MEMSChapter3Theoryanddesignofmicrofluidicdevices

1、AME/ABE 488/588Micro and Nano TransducerPhysics and DesignProf. Pak Kin WongMicrofluidicsCellFluidic Control in a MicrosystemSample PreparationMolecular IdentificationMixingFluidtransportGenomic & ProteomicInformationBiosensorConcentrationSeparationLab-on-a-chipMicrochannelsTypes of Fabrication

2、ProcessesBulk micromachining (Si, glass, quartz,.)Surface micromachining (Solid materials, polymers)Others (Thick-PR lithography, PDMS molding, Imprinting, replication,.)Paper based microfluidicsGeneral ConsiderationsChannel cross-sectional areas and other geometric constraintsChannel interior surfa

3、ce materials (whether or not all surfaces are ofone material type, and if the materials(s) is (are) biocompatableComplexity of fabrication (yield and cost)Flexibility in tubing and in integration with other fluidic componentsOptically accessible (Transparency, thickness of bonding glass,.)Leakage, s

4、urface roughnessMolecularly imprinted polymers (MIPs)Bulk Micromachined ChannelsMicromachined flow cytometry cell (Sobek)Needle-like neural probe(Chen & Wise)Allowed the controlled injection ofminute quantity (100 pl)Recording of neural signals10 m wide, , 4 cm long g11 torrr drive pressure, 1.3

5、 mm/sBulk Micromachined ChannelsThin fluidic channels (Tjerkstra)Buried, bulk-etched fluidicchannels in a Si substrate(Tjerkstra)Surface Micromachined ChannelsNeedle-like neural probe (Lin)Surface micromachinedorganic fluidic channel (Man)Low temperature processTwo-phase microfluidics Picoliter-volu

6、me droplets at a rate of 10 million per hour Each droplet is the functional equivalent of an individual test tube and can containa single molecule, reaction, or cell.Droplet generation Droplet loadingMerging dropletsSorting dropletshttp:/ flow 等效電路圖V1V2V3GNDJR1R2R3R4I1I2I3I4+800 V+300 VGND+300 Va+80

7、0 V+400 VGND+400 Vb+800 V+500 VGND+500 Vc夾流電壓條件實驗+800 V+300 VGND+300 Va+800 V+500 VGND+500 Vc+800 V+400 VGND+400 Vb流式細胞儀流式細胞儀MicrovalvesIdeal valves should have the following characteristics :Zero leakageZero power consumptionZero dead volumeInfinite differential pressure capability (壓差閥)Insensitivi

8、ty to particulate contaminationZero response timeAbility to operate with liquids and gases of any density/viscosity/chemistryMechanismsPassive (no power required)Active (require a powered actuation mechanism)Passive ValvesMicrofluidic valve fabricated using two-sidedbulk etching (Smith and Hok)KOH t

9、o form pyramidal pitsSlit widths 10 mThickness of leafletsLeakage problemPassive ValvesA two-wafer stack, bulk micromachined passive valve (Tiren)A single cantilever acts as a seal when forced against the upper waferby reverse flowIn addition to the bulk micromachined valve design combined with a fu

10、elinjection nozzleActive ValvesActuation MechanismsThermal actuation (linear thermal expansion, thermal bimorph, shapememory alloys):+ generate large forces,+ good when scaling down devices (thermal mass decreases)- relative slow (especially with passive cooling),- undesirably heat the sample fluid,

11、- consume a lot of powerPiezoelectric actuation+ yield very high forces- small movement even with large voltageElectrostatic actuation+ high forces, large movements- non-linear forcePneumatic and Thermopneumatic actuation+ high forces and movement- power consumption, undesirable heating in samplesPn

12、eumatic ValvesA silicone elastomer membrane, micromachined pneumatically actuatedmicrovalve. (Vieider)The design consists of three wafers in a stack, the central one containing themoving plunger and silicone membranePressure difference up to 500 kPaRequire an external pump, adding complexity in on-c

13、hip integrationThermopneumatic ValvesMicromachined thermal expansion valve(Zdeblick) Membrane thickness 50 m Sealed with anodic bonding (highsealing quality is required) Power required 1-2 WSilicon membrane do not have highflexibility = smaller deflection, higherleakageMicromachined, siliconemembran

