EP1883399A2 - Fluid delivery device having an electrochemical pump with an ion-exchange membrane and associated method - Google Patents
Fluid delivery device having an electrochemical pump with an ion-exchange membrane and associated methodInfo
- Publication number
- EP1883399A2 EP1883399A2 EP06771378A EP06771378A EP1883399A2 EP 1883399 A2 EP1883399 A2 EP 1883399A2 EP 06771378 A EP06771378 A EP 06771378A EP 06771378 A EP06771378 A EP 06771378A EP 1883399 A2 EP1883399 A2 EP 1883399A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- fluid delivery
- delivery device
- electrochemical pump
- fluid
- reservoir
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Definitions
- the present invention relates in general to a fluid delivery device that includes an electrochemical pump for controllably delivering small volumes of fluid with high precision and accuracy.
- the fluid delivery rate of the device can also be changed during operation by simple means.
- fluids and/or chemical agents may include, biologicals, drugs, lubricants, fragrant fluids, and chemical agents.
- a common example of such an application is the gradual administration of a pharmaceutical agent into the human body.
- a very common and traditional apparatus for the gradual administration of fluid into the human body is an intravenous administration set in which gravity induced hydrostatic infusion dispenses a fluid from a familiarly suspended bottle or bag above the patient.
- Additional transdermal technologies include: iontophoresis wherein low voltage electrical current is utilized to drive charged drugs through the skin; electroporation wherein short electrical pulses of high voltage is utilized to create transient aqueous pores in the skin; sonophoresis wherein low frequency ultrasonic energy is utilized to disrupt the stratum corneum; and thermal energy wherein heat is utilized to make the skin more permeable and to increase the energy of drug molecules. Even magnetic energy, or magnetophoresis, has been investigated as a means to increase drug flux across the skin. Of these transdermal technologies, only iontophoresis has been successfully developed into a marketable product, albeit for local pain relief.
- a transdermal system may not be the preferred method for gradually administering fluids in every case and various factors should be considered that may affect its usefulness, such as: the adhesive utilized to secure the system to the individual may not adhere well to all types of skin; some drug formulation may cause skin irritation or allergy; the transdermal system may be uncomfortable to wear or too costly; and some drugs that require high blood levels (low potency) cannot be properly administered.
- a mechanical pump dispenser is another mechanism for gradually administering fluids to an individual.
- the mechanical pump dispenser uses various types of mechanical pumps to expel the fluid from a reservoir.
- Some processes incorporating a mechanical pump dispenser include: a continuous intravenous infusion pump system, for example from Intevac Inc.; an epidural infusion system; and a subcutaneous infusion system, e.g., utilizing a portable insulin infusion pump.
- An externally worn pump is also conventionally used with a transcutaneous catheter, however, the external pump is often bulky and inconvenient because it is typically strapped onto the wearer, or carried on a belt or in a harness.
- a common drawback of the mechanical pump is that the required entry site into the body is susceptible to infection.
- most mechanical pumps are designed to deliver relatively large quantities of fluid and do not effectively dispense small volumes or for longer periods of time.
- a charged reservoir dispenser stores a fluid under pressure in a flexible reservoir and then selectively expels the fluid by the force of internal reservoir pressure — the rate of release often being regulated by a plurality of complex valve systems.
- a pressurized gas dispenser uses a pressurized gas to expel the fluid.
- an osmotic dispenser relies on a solute that exhibits an osmotic pressure gradient against water to dispense the fluid.
- the OROS ® system produced by ALZA Corporation is an example of an osmotically driven system in which osmosis is the energy source for drug delivery.
- the drug solution flows from the tablet at a constant zero-order rate as the tablet progresses through the gastro-intestinal (GI) tract until the entire solid drug in the core is dissolved or until the unit is eliminated.
- GI gastro-intestinal
- the release of the drug is controlled by the solubility of the drag in gastric fluid, the osmotic pressure of the core formulation, and the dimensions and permeability of the membrane.
- Smaller sized implantable drag delivery pumps are also available; such as the osmotic pump of the DUROS ® system.
- water is imbibed osmotically through a membrane into a salt chamber pressurizing a piston to expand into a drug chamber to force a drug out through a delivery orifice.
