Development of antibacterial quaternary ammonium silane coatings on polyurethane catheters

Polyurethene (PU) catheters were coated with 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride (QAS) by means of a multistep process which involved a vapor phase plasma-induced graft-polymerization of acrylic acid (AAc). The AAc coating, whose stability in aqueous media was assessed by immersion in Phospate Buffer Saline (PBS), was characterized by means of Attenuated Total Reflectance Fourier Transform Infrared (ATR/FTIR) spectroscopy. Moreover, the COOH surface density was evaluated by a colorimetric assay with Methylene Blue. Carrying a negative charge at neutral pH, AAc coatings were proficient in positively charged molecules (like QAS) adsorption. ATR/FTIR spectroscopy and a colorimetric assay with Bromophenol Blue allowed us to verify the presence and the uniformity of the QAS coating on the PU catheters and the positive effect of the AAc graft-polymerization on the QAS adsorption. Morphological characterization of the QAS-modified catheters was performed by means of Atomic Force Microscopy (AFM). QAS-coated catheters displayed in vitro antimicrobial activity against Gram-negative Escherichia coli bacterial cells.