U.S. patent application number 11/989984 was filed with the patent office on 2010-03-11 for microfabricated device.
This patent application is currently assigned to Auckland UniServices Limited. Invention is credited to Mark B. Cannell, Ralph Paul Cooney, Paul Kilmartin, Christian Soeller, Jadranka Travas-Sejdic.
Application Number | 20100061870 11/989984 |
Document ID | / |
Family ID | 37708901 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100061870 |
Kind Code |
A1 |
Cannell; Mark B. ; et
al. |
March 11, 2010 |
MICROFABRICATED DEVICE
Abstract
A microfabricated device (10) includes a structure (12) defining
a closed fluid delivery channel (14), the channel (14) having an
inlet (16) and an opposed outlet (18). A conducting polymer
actuator (20) is arranged within the fluid delivery channel (14).
At least a part of the actuator (20) is configured to vary its
cross sectional area in a direction transverse to a direction of
fluid flow in the channel (14). An actuator control arrangement
(22) is carried by the structure (12) for controlling the actuator
(20) to cause the actuator (20) to expand and contract cyclically
and sequentially along the length of the actuator (20) to vary the
cross sectional area of the channel (14) cyclically and
sequentially to effect a peristaltic pumping action to deliver
fluid from the inlet (16) of the channel (14) to the outlet (18) of
the channel (14).
Inventors: |
Cannell; Mark B.; (Remuera,
NZ) ; Cooney; Ralph Paul; (Mt. Eden, NZ) ;
Kilmartin; Paul; (Te Atatu Peninsula, NZ) ; Soeller;
Christian; (Mission Bay, NZ) ; Travas-Sejdic;
Jadranka; (One Tree Hill, NZ) |
Correspondence
Address: |
BENESCH, FRIEDLANDER, COPLAN & ARONOFF LLP;ATTN: IP DEPARTMENT DOCKET
CLERK
200 PUBLIC SQUARE, SUITE 2300
CLEVELAND
OH
44114-2378
US
|
Assignee: |
Auckland UniServices
Limited
Auckland
NZ
|
Family ID: |
37708901 |
Appl. No.: |
11/989984 |
Filed: |
August 1, 2006 |
PCT Filed: |
August 1, 2006 |
PCT NO: |
PCT/NZ2006/000199 |
371 Date: |
November 24, 2009 |
Current U.S.
Class: |
417/557 |
Current CPC
Class: |
F04B 43/082 20130101;
F04B 43/12 20130101; B81B 2201/036 20130101; F04B 43/043 20130101;
F04B 43/14 20130101; B81B 3/0021 20130101; A61M 5/14228
20130101 |
Class at
Publication: |
417/557 |
International
Class: |
F04B 39/00 20060101
F04B039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2005 |
AU |
2005904179 |
Claims
1. A microfabricated device which includes: a structure defining a
closed fluid delivery channel, the channel having an inlet and an
opposed outlet; a conducting polymer actuator arranged within the
fluid delivery channel, at least a part of the actuator being
configured to vary its cross sectional area in a direction
transverse to a direction of fluid flow in the channel; and an
actuator control arrangement carried by the structure for
controlling the actuator to cause the actuator to expand and
contract cyclically and sequentially along the length of the
actuator to vary the cross sectional area of the channel cyclically
and sequentially to effect a peristaltic pumping action to deliver
fluid from the inlet of the channel to the outlet of the
channel.
2. The device of claim 1 in which the structure includes a base and
a pair of spaced side walls extending upwardly from the base, the
side walls supporting a cover layer spaced from the base to define
the channel.
3. The device of claim 2 in which the cover layer is applied by
micromachining techniques.
4. The device of claim 2 in which the actuator is arranged in the
channel between the side walls.
5. The device of claim 2 in which the actuator supports the cover
layer in a spaced position relative to the base, a central part of
the actuator being configured to vary its cross sectional area
while side parts of the actuator function as side walls to support
the base and the cover member in spaced relationship.
6. The device of claim 1 in which the actuator is a unitary,
one-piece body.
7. The device of claim 1 in which the actuator is made up of a
plurality of discrete actuator elements arranged in series in the
channel.