- the driving force behind the drag delivery of this pump is osmotic pressure, which can be as high as 200 atmospheres depending on the salt used, even though the pressure required to pump the drag from the device is small and the drag delivery rate remains constant as long as some excess undissolved salt remains in the salt chamber.
- osmotic systems are small, simple, reliable, and less expensive to manufacture. Because of the small size of the osmotic system, it can be implanted during a simple procedure in the physician's office. On the other hand, the fixed delivery rate of the osmotic pump in not adjustable during its operation.
- Gas generating devices that are both portable and accurate for dispensing small volumes have also been used in drag delivery systems. These gas-generating methods include galvanic cells and electrolytic cells.
- galvanic gas generating cells hydrogen or oxygen gas is formed at the cathode or anode, respectively, as a result of a reaction between a metal or metal oxide and an aqueous electrolyte.
- a galvanic cell is an electrochemical cell that requires no externally applied voltage to drive the electrochemical reactions.
- the anode and cathode of the galvanic cell are connected through a resistor that regulates the current passed through the cell, and in turn, directly regulates the production of gas that exerts a force on a diaphragm or piston — thereby expelling the drug.
- a number patents have disclosed delivery systems based on the use of galvanic hydrogen generating cell, e.g., U.S. Pat. Nos. 5,951,538; 5,707,499; and 5,785,688.
- a zinc anode reacts with an alkaline electrolyte producing zinc oxide and water molecules are reduced on porous carbon electrode producing gaseous hydrogen.
- 5,242,565 and 5,925,030 disclose a galvanic oxygen-generating cell that is constructed much like a zinc/air button cell, wherein a reducible oxide is reduced at the cathode while hydroxyl ions are formed. The hydroxyl ions oxidize at the anode and release oxygen.
- an electrolytic cell In contrast to the galvanic cell, an electrolytic cell requires an external DC power source to drive the electrochemical reactions. When voltage is applied to the electrodes, the electrolyte gives off a gas that exerts a force on a diaphragm or piston — thus expelling the fluid.
- Three types of electrolytic gas generating cells have been proposed for use in fluid delivery devices. A first type is based on water electrolysis requiring an operating voltage over 1.23 V. A second type, also known as oxygen and hydrogen gas pumps, requires a lower DC voltage than that utilized in water electrolysis systems. Both of these cell types utilize an ion exchange polymer membrane.
- a third type of gas generating electrolytic cell is based on the use of an electrolytically decomposable chemical compound that produces a reduced metal at the cathode, and generates gaseous oxygen by oxidation of water at the anode.
- U.S. Pat. No. 5,891,097 discloses an electrochemically driven fluid dispenser based on the electrolysis of water.
- water is contained in an electrochemical cell in which porous metal electrodes are joined to both sides of a solid polymer cation exchange membrane, and both of the two electrodes are made to contact with the water so as to use oxygen or hydrogen generated from an anode or cathode respectively, upon current conduction.
- hydrogen, oxygen, or a gas mixture of hydrogen and oxygen — generated by electrolysis of water when a DC current is made to flow between the electrodes — is used as a pressurization source of the fluid dispenser.
- Electrochemical oxygen and hydrogen pumps are constructed in a similar manner to the above-discussed water electrolysis cell and are described in several U. S. patents, e.g., U.S. Pat. Nos. 5,938,640; 4,902,278; 4,886,514; and, 4,522,698.
- Electrochemically driven fluid dispensers disclosed within these patents have an electrochemical cell in which porous gas diffusion electrodes are joined respectively to the opposite surfaces of an ion exchange membrane containing water functioning as an electrolyte.
- the electrochemically driven fluid dispenser uses such a phenomenon that when hydrogen is supplied to an anode of the electrochemical cell and a DC current is made to flow between the anode and the cathode, the hydrogen becomes hydrogen ions at the anode.
- the hydrogen generated and pressurized at the cathode is used as a driving source for pushing a piston, a diaphragm, or the like.
- oxygen may be used in place of hydrogen as a reactant in this type of electrochemical cell, wherein the cell then acts as an oxygen pump.
