Special Issue of Journal of Bionic Engineering for Euromat 2005 (5−8 September, 2005), the Mechanical Testing and Characterisation of Natural Materials session.
Many people gathered to hear 14 talks on a range of topics covering the area of the mechanical testing of natural materials. In fact the Euromat conference had a distinct flavour of natural materials, with other parallel sessions cov-ering similar topics. Euromat is the biennial meeting of the Federation of European Materials Societies with its 23 member societies and is a premier pan-European event covering the complete range of Materials Science and Tech-nology. Over 50 sessions featured at the 2005 meeting, with a variety of topics covering a wide range of materials science. A large number of industrial representatives and publishing houses were also present at a trade exhibition, around which a vast number of posters also reporting materials science research were presented. The conference was also blessed by its location in Prague in the Czech Republic. This city offered delegates a rich cultural experience, not least the large number of beverages on offer!
In the natural materials session however it was encouraging to see over 100 people attending, and all contributing to this exciting area of research. Professor Julian Vincent (Bath, UK) opened the session on natural materials with an overview of work that he has been involved with since the 1970’s, when relatively fewer people were engaged in this area of research. We then went on to hear from a number of speakers on subjects such as the mechanics of bread dough, crisps and lobster cuticle. A session on hard materials, such as bone and shells, also featured as well as a highlight lecture by Professor Tim Wess (Cardiff) on the use of synchrotron X-ray diffraction for studying form and function in collagen and other bio-based fibres. The Max-Planck institutes of Germany also sent many delegates, and a couple of their researchers featured in the programme. A particular highlight from the Max-Planck institutes work included the use of FIB (Focussed Ion Beam) technology for preparing small tensile specimens from biological materials. It was also noted that a large number of doctoral research students from a wide range of European universities also attended the event and presented their work. This is encouraging, in that this area of science is fostering a new generation of researchers willing to study natural-based systems.
From this session I have had the pleasure of editing four contributions to Journal of Bionic Engineering. These contributions are from Peter Zioupos (Cranfield), Paul Mummery (Manchester), Steve Eichhorn (Manchester) and Tim Wess (Cardiff). All have been extensively reviewed, and we hope that the readers of Journal of Bionic Engineering find them useful and they indeed inspire them to join us at the next Euromat meeting in Nuremberg (10−13 September, 2007). If you want any more details on this meeting see the website at http://www.euromat2007.fems.org/.

The mechanical behaviour of trabecular bone is dependent on both the properties of individual trabeculae as well as their three-dimensional arrangement in space. In this study, nanoindentation was used to determine trabecular stiffness of bovine bone, both dehydrated and rehydrated. Values of 18.3 GPa and 14.3 GPa were obtained for dehydrated and rehydrated trabeculae re-spectively. These values were then used for finite element analysis where the mesh was generated directly from an X-ray mi-crotomography dataset. The relationship between intrinsic tissue properties and apparent stiffness was explored. Moreover, the important role of collagen in bone micromechanics was demonstrated by complementing the study with Raman spectroscopy.

Synchrotron microfocus small angle X-ray scattering was used to investigate the nanostructure and microscopic variation of eggshells. It uses a microbeam allowing the ability to probe interactions between the organic and inorganic components at nanometer level and is ideal for mapping over small areas to obtain a detailed analysis of structural variations. Thin sections of eggshells were scanned from the shell membrane (inner) to the cuticle (outer) surface. The data collected was used to produce two-dimensional maps showing microscopic changes within the different layers of the eggshell. The structural alterations ap-parently could have implications at the macroscopic level of the resulting eggshell. As the organic matrix is embedded within the eggshell this may contribute to the variations observed in calcite crystal form and texture. Structural information obtained about a biomaterial at different length scales is important in relating the structure to its functional properties. This knowledge and the principles behind the formation of biomaterials could be used in the attempt of bioengineering new systems.

Bone like tissues are biocomposites comprising an organic matrix (mostly collagen) and a reinforcement phase in the form of mineral crystals (poorly stoichiometric apatite). The composite properties are a result of the material characteristics of the two phases, their interaction, the relative composition, the orientation and the micro-architecture of the structure. The inherent spatial heterogeneity of these tissues (a result of evolutionary and functional requirements) and their exposure to various environmental and mechanical influences result in highly variable properties on the microscale, which can only be characterised by modern microanalytical methods. We present here results obtained by the complementary use of the modern nanoindentation and mi-cro-X-ray diffraction techniques, which were used to probe the properties and structure of human dentine and enamel of primary molar teeth. The results show that both the addition and the higher organization of mineral within the organic matrix produce stiffer and harder tissue and that the examination of properties within small tissue volumes can be reliably achieved by use of these two methods in parallel. This opens new avenues in the study of biomaterial in general, and for the local characterisation of regions of teeth that suffered bacterial attack, mechanical wear, fluoridisation, chemical bleaching, or dental treatment such as laser ablation or drilling.

This study reports the variation of residual strains within the posterior ventral area of the Ensis siliqua mollusc shell, as determined using glancing incidence synchrotron X-ray diffraction. The outer layer of this structure exhibits a tensile strain, in contrast to a compressive strain observed within the inner layer. Fluctuations in unit cell parameters for the inner layer have been determined, showing that the microscopic prismatic layer of the structure exhibits a compressive strain orientated parallel to the surface of the shell. This is thought to enhance the crack deflection properties of this layer, and aid in resisting catastrophic failure. Further analysis of residual strains has been performed using the same method, throughout several stages of compressive testing of the anterior dorsal region of the shell. This identified no variation in residual strains at various levels of loading, and it is therefore proposed that load may be transferred via the organic matrix of mollusc shell structures. A Raman spectroscopic in-vestigation, comparing whole and powdered shell with non-biogenic aragonite, has shown that residual strains are also present in this analagous material which is devoid of organic content. This indicates that the observed strain is not entirely due to the or-ganic matrix.

Publication rate of patents can be a useful measure of innovation and productivity in fields of science and technology. To assess the growth in industrially-important research, I conducted an appraisal of patents published between 1985 and 2005 on online databases using keywords chosen to select technologies arising as a result of biological inspiration.
Whilst the total number of patents increased over the period examined, those with biomimetic content had increased faster as a proportion of total patent publications. Logistic regression analysis reveals that we may be a little over half way through an initial innovation cycle inspired by biological systems.

Most multicellular organisms can be categorised by two words: hierarchy and composite. The underlying fractal geometry of nature – at least in terms of provision of infrastructure – provides much of the hierarchy, although many materials for which infrastructure is not an integral factor are also strongly hierarchical. Plants can therefore be modelled using recursive computer programs which add structures as the size increases. However, problems with mechanical stability also increase as the structure grows, so the plant changes from deriving stiffness from internal pressure to cross-linking the cell wall components permanently. However, this compromises the ability of the plant to grow and repair itself.