Meeting Abstract
The terrestrial slug Arion subfuscus produces a defensive secretion from its dorsal surface that rapidly sets into a tough, adhesive hydrogel. The gel can sustain stresses of over 100 kPa, and can extend to more than ten times its initial length. Thus, it requires far more energy to fracture than a typical hydrogel. The glue gains this toughness through a double network mechanism. In the proposed model, a network of cross-linked proteins makes the glue stiff, and an interpenetrating network of large polysaccharides causes it to deform extensively before failure. This model suggests that there will be a large number of “sacrificial bonds” within the protein network that provide stiffness, but rupture and thus dissipate energy as the glue deforms. Cyclic stress-strain measurements of the glue demonstrate that the glue behaves like an elastic, cross-linked network, but as it extends, bonds are continuously ruptured, leading to a dramatic reduction of modulus in subsequent trials. The primary structure of all the proteins in the glue was determined using high-throughput Illumina sequencing of the transcriptome followed by tandem mass spectrometry to identify specific proteins. Most of the proteins that form the cross-linked network consist of conserved calcium binding domains that typically mediate intermolecular cross-links. Biochemical evidence confirms that the proteins have a high capacity to bind to calcium. These data are consistent with a calcium-cross-linked protein network providing stiffness and energy dissipation.
