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First published online June 16, 2005
Journal of Experimental Biology 208, 2555-2567 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01683

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Adhesion of echinoderm tube feet to rough surfaces

Romana Santos^1,*, Stanislav Gorb², Valérie Jamar¹ and Patrick Flammang¹

¹ Académie Universitaire Wallonie-Bruxelles, Université de Mons-Hainaut, Laboratoire de Biologie Marine, 6 Avenue du Champ de Mars, B-7000 Mons, Belgium
² Max-Planck Institute for Metal Research, Department Arzt, Evolutionary Biomaterials Group, 3 Heisenbergstraße, D-70569 Stuttgart, Germany

View larger version (11K): [in a new window]   Fig. 1. Diagrammatic representations of the two models proposed for tube foot adhesion to rough surfaces. (A) The tube foot disc remains flat and the adhesive substances are secreted to fill the gaps between surface irregularities or (B) the disc deforms to match the substratum profile and the adhesive is released as an evenly thin film.

View larger version (12K): [in a new window]   Fig. 2. Micro-force tester used for measurements of the mechanical properties of the tube foot discs. The disc (D) of a cut-off tube foot was mechanically clamped to the platform (P). Driven by a motor, this platform moves the disc towards or away from a smooth glass plate (GP) attached to a glass spring (S). The deflection of the glass spring is monitored by the fibre-optic sensor (FOS) using the monochromatic light sent to and reflected from the mirror (M). The data obtained were transmitted to a computer with a sampling frequency of 25 Hz.

View larger version (42K): [in a new window]   Fig. 3. Typical force-time (A) and force-displacement (B) curves for the disc obtained with the micro-force tester. During the loading process (L), the platform was moved upwards and the disc brought into contact with the glass plate, thus increasing the compression force. Then, the disc and the glass plate were kept in contact for a certain time (resting time, R), during which a rapid decrease in the interacting force (relaxation) is observed. Finally, the platform was moved downwards, unloading the disc (U).

View larger version (19K): [in a new window]   Fig. 4. Force-dependent deformation of the disc. (A) Force-displacement curves during the loading process for the tube foot disc and for a hard sample. (B) Deformation-force curve for the tube foot disc; the solid line represents data linearly fitted with Statistica® software.

View larger version (17K): [in a new window]   Fig. 5. (A) Typical force-time curve, obtained for the evaluation of the viscous component of the mechanical response of the disc. The curve includes three distinct parts: loading (L), the resting period (R) and unloading (U). Generally, it took 5-7 s to reach a compression force of 1 mN (L) and then the disc was kept in contact with the glass plate for 10 s (R). During the resting period, the force decreased, indicating relaxation of the tissue. (B) Force-time curve of the resting period (R) fitted with a standard linear solid viscoelastic model comprising two elastic moduli (E0 and E1), representing two springs connected in parallel, and one time constant (), representing a dashpot serially connected to one of the springs (inset).

View larger version (17K): [in a new window]   Fig. 6. External morphology of non-attached tube feet of Paracentrotus lividus (A,C) and Asterias rubens (B,D). Abbreviations: C, cilia; CA, central area; CG, circular groove; D, disc; LC, long cilia; P, pore; PA, peripheral area; S, stem; SC, short cilia. Boxed areas in A and B are magnified in C and D.

View larger version (197K): [in a new window]   Fig. 7. Longitudinal sections through the discs of the tube feet of Paracentrotus lividus (A,C) and Asterias rubens (B,D; the section goes through the margin of the disc to show the connective tissue radial lamellae). Abbreviations: AE, adhesive epidermis; CL, connective tissue radial lamellae; CS, connective tissue septa; CT, connective tissue layer; Di, diaphragm; DP, distal pad; L, lumen; Sk, skeleton; TP, terminal plate.

View larger version (145K): [in a new window]   Fig. 8. 3-D images of the surface of the different substrata at low (5x, left column) and high (50x, right column) magnification. (A,B) Smooth polymethyl-methacrylate (PMMA); (C,D) rough PMMA; (E,F) smooth polypropylene (PP); (G,H) rough PP.

View larger version (81K): [in a new window]   Fig. 9. SEM images of the surface of smooth PMMA (A), rough PMMA (D) and rough PP (G) samples and of the distal surfaces of discs attached to each of these substrata (B,C; E,F and H,I; respectively). (B,E,H) Paracentrotus lividus; (C,F,I) Asterias rubens.

View larger version (175K): [in a new window]   Fig. 10. Mean tenacity (A) and corrected tenacity (B) (± S.D., N=30) of the tube feet of the sea urchin Paracentrotus lividus (black bars) and the sea star Asterias rubens (grey bars), using a separation speed of 15 mm min-1. Significant intraspecific differences between means for each type of substrata are indicated by letters in superscripts; means sharing the same letter are not significantly different (P 0.05, t-test).