- oxygen is reduced on one side of a water-containing electrolytic cell and water is oxidized on the opposite side to generate molecular oxygen, wherein the molecular oxygen so generated is used as the propellant to force liquid from an adjacent reservoir.
- a gas generating electrolytic cell using an electrolytically decomposable chemical compound that produces a reduced metal at the cathode, and generates gaseous oxygen by water oxidation at the anode is disclosed in U.S. Pat. No. 5,744,014.
- This cell generally includes a graphite anode, an aqueous electrolyte, and a copper hydroxide cathode.
- copper is plated out in the cathode and oxygen is released at the anode.
- an active cathode material is selected such that the cells require an applied voltage for the electrochemical reactions to proceed.
- a battery cell is provided in the circuit to drive the current through the gas-generating cell.
- the rate of oxygen generated at the anode is directly proportional to the current and acts as a pressurizing agent to perform the work of expelling a fluid from a bladder or other fluid-containing reservoir, which has a movable wall that is acted upon as the gas is generated.
- electrochemically driven fluid delivery devices are operable for certain applications, they are not optimal for others.
- gas generating cell based pumps are sensitive to temperature and atmospheric pressure. For this reason, osmotic and electroosmotic pumps are often more appropriate.
- the osmotic pump involves imbibing water or another driving fluid.
- the pump consists of three chambers: a salt chamber, a water chamber, and a fluid chamber.
- the salt and water chambers are separated by a semi-permeable membrane. This configuration creates a high osmotic driving force for water transport across the membrane. This membrane is permeable to water, but impermeable to salt.
- the fluid chamber is separated from the other two chambers by a flexible diaphragm. Water imbibes osmotically into the salt chamber creating substantial hydrostatic pressures, which in turn exert a force on the diaphragm — thus expelling the fluid.
- the use of osmotic pumps is typically limited to applications requiring constant fluid delivery.
- the osmotic pump In order to vary the fluid flow, it is typically necessary to provide numerous osmotic pumps with differing outputs.
- the osmotic pump also requires charging — the time required for liquid to diffuse through the semi-permeable membrane and begin dissolving the osmagent at steady state — which in turn delays delivery of the active and further limits its suitability for instantaneous or emergency use.
- the fluid delivery rate of the osmotically driven device can neither be changed nor is it possible to shut-off the delivery of the active after commencement of delivery. Hence, it is preferable to utilize a device that can be rapidly switched-on and allows the delivery rate to be changed by a remote controlling mechanism.
- An electroosmotic pump is an electrolytic cell having a permselective ion exchange membrane and therefore requires an external DC power source to drive the electrode reactions.
- U.S. Pat. No. 3,923,426 discloses an electrochemically driven fluid dispenser based on electroosmotic fluid transport.
- the pump comprises a plastic housing having a fluid inlet and outlet, a pair of spaced silver-silver chloride electrodes disposed in the housing and connected to a D. C.
- a porous ceramic plug that has a high zeta potential relative to the fluid, a cation exchange membrane positioned on each side of the ceramic plug between it and the electrode facing it, and a passageway in the housing extending from the fluid inlet to one side of the plug and from the other side of the plug to the outlet.
- a potential difference is applied across anode and cathode, the transport fluid will flow through the porous plug from the anode to the cathode.
- One particular disadvantage of this electroosmotic pump with a porous plug is that the delivery pressures are very low, well below 0.5 ATM. In addition, any ions in the driving fluid will substantially affect the zeta potential and reduce the electroosmotic flow.
- Another disadvantage of this electroosmotic pump is that it requires an external D. C. power source that lessens the overall volume efficiency of the fluid delivery device.
- an implantable volume efficient fluid dispenser including a highly accurate programmable delivery mechanism that can be quickly adjusted to change its delivery rate as desired.
- the delivery mechanism occupies a small portion of the fluid dispenser, is capable of delivering small volumes of fluid with precision and accuracy, and is impervious to barometric pressure and temperature.
- the present invention is directed to a controlled adjustable water transporting fluid delivery device, comprising: (a) an electrochemical pump, wherein the pump is capable of transporting water; (b) a pump product chamber, wherein the pump product chamber is capable of retaining water generated from the pump — including at high pressure; (c) a displaceable member positioned between the pump product chamber and a reservoir, wherein the displaceable member is controllably displaced upon generation of water from the electrochemical pump; (d) a reservoir, wherein the reservoir is capable of containing a fluid that is delivered upon displacement of the displaceable member; and, (e) a housing for containing the pump, the pump product chamber, the displaceable member, and a reservoir.
