title: Function-related adaptations of ultrastructure, mineral phase distribution and mechanical properties in the incisive cuticle of mandibles of Porcellio scaber Latreille, 1804.
abstract: In terrestrial isopods the mandibles consist of a corpus carrying strong muscle tissue, and a pars incisiva (PI) that cuts dry leaves into smaller ingestible pieces. We studied the cuticle of the PI of Porcellio scaber in order to understand region-dependent differences in its ultrastructure, composition, and the resulting mechanical properties, employing several microscopic and analytical techniques as well as nanoindentation experiments. The cuticle of the incisive tip is not mineralized and consists of an unusually thick epicuticle containing thin fibrils, two subjacent cuticular layers, and a central core containing fibrils of different orientation, either longitudinal or circumferential. A thick epicuticle of the middle region just behind the tip projects long epicuticular extensions into the subjacent endocuticle, likely to prevent delamination. A distinct exocuticular layer is lacking in the middle region. Most chitin-protein fibrils within the endocuticle are oriented in parallel pointing towards the tip. Surprisingly, the middle region is mineralized by amorphous calcium phosphate (ACP) only. Near the base, ACP is successively replaced by amorphous calcium carbonate and calcite is restricted to a distal layer in the base. At the transition between middle and base, the epicuticle forms a hybrid material containing fibrils of the exocuticle. Nanoindentation experiments reveal an increase of the stiffness and hardness from the tip towards the base and significantly higher values on transversal in comparison to longitudinal planes. The results suggest that ultrastructure and composition are adapted for conveying high forces from a rather thin cutting edge to the stable base of the PI.
authors.affiliation: Central Facility for Electron Microscopy, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Huber
authors.affiliation: Department Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany.
authors.forename: Helge-Otto
authors.initials: HO
authors.lastname: Fabritius
authors.affiliation: Department of Earth and Environmental Sciences, LMU, Theresienstr. 41, 80333 München, Germany.
authors.forename: Erika
authors.initials: E
authors.lastname: Griesshaber
authors.affiliation: Central Facility for Electron Microscopy, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany. Electronic address: andreas.ziegler@uni-ulm.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Ziegler
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry; D002686:Chitin / Q000737:chemistry*; D005109:Extracellular Matrix / Q000737:chemistry / Q000648:ultrastructure*; D033321:Isopoda / Q000737:chemistry / Q000648:ultrastructure; D008334:Mandible / Q000737:chemistry / Q000648:ultrastructure*; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry; D013059:Spectrum Analysis, Raman
chemical_list: D008903:Minerals; D002686:Chitin; D002119:Calcium Carbonate
keywords: Amorphous calcium carbonate; Amorphous calcium phosphate; Calcite; Electron backscatter diffraction; Isopoda; Mandible; Pars incisiva