Better Bonds from Mollusk Chemistry

By: Katie Schaefer, Cosmetics & Toiletries magazine

Posted: November 30, 2010, from the December 2010 issue of Cosmetics & Toiletries.

Most consumer attention to oysters and mussels has centered on their taste, beautiful by-products or aphrodisiac effects; however, their adhesive properties are what caught the attention of Jonathan Wilker, PhD, associate professor of chemistry, and his research team at Purdue University. Wilker’s team has been studying marine biological adhesives for years and has found that the two mollusks produce adhesives that form a non-toxic, strong bond in wet environments. Although Wilker mainly has worked to develop synthetic versions of the adhesives for medical use, he is investigating other applications, which may include personal care.

Mollusk Glue Composition

Wilker has studied the adhesives produced by various marine entities, including Mytilus edulis (the blue mussel) and Crassostea virginica (Eastern oyster)—an oyster popular in the human diet. He notes one similarity. “Mussels, oysters and barnacles all use cross-linked proteins, (long biological polymers), to make their adhesive,” said Wilker. The difference, however, is in the composition of the adhesive.

To study the adhesive, Wilker and his team cut open the shells of oysters and observed the interface where they were attached; he compared this with separate, unattached portions of shell as a control. “[Since] the oyster’s adhesive is comprised of materials similar to the shell, we speculate the cement comes from the same place, system or organ as the shell,” he furthered.

Both the oyster shell and adhesive consist of calcium carbonate and protein as starting materials but the shell is mostly calcium carbonate with a small amount of protein, whereas there is more protein and less calcium carbonate in the adhesive. “In the cement, the extra reactivity is added to the proteins so they crosslink together,” Wilker explained. The adhesive produced by oysters is 10-15% protein and 85-90% calcium carbonate (chalk), which according to Wilker results in a hard inorganic, cement-like material.

Unlike oysters, Wilker notes that mussels separately produce their adhesive and shell. “If you crack open a mussel, a separate organ [is present that] produces the adhesive,” said Wilker. He added that the adhesive produced by mussels is about 99% proteins and more like soft organic glue.