Researchers have synthesised organic crystals that can bend and twist in response to heat, ultraviolet light and mechanical force1.

On removing light and heat, the crystals regain their original shapes, making them potentially useful for making miniature moving parts such as gears and valves.

Other researchers had previously made crystals that could jump, bend, twist and even walk when exposed to heat or light. However, they could not make organic crystals with such properties.

An international research team including researchers from the National Institute of Technology, Meghalaya, in India, led by Naba Kamal Nath, prepared single organic crystals by slowly evaporating two organic compounds from a solution of an organic compound. These crystals, shaped like needle and block, were then separately exposed to heat, ultraviolet light and mechanical stress.

When heated, the crystals twisted. On cooling, they untwisted to regain their original shapes. The crystals could bend to form loops when mechanically stressed. They could regain their original shapes when the stress is removed.

When exposed to ultraviolet light, the crystals bent away from it. In the absence of light, they regained their original straight shape in less than a second. Such flexibility, the researchers say, could be attributed to several factors including weak intermolecular interactions between the building blocks of the crystals.

“The best part of the crystals is that even if they develop any crack during operation, they can be healed just by heating above 62 o C,” says Nath.