Biomechanics: Spider glue: sticky when wet

The mechanism by which spider aggregate glue is able to stick to surfaces in humid and wet conditions is identified in an article, published in Nature Communications this week. This finding could inspire the development of new adhesion systems that can be used in such environments.

In biology, adhesion systems that work reliably under humid conditions are common. Spiders, for example, use a glue-type material to hunt and capture their prey in humid or wet habitats. Effective approaches to guarantee adhesion in humid and wet environments include utilising specialized molecules, which can change their form or structure depending on the humidity. However, the exact mechanism by which spider glue continues to work in humid conditions had not been identified.

Ali Dhinojwala and colleagues investigated how orb-web spider aggregate glue sticks on a sapphire surface, to determine the adhesion mechanism under wet conditions. Using a spectroscopic method called sum frequency generation spectroscopy, they reveal that glycoproteins (proteins which consist of amino acids and sugar molecules) are the main component of spider aggregate glue, and can change their structure in wet conditions. By doing so, these proteins fold in a way that makes adhesion favourable in the presence of water. Additionally, small molecules, which are able to attract water, are also ubiquitous in spider aggregate glue. These compounds sequester free water that normally covers the substrate and glue interface and thus impede adhesion.

The authors suggest that understanding this mechanism could facilitate improved adhesion performance and reduce failure in wet environments.