A new an­tifoul­ing coat­ing cre­ates a “liquid sur­face” that pre­vents ma­rine life from at­tach­ing to hulls and docks.

Soundings - - Contents - By Kim Kavin

If mus­sels foul your boat or dock on a reg­u­lar ba­sis, you might think the mol­lusk is the en­emy. In re­al­ity, what you need to stop are the mus­sels’ byssal threads, or byssus, which the lit­tle bug­gers se­crete like Spi­der-Man web­bing when at­tach­ing them­selves to solid sur­faces. Stop the byssal threads from get­ting a grip, and no more mus­sels stuck to your hull or dock.

It’s a nifty trick, one that re­searchers think they’ve fi­nally mas­tered — and that busi­ness­men say will start ap­pear­ing in new an­tifoul­ing paint in early 2018. The magic ma­te­rial that is now ad­vanc­ing from the re­search phase to com­mer­cial use is called SLIPS, or Slip­pery Liquid- In­fused Por­ous Sur­faces. SLIPS is a flex­i­ble sil­i­cone with a lu­bri­cant layer that essen­tially cre­ates a liquid sur­face. It feels oily to the touch, and it has a reser­voir in the coat­ing’s pores to re­place the liquid sur­face layer when it wears off. The de­sign keeps the coat­ing in a phys­i­cal state that, to a mus­sel, seems dif­fer­ent from a solid sur­face.

A re­cent study in the jour­nal Science ex­plains how re­searchers used SLIPS to con­fuse mus­sels enough that they couldn’t, or wouldn’t, at­tach. In their first ex­per­i­ment, re­searchers placed Asian green mus­sels on a checker­board of sorts, with each square cov­ered in a dif­fer­ent an­tifoul­ing ma­te­rial. The squares with the SLIPS coat­ing con­fused the crea­tures. Mus­sels probed those sur­faces longer, didn’t re­lease their byssal threads at all or shot out the threads in a dif­fer­ent di­rec­tion, where a sur­face they read as solid seemed to be a bet­ter choice for at­tach­ment.

Want­ing to know why the mus­sels were averse to the coat­ing, the re­searchers next de­ter­mined that mus­sels’ feet con­tain pro­teins that sense pres­sure. Mea­sur­ing the amount of force that a mus­sel feels when its foot touches dif­fer­ent sur­faces led the re­searchers to re­al­ize that the SLIPS coat­ing cre­ates a pulling sen­sa­tion, as op­posed to a solid sen­sa­tion. Mus­sels read the pulling as a bad feel­ing prior to at­tach­ment, so they look else­where for a bet­ter spot.

The coat­ing was also tested in Sc­i­t­u­ate, Mas­sachusetts, in part­ner­ship with the National Oceanic and At­mo­spheric Ad­min­is­tra­tion’s Stell­wa­gen Bank National Ma­rine Sanc­tu­ary. Pan­els cov­ered in the coat­ing were sub­merged in Sc­i­t­u­ate Har­bor for 16 weeks to see whether they could re­sist the lo­cal blue mus­sel pop­u­la­tion. Again, the coat­ing worked — and kept tu­ni­cates (“sea squirts”), hy­droids and slime at bay, too.

Armed with this new re­search and three years’ worth of busi­ness de­vel­op­ment, SLIPS Tech­nolo­gies in Cam­bridge, Mas­sachusetts — a com­pany that grew out of the Har­vard Univer­sity-based re­search find­ings — is now work­ing to com­mer­cial­ize the coat­ing. Be­cause SLIPS can re­pel more than wa­ter, it could have uses far be­yond boating. SLIPS Tech­nolo­gies is look­ing into med­i­cal de­vices that need to re­sist blood and bac­te­ria; ma­chin­ery and stor­age busi­nesses that need to stop sticky liq­uids, in­clud­ing oil, from glom­ming onto other ma­te­ri­als; and even sky­scrapers and air­plane wings where ice buildup might be pre­vented. The SLIPS coat­ing can be ap­plied to plas­tics, met­als, ce­ram­ics, glass and con­crete, ei­ther by spray­ing, rolling it on or dip­ping ma­te­ri­als into it. Peel-and­stick films have also been de­vel­oped, along with in­jec­tion-molded parts.

Com­pany pres­i­dent David Ward told Sound­ings that boaters can ex­pect to see SLIPS-branded an­tifoul­ing paint in lim­ited quan­ti­ties by early 2018, with the goal of wider avail­abil­ity in 2019. SLIPS Tech­nolo­gies is now look­ing for ship­yards that want to part­ner on a lim­ited roll­out ahead of the sum­mer 2018 boating sea­son to help gather more real-world data be­fore the an­tifoul­ing paint be­comes widely avail­able.

“We’re not quite at the point where this is over-the-counter yet; we’re not at that phase of scale- up,” Ward says. “We want more field data. We haven’t been through a full sea­son with mul­ti­ple boats yet. When we launch a com­mer­cial-ready prod­uct, it has to be per­fect.”

Ward says the SLIPS coat­ing can be ap­plied to any type of boat — wood, fiber­glass, alu­minum or steel. The com­pany has been test­ing the coat­ing on a hand­ful of boats near Bos­ton for about six months, he says. “We’re a top coat in the nor­mal paint­ing sys­tem,” he says. “What­ever sur­face prep and prim­ing you use for your par­tic­u­lar un­der­ly­ing boat ma­te­rial, to get you to a top coat, you do the same stuff and re­place the top coat with us.”

The fed­eral gov­ern­ment, along with pri­vate in­vestors, is bet­ting that boaters and other con­sumers will like what they see when SLIPS- branded prod­ucts start to be­come widely avail­able. SLIPS Tech­nolo­gies re­cently an­nounced $8.6 mil­lion in fi­nanc­ing that’s ex­pected to go to­ward prod­uct de­vel­op­ment, test­ing and com­mer­cial­iza­tion. That money in­cludes a $2.95 mil­lion grant from the U.S. De­part­ment of En­ergy to de­velop and test SLIPS an­tifoul­ing paint — not just for recre­ational boats, but also for mil­i­tary and com­mer­cial ves­sels.

“Bar­na­cles, mus­sels and al­gae stick to the hulls of ships and boats, cre­at­ing ex­tra drag that costs the ship­ping in­dus­try ap­prox­i­mately $20 bil­lion each year in fuel,” the fund­ing an­nounce­ment stated. “SLIPS pro­vides su­pe­rior, en­vi­ron­men­tally friendly so­lu­tions to con­trol bio­foul­ing and keep ships clean. Tra­di­tional paints for ship bot­toms rely on cop­per bio­cides that leach into wa­ter, dam­ag­ing ma­rine ecosys­tems and re­quir­ing strict reg­u­la­tory over­sight. In con­trast, SLIPS ma­rine paints pro­vide a safer al­ter­na­tive while of­fer­ing en­hanced bio­foul­ing pro­tec­tion.”

SLIPS an­tifoul­ing can be ap­plied to hulls by rolling or spray­ing.

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