Academia.eduAcademia.edu

Outline

Title
Abstract
Figures
Introduction
Experimental Methods
Results and Discussion
Conclusions
References
All Topics
Engineering
Mechanics of Materials

Structure and mechanical properties of crab exoskeletons

Profile image of Marc MeyersMarc Meyers

2008, Acta Biomaterialia

https://doi.org/10.1016/J.ACTBIO.2007.12.010
visibility

…

description

10 pages

link

1 file

Abstract

The structure and mechanical properties of the exoskeleton (cuticle) of the sheep crab (Loxorhynchus grandis) were investigated. The crab exoskeleton is a natural composite consisting of highly mineralized chitin-protein fibers arranged in a twisted plywood or Bouligand pattern. There is a high density of pore canal tubules in the direction normal to the surface. These tubules have a dual function: to transport ions and nutrition and to stitch the structure together. Tensile tests in the longitudinal and normal to the surface directions were carried out on wet and dry specimens. Samples tested in the longitudinal direction showed a convex shape and no evidence of permanent deformation prior to failure, whereas samples tested in the normal orientation exhibited a concave shape. The results show that the composite is anisotropic in mechanical properties. Microindentation was performed to measure the hardness through the thickness. It was found that the exocuticle (outer layer) is two times harder than the endocuticle (inner layer). Fracture surfaces after testing were observed using scanning electron microscopy; the fracture mechanism is discussed.

