Materials Day 2011 – Biological and Bioinspired Materials

Invited Speakers

• Prof. Dr. Peter Fratzl
  Max Planck Institute of Colloids and Interfaces, Potsdam
  
• Prof. Dr. Friedrich G. Barth
  University of Vienna, Vienna
  
• Prof. Dr. Andrew Parker
  Natural History Museum, London
  
• Prof. Dr. Christine Ortiz
  Massachusetts Institute of Technology, Cambridge
  
• Prof. Dr. Robert O. Ritchie
  University of California, Berkeley
  
• Prof. Dr. Ludwik Leibler
  ESPCI, Paris
  
• Prof. Dr. Scott R. White
  University of Illinois, Urbana-Champaign
• Prof. Dr. Lennart Bergström
  Stockholm University, Stockholm
  
• Prof. Dr. André R. Studart
  ETH Zürich, Zürich

Plant movements and biomimetic actuators

Peter Fratzl

Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Potsdam
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The secondary plant cell wall is a composite of cellulose nano-fibrils and a water-swelling matrix containing hemicelluloses and lignin. Recent experiments showed that this swelling capacity helps generating growth stresses, e.g., in conifer branches or in the stem when subjected to loads. A similar mechanism also provides motility to wheat seeds. A simple mechanical model for the cell wall predicts that – depending on the detailed architecture of the cellulose fibrils – swelling may lead either to significant compressive or tensile stresses or to large movements at low stresses. The model reproduces most of the experimental observations in the wood cells and in the awns of wheat seeds. The general principle is based on the modification of the isotropic swelling of a gel by embedded oriented fibres, or on a non-symmetric distribution of swelling elements in an elastic body. More generally, actuation systems in plants provide guidelines for designing material architectures suitable to convert isotropic swelling into complex movements.

Clever Materials for Clever Sensors: Spider Mechanoreceptors

Prof. Friedrich G. Barth

Department of Neurobiology, Center for Organismal Systems Biology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria
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The importance of sensory information for the guidance of animal behavior is reflected by a fascinating wealth of sensory organs. These exhibit an enormous variety due to different evolutionary potentials and needs of individual species. All sensory organs and their neuronal pathways have to be tuned to the reception and perception of the biologically relevant stimulus patterns as they occur in the habitats of different species. It is the invertebrate animals in particular, where one finds the most exotic sense organs and sensory capacities, some of them alien to us humans.

The variation among sense organs serving the detection and analysis of stimuli of the same type of energy is not so much due to differences at the level of the sensory cells but to differences in the functional properties of the non-nervous structures responsible for the uptake and transformation of the stimulus on its way to the sensory cell. Here we have an impressive evolutionary playground and inventiveness for biologically applied physics. It is in particular here where engineers can hope for bio-inspiration and cleverly simple and unconventional solutions of technically demanding problems [1].

The lecture will illustrate this aspect using two examples of spider mechanoreceptors [2], [3] and also stress that no sense organ can be adequately understood without reference to its biological significance in normal behavior under biologically relevant conditions.

(i) The first example will address the structural design of mechanosensory hairs, the most common of all biological sensors. It will contrast a tactile hair [4] and an airflow sensor [5],[6], showing how one can be converted into the other by changing a few physical parameters only. Obviously, the properties of the materials involved and their adjustment to the particular measurement task are of prime importance. Whereas in a tactile hair sufficient mechanical sensitivity has to be combined with mechanical robustness, the outstandingly high sensitivity asks for particular attention in case of the flow sensors.

(ii) The second example are the slit sensilla, a type of sensor which in a way is the opposite of a hair [1,2], which can be classified as a movement detector. Slit sensilla are strain detectors embedded in the cuticular exoskeleton and responding to the slightest deformation due to loads caused by muscular activity, gravity, substrate vibrations etc. Among the several thousand slit sensilla monitoring strain in a spider exoskeleton the vibration detector will receive particular attention. Again, material properties are highly relevant in determining functional properties. A small cuticular pad in front of the organ has turned out to be the main cause of the organ´s high pass characteristic. Due to its viscoelastic properties energy loss of stimulus transmission at high frequencies is much reduced as compared to low frequency stimulation. The result is a biologically highly relevant selectivity of the organ for frequencies higher than about 30 Hz [3], [7].

