Published by the MIT News Office at the Massachusetts Institute of Technology, Cambridge, Mass.
Published by the MIT News Office at the Massachusetts Institute of
Technology, Cambridge, Mass.
Gel Technology Muscles on the Light Fantastic by Eugene F. Mallove Stretching the very fiber of his imagination, literally, physics Professor Toyoichi Tanaka hopes someday to turn creations from his laboratory into artificial muscle fibers that tug when activated by laser light. Dr. Tanaka and his associates have developed a fiber composed of a material called a gel--a cross-linked network of polymer molecules embedded in a fluid. Ordinarily, the liquid medium within the gel keeps the network of molecular chains from collapsing. But in some of Professor Tanaka's recent materials, the clear, hair-like fiber collapses when exposed to high intensity light, and expands when the light is cut off. The collapse and expansion of the fiber gives it an action like that of muscle fiber. In a future application of the phenomenon, a network of glass fiber- optic light tubes--the equivalent of activating ÒnervesÓ--could feed laser light to individual gel fibers bundled to create an artificial muscle. Dr. Tanaka developed the light-triggered fibers with Dr. Atsushi Suzuki of the Department of Materials Science at Yokohama National University in Japan. Since coming to MIT 19 years ago, Dr. Tanaka has carried out research on the basic principles of gels. In 1973, when he was a postdoctoral fellow working with Professor George B. Benedek, the group discovered that the network of polymer fibers within a gel was moving. They observed the thermal motion of the fibers with sophisticated laser scattering techniques. In 1978, Professor Tanaka's gel research group discovered the extraordinary phenomenon of a gel that experienced a very sudden expansion--an abrupt swelling--as the concentration of liquid (acetone) in the gel reached a certain critical value. The next year, the group discovered how to make a gel with its fluid concentration fixed that would experience the rapid swelling at a critical temperature change. The discoveries have been non-stop. In the early 1980s, the MIT gel researchers discovered that slight changes in chemical pH, tiny changes in electrical field, or a pulse of ultraviolet light could do the trick. Then in 1990 came the light fantastic--a gel that twitched when a pulse of visible blue light from an argon-ion laser passed through. Their discovery was reported in the journal Nature last July. Professor Tanaka and his colleagues envision a host of possible applications for their light-activated gels: robot actuators, for example, or even fiber-powered Òengines.Ó It is possible to imagine light-triggered optical shutters based on the gel technology. The many other conceivable applications of physically activated gels in general, says Professor Tanaka, include temperature, chemical, and electric field sensors; diapers and absorbers of toxic chemicals; fluid switches; oil recovery and desalination systems; and even implantable drug-delivery devices.