Shape-shifting crystals harness light power
17 April 2007
Imagine a microscopic machine powered only by light. Scientists now think such mini-marvels could be possible. They've made crystals that can bend in response to ultraviolet light, acting as tiny switches and levers. Antenna finds out more...
This research was published in the journal Nature on 12 April 2007.
This is one of the bendy crystals that Japanese scientists have created.
Image: Masahiro Irie
Usually crystals are hard and solid, but ingenious Japanese researchers have managed to make a new sort of crystal that's a little out of the ordinary - one that can bend and reversibly change its shape.
The tiny crystals move in different ways depending on their starting shape. Some switch between a square form and a lozenge. Others start off as a straight rod that can bend and unbend.
This crystal rod bends in ultraviolet light and straightens in visible light.
Video: Masahiro Irie
Researchers now hope to use these shape changes to power mini-machines. The crystals' bendiness can make other particles move and can also be harnessed to turn the crystals into switches and levers.
Because they're powered by light the crystals can also be operated remotely. This makes them ideal candidates for use in mini-machines.
Watch this rod-shaped crystal bat away a microscopic silica ball.
Video: Masahiro Irie
'Our crystals could be used to make smaller, faster electronic devices or even miniature medical machines,' says Masahiro Irie from Rikkyo University in Tokyo, the lead researcher on the crystals. 'In future we could see them being used as micro-tweezers to move cells or valves to control medical devices.'
Masahiro Irie, crystal researcher, Rikkyo University Tokyo.
Image: Masahiro Irie
It seems a simple idea, but it's actually really clever.
'The idea of bendy crystals, especially ones that move rapidly and reversibly in response to light, seems strange,' says crystal expert Michael McBride from Yale University in America. 'Most crystals are hard and solid - they would crack under pressure instead of bending.'
Michael McBride, crystal expert, Yale University USA.
Image: Michael McBride
But Masahiro's team managed to manipulate the crystals' usual properties by making them out of light-sensitive molecules that change colour in different lights. The change in these molecules alters the crystals' shape.
This is the first time scientists have made light-powered materials that can change shape quickly and reversibly. Until now shape changes in light-powered materials have been slow and unstable. But the new crystals shape-shift within microseconds and can keep changing again and again.
Ultraviolet light makes this crystal change its colour as well as its shape.
Video: Masahiro Irie
'Most chemical reactions make molecules change their shape,' explains Michael. 'Nature uses this effect to power biological machines like muscles, but science is still playing catch-up in harnessing this power. Deforming one molecule is easy, but moving billions of molecules together is a big challenge.'
So what's next for bendy crystals?
'We're still at the first stage of our research,' says Masahiro. 'Now we need to find a reliable way to produce high-quality crystals and turn them into miniature machines. If we can do this, people could be using these crystals within five years.'
Image: istockphoto.com/cezars
Michael thinks there's still a long way to go before we'll be seeing these crystals in action. 'We don't really understand how these crystals survive intact after so many shape changes without any signs of damage. We need to find out which features of the crystals let them flex in this way.'
But he still thinks this discovery is a big step forward. 'Simply demonstrating that crystals can behave in this way brings the possibility of tiny light-driven machines one step closer.'