Contents. 1. Introduction 2. Fluids 3. Physics of Microfluidic Systems 4. Microfabrication Technologies 5. Flow Control. 6.

Transcription

1 Contents ele 1. Introduction 2. Fluids 3. Physics of Microfluidic Systems 4. Microfabrication Technologies 5. Flow Control 7. Sensors 8. Ink-Jet Technology 9. Liquid Handling 10.Microarrays 11.Microreactors 12.Analytical Chips 13.Particle-Laden Fluids a. Measurement Techniques b. Fundamentals of Biotechnology c. High-Throughput Screening

2 ele 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous Micromembrane pump (Debiotech Lausanne, CH) Electroosmotic Pump) (M. Ramsey, ORNL, USA) Electrohydrodynamic Micropump (FhG-IFT, Munich)

3 ele h Pumping Transport of fluid h Against external forces / fields Gravity Pressure gradient Viscosity Etc. h Micropumps Peculiar scaling of forces in microworld Fabrication issues Novel pumping principles

4 ele 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

5 6.1. Microdisplacement Pumps ele h Constituents Pump chamber Actuation Flow rectifiers - Check valves - Fixed-geometry valves - Active valves Peristaltic Thermoviscous Actuation principles Mechanical Pneumatic Thermomechanical Thermopneumatic Piezoelectric Electrostatic Electromagnetic... h Pumping cycle Supply phase - Underpressure Pump phase - Overpressure

6 6.1. Microdisplacement Pumps ele 1. Modeling 2. Design Issues 3. Integrated Check Valves 4. Fixed-Geometry Valves 5. Pumping Valve

7 Modeling ele h Differential equations Physics h pv-diagram Mechanical engineering h Lumped element Electronic engineering

8 Dynamics ele h Dynamics results from complex coupling Mechanical displacer Rectifier - E.g. valve h Actuation of check valves by pressure within pump chamber h External control only by actuation of membrane h Motion of displacer governed by Actuator Inner pressure Etc.

9 Dynamics ele h Pressures In pump chamber p(t) Inlet pressure p 1 Outlet pressure p 2 h Volumes h Pump chamber V 0 h Membrane h Inlet h Outlet h Gas bubbles

10 Differential Equations ele h Volumes h Continuity of volumes (mass)

11 Mass Currents ele

12 Numerical Simulation ele h Final differential equation Solved numerically

13 pv-diagrams ele h Mechanical engineer

14 pv-diagrams ele Druckstutzen Totraum Zylinder Kolben Schubstange Hubvolumen V H p D p 2 Hingang Rückgang p p D p p o p S W i p S Saugstutzen oberer Totpunkt Hubvolumen dv unterer Totpunkt p 1 a. b. oberer Totpunkt V unterer Totpunkt Macroscopic displacement pump h Strong engines drive displacer Negligible feedback of pressure in pump chamber on motion h Pressure-controlled valves h Displacer merely transmits motion

15 pv-diagrams ele Druckstutzen Totraum Zylinder Kolben Schubstange Hubvolumen V H p D p 2 Hingang Rückgang p p D p p o p S W i p S Saugstutzen oberer Totpunkt Hubvolumen dv unterer Totpunkt p 1 a. b. oberer Totpunkt V unterer Totpunkt Macroscopic displacement pump h Pump rate Actuation frequency ν Stroke volume V I V = ν V

16 pv-diagrams Micro-displacement pump h Elastic membranes as displacers h Actuation principles Piezo-electrical Electrostatic Pneumatic Thermopneumatic, etc. h Properties of membrane govern dynamics Rigidity Restoring force, etc. h Pressure-controlled valves h Pressure in pump chamber governed by complicated interplay between Flow dynamics Mechanical motion Motion of displacer

17 pv-diagrams Example: displacement pump actuated by underpressure h Characteristic curve of MDP at A=0 (underpressure off) and A = A o (underpressure on) govern supply and pump phase h Assumption: switch-on (section I) and switch-off (section III) of actuation (underpressure) faster than liquid can react; Change in pressure w/o change in volume

18 pv-diagrams h pv-diagram Amplitude decreases with pressure head p 2 Minimum pressure in pump chamber increases with pressure head p 2

19 pv-diagrams h pv-diagram Fluidic capacitance of valves decreases amplitude Leak rate of valves decreases maximum back pressure

