Transcript pptx
http://symbiol.blogspot.com/ OPTICAL CAMOUFLAGE IN CEPHALOPODS ENGN/BIOL 267 Where’s Waldo…err, the octopus? Cuttlefish Camouflage How does it do it? If you are an octopus (or squid, or whatever cephalopod), what “equipment” do you need to pull off the color changes? Reflectors http://www.toolsandleisure.co.uk/round-amber-self-adhesive-reflector-294-p.asp Pigment + = Chromatophores: Pigment Sacks Mathger and Hanlon, 2007 Young et al, 2001 • Variable size/radius • Under muscarinic control • Color spectrum somewhat limited Chromatophores in Action http://blog.backyardbrains.com/2012/08/insane-in-the-chromatophores/ Biological vs. synthetic displays From Kreit et al 2013 Iridophores: Reflectors * Stacks of protein plates (reflectins) in cytoplasm Cytoplasm Protein plates * Single reflectins plate by itself is clear 1um * Located beneath chromatophores Cooper, 1990 Iridophores are active *Spacing between layers can change. * Changing layer spacing implies changing reflected wavelength Cytoplasm Protein plate • Scale bars: 250 nm Cooper, 1990 * Under neural and chemical control (Ach) • Cooper, 1990 Mathger, 2007 Mechanism for optical tuning Iridocyte (cell that contains iridophore) Reflectins plates exchange water into cytoplasm driven by ACh DeMartini, 2013 Two to Tango: ChromatophoreIridophore Interaction Yellow chromatophore + green iridophore = dark yellow Yellow chromatophore + red iridophore = orange! Getting under its skin Kreit et al 2013 Biomimicry in Cephalopods: Part Deux Modeling the Optics 1um Application of Optics Convenient Physics model The Real Thing Cytoplasm Protein plate Scale bars: 250 nm Traveling Waves Animation credit: Dan Russel, Penn St. : http://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html Wavenumber k = 2p/l How wave varies in space Frequency f How wave varies with time Different strokes for different folks lI lc lo Wavelength changes depending on medium in which it is traveling nolo= nili = nclc Wavelength changes depending on material/medium air cytoplasm iridophore Cytoplasm – Iridophore Optics * Reflection is the superposition of reflected waves * Take just one repeating unit for now How does the octopus or squid stack up? Color we see (wavelength most strongly reflected in ideal stack configuration: lo = 4nIdI = 4ncdc But are other colors (wavelengths) visible too? Why have >1 or 2 iridophore plates? What if the stack is non-ideal? Phasors! Sine wave can be represented by a rotating vector, called a phasor. * Super convenient to keep track of phase differences Animation: http://edumation.org/play_file.php?file_type=animation&file_id=84 Another great phasor animation *2 waves can interfere constructively or destructively *Many waves interfere in just the same way – sum them up. Survey says… More plates = better reflectance More plates = narrower bandwidth Range observed by Ghoshal, 2013 Figures from Land, 1972 Biomimicry in Cephalopods: Part Trois Bioinspired Designs 1um Bio-inspired Engineering Blockcopolymers photonic gels (Kang, 2007) Solvents modulate de/swelling l = 350 – 1600 nm Block Copolymers in action Decreasing Salt concentration Figures from Kang, 2007 Electrically Induced Color Change Apply voltage to electrochemical cell Redox Reaction Compression/Ex pansion Color change Wallish, 2009 The current state of the art Wallish, 2009 Biomimetic Chromatophores OFF state Conductive carbon grease ON state Elastomer Gel Rossiter 2012 Efficient everyday design? References RE Young, M Vecchione, KM Mangold, 2001. Tree of Life: Cephalopod Chromatophore: http://tolweb.org/accessory/Cephalopod_Chromatophore?acc_id=2038 LM Mathger and RT Hanlon. Cell Tissue Res (2007) 329: 179-186 LM Mathger and EJ Denton, J Exp Biol (2001) 204: 2103-2118 E Kreit et al., J. Royal Society Interface (2013) 10:20120601 Dan Russel, Penn State: http://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html KM Copper, RT Hanlon, BU Budelmann. Cell Tissue Res (1990) 259: 15-24 MF Land. Progress in Biophysics and Molecular Biology, 24: 75–106. Y Kang et al, 2007. Nature Materials, 6: 957-960 JJ Walish et al, 2009. Advanced Materials, 21: 3078-3081 D DeMartini et al, 2013. Proceedings of the National Academy of Sciences, 110(7), 25522556. A Ghoshal et al, 2013. Journal of The Royal Society Interface, 10(85), 20130386. J Rossieter et al, 2012. Bioinsp.Biomim. (7) 036009 Describing a sine wave with phasors v(t) = 5 cos(2pft) with f = 4 Hz 6 v(t) [Volts] 4 2 0 -2 -4 -6 -0.2 0 0.2 0.4 0.6 0.8 1 Time (sec) 5 4.33 2.5 0 1.2 Ideal vs Non-ideal stacks What if the stacks are non-ideal? Non ideal means: nidi != ncdc Land, 1972 The tradeoff: • Less reflectance • Narrower bandwidth, better chromatic selectivity Another coloration mechanism: viewing angle matters Mathger, 2001 Viewing angle Mathger and Hanlon, 2007 Does viewing angle matter? 10o 10o 50o 50o YES! X 2 Cross section of cephalopod a= 10 deg a= 50 deg lo = 4nIdIcosbI = 4ncdccosbc Apply Snell’s Law: a = angle of incidence b = angle of refraction Non-zero angle of incidence L n1 r d2 n2 Image credit: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/interf.html#c1 What is measured and how? To computer for data acq. and analysis--.e.g, the reflectance spectra! Photo Multiplier Tube: Collects light and amplifies Reflected from squid skin Light source with chromatic filter (and polarizer) Tissue prep: Thin slice of squid skin 1. Choose color of incident light and measure input intensity Iinc 2. Measure intensity of reflected light Iref, then compute: R = Iref/Iinc