8. The device of claim 1 in which the actuator control arrangement
comprises an electrode array arrangement.
9. The device of claim 8 in which the electrode array arrangement
comprises a plurality of electrode arrays to facilitate phased
cyclic expansion and contraction of the actuator elements to effect
the peristaltic pumping action.
10. The device of claim 8 in which the electrode array arrangement
is deposited on the structure by a deposition technique
11. The device of claim 1 in which conducting polymers of the
actuator are selected from the group consisting of polypyrrole and
its derivatives, polyaniline and its derivatives, polythiophene and
its derivatives poly(ethylenedioxythiphene), polyphenylene,
poly(pheylenevinylidene) and its derivatives.
12. The device of claim 1 in which a fluid to be pumped by the
device is an electrolyte which reduces and oxidises the actuator,
the actuator being exposed to the electrolyte in the channel.
13. The device of claim 1 in which a membrane separates a fluid to
be pumped through the device and an electrolyte in which the
actuator is immersed.
14. The device of claim 13 in which the membrane is a polymer
membrane.
15. The device of claim 12 in which the electrolyte is one of a
liquid electrolyte, a polymer electrolyte, a polymer gel
electrolyte and an ionic liquid.
16. The device of claim 15 in which the liquid electrolytes are
aqueous and organic based solvents.
17. The device of claim 16 in which the liquid electrolytes contain
supporting salts with either anion or cations being able to move in
and out of the conducting polymer material.
18. The device of claim 17 in which the salts are low molecular
salts selected from the group consisting of KCl, NaCl, KClO.sub.4,
tetrabutylammonium hexafluorophosphate, tetrabutylammonium
triflouromethanesulfonate.
19. The device of claim 17 in which the salts are surfactant type
salts.
20. The device of claim 17 in which the salts are polyelectrolyte
ionic liquids.
21. The device of claim 15 in which the polymer electrolytes and
polymer gel electrolytes are poly methyl methacrylate/lithium
perchlorate in a propolyene carbonate/acetonitrile mixture as a
solvent.
22. The device of claim 1 in which the actuator is grown on the
actuator control arrangement via electropolymerisation techniques
or deposited on the substrate surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from Australian
Provisional Patent Application No 2005904179 filed on 4 Aug. 2005,
the contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a microfabricated device. The
invention relates particularly, but not necessarily exclusively, to
a microfabricated pumping device. The microfabricated pumping
device shall be referred to below as a "micropump".
BACKGROUND OF THE INVENTION
[0003] The use of microfabricated devices for various applications
is becoming increasingly prevalent. Such devices have found
applications as pumps for controlled release of drugs into a
patient's body, as well as applications with microchips for
microfluidics and analytics.
[0004] To provide control of the device, electrical devices are
preferred and, generally, electrically powered pumps make use of
actuators requiring voltages of the order of 10-100 volts such as,
for example, piezoelectric actuators. Therefore, the devices need
to be made of materials having a dielectric strength which can
withstand such voltages. This increases the bulk of the devices.
Further, such devices may not be biocompatible and the voltage
required does not make them suitable for implantation. Still
further, the response time of such devices can, in certain
circumstances, be inadequate.
[0005] Also, such pumps do not sufficiently accurately meter fluids
in the microlitre, nanolitre or picolitre ranges which may be
required for analytical purposes, medical purposes or other
purposes. A number of these pumps are also only operable
unidirectionally.
[0006] Another type of device for use in the delivery of medication
makes use of an osmotic infusion pump. Generally the output from
such an infusion pump is essentially constant and cannot be
varied.
SUMMARY OF THE INVENTION
[0007] According to the invention there is provided a
microfabricated device which includes:
[0008] a structure defining a closed fluid delivery channel, the
channel having an inlet and an opposed outlet;
[0009] a conducting polymer actuator arranged within the fluid
delivery channel, at least a part of the actuator being configured
to vary its cross sectional area in a direction transverse to a
direction of fluid flow in the channel; and
[0010] an actuator control arrangement carried by the structure for
controlling the actuator to cause the actuator to expand and
contract cyclically and sequentially along the length of the
actuator to vary the cross sectional area of the channel cyclically
and sequentially to effect a peristaltic pumping action to deliver
fluid from the inlet of the channel to the outlet of the
channel.
