gel

Solid produced by the formation of a three-dimensional cage structure, commonly of linked large-molecular-mass polymers, in which a liquid is trapped. It is a form of colloid. A gel may be a jellylike mass (pectin, gelatin) or have a more rigid structure (silica gel).

Intelligent gels are polymer gels that respond ‘intelligently’ to their environments. Most gels shrink or swell in fairly strict proportion to the quality of solvent added to them, but some undergo a sudden change in dimension in response to relatively small fluctuations. This rapid response could make gels suitable for use as ‘muscle’ for robots, or as valves in engineering. They are also likely to have medical applications; for example, in long-term drug administration. The gel could sense conditions inside the body and vary drug delivery rate to maintain suitable levels in the bloodstream.

In biochemistry, gels are required for the separation of molecules either by their molecular weight or by their charge, in the process known as gel electrophoresis.