Meeting Abstract
The terrestrial slug Arion subfuscus produces a sticky defensive secretion that is a dilute gel. It is unlike most commercial gels, which are either stiff and brittle, like gelatin, or easily deformable like most mucus secretions. A. subfuscus glue combines a relatively high stiffness with high extensibility, so that it requires much more energy to fracture. We tested the hypothesis that this toughness was due to a double network mechanism. In a typical double network, a loose, deformable network of polymers interpenetrates a stiff, highly cross-linked network. These two separate networks combine to give toughness that is several orders of magnitude greater than either network individually. To test this hypothesis, we characterized the structure of the glue to see if there were two separate networks. Then we tested the impact of disrupting each network separately. Our results confirm the existence of two networks. There are large, highly sulfated polysaccharides that appear to be cross-linked transiently by calcium. In addition, native gel electrophoresis and co-purification assays demonstrated that most of the proteins form a cross-linked network that is distinct from the carbohydrate network. Targeted disruption of each network separately, using disulfide bond breakage, calcium removal, imine bond disruption or enzymatic hydrolysis completely disrupted the glue. Thus, neither network on its own is sufficient to maintain the integrity of the glue. Although they are not tightly connected to each other, they both must work together as predicted by the double network mechanism.
