G. Clarotti

Modification of the biocompatible and haemocompatible properties of polymer substrates by plasma-deposited fluorocarbon coatings

The polymerization of gases present in a low temperature plasma is a technique particularly well suited for biomedical material processing. Therefore, the possibilities this technique offers to increase the biocompatibility and haemocompatibility of polysulphone and poly(hydroxybutyrate) membranes to be used in a new bioartificial pancreas device were studied. The deposition of thin fluorocarbon coatings from an argon plasma containing perfluorohexane gave very smooth and hydrophobic surfaces without affecting the filtering properties of the treated membranes. Adding hydrogen increased the reaction yield, but gave rougher and less hydrophobic coatings. We characterized the biological properties of the treated surfaces and discussed the influence of the modified surface properties on the biological behaviour of the treated polymers. The good biocompatibility of the deposited coatings was established by following in vitro the insulin secretion of Langerhans islets cultured on the treated membranes and by examining the fibrous capsule that developed on plasma-treated polymer disks after three months of in vivo incubation in the peritoneum of Wistar rats. Rough and haemocompatible films of poly(hydroxybutyrate) and smoother, but more thrombogenic, polysulphone films were treated by perfluorohexane and perfluorohexane + H2 plasmas to study the relative influence of surface roughness and surface energy on polymer thrombogenicity. In vitro protein adsorption and total blood clotting tests proved that the surface roughness influences the thrombogenicity more than the other surface properties. This study seems to show that the plasma deposition of smooth and hydrophobic fluorocarbon coatings can increase the biocompatibility and reduce the surface thrombogenicity of the treated membranes without affecting their filtering properties.

Characterization of plasma-treated poly (hydroxybutyrate) membrane surfaces by ESCA and contact angle measurements☆

Poly (hydroxybutyrate) membranes were used as substrates for cold plasma treatment with perfluorohexane. By varying a gas mixture of perfluorohexane and hydrogen, surface coatings of different hydrophobicity were obtained. In addition, inorganic glass slides were treated correspondingly. The plasma-treated samples were analyzed by ESCA with respect to the surface composition and by contact angle measurements with respect to the surface free energy. Atomic structures and surface energies of the deposited layers on the polymer substrates were compared to those on inorganic substrates. In both cases a strong correlation was found between the fluorine/carbon ratio as well as the oxygen/carbon ratio and the surface free energy. Furthermore, the plasma-treated membranes were investigated and characterized by their changed permeation properties in order to identify the influence of the surface coatings on the bulk properties. Up to a coating density of 50–100 γ/cm2 the filtration properties of the treated membranes remained unaffected.

Plasma deposition of thin fluorocarbon films for increased membrane hemocompatibility

Abstract Plasma polymerization of gases present in a low temperature plasma is a “clean” technique that is particularly well suited for biomedical material processing. This paper presents the first results of a project which studies the possibilities offered by this technique to prepare commercial lowcost membranes with the required bio- and hemocompatibility to be implanted in an organism. The deposition on polysulfone of films from a plasma containing a mixture of ethylene oxide and perfluorohexane in order to obtain very hydrophobic, less hydrophobic and intermediate coatings was studied. Results obtained by adding hydrogen to perfluorohexane are also discussed. The deposition of a thin coating from a perfluorohexane and hydrogen plasma was studied in order to optimize the surface properties of the treated membranes without affecting their filtering properties. The treated substrates have been characterized by measuring mass variations, by surface profilometry and contact angle techniques as well as by scanning electron microscopy and electron spectroscopy for chemical analysis.