Crystal Ball

A bendy crystal. Credit: Masahiro Irie

Monday, April 16th, 2007--

Scientists have grown a bendable crystal. Masahiro Irie, a researcher at Osaka City University, Sugimoto in Osaka, Japan, and his colleagues grew microscopic, needle-shaped crystals from biological molecules. When zapped with ultraviolet light, the crystal bent a few degrees towards the incident light. It remained bent until it was exposed to visible light, which caused it to straighten. It bent and straightened eighty times without cracking and was even able catapult a gold ball that is ninety times heavier than itself, the researchers report in the journal Nature.

“It’s sort of a ‘gee whiz’ thing,” says J. Michael McBride, a researcher at Yale University in New Haven, CT and the author of an accompanying article in Nature. “It’s a much more dramatic example of the kinds of things people have done before. But the fact that it can go back and forth eighty times and it’s always exactly the same, that surprised me and it surprised other people I’ve mentioned it to.”

Light induces a chemical reaction in the molecule, which causes the bending. In this case, the light changes the bonds between the atoms, which changes the attraction of one molecule to another, which changes the shape of the crystal. The difficult part, McBride says, is getting billions of molecules to bend in unison. Crystals have the advantage of having ordered molecules, but for that reason, throwing them out of order by changing their bonds often results in cracking.

There are a few ways around cracking though. One way is to make sure the molecules are exposed evenly to the light by using light that isn't strongly absorbed. This way the light can travel through the crystal, reaching all the molecules, as opposed to being absorbed by the top layer of molecules.

In this study, however, Irie and his colleagues irradiated only part of the molecule. So how did it hold together? McBride isn't sure. “There must be something about these crystals, in the way the molecules touch one another, how they are packed together, that allows them to do a lot of bending without cracking,” McBride says, adding, “It’s not so obvious to me why these do it and others wouldn’t, but this is the first example I know of it working that dramatically.”

By pushing the gold ball, Irie has shown that these light-activated crystals have the capacity to do work. But the bendability is dependent on the crystal Irie created—no one else on record has grown a crystal so flexible. McBride is also a crystal-grower and says: “How you grow crystals to have a particular shape is mostly art now, not science. By chance, certain conditions or certain additives that you put into the solution while the crystal is growing cause its shape to change.”

In this study, Irie evaporated a solution and used the gas to grow the needle crystals. He got other shapes too—rectangles that turn into parallelograms when exposed to light. “Those are ones much more like what other people have seen,” says McBride, adding, “But this little fiber that bends and pushes the ball I thought was really cute. I’m not surprised it has attracted the attention of a lot of people.”

What did you think of the story? Send us some feedback.

--Flora Lichtman