14、e, thermopneumaticvalve (Yang)Membrane thickness 50 mPeak membrane deflection 860m at 970 mW20 psi at 280 mW with air flowrate 1.3 lpmThermal Bimorph ValvesDiffused resistors in betweenThermal bimorph valve (Jerman)A thin SiO2 “hinge” surrounding themembrane to increase thermalisolation and provides

15、 a hingedboundary for the membraneInlet pressure 1- 50 psi with an inputpower of 150 mWThermal bimorph valve (Barth)Other ValvesMicromachined piezoelectric valve(Shoji)Micromachined electrostatic /Pneumatic valve (Huff)Micromachined electromagneticvalve (Shoji)PDMS Valves (aka Quakes valve)http:/www

16、./cgi/content/abstract/1076996Three valves form a peristaltic pumpMicropumps/cgi/content/abstract/1076996MicropumpsMechanismsShare the same actuation mechanism in the design of active microvalvesThermal actuationPiezoelectric actuationElectrostatic actuationPneu

17、matic and Thermopneumatic actuationElectrostatic pump (Zengerle)Thermal Expansion pump (Benard)Incorporate two check valvesFrequency range: 0.1 Hz to 10 HzFlow rate : 250-850 l/minFlow rate 50 ul/min at 0.9 Hz with 0.6V, 0.9A (0.54W)Other MicropumpsElectroosmotic pump(Santiago)Electrohydrodynamic pu

18、mpTemperature gradientinduces conductivity andpermittivity gradientsTraveling wave of electricfield induces charges on theinterface and in the bulk flowThe traveling filed also drivethe induced charge, and thusthe flow(B. Wanger)Electrowetting Digital FluidicLippmans EquationC2(V Vo)2 o Contact angl

19、e changes withapplied potentialHydrophobicunder no potentialReversibleVHydrophilicunder electricpotentialC.- -J. Kim, UCLAReversibilityAn important thing about low Reynolds number is reversibilityReversibilityAn important thing about low Reynolds number is reversibilityD Influence of scaling on diff

20、usionDiffusion times (particle and thermal )x26D kT6rtDiff L2red blood cellviral DNA1 m secDiffusion Time16 minBench top p p processLab-on-a chipMixing at microscale mediated mainlyby diffusionTime to diffuse over 10 m milliontimes faster than over 1 cmribosomeglucose1m1mm1nm1 n secDiffusion lengthH

21、eat is conducted out of smallstructure quicklyMicro MixersRapid mixing can substantially save the time in a bioanalytical systemAt Low Reynolds number region, there is no turbulence for enhancingmixingEffective mixing requires that fluids be manipulated to increase theinterfacial surface areaActive

22、mixersthey exert some form of active control over the flow field through suchmeans as moving parts or varying pressure gradientPassive mixersthey utilize no energy input except the mechanism used to drive the fluidflow at a constant ratePassive Mixing in a 3-D Serpentine Microchannel“Twisted-pipe”Ch

23、aotic advection: simple regular velocity fieldsproduce chaotic particle trajectories. This typicallyindicates rapid distortion and elongation of materialinterfaces. This process significantly increases in thearea across which diffusion occurs.The flow change in direction result in flow separationcau

24、sed by momentum of the fluid, leading to folding ofthe flow(D. Beebe)Measuring at 18mmWorking rang : Re 1Hydrodynamic Focusing Micro MixerPsLumped ModelingPi: inlet pressurePs: side pressurePiPs(Austin)Active Chaotic MixersPressure-Driven ActuationInducing flow folding and stretching byadding unstea

25、dy hydrodynamic pressureperturbationBulk-flow perturbation(Lee & Ho)DEP-Driven ActuationLyapunov exponent: to characterize therate at which pairs of fluid particlesdiverge and characterize the degreechaotic effect 0.4Particles perturbation (Deval & Ho)Active Chaotic MixersMagnetic Force-Driven ActuationParticles perturbationCapillary ElectrophoresisElectrophoresis is performed in narrow-bore (50-250m), fused silica capillariesSmall volume required (1 to 50 nl injection)High voltage (10 to 30 kV) and high electric fields (100to 1000 V/c