Lab-grown shells mimic seashore version.

Lab-grown shells mimic seashore version

You don't have to be a shellfish to grow a seashell. Now even humans can accomplish this feat with a simple laboratory setup and some processing tips from sea-dwelling shell makers.

The technique could lead to novel ceramics, perhaps for surrogate bones and teeth.

Fabricating ceramics for tableware, tools and other products almost always involves high temperatures, rugged chemical conditions and lots of fuel. Yet marine animals such as clams and sea urchins fashion their intricate bioceramic shells and spines under mild, comfortable conditions. Collaborating scientists at Pennsylvania State University in University Park and the Royal Technical University in Bratislava, Czechoslovakia, sought to create tough synthetic ceramics through similar low-temperature reactions.

The team now reports growing shell-shaped formations composed mostly of calcium carbonate, the primary mineral in seashells, by adding hydroxyethyl cellulose (HEC) -- a complex sugar, or polysaccharide -- to mineral-saturated solutions. Small amounts of polysaccharides, proteins and other organic compounds play pivotal, though poorly understood, roles in biological mineralization processes such as bone formation and shell growth.

The experimental shell-growing apparatus held a beaker of calcium chloride powder within a larger beaker of sodium carbonate powder. The researchers added just enough HEC-spiked solution to each beaker to form a liquid bridge over the inner beaker's lip, linking the solutions in the two containers. As the solutions diffused into one another over several days, some lifelike mineralization occurred, says Rustum Roy of Penn State.

Along the outside of the inner beaker, calcium and carbonate ions assembled into a thin, white, solid layer with a gentle upward curve. "The overall shape of the body of the precipitate resembles that of a mollusk shell," the researchers write in the December 1990 JOURNAL OF MATERIALS RESEARCH. Scanning electron microscope observations suggest the resemblance partly extends to the shell's underlying arrangement of tiny crystal platelets, Roy adds.

However, this comparison breaks down in several ways, notes biomaterials scientist Mehmet Sarikaya of the University of Washington in Seattle. Calcium carbonate in the lab-made shells mostly assumes a structure known as vaterite, not the tougher calcite and aragonite mineral forms common in such biological edifices as abalone shells and sea urchin spines. The vaterite microcrystals also pack together less densely than related minerals in natural shells.

"The lesson we learned is how little we understand about biomineralization," Roy says. And that means more work for the new year.