Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat Magnetron co-sputtered TiO 2 /SiO 2 /Ag nanocomposite thin coatings inhibiting bacterial adhesion and biofilm formation Todorka Vladkova a, ⁎ , Orlin Angelov b , Dragomira Stoyanova c , Dilyana Gospodinova d , Luciana Gomes e , Alexandra Soares e , Filipe Mergulhao e , Iliana Ivanova c a Laboratory for Advanced Materials Research, University of Chemical Technology and Metallurgy, 8 “Kliment Ohridski” Blvd., 1756 Sofia, Bulgaria b Central Laboratory of Solar Energy, BAS, 72 Tsatigradsko shosse Blvd., 1784 Sofia, Bulgaria c Biological Faculty, SU “St. Kl. Ohridski”, 8 Dragan Tsankov Blvd, 1164 Sofia, Bulgaria d Faculty of Electrical Engineering, Technical University – Sofia, 8 “Kliment Ohridski” Blvd., 1756 Sofia, Bulgaria e Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal ARTICLE INFO Keywords: TiO 2 /SiO 2 /Ag nanocomposite coatings Antimicrobial Surface characteristics E. coli growth Biofilm in urine flow ABSTRACT Aim of this study is the development of new functional coatings for medical devices, using magnetron co- sputtering to deposit triple TiO 2 /SiO 2 /Ag nanocomposite thin films with expected antimicrobial activity. Some surface characteristics (elemental composition, hydrophilic/hydrophobic balance, surface energy and topo- graphy) were estimated to look for correlation with bacterial cells growth and biofilm formation on TiO 2 /SiO 2 / Ag coated samples. Strong inhibitory effect toward Escherichia coli growth was found: the number of viable bacterial cells approaches to zero at the first 30 min – 1 h, depending on the Ag content. Biofilm formation in urine flow at 48 h is reduced down to 92% compared to a control glass surface. Direct contact and eluted silver mediated killing were experimentally demonstrated as mechanisms of antibacterial action of the TiO 2 /SiO 2 /Ag coatings. These coatings are promising candidate for antimicrobial protection of urinary tract devices for at least 48 h, suggesting benefits over longer time. 1. Introduction Protection of medical devices against infections is a significant current challenge raised by increasing number of medical devices as- sociated infections and microbial resistance to conventional antibiotic and multi drugs treatments. Especially important is the protection of urinary tract devices because of the high number of associated with them infections, high economical prize of the healing, negative issues for the patients and high morbidity [1]. Deposition of coatings, in- hibiting microbial adhesion and reducing biofilm formation is one of the current approaches to mitigate the problem. Metal and metal oxide nanoparticles, antimicrobial peptides and others have been used in protective coatings [2,3]. Nanostructured TiO 2 coatings for anti- bacterial self-cleaning surfaces and recent advances in low-temperature deposition methods [4–6] are well established in the literature. Silver nanoparticles (Ag NPs) are often used as dopant because of their high potential against bacteria and fungi without toxicity, in some concentration intervals [7–9]. It was reported that new synthesized TiO 2 -Ag-nanocomposites demonstrate higher antifungal and antimicrobial efficacy than pure titanic [10]. Chemical grown of Ag NPs on magnetron sputtered TiO 2 coatings and their activity against Sta- phylococus aureus are presented in the literature [11]. Direct contact and released silver-mediated killing are proposed as a mechanism of their bactericidal action [11]. Inactivation of Gram-negative bacteria and especially of Escherichia coli (E. coli) by Ag NPs, incorporated in TiO 2 , was reported by Wahyuni and Roto [12]. SiO 2 is used as a seed for homogeneous immobilization of Ag NPs or a dispersing component of TiO 2 /SiO 2 and other nanocomposites [13–17]. Silica matrix reduces agglomeration and increases anti- microbial activity of embedded Ag NPs [18–21]. Chemical vapor de- positgered silver-silica coatings, active against clinical isolates are known [22,23]. Ag/SiO 2 , Ag/TiO 2 and Ag/Reduced Graphene Oxide (RGO) NPs embedded in tetraethoxysilane (TEOS), demonstrate im- proved antibacterial activity [24,25]. Ternary TiO 2 /SiO 2 /Ag nanocomposites are known, prepared by sol- gel synthesis of TiO 2 and mesoporous SiO 2 NPs, followed by decoration with Ag NPs [26] or through a biomimetic approach but their anti- microbial activity was not tested [27]. https://doi.org/10.1016/j.surfcoat.2019.125322 Received 21 October 2019; Received in revised form 13 December 2019; Accepted 28 December 2019 ⁎ Corresponding author. E-mail addresses: tgv@uctm.bg (T. Vladkova), dragomirastoyanova@nauka.bg (D. Stoyanova), dilianang@tu-sofia.bg (D. Gospodinova), luciana.gomes@fe.up.pt (L. Gomes), asoares@fe.up.pt (A. Soares), filipem@fe.up.pt (F. Mergulhao), iaivanova@biofac.uni-sofia.bg (I. Ivanova). Surface & Coatings Technology 384 (2020) 125322 Available online 28 December 2019 0257-8972/ © 2019 Published by Elsevier B.V. T