[0011] By "closed fluid delivery channel" is meant that a part of
the channel opposite the floor is covered by a cover member but the
channel is open at its opposed ends.
[0012] The structure may include a base and a pair of spaced side
walls extending upwardly from the base, the side walls supporting a
cover layer spaced from the base to define the channel.
[0013] The structure may be formed by microfabrication techniques
such as deposition and etching techniques. Thus, for example, the
structure may be formed of silicon or any other suitably rigid
material. A silicon structure has the advantage that interfacing
with other control circuitry is facilitated. Instead, the structure
may comprise a glass or other inert substrate on which the actuator
control arrangement is deposited. The cover layer may be applied by
micromachining techniques.
[0014] In one embodiment, the actuator may be arranged in the
channel between the side walls. Thus, an entire width of the
actuator may be able to have its cross sectional area varied. In
another embodiment, the actuator may support the cover layer in a
spaced position relative to the base, a central part of the
actuator being configured to vary its cross sectional area while
side parts of the actuator are fixed and non-varying and function
as side walls to support the base and the cover member in spaced
relationship.
[0015] The actuator may be a unitary, one-piece body or, instead,
the actuator may be made up of a plurality of discrete actuator
elements arranged in series in the channel. Where the actuator is a
single body, adjacent parts of the body may be able to expand and
contract independently of each other under the effect of the
actuator control arrangement to create a peristaltic wave-like
motion through the body from the inlet to the outlet. In the case
where the actuator comprises a series of discrete actuator
elements, the elements may be individually controlled by the
actuator control arrangement to cause the peristaltic motion
through the channel.
[0016] The actuator control arrangement may comprise an electrode
array arrangement. The electrode array arrangement may comprise a
plurality of electrode arrays to facilitate phased cyclic expansion
and contraction of the actuator elements to effect the peristaltic
pumping action.
[0017] At least three electrode arrays may be provided to provide a
three phase or higher phase actuation sequence to achieve
directional flow of the fluid from the inlet of the fluid delivery
channel to the outlet of the fluid delivery channel.
[0018] In the case where three electrode arrays are used, a counter
electrode arrangement may be provided. A counter electrode may be
associated with each electrode array.
[0019] Instead, the electrode arrangement may comprise four
electrode arrays arranged in two pairs. With this arrangement, one
of the electrode arrays of each pair may be used as a counter
electrode for the other electrode array of that pair.
[0020] The electrode array arrangement may be deposited on the
structure by an appropriate deposition technique, for example, by
sputtering, printing, or the like.
[0021] The conducting polymer actuator elements (or conjugated
polymers) have the capability to be reversibly oxidised and reduced
upon the application of a potential difference. The conducting
polymers of the actuator may be selected from the group consisting
of polypyrrole and its derivatives, polyaniline and its
derivatives, polythiophene and its derivatives
poly(ethylenedioxythiphene), polyphenylene,
poly(pheylenevinylidene) and its derivatives, or the like.
[0022] It will be appreciated that, to effect expansion and
contraction of the actuator elements, the actuator elements need to
be immersed in an electrolyte.
[0023] In one embodiment, a fluid to be pumped by the device is an
electrolyte which reduces and oxidises the actuator, the actuator
being exposed to the electrolyte in the channel. In another
embodiment, a membrane may separate a fluid to be pumped through
the device and an electrolyte in which the actuator is immersed.
The membrane may be a thin polymer membrane made of materials such
as siloxane-based polymers, polyvinylchloride film, polyvinylidene
fluoride, polyethylene, polypropylene, or other non-permeable
membrane. Further, the membrane could be of a silicone
material.
[0024] The electrolyte may be one of a liquid electrolyte, a
polymer electrolyte, a polymer gel electrolyte and an ionic
liquid.
