U.S. patent application number 12/964057 was filed with the patent office on 2011-06-02 for non-invasive acoustic technique for mixing and segregation of fluid suspensions in microfluidic applications.
This patent application is currently assigned to Los Alamos National Security, LLC. Invention is credited to Peter A. Adcock, Gregory Kaduchak, Dipen N. Sinha, Naveen Neil Sinha.
Application Number | 20110127164 12/964057 |
Document ID | / |
Family ID | 35732420 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110127164 |
Kind Code |
A1 |
Sinha; Naveen Neil ; et
al. |
June 2, 2011 |
NON-INVASIVE ACOUSTIC TECHNIQUE FOR MIXING AND SEGREGATION OF FLUID
SUSPENSIONS IN MICROFLUIDIC APPLICATIONS
Abstract
The present invention includes an apparatus and corresponding
method for fluid flow control in microfluidic applications. A
microchamber, filled with a fluid, is in fluid contact with a
flexible plate. A transducer is acoustically coupled to the
flexible plate. A function generator outputs a signal to excite the
transducer, which in turn induces drumhead vibration of the
flexible plate, creating a flow pattern within the fluid filled
microchamber.
Inventors: |
Sinha; Naveen Neil; (Los
Alamos, NM) ; Kaduchak; Gregory; (Los Alamos, NM)
; Sinha; Dipen N.; (Los Alamos, NM) ; Adcock;
Peter A.; (Campbellsville, KY) |
Assignee: |
Los Alamos National Security,
LLC
Los Alamos
NM
|
Family ID: |
35732420 |
Appl. No.: |
12/964057 |
Filed: |
December 9, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10958886 |
Oct 5, 2004 |
|
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12964057 |
|
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60592082 |
Jul 29, 2004 |
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Current U.S.
Class: |
204/451 |
Current CPC
Class: |
F04F 7/00 20130101; B01F
11/0045 20130101; B01L 3/5027 20130101; B01F 13/0059 20130101; Y10T
436/2575 20150115; B01F 11/0266 20130101; F04B 19/006 20130101 |
Class at
Publication: |
204/451 |
International
Class: |
C25B 7/00 20060101
C25B007/00 |
Goverment Interests
STATEMENT REGARDING FEDERAL RIGHTS
[0002] This invention was made with government support under
Contract No. W-7405-ENG-36 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A method for fluid flow control in microfluidic applications,
comprising: (a) outputting a signal from a function generator to a
transducer acoustically coupled to a flexible plate, and (b)
inducing drumhead vibration of said flexible plate in fluid contact
with one or more microchambers with said signal, creating one or
more flow patterns within said fluid.
2. The method of claim 1, further including adding a waveform of
high harmonics to said signal to increase the flow speed of said
fluid.
3. The method of claim 1, further including modulating an amplitude
of said signal to control the flow speed of said fluid.
4. The method of claim 1, further including sweeping through a
frequency range of said signal to mix said fluid.
5. The method of claim 1, further including separating particles of
differing physical properties suspended in said fluid with said one
or more flow patterns.
6. The method of claim 1, further including altering an inner
surface of said microchamber to create said one or more flow
patterns.
7. The method of claim 1, further including altering said one or
more microchamber dimensions to vary a flow speed of said
fluid.
8. The method of claim 1, further including varying the frequency
of said signal to create said one or more flow patterns.
9. A method for fluid flow control in microfluidic applications,
comprising: (a) outputting a signal from a function generator to
one or more flexible transducers in fluid contact with one or more
microchambers, and (b) inducing drumhead vibration of said one or
more flexible transducers in fluid contact with one or more
microchambers with said signal, creating one or more flow patterns
within said fluid.
10. The method of claim 9, further including adding a waveform of
high harmonics to said signal to increase the flow speed of said
fluid.
11. The method of claim 9, further including modulating an
amplitude of said signal to control the flow speed of said
fluid.
