Biomimetic antifouling coating

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A biomimetic antifouling coating is a treatment that prevents the accumulation of marine organisms on a surface. Typical antifouling coatings are not biomimetic but are based on synthetic chemical compounds that can have deleterious effects on the environment. Prime examples are tributyltin compounds, which are components in paints to prevent biofouling of ship hulls. Although highly effective at combatting the accumulation of barnacles and other problematic organisms, organotin-containing paints are damaging to many organisms and have been shown to interrupt marine food chains. [1] [2] [3]

Contents

Biomimetic antifouling coatings are highly lucrative because of their low environmental impact and demonstrated success. Some properties of a biomimetic antifouling coating can be predicted from the contact angles obtained from the Wenzel equation, and the calculated ERI. Natural materials such as shark skin continue to provide inspiration for scientists to improve the coatings currently on the market.

Chemical methods

Most antifouling coatings are based upon chemical compounds that inhibit fouling. When incorporated into marine coatings, these biocides leach into the immediate surroundings and minimize fouling. The classic synthetic antifouling agent is tributyltin (TBT). Natural biocides typically show lower environmental impact but variable effectiveness.

The chemical structure of bufalin (3,4-dihydroxybufa-20,22 dienolide) Bufalin.svg
The chemical structure of bufalin (3,4-dihydroxybufa-20,22 dienolide)

Natural biocides are found in a variety of sources, including sponges, algae, corals, sea urchins, bacteria, and sea-squirts, [4] and include toxins, anaesthetics, and growth/attachment/metamorphosis-inhibiting molecules. [5] As a group, marine microalgae alone produce over 3600 secondary metabolites that play complex ecological roles including defense from predators, as well as antifouling protection, [6] increasing scientific interest in the screening of marine natural products as natural biocides. Natural biocides are typically divided into two categories: terpenes (often containing unsaturated ligand groups and electronegative oxygen functional groups) and nonterpenes.

The most effective natural biocide is 3,4-dihydroxybufa-20,22 dienolide, or bufalin (a steroid of toad poison from Bufo vulgaris), which is over 100 times more effective than TBT at preventing biofouling. [5] Bufalin is however expensive. A few natural compounds with simpler synthetic routes, such as nicotinamide or 2,5,6-tribromo-1-methylgramine (from Zoobotryon pellucidum), have been incorporated into patented antifouling paints. [5]

A significant drawback to biomimetic chemical agents is their modest service life. Since the natural biocides must leach out of the coating to be effective, the rate of leaching is a key parameter. [7]

Where La is the fraction of the biocide actually released (typically around 0.7), a is the weight fraction of the active ingredient in the biocide, DFT is the dry film thickness, Wa is the concentration of the natural biocide in the wet paint, SPG is the specific gravity of the wet paint, and SVR is the percentage of dry paint to wet paint by volume.

Shark skin mimetics

One class of biomimetic antifouling coatings is inspired by the surface of shark skin, which consists of nanoscale overlapping placoid scales that exhibit parallel ridges that effectively prevent sharks from becoming fouled even when moving at slow speeds. The antifouling qualities of the shark skin-inspired designs appear highly dependent upon the engineered roughness index (ERI). [8]

Where r is the Wenzel roughness ratio, n is the number of distinct surface features in the design of the surface, and φ is the area fraction of the tops of the distinct surface features. A completely smooth surface would have an ERI = 0.

Using this equation, the amount of microfouling spores per mm2 can be modeled. Similar to actual shark skin, the patterned nature of Sharklet AF shows microstructural differences in three dimensions with a corresponding ERI of 9.5. This three-dimensional patterned difference imparts a 77% reduction in microfouling settlement. [9] Other artificial nonpatterned nanoscale rough surfaces such as 2-μm-diameter circular pillars (ERI = 5.0) or 2-μm-wide ridges (ERI = 6.1) reduce fouling settlement by 36% and 31%, respectively, while a more patterned surface composed of 2-μm-diameter circular pillars and 10-μm equilateral triangles (ERI = 8.7) reduces spore settlement by 58%. [9] The contact angles obtained for hydrophobic surfaces are directly related to surface roughnesses by the Wenzel equation. [10]

See also

Related Research Articles

A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products". When compared, the two definitions roughly imply the same, although the US EPA definition includes plant protection products and some veterinary medicines.

<span class="mw-page-title-main">Anti-fouling paint</span> Specialized paint for ship hulls

Anti-fouling paint is a specialized category of coatings applied as the outer (outboard) layer to the hull of a ship or boat, to slow the growth of and facilitate detachment of subaquatic organisms that attach to the hull and can affect a vessel's performance and durability. It falls into a category of commercially available underwater hull paints, also known as bottom paints.

<span class="mw-page-title-main">Biofouling</span> Growth of marine organisms on surfaces

Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that cause degradation to the primary purpose of that item. Such accumulation is referred to as epibiosis when the host surface is another organism and the relationship is not parasitic. Since biofouling can occur almost anywhere water is present, biofouling poses risks to a wide variety of objects such as boat hulls and equipment, medical devices and membranes, as well as to entire industries, such as paper manufacturing, food processing, underwater construction, and desalination plants.

