Exploring Biological Surfaces by Nanoindentation
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With the help of instrumented indentation, the mechanical behavior of a variety of biological systems was studied: the waxy zone of the pitcher plant (Nephenthes alata) adapted for attachment prevention, the head-to-thorax articulation system of a beetle (Pachnoda marginata) as an example of friction minimization, and the wing arresting system of the dung beetle (Geotrupes stercorarius) adapted for mechanical interlocking. We demonstrate that nanoindentation can successfully be applied to compliant and highly structured biological composite materials. Measuring the mechanical performance of these surfaces can provide important information for understanding the overall functioning of these systems. Tests on fresh and dried samples show the influence of desiccation on the results and point out the importance of native conditions during the measurements. However, these preliminary results also point to current limits of the test method and the need for adapting it and current theories to meet the specific requirements of biological materials.
I. INTRODUCTION
One goal of today’s materials science is to find solutions for a variety of mechanical problems from the macro- down to the nanoscale by optimizing both the surface and the microstructure of the materials used. Nature has been using this approach for millions of years; well adapted and flexible mechanisms have evolved which fulfill specific mechanical functions such as high flexibility, toughness, and wear resistance as well as specific adhesion or frictional properties.1,2 Studies of the structure and mechanics in biological systems combining the biologist’s and the materials scientist’s point-of-view may improve the understanding of natural solutions and advance the design of novel artificial materials. Because of the complexity in design and function, it is necessary to combine measurements of the local mechanical properties with high-resolution investigations of structure and surface, such as electron and atomic force microscopy. As a local mechanical probe, the nanoindentation technique is widely applied for studies of the mechanics of metals,3–6 polymers,7–9 and ceramics.10,11 In the last few years, it has also become a very useful tool for biomedical investigations of the relationship between the ultrastructure and the mechanical properties of stiff biological materials such as bone12–14 and dentin.15–17 The aim of this paper is to show the possibilities of instrumented indentation in the studies of the mechanical behavior of highly compliant and structured biological composite materials (Fig. 1). We studied surfaces adapted for attachment prevention, friction minimization, and mechanical interlocking. Wax-covered plant surfaces 880
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 3, Mar 2004 Downloaded: 16 Dec 2014
evolved to prevent the attachment of insects. The head joint of beetles contains surfaces specialized for minimizing friction and wear in the joint and for saving muscular energy during movements. Wing-to-body locking devices of b
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