Artificial cilia for microfluidics exploring the use of a horizontally micro-structured ferromagnetic PDMS composite graduation talk of Willem van Engen Eindhoven University of Technology Department of applied physics Molecular biosensors for medical diagnostics 19-08-2008
Microfluidics an Europa Valve plant site http://www-news.uchicago.edu/
Microfluidic chip Lee et al. in Science (2005) doi:10.1126/science.1118919
Microfluidic mixing R e = v s L 2300 turbulence Macroscopic: v s = R e ≈ 2.3 mm / s L Microscopic: Green in Int. Jnl. of Multiphysics (2007) doi:10.1260/175095407780130544 v s = R e ≈ 23 m / s so only mixing by diffusion L slow
Cilia in nature 5 μ m Dartmouth Electron Microscope Facility Mammalian lung SEM Nikon MicrosopyU digital video gallery, Paramecium (protozoan) Khatavkar et al. in Phys. Fluids (2007) doi:10.1063/1.2762206
Artificial cilia for microfluidics Goal → use artificial cilia to achieve pumping & mixing in microfluidics
Artificial cilia for microfluidics Goal → use artificial cilia to achieve pumping & mixing in microfluidics How? ● high aspect-ratio ● polymer material ● magnetic actuation
Magnetic artificial cilia ● Actuation by magnetic field Huber in Small (2005) doi:10.1002/smll.200500006 ● Magnetic iron-polymer composite small particles (ø<20nm) large particles (ø>20nm) superparamagnetic ferromagnetic induced permanent moment moment
Magnetic actuation forces gradient force torque and × ⋅∇ = 0 F i = 0 H 0 H 0 F p = 0 × L H 0 × e ∥ 3 F = 4 L µ 3 E T W (for small deflection)
Induced versus permanent superparamagnetic material, ferromagnetic material, induced magnetic moment permanent magnetic moment M = M = H 0 M r F i ∝ H 0 ⋅∇ ∝ M × H 0 , ≈ 0 F i = 0, H 0 p W = 4 0 M H 0 i 2 W = 0 j 3 3 r 4 ⋅ L 2 ⋅ L 2 R 3 3 E E W W ⋅∇ F i = 0 H 0 × = 0 H 0
Induced versus permanent superparamagnetic material, ferromagnetic material, induced magnetic moment permanent magnetic moment M = M = H 0 M r F i ∝ H 0 ⋅∇ ∝ M × H 0 , ≈ 0 F i = 0, H 0 W = 4 0 M H 0 p i 2 W = 0 j 3 3 r 4 ⋅ L 2 ⋅ L 2 R 3 3 E E W W scale-dependent scale-invariant
Validity p W = 4 0 M H 0 i 2 W = 0 j 3 3 r 4 ⋅ L 2 ⋅ L 2 R 3 3 E E W W W=10 μ m, L=120 μ m E=0.5MPa, =0.8, M=25mT
Large artificial cilium – fabrication Sylgard-184 Polymer polydimethylsiloxane agent base + cast cure (liquid) (solid silicone resin)
Large artificial cilium – fabrication Polymer polydimethylsiloxane (PDMS) ... made permanently magnetic by doping with ferromagnetic particles, 70nm Fe@C clusters 25 μ m 25 μ m
Large artificial cilium – fabrication Polymer polydimethylsiloxane (PDMS) ... made permanently magnetic by doping with ferromagnetic particles, 70nm Fe@C Cut out a rectangular slab
Large artificial cilium – response 3 M H 0 p W = 4 0 L 3 E W composite measurements: M r =96 kA/m M=11 kA/m W= 66 μ m, 2.2 vol% Fe@C
Micro-fabrication W ∝ W 3 L High aspect-ratio for high deflection Horizontal fabrication by sacrificial layer lift-off technique
Micro-fabrication – procedure Horizontal fabrication by sacrificial layer lift-off technique
Micro-fabrication – procedure
Micro-fabrication – result μ m 500 μ m 500 PDMS PDMS composite composite glass substrate glass substrate once sacrificial layer once sacrificial layer
Micro-fabrication – result SEM optical W~10 μ m L ≈ 250 μ m T ≈ 150 μ m
Micro-fabrication – result ≈ 183 μ m M~183kA/m
Micro-fabrication – long cilia
Conclusion ● Permanently magnetic artificial cilia bend in a perpendicular magnetic field scaling independent − p 3 aspect-ratio dependence − perform better than cilia with induced moment − ● Experiment confirms order-of-magnitude theory ● Micro-fabrication of artificial cilia was shown
Outlook ● Details of fabrication procedure image courtesy of Francis Fahrni parameters − ● Multiple cilia in a microfluidic channel mask design − 500 μ m ● Actuation for mixing and pumping
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