Laser-etched snake-inspired material reduces friction by 40%

A snake skin inspired surface, manufactured using laser etching, has smashed records by providing a 40 per cent friction reduction in tests of high performance materials. A paper discussing this finding is published today (1 June 2015) in IOP Publishing’s Bioinspiration & Biomimetics journal.

Lead researcher, Dr Christian Greiner and his 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.

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.

Greiner said: ‘If we’d managed just a one per cent reduction in friction, our engineering colleagues would have been delighted; 40 per cent really is a leap forward and everyone is very excited.’

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 IOP said that applications are likely to be in mechanical devices that are made to a micro or nano scale. Familiar examples include the sensors in car anti-lock braking systems, computer hard disk drives, and accelerometers.

Greiner added: ‘Our new surface texture will mainly come into its own when engineers are really looking to push the envelope.’ The snake skin surface could be used in high end automotive engineering; in highly sensitive scientific equipment, including sensors installed in synchrotrons such as the Diamond Light Source in the UK or the Large Hadron Collider in Switzerland; and anywhere the engineering challenge is to further miniaturise moving parts.

There is interest in snake skin inspired materials from the robotics sector, too, which is designing robots, inspired by snakes, which could aid exploration of very dusty environments on earth or even in space. This raises a new challenge for Greiner’s team—to make a material that decreases friction in only one direction.

A snake’s 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. It is, he says, early days and this later work is not yet scheduled for publication.

The only caution is that 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. Greiner explained: ‘Since 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.’

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Bio-inspired scale-like surface textures and their tribological properties

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