References

1. Barth FG, Humphrey JAC, Srinivasan MV (eds), Frontiers in Sensing: From Biology to Engineering. Springer Verlag, Wien,New York
2. F.G. Barth, A Spider’s World. Senses and Behavior, Springer Verlag, Berlin-Heidelberg-New York, 394p, (2002)
3. P. Fratzl, F.G. Barth, Biomaterial systems for mechanosensing and actuation. Nature, 462, 26, 442-448, (2009)
4. H.-E. Dechant, F.G. Rammerstorfer, F.G. Barth, Arthropod touch reception: stimulus transformation and finite element model of spider tactile hairs. J Comp Physiol A, 187, 313 – 323 (s. also Erratum p. 851), (2001)
5. J.A.C. Humphrey, F.G. Barth, Medium flow-sensing hairs: biomechanics and models, in: J.Casas, S.J. Simpson (eds.) Advances in Insect Physiology. Insect Mechanics and Control, 34, 1-80, Elsevier Ltd., (2008)
6. M.E. McConney, C.F. Schaber, M.D. Julian, W.C. Eberhardt, J.A.C. Humphrey, F.G. Barth, W. Tsukruk, Surface force spectroscopic point load measurements and viscoelastic modelling of the micromechanical properties of air flow sensitive hairs of a spider ( Cupiennius salei), J. R. Soc. Interface, 6, 681-694, (2009)
7. M.E. McConney, C.F. Schaber, M.D. Julian, F.G. Barth, W. Tsukruk, Viscoelastic nanoscale properties of cuticle contribute to high-pass properties of spider vibration receptor (Cupiennius salei Keys.), J. R. Soc. Interface 4, 1135-1143, (2007)

Original research supported by grants of the Austrian Science Fund (FWF) and DARPA project BioSenSE to FGB

Optical biomimetics

Andrew Parker

Department of Zoology, The Natural History Museum, London, and Green Templeton College, Oxford University
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There exists a diversity of optical devices at the nano-scale (or at least the sub-micron scale) in nature1. These include 1D multilayer reflectors, 2D diffraction gratings and 3D liquid crystals. In 2001 the first photonic crystal was identified as such in animals, and since then the scientific effort in this subject has accelerated. Now we know of a variety of 2D2 and 3D3 photonic crystals in nature, including some designs not encountered previously in physics.

Some optical biomimetic successes have resulted from the use of conventional (and constantly advancing) engineering methods to make direct analogues of the reflectors and anti-reflectors found in nature4, 5. However, recent collaborations between biologists, physicists, engineers, chemists and material scientists have ventured beyond merely mimicking in the laboratory what happens in nature, leading to a thriving new area of research involving biomimetics via cell culture. Here, the nano-engineering efficiency of living cells is harnessed, and nanostructures such as diatom “shells” can be made for commercial applications via culturing the cells themselves.

Additionally, optical devices in nature can be combined with those possessing other functions, such as water management structures. These include the water- collecting structures of beetles and plants in the fog-laden Namibian desert6, and the Australian “thorny devil” lizards that can suck water from damp soil.

References

1. Parker, A.R. 515 Million years of structural colour. J. Opt. A 2, R15-28 (2000).
2. Parker, A.R., McPhedran, R.C., McKenzie, D.R., Botten, L.C. and Nicorovici, N.-
   A.P. Aphrodite’s iridescence. Nature 409, 36-37 (2001).
3. Parker, A.R.,Welch, V.L., Driver, D & Martini, N. An opal analogue discovered in
   a weevil. Nature 426: 786-787 (2003).
4. Parker, A.R., Hegedus, Z. and Watts, R.A. Solar-absorber type antireflector
   on the eye of an Eocene fly (45Ma) Proc. R. Soc. Lond. B 265, 811-815
   (1998).
5. Parker, A.R. & Townley, H. E. 2007. Biomimetics of photonic nanostructures.
   Nature Nanotechnology 2, 347-353.
6. Parker, A.R. and Lawrence, C.R. Water capture from desert fogs by a Namibian
   beetle. Nature (2001) 414, 33-34.

