77.2 Sunday, Jan. 6 Metals, molluscan glues and gel mechanics SMITH, A. M.; Ithaca College firstname.lastname@example.org
Molluscan adhesive gels possess many useful properties, most notably their remarkable combination of strength and deformability, as well as their ability to adhere to wet, irregular surfaces. Recent work has found that the glue of the terrestrial slug Arion subfuscus contains substantial amounts of iron, manganese, zinc and some copper. Furthermore, the presence of transition metals was critical for the glue to set. This study addresses the relative roles of the different metals. Do they all function similarly, with similar effectiveness? Are they incorporated into the glue in a similar way? We used atomic absorption spectroscopy to characterize the metal content of several different gastropod glues. We also tested the effect of these metals on the mechanics of several commercial gels. The metal content of the glue from the terrestrial snail Helix aspersa and the terrestrial slugs A. subfuscus and Ariolimax columbianus was markedly similar. When hydrated, all three had over 40 mM calcium and 0.07-0.08 mM iron. A. subfuscus also had 0.9 mM zinc while A. columbianus had 0.5 mM manganese. For comparison, sodium and chloride concentrations were roughly 10 mM. Soaking A. subfuscus glue in EDTA caused all the metal concentrations to drop to 1-5% of their original value, except iron, which was not significantly different (t-test, P = 0.18). All the metals stiffened agar and pectin gels. Notably, despite its poor solubility iron was 20-40x as effective as calcium. Zinc was roughly 10x as effective as calcium. These results suggest that iron is more effective in controlling the gel mechanics than other metals, and it is more tightly incorporated into the glue. The other metals are present in higher concentrations, so they would still contribute substantially, but likely in different ways.