U.S. patent application number 10/697412 was filed with the patent office on 2004-07-01 for surface micromachined mechanical micropumps and fluid shear mixing, lysing, and separation microsystems.
Invention is credited to Chen, Ching Jen, Galambos, Paul Charles, Haik, Yousef, Kilani, Mohammad Ibrahim.
Application Number | 20040126254 10/697412 |
Document ID | / |
Family ID | 32659291 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040126254 |
Kind Code |
A1 |
Chen, Ching Jen ; et
al. |
July 1, 2004 |
Surface micromachined mechanical micropumps and fluid shear mixing,
lysing, and separation microsystems
Abstract
A micropump formed from a monolithic body and rotatable disc
contained within the body. The rotatable disc may include one or
more prostrusions for drawing a fluid through an inlet and
expelling it through an outlet. The protrusions may be formed in a
spiral formation, extend as radial vanes from a central point, or
have another configuration. The micropump may have a thickness no
more than about 12 microns. In other embodiments, the rotatable
disk includes one or more gears that utilize positive displacement
to pump fluids. The micrompump may be used with other
microelectromechanical systems and devices.
Inventors: |
Chen, Ching Jen;
(Tallahassee, FL) ; Galambos, Paul Charles;
(Albuquerque, NM) ; Haik, Yousef; (Tallahassee,
FL) ; Kilani, Mohammad Ibrahim; (Amman, JO) |
Correspondence
Address: |
Michael K. Dixon
Akerman Senterfitt
4th Floor
222 Lakeview Avenue
West Palm Beach
FL
33401
US
|
Family ID: |
32659291 |
Appl. No.: |
10/697412 |
Filed: |
October 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60422548 |
Oct 31, 2002 |
|
|
|
Current U.S.
Class: |
417/423.1 |
Current CPC
Class: |
F04C 2/101 20130101;
F04B 19/006 20130101; F04C 2/113 20130101; F04C 2/08 20130101; F04D
13/06 20130101 |
Class at
Publication: |
417/423.1 |
International
Class: |
F04B 017/00 |
Goverment Interests
[0002] Development for this invention was supported in part by U.S.
Department of Energy Contract No. DE-AO385. Accordingly, the United
States Government may have certain rights in this invention.
Claims
We claim:
1. A micropump, comprising: a pumping chamber, wherein said pumping
chamber includes an inlet for drawing fluid therein and an outlet
for expelling said fluid out of said chamber, and structure for
mechanically urging said fluid from said inlet to said outlet,
wherein said micropump is fully monolithic forming a monolithic
body, said pump having a total thickness of no more than about 12
microns.
2. The micropump of claim 1, wherein said pumping chamber includes
at least one rotatable disc in fluid communication with said fluid,
said structure for mechanically urging comprising said rotatable
disc.
3. The micropump of claim 2, wherein the at least one rotatable
disc comprises at least one protrusion extending from the disc.
4. The micropump of claim 3, wherein the at least one protrusion
forms a spiral shaped fluid pathway concentric with the at least
one rotatable disc.
5. The micropump of claim 3, wherein the at least one protrusion
forms a plurality of radial vanes extending from an axis of
rotation of the rotatable disc.
6. The micropump of claim 2, wherein at least one rotatable disc
further comprises a plurality of gear teeth on a side surface of
the rotatable disc.
7. The micropump of claim 6, further comprising at least one
crescent shaped diverter positioned in the pumping chamber
proximate to the at least one rotatable disc, and wherein an inner
surface of the monolithic body includes a plurality of gear teeth
for meshing with the at least one rotatable disc.
8. The micropump of claim 2, further comprising at least one cap
forming a portion of the monolithic body and having an opening
enabling a driving gear to contact the at least one rotatable disc
contained in the monolithic body.
9. The micropump of claim 2, further comprising a labyrinth seal
formed from a first protrusion forming a ring extending generally
vertically from a base layer and surrounding the rotatable disc, a
second protrusion forming a ring extending generally vertically
from the base layer and positioned inside the first protrusion, and
a third protrusion forming a ring extending generally vertically
from the at least one rotatable disc and positioned between the
first and second prostrusions.
10. The micropump of claim 2, further comprising at least one
electrostatic comb drive for rotating the at least one rotatable
disc.
11. The micropump of claim 10, further comprising at least one gear
in contact with the electrostatic comb drive and in contact with
the at least one rotatable disc.
12. The micropump of claim 11, wherein the at least one gear
comprises a 12:1 torque amplification gear train.
13. The micropump of claim 1, wherein said pumping chamber includes
at least two rotatable gears therein, said structure for
mechanically urging comprising said rotating gears.)
14. The micropump of claim 13, wherein the at least two rotatable
gears comprises at least three rotatable gears, wherein a first
rotatable gear is rotatably attached to a pin substantially at a
center point of the base layer and includes a plurality of gear
teeth, a second rotatable gear including a plurality of teeth on a
side surface is positioned between the first rotatable disc and a
side wall of the monolithic body, and a third rotatable gear
including a plurality of teeth on a side surface and having a
diameter larger then the second rotatable gear is positioned
between the first rotatable gear and a side wall of the monolithic
body.