Natural Armor: Interdisciplinary Convergence Among Engineering, Architecture and Evolutionary Biology

Christine Ortiz

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Biological exoskeletons or "natural armor" systems are multilayered, hierarchical structures that serve many functions, in particular protective mechanical roles such as: penetration, wear, and scratch resistance, minimization of back deflection and potential blunt trauma, damage detection and sensing, self-repair and regeneration, and, in certain cases, flexibility and mobility.

We can learn much from biological organisms that have evolved over millions of years a veritable encyclopedia of environmentally-friendly engineering designs for protection against specific predatory and environmental threats. Natural armor functions efficiently by elegantly balancing protection, tissue damage tolerance, weight, and mobility requirements to maximize survivability. In order to elucidate the design principles of these fascinating materials, nanomechanics methodologies have been employed including: the measurement and prediction of extremely small forces and displacements, the quantification of nanoscale spatially-varying mechanical properties, the identification of local constitutive laws, the formulation of molecular-level structure-property relationships, and the investigation of new mechanical phenomena existing at small length scales. Additionally, the quantification and understanding of how animal exoskeletons utilize morphometry or shape to achieve maximum survivability from predatory and environmental threats will be discussed. Exoskeletons are imaged in three-dimensions using X-ray microcomputed tomography and then these data are used to fabricate, experimentally test and simulate the mechanical behavior of macroscopic 3D printed bio-inspired prototypes of exoskeletal assemblies in order to elucidate morphometric design principles, the interplay between morphometry and materiality, and to create new bio-inspired hybrid flexible protective designs.

This talk will focus on a number of classes of natural armor: flexible, transparent, those that exhibit resistance to biochemical toxins, kinetic attacks, extreme thermal fluctuations, and blast. Model systems to be discussed include "living fossils" such as armored fish, deep sea hydrothermal vent species, echinoderms and molluscs with articulating segmented armor (e.g. chitons, urchins), and the transparent exoskeletons of certain crustaceans.

Human Bone as a Structural Material: Origins of its Fracture Resistance and Biological Degradation

Robert O. Ritchie

Materials Sciences Division, Lawrence Berkeley National Laboratory, and Department of Materials Science and Engineering, University of California, Berkeley
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The hierarchical structure of human cortical bone evolves over multiple length-scales from its basic constituents of collagen and hydroxyapatite at the nanoscale to osteonal structures at near-millimeter dimensions, all of which provide the basis for its mechanical properties. To resist fracture, bone’s toughness is derived intrinsically through plasticity (e.g., fibrillar sliding) at structural-scales typically below a micron and extrinsically (i.e., during crack growth) through mechanisms (e.g., crack deflection/bridging) generated at larger structural-scales. Biological factors such as aging lead to a markedly increased fracture risk, which is often associated to a loss in bone mass (bone quantity). However, biologically-related structural changes can significantly degrade bone quality, again occurring at varying multiple length-scales. Using FTIR/UV-Raman spectroscopy and in situ small-/wide-angle x-ray scattering/diffraction to characterize phenomena at molecular to sub-micron scales and synchrotron x-ray computed tomography and in situ fracture-toughness measurements in the SEM to characterize effects at micron- to macro-scales, the mechanisms responsible for the diminished fracture resistance of human bone due to factors such as aging, irradiation and disease are examined.