[0025] The liquid electrolytes are aqueous and organic based
solvents, such as propylene carbonate, acetonitrile and
gamma-butyrolactone. The liquid electrolytes may contain supporting
salts with either anion or cations being able to move in and out of
the conducting polymer material. The salts may be low molecular
salts selected from the group consisting of KCl, NaCl, KClO.sub.4,
tetrabutylammonium hexafluorophosphate, tetrabutylammonium
triflouromethanesulfonate; surfactant type salts such as sodium
dodecylsulphonate; polyelectrolytes ionic liquids, such as
1-butyl-3-methyl imidazolium tetrafluoroborate; or the like.
[0026] The polymer electrolytes and polymer gel electrolytes may be
poly methyl methacrylate/lithium perchlorate in a propolyene
carbonate/acetonitrile mixture as a solvent.
[0027] The actuator may be grown on the actuator control
arrangement via electropolymerisation techniques or deposited on
the substrate surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Embodiments of the invention are now described by way of
example with reference to the accompanying drawings in which:
[0029] FIG. 1 shows a schematic, side view of a microfabricated
device, in accordance with one embodiment of the invention;
[0030] FIG. 2 shows a schematic side view of a microfabricated
device, in accordance with another embodiment of the invention;
[0031] FIG. 3 shows a schematic end view of the device of FIG.
1;
[0032] FIG. 4 shows a schematic plan view of an actuator control
arrangement for the device of FIG. 1 or FIG. 2;
[0033] FIG. 5 shows a schematic side view of operation of the
device of FIG. 1 using the actuator control arrangement of FIG.
4;
[0034] FIG. 6 shows a schematic plan view of a further actuator
control arrangement;
[0035] FIGS. 7A and 7B show two sequences of operation of the
actuators using the control arrangement of FIG. 6;
[0036] FIG. 8 shows a schematic, side view of a microfabricated
device, in accordance with another embodiment of the invention;
[0037] FIG. 9 shows a schematic, end view of a microfabricated
device, in accordance with yet a further embodiment of the
invention;
[0038] FIG. 10A shows, above, a three dimensional AFM topographic
image and, below, a cross-sectional line drawing end view of a
first polypyrrole actuating element prepared for experimental
purposes; and
[0039] FIG. 10B shows, above, a three dimensional AFM topographic
image and, below, a cross-sectional line drawing end view of a
second polypyrrole actuating element prepared for experimental
purposes.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0040] In the drawings, reference numeral 10 generally designates a
microfabricated device, in accordance with an embodiment of the
invention. The device 10 includes a structure 12 defining a channel
14. The channel 14 has an inlet 16 and an opposed outlet 18. A
plurality of conducting polymer actuator elements, or actuators, 20
is arranged in the channel 14 of the structure 12.
[0041] The device 10 includes an actuator control arrangement in
the form of an electrode array arrangement 22 for controlling
operation of the actuators 20, as will be described in greater
detail below. One example of an electrode array arrangement 22 is
shown in FIG. 4 of the drawings with another example of the
electrode array arrangement 22 being shown in FIG. 6 of the
drawings.
[0042] A particular application of the device 10 is as a micropump.
The invention will be described with reference to that application
below although it will readily be appreciated by those skilled in
the art that the invention could be used in other applications. The
micropump 10 is a miniature device having dimensions in the
micrometre scale.
[0043] The structure 12 comprises a substrate 24 having a pair of
opposed sidewalls 26 defining the channel 14. A sealing, or cover,
layer 28 is mounted on the walls 26 to define a closed fluid
delivery channel 14 (as defined).
[0044] The structure 12 is formed by any suitable microfabrication
techniques such as, for example, deposition and etching techniques.
Thus, the substrate 12 is a suitable material able to be deposited
and etched such as silicon or any other suitable rigid material
that allows for electrodeposition. An advantage of using silicon
for the substrate 24 is its ability to interface electrically with
other control circuitry.
[0045] The electrode array arrangement 22 can either be a three
phase arrangement comprising three electrode arrays 30, 32 and 34
(FIG. 4) or a four electrode array arrangement comprising four
electrode arrays 36, 38, 40 and 42 (FIG. 6). Regardless of the
configuration of the electrode array arrangement 22, the electrode
array arrangement 22 is deposited or otherwise applied to the
substrate 24 in a suitable manner, for example, by sputtering,
printing, or other suitable microfabrication techniques. It will be
appreciated that the electrode arrays 30, 32 and 34 or 36-42 are
electrically insulated from each other so that each array controls
every third or fourth actuator 20, as the case may be.