<span class="mw-page-title-main">Organotin chemistry</span> Branch of organic chemistry

Organotin chemistry is the scientific study of the synthesis and properties of organotin compounds or stannanes, which are organometallic compounds containing tin–carbon bonds. The first organotin compound was diethyltin diiodide, discovered by Edward Frankland in 1849. The area grew rapidly in the 1900s, especially after the discovery of the Grignard reagents, which are useful for producing Sn–C bonds. The area remains rich with many applications in industry and continuing activity in the research laboratory.

<span class="mw-page-title-main">Fouling</span> Accumulation of unwanted material on solid surfaces

Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms or a non-living substance (inorganic). Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system, or plant performing a defined and useful function and that the fouling process impedes or interferes with this function.

<span class="mw-page-title-main">Tributyltin oxide</span> Chemical compound

Tributyltin oxide (TBTO) is an organotin compound chiefly used as a biocide (fungicide and molluscicide), especially a wood preservative. Its chemical formula is [(C4H9)3Sn]2O. It is a colorless viscous liquid. It is poorly soluble in water (20 ppm) but highly soluble in organic solvents. It is a potent skin irritant.

<span class="mw-page-title-main">Tributyltin</span> Group of organotin compounds

Tributyltin (TBT) is an umbrella term for a class of organotin compounds which contain the (C4H9)3Sn group, with a prominent example being tributyltin oxide. For 40 years TBT was used as a biocide in anti-fouling paint, commonly known as bottom paint, applied to the hulls of oceangoing vessels. Bottom paint improves ship performance and durability as it reduces the rate of biofouling, the growth of organisms on the ship's hull. The TBT slowly leaches out into the marine environment where it is highly toxic toward nontarget organisms. TBT toxicity can lead to biomagnification or bioaccumulation within such nontarget organisms like invertebrates, vertebrates, and a variety of mammals. TBT is also an obesogen. After it led to collapse of local populations of organisms, TBT was banned.

Imposex is a disorder in sea snails caused by the toxic effects of certain marine pollutants. These pollutants cause female sea snails to develop male sex organs such as a penis and a vas deferens.

<span class="mw-page-title-main">Environmental impact of paint</span>

The environmental impact of paint can vary depending on the type of paint used and mitigation measures. Traditional painting materials and processes can have harmful effects on the environment, including those from the use of lead and other additives. Measures can be taken to reduce its environmental effects, including accurately estimating paint quantities so waste is minimized, and use of environmentally preferred paints, coating, painting accessories, and techniques.

<i>Voluta ebraea</i> Species of gastropod

Voluta ebraea, common name the Hebrew volute, is a species of medium-sized sea snail, a marine gastropod mollusk in the family Volutidae, the volutes. The Hebrew volute is endemic to Brazil, where it is collected both for food and for its shell, which is highly desired for ornamental purposes. Recent studies indicate that natural populations of Voluta ebraea may be suffering declines due to overfishing and overexploitation.

Tin poisoning refers to the toxic effects of tin and its compounds. Cases of poisoning from tin metal, its oxides, and its salts are "almost unknown"; on the other hand, certain organotin compounds are almost as toxic as cyanide.

<span class="mw-page-title-main">Copper alloys in aquaculture</span>

Copper alloys are important netting materials in aquaculture. Various other materials including nylon, polyester, polypropylene, polyethylene, plastic-coated welded wire, rubber, patented twine products, and galvanized steel are also used for netting in aquaculture fish enclosures around the world. All of these materials are selected for a variety of reasons, including design feasibility, material strength, cost, and corrosion resistance.

Sharklet, manufactured by Sharklet Technologies, is a bio-inspired plastic sheet product structured to impede microorganism growth, particularly bacterial growth. It is marketed for use in hospitals and other places with a relatively high potential for bacteria to spread and cause infections.

Biofilm formation occurs when free floating microorganisms attach themselves to a surface. Although there are some beneficial uses of biofilms, they are generally considered undesirable, and means of biofilm prevention have been developed. Biofilms secrete extracellular polymeric substance that provides a structural matrix and facilitates adhesion for the microorganisms; the means of prevention have thus concentrated largely on two areas: killing the microbes that form the film, or preventing the adhesion of the microbes to a surface. Because biofilms protect the bacteria, they are often more resistant to traditional antimicrobial treatments, making them a serious health risk. For example, there are more than one million cases of catheter-associated urinary tract infections (CAUTI) reported each year, many of which can be attributed to bacterial biofilms. There is much research into the prevention of biofilms.

An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital-associated infections, which have accounted for almost 100,000 deaths in the United States. In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.

<i>Ulva linza</i> Species of seaweed

Ulva linza is a green alga in the family Ulvaceae that can be found in British Isles.

<span class="mw-page-title-main">International Paint</span>

International Paint, abbreviated as International, is a brand of the Marine & Protective Coatings business unit of AkzoNobel.