12. The method of claim 9, further including sweeping through a
frequency range of said signal to mix said fluid.
13. The method of claim 9, further including separating fluid
particles of differing physical properties suspended in said fluid
with said one or more flow patterns.
14. The method of claim 9, further including altering an inner
surface of said microchamber to create said one or more flow
patterns.
15. The method of claim 9, further including altering said one or
more microchamber dimensions to vary a flow speed of said
fluid.
16. The method of claim 9, further including varying the frequency
of said signal to create said one or more flow patterns.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/958,886 filed Oct. 5, 2004, titled
"Non-Invasive Acoustic Technique for Mixing and Segregation of
Fluid Suspensions in Microfluidic Applications" which claims
priority to U.S. Provisional Patent Application No. 60/592,082
filed Jul. 29, 2004.
FIELD OF THE INVENTION
[0003] The present invention relates generally controlling fluid
flow and fluid suspensions, and, more particularly, to use of low
frequency vibrations to control fluidic functions, such as pumping,
stirring, filtering and manipulation of fluids and suspensions in
microfluidic applications.
BACKGROUND OF THE INVENTION
[0004] The field of microfluidics includes the manipulation and
control of fluids on small-scales (one dimension less than 1 mm).
These fluids may be pure fluids or suspensions containing
particulate matter (e.g. biological cells). There are a wide range
of microfluidic applications within the chemical and biotechnology
industries, including combinatorial chemistry, biological assays,
and biochemical synthesis.
[0005] Current efforts include making more complex and versatile
systems like a "Lab on a Chip," which would replace a room full of
bench-top equipment with a small-scale system of microchannels and
reaction chambers. To facilitate chemical or biological reactions
in such systems, the ability to control and mix various reagents
and chemicals in the micro-scale is necessary. This includes
propelling fluids from one part of the device to another,
controlling fluid motion, providing enhanced mixing, and separating
fluids and suspended particles. Thus, mesoscopic equivalents of
traditional fluid control components need to be developed, such as
pumps, valves, mixers, and filters. Since fluids behave differently
when confined to small length scales compared to macroscopic
systems, new technologies are required for microfluidic
applications.
[0006] There are no general-purpose techniques for the performance
of multiple functional manipulations within fluid systems on the
microfluidic scale. Current methods include small magnetic stir
bars, micro-pumps, electro-hydrodynamics devices, high frequency
flexural wave devices, and ultrasonic actuation. However, all of
these techniques are limited in scope, i.e., perform only a single
function, such as either to mix or to pump fluids
[0007] To date there are three main approaches involving the use of
vibration to manipulate fluids in a small-scale confined
geometry:
[0008] The first, a high-frequency approach, uses acoustic
streaming to pump the fluids away from a piezoelectric element.
U.S. Pat. No. 6,326,211, "Method of Manipulating A Gas Bubble in a
Microfluidic Device", by Anderson et al., teaches this first
technique. An example taught by Anderson et al. involves the use a
PZT element in contact with a rigid wall, adjacent to the mixing
(reaction) chamber, which generates sonic vibrations that traverse
the solid wall and into the sample, providing the motive force to
mix the sample. However, this technique uses high power, leading to
cavitation that may damage the contents (e.g. biological cells) of
the subject microfluidic chamber.
[0009] The second, a low frequency approach, uses an oscillating
rod to create stable vortices and to trap suspended particles.
However, this technique is invasive, which is a major drawback.
(Reference: Barry R. Lutz, Jian Chen, and Daniel T. Schwartz,
Microfluidics without Microfabrication, PNAS, April 2003; 100:
4395-4398)
[0010] The third, a bubble-based approach, uses a series of
microscopic resonating bubbles that create flow patterns around the
oscillating pocket of gas. This technique has the disadvantage of
requiring a collection of identically sized bubbles and accurately
machined bubble traps, which can be difficult to produce in
practice. Another bubble-based approach, the use of thermally
generated bubbles has also been used as a form of micro-pump.