[0046] Thus, each electrode array 30-42 is a substantially
comb-like structure and has a conductive strip 44 with a plurality
of conductor pads, or electrodes, 46 extending orthogonally from
the conductive strip 44. The conductor pads 46 are located on the
base of the channel 14 and each conductor pad 46 has an actuator 20
associated with it.
[0047] In the three phase arrangement 22 shown in FIG. 4 of the
drawings, each electrode array 30, 32, 34 may have a counter
electrode (not shown) associated with it. However, if the phases
are controlled appropriately, i.e. by being 120.degree. out of
phase with one another, any two electrodes can act as the counter
electrode for the third electrode obviating the need for
independent counter electrodes. In contrast, in the case of the
electrode arrays 36-42 as shown in FIG. 6 of the drawings, the
electrode arrays 36-42 are arranged in pairs so that one electrode
array of each pair serves as a counter electrode for the other
electrode array of the pair. Thus, because the electrode arrays 36
and 40 are 180.degree. out of phase with each other, they form an
electrode array pair with the electrode arrays 36 and 40 forming
counter electrodes for each other. Similarly, the electrode arrays
38 and 42 are arranged in a counter electrode pair.
[0048] The actuators 20 are conjugated polymer actuators, such as
polypyrrole actuators, which are grown on the conducting pads or
electrodes 46 of the electrode arrays by electropolymerisation.
[0049] Because the actuators 20 are conducting polymer actuators,
they require the presence of an electrolyte for expansion and
contraction, i.e., oxidation and reduction. In the embodiment shown
in FIG. 1 of the drawings, it is assumed that the fluid to be
pumped is the electrolyte and the actuators 20 are in direct
contact with the fluid in the channel 14. In the embodiment shown
in FIG. 2 of the drawings, it is assumed that the fluid to be
pumped is not a suitable electrolyte. In that case, the channel 14
is separated into two zones, a pumping zone 14.1 and an actuator
zone 14.2, by a membrane 48. The membrane 48 is of any suitable
material such as a thin, polymer material. The polymer material is
a siloxane-based polymer, polyvinylidene fluoride, polyethylene,
polypropylene, or the like. The membrane 48 is applied via suitable
microfabrication techniques, such as, for example, deposition and
etching techniques.
[0050] The electrolyte is chosen from liquid electrolytes, polymer
electrolytes, polymer gel electrolytes and ionic liquids. The
liquid electrolytes are aqueous and organic solvent based. They
contain supporting salts with either anions or cations being able
to move in and out of the material of the polymer actuators 20. The
salts are chosen from any suitable salt such as a low molecular
salt, for example, KCl, KClO.sub.4, TBAPF.sub.6,
TBACF.sub.3SO.sub.3, or the like; surfactant type salts, for
example dodecylbenzenesulphonate or alkyl sulphonates,
polyelectrolytes, for example, polystyrenesulphonate or polyacrylic
acid, and ionic liquids, for example, 1-butyl-3-methyl imidazolium
tetrafluoroborate.
[0051] Polymer electrolytes and polymer gel electrolytes are
selected from suitable polymer electrolytes such as poly(methyl
methacrylate)/LiClO.sub.4 in propylene carbonate/acetonitrile
mixture as a solvent.
[0052] The polymer of the actuators and the small size of the
actuators 20, having a height in the order of 1 .mu.m to a few
.mu.m's, is exploited to achieve high speed operation of the
micropump 10 and high density of actuators 20 on the substrate.
Conducting polymers have large strains/deformations in comparison
with actuators in piezoelectric devices. These large
strains/deformations offer significant advantages. However, whilst
polymer actuators with strains/deformations of more than 20% are
preferred, devices of the invention are still practical with lower
strains/deformations, just requiring higher or deeper actuating
elements. The actuators 20 also have fast actuation, in the order
of 1 Hz. In addition, the channel 14 is designed to have a small
fluid channel cross-section relative to the width of the actuators
20 in order to exploit hydraulic viscosity to improve hydrostatic
pressures. With this configuration, the micropump 10 is able to
operate without any valves.
