Igor Aronson/Argonne
Active magnetic colloids
magnetic particles
oil
water
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novel feature: liquid-liquid interface
reduced density contrast/tension →reduction of size
new control knobs
novel self-assembled structures
dispersion relation
 
2
1   2
1   2
kg 

1   2
k
g  gravity acceleration
A Snezhko & I Aronson, Magnetic Manipulation of Self-Assembled
Colloidal Asters, Nature Materials 2011
 1,2  densities of liquids
  interfacial tension
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Localized self-assembled magnetic asters
 two flavors: asters & anti-asters
 remotely controlled locomotion
 speed/direction/shape controlled by dc in-plane field (not by the field gradient)
asters
anti-asters
self-generated flow
aster/anti-aster pair
speed (cm/s)
aster’s speed vs in-plane
dc magnetic field
Hdc
magnetic field (Oe)
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Self-assembled colloidal robots at liquid-liquid interface
 perform simple robotic functions (gripper)
 remotely controlled by dc in-plane magn field
 shape change and self-repair
“soft” colloidal robot: grip, move, release
Materials opportunities for soft robotics, George
Whitesides, Ang Chem 2011:
materials with actively tunable compliance …
enable fundamentally new strategies for
manipulation
4 aster-array: new functionality
1 mm
YouTube Movie
YouTube Movie
Energy.gov: Tiny Terminators: New Micro-Robots Assemble, Repair Themselves and Are Surprisingly Strong
youtube views>100,000
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Unique GPU Modeling Capabilities at Argonne
hive.msd.anl.gov GPU
cluster
Nvidia GTX 480
ngene, 4 GPUs cluster,
 3D hydrostatic Navier-Stokes equation
 liquid-liquid system
-novel features: toroidal flows in the bulk
-modeling of asters and array of asters
MSD GPU cluster, BES DOE capital equipment (42 Fermi GPU cards, 50 TFlops,
single precision)
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Igor Aronson, Argonne: Simple Bacterial Machines

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second law of thermodynamics prohibits rectification of Brownian motion
bacteria live in out-of-equilibrium world and thus can extract useful energy
important step for the design of hybrid bio-mechanical systems powered by
microorganisms or synthetic swimmers
1 mm
YouTube Movie
•1-2 rotations per minute
•mass of the gear ~ 106 mass of bacterium
•power of about 1 femtowatt=10-15 Watt
•about 300 bacteria power the gear
YouTube Movie
featured in NY Times,Forbes, Wired, SciAmerican
highlighted as Argonne’s major success in 2010
YouTube > 100,000 views
Sokolov, Apodaca, Grzybowski, I. Aronson,
PNAS, 2010
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Next step: swimmers-assisted assembly
preliminary results
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swimming bacteria spin microscopic gears
self-assembled primitive machines – gears assembly
can bacteria assemble gears from properly functionalized units?
massive parallel approach to assemble thousands of microscopic structure
magnetically-controlled micro-shuttle
powered by bacteria
gears assembly
500 mm
100 mm
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Alber Research group bacteria Experiments and
Simulations
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Image analysis of bacteria movies
– Cell Segmentation and tracking
– Illumination of Cell “slime tracks”

Observations include:
– Cell division
– Slime Track navigation by cells
• Cells Turning to follow tracks
• Cells bending as the move along tracks
– Cell Clutsers Dynamics
• Bending and Cell Oreintation in groups of cells

Simulations of rod-shaped bacteria moving on surfaces
Cell Division
Preliminary data suggests that cells stall during division. (Yellow arrow highlight
additional time between frames during division. Red arrow point to septum forming)
Questions: How does polarity of mother cell relate to daughter cells?
Does phase of reversal period get passed to daughter cells?
Cell Turn on Slime Tracks
M. xanthus is known to produce slime tracks when gliding on agar.
By highlighting cell trajectories, cell-slime track locations can be visualized
and cell-track interactions can be analyzed
Questions: How much turning can cells undergo to get onto track?
Detailed Segmentation can analyze cell bending on
Slime Tracks
Segmentation of raw image data is processed to
form meshes on each cell. The mesh can be used
to extract a central line that can be analyzed for
bending of cells during collisions or during cell-trail
interaction.
Cell Bending and Orientation in Clusters
We are also interested in cell bending and cell
orientation and spatial ordering as cells dynamical
form and move as groups.
Sub-Cellular Elements Simulations
Simulation Movie Link (http://biomath.math.nd.edu/compbio/CellSim4.gif)
Simulations are being run to study flexibility, adhesion and cell reversals on cell
clustering dynamics. Also, simulations that look at cell–slime track interaction are being
run by coupling cells to a 2D substrate that simulates slime trails left by cells. (Slime not
shown, but the 2d grid represents the scaler field discretization)
Simulations prospects for Aneromyxobacter

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Model for Rod Shaped bacteria moving on surfaces is established.
The substrate can be created to simulated Iron-hydroxide substrate or other
environments to simulate chemical reactions at positions of cells.
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