Figures (14)
Fig. 1. (a) SEM micrograph of a cross-sectional fracture surface showing three different layers in the exoskeleton: epicuticle, exocuticle, and endocuticle. (b) Hierarchical structure of the exoskeleton of sheep crab, Loxorhynchus grandis. Chitin fibrils (~3 nm in diameter) wrapped with proteins form a fiber of ~60 nm in diameter. Fibers further assemble into bundles, which form horizontal planes (x—y plane) superposed in a helicoid stacking, creating a twisted plywood structure (180° rotation). In the z-direction there are ribbon-like tubules, 1 jum wide and 0.2 um thick, running through the pore canals.
Fig. 1. (a) SEM micrograph of a cross-sectional fracture surface showing three different layers in the exoskeleton: epicuticle, exocuticle, and endocuticle. (b) Hierarchical structure of the exoskeleton of sheep crab, Loxorhynchus grandis. Chitin fibrils (~3 nm in diameter) wrapped with proteins form a fiber of ~60 nm in diameter. Fibers further assemble into bundles, which form horizontal planes (x—y plane) superposed in a helicoid stacking, creating a twisted plywood structure (180° rotation). In the z-direction there are ribbon-like tubules, 1 jum wide and 0.2 um thick, running through the pore canals.
The properties are the average including their standard deviation: /, gage length; w, gage width; ¢, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Mechanical properties of crab exoskeletons from tensile testing in the longitudinal direction Table 1
The properties are the average including their standard deviation: /, gage length; w, gage width; ¢, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Mechanical properties of crab exoskeletons from tensile testing in the longitudinal direction Table 1
Fig. 2. Schematic representation of mechanical tests: (a) microindentation hardness test; (b) tensile test in the longitudinal direction; (c) tensile test in the z direction; (d) compressive test in the z-direction.
Fig. 2. Schematic representation of mechanical tests: (a) microindentation hardness test; (b) tensile test in the longitudinal direction; (c) tensile test in the z direction; (d) compressive test in the z-direction.
Mechanical properties of crab exoskeletons from tensile testing in the z-direction The properties are the average values including their standard deviation: d, diameter; t, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Table 2
Mechanical properties of crab exoskeletons from tensile testing in the z-direction The properties are the average values including their standard deviation: d, diameter; t, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Table 2
Mechanical properties of crab exoskeletons from compressive testing in z-direction The properties are the average values including their standard deviation: d, diameter; t, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Table 3
Mechanical properties of crab exoskeletons from compressive testing in z-direction The properties are the average values including their standard deviation: d, diameter; t, thickness; E, Young’s modulus. of, stress to fracture; and é, strain to fracture. Table 3
Fig. 3. (a) SEM micrograph showing the layered structure in endocuticle; (b) SEM micrograph showing the Bouligand structure, pore canals and pore canal tubules.
Fig. 3. (a) SEM micrograph showing the layered structure in endocuticle; (b) SEM micrograph showing the Bouligand structure, pore canals and pore canal tubules.
Fig. 5. Microindentation hardness showing a discontinuity through the thickness of crab claws and walking legs (data point: average; scale bar: standard deviation). The SEM micrograph above the plot documents the location where indentations were taken.
Fig. 5. Microindentation hardness showing a discontinuity through the thickness of crab claws and walking legs (data point: average; scale bar: standard deviation). The SEM micrograph above the plot documents the location where indentations were taken.
Fig. 4. SEM micrographs showing (a) ribbon-shaped pore canal tubules (arrows); (b) necked configuration of tubules in tensile traction (arrows); (c) tc view of the pore canal tubules showing (A) pore canals; (B) pore canal tubules; (C) chitin fibers.
Fig. 4. SEM micrographs showing (a) ribbon-shaped pore canal tubules (arrows); (b) necked configuration of tubules in tensile traction (arrows); (c) tc view of the pore canal tubules showing (A) pore canals; (B) pore canal tubules; (C) chitin fibers.
Fig. 6. Typical tensile stress-strain response of sheep crab exoskeleton in both dry and wet states in the y-direction. The results are compared with the mud crab exoskeleton by Hepburn et al. [18]. iLypical stress-strain curves in the dry and wet condi- tions are shown in Fig. 6. They exhibit a slightly convex shape stress-strain response which corresponds to elastic deformation. Table 1 summarizes the mechanical proper- ties of 34 tests taken from three different crabs. The wet samples have an average ultimate tensile strength of 31.5+5.4MPa at an average strain to fracture of 6.4 + 1.0%. The dry samples break at an average ultimate tensile strength of 12.9 + 1.7 MPa at an average strain to fracture of 1.8+0.3%. The stress-strain curves for wet samples are not perfectly linear. This may be due to sample alignment at the initial stage. The Young’s modulus was measured by taking the data points after 2% of strain and linear fitting. The average value of Young’s modulus for the wet samples was 518 +72 MPa, whereas it was 764 + 83 MPa for the dry samples. The work-of-fracture or toughness, as measured by the area under the stress— strain curve, is significantly affected by gradual fracture. The toughness for wet samples is 1.02 + 0.25 MPa, which is almost 10 times higher than that for dry samples, which is 0.11 + 0.03 MPa. Hepburn and co-workers [17] investi- gated the mechanical properties of mud crab, S. serrata, in tension. The stress-strain curves for both wet and dry mud crab samples are plotted in Fig. 6 along with the cur- rent results. There is a load drop in stress-strain curves at low strain. Hepburn et al. [17] concluded that this may due to the failure of inorganic minerals at low strain, followed
Fig. 6. Typical tensile stress-strain response of sheep crab exoskeleton in both dry and wet states in the y-direction. The results are compared with the mud crab exoskeleton by Hepburn et al. [18]. iLypical stress-strain curves in the dry and wet condi- tions are shown in Fig. 6. They exhibit a slightly convex shape stress-strain response which corresponds to elastic deformation. Table 1 summarizes the mechanical proper- ties of 34 tests taken from three different crabs. The wet samples have an average ultimate tensile strength of 31.5+5.4MPa at an average strain to fracture of 6.4 + 1.0%. The dry samples break at an average ultimate tensile strength of 12.9 + 1.7 MPa at an average strain to fracture of 1.8+0.3%. The stress-strain curves for wet samples are not perfectly linear. This may be due to sample alignment at the initial stage. The Young’s modulus was measured by taking the data points after 2% of strain and linear fitting. The average value of Young’s modulus for the wet samples was 518 +72 MPa, whereas it was 764 + 83 MPa for the dry samples. The work-of-fracture or toughness, as measured by the area under the stress— strain curve, is significantly affected by gradual fracture. The toughness for wet samples is 1.02 + 0.25 MPa, which is almost 10 times higher than that for dry samples, which is 0.11 + 0.03 MPa. Hepburn and co-workers [17] investi- gated the mechanical properties of mud crab, S. serrata, in tension. The stress-strain curves for both wet and dry mud crab samples are plotted in Fig. 6 along with the cur- rent results. There is a load drop in stress-strain curves at low strain. Hepburn et al. [17] concluded that this may due to the failure of inorganic minerals at low strain, followed
Fig. 7. Typical tensile response of sheep crab exoskeleton in the z- direction (dry condition).
Fig. 7. Typical tensile response of sheep crab exoskeleton in the z- direction (dry condition).
Fig. 8. Typical compressive stress-strain response of sheep crab exoskel- eton in the z-direction (dry and wet conditions).
Fig. 8. Typical compressive stress-strain response of sheep crab exoskel- eton in the z-direction (dry and wet conditions).
‘ig. 9. Fracture surfaces of the exoskeleton in (a) dry and (b) wet conditions; A indicates chitin/mineral bundle fracture and B shows bundle separatior Fig. 11 shows a schematic representation of the fracture processes. The breaking of chitin bundles when they are parallel to the loading direction (regions A in Fig. 9a) and their separation when they are parallel (regions B in Fig. 9a) are the main fracture modes. Intermediate orienta- tions in the Bouligand will fail by either normal bundle fracture or bundle separation. Fracture in the x—y tensile specimens will preferentially travel through the orifices which provide the stress concentration sites. This is shown in Fig. lla. For failure when loading is parallel to the z- direction (Fig. 11b), separation of the chitin bundles is fol- Fig. 9 shows the surface of a tensile specimen fractured in the longitudinal direction (dog-bone-shaped sample). The fracture surface of a dry sample is shown in Fig. 9a.
‘ig. 9. Fracture surfaces of the exoskeleton in (a) dry and (b) wet conditions; A indicates chitin/mineral bundle fracture and B shows bundle separatior Fig. 11 shows a schematic representation of the fracture processes. The breaking of chitin bundles when they are parallel to the loading direction (regions A in Fig. 9a) and their separation when they are parallel (regions B in Fig. 9a) are the main fracture modes. Intermediate orienta- tions in the Bouligand will fail by either normal bundle fracture or bundle separation. Fracture in the x—y tensile specimens will preferentially travel through the orifices which provide the stress concentration sites. This is shown in Fig. lla. For failure when loading is parallel to the z- direction (Fig. 11b), separation of the chitin bundles is fol- Fig. 9 shows the surface of a tensile specimen fractured in the longitudinal direction (dog-bone-shaped sample). The fracture surface of a dry sample is shown in Fig. 9a.
Fig. 11. Schematic drawings showing tensile failure in the (a) y-direction and (b) z-direction.
Fig. 11. Schematic drawings showing tensile failure in the (a) y-direction and (b) z-direction.
Fig. 10. Fracture surfaces of the exoskeleton after tensile test in the z-direction: (a) fracture between exocuticle and endocuticle; (b) fracture withi endocuticle; (c) schematic drawing showing the arc pattern on oblique surface.
Fig. 10. Fracture surfaces of the exoskeleton after tensile test in the z-direction: (a) fracture between exocuticle and endocuticle; (b) fracture withi endocuticle; (c) schematic drawing showing the arc pattern on oblique surface.

