These are 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.
<b>What is a Smart Gel?</b>
A smart gel is a material that gels in response to a specific physical property. For example, it may gel at a specific temperature or pressure.
Why Study Smart Gels?
The mechanisms that create a gel in response to a given environment are not well understood. So developing this understanding is key to being able to create materials that gel at designated points.
The potential for applications of smart gels is enormous. Since smart gels expand or contract in response to external stimuli, they could be useful in applications such as an artificial pancreas that releases insulin inside the body in response to high sugar level. Smart gels might someday be used to make exotic foods, cosmetics, medicines, and sensors.
The NIST team is studying a subclass of these materials called shake gels. Through some complex and as yet unknown process, these watery mixtures of clays and polymers firm up into gels when shaken, and then relax again to the liquid phase after some time has passed. A shake gel might be used, for example, in shock absorbers for cars. The material would generally be a liquid but would form a gel when the car drove over a pothole; the gel thickness would adjust automatically to the weight of the car and the size of the pothole. A more esoteric application might be the formation of gelled areas within a liquid where holograms could be created using a laser.
<b>Why Visualize Smart Gels?</b>
Immersive visualization helps scientists understand how the molecules in the smart gel interact. Scientists immerse themselves in the 3D environment constructed using data from theoretical studies. This enables researchers to answer questions that might otherwise defy attempts at solution. The 3-D visualization helped the scientists see that for the shake gel it is the polymer’s oxygen atoms, instead of the hydrogen atoms as previously thought, that attach to the clay.
The team has also made theoretical calculations that may help to explain why and how the components of the liquid mixture bind together into a semisolid form. Electrical charges affect the binding process, resulting in water binding to clay surfaces in a perpendicular arrangement, which is believed to help create the firmness of the gel.