Final Report Summary - SEACOAT (Surface Engineering for Antifouling - Coordinated Advanced Training)
‘SURFACE ENGINEERING FOR ANTIFOULING: COORDINATED ADVANCED TRAINING (SEACOAT)’
WHY IS RESEARCH ON MARINE BIOFOULING IMPORTANT?
‘Marine biofouling’, the colonisation of submerged surfaces by unwanted marine organisms such as barnacles and seaweeds, has detrimental effects on shipping and leisure vessels. The growth of these organisms increases the roughness of ships’ hulls, affecting manoeuvrability, increasing drag, and raising a vessel’s fuel consumption by up to 40%. Without effective antifouling measures, in order to maintain speed, fuel consumption (and therefore greenhouse gas emissions) increases significantly. The global annual cost of hull fouling, in terms of wasted fuel, is estimated to be $180 to $260 billion. Biofouling also drastically reduces the efficiency of heat exchangers, oceanographic sensors and aquaculture systems.
The current, primary commercial strategy for combating marine fouling is to use paints containing biocides. However, environmental concerns and legislation are driving science and technology towards non-biocidal solutions based solely on physico-chemical and materials properties of coatings. The aim is to produce coatings that either resist the attachment of fouling organisms in the first place, or if they do attach, to minimize their adhesion strength so that they are easily detached when the ship gets underway. Rational design of such ‘green’ coatings requires a better understanding of the influence of surface properties on the fouling organisms. This requires interdisciplinary research for precision engineering of coatings/surfaces, state-of–art surface analytics to characterize them, and a comprehensive assessment of how these coatings perform against fouling organisms.
WHAT DID THE SEACOAT PROJECT DO?
The SEACOAT project started work in 2010. Funded by the European Commission as a Marie-Curie Initial Training Network, the project consisted of 8 organisations from the UK, Switzerland, Germany, Italy and Sweden.
• University of Birmingham (Coordinator)
• International Paints Ltd (a division of AkzoNobel)
• Newcastle University
• Linköping University
• Ruprecht-Karls University Heidelberg
• ETH Zurich
• SuSoS AG
• University of Pisa
This consortium was specifically set up to provide the necessary combination of expertise in polymer science, nanotechnology, surface science and marine biology to ensure interdisciplinary training to 21 early career researchers (PhD and early post-doctoral). The involvement of 2 industrial partners provided an important applied dimension to the project. The key research objective was to study the processes involved in the colonisation of surfaces by marine fouling organisms, and to develop novel materials and coatings to counteract them. In particular the project focused on those physical and chemical properties of surfaces at nano- and micro-scale that influence the adhesion of fouling organisms. Our vision is that this enhanced understanding will inform the future development of new, environmentally-benign coatings for the practical control of marine biofouling.
All fellows were trained in 3 Thematic Areas (Surface Engineering, Surface Analytics and Biofouling) through a range of interdisciplinary projects and training courses. The Network also provided training in a range of transferable and generic skills to enhance the future career prospects of the training fellows in academia or industry.
Surface engineering technologies were used to fabricate coatings that varied systematically in relevant surface properties and length scales. We then used advanced surface analytical methods to characterize test surfaces for relevant physico-chemical surface properties and show how these change after immersion. Parallel adhesion bioassays using a range of representative marine organisms (barnacles, algae, bacteria) tested the intrinsic antifouling properties of the surfaces. We also studied how the behaviour of fouling organisms is affected by coating properties through the use of advanced imaging techniques such as digital holography.
WHAT DID WE DISCOVER?
Microporous polymer surface infused with lubricant liquids to create a ‘slippery’ surface that marine organisms cannot attach to . A novel stereoscopic technique has been developed that enables the swimming behaviour of individual barnacle cypris larvae to be tracked, as they explore different surfaces. Protein repellence by hydrogel polymer brushes. Organisms stick to surfaces through the secretion of adhesive polymers such as proteins. The repulsion of such proteins therefore reduces the adhesion strength of fouling organisms.
Examples of our findings include the following:
• A proof-of-principle demonstration that voltage-switchable coatings can control the adhesion of marine bacteria by switching between an attractive and repellent state.