15. A micropump, comprising: a monolithic body formed from between
about two layers of silicon and about five layers of silicon and
having a thickness no more than about 12 microns, wherein the
monolithic body comprises a base layer and side walls forming an
pumping chamber containing at least one rotatable disc; wherein
said pumping chamber includes an inlet for drawing fluid therein
and an outlet for expelling said fluid out of said cavity; and at
least one rotatable disc positioned in the pumping chamber for
drawing a fluid through the inlet and expelling the fluid out of
the outlet.
16. The micropump of claim 15, wherein the at least one rotatable
disc comprises at least one protrusion extending from the disc.
17. The micropump of claim 15, wherein the at least one protrusion
forms a spiral shaped fluid pathway concentric with the at least
one rotatable disc.
18. The micropump of claim 15, wherein the at least one protrusion
forms a plurality of radial vanes extending from an axis of
rotation of the rotatable disc.
19. The micropump of claim 15, wherein at least one rotatable disc
further comprises a plurality of gear teeth on a side surface of
the rotatable disc.
20. The micropump of claim 19, further comprising at least one
crescent shaped diverter positioned in the pumping chamber
proximate to the at least one rotatable disc, and wherein an inner
surface of the monolithic body includes a plurality of gear teeth
for meshing with the at least one rotatable disc.
21. The micropump of claim 15, wherein the at least one rotatable
disc comprises at least three rotatable discs, wherein a first
rotatable disc is rotatably attached to a pin substantially at a
center point of the base layer and includes a plurality of gear
teeth, a second rotatable disc including a plurality of teeth on a
side surface is positioned between the first rotatable disc and a
side wall of the monolithic body, and a third rotatable disc
including a plurality of teeth on a side surface and having a
diameter larger then the second rotatable disc is positioned
between the first rotatable disc and a side wall of the monolithic
body.
22. The micropump of claim 15, further comprising at least one cap
forming a portion of the monolithic body and having an opening
enabling a driving gear to contact the at least one rotatable disc
contained in the monolithic body.
23. The micropump of claim 15, further comprising a labyrinth seal
formed from a first protrusion forming a ring extending generally
vertically from the base layer and surrounding the rotatable disc,
a second protrusion forming a ring extending generally vertically
from the base layer and positioned inside the first protrusion, and
a third protrusion forming a ring extending generally vertically
from the at least one rotatable disc and positioned between the
first and second prostrusions.
24. The micropump of claim 15, further comprising at least one
electrostatic comb drive for rotating the at least one rotatable
disc.
25. The micropump of claim 24, further comprising at least one gear
in contact with the electrostatic comb drive and in contact with
the at least one rotatable disc.
26. The micropump of claim 25, wherein the at least one gear has a
12:1 torque amplification gear train.
27. A method of pumping fluids, comprising: rotating at least one
rotatable disc positioned in a pumping chamber of a miropump formed
from a monolithic body having a thickness no more than about 12
microns and containing the at least one rotatable disc; wherein a
fluid is drawn through an inlet in the pumping chamber and expelled
from an outlet in the pumping chamber.
28. The method of claim 27, wherein rotating at least one rotatable
disc comprises rotating at least one disc comprising at least one
protrusion extending from the disc.
29. The method of claim 28, wherein rotating at least one rotatable
disc having at least one protrusion extending from the disc
comprises rotating at least one disc having a spiral shaped
protrusion extending from the disc.
30. The method of claim 28, wherein rotating at least one rotatable
disc having at least one protrusion extending from the disc
comprises rotating at least one disc having a spiral shaped
protrusion extending from the disc.
31. The method of claim 27, wherein rotating at least one rotatable
disc is accomplished using at least one electrostatic comb
drive.
32. The method of claim 27, wherein rotating at least one rotatable
disc drives at least one idler gear positioned in the pumping
chamber of the at least one rotatable disc.
33. The method of claim 27, wherein rotating the at least one
rotatable disc comprises rotating at least three gears in the
pumping chamber.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/422,548 entitled "SURFACE MICROMACHINED
MICROPUMPS AND FLUID SHEAR MIXING, LYSING, AND SEPARATION
MICROSYSTEMS", filed on Oct. 31, 2002, which is incorporated by
reference into the current application in its entirety.
FIELD OF THE INVENTION
[0003] The invention is directed generally to micromachined
mechanical devices, and more particularly, to micromachined pumps
capable of pumping fluids at micro and nano scales and related
shear driven mixing, lysing, and separation devices.
BACKGROUND
[0004] Miniature pumps, hereafter referred to as micropumps, are in
great demand for environmental, biomedical, medical, biotechnical,
printing, analytical instrumentation, and miniature cooling
applications. Other typical applications include use of micropumps
in drug delivery systems, including both transdermal and impantable
systems, micro total analysis systems, and electronic cooling
devices. Just as in lager-scale applications, various pump designs
are required for different micropump systems. For certain
applications in which space is at a premium and in which fluid
volumes are small, pumps with minimal dimensions, particularly pump
cavity dimensions, are of interest.
[0005] Currently available micropumps typically are fabricated
using etched silicon or glass substrates that are bonded together
and utilize an actuation mechanism that most often is a
piezo-electric bimorph, or in the case of electrokinetic
micropumps, embedded electrodes. Typically, each component is
individually bonded to other components to form a pump. As a
result, this process is labor intensive and expensive. The
resulting high price of the micropumps may preclude profitable
commercialization of these micropumps. Moreover, the bonding of a
plurality of components renders these pumps susceptible to
reliability problems, such as separation of the bonds.
[0006] Thus, a need exists for an efficient, inexpensive micropump
that is capable of being produced in mass quantities with little or
no assembly required.
[0007] In addition, many fluids of interest in microfluidic
applications are biological or contain complex chemical mixtures.
Such solutions often must be analyzed or manipulated to separate a
constituent of interest or to mix in chemical reagents. Because the
flow in microfluidic devices essentially is laminar having a low
Reynolds number, it is difficult to complete these tasks using the
turbulence and inertia based methods effective at larger
scales.
[0008] Also, in certain applications it can be necessary to lyse
cells in order to access cellular constituents (e.g. DNA or RNA).
Typically, cell lysis is accomplished using a centrifuge or
sonication in a bead solution. However, neither method is readily
scaleable to microdevices. Therefore, a need exists for
microfluidic cell lysis, mixing and separation devices.
SUMMARY OF THE INVENTION
[0009] This invention is directed to micropumps formed from
monolithic structures having thicknesses of no more than about 12
microns and include pumping chambers with inlets and outlets, and
structures for mechanically urging fluid from the inlet to the
outlet. The micropumps may be capable of pumping fluids on the
micro and nano scales. Each of these pumps may be capable of being
produced complete with the actuation and transmission mechanisms in
batches of hundreds to thousands per batch using surface
micromachining. Consequently, pumps according to this invention can
provide increased reliability and can be produced with little, if
any, costs associated with manual assembly.
[0010] Micropumps embodiments include viscous micropumps and ring
gear micropumps. The viscous micropumps include spiral micropumps,
centrifugal micropumps, and micropumps without spiral protrusions,
which are referred to as Von Karman micropumps. The ring gear
micropumps include crescent micropumps and planetary gear
micropumps.
[0011] According to one aspect of this invention, a micropump,
referred to as a spiral micropump, includes a rotatable disk and a
stationary plate. A spiral protrusion is attached to the rotatable
disk and draws a fluid through an inlet port in the micropump. The
fluid passes through a spiral channel formed by the spiral
protrusion and between the rotatable disk and stationary plate. The
fluid is expelled through an outlet port. The rotatable disk and
stationary plate may be sealed with a variety of seals, which may
include, but are not limited to, a seal resembling a labyrinth or a
housing.
[0012] In another embodiment of this invention, a micropump is
configured identically to the spiral micropump, but does not
include the spiral protrusion. This micropump is referred to as the
Von-Karman pump and operates using the viscous drag that develops
in the fluid in the micropump as the rotatable disk rotates. This
embodiment is advantageous because this micropump is not limited by
the small aspect ratio that characterizes surface micromachined
devices.
[0013] In yet another embodiment of this invention, a micropump is
configured to include a radial array of vanes attached to a gear
disk that defines an impeller of the micropump. This micropump is
referred to as the centrifugal micropump.
[0014] Certain pumping devices described herein can generate a
shear field. Such a field can be used to lyse cells at the
microscale where centrifugation and sonication are less effective.
Also, by positioning different solution constituents at different
streamlines in the shear field, cells can be separated and eluted
at the end of the micropump according to their position in the
shear field. Those constituents closest to the moving plate will be
eluted first and those constituents closest to the stationary plate
will be eluted last. This type of constituent separation can be
enhanced by operating the shear pump against a pressure gradient.
Methods of manipulating constituents as to their location in
different layers of a varying cross-stream shear field include
but-are not limited to electrical fields (AC and DC), hydrodynamic
forces, sedimentation forces, thermal gradients and diffusion.
[0015] Other embodiments of this invention include ring gear
micropumps. One type of ring gear micropump is a crescent micropump
that is formed from a ring gear having a plurality of teeth on its
inner and outer surfaces. The teeth on the inner surface are
configured to mesh with an idler positioned within the inner
aspects of the ring gear, and the teeth on the outer surface are
configured to mesh with teeth on a transmission gear used to drive
the ring gear. The micropump includes an inlet port and an outlet
port in the inner aspects of the ring gear. The crescent micropump
further includes a crescent shaped component for positioning the
idler and the ring gear relative to each other. The crescent
micropump operates by rotating the ring gear using, for instance, a
transmission gear, which in turn causes the idler to rotate. The
rotating idler draws a fluid from the inlet port and expels the
fluid through the outlet port.
[0016] In yet another embodiment of a ring gear micropump, the
micropump, referred to as a planetary gear micropump, is composed
of a ring gear having a sun gear and first and second planetary
gears positioned in interior aspects of the ring gear. The ring
gear has a plurality of teeth positioned on an inner surface of the
ring gear that mesh with the planetary gears. The sun gear is
coupled to a pivot positioned eccentrically within the sun gear,
and the diameter of the first planetary gear may be larger than the
diameter of the second planetary gear.
[0017] This micropump is operable by rotating the ring gear, which
causes the planetary and sun gears to rotate. The eccentric pivot
causes the sun gear to rotate around the pivot and oscillate. This
oscillation creates successive increasing and decreasing volumes on
either side of the sun gear and the first and second gears, which
draws fluid into the micropump through an inlet port and expels
fluid out of the micropump through an outlet port.
[0018] The various gearing systems and mechanisms of the ring gear
micropumps can be used to move fluids continuously through the
micropump using positive displacement. The gears may also act to
lyse cells, which is also referred to as cell lysis, when a
cellular solution is pumped by the gears.
[0019] An advantage of micropumps according to the invention is
that the micropumps have a monolithic body. For example, these
pumps may be constructed using Sandia National Laboratories'
Ultraplanar Multi-level MEMS Technology (SUMMiT.TM.) process or
similar process. As the micropumps formed by this process are
monolithic, the micropumps do not require additional assembly. The
SUMMiT.TM. process uses three our four movable polysilicon layers
together with one stationary polysilicon layer. The polysilicon
layers are separated from adjacent layers by sacrificial oxide
layers.
[0020] Another advantage of these pumps is their ability to operate
in micro and nano scales.
[0021] Yet another advantage of this invention is that the
micropumps can operate without valves, thereby making the
micropumps more reliable and having less components as compared to
micropumps having valve requirements. Furthermore, because the pump
is continuous flow rather than pulsatile flow, a continuously and
smoothly varying flow rate may be generated without use of
microfluidic capacitors to dampen the oscillations.
[0022] These and other features and advantages of the present
invention will become apparent after review of the following
drawings and detailed description of the disclosed embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are incorporated in and
form a part of the specification, illustrate preferred embodiments
of the presently disclosed invention(s) and, together with the
description, disclose the principles of the invention(s). These
several illustrative figures include the following:
[0024] FIG. 1 is a schematic perspective illustration of a partial
cutaway of a spiral micropump;
[0025] FIG. 2 is an exemplary spiral micropump coupled to a typical
electrostatic comb drive system for supplying rotational motion to
the micropump;
[0026] FIG. 3 is a cross-sectional view of the spiral micropump of
FIG. 2;
[0027] FIG. 4 is a picture of a spiral micropump expelling a
droplet of fluid under experimental conditions;
[0028] FIG. 5(a) is a cross-sectional view of spiral micropump of
FIG. 2;
[0029] FIG. 5(b) is a detail view of a portion of the spiral
micropump of FIG. 5(a);
[0030] FIG. 6(a) is a top view of the spiral micropump of FIG. 2
including a housing seal;
[0031] FIG. 6(b) is a cross-sectional view taken at section line
A-A in FIG. 6(a);
[0032] FIG. 6(c) is a cross-sectional view taken at section line
B-B in FIG. 6(b);
[0033] FIG. 6(d) is a detail view of a portion of the spiral
micropump shown in FIG. 6(a);
[0034] FIG. 7 is a schematic illustration of a crescent
micropump;
[0035] FIG. 8 is a picture of two exemplary crescent micropumps,
the micropump on the left side having a top cover and the micropump
on the right side without a top cover;
[0036] FIG. 9 is a cross section of the crescent micropump of FIG.
7;
[0037] FIG. 10 is a schematic illustration of a planetary gear
micropump;
[0038] FIG. 11 is a collection of schematic illustrations of the
micropump of FIG. 10 in various orientations during operation;
[0039] FIG. 12(a) is a cross-sectional top view of a Von Karman
micropump;
[0040] FIG. 12(b) is a cross-sectional front view of the Von Karman
micropump of FIG. 12(a); and
[0041] FIG. 13 is a cross-sectional top view of a centrifugal
micropump.
DETAILED DESCRIPTION OF THE INVENTION
[0042] This invention includes numerous embodiments of monolithic
micropumps that are capable of pumping fluids and are configured
for use in microelectromechanical systems (MEMSs). These micropumps
are monolithic structures having thicknesses of no more than about
12 microns and include pumping chambers with inlets and outlets,
and structures for mechanically urging fluid from the inlet to the
outlet. As used herein, the term monolithic refers to the resulting
structure obtained from an integrated circuit formation process,
which generally comprises a plurality of lithography, etching, and
deposition steps. Thus, no assembly steps, such as bonding steps,
are needed as the various layers are inherently self-assembled.
Although the micropumps according to the invention are fully
monolithic, use of this term does not preclude substantially free
movement of one layer relative to another layer, such as in the
case of a spinning rotatable disk.
[0043] Micropumps according to the invention have a total thickness
of no more than about 12 microns. Thicknesses of the micropumps
described herein are less than the thicknesses of conventional
piezoelectric driven membrane pumps having, which have thicknesses
of between about 80 microns and about 100 microns. The relatively
high efficiency of pumps having thicknesses of 12 microns or less
is an unexpected result because as the thickness is reduced to no
more than 12 microns, the Reynolds number decreases and the
effective viscosity increases. Therefore, it would be expected that
the low Reynolds number would render pumps according to the
invention ineffective. However, it has been found for thickness of
no more than about 12 microns, that viscous effects actually begin
aiding pumping as the mechanism for pumping is based on viscous
drag and not on inertial effects.
[0044] Embodiments of these micropumps, which are described in
detail below, include viscous micropumps formed from rotatable
discs and ring gear micropumps. The viscous micropumps include a
spiral micropump, a Von Karman micropump, which is a spiral
micropump without a spiral protrusion, and a centrifugal micropump.
The ring gear micropumps include a crescent micropump and a
planetary gear micropump. The micropumps may be actuated
electrostatically using on-chip micro-engines. Slightly larger
meso-scale versions of these pumps can be fabricated using more
conventional machining techniques and powered using small electric
motors.
[0045] These micropumps may be used in a variety of applications.
For instance, these micropumps may be included as a component of an
integrated circuit system and be placed in communication with
microprocessors, amplifiers, actuators, voltage controllers for the
actuators, sensors and other appropriate devices. These micropumps
may be used as a component in microlabs, which may also be referred
to as a lab-on-a-chip, in medical devices, such as insulin pumps,
chemical synthesis, for cooling systems in integrated circuits, and
other applications.
[0046] Each of these embodiments is preferably formed using surface
machining processes capable of fabricating hundreds or thousands of
devices together with no part assembly being required. Surface
micromachined devices are planar in nature, and are characterized
by very shallow depths, such as, but not limited to, no more than
about 12 microns. The micropumps may be fabricated using Sandia
National Laboratories' Ultraplanar Multi-level MEMs Technology
(SUMMiT.TM.) process or similar process. The SUMMiT.TM. process
uses three or four movable polysilicon layers together with one
stationary polysilicon layer ("Poly"). The polysilicon layers are
separated from adjacent layers by sacrificial oxide layers that are
removed during the final etch release process step. See e.g. I-C
Compatible Polysilicon Surface Micromachining by J. J. Sniegowski
and M. P. de Boer, Annu. Rev. Mater. Sci. 2000, 30:299-333.
[0047] 1. Monolithic Viscous Micropumps
[0048] A. Spiral Micropump
[0049] One embodiment of this invention, as shown in FIG. 1 and
referred to hereinafter as the spiral micropump, includes a
rotatable disk 12 coupled to a stationary plate 14 using a pin
joint 16, which is positioned generally within the center of
stationary plate 14. Rotatable disk 12 includes a spiral protrusion
21 that directs fluids from an inlet port 18 to an outlet port 20.
Stationary plate 14 is a generally flat shaped component and
includes two generally flat surfaces. One of these flat surfaces is
positioned in close proximity to spiral protrusion 21. In one
embodiment, the combined thickness of rotatable disk 12, stationary
plate 14, and spiral protrusion 21 is no more than about 12
microns. In at least one embodiment, the spiral micropump may be
formed from as few as 2 silicon layers. However, the sprial
micropump may be formed from between 3 and 5 silicon layers as
well.
[0050] In another embodiment, the micropump contains the components
described above; however, spiral protrusion 21 is not included.
Rather, this embodiment, which is referred to as a viscous
micropump, pumps fluids using viscous phenomena as the driving
mechanism.
[0051] During operation, a fluid enters inlet port 18 and flows
through spiral channel 22 to outlet port 20. Spiral channel 22 is
formed by spiral protrusion 21 that is bounded by stationary plate
14 on one side and rotatable disk 12 on the other side. Fluids,
with or without suspended particles, are drawn through spiral
channel 22 as a result of a velocity profile created by rotatable
disk 12 rotating around pin joint 16. The velocity profile consists
of fluids having velocities that vary between about zero at the
surface of stationary plate 14 and a velocity approximately equal
to the rotational velocity of the rotatable disk at a location
proximate to the inner surface 24 of rotatable disk 12. Viscous
stresses on upper surfaces of the spiral channel 22 allow fluids to
be transported against an imposed pressure difference. The spiral
micropump is capable of expelling a sufficient amount of fluids to
produce droplets of fluid visible to the unassisted human eye, as
shown in FIG. 4.
[0052] Rotatable disk 12 may be rotated through numerous methods.
In one embodiment, rotatable disk 12 is rotated using an
electrostatic comb drive microengine, as shown in FIG. 2, that
provides continuous mechanical power transmitted to rotatable disk
12 through a transmission 26, which may be a torque amplification
gear mechanism operating at 12:1. Transmission 26 includes an
output gear 28 that includes a plurality of teeth positioned on a
perimeter 30 of output gear 28. The teeth on output gear 28 mesh
with the teeth located on the perimeter 30 of rotatable disk
12.
[0053] FIG. 3 is a cross-sectional view of the spiral micropump
taken through the centerline to illustrate the relationships
between the layers forming the spiral micropump. Rotatable disk 12
is formed from a polysilicon layer, which is identified as Poly 4,
and stationary plate 14 is formed from another polysilicon layer,
which is identified as Poly 0. Spiral protrusion 21 is formed from
three polysilicon layers, which are identified as Poly 1, Poly 2,
and Poly 3, and is anchored to rotatable disk 12. This
configuration leaves a small gap between spiral protrusion 21 and
stationary plate 14.
[0054] The spiral micropump may be contained using a variety of
seals or components for preventing fluids from leaking out. In one
embodiment, seal 32 resembles a labyrinth seal positioned around
the periphery of the spiral micropump, as shown in FIG. 5. The seal
32 can be formed from three polysilicon layers. In one embodiment,
the three layers may be concentric and cylindrical. However, the
layers are not limited to this shape or number. Rather, seal 32 may
be formed from any other number of layers or alternative
shapes.
[0055] The three layers are positioned between the rotatable disk
and the fixed plate. The inner and outer layers form protrusion
extending from the stationary plate 14 and Poly 0, and the middle
layer forms a protrusion extending from the rotatable disk 12 and
Poly 4 and positioned between the protrusions extending from the
stationary plate 14. The middle layer rotates with the rotatable
disk 12. A small clearance gap is located between adjacent layers.
As shown in FIG. 5, the three cylindrical layers are defined by
interconnected layers designated as Poly 1, Poly 2, and Poly 3.
[0056] In another embodiment, as shown in FIG. 6, seal 32 may be a
housing that nearly entirely encloses rotatable disk 12, stationary
plate 14, and spiral protrusion 21, except for a small opening
through which transmission 26 contacts rotatable disk 12. FIG. 6(b)
is a cross-sectional view of the spiral micropump and shows seal 32
formed from a top cover 36 that is formed from a Poly 4 layer, a
side wall 38 that is formed from Poly 1, Poly 2 and Poly 3 layers,
and a bottom cover 40 that is formed from a Poly 0 layer. Top cover
36 and side wall 38 form a closed chamber that surrounds rotatable
disk 12 and stationary plate 14. In this embodiment, spiral
protrusion 21 is defined by the Poly 1 and 2 layer and is attached
to rotatable disk 12. The Poly 1 layer may also include dimples
that create protrusions below the spiral protrusion 21 to improve
the seal between the poly layers forming spiral protrusion 21. Seal
32 may further include a cantilever seal 42, as shown in FIG. 6(d),
for reducing leakage from the bottom of pumping chamber 44 through
an opening. Seal 32 may also include a dimple 48, which may be
formed by a dimple cut in the Poly 3 layer, for minimizing leakage
from the top of pumping chamber 44 through a window.
[0057] Micropumps according to the invention may also be used to
lyse cells by pumping a cellular solution at a shear rate
sufficient to destroy the cell membrane. In addition, the shear
field created in the spiral or viscous micropumps can be used to
spatially separate constituents as the constituents are eluted from
the micropump.
[0058] In operation, a liquid containing cells is introduced at the
inlet 18 of the spiral or viscous micropump. As the rotatable disk
12 is turned rapidly, the solution is pumped towards outlet 20, and
a shear field is developed between rotatable disk 12 and stationary
plate 14 that is proportional to the velocity of the rotating disk.
If the resulting shear stress induced in the cells in solution is
high enough, the cell membrane of the cells will rupture, which
results in lysis of the cells. After the cells rupture, the fluid
stream will continue to be pumped out of spiral channel 22 through
outlet 20. Cellular constituents, such as DNA and cell membrane
material, may be separated while flowing through spiral channel 22,
as described in detail below.
[0059] The shear field developed by a viscous micropump may be used
to separate constituents in a fluid stream flowing through a
channel fed by the pump. Separation of the constituents is possible
due to a variation in velocity of the fluid across the fluid
stream. In the simplest case, the fluid near rotatable disk 12 is
moving at approximately the velocity of the rotatable disk 12, and
the fluid near the stationary plate 14 has a velocity approximately
equal to zero, which is the velocity of stationary plate 14. The
velocity varies linearly between zero and the moving disk velocity
as the fluid stream is traversed from the stationary plate to the
rotatable disk. Because the flow field through channel 22 is
essentially laminar, constituents stay in layers, or lanes, as the
constituents move through the micropump. The constituents closest
to rotatable disk 12 are expelled from the micropump ahead of the
slower moving constituents that are located closer to stationary
plate 14. Because of this phenomena, constituents are separated in
space and time in an exit channel as a result of the constituents
occupying different layers within the fluid flow. The separation
between constituents may be increased by increasing the speed of
the micropump. For best operation, different constituents should be
positioned at different locations across channel 22 in the flow
stream. In some cases, such a constituent configuration occurs
naturally because of the shear field. Different constituents occupy
different lamina because of the way the constituents respond to the
shear field.
