Effect of the adhesion of Ag coatings on the effectiveness and durability of antibacterial properties

The adhesion force between metal-based antibacterial coatings and polymer substrate decides the effectiveness and durability of antibacterial performance. In this study, the silicone rubber substrate was modified by molecular bridge, i.e., polyvinylpyrrolidone, chitosan and (3-mercaptopropyl) trimethoxysilane, to provide “anchors” which captured Ag⁺ during electroless plating, and Ag coatings were resultantly produced. Different molecular bridge offered different adhesion. The spread plate counting, fluorescent staining assay and bacterial growth kinetics test showed that the antibacterial and anti-biofilm performance against Escherichia coli and Staphylococcus aureus was directly related to coating–substrate adhesion strength. A relative weaker adhesion resulted in rapid bactericidal and bacteria growth inhibition effect, and vice versa. The inductively coupled plasma atomic emission spectrometry indicated that relative weak adhesion provided fast Ag⁺ release, and strong adhesion gave lower Ag⁺ cumulative concentration, which may be attributed to different bonding strength. The coatings displayed sustained-release kinetics with the maximum cumulative Ag⁺ concentration of only 0.45 mg/L after 45 days of immersion in PBS solution, which was far below the human cell toxicity concentration. Nevertheless, all tested Ag coatings exhibited effective and long-lasting antibacterial properties. The tailored adhesion and consequent different antibacterial effect provided a choice for clinical applications.