1. Actuated cilia regulate deposition of microscopic solid particles Rajat Ghosh and Alexander Alexeev George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology, Atlanta, Georgia Gavin A. Buxton Department of Science Robert Morris University, Pittsburgh, Pennsylvania O. Berk Usta and Anna C. Balazs Chemical Engineering Department University of Pittsburgh, Pittsburgh, Pennsylvania November 22, 2009

2. Motivation
Controlling motion of microscopic particle in fluid-filled micro-channel
Use bio-inspired oscillating cilia
Finding new routes to regulate micro-particle deposition in micro-fluidic devices
Lung Cilia
(NewScientist, April 2007)
Synthetic Cilia
(NewScientist, April 2007)

3. Computational Setup z x Fluid-filled microchannel
Elastic ciliated layer tethered to wall
Arranged in square pattern
Neutrally buoyant particle of radius R
Small enough to move freely
Not affected by Brownian fluctuations
Simulation Box
Four oscillating cilia
Suspended particle
Viscous fluid
Actuation
External period force
Methodology
Hybrid LBM/LSM z x L R B b h w F y X z
L=4R
B=3R
b=0.4R
h=10R
W=6R

4. Parameters Cilia dynamics characterized by Sp Sperm Number,
Vary by modulating actuation frequency
Range: 3-5
Cilia actuated by external periodic force
Applied at free end
Oscillating in x-direction (x-y plane)
Amplitude a and angular frequency ω
Amplitude characterized by, A=(1/3)aL2 /(EI)
Study effect of oscillating cilia on motion
Use hybrid LBM/LSM
LBM for hydrodynamics of viscous incompressible fluid
LSM for micromechanics of elastic cilia
Coupled by boundary conditions ζ
Drag Coefficient EI
Flexure Modulus R
Particle Radius

5. Lattice Boltzmann Model
Dynamic behavior governed by Navier-Stokes equation
Particles move along lattice while undergoing collisions
Collisions allow particles to reach local equilibrium
Simple two step algorithm
Collision and propagation steps
Local in space and time
Needs only local boundary conditions (bounce back rule)
Collisions
Propagation

6. Lattice Spring Model Poisson ratio = 1/4 Dx k M
Dynamic behavior governed by continuum elasticity theory
Network of harmonic springs connecting mass points
3D: 18 springs connecting regular square lattice
Integrate Newton’s equation of motion
Verlet algorithm
Poisson ratio = 1/4 M Dx k

7. Particle Motion in a Periody x z
Actuated cilia induce periodic particle oscillations
Particle entrained via fluid viscosity
No inertia effects at low Re

8. Trajectory Path Direction of particle drift motion changes with Sp
Sp=3: particle moves towards wall
Sp=5: particle moves away from wall
Sp controls particle drift across cilial layer
Change Sp to regulate drift direction y x
Sp=3
Sp=5

9. Drift Characterization
Unidirectional motion normal to channel wall
Cilia transport particles through entire layer
Can deliver particle from free flow to wall surface and vice versa y
Upward
Drift
Sp=5
Sp=4
Sp=3
Downward
Drift

10. Effect of Particle Initial Position
Shifting particle at different off-centric locations
δ = 0, δ = 0.25c and δ = 0.5c
c is inter-cilial distance z x
Sp=3
Sp=5
Particle transport direction remains unchanged (most of the cases)

11. Mechanism for Particle Drift
Mode of cilia oscillation changes with Sp
Different secondary flow patterns
Secondary flow changes direction with Sp
Sp= Sp= Sp=3
Secondary flows transport particle across cilial layer z x
: Forward
:Backward y X y
Sp=5 x z

12. Summary Use actuated cilia to control of particle deposition
Regulate drift direction by changing frequency
Low frequency: particle moves down
High frequency: particle moves up
Applications
Regulate particle deposition in microchannel
Lab-on-a-chip systems
Self-cleaning substrates
Ghosh, Buxton, Usta, Balazs, Alexeev, “Designing Oscillating Cilia That Capture or Release Microscopic Particles” Langmuir, ASAP 2009