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Structural and Functional Design Strategies of Biological Keratinous Materials

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Structural and Functional Design Strategies of Biological Keratinous Materials UNIVERSITY OF CALIFORNIA, SAN DIEGO Structural and Functional Design Strategies of Biological Keratinous Materials A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Materials Sciences and Engineering by Bin Wang Committee in charge: Marc A. Meyers, Chair David J. Benson Vlado Lubarda Xanthippi Markenscoff Joanna McKittrick 2016 Copyright Bin Wang, 2016 All rights reserved The Dissertation of Bin Wang is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2016 iii DEDICATION This work is dedicated to my family – you have always been so supportive to my endeavors. iv TABLE OF CONTENTS SIGNATURE PAGE .......................................................................................................... iii DEDICATION ................................................................................................................... iv TABLE OF CONTENTS .....................................................................................................v LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES .............................................................................................................xx ACKNOWLEDGEMENTS ............................................................................................. xxi VITA .............................................................................................................................. xxiv ABSTRACT OF THE DISSERTATION .........................................................................xxv 1 Introduction .......................................................................................................................1 1.1 Materials Science and Engineering ........................................................................... 1 1.2 Biomimetics and Biological Materials Science ......................................................... 2 1.3 Natural designs: structure and mechanical properties ............................................... 4 1.4 Hierarchical structure and polymer composites ........................................................ 7 1.5 Keratinous materials and research focus ..................................................................11 2 Research outline ..............................................................................................................14 3 Review of keratins and keratinous materials ..................................................................15 3.1 Classification of keratin ........................................................................................... 15 3.2 Biochemistry, molecular structure and mechanical properties of α- and β-keratins 17 3.2.1 Biochemistry of α- and β-keratins .................................................................... 17 3.2.2 Molecular structure of α- and β-keratins........................................................... 28 3.3 Keratin research history ........................................................................................... 34 3.4 Structure and mechanical properties of keratinous materials .................................. 36 3.4.1 Keratinous materials based on α-keratin ........................................................... 40 3.4.2 Keratinous materials based on β-keratin ........................................................... 64 v 3.4.3 Keratinous materials based on α- and β-keratin................................................ 73 3.5 Bioinspired designs ................................................................................................. 82 3.5.1 Tradional bioinspiration .................................................................................... 82 3.5.2 Molecular-based bioinspiration ........................................................................ 89 Acknowledgements ....................................................................................................... 90 4 Pangolin scales ................................................................................................................91 4.1 Materials .................................................................................................................. 91 4.2 Experimental procedures ......................................................................................... 94 4.2.1 Structural characterization ................................................................................ 94 4.2.2 Mechanical testing ............................................................................................ 97 4.3 Results and discussion ............................................................................................. 99 4.3.1 Scale overlapping mechanism ........................................................................... 99 4.3.2 The structure of pangolin scale ....................................................................... 103 4.3.3 Mechanical behavior ........................................................................................117 4.4 Summary ............................................................................................................... 132 Acknowledgements ..................................................................................................... 132 5 Feather shaft ..................................................................................................................134 5.1 Materials ................................................................................................................ 135 5.2 Experimental procedure ........................................................................................ 135 5.2.1 Structural observation ..................................................................................... 135 5.2.2 Mechanical testing .......................................................................................... 137 5.3 Results and discussion ........................................................................................... 144 5.3.1 Shape factor of flight feather shaft.................................................................. 144 5.3.2 Layered fibrous structure of cortex ................................................................. 153 5.3.3 Porous and fibrous medulla ............................................................................ 169 5.3.4 Tensile response .............................................................................................. 171 5.3.5 Compressive behavior ..................................................................................... 177 5.3.6 Flexural properties .......................................................................................... 186 5.4 Thoughts on bioinspired designs ........................................................................... 195 5.5 Summary ............................................................................................................... 196 Acknowledgements ..................................................................................................... 198 6 Conclusions ...................................................................................................................199 vi 6.1 Concluding remarks .............................................................................................. 199 6.2 Pangolin scales ...................................................................................................... 200 6.3 Feather shaft .......................................................................................................... 202 7 Future work ...................................................................................................................205 References ........................................................................................................................206 vii LIST OF FIGURES Figure 1.1 Biological materials science at the intersection of physics, chemistry and biology. ......................................................................................................................... 3 Figure 1.2 Schematic representation of characteristic constraints (inspired by [9]) [20]. .. 6 Figure 1.3 Young’s modulus as a function of density for biological materials, overlaid with synthetic materials [10], [12], [25]. ..................................................................... 8 Figure 1.4 Sketch of the hierarchical structure of a human femur [28]. ............................. 9 Figure 1.5 A material property chart for natural materials, plotting toughness against Young’s modulus [25]. ................................................................................................11 Figure 3.1 X-ray diffraction patterns of (a) α-keratin and (b) β-keratin [48]. .................. 16 Figure 3.2 Molecular units of (a) α intermediate filament and (b) β-keratin filament. (a) The heterodimer includes non-helical N- and C-terminal domains and a central region (~46 nm in length), which has the α-helical coiled coil segments (1A, 1B, 2A, 2B), short links (L1, L12 and L2) and a ‘stutter’ (adapted from [39], [65]). (b) The upper illustrates the distorted sheet and the lower schematic represents a molecule with central domain and N- and C-terminal domains. The central domain (~34 residues in length) consists of β-forming residues (adapted from [48], [54]). .........
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