Adhesion of yeasts and bacteria to fluoro-alkylsiloxane layers chemisorbed on silicone rubber

Abstract

Indwelling voice prostheses are most often made of silicone rubber. However, the silicone rubber surface attracts huge quantities of adhering yeasts and bacteria and their colonization on the valve side of voice prostheses leads to frequent malfunctioning. On average, indwelling voice prostheses have to be replaced every three to four months. In this paper, we report on the in vitro adhesion of yeasts and bacteria to fluoro-alkylsiloxane layers chemisorbed on silicone rubber surfaces, as measured in a parallel plate flow chamber. Silicone rubber surfaces were first oxidized with an argon plasma treatment (Ar-SR). In a second step, organic layers were created by chemisorption of fluoro-alkyltrichlorosilanes onto the Ar-SR surfaces, denoted as Ar-SR-CF 3 and Ar-SR-C 8F 17, respectively. Physico-chemical properties of the chemisorbed layers were studied by using water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Using a parallel plate flow chamber, adhesion of Streptococcus salivarius, Staphylococcus epidermidis, Candida albicans and Candida tropicalis strains, isolated from explanted voice prostheses, was investigated to the chemisorbed fluoro-alkylsiloxane layers with and without a salivary conditioning film. Ar-SR-CF 3 and Ar-SR-C 8F 17 surfaces showed significantly reduced microbial adhesion as compared to original silicone rubber, both with respect to initial deposition rates and adhesion in a stationary end-point. Furthermore, adhering microorganisms were more easily detached when applying an air–liquid interface. Silicone rubber surfaces with chemisorbed, long fluorocarbon chains (Ar-SR-C 8F 17) showed the greatest reduction in microbial adhesion, probably because of their low surface free energy combined with a higher surface mobility.