- the displaceable member is selected from the group consisting of a piston, bladder, bellows, diaphragm, plunger, and combinations thereof.
- the fluid delivery device can also include a catheter for delivering fluid at a desired location.
- a pump engine comprises a protective porous separator, a first electrode, a second electrode, an ion exchange membrane, and an electric controller.
- the pump may further include an activation switch to start the fluid delivery; a controller, e.g., an electrical resistor or circuit that may or may not be controlled remotely, capable of enabling a faster fluid delivery start-up and shut- off, and quicker adjustability; and a support member(s) for providing physical support for the membrane.
- the reservoir includes one or more apertures, e.g., outlet and filling/refilling port, and contains a fluid selected from the group consisting of a biological, drug, lubricant, fragrant fluid, chemical agent, and mixtures thereof.
- a process for delivering a fluid comprising the steps of: (a) providing a fluid delivery device having an electrochemical water transporting pump; (b) transporting water through the water transporting pump, thereby expanding a volume of a pump product chamber; (c) generating sufficient pressure from the expanded pump product chamber; and, (d) displacing a displaceable member wherein a fluid is controllably expelled from the fluid delivery device.
- An object of the present invention is to provide a fluid delivery device that includes a volume efficient fluid dispenser wherein the delivery mechanism occupies a small part of the overall device.
- Another object of the present invention is to provide a fluid delivery device that is small, portable, and capable of being implanted.
- a further object of the present invention is to provide a fluid delivery device that is highly accurate and capable of precisely delivering small volumes of fluid.
- a still further object of the present invention is to provide an adjustable fluid delivery device that can be controlled to quickly change the delivery rate.
- Yet another object of the present invention is to provide a fluid delivery device that utilizes few moving parts, is simple to construct, and is less susceptible to mechanical failure.
- Yet a still further object of the present invention is to provide a fluid delivery device that does not utilize compressible components and thus enables the device to operate at different altitudes and a wide range of barometric pressures.
- FIG. 1 is a cross-sectional schematic representation of a fluid delivery device having an anionic exchange membrane fabricated in accordance with the present invention
- Fig. 2 is a graph of volume flux versus current density in the volume flux range from 2.0 to 10.0 ⁇ L h "1 cm “2 for a fluid delivery device having an anionic exchange membrane fabricated in accordance with the present invention;
- Cell parameters AMI 7001 ion exchange membrane, powder zinc anode, nickel mesh cathode, 0.9% NaCl electrolyte;
- Fig. 3 is a graph of volume flux versus current density in the volume flux range from 0 to 2.5 ⁇ L h "1 cm “2 for a fluid delivery device having an anionic exchange membrane fabricated in accordance with the present invention;
- Cell parameters Neosepta AFN ion exchange membrane, solid zinc anode, silver chloride cathode, 0.9% NaCl electrolyte;
- Fig. 4 is a graph of volume flux versus current density in the volume flux range from 0.5 to 2.5 ⁇ L h "1 cm “2 for a fluid delivery device having an anionic exchange membrane fabricated in accordance with the present invention;
- Cell parameters Neosepta ® AMX ion exchange membrane, solid zinc anode, silver chloride cathode, 0.9% NaCl electrolyte;
- Fig. 5 is a graph of volume flux versus current density in the volume flux range from 0.2 to 1.2 ⁇ L h "1 cm “2 for a fluid delivery device having an cationic exchange membrane fabricated in accordance with the present invention;
- Cell parameters NAFION ® 117 cation exchange membrane, solid zinc anode, silver chloride cathode, 0.9% NaCl electrolyte;
- Fig. 6 is a graph of volume flux vs. pressure applied to the electrochemical product chamber at two different current density values for a fluid delivery device having an anionic exchange membrane fabricated in accordance with the present invention; Cell parameters: Neosepta ® AFN ion exchange membrane, solid zinc anode, silver chloride cathode, 0.9% NaCl electrolyte; and,
- Fig. 7 is a graph of volume flux vs. pressure applied to the electrochemical product chamber at two different current density values for a fluid delivery device having an cationic exchange membrane fabricated in accordance with the present invention; Cell parameters: NAFION ® 117 cation exchange membrane, solid zinc anode, silver chloride cathode, 0.9%
- a fluid delivery device 10 comprises a reservoir 12, a displaceable member 14, an electrochemical pump product chamber 16, an electrochemical pump 18, and a housing 20. It is to be further understood that Fig. 1 is merely a schematic representation of the fluid delivery device 10 of the present invention and as such, some of the components have been distorted from their actual scale for pictorial clarity.