20 Electric Equivalent Conclusions p 1 p 2 Valve with capacitance acts as low-pass filter At high frequencies, whole current goes into capacitive branch - Only motion of valve membrane - No net pumping of current Membranauflage Strömungskanal Silizium Ventilmembran 0,5 mm

21 Electric Equivalent: Passive Valve System h Lumped-element representation of two passive valves Rectification of flow

22 Electric Equivalent: Passive Valve

23 Electric Equivalent: Pump Martin Richter Modellierung und experimentelle Charakterisierung von Mikrofluidsystemen Dissertation, München 1998;

24 6.1. Microdisplacement Pumps 1. Modeling 2. Design Issues 3. Integrated Check Valves 4. Fixed-Geometry Valves 5. Pumping Valve

25 Design Issues h Market requirement Fail-safe pump h Bubble-tolerant pumping of liquids Trapped gas bubbles in pump chamber Highly compressible Malfunctioning of displacement principle Solution: High compression ratios h Clogging Particles carried by liquid Solution: Prefiltering of liquids

26 Fixed-Stroke MDP Debiotech; Switzerland; 1998 h Based in pump design by Harald van Lintel h Integrated particle filter h Membrane moves between two mechanical stops h Drawback: expensive concept

27 Fixed-Stroke MDP Debiotech; Switzerland; 1998 h Membrane moves between 2 mechanical strops fixed amplitude Independent of pressure on inlet and outlet port

28 6.1. Microdisplacement Pumps 1. Modeling 2. Design Issues 3. Integrated Check Valves 4. Fixed-Geometry Valves 5. Pumping Valve

29 Peristaltic Micromembrane Pump h J.G. Smits; MESA; 1983 Piezoelectric micropump for peristaltic fluid displacement ; Patent NL h 3 active displacers (microvalves) h Piezoelectric actuation

30 Milestones Milestones in evolution of microdisplacement pumps 1980 peristaltische Verdrängerpumpe 1988 Verdrängerpumpe mit Rückschlagventilen

31 Displacement Pump with Check Valves h Harald van Lintel et al.; MESA, 1988 A piezoelectric micropump based on micromachining of silicon h Piezoelectrically actuated displacer h Two membrane valves

32 Pump Performance

33 6.1. Microdisplacement Pumps 1. Modeling 2. Design Issues 3. Integrated Check Valves 4. Fixed-Geometry Valves 5. Pumping Valve

34 6.1. Milestones Milestones in evolution of microdisplacement pumps 1980 peristaltische Verdrängerpumpe 1993 ventillose Verdrängerpumpe 1988 Verdrängerpumpe mit Rückschlagventilen

35 Fixed-Geometry Valves

36 Fixed-Geometry Valves h Göran Stemme et al.; KTH; Stockholm, 1993 A novel piezoelectric valve-less fluid pump h Piezoelectrically actuated displacer h Diffuser / nozzle as rectifier Piezoaktor Membran

37 Fixed-Geometry Valves Anders Olson Valve-Less Diffuser Micropumps Dissertation, Stockholm 1998;

38 Fixed-Geometry Valves Anders Olson Valve-Less Diffuser Micropumps Dissertation, Stockholm 1998; Described by set of differential equations:

39 Fixed-Geometry Valves

40 Fixed-Geometry Valves h Thorsten Gerlach et al.; TU-Illmenau; 1995 h Piezoelectrically actuated displacer h KOH-etched diffuser / nozzle

41 Tesla Valve Components: h Bypass at deviating angles Pros: h simple h compact vorwärts Drawbacks: h Low forward/backward ratio h High leak rate rückwärts

42 Tesla Valve Components: h Bypass at deviating angles Pros: h simple h compact vorwärts Drawbacks: h Low forward/backward ratio h High leak rate rückwärts

43 Tesla Valve h Fred Forster et al.; University of Washington; 1998 h Piezoelectrically actuated displacer h Bypass-valves (TESLA-valve) as rectifier

44 6.1. Microdisplacement Pumps 1. Modeling 2. Design Issues 3. Integrated Check Valves 4. Fixed-Geometry Valves 5. Pumping Valve