• A novel method for quantifying bacterial adhesion, in real time, to different surfaces using surface plasmon resonance (SPR) has been developed. Understanding how bacteria adhere to a surface is a critical step in the development of novel coatings to prevent bacteria forming biofilms.
• A range of polymer brush coatings and hydrogels formed from protein-resistant polymers has been prepared, characterised and shown to influence the adhesion of marine organisms. Studies on the effects of thickness of hydrogel layers show that the antifouling effect is linked to the level of hydration at the surface of the coating, which varies with coating thickness.
• Novel techniques for making gradients of varying polymer composition and surface wettability have been developed and successfully applied to the analysis of the adhesion preferences of marine organisms. Such surface gradients provide a powerful analytical approach to cell biologists interested in determining critical surface properties involved in cell adhesion and motility, whilst minimising experimental variability.
• Several types of novel amphiphilic copolymers were prepared, characterized and used to create experimental coatings with good antifouling and fouling-release properties. Statistical analysis and modelling of relevant datasets across the project has shown that glass transition temperature (Tg) and elastic modulus (E) of the surface can explain up to 80% of the variability in the settlement of barnacle larvae on these coatings. Surface wettability as measured by underwater contact angle is also a predictor of barnacle settlement for these coatings.
• Novel surface gradient microtopographies inspired by dolphin skin have been prepared and shown to influence the adhesion of marine organisms.
• Microporous polymer surfaces infused with lubricating fluids that are immiscible in seawater, provide ‘slippery’ surfaces that resist the attachment of fouling organisms.
• A novel polymeric coating with a range of chemical functionalities has been developed with the ability to bind to a wide variety of substrates. The strength of attachment of a coating to its substrate influences its functional efficiency. This versatile coating is therefore relevant to antifouling coating development in the marine and biomedical sectors, and the food industry.
• The presence of a primary bacterial biofilm has been shown to moderate the initial adhesion of spores of fouling algae and also influences the strength of attachment of adhered spores and young plants developed from them. Spores of algae are able to displace bacteria from a surface biofilm, adhering to the substrate underneath the biofilm.
• A polychaete tubeworm species (Ficopomatus enigmaticus) that causes biofouling, has been cultured, different stages in the life cycle have been characterized and new settlement and adhesion assays have been established and applied to a range of test surfaces. The protocols developed for this problematic fouling species will be used in the FP7 project ‘SEAFRONT’ and it is anticipated that they will be adopted by industry, especially for evaluating new fouling-release technologies.
• Novel imaging methods including digital holographic microscopy, stereology and imaging Surface Plasmon Resonance Spectroscopy (iSPR) have provided new insights into the behaviour of fouling organisms as they explore surfaces with different properties. In addition a method to improve the resolution of imaging spectroscopic techniques using nanoparticles has been developed. This will enable future studies to be performed at higher resolution.
• Well-characterized self-assembled monolayers with different properties in relation to charge and wettability have been used to show that settlement of cypris larvae of the barnacles Balanus amphitrite and B. improvisus are influenced more by surface charge than surface energy. The deposition of adhesive ‘footprints’ as larvae explore a surface, has been shown to be influenced by surface properties.
• Novel spectroscopic observations using in situ methods have demonstrated the occurrence of specific elements and protein motifs at barnacle/substrate interfaces that may provide clues to adhesive functionality.
More details of these results can be found in the papers published by the consortium, available from the project website (http://www.birmingham.ac.uk/generic/seacoat/index.aspx).
HOW MIGHT OUR RESULTS BE USEFUL?
Advances in nanotechnology and polymer science, and the development of novel ‘bioinspired’ surface designs will help us to understand better the relationship between the structure and properties of a coating, and its biological performance. That understanding is further enhanced by knowledge of the biointerfacial processes involved in fouling, including how organisms explore different surfaces, the interrelationships between different fouling organisms, and the nature of the bioadhesives themselves. Taken together this understanding will inform the development of a new generation of environmentally-friendly marine coatings that have the potential to reduce the use of fossil fuels and greenhouse-gas emissions, and to reduce the release of biocides into the marine environment.