Related papers

The exoskeleton of the lobster< i> Homarus americanus</i> as an example of a smart anisotropic biological material
Dierk Raabe

Acta biomaterialia, 2007

Many biological materials are composed of fibrils arranged according to well-ordered three-dimensional patterns. These materials often show a strong anisotropy in their properties. An essential characteristic of biological structures is their hierarchical organization from the nanometer to the millimeter scale. Lobster cuticle is a good example of this and a suitable model for studying these properties. In this study the structure of untreated as well as chemically and physically treated cuticle from the exoskeleton of the American lobster (Homarus americanus) was investigated using scanning electron microscopy. Fresh samples have been chemically decalcified and deproteinated and thermally treated to evaluate their resistance to degradation. Results showed that their structure is more complex than the commonly assumed model for arthropod cuticles. Stacked chitin-protein planes create the characteristic twisted plywood pattern found in arthropod cuticles. However, due to a well-developed pore canal system these planes are not simple arrays of parallel chitin-protein fibers. In lobster cuticle, interconnected fibers bend around the continuous lenticellate cavities of the pore canals to form a planar honeycomb-like structure. The chemically and thermally treated samples showed that the organic matrix retains its shape and structure despite the attack of chemical compounds or heat. It was also possible to study the distribution of the biominerals after the removal of the organic matrix. The observed residual structure gives a good impression of how the minerals (mainly calcite) are distributed inside the polymeric network.

View PDFchevron_right
The composition of the exoskeleton of two crustacea: The American lobster Homarus americanus and the edible crab Cancer pagurus
Dierk Raabe

Thermochimica Acta, 2007

The exoskeletons of the American lobster Homarus americanus and of the edible crab Cancer pagurus were analysed with structural and chemical methods. The exoskeletons consist of crystalline magnesian calcite in the form of nanocrystals (domain size about 20 nm), amorphous calcium phosphate (ACP), and α-chitin. The composition varies among different parts of the skeleton and also between the two species. Differences are related to the mechanical requirements and biological escape behaviour of the animals. The finger and claw are strongly mineralized and very hard. The shell of the body (the carapace) is less mineralized and more elastic. The lobster, as a mobile, fast-swimming animal, typically escapes from a predator whereas the crab clings to the ground and burrows into the sand. Consequently, the shell of the lobster is less mineralized (and therefore lighter and less hard) than the shell of the crab.

View PDFchevron_right
Microstructure and crystallographic texture of the chitin–protein network in the biological composite material of the exoskeleton of the lobster Homarus americanus
Dierk Raabe

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline α-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the α-chitin–protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the α-chitin. According to these data, a large fraction of the α-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the α-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.

View PDFchevron_right
Correlation of structure, composition and local mechanical properties in the dorsal carapace of the edible crab Cancer pagurus
Dierk Raabe

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline ␣-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the ␣-chitin-protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the ␣-chitin. According to these data, a large fraction of the ␣-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the ␣-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.