45 6.1. Milestones Milestones in evolution of microdisplacement pumps 1980 peristaltische Verdrängerpumpe 1988 Verdrängerpumpe mit Rückschlagventilen 1993 ventillose Verdrängerpumpe 1995 Verdrängerpumpe mit Vorwärts- & Rückwärtsgang

46 Bidirectional MDP h R. Zengerle et al; FhG-IFT, 1995 A bidirectional silicon micropump h Electrostatic actuation h Flap valves

47 Bidirectional MDP h R. Zengerle et al; FhG-IFT, 1995 A bidirectional silicon micropump Bewegung Motion der of Ventilklappe flap... m x + k x + D x = f (t) x(f,t) = A(f) e flap i(2πft - α(f) ) Ventilklappe A(f) Silizium 0 x phase shift α (f) π π / 2 0 frequency f

48 Bidirectional MDP driving pressure 0 harmonic actuation 0 valve movement 0 α = 0 valve is closed at: x = 0 phase shift between driving pressure and valve opening α = 3 / 4 π 0 transient valve flow 0 Φ > 0 check valve prevents back flow valve is open when the driving pressure is directed in reverse direction back flow Φ< 0 0 time [unscaled] time [unscaled]

49 Milestones Milestones in evolution of microdisplacement pumps 1996 pumpendes Mikroventil mit Vorwärts- & Rückwärtsgang 1980 peristaltische Verdrängerpumpe 1988 Verdrängerpumpe mit Rückschlagventilen 1993 ventillose Verdrängerpumpe 1995 Verdrängerpumpe mit Vorwärts- & Rückwärtsgang

50 VAMP h M. Stehr et al; HSG-IMIT; 1996 The VAMP - A microvalve with bidirectional pump effect Spannung < 0: Ventil geschlossen Spannung > 0: Ventil ist offen Spannung Mikropumpe pump rate [µl/min] Variable Gap Mechanism 1 --> 2 type A1 voltage 150 V fluid: water 2 --> actuation frequency [Hz] Dichtfläche h p Anschluß 1 Anschluß 2 Grundplatte

51 6.1. Milestones Milestones in evolution of microdisplacement pumps? 1996 pumpendes Mikroventil mit Vorwärts- & Rückwärtsgang 1980 peristaltische Verdrängerpumpe 1988 Verdrängerpumpe mit Rückschlagventilen 1993 ventillose Verdrängerpumpe 1995 Verdrängerpumpe mit Vorwärts- & Rückwärtsgang

52 6.1. Check-Valved Microdisplacement Pumps Common sources of failure h Failure due to gas bubbles Reduced volume of pump chamber Higher compression ratio FhG-IFT: 1996 h Leakage External or integrated particle filters Economical h High fabrication costs h Low production numbers IMM-Mainz Forschungszentrum Karlsruhe

53 6.1. Pressure-Controlled Microdosage Operating principles h Pressurized reservoir h Capillary (glass, silicon-etched) High hydrodynamic resistance h Adjustment of resistance to desired flow rate h Flow rate Constant in time Unchangeable Optional h Active valve to interrupt flow

54 6.1. Implantable Drug-Delivery System Tricumed (Kiel) h Spring mechanism exerts pressure on reservoir h Resistance by long and tiny capillary etched in silicon

55 6.1. Extracorporal Drug-Delivery System Electrochemical Dosage h Pressure generated by electrochemical reaction h No resistance required

56 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

57 6.2. Electric-Field Mediated Pumping h Advantages No moving parts Fabrication of electrodes well compatible with microtechnology Planar flow profiles h Two technological branches Static fields - Charge carriers Interfaces Injected Traveling fields - Gradient of electrical properties Conductivity Permittivity

58 6.2. Electric-Field Mediated Pumping 1. Electro-Osmotic Pumping 2. Static Electrohydrodynamic Pumping 3. Traveling-Wave EHD Pumping

59 Electro-Osmotic Pumping h Electric field h Electric double layer on wall of capillary h Net motion of bulk fluid h Characteristics Flow controlled by electric potential Pulseless pumping Planar flow profile No moving parts

60 Electro-Osmotic Pumping h Speed of flow Speed on mm s -1 time scale h Pump rate Against back pressure p Porosity Tortuosity Detailed treatment of potential

