Collaborating Professor: Prof. Marc Madou (UC Irvine, USA) Ph.D Student: Debapriya Chakraborty (currently at Shell) Funding Agencies:

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1 Microfluidics on a Compact Disk Suman Chakraborty Professor Department of Mechanical Engineering Indian Institute of Technology (IIT) Kharagpur, India suman@mech.iitkgp.ernet.in December, 2011

2 Acknowledgements Collaborating Professor: Prof. Marc Madou (UC Irvine, USA) Ph.D Student: Debapriya Chakraborty (currently at Shell) Funding Agencies: NSF, USA DST, India Indo US Science and Technology Forum DBT, India

3 Driving forces in microfluidics Pressure gradient Capillary effects Electrical forces Magnetic forces Rotational forces Sound Light Microflow Actuation Remarks Large pressure gradients required to drive flow through channels with small hydraulic diameter Direct use of surface tension forces or their differentials due to thermo-/solutal gradients Electroosmosis, electrophoresis etc. MHD stirring Centrifugal / Coriolis/ Angular Acceleration effects Acoustic streaming Effective actuation of microflows by light-induced surface tension modulation, with spatio-temporal control?

4 CD based Microfluidics

5 Pertinent Forces Centrifugal force Fr ( ω ω r) = ρ Rotat ting frame Coriolis force F c = 2 ρ ω v Euler force Interfacial forces Surface Tension force F = Pσ cosθ ST Fu ( ω& r) = ρ Viscous Drag force F D = 12µ u l H

6 Fundamental Operations Valving Gating of fluids Burst Frequency F ST vs. F r Mixing Mixing of fluids Rotation Speed F r vs. F C Aliquoting Metering of fluids Design restrictions F r vs. F C

7 Why CD as a microfluidic platform? Bio-compatibility Effective substitute for standard consumables such as: slides, microwells, centrifuge tubes. Versatility in handling a wide variety of sample types the ability to gate the flow of liquids (non-mechanical valving) simple rotational motor requirements Economised fabrication methods Possibility of performing simultaneous and identical fluidic operations

8 Features of rotational actuation flow rates ranging from less than 10 nl s 1 to greater than 100 µl s 1 Pumping is relatively insensitive to physicochemical properties such as ph, ionic strength, or chemical composition (in contrast to AC and DC electrokinetic means of pumping). Aqueous solutions, solvents(e.g., DMSO), surfactants, and biological fluids (blood, milk, and urine) have all been pumped successfully. miniaturization and multiplexing -> easily implementable A whole range of fluidic functions, including valving, decanting, calibration, mixing, metering, sample splitting, and separation, can be implemented on this platform, and analytical measurements may be electrochemical, fluorescent, or absorption based and informatics embedded on the same disc could provide test specific information.

9 Fabrication of CD CDs are fabricated mainly two ways 1. Using PDMS bonding (3 layer approach) Usually used for low speed rotation Uses photolithography techniques to fabricate channels; hence has larger flexibility in designs 2. Using CNC machined (5 layer approach) In order to avoid overdependence on the PDMS bonding, CNC machining and clamps are used at very high rpm (hypergravity simulations) Usually difficult to produce very complex arrays. Burger Model No clean room fabrication

10 Fabrication: 5 Layer Approach

11 Experimental setup Computer and CCD camera to acquire image Detector + Computer to obtain data and also feed back of the motor unit AC servo motor for rotating the CD Stoboscope for making a cyclically moving object appear to be slowmoving or stationary.

12 Illustrative Examples and Applications Bubble Generation on CD CD Based Mixing Drug Delivery Ultrasound activated bubbles Gene therapy Contrast Agents Bubble with tagged antibody for healing ovarian, breast and Optical path difference pancreatic cancerous tumours Cell Membrane Poration Foamed Emulsion Bioreactor Microjet from collapsing bubbles large gas/liquid interfacial area, high mass transfer rate Ref: Advanced Drug Delivery Reviews 56 (2004) Journal of Controlled Release 138 (2009)

13 Bubble Generation on CD Ref: D. Chakraborty and S. Chakraborty, Applied Physics Letters, vol. 97, pp (1-3), 2010

14 Scaling of Forces β = ρω 2 x xr (centrifugal force to the surface tension force) ~1 σ µ U Ca = σ (the viscous force to the surface tension force) ρul Re = µ (the inertial force to the viscous force) ~10-3 Ro U = (coriolis force to the centrifugal force) ωx 2 U l ρ W e = σ ϕ = ρω& xr µ U 2 (inertial force to the surface tension force) (transverse driving force due to angular acceleration to the opposing viscous resistances ) ~10-4 ~1

15 Dripping vs. Jetting β<<1 surface tension dominates (gas thread retracts from the junction) β>>1 gas experiences a strong centrifugal force yielding a two phase jet β~o(1) gas thread at the junction is not dynamically stable -> yields bubble The dripping-to-jetting transition is sharp if the liquid viscosity is significantly higher as compared to the gas viscosity.

