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 ).

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&#39;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 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° 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° 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 4 , TBAPF 6 , TBACF 3 SO 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 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 μm to a few μm&#39;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° 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° 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×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 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 2 ), to obtain a film thickness of about 2 μm. The PPy elements  80  were cycled in pyrrole-free solution of 0.1 M TBAPF 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 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 6   −  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: 
         [0000]      PPy+PF 6   − →PPy + .PF 6   − +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 3 SO 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 3 SO 3   −  anions being immobilized deep within the polymer structure during electropolymerisation. As the polymer is reduced and positive charges removed from the polymer, TBA +  cations and solvent need to move in to the film to balance the negative charge of the residual CF 3 SO 3   −  ions as shown by the following: 
         [0000]      PPy + .CF 3 SO 3   − +TBA + +e − →PPyTBACF 3 SO 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&#39;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&#39;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.