Ultra-low fouling is a rating of a surface's ability to shed potential contamination. Surfaces are prone to contamination, which is a phenomenon known as fouling. Unwanted adsorbates caused by fouling change the properties of a surface, which is often counter-productive to the function of that surface. Consequently, a necessity for anti-fouling surfaces has arisen in many fields: blocked pipes inhibit factory productivity, biofouling increases fuel consumption on ships, medical devices must be kept sanitary, etc. Although chemical fouling inhibitors, metallic coatings, and cleaning processes can be used to reduce fouling, non-toxic surfaces with anti-fouling properties are ideal for fouling prevention. To be considered effective, an ultra-low fouling surface must be able to repel and withstand the accumulation of detrimental aggregates down to less than 5 ng/cm2. A recent surge of research has been conducted to create these surfaces in order to benefit the biological, nautical, mechanical, and medical fields.

Ultrasonic antifouling is a technology that uses high frequency sound (ultrasound) to prevent or reduce biofouling on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound. Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and cavitation intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods inhibit or prevent biofouling by algae and other single-celled organisms.

Self-cleaning surfaces are a class of materials with the inherent ability to remove any debris or bacteria from their surfaces in a variety of ways. The self-cleaning functionality of these surfaces are commonly inspired by natural phenomena observed in lotus leaves, gecko feet, and water striders to name a few. The majority of self-cleaning surfaces can be placed into three categories:

  1. superhydrophobic
  2. superhydrophilic
  3. photocatalytic.

References

  1. ↑ Salta, M., Wharton, J. A., Stoodley, P., Dennington, S. P., Goodes, L. R., Werwinski, S., Mart, U., Wood, R. J. K., Stokes, K. R., "Designing biomimetic antifouling surfaces", Philos. Trans. R. Soc., A 2010, 368, 4729. doi : 10.1098/rsta.2010.0195
  2. ↑ Mueller, W. E. G., Wang, X., Proksch, P., Perry, C. C., Osinga, R., Garderes, J., Schroeder, H. C., "Principles of Biofouling Protection in Marine Sponges: A Model for the Design of Novel Biomimetic and Bio-inspired Coatings in the Marine Environment?", Mar. Biotechnol. 2013, 15, 375. doi : 10.1007/s10126-013-9497-0
  3. ↑ 1. Gittens, J. E., Smith, T. J., Suleiman, R., Akid, R., "Current and emerging environmentally-friendly systems for fouling control in the marine environment", Biotechnol. Adv. 2013, 31, 1738. doi : 10.1016/j.biotechadv.2013.09.002
  4. ↑ Chambers, LD; Stokes, KR; Walsh, FC; Wood, RJK (2006). "Modern approaches to marine antifouling coatings" (PDF). Surface and Coatings Technology. 6 (4): 3642–3652. doi:10.1016/j.surfcoat.2006.08.129.
  5. 1 2 3 Omae, Iwao (2003). "General Aspects of Tin-Free Antifouling Paints" (PDF). Chemical Reviews . 103 (9). American Chemical Society: 3431–3448. doi:10.1021/cr030669z. PMID   12964877. Archived from the original (PDF) on June 24, 2010. Retrieved May 23, 2012.
  6. ↑ Bhadury, P; Wright, Phillipc. (2004). "Exploitation of marine algae: Biogenic compounds for potential antifouling applications". Planta. 219 (4): 561–578. doi:10.1007/s00425-004-1307-5. PMID   15221382. S2CID   34172675.
  7. ↑ "Emission Scenario Document on Antifouling Products Annex" (PDF). Biocides Publications. Organisation for Economic Co-operation and Development. Retrieved 6 June 2011.
  8. ↑ Long, C; Schumacher, James F.; Robinson, Paul A.C.; Finlay, John A.; Callow, Maureen E.; Callow, James A.; Brennan, Anthony B. (2010). "A model that predicts the attachment behavior of Ulva linza zoospores on surface topography". Biofouling. 26 (4): 411–419. doi:10.1080/08927011003628849. PMID   20191401. S2CID   5350118.
  9. 1 2 Schumacher, J; Carman, Michelle L.; Estes, Thomas G.; Feinberg, Adam W.; Wilson, Leslie H.; Callow, Maureen E.; Callow, James A.; Finlay, John A.; Brennan, Anthony B. (2007). "Engineered antifouling microtopographies - effect of feature size, geometry, and roughness on settlement of zoospores of the green alga Ulva". Biofouling. 23 (1): 55–62. doi:10.1080/08927010601136957. PMID   17453729. S2CID   5925449.
  10. ↑ Cheng, Y; Rodak, D; Wong, C; Hayden, C (2006). "Effect of micro- and nano-structure on the self-cleaning behaviour of lotus leaves". Nanotechnology. 17 (5): 1359–1362. Bibcode:2006Nanot..17.1359C. doi:10.1088/0957-4484/17/5/032. S2CID   137211738.
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