Micromechanical properties of biological silica in skeletons of deep-sea sponges
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James C. Weaver Institute for Collaborative Biotechnologies and the Materials Research Laboratory, University of California, Santa Barbara, California 93106-5100
Murat Kazanci Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, D-14424 Potsdam, Germany
Yannicke Dauphin UMR 8148 IDES, Universite Paris XI-Orsay, 91405 Orsay cedex, France
Joanna Aizenberg Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974
Daniel E. Morse Institute for Collaborative Biotechnologies and the Materials Research Laboratory, University of California, Santa Barbara, California 93106-5100
Peter Fratzla) Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, D-14424 Potsdam, Germany (Received 15 December 2005; accepted 20 April 2006)
The silica skeleton of the deep-sea sponge Euplectella aspergillum was recently shown to be structured over at least six levels of hierarchy with a clear mechanical functionality. In particular, the skeleton is built of laminated spicules that consist of alternating layers of silica and organic material. In the present work, we investigated the micromechanical properties of the composite material in spicules of Euplectella aspergillum and the giant anchor spicule of Monorhaphis chuni. Organic layers were visualized by backscattered electron imaging in the environmental scanning electron microscope. Raman spectroscopic imaging showed that the organic layers are protein-rich and that there is an OH-enrichment in silica near the central organic filament of the spicule. Small-angle x-ray scattering revealed the presence of nanospheres with a diameter of only 2.8 nm as the basic units of silica. Nanoindentation showed a considerably reduced stiffness of the spicule silica compared to technical quartz glass with different degrees of hydration. Moreover, stiffness and hardness were shown to oscillate as a result of the laminate structure of the spicules. In summary, biogenic silica from deep-sea sponges has reduced stiffness but an architecture providing substantial toughening over that of technical glass, both by structuring at the nanometer and at the micrometer level.
I. INTRODUCTION
Much is known about the structure and properties of the skeleton of the sponge Euplectella aspergillum, but fairly little is known about the biology and ecology of
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0251 2068 J. Mater. Res., Vol. 21, No. 8, Aug 2006 http://journals.cambridge.org Downloaded: 12 Mar 2015
this species. It belongs to the phylum Porifera and is a member of the class Hexactinellida, which includes the predominantly deep-sea glass sponges. Hexactinellids occur in all oceans, especially around the Antarctic continent at depths of 100–1000 m, where they can be up to 90% of the benthic biomass. These unique sponges are among the earliest multicellular animals known from the fossil record, found in rock formations up to 540 million years old.1,2 Many of the hexactinellids host a wide range © 2006
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