David Blicq  dblicq@rrc.mb.ca  (update 01/04/2010)         DIRECTORY I BIO I NOTICE BOARD

The ability of marine life to "slide" through water has always fascinated humankind. Evolutionary forces have ensured aquatic organisms have the most efficient surfaces for interacting with (and gliding through) the aquatic environment. Although there is interest in aquatic biomaterials over a wide range of areas there is keen interest in natural drag-resistant surfaces.

Drag-resistant Aquatic surfaces

The design of materials which mimic the minimal drag-resistance of natural aquatic life has many applications: hull design for more efficient ships, submarine design, bridge and aquatic structure construction are but a few examples.

Shark Skin

Shark skin has several remarkable properties. As a start, sharkskin is thick and has the unique property of being slippery or rough, depending on direction. This occurs because shark skin is made up of small rectangular scales tthat have tiny  spines /  bristles which can be rough to the touch.

Historic peoples have long employed shark skin as a useful abrasive, as a natural fabric, drum skins and many other uses. In modern times "shark leather" is used to make fine leather goods, including purses, shoes, boots and wallets.

Despite their obvious fluidity of movement  in water, shark skin is similar to organic chain mail (armor) that provides physical protection without sacrificing mobility and flexibility. This "organic armor" moves and flexes as the animal swims.

The shark skin's outer cells (dentine layer) is made of a hard, crystalline material, which is embedded in a soft protein; resulting in a material that is rigid without being brittle.

Each cell also contributes to the organism's fluidity tin the water. Each scale has a highly streamlined shape in which there are little channels (see figure above). This streamlined shape tremendously reduces friction by channeling the water flow through the scale grooves. This causes the shark's skin to contact only organized flowing water, rather than turbulent disorganized flow - greatly reducing friction. Estimates of drag reduction range from 6-10%, an efficiency which could be translated into reduced energy and fuel costs.

Swimwear: The swimsuit manufacturer Speedo has already capitalized by producing biomimetric swimsuits. They have produced  a novel material (Fastskin) which is based on the properties of the shark skin. The fabric contains tiny ridges designed to reduce turbulence and minimize drag in the water. Measurements have indicated these suits improve swimmer's speed by as much as 7.5% by reducing the drag in the water (compared to un-clad human flesh).

Intentional Deformation to resist Pressure

Still in the research stages, intentional surface deformation is an area of key interest. How do aquatic organisms survive at crushing depths without some significant adaptations. One of the most obvious alterations in structure is an intentional deformation of surfaces to resist pressure, not unlike the "bend don't break" characteristics of trees. How to successfully mimic this biodesign is an area of active research, but potential applications are significant:

	Submarine-hulls
	Aircraft fuselages
	Automobile collision protection
	Other ergonomic surfaces