[0053] The small channel 14 in combination with rapid actuation of
the actuators 20 ensures that viscous effects of the fluid being
pumped assists in avoiding backflow of the pumped fluid even in the
presence of an adverse pressure gradient. The viscous effects of
the fluid being pumped cause a dynamic seal between the top of the
actuators and the sealing layer 28 and around the sides of the
actuators 20 and the internal surfaces of the walls 36 of the
structure 12 due to fluid friction and inertia. In addition, a
further consequence of the small fluid channel 14 is the presence
of a small dead volume with capillary effects being exploited to
make the pump 10 self-priming.
[0054] Referring now to the electrode arrangement 22 shown in FIG.
4 and the actuators of FIG. 5, three separately controllable
electrode arrays 30, 32, 34 are provided so that every third
actuator 20 moves in phase. Thus, as shown in FIG. 1 of the
drawings, the actuators 20.1 move in phase with each other, the
actuators 20.2 move in phase with each other and the actuators 20.3
move in phase with each other. A similar arrangement applies with
respect to the embodiment of the micropump 10 shown in FIG. 2 of
the drawings where the actuators 20 act on the membrane 48. In both
embodiments, appropriate control of the actuators 20 in a cyclic
and sequential manner causes a peristaltic pumping action from the
inlet 16 to the outlet 18 of the channel 14. Thus, by introducing
an appropriate phase delay (120.degree. in the case of the
electrode array arrangement 22 of FIG. 4) between adjacent
actuators 20.1 and 20.2, 20.2 and 20.3 and 20.3 and 20.1,
directional fluid motion in a direction of arrow 50 (FIG. 5) and a
driving pressure gradient is achieved. In FIG. 5, actuator motion
is shown by the arrows 52.
[0055] The pressure gradient can be increased by increasing the
number of groups of actuators 20 (i.e. the number of units of 3 or
4 actuators) along the array arrangement 22 between the inlet 16
and the outlet 18. As a general rule, the total pressure difference
will increase with an increasing number of recurrent actuator
groups used, all other parameters being kept constant.
[0056] As previously indicated, with the electrode arrangement 22
of FIG. 4 of the drawings, any two electrodes may act as counter
electrodes for the third electrode providing that there is no phase
error, or each electrode array 30, 32, 34 may have a counter
electrode associated with it. Thus, as an actuator 20 is reduced or
oxidised opposite charge movement of equal magnitude occurs at a
counter electrode.
[0057] Referring to the embodiment of the invention shown in FIGS.
6 and 7 of the drawings, with the provision of four electrode
arrays 36-42 adjacent actuators 20 are always 90.degree. out of
phase with each other. Hence a travelling peristaltic "wave" motion
can be generated as shown in the two sequences in FIG. 7 of the
drawings. Once again, arrows 52 indicate direction of actuator
movement. Also, as previously described, with the electrode
arrangement of FIG. 6, the electrode array pairs serve as counter
electrodes for each other and the need for further counter
electrodes is obviated.
[0058] Referring now to FIG. 8 of the drawings, another embodiment
of the micropump 10 is shown. With reference to the previous
drawings, like reference numerals refer to like parts unless
otherwise specified.
[0059] In this embodiment, the actuator is comprised of a single or
unitary body 60 arranged in the channel 14. The electrolyte is
contained in the body 60 or some external reservoir in
communication with the body. Adjacent parts of the body are
individually addressable by the electrode array arrangement 22 to
cause the parts of the body 60 to oxidise and reduce independently
of each other as electrolyte is absorbed or expelled, as the case
may be. As a result, by appropriate control of the body 60, a
peristaltic wave-like motion is imparted to the body to drive fluid
through the channel from the inlet 16 to the outlet 18.
[0060] In FIG. 9 of the drawings, yet a further embodiment of the
micropump 10 is illustrated. Once again, with reference to the
previous drawings, like reference numerals refer to like parts
unless otherwise specified.
