Number 130 (Story #3), May 27, 1993 by Phillip F. Schewe and Ben Stein INTELLIGENT GELS , gels that can adjust their properties to changes in their surroundings, promise to lead to synthetic muscles and body-implanted medicine dispensers that respond to environmental cues. Easier to recognize than to define, gels have two elements: a liquid solvent and polymer molecules that link together in long chains, some of which span the entire solvent, endowing the substance with the properties of a solid. The polymers and solvent can be made especially sensitive to changes in such properties as temperature or pH. Ronald A. Siegel and his colleagues at UC-San Francisco have designed a gel-based membrane that shrinks in acidic regions but expands in alkaline ones. Such a design can be applied to encapsulate drugs in the body, preventing or allowing their release depending on the size of the membrane's pores, which is determined by the environment. Yoshihito Osada and his colleagues at Hokkaido University in Japan have designed a "gel looper," a wormlike device that moves by alternately curling and straightening itself under changing electric fields. Devices like the gel-looper are precursors to "soft machines," devices that will perform work by interacting with their liquid surroundings. (Scientific American, May 1993.)