**5. Acknowledgments**

256 Biomaterials – Physics and Chemistry

Some reports suggest that proteins may play an important role in the adhesion of Cuvierian tubules from *H. forskåli* (DeMoor et al., 2003; Flammang & Jangoux, 2004; Müller et al., 1972). For example, the adhesive residue left when tubules are peeled from a surface consists mainly of protein (DeMoor et al., 2003), and the treatment of tubules with proteases causes loss of adhesion (Müller et al., 1972). However, it has been reported that the proteins most likely differ between species (Flamman & Jangoux, 2004), making further comparative

The effect of urea on tubule-glass adhesion showed that bond strength decreased progressively with increasing urea concentration until it was completely lost at 2 M urea (Figure 7). However, if tubules that had been incubated for about 60 sec in 2 M urea were then rinsed for about 60 sec in simulated sea water, some adhesion was restored, although the extent was rather variable. Urea disrupts hydrogen bonding, and its effect on adhesion may reflect some partially reversible protein unfolding (Zahn et al., 1972). The rapidity and partial reversibility of the effect indicates that there is not a complete urea-mediated release

Fig. 7. The effect of different washing solutions on the adhesiveness of *H. dofleinii* Cuvierian tubules for glass. (C) The effect of urea concentration, where ▲ indicates conditions where

The distinct features of the Cuvierian tubule adhesion mechanism, especially its rapid action under water, are unique. If the mechanism can be understood, then it may be possible to design a synthetic system with analogous properties. An adhesive that provided instant grip in an aqueous environment would be very valuable, especially in medical applications, as

It appears that although the tubules of *H.dofleinii* are distinct from those of other species, especially in their size and the number expelled, the adhesive properties of these Cuvierian tubules (including preferences for hydrophilic surfaces, pH optima, etc.) are similar to those found in other species, even if mechanistic details may differ between species as has been proposed previously (Flammang and Jangoux, 2004). It is thought that during expulsion and tubule elongation, granular cells that are internal in the pre-release tubule become located

biochemical surveys important for elucidating the mechanism.

of proteins from the tubule surface.

the force per unit width exceeded 0.05 N/mm.

the majority of existing adhesives bind well only to dry surfaces.

**4. Conclusion**

We wish to thank Nicole Murphy for assistance with Holothurian collection and Dr Anita Hill for helpful discussions. This study was facilitated by access to the Australian Proteome Analysis Facility supported under the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS). The project received support from the CSIRO Wealth from Oceans National Research Flagship.
