Biomimetic surfaces: copying nature to stop bacteria and keep ship hulls smooth

You might not think that keeping a boat hull smooth in the water has anything in common with keeping a surgical scalpel clean, but here it is: in both cases, you’re trying to prevent nature from growing on the surface. . Science has looked at nature and found that the micro-patterns that form in the scales of some sharks or the leaves of lotus plants are a very beautiful technique that we can copy to prevent bio-pollution.

When marine growth adheres to and grows on a ship’s hull, the main problem is to increase drag. This increases fuel usage and reduces overall vessel efficiency, requiring regular cleaning to remove biofouling. In the hospital setting, this layer of growth becomes even more important. Despite the annual use of disposable catheters and sterile dressings, a large number of hospital patients develop infections.

Biofilm formation

Placoid scales as seen through an electron microscope. Also called incisors, these are structurally homologous to vertebrate teeth.

An interesting aspect of evolution is that it tends to solve many of the problems we try to solve today. For marine animals, the presence of biofilms and other growths on their skin is obviously problematic because for them it means increased drag, just like on a ship. This means that the animal expends more energy while swimming, in addition to the possibility of developing skin and other diseases due to the proximity of so many bacteria.

Many marine animals rub against rocks, live in symbiotic relationships with skinning fish species, or use the same process of shedding and molting that we land-dwelling species do. The most interesting approach, however, involves micro-patterning, which is part of the initial colonization step of biofilm formation.

Although scales are common among marine and other animals, the scales of sharks and rays are unique in their microscopic patterns. Experimental testing shows a clear lack of biofilm formation. This Damodaran et al. (2016) in Biomaterials Research. It summarizes the following methods:

  1. Biological molecules:
    1. Substances that emit nitrogen oxides.
    2. Peptide and Peptide Modified Surfaces.
  2. Chemical modification of surfaces:
    1. Hydrophilic polymers.
    2. PEG immobilization.
    3. Zwitterionic polymers.
    4. Hydrophobic polymers.
  3. Page thumbnails:
    1. The lotus effect.
    2. Shark skin samples.

As for what we can copy from nature, biological molecules and surface modification techniques are subject to high costs, limited lifetimes, and limited applications in terms of which species of bacteria they affect. Poisoning risk of hydrophobic polymers.

Damodaran et al. (2016).

This leaves the micropatterning. Instead of a substance that must be synthesized and continuously applied, these micropatterns can be etched onto a surface, with the duration of the effect depending on the durability of the material being etched. Self-assembling patterns can also be used, for example, in paints with nanoparticles.

Damodaran et al. (2016).

The placoid scales of sharks are particularly interesting for boat hull use. They reduce drag by disrupting the laminar flow near the skin, preventing bacterial adhesion. It is likely that drag reduction was a relevant evolutionary factor in the development of these skin teeth, and also provides an interesting aspect to this type of antifouling—the micropatterns reduce the drag of the ship’s hull over and above the “clean” hull. .

Scale it up

As with many antipollution techniques, the key issues are getting it to a level that is economically feasible and making it sustainable. The lotus effect is most commonly used in this case, as its ever-repeating pattern lends itself to everything from roof tiles and fabrics to paints. In outdoor settings, using self-cleaning surfaces is self-explanatory, as it prevents the growth of algae and lichen, and resists things like graffiti.

Sharkskin patterns are a bit more complicated because it is not easy to assemble yourself. Perhaps the best-known commercial version of this technology Sharklet Material sold by Sharklet Technologies and their patented micro pattern. They primarily target hospitals and similar settings for their product, and a body of research shows their effectiveness in the context of preventing foreign body reactions with neural implants.

What ship hulls and medical tubes can’t yet do is grow skin denticles like shark skin. A shark constantly renews its skin surface. A combination of approaches will continue to be necessary to combat biofouling, but in the future, we’ll see less drag for a cleaner and safer world where microboring will be more widely used.

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