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First published online January 31, 2006
Journal of Experimental Biology 209, 722-730 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02065
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Local mechanical properties of the head articulation cuticle in the beetle Pachnoda marginata (Coleoptera, Scarabaeidae)

N. Barbakadze, S. Enders*, S. Gorb and E. Arzt

Evolutionary Biomaterials Group, Department Arzt, Max-Planck-Institute for Metals Research, Heisenbergstr. 3, 70569, Stuttgart, Germany


Figure 1
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  		Fig. 1. Diagram of the multilayered structure of the insect cuticle. The shaded areas represent the single cuticle layers: non-chitinous epicuticle; procuticle consisting of exocuticle and endocuticle with chitin fibers usually oriented parallel to the surface. An epidermal cell layer underlies the endocuticle.

 

Figure 2
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  		Fig. 2. Diagram of the location of the gula surface in the beetle body. Parasagittal (A) and frontal (B) virtual sections through the head-neck articulation. a, anterior direction; l, lateral direction; md, midline.

 

Figure 3
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  		Fig. 3. (A) Diagram of the nanoindenter system used (Enders, 2000Go). The force imposed on the indenter is generated through a coil that sits within a circular magnet. The displacement sensing system consists of a three-plate (circular disks) capacitor. (B) Berkovich tip: a pyramid with an equilateral triangle as the base area.

 

Figure 4
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  		Fig. 4. Schematic representation of a load-displacement curve with the key experimental parameters. Fmax, peak indentation load; hmax, indenter displacement at peak load; S, contact stiffness (after Oliver and Pharr, 1992Go).

 

Figure 5
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  		Fig. 5. Schematic representation of a section through an indentation, showing various quantities used in the analysis (Oliver and Pharr, 1992Go): F, indentation load; h, indenter displacement at peak load; hc, contact depth; hs, elastic deformation of the surface at the contact perimeter.

 

Figure 6
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  		Fig. 6. SEM images of the dry gula. (A,C,D) Surface of the gula. (B) Cross fracture of the gula cuticle showing the epicuticle (epi), exocuticle (exo) and endocuticle (endo). Fibres of the outer part of the exocuticle are oriented perpendicular to the surface but are parallel in the deeper layers of the exocuticle and in the endocuticle. Pores (pr), dried organic substances (se) and cracks (cr) can be seen on the cuticle surface. c, d, rectangles indicate parts of the sample magnified in C and D, respectively.

 

Figure 7
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  		Fig. 7. TEM micrographs of the gula. (A) Detail of the epicuticle (epi). (B) Cross section of the epi- and exocuticle. (C) Detail of the upper part of the exocuticle (exo). (D) Detail of the deeper part of the exocuticle. a, c, d, rectangles indicate parts of the sample magnified in A, B, and C, respectively; black arrows indicate direction towards surface; white arrow indicates the indentation depth. Abbreviations: pc, porous channels; sf, surface.

 

Figure 8
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  		Fig. 8. Desiccation curves of the entire head in comparison with the dissected gula cuticle. Mass is shown as % of the initial head mass of the sample versus time of drying. The initial mass of each head was 25-30 mg. The data points are mean values of three measurements.

 

Figure 9
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  		Fig. 9. Typical load-displacement curves for one sample in the fresh, dry and chemically treated conditions.

 

Figure 10
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  		Fig. 10. Hardness (A) and elastic modulus (B) values from indentation tests (CSM technique) plotted versus displacement for fresh, dry and chemically treated samples. Each data point corresponds to the mean value of approximately 150 measurements ± s.d.

 

Figure 11
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  		Fig. 11. AFM image of the cuticle surface after the indentation test. The image shows signs of the residual deformation and elastic recovery.

 




© The Company of Biologists Ltd 2006