Potential roles of fluorine-containing sol-gel coatings against adhesion to control microbial biofilm

The undesired colonization of submerged surfaces by marine micro- and macro-organisms such as bacteria, diatoms, algae, barnacles, and seaweeds is called biofouling. It has detrimental effects among which on aquaculture systems and oceanographic sensors. Moreover, this natural phenomenon on shipping and leisure vessels causes severe problems for marine industries due to corrosion and hydrodynamic drag, which leads to elevated fuel consumption and higher maintenance costs [1]. In order to reduce both economic and environmental penalties, the primary strategy for combating marine fouling is to use biocide-containing paints. At the same time, environmental concerns and legislation are driving science and technology towards non-biocidal solutions based solely on physico-chemical and materials properties of coatings. From this point of view, advances in nanotechnology and recent knowledge of marine chemistry and biology are improving significant impact on the development of a new generation of surface designs 'bioinspired' by the nature [2]. One approach to the development of novel coatings is to create a 'deterrent' surface that inhibits the initial attachment of the settling stages of microorganisms. Recently, extensive research has been realized on newer anti-fouling technologies using fluoropolymers [3]. Fluoropolymers can be used to form non-sticking surfaces with low critical surface energy, thanks the presence of the exposed CF2 and CF3 moieties at the interface. Moreover, since the fluorine atoms results in limited mobility around the backbone bonds, the so obtained stiffness reduce the adhesion of fouling [4]. Furthermore, amphiphilic coatings, which incorporate some of the benefits of both hydrophobic and hydrophilic functionalities, have been developed in order to create an engineered surface with local variations in surface chemistry, topography and mechanical properties. The treatment of materials by sol-gel technique can be an excellent tool to convey new properties to their surfaces, particularly if organic components are incorporated into the formulation. In this composition, the hybrid organic-inorganic materials show the properties of both phases, contributing to the obtainment of an anti-fouling coating with the properties just discussed. In this research, an easy to handle procedure for the preparation of fluorine containing coatings were investigated. The procedure includes the co-condensation of silane coupling agents with epoxide and amine tail-groups, (3-Glycidyloxypropyl)trimethoxysilane (GPTMS) and (3-Aminopropyl)triethoxysilane (APTES) respectively, in combination with two perfluoro silane precursors, namely 1H,1H,2H,2H-Perfluorooctyltriethoxysilane and trimethoxy-(3,3,3-trifluoropropyl)silane, either individually or together. This synthetic approach permits to obtained stable hydrophobic, non-toxic, anti-fouling coatings that were investigated to study their morphology and chemical structure by different physico-chemical technique. The anti-fouling properties were evaluated through test on treated glass slides in different microbial suspension in sea water (Gram positive and Gram negative bacteria as well as diatoms) per 24 h at room temperature. During tests, each suspension was maintained in continuous agitation to simulate the natural movement of sea water on the supports. The anti-fouling efficiency was evidenced by comparing the attachment of cells on bare degreased glass slides (considered as 100% of attachment) with that occurring on the treated slides. Results show that the fluoro-containing coatings have good antimicrobial activities and low adhesive properties towards the studied bacteria The eventual biocide effect due to the product release in the liquid medium was evaluated by counting the microbial cells before and after the period of incubation; no biocidal effects were observed in the microbial suspension due to the release of toxic compounds.