Industry News

Novel Non-toxic SLIPS Hull Coatings Prevent Attachment of Mussels

Published on 2017-08-21. Author : SpecialChem

Wyss researchers and collaborators at NTU Singapore have developed a non-toxic, lubricant-infused coatings that prevent mussels from attaching.

Marine fouling Asian green mussel
An Asian green mussel’s foot protrudes from its shell to probe
the surface, evaluating whether it can attach byssal threads.

Wyss’ SLIPS Technology

  • The Wyss’ SLIPS technology, inspired by the slick lip of a carnivorous pitcher plant that sends insects sliding down to their doom, takes advantage of the fact that it is very difficult for an organism to attach to a liquid surface
  • SLIPS consists of a solid surface infused with a liquid lubricant overlayer that is retained in place so that anything that comes into contact with the liquid layer will simply slide right off
  • SLIPS have previously been shown to be effective against bacteria and algae, but mussels represent a particularly intimidating foe
  • Their muscular feet produce adhesive filaments called byssal threads whose tips, called adhesive plaques, contain special adhesive proteins that remove water molecules from the target surface to enable the plaques to bind to it

Mussels have mastered the skill of sticking in an underwater environment, despite water being the biggest enemy of adhesion,” says Miserez. This system allows them to bind to surfaces extremely well: large accumulations of mussels can weigh as much as 1,700 pounds per square foot.

SLIPS Technology Against Mussels

To investigate whether SLIPS could hold their own against these expert biofoulers, the NTU team led by Miserez placed Asian green mussels on panels with a “checkerboard” pattern of different types of non-biocidal antifouling surfaces underwater, and let the mussels choose where to attach.

Two different types of slippery surfaces infused with silicone oil as a lubricant were evaluated:
  • A very thin, silica-based and nanostructured 2D coating applied layer-by-layer (i-LBL) 
  • A thicker, matrix-like 3D coating made of the common polymer polydimethylsiloxane (i-PDMS)

Non-lubricant-infused versions of those coatings, a tungsten oxide-based 2D coating, uncoated glass, and two commercially available non-biocidal foul release coatings (Intersleek® 700 and Intersleek® 900) were included for comparison. After 24 hours, Intersleek® 700 had ~75 mussel adhesive plaques per panel while i-PDMS had only five mussel plaques on one out of a total of fifteen panels, indicating that the mussels did not, in fact, stick well to i-PDMS.

Continuation of Investigation

Marine Fouling Over Time
A comparison of three different anti-fouling surfaces after eight and
sixteen weeks of being submerged in the water in Scituate,
MA, showing that i-PDMS consistently outperforms other
materials at preventing mussel adhesion.

the NTU researchers continued their investigation to determine exactly why the mussels did not readily bind to i-PDMS. The team measured the force needed to pull the mussels’ byssal threads off the various surfaces, and found that threads attached to the Intersleek® coatings required two to six times the force needed to remove threads from i-PDMS, and threads attached to the non-infused coatings needed ten times more force.

This is likely because the liquid overlayer of the lubricant-infused surfaces resists displacement by the mussels’ adhesive proteins, keeping the surface lubricated and therefore preventing the byssal threads from binding,” says co-first author Shahrouz Amini. Indeed, when a detailed biochemical analysis of the mussel footprints was performed, biomolecular signatures of the adhesive proteins were found on all the control materials but not on the Wyss’ slippery surfaces.

To see whether the mussels were also attempting to attach fewer byssal threads, the researchers placed them on each of the surfaces and observed them in real-time. Mussels on the non-infused LBL and PDMS surfaces behaved normally, probing them with their feet for a few seconds before secreting threads, which formed within about 30 seconds.

Those on 2D slippery surfaces, however, probed them for a significantly longer amount of time (30-80 seconds) and did not secrete threads, while those on i-PDMS displayed several aberrant behaviors: they chose to attach their threads either to their own shells or to a neighboring, non-SLIPS-coated surface; they secreted a viscous gel that did not solidify into a thread; or they probed the surface for only a few seconds before swiftly retracting their foot into their shell without attempting to secrete a thread. “In addition to disrupting the byssal threads themselves, the lubricant-infused surfaces were confusing the mussels, making them decide they weren’t valid places to attach,” says Amini.

Partnership with NOAA Stellwagen Bank National Marine Sanctuary

Finally, the Wyss team partnered with the NOAA Stellwagen Bank National Marine Sanctuary in Scituate, Mass, submerging panels of all the lab-tested materials into Scituate Harbor for sixteen weeks to see whether organisms would grow on them.

This field site exhibits a typical North Atlantic biofouling community, most notably a population of blue mussels (Mytilus edulis), which allowed to compare the findings obtained in the laboratory with observations in real-world conditions,” says Stefan Kolle, a Research Associate in the Aizenberg lab at the Wyss Institute and SEAS who is also a co-first author of the paper.

Not only did the i-PDMS show four times less mussel settlement than Intersleek® 900 and 30 times less than non-infused PDMS, it also outperformed the other materials in resisting other biofouling species such as tunicates, hydroids, and slime.

Many of the organisms in the field use different strategies and adhesives to attach themselves to underwater surfaces, but we have a solution that can work across most species,” says Onye Ahanotu, a Senior Research Scientist at the Wyss Institute and co-author of the paper.

Importantly, i-PDMS can be chemically modified to hold a substantial store of lubricant in the polymer network that resupplies the liquid overlayer, and formulated into a long-lasting, high-performance paint. The team is currently testing it in five high-biofouling marine locations around the world, and so far it has held up against the onslaught of mussels and other organisms, consistently preventing biofouling for more than two years.

This collaboration exemplifies the Wyss’ goal of combining the curiosity of basic science research with the problem-solving of engineering, taking cues from nature to develop and deploy solutions to real-world problems,” says Wyss Institute Founding Director Donald Ingber, M.D., Ph.D.

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Source: The Wyss Institute
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