View PDFchevron_right
Correlation of structure, composition and local mechanical properties in the dorsal carapace of the edible crab <i>Cancer pagurus</i>
Sabine HIld

Zeitschrift für Kristallographie, 2012

The exoskeleton of crustaceans is formed by the cuticle, a chitin-protein-based nano-composite with hierarchical organization over at least eight levels. On the molecular level, it consists of chitin associated with proteins forming fibres, which are organized in the form of twisted plywood. On the higher levels, the twisted plywood organization is modified and forms skeletal elements with elaborate functions. The load-bearing parts of crustacean cuticle are reinforced with both crystalline and amorphous biominerals. During evolution, all parts of the exoskeleton were optimized to fulfill different functions according to different ecophysiological strains faced by the animals. This is achieved by modifications in microstructure and chemical composition. In order to understand the relationship between structure, composition, mechanical properties and function we structurally characterized cuticle from the dorsal carapace of the edible crab Cancer pagurus using light and scanning electron microscopy (SEM). The local chemical composition was investigated using energy dispersive X-ray spectroscopy (EDX) and confocal m-Raman spectroscopy. Nanoindentation tests were performed to study the resulting local mechanical properties. The results show local differences in structure on several levels of the structural hierarchy in combination with a very heterogeneous mineralization. The distal exocuticle is mineralized with calcite, followed by a layer containing a magnesium, phosphate and carbonate rich phase and ACC in the proximal part. The endocuticle contains magnesian calcite and ACC in special regions below the exocuticle. Structure and mineral phase are reflected in the local stiffness and hardness of the respective cuticle regions. The heterogeneity of structural organization and mechanical properties suggests remarkable consequences for the mechanical behaviour of the bulk material.

View PDFchevron_right
Microtexture and Chitin/Calcite Orientation Relationship in the Mineralized Exoskeleton of the American Lobster
Dierk Raabe

Advanced Functional Materials, 2008

The exoskeleton of the American lobster Homarus americanus is a hierarchical nanocomposite consisting of chitin-protein fibers, reinforced with amorphous calcium carbonate (ACC) and a small amount of crystalline calcite. Crystallographic polefigure analysis reveals two texture components of the crystalline a-chitin in the exoskeleton. One component represents the wellknown twisted plywood structure of chitin-protein fibers within the cuticle plane, and the second component represents fibers oriented roughly perpendicular to the cuticle surface. These perpendicular fibers interpenetrate the open canals of the planar honeycomblike structure originating from the well-developed pore-canal system present in this material. The calcite crystallites reveal fiber texture with the crystallographic c-axis oriented perpendicular to the cuticle surface, suggesting an orientation relationship between calcite and the organic chitin-protein fibers. Local orientation analysis using X-ray microdiffraction reveals that the crystalline calcium carbonate fraction is associated with the chitin-protein fibers oriented perpendicular to the surface. Calcite is exclusively found in the exocuticle and is mostly restricted to a thin layer in the outermost region, while the major part of the exocuticle and the whole endocuticle contain ACC exclusively. It is therefore speculated that the most likely function of calcite in the exoskeleton of the American lobster is related to impact-and wear-resistance.

View PDFchevron_right
Influence of microstructure on deformation anisotropy of mineralized cuticle from the lobster Homarus americanus
Dierk Raabe

Journal of Structural Biology, 2008

The exoskeleton of the American lobster Homarus americanus is a hierarchically organized nano-composite material consisting of organic chitin–protein fibers associated with inorganic calcium carbonate. The presence of a well-developed and periodically arranged pore canal system leads to a honeycomb-like structure. The concomitant presence of the twisted plywood arrangement of the mineralized chitin–protein fibers alters the elastic properties, the deformation behavior, and fracture behavior compared to classical honeycomb structures. By performing compression tests in various directions of the cuticle we examined the anisotropic elastic–plastic deformation and fracture behavior of mineralized parts of the exoskeleton. By applying digital image correlation during compression testing, the evolution of the elastic–plastic deformation at the microscopic scale was observed with high resolution and simultaneously global stress and strain data were acquired. Shear tests were performed in order to determine the fracture energy for different shear planes and directions. The investigation of the microstructure after plastic deformation revealed the underlying deformation mechanisms of lobster endocuticle from the claws under different loading conditions. For evaluating the effect of hydration the samples were tested both in the dry and in the wet state.

View PDFchevron_right
Mechanical behavior of bio-inspired laminated composites
James Glancey

Composites Part A: Applied Science and Manufacturing, 2011

View PDFchevron_right
Exoskeleton anchoring to tendon cells and muscles in molting isopod crustaceans
Jasna Štrus

2012

Specialized mechanical connection between exoskeleton and underlying muscles in arthropods is a complex network of interconnected matrix constituents, junctions and associated cytoskeletal elements, which provides prominent mechanical attachment of the epidermis to the cuticle and transmits muscle tensions to the exoskeleton. This linkage involves anchoring of the complex extracellular matrix composing the cuticle to the apical membrane of tendon cells and linking of tendon cells to muscles basally. The ultrastructural arhitecture of these attachment complexes during molting is an important issue in relation to integument integrity maintenance in the course of cuticle replacement and in relation to movement ability. The aim of this work was to determine the ultrastructural organization of exoskeleton – muscles attachment complexes in the molting terrestrial isopod crustaceans, in the stage when integumental epithelium is covered by both, the newly forming cuticle and the old detache...

