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Motivation

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Motivation

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  1. Actuated cilia regulate deposition of microscopic solid particlesRajat Ghosh and Alexander AlexeevGeorge W. Woodruff School of Mechanical EngineeringGeorgia Institute of Technology, Atlanta, Georgia Gavin A. BuxtonDepartment of ScienceRobert Morris University, Pittsburgh, PennsylvaniaO. Berk Usta and Anna C. BalazsChemical Engineering DepartmentUniversity of Pittsburgh, Pittsburgh, PennsylvaniaNovember 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. F b B R h L w w Computational Setup • 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 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

  5. Collisions Propagation 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)

  6. Dx k M Lattice Spring Model • 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

  7. Particle Motion in a Period x y 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=3 Sp=5 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

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