[0060] Constituents may also be positioned in different fluid
lamina using other methods.
[0061] For instance, an electrode or an array of electrodes can be
incorporated in stationary plate 14 to apply an electric field
consisting of alternating or direct current (AC or DC,
respectively), to the electrode or electrodes while rotatable disk
12 is grounded. Rotatable disk 12 may be grounded through the drive
mechanism. This configuration produces an electric field that is
generally perpendicular to the direction of fluid flow. The
solution constituents are positioned differently within the
cross-stream field and are therefore, in different fluid lamina.
The position of the solution constituents is dictated by the
constituents' electrophoretic or dielectrophoretic properties. The
electrophoretic properties determine the DC signal response, and
the dielectrophoretic properties determine the AC signal response.
Constituents positioned in lamina nearest rotating disk 12, which
is the ground, travel further through the micropump in a particular
time period than other fluids.
[0062] Other methods of establishing cross-stream fields include
sedimentation processes in which different specific gravity
constituents are positioned at different locations in a
cross-stream gravity field, and chemical affinity processes,
whereby a wall of a micropump, whether stationary or rotating, is
coated which causes chemical constituents to be adsorbed and
removed from the fluids at different rates. Differences in
diffusion coefficients correlating with different constituents
causes some separation of constituents but also leads to broadening
of the bands of eluted constituents as the fluids are expelled from
the micropump, thereby reducing resolution.
[0063] These separation effects can be enhanced when the pump is
operated against a pressure gradient, such as where the pressure at
outlet 20 is greater than the pressure at inlet 18. This pressure
gradient forces the fluids against the flow induced by rotatable
disk 12. The fluid near stationary plate 14 is more affected by the
pressure gradient than the fluid in streamlines located near
rotatable disk 12. If the pressure gradient is sufficient, the
fluid near stationary plate 14 will be pushed backward against the
shear driven flow. This causes the solution constituents to be
separated more widely because while the fluid near the stationary
wall is pushed back towards inlet 18 by the pressure gradient,
solution constituents near rotatable disk 12 are pulled in the
usual flow direction.
[0064] While these processes produce constituent separation, the
same processes may also be used for constituent mixing. Enhanced
diffusion (dispersion) in the shear field occurs when the
constituent concentration gradient across the stream due to along
stream convection reduces the mixing time required. Another method
of mixing constituents is to stop the flow at outlet 20. In this
embodiment, a re-circulation system is established in which the
fluids first travel through the micropump in the forward direction
along rotatable disk 12 and then travel back along stationary plate
14 due to the pressure driven flow in the low velocity streamlines
positioned closely to stationary plate 14. This re-circulation
region is an effective microfluidic mixer.
[0065] B. Von Karman Micropump.
[0066] In another embodiment of this invention, a micropump, which
is referred to as a Von Karman micropump is shown in FIGS. 12a and
12b. The Von Karman micropump is composed of a rotatable plate 82
that rotates on top of a parallel fixed plate 84 about pin joint
85. A cavity 86 is formed between the disk 82 and the plate 84 and
for pumping the fluid. The fixed plate 84 has an inlet port 88 and
an outlet port (not shown). The viscous forces caused by the
rotating flat disk 82 carry the fluid from the inlet port 88 to the
outlet port.
[0067] FIG. 12b illustrates a Von Karman micropump that may be
formed using the SUMMiT-V.TM. process and may have a thickness no
more than about 12 microns. In at least one embodiment, the Von
Karman micropump may be formed from as few as 2 silicon layers.
However, the Von Karman micropump may be formed from between 3 and
5 silicon layers as well. The fixed plate 84 may be formed in Poly
0 and the inlet port 88 and may be created by a Bosch etch through
the wafer. The rotatable plate 82 may be formed in the Poly 3 and
may create a cavity 86 whereby the rotatable plate 82 is about six
microns from the fixed plate 84. The rotatable plate 82 may be
driven using gear teeth on the outer surface of the rotatable plate
82. The Poly 4 layer may form a top cover 90 that may be connected
seamlessly to the housing walls 92, which may be anchored to the
ground. The housing walls 92 and the Poly 4 top cover 90 provide a
continuous seal around the entire micropump, except for the area
proximate to the driving gears 94. Surface tension forces prevent
the fluid in the micropump from leaking through the very small gap
proximate to the drive gears 94.