View PDFchevron_right
Preferred crystallographic texture of a-chitin as a microscopic and macroscopic design principle of the exoskeleton of the lobster Homarus americanus
Dierk Raabe

The crystallographic texture of the crystalline a-chitin matrix in the biological composite material forming the exoskeleton of the lobster Homarus americanus has been determined using synchrotron X-ray pole figure measurements and the calculation of orientation distribution functions. The study has two objectives. The first one is to elucidate crystallographic building principles via the preferred synthesis of certain orientations in crystalline organic tissue. The second one is to study whether a general global design principle exists for the exoskeleton which uses preferred textures relative to the local coordinate system throughout the lobster cuticle. The first point, hence, pursues the question of the extent to which and why a-chitin reveals preferred textures in the lobster cuticle. The second point addresses the question of why and whether such preferred textures (and the resulting anisotropy) exist everywhere in the exoskeleton. Concerning the first aspect, a strong preference of a fiber texture of the orthorhombic a-chitin is observed which is characterized by a h0 2 0i crystal axis normal to the exoskeleton surface for the chitin matrix. The second question is tackled by studying samples from different parts of the carapace. While the first aspect takes a microscopic perspective at the basic structure of the biological composite, the second point aims at building a bridge between an understanding of the microstructure and the macroscopic nature of a larger biological construction. We observe that the texture is everywhere in the carapace optimized in such a way that the same crystallographic axis of the chitin matrix is parallel to the normal to the local tangent plane of the carapace. Notable differences in the texture are observed between hard mineralized parts on the one hand and soft membranous parts on the other. The study shows that the complex hierarchical microstructure of the arthropod cuticle can be well described by surprisingly simple crystallographic textures.

View PDFchevron_right

References (38)

  1. Neville AC. Biology of the arthropod cuticle. New York: Springer- Verlag; 1975.
  2. Vincent JFV. Structural biomaterials. Princeton, NJ: Princeton University Press; 1991.
  3. Vincent JFV. Arthropod cuticle: a natural composite shell system. Composites A 2002;33:1311-5.
  4. Vincent JFV, Wegst UGK. Design and mechanical properties of insect cuticle. Arthropod Struct Dev 2004;33:187-99.
  5. Sanchez C, Arribart H, Giraud-Guille MM. Biomimetism and bioinspiration as tools for the design of innovative materials and systems. Nat Mat 2005;4:277-88.
  6. Raabe D, Sachs C, Romano P. The crustacean exoskeleton as an example of a structurally and mechanically graded biological nano- composite material. Acta Mater 2005;53:4281-92.
  7. Bouligand Y. Twisted fibrous arrangements in biological materials and cholesteric meso phases. Tissue Cell 1972;4:189-217.
  8. Giraud-Guille MM. Fine structure of the chitin-protein system in the crab cuticle. Tissue Cell 1984;16:75-92.
  9. Giraud-Guille MM. Chitin crystals in arthropod cuticles revealed by diffraction contrast transmission electron microscopy. J Struct Biol 1990;103:232-40.
  10. Weiner S, Addadi L. Design strategies in mineralized biological materials. J Mater Chem 1997;7:689-702.
  11. Roer R, Dillaman R. The structure and calcification of the crustacean cuticle. Am Zool 1984;24:893-909.
  12. Giraud-Guille MM. Plywood structure in nature. Curr Opin Solid State Mater Sci 1998;3:221-8.
  13. Lowenstam HA. Minerals formed in organisms. Science 1981;211:1126-31.
  14. Mann S, Webb J, Williams RJP. On biomineralization. New York: VCH; 1989.
  15. Lowenstam HA, Weiner S. On biomineralization. New York: Oxford University Press; 1989.
  16. Giraud-Guille MM, Bouligand Y. Crystal growth in a chitin matrix: the study of calcite development in the crab cuticle. In: Karnicki ZS, Brzeski PJ, Wojtasz-Pajak A, editors. Chitin World. Bremerhaven: Wirtschaftsverlag NW; 1994. p 136-144.
  17. Cameron JN. Post-molt calcification in the blue crab, Callinectes sapidus -timing and mechanism. J Exp Biol 1989;143:285-304.
  18. Hepburn HR, Joffe I, Green N, Nelson KJ. Mechanical properties of a crab shell. Comp Biochem Physiol 1975;50A:551-4.
  19. Joffe I, Hepburn HR, Nelson KJ, Green N. Mechanical properties of a crustacean exoskeleton. Comp Biochem Physiol 1975;50A:545-9.
  20. Melnick CA, Chen S, Mecholsky JJ. Hardness and toughness of exoskeleton material in the stone crab Menippe mercenaria. J Mater Res 1996;11:2903-7.
  21. Raabe D et al. Discovery of a honeycomb structure in the twisted plywood patterns of fibrous biological nanocomposite tissue. J Cryst Growth 2005;283:1-7.
  22. Raabe D et al. Structure and crystallographic texture of arthropod bio-composites. Mater Sci Forum 2005;495-497:1665-74.
  23. Raabe D et al. Microstructure and crystallographic texture of the chitin-protein network in the biological composite material of the exoskeleton of the lobster Homarus americanus. Mater Sci Eng A 2006;421:143-53.
  24. Sachs C, Fabritius H, Raabe D. Hardness and elastic properties of dehydrated cuticle from the lobster Homarus americanus obtained by nanoindentation. J Mater Res 2006;21:1987-95.
  25. Romano P, Fabritius H, Raabe D. The exoskeleton of the lobster Homarus americanus as an example of a smart anisotropic biological material. Acta Biomater 2007;3:301-9.
  26. Jensen GC. Pacific Coast Crabs and Shrimps. Monterey: Sea Challengers; 1995.
  27. Debelius H. Crustacea: Guide of the World. Frankfurt: IKAN- Unterwasserarchiv; 2001.
  28. Menig R, Meyers MH, Meyers MA, Vecchio KS. Quasi-static and dynamic mechanical response of Haliotis rufescens (abalone) shells. Acta Mater 2000;45:2389-98.
  29. Mayer G. Rigid biological systems as models for synthetic compos- ites. Science 2005;310:1144-7.
  30. Mayer G. New classes of tough composite materials -lessons from nature rigid biological systems. Mater Eng Sci C 2006;26:1261-8.
  31. Seki Y, Schneider MS, Meyers MA. Structure and mechanical properties of the toucan beak. Acta Mater 2005;53:5281-96.
  32. Seki Y, Kad B, Benson D, Meyers MA. The toucan beak: structure and mechanical response. Mater Sci Eng C 2006;26:1412-20.
  33. Altman GH et al. Silk-based biomaterials. Biomaterials 2003;24:401-16.
  34. Drach P. Mue et cycle d'intermue chez les crustace ´e ´decapods. Ann Inst Oceanogr 1939;19:103-391.
  35. Hegdahl T, Silness J, Gustavsen F. The structure and mineralization of the carapace of the crab (Cancer pagurus L) -1. The endocuticle. Zool Scr 1977;6:89-99.
  36. Roer RD. Mechanisms of resorption and deposition of calcium in the carapace of the crab Carcinus maenas. J Exp Biol 1980;88:205-18.
  37. Currey JD, Nash A, Bonfield W. Calcified cuticle in the stomatopod smashing limb. J Mater Sci 1982;17:1939-44.
  38. Hayes DK, Armstrong WD. The distribution of mineral material in the calcified carapace and claw shell of the American lobster, Homarus americanus, evaluated by means of microroentgenograms. Bio Bull 1961;121:307-15.