(Reference: Liu, R H; Yang, J N; Pindera, M Z; Athavale, M;
Grodzinski, P; Bubble-induced Acoustic Micromixing LAB ON A CHIP;
2002; v. 2, no. 3, p. 151-157).
[0011] Various objects, advantages and novel features of the
invention will be set forth in part in the description which
follows, and in part will become apparent to those skilled in the
art upon examination of the following or may be learned by practice
of the invention. The objects and advantages of the invention may
be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
[0012] In accordance with the purposes of the present invention, as
embodied and broadly described herein, the present invention
includes an apparatus and corresponding method for fluid flow
control in microfluidic applications. A microchamber, filled with a
fluid, is in fluid contact with a flexible plate. A transducer is
acoustically coupled to the flexible plate. A function generator
outputs a signal to excite the transducer, which in turn induces
drumhead vibration of the flexible plate, creating a flow pattern
within the fluid filled microchamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, which are incorporated in and
form a part of the specification, illustrate the embodiments of the
present invention and, together with the description, serve to
explain the principles of the invention. In the drawings:
[0014] FIGS. 1a and 1b are cross-sectional illustrations of the
present invention.
[0015] FIG. 2 is a pictorial illustration demonstrating the flow
pattern generation mechanism of the present invention.
[0016] FIG. 3 is a pictorial illustration of drum head resonance
leading to dipole and quadrupole flow patterns within a
microfluidic chamber.
[0017] FIGS. 4a, 4b, and 4c are pictures of actual flow patterns
created within a microfluidic chamber by the present invention.
[0018] FIG. 5 is a picture detailing the use of tape within a
microfluidic chamber to direct fluid and particle flow created by
the present invention.
[0019] FIG. 6 is a pictorial illustration displaying a functional
use of the present invention.
[0020] FIGS. 7a and 7b are a pictorial illustration of a separation
technique provided by the present invention.
DETAILED DESCRIPTION
[0021] The present invention is an apparatus and method for
controlling fluid flow, mixing fluids, or segregating fluids within
one or more microfluidic chambers. The differing operations can all
be accomplished with the same apparatus, allowing for versatility
of application.
[0022] The apparatus comprises a flexible plate in fluid contact
with a thin fluid chamber. Through induction of a low frequency
(<1 MHz), by an appropriate transduction method, vibration of
the flexible plate induces a flow pattern within the fluid chamber.
Changing the frequency, amplitude, and waveform of the electrical
signal that drives the plate vibration controls the fluid flow
patterns within the chamber, allowing the contents of the chamber
to be mixed or separated according to physical properties. For
example, applications for separation may include separating white
blood cells from red blood cells, or simply separating blood cells
from the plasma. Applications for mixing may include the field of
electrochemistry, where an electrochemical reaction on micro- or
nano-particles is performed within the confines of a
microchannel.
[0023] Simply adjusting the drive signal characteristics of the
transducer can control the fluid flow speed. For example, the fluid
flow can be completely stopped and restarted without using a valve
simply by applying an amplitude modulated excitation signal. The
flow speed can be varied either by the amplitude of the excitation
signal or varying the waveform, such as square wave instead of sine
wave. This technique is particularly well suited for working with
larger amounts of fluids (>nanoliters) than the traditional
amount (<nanoliters, and as small as picoliters) used in
microfluidics.
[0024] The present invention may be used in a wide variety of
applications and corresponding configurations. The setup in FIGS.
1a and 1b were chosen for ease of visualizing the effects of the
present invention on the contents of a microfluidic chamber.
