A gel that expands and contracts when hit with light could work to cut off the blood supply to a tumor.


by Akira Harada, a professor of Macromolecular Science and his team at

Osaka University in Japan, the gel could also be used inside a person's

body to pump drugs in a specific location at a specific time.


gel is made from a polymer called a hydrogel and two chemicals –

alpha-cyclodextrin and azobenzene — that work similar to

muscle-contracting enzymes in the body. When exposed to ultraviolet light, the gel expands. When exposed to red light, it contracts.

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a strip of the gel with UV light from different directions makes it

bend away from the light. "Only the surface irradiated by UV absorbs the

light, while the other side does not," Harada told Discovery News.

"Therefore, the [strip of] gel bends. The same is true for irradiation

by visible light." After exposure to UV light for 15 minutes, the gel

formed curly shapes like spirals.

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The gel expands and contracts

because of the way the two added chemicals change when the light hits

them. When inside the gel, the cyclodextrin and azobenzene molecules are

bound to each other and molecules that make up the gel. Ultraviolet

light disturbs those bonds and changes the shape of the azobenzene

molecule. The azobenzene breaks from the cyclodextrin. This allows the

gel molecules to spread out, expanding the volume. Red light restores the molecules' original shapes, which makes them bind tightly again, which shrinks the gel.

Harada said that he was able to repeat the expansion and contraction at least

five times without the gel losing its ability to do it, and there's no

reason it couldn't continue.

Using the light to alter the chemical bonds and change the shape of the gel is new, said Albert Schenning, an associate

professor of chemistry at the Eindhoven University of Technology in the


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Using the gel in a

medical situation might involve a doctor injecting the gel into a vein

and then running an very thin optical fiber to the location to deliver

the light. A gel laced with drugs would theoretically release them at

the sight as it expanded. Or it could be expanded inside a blood vessel

feeding a tumor to cut off the supply.


is still some work to do. The reaction is still slow — to get the gel

to expand or contract took an hour. Schenning said future experiments

might show how to speed that up.

Harada's work appears in the Dec. 11 edition of Nature Communications.

Photo: Blood vessels feed cancer cells, but a new technique could choke those vessels off and stop cancerous growth. Credit: Sciepro/Science Photo Library/Corbis