Axially aligned organic fibers and amorphous calcium phosphate form the claws of a terrestrial isopod (Crustacea).
Skeletal elements that are exposed to heavy mechanical loads may provide important insights into the evolutionary solutions to mechanical challenges. We analyzed the microscopic architecture of dactylus claws in the woodlice Porcellio scaber and correlated these observations with analyses of the claws' mineral composition with energy dispersive X-ray spectrometry (EDX), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED). Extraordinarily, amorphous calcium phosphate is the predominant mineral in the claw endocuticle. Unlike the strongly calcified exocuticle of the dactylus base, the claw exocuticle is devoid of mineral and is highly brominated. The architecture of the dactylus claw cuticle is drastically different from that of other parts of the exoskeleton. In contrast to the quasi-isotropic structure with chitin-protein fibers oriented in multiple directions, characteristic of the arthropod exoskeleton, the chitin-protein fibers and mineral components in the endocuticle of P. scaber claws are exclusively axially oriented. Taken together, these characteristics suggest that the claw cuticle is highly structurally anisotropic and fracture resistant and can be explained as adaptations to predominant axial loading of the thin, elongated claws. The nanoscale architecture of the isopod claw may inspire technological solutions in the design of durable machine elements subjected to heavy loading and wear.
Department of Biology, Biotechnical Faculty, University of Ljubljana, Večna pot 111, SI-1000 Ljubljana, Slovenia. Electronic address: milos.vittori@bf.uni-lj.si.
Miloš
M
Vittori
Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
Vesna
V
Srot
Department for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.
Kristina
K
Žagar
Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
Birgit
B
Bussmann
Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
Peter A
PA
van Aken
Department for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.
Miran
M
Čeh
Department of Biology, Biotechnical Faculty, University of Ljubljana, Večna pot 111, SI-1000 Ljubljana, Slovenia.
Jasna
J
Štrus
D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry*; D002686:Chitin / Q000737:chemistry*; D003445:Crustacea / Q000737:chemistry; D006724:Hoof and Claw / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman
D002130:Calcium Phosphates; D008903:Minerals; C519480:amorphous calcium phosphate; D002686:Chitin; D002119:Calcium Carbonate
Arthropod; Biomineralization; Composite; Cuticle; Halogen