Referring now to FIG. 1a, the embodiment shown comprises fluid 5
within microchamber 10 created by Plexiglas.RTM. block 20, spacer
30, and flexible plate 40. A microchamber is defined as any
enclosure with at least one dimension (length, width, or height)
less than or equal to 1 millimeter. Any solid flexible material
(metals, graphite, polymers, semiconductors, insulators, composite
material, etc.) may be used for flexible plate 40 in order to adapt
the present invention to a wide range of applications. The function
of flexible plate 40 is to allow periodic spatial deformation of
the plate surface to produce a desired pattern of surface
deflections, or, in other words, capable of forming a drumhead
response under applied acoustic frequencies. Other rigid materials
(e.g. microscopic slide, metal plate, polycarbonate, semiconductor
plates) may also be used instead of the Plexiglass.RTM. block 20.
Plexiglass.RTM. was used to facilitate flow visualization because
it is optically transparent. If visualization is not required, then
any material that is stiff enough to resist deformation may be
used.
[0025] Transducer 50 is acoustically coupled with ultra sonic
coupling gel, or other similar substance, to plate 40 and transmits
a signal from function generator 60. Any suitable voltage source
circuit known to those skilled in the art that generates a variety
of voltage waveforms of varying frequencies (e.g. sine-wave, square
wave, triangle wave, frequency modulated signal, amplitude
modulated signal, frequency sweep signal, etc.) may be used for
function generator 60. Any transducer known to those skilled in the
art that converts an input signal into an acoustic vibration may be
used as transducer 50. Referring to FIG. 1b, in another embodiment,
a flexible transducer 55 may be used in lieu of flexible plate 40,
thus, incorporating the function of flexible plate 40.
[0026] In one embodiment, transducer 50 is a piezoelectric
transducer (also called a "disc bender") that comprises a thin
piezoelectric disc glued to a larger brass disc 50 mm in diameter.
Transducer 50 vibrates like the surface of a drumhead at low
frequency (<50 Hz), producing relatively large displacements
compared to ordinary piezoelectric discs that vibrate at higher
frequencies (>1000 Hz).
[0027] Transducer 50 may be selected from any transducer known to
those practiced in the art, to include: piezoceramic, piezosalt,
piezopolymer, piezocrystal, magnetostrictive, or electromagnetic
transducers. Note that since transducer 50 is simply used to
vibrate flexible plate 40 other electromagnetic or mechanical
methods known to those skilled in the art may also be used for this
application. In fact, any means that allows a periodic spatial
deformation of flexible plate 40 will suffice. In particular, one
embodiment of transducer 50 includes a 2-dimensional array of
smaller piezoelectric elements that can be controlled individually
to produce a number of spatial surface deflection patterns on
flexible plate 40. This embodiment would be particularly suitable
for very thin fluid chambers, providing enhanced flexibility in
creating very complex spatial patterns by controlling individual
piezoelectric elements separately.
[0028] Microchamber 10 is not limited to any particular shape or
size. Various fluids (e.g., pure fluids, emulsions, suspensions,
mixtures, etc.) may be used as fluid 5. The speed of the fluid flow
within microchamber 10 depends on the viscosity of fluid 5 and the
local volume change resulting from the "squeezing" action of
flexible plate 40.
[0029] Separation of differing materials occurs due to centripetal
forces on individual particles suspended within the fluid. The
different material particles will experience different amounts of
force based on inherent physical characteristics, and will separate
from each other over time. The degree of separation will depend on
amplitude of vibration, fluid layer thickness, and viscosity of the
fluid.
[0030] Mixing of fluid and suspended particles occurs when the
vibration mode is changed such that the fluid is forced from one
flow pattern to another. The flow speed may be controlled through
signal amplitude modulation, to include starting and stopping flow
in a periodic manner.
[0031] Particular flow patterns (e.g. mixing and segregation) occur
over a relatively wide range of frequencies, rather than at exact
drum-head modes frequencies, due primarily to asymmetries in the
shape of the given microchamber used. Thus, the microchamber
asymmetry tends to broaden the width of the drumhead resonance
modes.
