Rob Lichty
MEDdesign

Biomimicry Lessons from Sharks

By Rob Lichty
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Rob Lichty

Apart from Speedo swimsuits, what other biomimicry learnings from Shark skin can we use for medical devices?

In June of 2000, the board of USA Swimming banned Speedo bodysuits in the Olympic trials. However, the suits were eventually allowed to be used in the Olympic Games. This swimsuit was worn by 83 percent of swimmers winning medals and 13 of the 15 World Records broken in Sydney that year. In the 2008 Beijing Olympics, 92 percent of all medalists in swimming competitions were wearing a Speedo swimsuit! How could it be that one swimsuit (Speedo Fastskin®) could make that much of a difference? 
Speedo-Fastskin
Speedo’s Fastskin® swimsuit Source: Speedo website

There are two innovations of particular importance. Let’s first briefly look at the use of the material itself. Speedo has gone to great length to study the human body while swimming, and place bands of fabric in all the right places. Mimicking the muscles and tendons of great swimmers, the stretchy polyurethane can increase muscle compression and help maintain muscle shape to reduce fatigue and power loss. This is a simple, yet effective case of bionics.

The really exciting Biomimetic innovation again lies in the material but this one does not emulate anything human. In this case, Speedo took the help of scientists at the Natural History Museum in London to take a look at shark skin. These slippery and super fast creatures have a simple pattern to their rough (yes! … rough, not smooth) skin. Shark’s skin has many tiny teeth (they are actually covered in dental enamel) called dermal denticles that contain many riblets and are arranged in a saw-tooth pattern. This rough pattern reduces drag (friction) with water by preventing eddies in the boundary layer by holding water close to the body.  

Thus, a shark’s skin can:
Channel the direction of water flow;
Use riblets to reduce the difference in water speed at the skins surface as compared to the water speeds beyond the skin (think of  wind howling through a canyon); and 
Reduce turbulence by breaking up water flow hence creating many small turbulences rather than larger vortices.

Relate this back to the “Life’s Principles” (developed by the Biomimcry Group) mentioned in the previous blog. Sharkskin is a great teacher of what is meant by Fit Form to Function. The shape of the shark denticles are what allow the shark, and now competition swimmers, to move efficiently through the water with lesser effort.

Sharklet Technologies' urinary tract catheter
Sharklet Technologies’ urinary tract catheter Source: Sharklet Technologies website

Recalling another of the Life’s Principles, Use Multi-Functional Design, I’d like to bring this back to the medical device community. At about the same time Speedo made their discovery of shark skin, Dr. Anthony Brennan looked at slow moving sharks. Unlike whales, sharks do not have a buildup of barnacles or other micro-organisms. As it turns out, the shape that allows sharks to move fast through water also discourages microorganisms from attaching to the sharks skin. In fact, Dr. Brennan found that green algae settlement was reduced by 85 percent… enough to prevent a colony from being able to take hold. While conducting further research for the U.S. Office of Naval Research, Dr. Brennan discovered other uses for this technology. He then started Sharklet Technologies, Inc. which focuses on antimicrobial and antibacterial technologies. Some of the focus has been on antibacterial surfaces for hospitals (e.g. nurse call buttons) as well as medical devices (e.g. urinary tract catheters).

The wonderful thing about the three-micrometer wide diamond pattern on the sharks, is that there is nothing for bacteria to become resistant to because it does not kill them. With the correct combination of surface chemistry, surface topography, mechanical properties, feature dimensions, tortuosity through the pattern and surface energy, microbes decide that it would use too much energy to establish a colony on the surface and simply move on. There are no drugs, toxic chemicals or metals used… just a surface pattern.
 
Now that we have discovered how a pattern embossed on a swimsuit can make a difference in the medical device community, I have a question for you:  How can the muscle technology of a swimsuit be transferred to the medical device community?  What can we do, for instance, for someone with Multiple Sclerosis or Cerebral Palsy…? 
 

Until next time,
Rob Lichty

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