Related papers

INVESTIGATION OF MECHANICAL PROPERTIES OF CRAB SHELL: A REVIEW
Dr. K. K . Gadgey

І. INTRODUCTION Crab Shell is the second most common natural composite material in the world, and one of the most versatile. Very few mechanical studies have been made on the hard shells (solid cuticle) characteristic of the arthropod integument and it is therefore not yet possible to provide a general model for the mechanical behavior of the exoskeletons of this phylum. Arthropods are the largest animal phylum. They include the trilobites, chelicerates, myriapods, hexapods, and crustaceans. All arthropods are covered by an exoskeleton, which is periodically shed as the animal grows. The exoskeleton of arthropods consists mainly of chitin. In the case of crustaceans, there is a high degree of mineralization, typically calcium carbonate, which gives mechanical rigidity. The various studies carried out on insect solid cuticle[1-4] and prawn shells [5] indicate a number of similarities in the mechanical behaviour of insect and prawn solid cuticle as well as differences apparently due to the fact that the former are two-phase composite materials consisting of chitin fibres in a protein matrix while the latter include another phase, namely inorganic alts, resulting in a three-phase material. In the present review, the mechanical behavior of the solid cuticle of the crab, Scylla serrata, was investigated in order to determine their fracture behavior, micro-hardness properties and general mechanical behavior as composite materials. This crustacean Abstract-The present review describes the development of investigations of mechanical properties of crab shell. The mechanical behavior of crab shell was investigated. There was low strain discontinuity in their bulk tensile stress-strain curves. The crab cuticle fails in an entirely brittle manner. The cutile of the crab is a composite material, the properties of which are closely analogous to those of pre-stressed concrete. The mechanical properties of the exoskeleton of the sheep crab (Loxorhynchus grandis) were investigated earlier. It was found that the crab exoskeleton is a natural composite consisting of highly mineralized chitin–protein fibers arranged in a twisted plywood pattern. It was observed that there is a high density of pore canal tubules in the direction normal to the surface. Tensile tests were carried out on wet and dry specimens in longitudinal as well as normal directions. Samples tested in the longitudinal direction showed a convex shape and no evidence of permanent deformation prior to failure, whereas samples tested in the normal orientation exhibited a concave shape. The results show that the composite is anisotropic in mechanical properties. Micro indentation was performed to measure the hardness through the thickness. It was found that the outer layer is two times harder than the inner layer.

