Logos to go: hydrogel coatings provide removable color.

A biodegradable coating could add a temporary splash of color to sports fields, buildings, or even people's bodies. This is the first example of a removable color coating made from environmentally benign ingredients, its inventors say.

Cornell University's D. Tyler McQuade usually works on chemical-reaction systems that mimic those of cells. Last year, he and his colleagues began examining calcium alginate as a component of such a system. Alginate is a polysaccharide extracted from kelp that, with the addition of calcium, forms a hydrogel used to thicken food and encapsulate drugs.

When they heard that a local company was interested in colored, removable decorations for playing fields, McQuade and his graduate student Muris Kobaslija suspected that a coating of calcium alginate might serve as such a product.

To make the coating, the researchers first sprayed a solution of calcium chloride onto a piece of artificial turf. Next, they sprayed on a solution of sodium alginate that they had colored with red food dye.

When the sodium alginate contacted the calcium chloride, the calcium displaced the sodium and formed a network of bonds between chains of the polysaccharide, explains McQuade. Water didn't remove the resulting rubbery coating although it did wash out some of the color. However, contact with disodium ethylenediamine tetraacetate (EDTA), a food preservative, dissolved the coating.

"It's an excellent example of green chemistry," comments John C. Warner, director of the Center for Green Chemistry at the University of Massachusetts at Lowell.

McQuade and Kobaslija also tested a coating made from a lower concentration of calcium chloride. The resulting film lost 91 percent of its dye after 1 hour under a water shower mimicking rain, as compared with a film from a more concentrated solution, which lost 64 percent of its dye, the researchers report in the August Biomacromolecules.

The researchers have also made blue and green coatings, but overall, "the color density isn't super yet," McQuade acknowledges. They are looking for a research partner to further develop the system, which they've agreed to license to the local company.

"It strikes me as a creative and innovative use of hydrogel-type systems," says Christopher S. Brazel, a chemical engineer at the University of Alabama in Tuscaloosa. He adds, though, that "alginate is pretty thick," and so a lot of water might be needed to remove decorations from a real playing field.