J.G.A. Terlingen

Introduction of amine groups on poly(ethylene) by plasma immobilization of a preadsorbed layer of decylamine hydrochloride

In order to introduce amine groups on poly(ethylene) (PE) surface, PE surfaces were preadsorbed with decylamine hydrochloride (DA.HCl) and subsequently treated with an argon plasma. It was shown by XPS (X-ray Photoelectron Spectroscopy), that approximately half of the preadsorbed (mono)layer was immobilized and that a substantial part (60-70%) of the incorporated nitrogen containing groups were amine groups. The availability of the surface amine groups for reactions was investigated by applying a gas phase reaction with 4-trifluoromethylbenzaldehyde and by a reductive methylation reaction in aqueous solution with 14C formaldehyde. A maximal number of reactive amine groups was found after a plasma treatment time of 2 s. The reductive methylation reaction was used to estimate the surface concentration of amine groups resulting in a typical surface concentration of 1 x 10(-6) mol/m2 after a plasma treatment time of 2 s.

In vitro leucocyte adhesion to modified polyurethane surfaces. I. Effect of ionizable functional groups

To study the effect of ionizable functional groups on the adhesion of leucocytes to surfaces, both poly(ethyleneimine) and poly(acrylic acid) were immobilized on polyurethane films, resulting in the introduction of amine and carboxylic acid groups, respectively. This was confirmed by contact angle measurements and XPS analysis. In vitro adhesion of granulocytes and lymphocytes on untreated and modified surfaces was compared. The number of adherent cells on modified surfaces as a function of time was significantly higher than on untreated surfaces. This effect was most pronounced for the adhesion of lymphocytes to surfaces modified with amine groups. In this case, the number of adherent cells after 1 h of exposure was three times higher than on untreated surfaces. A moderate enhancement of leucocyte adhesion was observed in the case of surfaces modified with carboxylic acid groups. There is evidence that these groups were not ionized under the experimental conditions used. The modification procedures described may be used to improve polyurethane filters for the removal of leucocytes from blood.

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.

A new gas discharge process for preparation of non-fouling surfaces on biomaterials

A non-fouling surface containing immobilized polyethylene oxide (PEO) was achieved using an argon radio-frequency glow discharge treatment (RFGD) of polyethylene films precoated with Brij hydrocarbon-PEO surfactants. Surface wettability of RFGD-treated and washed surfaces increased the most when PEO surfactants with unsaturated and/or long alkyl tails were used. ESCA measurements of treated and washed surfaces showed increases of surface O/C ratios and ether carbon peaks in high resolution Cls spectra. These results demonstrate the retention of the PEO surfactants on the treated surfaces. Fibrinogen adsorp tion on these treated surfaces was significantly reduced, from 500 to 50 ng/cm2, indicating the non-fouling properties of the RFGD-immobilized PEO surfactants.

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.

Immobilization of surface active compounds on polymer supports using a gas discharge process

By applying an argon plasma treatment to a layer of a surface active agent pre-adsorbed on a polymer substrate, it is possible to covalently couple this layer to the substrate. This method offers a direct route to tailor the surface properties of polymers.

Adsorption of proteins from plasma at polyester non-wovens

Polyester non-wovens in filters for the removal of leukocytes from platelet concentrates (PCs) must be platelet compatible. In PC filtration, the adsorption of proteins at the plasma-non-woven interface can be of great importance with respect to the yield of platelets. Unmodified and radio frequency glow discharge (RFGD) treated poly(ethylene terephthalate) non-woven (NW-PET) and two commercial surface-modified non-wovens were contacted with human plasma. Protein desorption by sodium dodecyl sulphate (SDS) was evaluated by X-ray photoelectron spectroscopy (XPS). The desorbed proteins were characterized by gel electrophoresis and immunoblotting. Compared to the commercial surface-modified non-wovens, unmodified and RFGD-treated NW-PETs adsorbed a relatively high amount of protein. Significantly more protein was removed from the hydrophobic NW-PET by SDS than from the hydrophilic RFGD-treated non-wovens. RFGD treatment of NW-PET reduces the reversibility of protein adsorption. Less albumin and fibrinogen were removed from the RFGD-treated non-wovens than from NW-PET. In addition, a large amount of histidine-rich glycoprotein was removed from RFGD-treated non-wovens, but not from NW-PET. The different behaviour of RFGFD-treated non-wovens towards protein adsorption is probably caused by differences in the chemical reactivity of the non-woven surfaces.

Treatment of PET nonwoven with a water vapor or carbon dioxide plasma

Gas plasma treatment of poly(ethylene terephthalate) nonwoven (NW-PET) was used to increase the hydrophilicity of single- and multilayer NW-PET. NW-PET was treated with a pulsatile CO2 or with a pulsatile H2O glow discharge. X-ray photoelectron spectroscopy (XPS) showed significantly more oxygen with CO2 glow-discharge-treated NW-PET than with H2O glow-discharge-treated-NW-PET surfaces. Moreover, the introduction rate of oxygen at a single layer of NW-PET was higher for a CO2 than for a H2O glow-discharge treatment. Titration data revealed significantly higher surface concentrations of carboxylic groups for CO2 glow-discharge NW-PET than for H2O glow-discharge-treated NW-PET. Mass spectrometry analysis revealed that the entire internal surface of a single layer of NW-PET was modified. XPS and contact measurements confirmed the modification of the internal surface of multilayers of NW-PET. H2O and CO2 glow-discharge-treated substrates consisting of six layers of NW-PET had a nonuniform surface concentration of carboxylic acid groups as determined with titration experiments. The outside layers of the substrate contained a higher surface concentration of carboxylic acid groups than did the inside layers. XPS analysis and titration data showed that the rinsing of H2O and CO2 glow-discharge-treated NW-PET with water changed the surface composition considerably. Part of the carboxylic acid group-containing species were washed off.