Bioinspired lightweight cellular materials - Understanding effects of natural variation on mechanical properties Joseph Cadman a , Che-Cheng Chang a , Junning Chen a , Yuhang Chen b , Shiwei Zhou c , Wei Li a , Qing Li a, ⁎ a School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia b School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK c Center for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne 3001, Australia abstract article info Article history: Received 16 March 2012 Received in revised form 21 February 2013 Accepted 18 March 2013 Available online 27 March 2013 Keywords: Finite element-based homogenization Systematic and random variation Cuttlebone morphology Biomimetic materials Multi-cell domain Cuttlebone is a natural marine cellular material possessing the exceptional mechanical properties of high com- pressive strength, high porosity and high permeability. This combination of properties is exceedingly desirable in biomedical applications, such as bone tissue scaffolds. In light of recent studies, which converted raw cuttle- bone into hydroxyapatite tissue scaffolds, the impact of morphological variations in the microstructure of this natural cellular material on the effective mechanical properties is explored in this paper. Two extensions of the finite element-based homogenization method are employed to account for deviations from the assumption of periodicity. Firstly, a representative volume element (RVE) of cuttlebone is systematically varied to reflect the large range of microstructural configurations possibly among different cuttlefish species. The homogenization re- sults reveal the critical importance of pillar formation and aspect ratio (height/width of RVE) on the effective bulk and shear moduli of cuttlebone. Secondly, multi-cell analysis domains (or multiple RVE domains) permit the in- troduction of random variations across neighboring cells. Such random variations decrease the bulk modulus whilst displaying minimal impact on the shear modulus. Increasing the average size of random variations in- creases the effect on bulk modulus. Also, the results converge rapidly as the size of the analysis domain is in- creased, meaning that a relatively small multi-cell domain can provide a reasonable approximation of the effective properties for a given set of random variation parameters. These results have important implications for the proposed use of raw cuttlebone as an engineering material. They also highlight some potential for biomi- metic design capabilities for materials inspired by the cuttlebone microstructure, which may be applicable in bio- medical applications such as bone tissue scaffolds. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The development of advanced lightweight materials has been driving a full range of technological innovations, in which the search for new cel- lular structures signifies a key research area with extensive theoretical and practical value in engineering and biomedical applications. Mean- while, nature has evolved to its current form over millions of years to adapt to varying environmental challenges, resulting in natural materials or structures attaining a certain form of optimum. This has inspired a rel- atively new discipline of biomimetics that promotes understanding and learning from nature [1]. In material science and engineering, bioinspired architecture, e.g. honeycomb, bamboo and cork, has demonstrated its outstanding advantages and benefits over traditional trial-and-error ap- proaches. Indeed, biomimetic material design has enjoyed renewed pop- ularity recently with new explorations into the design and fabrication of micro/nano hierarchical materials inspired by nature [2–7]. As a specific example of natural marine materials, cuttlebone pre- sents a unique cellular architecture with a high ratio of compressive stiffness to weight, which represents a highly desirable mechanical feature in many engineering and biomedical applications [8]. Most important to the cuttlefish, it is also strong enough to withstand hy- drostatic pressures up to habitation depths (ranging from 100 to 500 m depending on the species) whilst possessing a very high po- rosity of around 90% in most cases [9]. Such extraordinary properties have driven research devoted to understanding how the microstruc- ture of cuttlebone contributes to its mechanical performance [9–12]. Recently, novel applications for cuttlebone have been proposed based on its microstructural and chemical characteristics. Interesting- ly, the use of cuttlebone to fabricate hydroxyapatite bone tissue scaf- folds [13–16] has inspired further investigation into the effective material properties of this natural cellular material. Ideally, tissue scaffolds aim to match the material properties of the native bone tis- sue [17–19], which suggests that the effective material properties of scaffolds are a significant consideration in their design. However, mi- croscopic measurements show that cuttlebone morphologies vary no- tably and it remains unclear how these structural variations affect the Materials Science and Engineering C 33 (2013) 3146–3152 ⁎ Corresponding author. Tel.: +61 2 9351 8607; fax: +61 2 9351 7060. E-mail address: Qing.Li@Sydney.edu.au (Q. Li). 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.03.031 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec