Actuator in a microfluidic system for inducing electroosmotic liquid movement in a micro channel

• US 7,708,872 B2
• Filed: 07/15/2003
• Issued: 05/04/2010
• Est. Priority Date: 07/15/2002
• Status: Active Grant

• Current Assignee: Osmolife A.S.
• Original Assignee: Osmolife A.S.
• Inventors: Heldal, Trond, Mishchuk, Natalyia, Eidsnes, Trond, Ellingsen, Olav
• Primary Examiner(s): NOGUEROLA, ALEXANDER STEPHAN
• Application Number:
  US10/517,835
• Publication Number:
  US 20050230251A1
• Time in Patent Office: 2,485 Days
• Field of Search: 204600-605, 204450-455
• US Class Current: 204/451
• CPC Class Codes: A41D 31/12 Hygroscopic; Water retaining
• CPC Class Codes: B01D 61/00 Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor separation of gases or vapours by diffusion B01D53/22
• CPC Class Codes: B32B 15/04 comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material next to a bituminous or tarry layer B32B11/08; next to a water-setting substance layer B32B13/06; next to a glass layer B32B17/061; next to a cellulosic plastic layer B32B23/042
• CPC Class Codes: B32B 2250/40 Symmetrical or sandwich layers, e.g. ABA, ABCBA, ABCCBA
• CPC Class Codes: B32B 2305/026 Porous
• CPC Class Codes: B32B 2305/188 Woven fabrics
• CPC Class Codes: B32B 2305/20 in the form of a non-woven mat
• CPC Class Codes: B32B 2307/726 Permeability to liquids, absorption
• CPC Class Codes: B32B 2311/00 Metals, their alloys or their compounds
• CPC Class Codes: B32B 2323/04 Polyethylene
• CPC Class Codes: B32B 2325/00 Polymers of vinyl-aromatic compounds, e.g. polystyrene
• CPC Class Codes: B32B 2419/04 Tiles for floors or walls tiles for roofs B32B2419/06
• CPC Class Codes: B32B 2419/06 Roofs, roof membranes
• CPC Class Codes: B32B 2437/02 Gloves, shoes
• CPC Class Codes: B32B 2457/00 Electrical equipment
• CPC Class Codes: B32B 2471/02 Carpets
• CPC Class Codes: B32B 2605/003 Interior finishings
• CPC Class Codes: B32B 2605/08 Cars
• CPC Class Codes: B32B 2605/10 Trains
• CPC Class Codes: B32B 2605/12 Ships
• CPC Class Codes: B32B 2605/18 : Aircraft blades, propellers B32B2603/00
• CPC Class Codes: B32B 2607/00 : Walls, panels
• CPC Class Codes: B32B 27/065 : of foam
• CPC Class Codes: B32B 27/08 : of synthetic resin
• CPC Class Codes: B32B 27/302 : comprising aromatic vinyl (co)polymers, e.g. styrenic (co)polymers
• CPC Class Codes: B32B 27/32 : comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: B32B 3/10 : characterised by a discontinuous layer, i.e. formed of separate pieces of material
• CPC Class Codes: B32B 5/022 : Non-woven fabric
• CPC Class Codes: B32B 5/024 : Woven fabric
• CPC Class Codes: B32B 5/18 : characterised by features of a layer of foamed material
• CPC Class Codes: B32B 5/245 : another layer next to it being a foam layer
• CPC Class Codes: E04B 1/625 : Sheets or foils allowing passage of water vapor but impervious to liquid water; house wraps
• CPC Class Codes: F04B 17/03 : driven by electric motors
• CPC Class Codes: F04B 19/20 : Other positive-displacement pumps

Abstract

The present invention describes an actuator in a microfluidic system for inducing an electroosmotic liquid movement in a microchannel.

Claims

1. A microfluidic system comprising:

a microchannel;

a pump; and

electrical connection means for application of an electric field across a segment of said microchannel,

wherein said segment comprises conducting means,

wherein the conducting means comprises a perm selective ion conducting material, and

wherein a surface portion of said conducting means is curved, or inclined, with respect to the electrical field, whereby, in use, the electric field has a component tangential to the surface portion and a component normal to the surface portion, such that fluid flow is induced in said microchannel segment under the action of secondary electroosmosis.

2. The system as claimed in claim 1, wherein the system is a fluid network formed in a substrate,

wherein the conducting means is disposed in the segment of said microchannel and the electrical connection means comprises electrodes positioned to apply the electric field across the segment, and wherein the space between the conducting means and the walls of the microchannel, and between different conducting means, is between 0 a_char and 2 a_char, the surface of the conducting means being smooth such that the surface irregularities are less than 5% of d_char.

3. The system as claimed in claim 2, wherein the space between the conducting means and the channel walls, and between different conducting means, is between ⅛

a_char and ½

a_char, and wherein the surface irregularities are less than 1% of d_char.

4. The system as claimed in claim 2, wherein the conducting means has the shape of an ellipsoid, sphere, cylinder or elliptical cylinder.

5. The system as claimed in claim 2, wherein the conducting means consists of a small cylinder with the longitudinal axis normal with respect to the fluid flow direction.

6. The system as claimed in claim 2, wherein the conducting means has the shape of a particle with planes which are inclined with respect to the imposed electric field.

7. The system as claimed in claim 6, wherein the particle constituting the conducting means has a size of 0.1 μ

m-5 mm, measured in parallel to the externally imposed electric field.

8. The system as claimed in claim 7, wherein the particle constituting the conducting means has a size of 1.0 μ

m to 500 μ

m measured in parallel to the externally imposed electric field.

9. The system as claimed in claim 6, wherein the angle λ

between the inclined surface portion and the microchannel walls is 1-80 degrees.

10. The system claimed in claim 9, wherein, the angle λ

between the inclined surface portion and the microchannel walls is 30-60 degrees.

11. The system claimed in claim 2, wherein the conducting means contains several layers of conducting particles, spaced both axially and longitudinally in relation to the flow direction.

12. The system claimed in claim 2, wherein the conducting means has a conductivity of at least 5 times the conductivity of said fluid.

13. The system claimed in claim 12 wherein the conducting means has a conductivity of at least 10 times the conductivity of said fluid.

14. The system as claimed in claim 2, wherein the electrodes are arranged upstream or downstream with respect to the microchannel segment.

15. The system as claimed in claim 2, wherein the electrodes are adapted to provide an electrical field parallel to the direction of the transported fluid.

16. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field.

17. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field which has sine, square, triangular or sawtooth shape, or a combination of said shapes.

18. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field where the signal has an offset resulting in a strong and a weak pulse within the signal period, and also a duty-cycle of 29%, so that the strong pulse lasts 29% of the signal period, and where the offset and duty cycle are tuned to give a zero average direct electric signal component.

19. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field where the signal has an overloaded direct component.

20. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field where the electric signal is applied in the potentiostatic regime.

21. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field with a maximum amplitude in V/mm equal to or larger than an amplitude for which the base −

10-logarithm is the linear interval between −

2 and 2, for corresponding a_char, measured in μ

m, for which the base −

10-logarithm is in the linear interval between 0 and 3.7.

22. The system as claimed in claim 2, wherein the electrodes are arranged to apply an alternating field with a signal period in seconds equal to or larger than a period for which the base −

10-logarithm is in the linear interval between −

6 and zero, for corresponding a_char, measured in μ

m, for which the base −

10-logarithm is in the linear interval between 0 and 3.

23. The system as claimed in claim 2, wherein the electrodes are arranged to apply a direct electric field.

24. The system as claimed in claim 2, wherein the distance between each electrode and the conducting means is between 0.1 and 5 mm.

