Lessons for New Classes of Inorganic/Organic Composites from the Spicules and Skeleton of the Sea Sponge Euplectella asp
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Lessons for New Classes of Inorganic/Organic Composites from the Spicules and Skeleton of the Sea Sponge Euplectella aspergillum G. Mayer1*, R. Trejo2, E. Lara-Curzio2, M. Rodriguez1, K. Tran1, H. Song1, and W. H. Ma1 1
Dept. of Mat. Sci. & Eng., University of Washington, Seattle, WA 98195-2120 High Temperature Materials Laboratory, ORNL, Oak Ridge, TN 37831-6062 * Author for correspondence: [email protected]
ABSTRACT Studies have been carried out on the structures and mechanical characteristics of an unusual family of sea sponges under the classification of Hexactinellida, genus Euplectella. The sponge spicules have been of interest to materials scientists because of their potentially important optical, coupled with mechanical, properties. The structures of the class Hexactinellida are characterized by a concentric ring appearance in the cross-section, which is a composite of hydrated silica, coupled with silicatein as a thin layer at the ring interfaces. The mechanical behavior and the toughness of the spicules have been examined with the aid of a special fiber testing method, coupled with scanning electrom microscopy (SEM) observations. It appears that there may be common mechanisms underlying toughness in rigid natural composites with high ratios of mineral/organic phase. In addition, novel pressurization tests of a portion of the sponge skeleton have provided information about the resilience of the skeleton, which resembles a selfsupporting glass winding of a cylindrical composite structure. INTRODUCTION In recent years, the design of new classes of hybrid ceramic/organic composite materials has been strongly influenced by biomimetic considerations. For example, shell structures composed of >95 v/o ceramic phase, with a minor component surrounding the ceramic components, have shown very high levels of toughness when compared with monolithic ceramics of the same material. In a similar vein, sponge spicules, comprising a predominantly glass phase (hydrated silica) and thin layers of a silicon protein (silicatein) have demonstrated much higher toughness than monolithic silica [1,2]. By way of sponge classification, in general, sponges with rigid skeletons that live in warmer waters are primarily mineralized from calcium (calcareous), and those sponges with rigid skeletons that inhabit cold, or deeper, waters are mineralized from silicon. This observation also conveys to the thin organic layers that exist in shells and spicules, as they are calcium-based proteins, or silicon-based proteins. Figure 1 shows a classification system for sponges (figure developed from data in Bergquist, [3]), and indicates the genus of the sponge of interest in this study, Euplectella aspergillum (also known as the Venus Flower Basket), which falls under the class Hexactinellida.
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Porifera Hexactinellida Amphidiscophora
Calcarea
Demospongiae
Sclerospongiae
Hexaterophora Lyssacina Euplectella Lophocalyx
Rosella
Dictyonina
Figure 1. Sponge classification (derived from Bergquist [3]). Much has been written i
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