Cells in gels.

The notion of a synthetic material that is alive sounds far-fetched. Somewhat less fantastic, though, is a material that contains, or coexists with, living components.

In an effort to produce such a material, Edward J.A. Pope, a materials scientist at MATECH in Westlake Village, Calif., has produced a transparent gel, made of porous silica, that can encapsulate living cells. The gel forms a clear matrix around the cells, suspending them without killing them - "like raisins in a loaf of bread," he says.

Pope demonstrated the concept by mixing cells of Saccharomyces cerevisiae, a type of yeast commonly used to ferment beer, into a gel. The gel formed a porous shell around each organism - trapping it, yet permitting nutrients to flow in and by-products to flow out.

Pope believes silica gels can encapsulate capsulate many types of microorganisms, including genetically altered Escherichia coli and Streptomyces bacteria. He also sees such gels as someday facilitating cell transplants.

"Silica gel is compatible with living tissues," he says, "so it's a good candidate for implanting live cells into a human body." For instance, insulin-producing cells suspended in gel could be inserted into the pancreas of a diabetic. The gel would permit glucose and insulin to come and go, yet protect the cells from immune response. Similar implants could help patients suffering from liver failure or thyroid deficiencies, Pope adds.