Polydimethyl siloxane nanocomposites: Their antifouling efficacy in vitro and in marine conditions G. Gomathi Sankar a, b , S. Sathya a, b , P. Sriyutha Murthy b , Arindam Das c , R. Pandiyan c , V.P. Venugopalan b, * , Mukesh Doble a, * a Bioengineering and Drug Design Lab, Department of Biotechnology, Indian Institute of Technology, Chennai 600 025, India b Biofouling and Biofilm Processes Section, Bhabha Atomic Research Centre, Kalpakkam 603 102, India c Surface & Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India article info Article history: Received 7 January 2015 Received in revised form 29 May 2015 Accepted 29 May 2015 Available online xxx Keywords: PDMS CuO ZnO CuO (CTAB) Nanocomposites Biofilm inhibition abstract Polydimethyl siloxane (PDMS), in spite of possessing excellent foul-release properties, is prone to mi- crobial fouling caused by organisms such as bacteria and diatoms. In the present study, we incorporated metal oxide nanoparticles in PDMS matrix to create composites with enhanced antifouling properties. The nanocomposites were prepared by incorporating small amounts (0.1 wt per cent) of CuO, CTAB- capped CuO and ZnO nanoparticles in PDMS. Their antibiofilm properties were tested in vitro against a marine bacterium and a diatom and also in the field. ZnO nanocomposite, exhibiting highest hydro- phobicity, surface roughness and good antimicrobial activity, prevented biofouling in the sea for 45 days. PDMS with CTAB-capped CuO showed minimum roughness and hydrophobicity and performed well against the bacterium Bacillus flexus and the diatom Navicula sp. Metal leaching rates from the nano- composites were quite low when compared to reported data, indicating that environmental effects of the nanocomposites would be minimal. The study indicates that the antifouling property of a foul-release polymer such as PDMS can be further increased by incorporation of nanoparticles, so that the formu- lation remains fouling-free even without extra shear forces. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Marine biofouling is a major problem caused by the attachment of micro and macro organisms on ship hulls, in heat exchangers in power plants, and on underwater structures (Youngblood et al., 2003). Biofouling can increase the drag and friction of ocean- going vessels, leading to increased fuel consumption and reduced speed (Schultz, 2007). To overcome this problem, antifouling bio- cides have been used for decades. Tributyltin (TBT)-based anti- fouling (AF) paints, though extremely effective, have been banned by International Maritime Organization (IMO), since they are very toxic to marine biota (Thomas and Brooks, 2010). Other approaches such as polymer coatings with antibacterial compounds and use of non-toxic silicone-based foul-release coatings (FRC) are being researched (Chambers et al., 2006, Sawant et al., 2013). The latter does not prevent biofouling, but allows it to be easily dislodged, as it possesses properties such as low surface energy, hydrophobicity and low elastic modulus (Brady and Singer, 2000; Brady, 2001). Therefore, foulants such as barnacles and mussels adhere so weakly that they get detached under the hydrodynamic forces generated as the vessel moves in water (Kavanagh et al., 2005) or during me- chanical cleaning operations (Tribou and Swain, 2010). Neverthe- less, these coatings have some disadvantages. They are mechanically weak, can be damaged easily and are inefficient against the initial microfouling caused by bacteria and diatoms (Molino and Wetherbee, 2008; Molino et al., 2009). Diatoms adhere to the surfaces through the production of extracellular polymeric substances (EPS) (Hoagland et al., 1993; Wustman et al., 1997; Wetherbee et al., 1998). Diatom fouling can increase hydrody- namic drag, resulting in increased fuel consumption (Lewthwaite et al., 1985; Schultz, 2004, 2007). Hydrodynamic forces are required to remove the attached organisms, and so they are inef- fective at low shear forces and on slow moving vessels (Finnie and Williams, 2010). Finlay et al. (2002) reported the importance of surface wettability in the attachment and detachment of diatom cells and the preference shown by Amphora to hydrophobic * Corresponding authors. E-mail addresses: vpv@igcar.gov.in (V.P. Venugopalan), mukeshd@iitm.ac.in (M. Doble). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod http://dx.doi.org/10.1016/j.ibiod.2015.05.022 0964-8305/© 2015 Elsevier Ltd. All rights reserved. International Biodeterioration & Biodegradation 104 (2015) 307e314