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Session Schedule & Abstracts

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Sunday 3rd July, 2016

Symposium: Interdisciplinary and evolutionary approaches to vertebrate biological materials 3

Room: Salon B   2:30 pm–4:00 pm

Moderator(s): M. Dean, A. J. Crosby, D. Irschick, & L. Li
MAT3-1  2:30 pm  Co-evolution of teeth and food: Probing the interplay between tooth materials, tooth structures and foods. van Casteren A*, Max Planck Institute for Evolutionary Anthropology; Crofts S B, New Jersey Institute of Technology
Abstract: Teeth are agents of fracture: their job is to access and reduce food to an ingestible size and increase the surface area of food to promote more efficient digestion. This means that teeth are subjected to a great deal of potential damage, via contact with foods, with themselves, and other environmental pollutants. Enamel serves as the front line of defence against this damage, and is a highly mineralised biological composite, composed of relatively few ingredients: hydroxyapatite plates (96%), organic protein (1%) and water (3%). Through a structural hierarchy of organisation, enamel manages to be optimised for seemingly competing selective pressures. Its high mineral content endows the material with high hardness and stiffness whilst the remnant proteins and hierarchical structural arrangement provide the material with toughness protecting against fracture. Therefore due to its composite nature, enamel can display quite different mechanical behaviour, dependent on the scale of measurement. In addition to changes in material structure, the arrangement of this material into different tooth morphologies also serves to control the damages dealt by everyday use. General patterns of tooth specializations associated with different diets have been well documented across taxa, mammalian and otherwise, and the functional significance of different tooth shapes remains a topic of interest. Here we present recent methodological advances and results that are allowing researchers a more in depth understanding of the behaviour of enamel and teeth, not only as standalone entities but also, through defining the interaction between tooth and food, helping to understand how the pressures of diet may be shaping dental optimisations at many scales.

MAT3-2  3:00 pm  Structure and mechanics of natural scales: inspiration for novel flexible protective systems . Martini R, McGill University; Van Zyl D, McGill University; Barthelat F*, McGill University
Abstract: Many animals need tough protection against predators, collisions and other mechanical threats. Their skin must be hard to resist puncture and lacerations, yet sufficiently compliant and light for unimpeded movements. These conflicting requirements can be resolved by the segmentation of hard materials into scales of finite size, a common strategy in nature. Individual scales combine hardness and toughness, and are also several orders of magnitude stiffer than the underlying dermis and other soft tissues (muscles and other internal organs). This extreme contrast of stiffness leads to a rich set of deformation and failure modes: Ring cracks initiated by contact stresses or radial cracks initiated by flexural stresses. Interestingly, we found that when flexural failure prevails, segmented hard scales are more resistant to puncture than a continuous protective layer of the same material (in addition to being also more flexible). Our experiments on natural and synthetic scales also recently highlighted a third failure mode where the tablet suddenly tilts under the action of the indenter, leading to the rapid sliding of the indenter onto its surface. From these results we built a comprehensive failure map that captures the effects of material properties and scale size on the failure mode of individual scales. In addition, we used mechanistic models and 3D printed synthetic scaled skins to show how the interaction between neighboring scales also controls puncture and flexural performance. These interactions are governed by the size of the scales, their overlap, their attachment, friction and the properties of the backing membrane. Enriching the geometry of the scales can also generate interlocking mechanisms between adjacent scales, resulting in improved stability. We now use these results to guide the design and optimization of synthetic bio-inspired flexible protective systems for a variety of applications, from industrial gloves to touch screens.

MAT3-3  3:30 pm  Additive manufacturing of composites inspired by vertebrates. Studart A.R.*, ETH Zurich
Abstract: Composite materials made by vertebrates exhibit heterogeneous architectures that are tuned to fulfill the functional demands imposed by the surrounding environment. Examples range from the bilayer dentin-enamel structure of teeth to the complex, multiscale architecture of bone. Because they are often utilized to combine opposing properties such as strength and low-density or stiffness and wear resistance, the heterogeneous architecture of natural materials can potentially address several of the technical limitations of artificial homogeneous composites. However, current man-made manufacturing technologies do not allow for the level of composition and fiber orientation control found in natural heterogeneous systems. In this talk, I will show that additive manufacturing (AM) routes might offer a new exciting pathway for the fabrication of biologically-inspired composite materials with unprecedented heterogeneous architectures.

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