimide. The immobilization of alb-hep conjugate and the subsequent interactions of the heparinized surface with antithrombin III (ATIII, a heparin cofactor) and thrombin were monitored with surface plasmon resonance (SPR). The surface concentration of conjugate as determined with SPR deviated quantitatively from the results obtained with radiolabelled conjugate. The difference in surface concentrations of conjugate obtained with the two methods probably originates from the uncertainty of the refractive index of the alb-hep conjugate in the SPR technique. ATIII could be bound to the surface modified with alb-hep conjugate but not to a polystyrene surface modified with albumin. Rabbit anti-human ATIII did bind to the alb-hep surface previously exposed to ATIII, confirming the presence of surface bound ATIII. The alb-hep immobilized surface was able to bind much more thrombin than ATIII, which is probably due to the less specific heparin-thrombin interaction as compared to the heparin-ATIII interaction. This study shows that SPR is a technique that can be used to study, in real time, both the modification of polymer surfaces and the subsequent interactions of the modified surfaces with proteins.

Immobilization of functionalized alkyl-poly(ethylene oxide) surfactants on poly(ethylene) surfaces by means of an argon plasma treatment

Alkyl-poly(ethylene oxide) (PEO) surfactants containing a terminal hydroxyl, sulfate, or carboxylate group were grafted at the surface of poly(ethylene) (PE) samples to improve their blood compatibility. Grafting was achieved by immobilizing PEO surfactants on PE using an argon plasma treatment. The sulfate group containing PEO surfactant was synthesized by sulfating polyoxyethylene(20)stearylether (Brij78; B) with chlorosulfonic acid. A carboxylate-terminated surfactant was synthesized by a substitution reaction of the sodium alkoxide form of B with sodium iodoacetate. XPS analysis of the modified PE samples showed that at short plasma treatment times of up to 5 s the structure of the immobilized surfactants is largely retained. When plasma treatment times longer than 30 s were applied, the PEO chains of the surfactants were degraded. The wettability of the modified PE samples was improved compared to the unmodified PE samples. The wettability of the modified samples did not change when they were stored in air at room temperature for at least 12 weeks.

PREPARATION OF HEPARIN-LIKE SURFACES BY INTRODUCING SULFATE AND CARBOXYLATE GROUPS ON POLY(ETHYLENE) USING AN ARGON PLASMA TREATMENT

Carboxylate and sulfate groups were introduced at the surface of poly(ethylene) (PE) samples. This was accomplished by coating and immobilizing sodium 10-undecenoate (C11(:)) and 10-undecene sulfate (S11(:)) on the polymer by means of an argon plasma treatment. The composition of the coated surfactant layer was proportional to the composition of the coating solution. The thickness of the surfactant layer on the surface of PE samples, which were precoated from an aqueous solution with a total surfactant concentration of 0.30 M, was about 55 A. The presence of carboxylate and sulfate groups after plasma treatment of the precoated surfaces was confirmed by X-ray photoelectron spectroscopy (XPS). About 20% of the initial amount of functional groups of the coated surfactants was retained at the PE surface. The ratio of carboxylate/sulfate groups at the plasma treated surfaces was dependent on the composition of the precoated surfaces. The minimum surface density of these groups on the resulting samples was about one group per 40 A2.

Mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment: Influence of UV radiation

The mechanism of the immobilization of the surfactant sodium 10-undecenoate (C11(:)) on poly(ethylene) (PE) by means of an argon plasma treatment has been investigated. In particular, the influence of the vacuum ultraviolet (UV) radiation emitted by the argon plasma on the immobilization was studied. For this purpose, PE samples were coated with C11(:) (PE/C11(:) samples) and treated with an argon plasma under different conditions. PE/C11(:) samples were placed inside (glow) and outside (afterglow) the visible region of the plasma. Additionally, polymer samples that were placed in the glow of the plasma were covered with lithium fluoride or quartz crystals. These materials are transparent for electromagnetic radiation with a wavelength longer than 104 and 150 nm, respectively. Derivatization X-ray Photoelectron Spectroscopy was applied to characterize the modified polymer surfaces. It was demonstrated that vacuum UV radiation with a wavelength shorter than 150 nm made a predominant contribution to the process of immobilization. Under certain conditions it was possible to retain about 30% of the functional groups of the initially coated surfactant layer on PE. Furthermore, the UV radiation accounted for etching of PE and PE/C11(:) surfaces and initiated oxidation of the polymer surfaces.

Introduction of sulfate groups on poly(ethylene) surfaces by argon plasma immobilization of sodium alkyl sulfates

Sulfate groups were introduced at the surface of poly(ethylene) (PE) samples. This was accomplished by immobilizing a precoated layer of either sodium 10-undecene sulfate (S11(:)) or sodium dodecane sulfate (SDS) on the polymeric surface by means of an argon plasma treatment. For this purpose, S11(:) was synthesized by sulfating 10-undecene-1-ol using the pyridine-SO3 complex. The presence of sulfate groups at the polymeric surfaces was confirmed by X-ray Photoelectron Spectroscopy (XPS). The presence of an unsaturated bond in the alkyl chain of the surfactant improved the efficiency of the immobilization process. About 25% of the initial amount of sulfate groups in the precoated S11(:) layer was retained at the PE surface compared to only 6% for SDS. The maximum surface density of sulfate groups on the resulting samples was one group per 45 and 127 A2 respectively.

Mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment: Influence of the chemical structure of surfactant and substrate

In this article, a study on the mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment is described. The unsaturated surfactant sodium 10-undecenoate [C11(:)] and the saturated surfactant sodium dodecanoate (C12) were immobilized on poly(ethylene) (PE), poly(propylene) (PP), and poly(cis-butadiene) (PB) surfaces. This was accomplished by treating polymeric substrates that were coated with C11(:) or C12 with an argon plasma. Derivatization X-ray Photoelectron Spectroscopy (XPS) and Static Secondary Ion Mass Spectrometry (SSIMS) showed that during the plasma treatment surfactants were covalently coupled to the polymeric surfaces. The chemical structure of both the surfactant and the polymeric substrate influenced the immobilization efficiency. At an optimal treatment time of 5 s, about 28 and 6% of the initial amount of carboxylate groups in the precoated C11(:) and C12 layer, respectively, was retained at the PE surface. The immobilization efficiencies of C11(:) and C12 on PP were about 20 and 9%, respectively. The immobilization efficiency of C11(:) and C12 on PB were both about 7%. The results obtained in this study indicate that the immobilization proceeds via a radical mechanism.