[0032] Using the apparatus described in FIGS. 1a and 1b, fluid
flow, mixing, and separation behavior were observed in microchamber
10. Microchamber 10 dimensions were approximately 3 cm in diameter
with a depth ranging from 200 microns to 1 mm. Spacer 30, about 200
to 1000 .mu.m thick, was made from Teflon.RTM.. Plate 40 was a 127
.mu.m (0.005'') thick brass plate. Carbon black particles were
added to the water inside microchamber 10 in order to facilitate
visualization and monitoring of fluid motion.
[0033] Transducer 50, a piezoelectric transducer (also called a
"disc bender"), comprised a thin piezoelectric disc glued to a
larger brass disc. Transducer 50, 50 mm in diameter, vibrated like
the surface of a drumhead, producing relatively large displacements
compared to ordinary piezoelectric discs. Transducer 50 was coupled
to metal plate 40 using ultrasonic coupling gel and was excited by
function generator 60 (Stanford Research System DS345). Power
amplifier 70 (Krohn-Hite Model DCA-10) amplified the output of
function generator 60, but is not required to practice the present
invention. Note that with proper impedance matching, e.g., use of a
transformer, the power requirements for observing the acoustic flow
patterns described can be reduced below 1 Watt. Note, by using a
commercial laser Doppler vibrometer that senses vibrations of a
surface with sub-micron resolution, it was determined that the
surface vibration pattern of flexible plate 40 was primarily the
result of drumhead mode excitation.
[0034] When function generator 60 applied a low frequency (<1
kHz) sonic vibration to plate 40, convection-like patterns were
created in the fluid within chamber 10.
[0035] The flow patterns that arise within the chamber result from
a combination of the periodically changing dimensions of the fluid
height within chamber 10. Referring now to FIG. 2, as flexible
plate 40 vibrates, the width of fluid chamber 10 alternately
compresses and expands, exhibiting a particular pattern that is a
function of the signal from transducer 50. As plate 40 compresses
fluid 5, fluid 5 is forced away from the locations of compression
to locations not in compression.
[0036] Flexible plate 40 movements at the lowest frequencies
(<50 Hz) produced chamber 10 volume changes that were less than
0.1% of the total volume as determined by observing a fluid
meniscus in a tube (not shown) attached to chamber 10. At higher
frequencies, the volume change was not observable. The flow
patterns observed within chamber 10 were not induced by acoustic
streaming or an acoustic field within chamber 10, as is the case
for plate wave fluid transport, but rather a process equivalent to
mechanical pumping of a fluid in a confined space induced by
flexible plate 40, where the distribution of fluid is manifest by
the bending pattern created by the mode of excitation provided by
transducer 50.
[0037] To create specific flow patterns that are stable over time,
it is necessary to establish particular vibration patterns with
plate 40. In particular, the dipole and quadruple flow patterns
exhibited in FIG. 2 were created from the associated drum head
resonance of plate 40. Note that drumhead resonance modes may not
be perfect, as shown in FIG. 3, due to the varying geometries that
may be employed in differing embodiments of chamber 10. The
resulting asymmetry in the configuration tends to broaden the
resonance frequencies due to the degenerate resonance modes
(multiple resonance modes having same resonance frequency) that
tend to separate out the resonance frequencies that normally
overlap in a symmetric system. This allows for a range of flow
patterns observed over a large frequency range that are slightly
different in characteristics but reproducible.
[0038] FIGS. 4a, 4b and 4c display the various flow patterns
generated within a homogeneous mixture of carbon black and titanium
dioxide particles in water located in microchamber 10 by varying
the frequency applied to transducer 50.
[0039] Three distinct flow patterns were created at different
frequencies. Referring to FIG. 4a, at frequencies less than 30 Hz,
the carbon black particles moved symmetrically towards and away
from the center of the chamber. At frequencies of 70 to 200 Hz,
FIG. 4b shows convection-like, dipole patterns were
established.