[0061] The substrate 24 of the structure 12 and the cover layer 28
are separated from each other by a conjugated polymer actuator 70
interposed between the substrate 24 and the cover layer 28. When
viewed from the end, the actuator 70 has a central part 72 that is
responsive to electric fields generated by the electrode array
arrangement 22. In contrast, side parts 74 of the actuator 70 are
not responsive to the electric fields. The side parts 74 of the
actuator 70 therefore serve as side walls to support the cover
layer 28 in spaced relationship relative to the substrate 24. When
an electric field is applied to the actuator 70 the central part 72
is reduced causing a channel 76 to open as shown in dotted lines.
By cyclically and sequentially energising the central part 72 of
the actuator 70, a peristaltic wave-like motion is generated to
cause fluid flow from the inlet 16 to the outlet 18 of the
micropump 10.
[0062] It will be appreciated that the actuator 70 could be
implemented either as a single body, as described above with
reference to the previous embodiment, or it could be implemented as
a series of discrete actuators such as the actuators 20 of the
embodiment described with reference to FIGS. 1-7 of the drawings.
Optionally, a membrane is interposed on that surface of the
actuator 70 which is displaced, normally the surface facing an
inner surface of the cover layer 28. The membrane serves to inhibit
leakage of fluid through sides of the actuator 70. The membrane may
be bonded to the surface of the actuator 70. The membrane, could be
preformed to form the channel 76 with the actuator 70 being
activated to compress the membrane to reduce the channel 76 to
achieve the peristaltic pumping action.
[0063] Set out below are two examples of the preparation of
polypyrrole (PPy) actuating elements suitable for use in the device
10.
EXAMPLE 1
[0064] FIG. 10A shows a polypyrrole (PPy) actuating element 80. In
FIG. 10A, the upper illustration shows a three dimensional atomic
force microscopy (AFM) topographic image of the polypyrrole (PPy)
actuating element 80 and the lower illustration shows a
cross-sectional line drawing end view of the polypyrrole (PPy)
actuating element 80.
[0065] To form the element 80, polypyrrole (PPy) was deposited
potentiostatically at 0.85 V against Ag/AgCl on patterned parallel
gold strips (not shown) on a chip-like substrate on a 1.5
cm.times.1.5 cm glass plate (not shown) using a common connector
for the working electrodes. The deposition solution was 0.1 M
pyrrole and 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF.sub.6) in propylene carbonate (PC). The electrochemical
polymerization was stopped once the consumed charge reached 1 mC
(for a working electrode area of 0.024 cm.sup.2), to obtain a film
thickness of about 2 .mu.m. The PPy elements 80 were cycled in
pyrrole-free solution of 0.1 M TBAPF.sub.6 in propylene carbonate.
The alternative strips were then oxidized and reduced at a constant
potential of +1 V or -1 V for approximately 3 minutes. After the
oxidation/reduction step, the chip was taken out of the electrolyte
solution, patted briefly to remove the electrolyte solution from
the surface and measured by AFM (Nanoscope II). The section
analysis measurements were performed on at least 5 different
positions.
[0066] When the PPy/PF.sub.6 elements 80 were oxidized at +1V the
oxidation caused an expansion of the film while reduction at the
adjacent electrode caused a shrinkage as illustrated in FIG. 10A.
In FIG. 10A, a PPy strip 82 to the left of a channel 84 was reduced
at -1 V and a PPy strip 86 to the right of the channel 84 was
oxidized at +1 V. The difference in the height of oxidized and
reduced PPy elements was 66.+-.4%. On oxidation positive charges
(polarons and bipolarons) were created on the polymer backbone and
PF.sub.6.sup.- anions and accompanying solvent entered the PPy
elements 80 to balance the positive charges on the polymer and, as
a result, the polymer expanded considerably arising from the
following:
PPy+PF.sub.6.sup.-.fwdarw.PPy.sup.+.PF.sub.6.sup.-+e
EXAMPLE 2
[0067] FIG. 10B shows a second polypyrrole (PPy) actuating element
80. With reference to FIG. 10A, like reference numerals refer to
like parts unless otherwise specified. Once again, in FIG. 10B, the
upper illustration shows a three dimensional atomic force
microscopy (AFM) topographic image of the polypyrrole (PPy)
actuating element 80 and the lower illustration shows a
cross-sectional line drawing end view of the polypyrrole (PPy)
actuating element 80.