61 Electro-Osmotic Pumping h Equivalent pressure Without back pressure Equivalent flow rate of PDF h Thermodynamic efficiency

62 EOF-Induced Hydraulic Pumping h Tee section h Potential drives flow from (sep) to (g) h Coating of ground channel (g) Continuity of mass Pressure on liquid located in intersection Pumping into free-floating channel (ff)

63 6.2. Electric-Field Mediated Pumping 1. Electro-Osmotic Pumping 2. Static Electrohydrodynamic Pumping 3. Traveling-Wave EHD Pumping

64 Static Electrohydrodynamic Pumping h Charge surplus in insulating liquid h Pair of grid electrodes h Coulomb force on bulk liquid in electric field h Pump rate scales with field strength h Direct conversion of electric into mechanical energy

65 6.2. Electric-Field Mediated Pumping 1. Electro-Osmotic Pumping 2. Static Electrohydrodynamic Pumping 3. Traveling-Wave EHD Pumping

66 Traveling-Wave EHD Pumping h Gradient Conductivity Permittivity h Traveling E-field h Net pumping action Layered fluids Suspended particles Externally generated fluid anisotropy Self-generating fluid anisotropy

67 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

68 Magneto-Hydrodynamic Pumping Lorentz force current h Pressure head h Pump rate

69 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

70 6.4. Acoustic Streaming h Characteristics Active-channel technique Valve-less Ultrasonic h Momentum transfer from channel wall to fluid

71 6.4. Acoustic Streaming h Flexural plate wave (FPW) Traveling mechanical wave Grazing channel wall h Interdigital transducer Thickness of few µm Spacing of electrodes by about 100 µm Frequencies of some MHz

72 6.4. Acoustic Streaming h Velocity profile Evanescent length Flow velocities ver small for y > l evan h For y > l evan : Flow rate widely independent of channel height

73 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

74 6.5. Pumping by Interfacial Tension h Capillary effects h Variations in surface tension h Variations in contact angle h Contact between different phases Transport of discrete sampels - Plugs - Droplets

75 6.5. Pumping by Interfacial Tension 1. Thermocapillary Pumping 2. TCF of Droplets on Free Surfaces 3. Electrowetting 4. Electrocapillary Pumping

76 Thermocapillary Pumping h Thermocapillary flow (TCF) Difference in surface tension Thermal gradient Difference in internal pressures at menisci of liquid plug h Implementation by precisely controlled heaters

77 6.5. Pumping by Interfacial Tension 1. Thermocapillary Pumping 2. TCF of Droplets on Free Surfaces 3. Electrowetting 4. Electrocapillary Pumping

78 TCF of Droplets on Free Surfaces h TCF based delivery of droplets on free surface Chemically patterned substrate Hydrophilic stripes h Equation of motion Direction of flow x Lateral coordinate y Height profile h(x) Temperature profile T(x) Width of stripes w h Flow speed of 600 µm s -1 Viscosity of 5 mpa s Width of 800 µm Temperature gradient of 14.4 K cm -1

79 6.5. Pumping by Interfacial Tension 1. Thermocapillary Pumping 2. TCF of Droplets on Free Surfaces 3. Electrowetting 4. Electrocapillary Pumping

80 Electrowetting h Gradient in local cohesion energy Controlled by voltage on electrodes Voltage-induced surface charges h Gradient in cohesion energy h Net capillary pressure h Pumping

81 6.5. Pumping by Interfacial Tension 1. Thermocapillary Pumping 2. TCF of Droplets on Free Surfaces 3. Electrowetting 4. Electrocapillary Pumping

82 Electrocapillary Pumping h Control of contact angle by voltage h Array of 1000s of hydrophobically coated 3D microchannels h Electrostatic control of interfacial tension Induced image charges Reversible fluid displacement h Electrocapillary pressure

83 1. Microdisplacement Pumps 2. Electric-Field Mediated Pumping 3. Magneto-Hydrodynamic Pumping 4. Acoustic Streaming 5. Pumping by Interfacial Tension 6. Miscellaneous

84 6.6. Miscellaneous h Working diagram Flow rate Backpressure h Maximum flow rate ( p = 0 ) h Maximum backpressure ( I = 0 ) h Working point

85 6.6. Miscellaneous h Comparison of pump principles Maximum backpressure Maximum flow rate