[0040] Referring to FIG. 4c, at frequencies of 200 Hz to 1 kHz,
more complicated mixing patterns were observed, and stable
patterns, such as quadrupoles were established. Note, at
frequencies greater than 1 kHz, very little flow or mixing was
observed because the corresponding flexible plate 40 vibration
amplitude was too low to create significant hydrodynamic flow
within the chamber 10.
[0041] At higher frequencies, higher mode vibrations are created.
This means that the spatial pattern on the plate surface is more
finely dimpled (closely spaced amplitude variation). At these
higher frequencies, the suspended particles respond slowly to fast
changes in fluid motion due to viscous drag effects. This effect
depends on the size of the suspended particles and the viscosity of
the fluid. Note, for smaller particles in a lower viscosity fluid,
one may observe this effect to take place at frequencies higher
than 1 kHz. This limiting frequency scales with the physical
parameters mentioned previously.
[0042] In general, the flow patterns observed were stable over a
frequency range that exceeded 30% (.about.100 Hz) of the resonance
frequency of any induced drumhead mode (dipole, quadrupole etc.). A
few specific frequencies corresponding to the dipole and quadrupole
modes created flow patterns that were symmetric (e.g., equal size
flow loops), but as the frequency deviated on either side of these
frequencies, the flow patterns became more asymmetric (e.g. one
flow loop larger than the other or particles collecting around the
edges of one flow loop and in the center of another). Thus, it was
demonstrated that by simply adjusting the frequency finer control
over the exhibited flow pattern is possible.
[0043] The speed exhibited by fluid 5, while moving in the various
patterns, depends on several factors: the dimensions of chamber 10,
the amplitude of transducer 50 vibrations, the thickness of plate
40, and the waveform used to excite transducer 50. The fluid flow
speed is approximately proportional to the amplitude of the signal
used to excite the transducer. This is a linear approximation from
Bernoulli's law, which states that the velocity of the flow would
be inversely proportional to the fractional change in dimension of
microchamber 10 due to plate 40. The amplitude of vibration of the
flexible plate 40 is directly related to the amplitude of the
excitation signal from transducer 50. The highest fluid 5 flow
speed observed was approximately 3 cm/s; this value was determined
by frame-by-frame analysis of video pictures taken with a digital
video camera.
[0044] Through amplitude modulation of the excitation signal, fluid
flow can be made to alternate between flowing and stationary
states, similar to flow control with a valve. This type of simple
flow control can be very useful in designing various microfluidic
applications, including biological cell manipulations.
[0045] The velocity of the fluid within the flow patterns decreased
as the thickness of plate 40 was increased. Observable flow
patterns exist from 127 .mu.m (0.005'') to 381 .mu.m (0.015'').
Fluid flow velocity decreased as the width of chamber 10 was
increased because the amplitude of vibration depends on the power
applied and the plate thickness. As a result of the confined space
within the microchannel, a combination of the finite displacement
of the plate (drum-head mode vibration) with respect to the total
thickness of the confined fluid determines the effectiveness of
inducing fluid flow. If the ratio of the vibration amplitude to the
fluid depth (microchannel depth) is too small, the induced flow
velocity will become small as well and will disappear below a
minimum threshold value that depends on the particular geometry of
microchamber 10.
[0046] There are several methods that may be employed to modify the
shape of flow patterns. One method is to change the position of the
transducer relative to the center of microchamber 10. Another
method is to alter the inner surface of microchamber 10, for
example by placing strips of tape or creating grooves on the
surfaces within microchamber 10.
[0047] Fluid flow patterns were not affected by tightening screws
around fluid chamber 10, applying pressure to the back of
transducer 50, or changing the orientation of transducer 50 with
respect to chamber 10. Note that fluid flow patterns are not
dependent on whether chamber 10 is oriented vertically or
horizontally, as the strength of the mechanical pushing exhibited
by the drum-head vibration of plate 40 on fluid 5 is orders of
magnitude higher than the force of gravity on fluid 5.