[0068] The experiment was performed similarly to Example 1 above
except that tetrabutylammonium triflouromethanesulfonate
(TBACF.sub.3SO.sub.3) was used as an electrolyte both for
polymerisation and actuation. The AFM topographic image shows that,
in this case, the PPy strip 82 oxidized at +1V (to the left of the
channel 84) shrank and the PPy strip 86 reduced at -1 V (to the
right of the channel 84) expanded, which is opposite to Example 1.
The section analysis showed that the average height change between
1.0 V and -1.0 V was 47.+-.10%.
[0069] The reduced state displayed a larger volume due to a cation
insertion process caused by large CF.sub.3SO.sub.3.sup.- anions
being immobilized deep within the polymer structure during
electropolymerisation. As the polymer is reduced and positive
charges removed from the polymer, TBA.sup.+ cations and solvent
need to move in to the film to balance the negative charge of the
residual CF.sub.3SO.sub.3.sup.- ions as shown by the following:
PPy.sup.+.CF.sub.3SO.sub.3.sup.-+TBA.sup.++e.sup.-.fwdarw.PPyTBACF.sub.3-
SO.sub.3
[0070] This results in film swelling.
[0071] Examples 1 and 2 demonstrate that both anion and cation
movement can be used for the actuation of PPy actuating elements
depending on the choice of electrolyte used during the polymer
synthesis and actuation.
[0072] Hence, by means of the invention, a micropump 10 is provided
which can be accurately controlled electrically, has actuators 20
which exhibit large strains, i.e. deformation of the actuators 20,
and requires low voltage to operate, the applied voltage being of
the order of about 1 volt. As a result, the micropump 10 can be
manufactured from very small components and the dielectric strength
of the material need not be selected to withstand high voltages. In
addition, the micropump 10 can be made from or encapsulated in
biocompatible materials for implantation in the human body to be
used for controlled released drug delivery or related applications.
The micropump 10 can also be used in microfluidic applications and
"lab-on-a-chip" applications. Still further, the micropump 10 can
be used in analytic devices and portable desalination systems.
[0073] It is an advantage of the invention that a micropump 10 is
provided which, being of all solid-state fabrication, can be
manufactured by micromachining techniques, including, for example,
photolithography. It is of compact dimensions and lightweight.
Further, as indicated above, the micropump 10 can be of a
biocompatible material or encapsulated in a biocompatible material
for implantation purposes. Due to the fact that non-metallic
components are used, the need for biocompatible metallic
components, such as titanium components, is obviated. In addition,
the micropump 10 has no mechanically moving parts and, as a result,
should be able to operate over long periods of time. Related to
this is the fact that no valves are required thereby further
improving the wear resistance of the micropump 10. The micropump 10
can also be used in a bi-directional manner by appropriate
actuation of the actuators 20.
[0074] The micropump 10 is a small volume device enabling metering
of fluids in the picolitre, nanolitre and microlitre ranges and is
able to be implanted into patients for controlled released drug
delivery.
[0075] The use of conducting polymers as actuators enables large
strains/deformations at low voltages in comparison with
piezoelectric devices, which carries the benefit of reducing the
overall height of the device. Further, the use of polymers
simplifies manufacture and results in a relatively inexpensive,
disposable device which is also less fragile than existing
micropumps.
[0076] The use of a silicon substrate 24 for the structure 12
renders the micropump 10 suitable for interconnection with control
circuitry to enable the micropump 10 to be controlled, possibly
externally of the patient's body, by suitable wireless interfaces.
The micropump 10 can also be integrated with a microprocessor to
provide refined control of drug delivery. Hence dosages can be
altered externally of the patient's body by means of the processor
and the wireless interface.
[0077] It will be appreciated by persons skilled in the art that
numerous variations and/or modifications may be made to the
invention as shown in the specific embodiments without departing
from the spirit or scope of the invention as broadly described. The
present embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive.
* * * * *