[0068] C. Centrifugal Micropump
[0069] FIG. 13 shows yet another embodiment of a viscous drag
micropump and is referred to as a centrifugal micropump. The
centrifugal micropump may have a thickness no more than about 12
microns. In at least one embodiment, the centrifugal micropump may
be formed from as few as 2 silicon layers. However, the centrifugal
micropump may be formed from between 3 and 5 silicon layers as
well. The configuration of the centrifugal micropump resembles the
spiral micropump; however, the centrifugal micropump does not
include a spiral protrusion. Rather, the centrifugal micropump
includes a radial array of vanes 96 attached to a rotatable disk
98. The rotatable disk 98 functions as an impeller of the
centrifugal micropump.
[0070] 2. Monolithic Ring Gear Micropumps
[0071] A. Crescent Micropump
[0072] The invention also includes planar gear pumps, such as the
crescent micropump and the planetary gear micropump, for pumping
fluids and for lysing cells. The planar gear micropumps may have
thicknesses no more than about 12 microns. In at least one
embodiment, the planar gear micropump may be formed from as few as
2 silicon layers. However, the planary gear micropump may be formed
from between 3 and 5 silicon layers as well. The planar gears may
be used to lyse cells, as described in detail above, by pumping a
cellular solution through the micropump. The crescent micropump, as
shown in FIG. 7, includes a ring gear 48 having a plurality of
teeth on its outer and inner surfaces. In at least one embodiment,
the ring gear 48 may be formed from three or four layers of silicon
and a base layer 49 may be formed from one or more layers of
silicon. The teeth on the outer surface mesh with teeth on a drive
gear, and the teeth on the inner surface mesh with an idler 52. In
this configuration, a drive gear rotates and causes ring gear 48 to
rotate, which in turn causes idler 52 to rotate. This action causes
a fluid to be drawn into interior aspects of ring gear 48 from
inlet 54 and expelled through outlet 56. Idler 52 and ring gear 50
are kept in position with a crescent diverter 58.
[0073] FIG. 8 depicts two crescent micropumps 51 and 53, micropump
51 having a top cover in place and micropump 55 having the top
cover removed. The crescent micropumps can be driven with torsional
ratchet actuators 60, or other structure for providing rotational
motion to micropumps. Torsional ratchet actuators are independently
attached to transmissions 62 for applying rotational motion to ring
gears 48. The crescent micropump on the right may have a cover
installed using a post fabrication technique such as, but not
limited to, anodic bonding.
[0074] FIG. 9 depicts a cross-section of ring gear 48 including a
seal 64 positioned around pumping chamber 66, which is formed as an
integral part of ring gear 48. Seal 64 resembles a labyrinth seal
and is formed from a dimple in the Poly 1 layer. In addition, seal
64 includes a plurality of rollers that are created using a pin
joint process and act as axial bearings that support the walls of
the seal during rotation and thus minimize friction.
[0075] B. Planetary Gear Micropump
[0076] Yet another embodiment of this invention, as shown in FIG.
10 and referred to hereinafter as a planetary gear micropump, may
be used to pump fluids or lyse cells. The planetary gear micropump
may have a thickness no more than about 12 microns. In at least one
embodiment, the planetary gear micropump may be formed from as few
as 2 silicon layers. However, the planetary gear micropump may be
formed from between 3 and 5 silicon layers as well. The micropump
includes a ring gear 68 mechanically coupled to a sun gear 70 using
first and second planetary gears, 72 and 74 respectively. Sun gear
70 pivots eccentrically around pivot 76 that is not in the center
point of sun gear 70. Ring gear 68 drives the rotation of first and
second planetary gears 72 and 74 and sun gear 70. The diameter of
the first planetary gear 72 is larger than the diameter of the
second planetary gear 74, or vice versa, and the sum of the
diameters of sun gear 70 and first and second planetary gears 72
and 74 is approximately equal to the pitch diameter of ring gear
68. The ring gear 68 may be formed from three or more layers of
silicon. A base layer may be formed from one or more layers of
silicon.
[0077] Operation of the planetary gear micropump is shown in FIG.
11. As ring gear 68 rotates, first and second planetary gears 72
and 74 rotate around sun gear 70. Rotation of first and second
planetary gears 72 and 74 around sun gear 70 causes sun gear 70 to
rotate because the gap 78 between the right side of sun gear 70 and
the inner wall of ring gear 68 is smaller than the gap 80 between
the left side of sun gear 70 and the inner wall of ring gear 68. As
sun gear 70 rotates around pivot 76, gap 78 continues to shrink in
size and sun gear is forced to make a full revolution around pivot
76. This eccentric rotation of sun gear 70 produces successive
increasing and decreasing volumes on either side of sun gear 70 and
the first and second gears 72 and 74. Such action provides pumping
action necessary for the pump to operate.
[0078] The foregoing is provided for purposes of illustrating,
explaining, and describing embodiments of this invention.
Modifications and adaptations to these embodiments will be apparent
to those skilled in the art and may be made without departing from
the scope or spirit of this invention.
* * * * *