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Merkel, Casjen; Deuschle, Julia; Griesshaber, Erika; Enders, Susan; Steinhauser, Erwin; Hochleitner, Rupert; Brand, Uwe; Schmahl, Wolfgang W. (2009): Mechanical properties of modern calcite- (Mergerlia truncata) and phosphate-shelled brachiopods (Discradisca stella and Lingula anatina) determined by nanoindentation. In: Journal of Structural Biology, Vol. 168, Nr. 3: S. 396-408
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Abstract

We measured distribution patterns of hardness and elastic modulus bynanoindentation on shells of the rhynchonelliform brachiopod Mergerliatruncata and the linguliform brachiopods Discradisca stella and Lingulaanatina. The rhynchonelliformea produce calcitic shells while thelinguliformea produce chitino-phosphatic shells. Dorsal and ventralvalves, commissure and hinge of the calcitic shell of M. truncata showdifferent nanohardness values (from 2.3 to 4.6 GPa) and E-modulus (from52 to 76 GPa). The hardness of the biocalcite is always increasedcompared to inorganic calcite. We attribute the effects to differentamounts of inter- and intracrystalline organic matrix. Profiles parallelto the radius of curvature of the valves cutting through the differentlayers of shell material surprisingly show quite uniform values ofnanohardness and modulus of elasticity. Nanoindentation tests on thechitinophosphatic brachiopods D. stella and L. anatina reflect thehierarchical structure composed of laminae with varying degree ofmineralization. As a result of the two-phase composite of biopolymernanofibrils reinforced with Ca-phosphate nanoparticles, nanohardness,