[0048] In other embodiments, modification of the surface of plate
40 resulted in alteration of exhibited fluid flow patterns. For
example, placing tape with a 50 .mu.m thickness on to the fluid
side of plate 40 in various shapes and different numbers of layers
resulted in fluid flow velocities that were considerably higher
over the area where the pieces of tape overlapped (where the liquid
layer was the thinnest); this is consistent with Bernoulli's
principle. Thus, with use of this type of application, one can
modify flow characteristics to meet any number of operational
needs, e.g., sampling. It was determined that a grid of overlapping
tape strips, as shown in FIG. 5, induced particles entrained in
fluid 5 to collect at the points where the strips of tape
overlapped, providing for functional manipulation of fluid 5 within
microchamber 10.
[0049] Functional use of the stable flow patterns provided by the
present invention makes possible the ability to perform
microfluidic mixing operations. For example, referring to FIG. 6,
microfluidic mixing chamber 100 is fluidly connected to chambers
110, 120, and 130. Using the present invention, a stable loop flow
pattern within chamber 100 may be used to siphon different chemical
fluids from chambers 110, 120 and mix them together within chamber
100. Once the desired chemical reaction has taken place, another
flow pattern may be induced to direct the mixture into chamber 130
for storage or further processing.
[0050] Another function provided by the present invention is the
ability to segregate suspended particles. Referring back to FIG.
4b, activation of transducer 50 created a stable loop flow pattern.
After a brief period, the carbon black and titanium dioxide
particles separated, with the carbon black particles in the centers
of the induced flow loops and the titanium dioxide particles
flowing around them on the outside. This phenomenon is explained by
recognizing that the suspended particles within the circular flow
loops experience centrifugal force. Thus, if the densities and the
size of the particles are different, this force tends to separate
the particles spatially so that these can be extracted from the
chamber.
[0051] For example, referring to FIGS. 7a and 7b, a solution
comprising two distinct particles, e.g. red and white blood cells,
enters microfluidic chamber 200 through inlet tube 210. Over time,
the circular dipole motion created by the present invention within
chamber 200 and the differing physical characteristics of the
differing particles, leads to particle separation, where one set of
particles circulates within dipole pattern 230 and the other set
collects within dipole pattern 230 where outlet tube 220 is located
and are then drawn out to another location for processing or
analysis.
[0052] The present invention is a simple, inexpensive apparatus and
corresponding method that may be, used to concentrate or mix the
contents of thin fluid layers. For example, the transducers used
for the example were manufactured by APC International, Limited,
and are considered inexpensive at less than ten dollars.
[0053] The present invention is simple to implement and does not
require photolithography. Traditional microfluidic operations are
performed using a photolithography process to make microchannels on
a silicon wafer or other material. This process is very similar to
making semiconductor integrated circuits and is complicated. Thus,
the present invention obviates the need for such sophisticated and
expensive processing and opens up possibilities for widespread use
by rendering the whole process significantly simpler than currently
practiced. The present invention is completely non-invasive as
transducer 50 is located outside fluid chamber 10. Finally, the
present invention allows for precise control of fluid flow inside
microchamber 10 by adjusting the frequency, amplitude, and waveform
of the signal inducing the drumhead vibration of flexible plate
40.
[0054] The present invention has several applications in the field
of microfluidics: first, by controlling the flow rate, the rates of
chemical and/or biological reactions can be controlled; second,
stationary fluid flow patterns can be set up, acting as
micro-chemical traps in a larger application; third, chaotic mixing
of two fluids may be performed to provide thorough mixing; and,
fourth, fluid flow can be directed along micro-channels existing
within a given chamber.
[0055] The foregoing description of the invention has been
presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the precise
form disclosed, and obviously many modifications and variations are
possible in light of the above teaching.
[0056] The embodiments were chosen and described in order to best
explain the principles of the invention and its practical
application to thereby enable others skilled in the art to best
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto.
* * * * *