View PDFchevron_right
Influence of Structural Principles on the Mechanics of a Biological Fiber-Based Composite Material with Hierarchical Organization: The Exoskeleton of the Lobster Homarus americanus
Dierk Raabe

The cuticle of the lobster Homarus americanus is a nanocomposite, such as most structural biological materials. It consists of a matrix of chitin-protein fibers associated with various amounts of crystalline and amorphous calcium carbonate in the rigid parts of the body, and is organized hierarchically at all length scales. One prominent design principle found in the hierarchical structure of such biological fibrous composite materials is the twisted plywood structure. In the lobster cuticle, it is formed by superimposing and gradually rotating planes of parallel aligned chitin-protein fibers. To adjust the mechanical properties to the requirements on the macroscopic level, the spatial arrangement and the grade of mineralization of the fibers can be modified. A second design principle of lobster cuticle is its honeycomb-like structure, generated by the well-developed pore canal system, whose twisted ribbon-shaped canals penetrate the cuticle perpendicular to its surface. Due to the hierarchical structure, the mechanical properties of the lobster cuticle have to be investigated at different length scales, which is essential for the understanding of the structure–mechanical function relations of mineralized tissues (e.g., potentially also bone and teeth). In order to investigate the influence of the structural principles on the mechanical properties on the macroscopic scale miniaturized tensile, compression, and shear tests were carried out to obtain integral mechanical data. Characterization of the microstructure included scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) measurements.

View PDFchevron_right
The crustacean exoskeleton as an example of a structurally and mechanically graded biological nanocomposite material
Dierk Raabe

Acta Materialia, 2005

This is an experimental study on the mechanical and structural gradients through the cuticle of Homarus americanus (American lobster). The exocuticle (outer layer) is characterized by a very fine woven structure of the fibrous chitin-protein matrix (Ôtwisted plywoodÕ structure) and by a high stiffness (8.5-9.5 GPa). The hardness increases within the exocuticle between the surface region (130 MPa) and the region close to the interface to the endocuticle (270 MPa). In the endocuticle, which is characterized by a much coarser twisted plywood structure, both the stiffness (3-4.5 GPa) and hardness (30-55 MPa) are much smaller than in the exocuticle. The transition in mechanical properties and structure between the exocuticle and endocuticle is abrupt. The differences underline the important role of the internal structure of the twisted plywood structure and of the interface between the two cuticle layers for the overall mechanical behavior of the exoskeleton. The excellent mechanical stability of the interface (irrespective of the change in the mechanical properties) is attributed to the fact that the structural change of the twisted plywood pattern across the interface consists only of a change of the stacking density of the chitin-protein layers. The observed gradients in stiffness and hardness through the cuticle thickness are interpreted in terms of honeycomb mechanics of the twisted plywood structure. The possible role of gradients in protein cross-linking and in the mineral content is also discussed.

View PDFchevron_right
The exoskeleton of the lobster Homarus americanus as an example of a smart anisotropic biological material
Dierk Raabe

Many biological materials are composed of fibrils arranged according to well-ordered three-dimensional patterns. These materials often show a strong anisotropy in their properties. An essential characteristic of biological structures is their hierarchical organization from the nanometer to the millimeter scale. Lobster cuticle is a good example of this and a suitable model for studying these properties. In this study the structure of untreated as well as chemically and physically treated cuticle from the exoskeleton of the American lobster (Homarus americanus) was investigated using scanning electron microscopy. Fresh samples have been chemically decalcified and deproteinated and thermally treated to evaluate their resistance to degradation. Results showed that their structure is more complex than the commonly assumed model for arthropod cuticles. Stacked chitin-protein planes create the characteristic twisted plywood pattern found in arthropod cuticles. However, due to a well-developed pore canal system these planes are not simple arrays of parallel chitin-protein fibers. In lobster cuticle, interconnected fibers bend around the continuous lenticellate cavities of the pore canals to form a planar honeycomb-like structure. The chemically and thermally treated samples showed that the organic matrix retains its shape and structure despite the attack of chemical compounds or heat. It was also possible to study the distribution of the biominerals after the removal of the organic matrix. The observed residual structure gives a good impression of how the minerals (mainly calcite) are distributed inside the polymeric network.