25. The system as claimed in claim 2, wherein the electrodes comprise four electrodes, a first pair of electrodes for inducing the SCR, and a second pair of electrodes for setting ions in the fluid in motion.

26. The system as claimed in claim 25, wherein a first pair of electrodes is arranged upstream or downstream of said segment of the microchannel, anywhere in the microchannel or microfluidic system, and wherein the second pair of electrodes is positioned on each side of said segment.

27. The system as claimed in claim 25, wherein the first pair of electrodes and the second pair of electrodes each applies an alternating electric field, where the two electric fields are out of phase.

28. The system as claimed in claim 2, wherein the conducting means is a portion of the microchannel wall effecting a deflection of the local electrical field so that the field is inclined with respect to the conducting means.

29. The system as claimed in claim 1, arranged to act as a micropump.

30. The system as claimed in claim 29, wherein the system is part of a lab-on-a chip assembly.

31. The system as claimed in claim 29, arranged to provide electronics cooling.

32. The system as claimed in claim 1, arranged to act as a mixer.

33. The system as claimed in claim 1, arranged to provide drug delivery.

34. A method for pumping fluid in a microchannel wherein said microchannel is in a microfluidic system as claimed in claim 1.

35. A system as claimed in claim 1, wherein the conducting means has a characteristic dimension which is its dimension measured parallel to the electric field and which is at least 10 μ

m, and wherein a flow passage is defined between said surface portion of the conducting means and another conducting means or between said surface portion and a portion of the wall of said microchannel, the flow passage having a minimum diameter of at least 1/16 of the characteristic dimension of said conducting means.

36. A system as claimed in claim 35, wherein the characteristic dimension of the conducting means is between 10 μ

m and 500 μ

m.

37. A system as claimed in claim 35, wherein the minimum diameter of the flow passage is between 1/16 and 1 times the characteristic dimension of the said conducting means.

38. A system as claimed in claim 35, wherein the surface of the said conducting means is smooth such that any surface irregularities are less than 5% of the characteristic dimension thereof.

39. A system as claimed in claim 35, wherein the surface of the conducting means is at an angle of between 30 and 60 degrees to the direction of the electric field.

40. A system as claimed in claim 35, wherein the conducting means has a conductivity of at least 5 times that of a liquid which in use is to flow in the microfluidic system.

41. A system as claimed in claim 35, wherein the microfluidic system is arranged on or in a substrate.

42. A system as claimed in claim 35, wherein the electrical connection means comprises a pair of electrodes respectively arranged upstream and downstream with respect to the microchannel segment, and

wherein the distance between each electrode and the said conducting means is between 0.5 and 5 mm.

43. A system as claimed in claim 35, wherein the microchannel has an inlet and an outlet, and the pump is arranged to cause fluid to flow from the inlet, along the microchannel and adjacent to said surface of the conducting means, to the outlet.

44. A method for pumping fluid in a microchannel wherein said microchannel is in a microfluidic system as claimed in claim 1, the method comprising applying said electric field to cause fluid to flow under the action of secondary electroosmosis.

45. A method as claimed in claim 44, wherein an electric field E is applied to said member, and wherein

E>

0.013 V/a_char

where V is the potential drop across the characteristic dimension of the conducting means and a_char is 0.5 times the characteristic dimension.

46. A method for pumping fluid in a microchannel comprising:

the step of applying an electric field to a segment of the microchannel, the segment comprising;

conducting means, the conducting means comprising a perm selective ion conducting material and having a surface portion which is curved or inclined with respect to the electric field, whereby the electric field has a component tangential to the surface portion and a component normal to the surface portion, to cause fluid in said microchannel segment to flow as a result of secondary electroosmosis.

47. The method as claimed in claim 46, wherein said electric field is an asymmetric alternating field.

48. The method as claimed in claim 47, wherein, with one polarity, said electric field is insufficient to cause fluid to flow as a result of secondary electroosmosis.

49. The method as claimed in claim 48, wherein a time integral of said electric field is zero.