The non-stick & foul release property of silicones was first reported in the early 1970s, with surface free energy of 22 – 24 dynes/cm offering a minimally adhesive surface to biological organisms. The superior antifouling performance of tri-butyl tin- self-polishing coatings TBT-SPC systems outshone all other antifouling formulations from 1970 to 1980s until environmental regulations warranted a total ban on the use of the TBT-SPC system. Foul release coatings (FRC’s) use hydrodynamic stress during navigation to minimize adhesion between fouling organisms and coating surfaces so that fouling can be removed. Addition of hydrophobic silicone oils along with other properties like low surface energy, elasticity and low glass transition temperature, low micro-roughness, attributed to the foul release property of siloxane polymers. Inhibition of fouling on FRC is dependent on several factors like chemical bonding of marine bio adhesives, electrostatic interactions, physical adsorptions between coatings and secreted bio adhesives, diffusion, penetration and interlocking of bio adhesives within the coating matrix. Foul release coatings are prone to biofouling and their fouling load decreases with an increase in hydrodynamic stress due to water flow. Fouling release occurs due to weak interfacial bond created by the organism’s cement and the coating surfaces as a result of low surface free energy (SFE) and cohesive failure of bio adhesives occurs due to shear forces created by flowing water across the coatings. Even though FRC has been shown to be eco-friendly & reduce drag they have many drawbacks viz: weak adhesion strength between coating and substrate, weak mechanical properties, poor AF performance under static conditions, inefficient against diatom and bacterial slimes. Bacterial and diatom biofilms on FRC’s increase frictional resistance reduce drag reduction and fuel savings. To improve the biofouling resistance of FRC, several approaches like amphiphiles, zwitterions, quaternary ammonium salts (QAs), and metal oxide nanoparticles have been investigated. PEG-based amphiphiles is one such example where findings have translated into a commercial paint Intersleek 1100SR and HempasilX3 formulations which have been reported to offer better fouling release of barnacles and diatoms. Surface chemistry, mechanical property, binding to substrates, and durability are vital factors in designing modern-day antifouling coatings and fouling resistance is a ubiquitous parameter in consideration. This review reports the advancements and modifications to the siloxane backbone by each of these parameters which have enabled in development of superior and environmentally benign foul release coatings.

Poly (methyl methacrylate) (PMMA) is an extensively used implant material in biomedical devices. Biofilm formation creates issues in PMMA-based biomedical implants, while emergence of drug resistant pathogens poses an additional complication. Hence development of surfaces that resist bacterial colonisation is extremely desirable. In this context, nanomaterials are among the potential choices. In the present work, nanocomposites (NCs) were developed by incorporation of chemically synthesized nanoparticles of CuO, cetyl trimethyl ammonium bromide (CTAB) capped CuO and ZnO (singly and in combination) in PMMA. The efficacy of these NCs was assessed against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria which are prevalent in many implant-associated infections. Results revealed species-specific response of the bacteria towards nanomaterials. CuO NC (0.1% (w/v)) was more effective against E. coli, while CTAB capped CuO NC and ZnO NC were very effective against S. aureus. Furthermore, combination of nanoparticles improved efficacy of nanocomposites against both the bacterial species. In vitro cytotoxicity assay using L6 myoblast cell line showed that all NCs at 0.1% (w/v) were biocompatible, showing >85% cell viability. The present study suggests that combination of NPs is a promising option to combat implant infection by multiple organisms.

Polydimethyl siloxane (PDMS) is an excellent implant material for biomedical applications, but often fails as it is prone to microbial colonization which forms biofilms. In the present study CuO, CTAB capped CuO, and ZnO nanoparticles were tested as nanofillers to enhance the antibiofilm property of PDMS against Staphylococcus aureus and Escherichia coli. In general S. aurues (Gram positive and more hydrophobic) favor PDMS surface than glass while E. coli (Gram negative and more hydrophilic) behaves in a reverse way. Incorporation of nanofillers renders the PDMS surface antibacterial and reduces the attachment of both bacteria. These surfaces are also not cytotoxic nor show any cell damage. Contact angle of the material and the cell surface hydrophobicity influenced the extent of bacterial attachment. Cell viability in biofilms was dependent on the antimicrobial property of the nanoparticles incorporated in the PDMS matrix. Simple regression relationships were able to predict the bacterial attachment and number of dead cells on these nanocomposites. Among the nanocomposites tested, PDMS incorporated with CTAB (cetyl trimethylammonium bromide)-capped CuO appears to be the best antibacterial material with good cyto-compatibility. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1075-1082, 2017.

In the present work, hydrophobic (contact angle 108) poly methyl methacrylate (PMMA) films were developed by a simple room temperature drop-cast method based on slow solvent evaporation process. Further, PMMA nanocomposites (NCs) were developed by impregnating PMMA with nanoparticles (0.1% w/v) of copper oxide (CuO), cetyltrimethyl ammonium bromide (CTAB) capped CuO (CuO-CTAB) and zinc oxide (ZnO). The PMMA and NCs were tested against attachment of marine bacteria, microalgae (diatoms) and barnacle larvae in laboratory as well as in the sea. At low loading of nanoparticles (0.1% w/v), the PMMA NCs inhibited bacterial settlement (24 h assay) by 97-99% in the laboratory and by 40-69% in the field exposure studies. They also inhibited diatom attachment (24-38%) in laboratory and in the sea (80-95%). NCs successfully inhibited (100%) barnacle settlement and metamorphosis and caused mortality to the extent of 22-44% in exposed cypris larvae. Incorporation of nanoparticles in PMMA confers antifouling property to the polymer at greatly reduced metal release rates as compared to conventional antifouling paints. Results of the study indicate that PMMA NCs are promising as low cost antifouling coatings for static moored/submerged structures in the ocean due to their efficacy at low environmental metal release. (C) 2016 Elsevier Ltd. All rights reserved.

Polydimethyl siloxane (PDMS), in spite of possessing excellent foul-release properties, is prone to microbial 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 hydrophobicity, 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 nanocomposites 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 formulation remains fouling-free even without extra shear forces. (C) 2015 Elsevier Ltd. All rights reserved.