View PDFchevron_right
Structure of Hard And Soft Carapace Exoskeleton Biomaterial Through SEM-EDXRS at Various Stages of Development Scylla paramamosain Mud Crab
Haryo triajie

International Journal of Biology and Biomedical Engineering

Crustacean carapace has various functions which can be seen from the composition of the biomaterial in it. Various concentrations of inorganic biomaterial elements were investigated from the hard carapace and the newly molted (soft-shelled) (Scylla paramamosain) with SEM-EDXRS (scanning electron microscopy-Energy Dispersive X-ray Spectrometer) technique. This study traced the composition of the inorganic elements of the premolt, postmolt, intermolt and soft (exuvium) crab hard carapace tissue of mangrove crabs from the point of view. Various stages of development. Important elements such as C, O2, Mg, P, Ca, S, Na, Si, Cl, and others, are reabsorbed from the carapace into the body tissues to fulfill further needs in soft-shelled crabs and are reused to some extent during formation new carapace. This study provides evidence that, inorganic elements in freshly molted soft carapace crabs are less common than hard carapace crabs

View PDFchevron_right

Related topics

  • Fracture Mechanic

    • Cited by

    Host-Specific Phenotypic Plasticity of the Turtle Barnacle Chelonibia testudinaria: A Widespread Generalist Rather than a Specialist
    T. Bello, Chi Cheang

    PLoS ONE, 2013

    Turtle barnacles are common epibionts on marine organisms. Chelonibia testudinaria is specific on marine turtles whereas C. patula is a host generalist, but rarely found on turtles. It has been questioned why C. patula, being abundant on a variety of live substrata, is almost absent from turtles. We evaluated the genetic (mitochondrial COI, 16S and 12S rRNA, and amplified fragment length polymorphism (AFLP)) and morphological differentiation of C. testudinaia and C. patula from different hosts, to determine the mode of adaptation exhibited by Chelonibia species on different hosts. The two taxa demonstrate clear differences in shell morphology and length of 4-6 th cirri, but very similar in arthropodal characters. Moreover, we detected no genetic differentiation in mitochondrial DNA and AFLP analyses. Outlier detection infers insignificant selection across loci investigated. Based on combined morphological and molecular evidence, we proposed that C. testudinaria and C. patula are conspecific, and the two morphs with contrasting shell morphologies and cirral length found on different host are predominantly shaped by developmental plasticity in response to environmental setting on different hosts. Chelonibia testudinaria is, thus, a successful general epibiotic fouler and the phenotypic responses postulated can increase the fitness of the animals when they attach on hosts with contrasting life-styles.

    View PDFchevron_right
    Structural Biological Materials: Critical Mechanics-Materials Connections
    Marc Meyers

    Science, 2013

    View PDFchevron_right
    Nanomaterials for electrochemical energy storage
    Mauro Pasta

    Frontiers of Physics, 2014

    The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials with desirable electronic, ionic, photonic, and mechanical properties. This development has also contributed to the advance in energy storage, which is a critical technology in this century. In this article, we will review how the rational design of nanostructured materials has addressed the challenges of batteries and electrochemical capacitors and led to high-performance electrochemical energy storage devices. Four specific material systems will be discussed: i) nanostructured alloy anodes for Li-batteries, ii) nanostructured sulfur cathodes for Li-batteries, iii) nanoporous openframework battery electrodes, and iv) nanostructured electrodes for electrochemical capacitors.

    View PDFchevron_right
    Measuring strain in the exoskeleton of spiders—virtues and caveats
    Friedrich Barth

    Journal of Comparative Physiology A

    The measurement of cuticular strain during locomotion using foil strain gauges provides information both on the loads of the exoskeleton bears and the adaptive value of the specific location of natural strain detectors (slit sense organs). Here, we critically review available literature. In tethered animals, by applying loads to the metatarsus tip, strain and mechanical sensitivity (S = strain/load) induced at various sites in the tibia were determined. The loci of the lyriform organs close to the tibia–metatarsus joint did not stand out by high strain. The strains induced at various sites during free locomotion can be interpreted based on S and, beyond the joint region, on beam theory. Spiders avoided laterad loading of the tibia–metatarsus joint during slow locomotion. Balancing body weight, joint flexors caused compressive strain at the posterior and dorsal tibia. While climbing upside down strain measurements indicate strong flexor activity. In future studies, a precise calculat...

    View PDFchevron_right
    Insect Chitin-Based Nanomaterials for Innovative Cosmetics and Cosmeceuticals
    Elena Tafi

    Cosmetics

    Chitin and its derivatives are attracting great interest in cosmetic and cosmeceutical fields, thanks to their antioxidant and antimicrobial properties, as well as their biocompatibility and biodegradability. The classical source of chitin, crustacean waste, is no longer sustainable and fungi, a possible alternative, have not been exploited at an industrial scale yet. On the contrary, the breeding of bioconverting insects, especially of the Diptera Hermetia illucens, is becoming increasingly popular worldwide. Therefore, their exoskeletons, consisting of chitin as a major component, represent a waste stream of facilities that could be exploited for many applications. Insect chitin, indeed, suggests its application in the same fields as the crustacean biopolymer, because of its comparable commercial characteristics. This review reports several cosmetic and cosmeceutical applications based on chitin and its derivatives. In this context, chitin nanofibers and nanofibrils, produced from...

    View PDFchevron_right
    580 California St., Suite 400
    San Francisco, CA, 94104
    © 2025 Academia. All rights reserved