Viana AS and Santos R (2018), Nanoscale characterization of the temporary adh...

ECB-ART-46583

Beilstein J Nanotechnol 2018 Jan 01;9:2277-2286. doi: 10.3762/bjnano.9.212.

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Nanoscale characterization of the temporary adhesive of the sea urchin Paracentrotus lividus.

Viana AS , Santos R .

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Background: Unlike the thin homogeneous films that are typical for adhesives produced by humans, biological adhesives present complex hierarchical micro- and nanostructures. Most studies on marine adhesives have focused on permanent adhesives, whereas the nanostructures of nonpermanent, temporary or reversible adhesives have only been examined in some organisms such as marine flatworms, barnacle cyprids, freshwater cnidaria and echinoderms such as sea cucumbers and sea stars. In this study, the first nanoscale characterization of sea urchin temporary adhesives was performed using atomic force microscopy (AFM). Results: The adhesive topography was similar under dry and native (seawater) conditions, which was comprised of a honeycomb-like meshwork of aggregated globular nanostructures. In terms of adhesion forces, higher values were obtained in dry conditions, reaching up to 50 nN. Under native conditions, lower adhesive forces were obtained (up to 500 pN) but the adhesive seemed to behave like a functional amyloid, as evidenced by the recorded characteristic sawtooth force-extension curves and positive thioflavin-T labelling. Conclusion: Our results confirm that like other temporary adhesives, the sea urchin adhesive footprint nanostructure consists of a meshwork of entangled globular nanostructures. Under native conditions, the adhesive footprints of the sea urchin behaved like a functional amyloid, suggesting that among its proteinaceous constituents there are most likely proteins with amyloid quaternary structures or rich in β-sheets. These results extend our knowledge on sea urchin adhesive composition and mechanical properties essential for the engineering of biomimetic adhesives.

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Genes referenced: LOC100887844 LOC100893907

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	Figure 1. a) Collection of Paracentrotus lividus footprints on mica. b) Detailed view of a sea urchin tube foot attached to mica, showing the adhesive disc (D) and the stem (S). c) Optical microscopy (10×) illustrating the positioning of the moist adhesive footprint (indicated by the arrow) beneath the triangular-shaped AFM cantilever.
	Figure 2. Peak force tapping AFM (PFT-AFM) image (a) and height profile (b) of Paracentrotus lividus moist footprints at the edge of the adhesive material. Image obtained with a ScanAsyst-Air probe.
	Figure 3. Peak force tapping AFM (PFT-AFM) images of moist adhesive material deposited by the tube feet of Paracentrotus lividus on mica. a) Height image observed in air. b) Higher resolution of the same area showing the honeycomb appearance of the meshwork. c) Detailed topography view showing that the meshwork is composed of aggregated globular nanostructures. d) Detailed topography view of a different area showing bigger globular structures denoted by white arrows. Images were obtained with a ScanAsyst-Air probe.
	Figure 4. Peak force tapping AFM (PFT-AFM) 3D height images and profiles of small-sized areas of the moist adhesive material deposited by the tube feet of Paracentrotus lividus on mica. a) Height image and c) profile of the threads of aggregated globular nanostructures in a thinner peripheral area of the adhesive material. b) Height image and d) profile of the larger, globular structures in a thicker central area of the adhesive material. Images were obtained with a ScanAsyst-Air probe.
	Figure 5. Peak force tapping AFM (PFT-AFM) with quantitative nanomechanical (QNM) software for analysis of height (a, c) and adhesion (b, d) of the adhesive material deposited by the tube feet of Paracentrotus lividus on mica obtained in air (a, b) and artificial seawater (c, d). a) Height and b) adhesion images of dry adhesive material observed in ambient air with a ScanAsyst-Air probe. c) Height and d) adhesion images of wet adhesive material observed in artificial seawater with a ScanAsyst-Fluid probe. Arrows indicate the location of some of the larger globular nanostructures assigned as being most likely adhesive secretory granules.
	Figure 6. Force–distance retracting curves of the adhesive material deposited by the tube feet of Paracentrotus lividus on mica. The adhesive material was observed either dry (a), moist (b) or under native (c) conditions. The data was obtained either with a ScanAsyst-Air probe (a, b) or a silicon nitride probe (SNL, Bruker) (c). Different coloured lines represent three independent trials.
	Figure 7. a) Histological staining of the adhesive material deposited by the tube feet of Paracentrotus lividus on glass with thioflavin-T and b) illustration of different adhesive footprints.

References [+] :

Demeuldre, Instantaneous adhesion of Cuvierian tubules in the sea cucumber Holothuria forskali. 2014, Pubmed, Echinobase