Biofouling and Anti-adhesive Coatings

Adhesion of marine fouling organisms to underwater structures adversely impacts the shipping industry, port infrastructures, and aquaculture facilities with high maintenance costs. Organisms such as barnacles and mussels, settle on the ships, leading to serious environmental repercussions. Their attachment decreases ship's hydrodynamic performance, and lowers maneuverability, severely impacting fuel consumption, emission of air pollutants and greenhouse gases. Therefore, managing biofouling is an effective strategy to enhance the energy efficiency of ships and reduce CO2 emissions. Furthermore, invasive species are translocated to new environments by ships mainly through hull or ballast water, posing dramatic alterations in the ecological balance of coastlines.

In Singapore, major macro-fouling vectors are the green mussel Perna viridis, barnacles, bryozoans, and tubeworms. Some of these invasive species stick to virtually all submerged structures in high density. To prevent these adverse effects, the development of eco-friendly and non-toxic anti-fouling coatings is crucial. The key characteristic that drives biofouling lies in the adhesive proteins. Invasive aquatic organisms use these proteins to stick to immersed surfaces and form a primary interfacial layer with the substrates.

We approach to manage biofouling by identifying these adhesive proteins and understand their fundamental mode of action by which they strongly adsorb and stick to solid surfaces. Recently, we have also developed novel strategies to assess fouling and anti-adhesiveness of coatings using multi-scale methods. The experimental designs are amenable to lab-scale testing and provide initial screening methods of anti-fouling coatings before progressing to the time-consuming empirical field-testing. With these optimized methods, we can comprehensively understand the underlying mechanism for minimized adhesive strength of organisms to certain anti-fouling coatings.

Green mussel's (Perna viridis) adhesion and anti-fouling coatings

Research in this domain was initiated by exploring the green mussel as a model system. In collaboration with Dr. Shawn Hoon from MEL (A*Star, Singapore), we pioneered the usage of RNA-sequencing in the field of biomaterials, including bio-adhesives. All proteins involved in the adhesive threads and plaques of the green mussel were sequenced using this technique. The research article featured on the cover page of Nature Biotechnology.

Further, we demonstrated that the formation of the green mussel's adhesive plaque is a carefully orchestrated mechanism that involves the time-resolved secretion of adhesive proteins. One of the proteins (the Perna viridis foot protein-5, pvfp-5) plays a critical functional role, as it eliminates molecular-bound water from the interface, providing a water-free surface for subsequent adsorption. Additionally, we also predicted the tertiary structure of green mussel adhesive proteins to elucidate their functional mechanism in adhesion (Link).

Using these fundamental findings, we developed lab-scale assays to assess biofouling across multiple length scales (from the molecular scale of protein adsorption to the nanoscale contact mechanics of coatings to macro-scale testing). In collaboration with Prof. Joanna Aizenberg's research group at the Wyss Institute at Harvard, we successfully demonstrated that Slippery Infused Porous Surfaces (SLIPS) are notably efficient at deterring mussel fouling and at minimizing adhesion. The findings were reported in Science.

Molecular mechanisms of barnacle adhesion

Recently, we instigated research on barnacle cement proteins. So far, we have characterized the 3D structure of the cement protein from the M. rosa barnacle CP20 using solution NMR and molecular dynamics simulations. Barnacles secrete a strong wet-resistant adhesive and CP20 is a major component of this proteinaceous-cement. This is the first report describing the tertiary structure of an extracellular biological adhesive protein at the molecular level. The findings published in a theme issue of the Philosophical Transactions B illustrate the multi-domain conformation of CP20 with partial disorder and a few structured domains that are predicted to drive various functional roles in the cement.

The ongoing research aims to elucidate the basic adsorption and adhesion mechanisms on solid surfaces, utilizing structural information from the cement proteins. The work is performed in collaboration with Prof. Konstantin Pervushin (SBS, NTU, Singapore) and Dr. Chandra Verma (Bioinformatics Institute, A*Star, Singapore).

Over the years, this work has been funded by grants from (i) the Maritime Port Authority of Singapore (MPA) under the umbrella of the Maritime Clean Energy Research Program (MCERP) from the Energy Research Institute at NTU (ERI@N), (ii) the “Singapore Maritime Institute (SMI), (iii) the US Office of Naval Research - Global (ONR-G) and (iv) the Marine Science and Development Research Program (MSRDP) of the Singapore National Research Foundation (NRF).