http://symbiol.blogspot.com/
OPTICAL MIMICRY AND
COMMUNICATION 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/
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
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
Two to Tango: ChromatophoreIridophore Interaction
Yellow
chromatophore
+ green
iridophore =
dark yellow
Yellow
chromatophore
+ red
iridophore =
orange!
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
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
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
The Play-Dough Principle
Dielectric
elastomers use
voltage in
place of
pressure
applied kid’s
hand
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

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