Self-healing materials from hydrogen bonding and mesoscopic organization

Ludwik Leibler

Laboratoire Matière Molle et Chimie, Ecole Supérieure de Physique et Chimie Industrielles, Paris
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Imagine an elastic solid that does not stick to itself. Yet, when broken or cut, it can be simply repaired by bringing together fractured surfaces to self-heal without need to apply heat or other stimuli. It recovers its initial properties. Such a material can be made by controlling supramolecular interactions, organization and dynamics and I will discuss design principles, underlying chemistry and physics as well as remaining challenges.

Emerging Areas in Self-Healing Materials

Scott R. White

Beckman Institute for Advanced Science and Technology
University of Illinois at Urbana-Champaign
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Self-healing materials have emerged over the past decade as a major new research area in materials science and engineering. They promise more robust behavior, longer lifetime, increase safety, lower maintenance costs, and many other unique attributes attractive to industries from transportation to medicine to infrastructure. Since their inception in 2001, self-healing research has primarily focused on restoration of mechanical integrity in microcapsule-based systems, or in polymers with intrinsic self-healing functionality. A review of the state-of-art in self-healing materials will be presented along with translation of these same concepts to new functionalities. In particular, the use of microcapsules in Li-ion batteries for improved safety and longevity will be presented. Finally, the integration of vascular networks in structural composites will be described and initial results demonstrating unprecedented functionality from thermal management to self-healing to electromagnetic modulation.

Biomimetic synthesis and assembly of nanoparticle and nanocellulose hybrids

Lennart Bergström and German Salazar-Alvarez

Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Sweden and Wallenberg Wood Science Center, Royal Institute of Technology, Sweden
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The ability to control structure and functionality at all length scale has developed tremendously in the last decades. While traditional solid state chemistry has perfected the design of materials at the atomic scale where the chemical composition and the atomic structure are of fundamental importance for the properties and functionality of the desired material, it is clear that optimal design of nanostructured materials require integration of various approaches to synthesize, functionalize, characterize and process the nanosized species for various applications. Examples will be given how bio-inspired synthesis and assembly can offer a high degree of versatility, simplicity and flexibility in the production of bulk materials and coatings and allows the introduction of specific functions.

We will demonstrate how self-assembly of surfactant-capped inorganic particles can result into ordered arrays with both translational and orientational order, and elaborate on the requirements for successful deposition of textured nanostructured oxide films on substrates. The possibility to assemble iron oxide nanocrystals into superlattices with a pronounced long-range order will be demonstrated and related to the magnitude, range, direction and duration of the intrinsic and induced interparticle forces [1, 2]. Recent attempts on how lipid-coated mesoporous silica particles can be designed for controlled uptake of ions through the incorporation of membrane proteins will also be presented [3].

Our recent work on the fabrication of multifunctional materials based on nanocellulose and different classes of nanoparticles will also be demonstrated. The impact of different approaches used for the fabrication of the hybrids on the magnetic, mechanical, and optical properties will be elucidated. Hybrids composed of bacterial nanocellulose and CoFe2O4 nanoparticles can be prepared both as a stiff magnetic nanopaper or a flexible magnetic aerogel by adjusting the freeze-drying conditions [4]. Hybrids based on nanocellulose crystals and amorphous calcium carbonate results in a stiff and brittle nanopaper, where the system can be tailored to mimic synthetic nacre-like structures [5].

Selected references

1. Sabrina Disch et al, Nano Letters, (2011), 11 (4), 1651-1656.
2. Ahniyaz, A., Sakamoto, Y. & Bergström, L. Proc. Natl. Acad. Sci., 104, 17570-17574 (2007).
3. Gustav Nordlund, Jovice Boon Sing Ng, Lennart Bergström, and Peter Brzezinski, ACS Nano, 3, 2639-2646 (2009)
4. R. T. Olsson, M. A. S. Azzizi Samir, G. Salazar-Alvarez, et al. Nature Nanotechnology 2010, 5, 584.
5. Denis Gebauer, et al, Nanoscale, 3, 3563-3566, 2011.