16 Constant RPM β~o(1) Dripping Mode Time nondimensionalised by: period-1 state µ ρσ 3 t 0 = 2 τ r /β dimensionless time linear with 1/β β length of each bubble is proportional to β

17 Varying RPM Dynamics of Breakup Controlling space Controlling between bubbles size of bubbles t=0 t= sys-rev/sec 9 8 sys-rev/sec 9 8 t= t (sec) t (sec) t=0.139 Unstable t=0.203 Stable t=0.422

18 Simulation Volume of Fluid (VOF) Dynamic Mesh Adaptation t r +. v = 0 ( α ρ ) ( α ρ ) i i i i i α i = 1 ρ = i i i i α ρ r r r r r r r r r ( ρvr ) +.( ρvrvr ) + ρ(2 ω vr + ω ω ) = p + τ r + F t r r T 2 r τ r = µ [( vr + vr ). vr I ] 3 ρκi αi F = σ ij 1 Modeling Surface Tension ( ρi + ρ j ) 2 Methodology: SIMPLE algorithm Pressure-velocity coupling Velocity staggering scheme Discretized continuity equation

19 CD-based Microfluidic Mixing Ref: D. Chakraborty, M. Madou, S. Chakraborty, Lab on a Chip, vol. 11, pp , 2011 Issues in Microscale mixing: 1. Low Re (no turbulent mixing) 2. High Pe (strong effect of advection) 3. Specialised fabrication procedures 4. Sustaining transverse circulation downstream to compensate for the incompatibility between flow and diffusion timescales Advantages of CD based platform: 1. Sustainable transverse force both along the cross-stream direction as well as in the axial driving direction 2. Fabricated without using expensive lithography/clean-room based procedures 3. Simple Rotational Requirements - can be tuned using controlling rpm

20 Scaling of Forces Reservoir Outlet ω r a v T-Microchannel L r r U ρω 8µ 2 2 av h ι 2 ρωr γ = h (Coriolis force to the centrifugal force) <<1 ~1 >>1 8 µ 32µσ lg cosθ (Surface tension force to Coriolis force) ρ Lr ω d = 593 av rpm Re R o = ρulw µ ωl = w U (the inertial force to the viscous force) (Coriolis force to the inertial force ) Important when γ>>1

21 Mixing Regimes Three regimes of Mixing Diffusion based mixing (γ<1) Coriolis force based mixing (γ ~1) Instability based mixing (γ>1)

22 Diffusion based Mixing Effect of Coriolis force Standard deviation based on ( ) σ D = I I Mixing length x m - 90% of inlet σ D σ D δx (cm) 1 2 x m decreases as Pe γ=0.26 γ=0.36 γ=0.47 γ=0.57 γ=0.78 γ=0.89 γ=0.99

23 Coriolis force based mixing x δ(x) γ=1.3 γ=1.6 Scaling Analysis: 2 ( u ) Pe. C = C diffusive length scale δ δ ( x) = ( ) 1 3 D x G transverse strain rate (G) proportional to ω 3 as Coriolis force is 2ρω U Where is the axial velocity scales as 2 ω Mixing length can be determined: δ ( x) st as x xm 3 x m proportional to ω and 3 s t x m s t 3 ω 3 Match of Experimental and scaling

24 Instability based Mixing t=0.045s t=0.075s Perturbation Equations: u x i i = 0 t=0.09s t=0.15s ' ( ) U 2 R u u u u t x x R e x x 0 1 o 2 2 i i P 1 i + U R ou 1 = + 1 i j j Perturbation: = ˆ ˆ i x3 t u, P u ( x ), P( x ) e α + σ i i 2 2 Boundary Conditions: uˆ (0) = uˆ (1) = vˆ (0) = vˆ (1) = Dvˆ (0) = Dvˆ (1) = 0 Considering a parabolic base state flow Disturbance Equation: 6x D 2 α 2 σ Re D 2 α 2 vˆ + 4α 2 Re 2 R (3 ) 1 2 ˆ o Ro v = 0 3 Ro 2 ( ) ( )

25 Alternative Strategy 1 Pulsed Mixing (a) sequence of images with varying rotation speed alternatively at γ=0.25 clockwise and anticlockwise. (b) Matching of the numerical and experimental images (in the inset) for γ=0.25 (c) Effect of alternating rotation speed in the mixing

26 Alternative Strategy 2 Multiphase flow Parameter m ( U U ) U 0.5 = < recirculation b f f Predicted streamlines by Taylor

27 Lab on a CD-based Medical Diagnostics: Perspectives in India Blood Sample Analysis Rapid diagnosis of blood, saliva, and urine samples with multiple tests executed simultaneously. Inexpensive Portable Biocompatible Low sample volume consumption DNA hybridization Raw Sample Cell separation Bacteria, Cancer cell, WBC etc Sample Preparation Cell lysis, purification DNA RNA Protein Amplification Hybridization Electrophoresis sequencing Put blood On tracks

28 Conclusions CD is an excellent microfluidic platform Microbubbles may be elegantly generated on a CD by dynamically tuning the rotational speeds. It provides a simplistic design basis, taking advantage of the competing influences of surface tension, centrifugal and angular acceleration originated forces in tandem, to produce microbubbles of desired specifications on demand. CD may be utilized as an efficient mixing platform, by effectively exploiting the interplay of Coriolis and centrifugal forces. Three distinctive regimes for mixing may be realized in this regard, namely, diffusion based mixing, Coriolis based mixing and instability based mixing. CD may be used as an excellent platform for medical diagnostics

29 Experiments + Theory Microfluidics Research towards betterment of Science and Society