This friction reduction breakthrough is no snake oil
01 July 2015
Snake skin inspired surfaces smash records, providing an astonishing 40 percent friction reduction in tests of high performance materials.
These new surfaces could improve the reliability of mechanical components in machines such as high performance cars and add grist to the mill of engineers designing a new generation of space exploration robots.
A paper discussing this finding is published today (July 1) in the journal Bioinspiration & Biomimetics.
The skin of many snakes and lizards has been studied by biologists and has long been known to provide friction reduction to the animal as it moves. It is also resistant to wear, particularly in environments that are dry and dusty or sandy.
The team used a laser to etch the surface of a steel pin so that it closely resembled the texture of snake skin. They then tested the friction created when the pin moved against another surface.
In dry conditions - with no oil or other lubricant - the scale-like surface created far less friction (40 percent less) than its smooth counterpart.
"If we'd managed just a 1 percent reduction in friction, our engineering colleagues would have been delighted; 40 percent really is a leap forward," says lead researcher, Dr Christian Greiner.
Applications are likely to be in mechanical devices at the micro or nano scale. Familiar examples include the sensors in car anti-lock braking systems, computer hard disk drives, and sensors used in mobile phones, such as accelerometers.
There is interest in snake skin inspired materials from the robotics sector, where robots inspired by snakes could aid exploration of very dusty environments. This raises a new challenge for Dr Greiner's team - to make a material that decreases friction in only one direction.
With snake's skin, the scales all lie in the same direction and are articulated to aid the snake in its forward motion, whilst resisting backwards motion. The steel pins tested in this research mimic only the overall surface texture of snake skin and reduce friction in at least two directions.
Dr Greiner has made some progress with polymers that even more closely mimic snake skin to reduce friction in only one direction, but this work is not yet scheduled for publication.
This new surface doesn't work well in an environment where oil or another lubricant is present. In fact, the snake skin effect created three times more friction, with lubricant, than an equivalent smooth surface.
"This wasn't a huge surprise," says Dr Greiner. "We were looking to nature for inspiration and the species we mimicked - the royal python and a lizard called a sandfish skink - live in very dry environments and don't secrete oils or other liquids onto their skin."
The Bioinspiration & Biomimetics paper can be downloaded here.