- the reservoir 12 is capable of containing a fluid 22, such as a biological, drug, lubricant, fragrant fluid, chemical agent, or mixtures thereof, which is delivered upon displacement of the displaceable member 14.
- a fluid 22 is herein defined as a liquid, gel, paste, or other semi-solid state material that is capable of being delivered out of a reservoir.
- the reservoir 12 may include one or more apertures 24 for directing delivery of the fluid 22 from the fluid delivery device 10.
- the reservoir 12 may be fabricated from any one of a number of materials, including, for example, metal, glass, natural and synthetic plastic, and composites.
- the displaceable member 14 is positioned between the reservoir 12 and the electrochemical pump product chamber 16.
- the displaceable member 14 is shown in Fig. 1 as comprising a piston, however, other displaceable members that would be known to those having ordinary skill in the art having the present disclosure before them are likewise contemplated for use; including, but not limited to: a bladder, a diaphragm, a bellows, and a plunger.
- the electrochemical pump product chamber 16 is positioned between the displaceable member 14 and the electrochemical pump 18, and is capable of containing water 26 that — as will be discussed in greater detail below — is controllably generated during operation of the electrochemical pump 18. Similar to the reservoir 12, the electrochemical pump product chamber 16 may be fabricated from any one of a number of materials, such as metal, glass, natural and synthetic plastic, composites, etc.
- the electrochemical pump 18 shown in Fig. 1 includes a protective porous separator 28, an auxiliary electrode compartment 30, an auxiliary electrode 32, an ion exchange membrane 34, an active electrode 36, an electric resistor 38, an activation switch 40, and a support member(s) 42.
- the protective porous separator 28 is positioned at an end of fluid delivery device 10 distal from the reservoir 12.
- the protective porous separator 28 is generally permeable to H 2 O molecules from the body, and its cooperation with saline from the auxiliary electrode compartment 30 — e.g., metal halides, such as NaCl — enables the water from an external source 46 — e.g., an inside of a living being's body — to diffuse or migrate into the auxiliary electrode compartment 30.
- the protective porous separator 28 may be fabricated from any one of a number of materials; including, but not limited to metal, glass, natural and synthetic plastic, and composites. Additionally, a porous protective gel may be used to serve the purpose of the separator.
- the protective porous separator or protective porous gel is generally permeable to H 2 O molecules or saline.
- the protective porous separator or gel may also include a water or saline reservoir.
- the use of the protective porous separator 28 is not required and the auxiliary electrode compartment 30 may be self-contained without the presence of the protective porous separator.
- the auxiliary electrode can be exposed directly to fluid and the necessary amount of water is carried in the auxiliary electrode compartment 30 without any migration of water from external source 46.
- an anionic exchange membrane, the auxiliary electrode 32, the anionic exchange membrane 34, and the active electrode 36 are respectively positioned adjacent to the protective porous separator 28.
- the auxiliary electrode 32 is a porous cathode pellet that can be readily reduced when coupled with the active metal anode 36.
- the auxiliary electrode 32 may be fabricated from porous silver chloride, manganese dioxide, or other materials that can be readily reduced or may catalyze reduction reaction — e.g., reduction of oxygen or evolution of gaseous hydrogen from water — when coupled with the active metal anode.
- the active metal anode 36 is a solid pellet, mesh, or metal powder type electrode fabricated from zinc, iron, magnesium, aluminum, or another corrosion stable metal or alloy.
- the auxiliary electrode 32 may include a conventional current collector, such as screen, mesh, or wire current collector fabricated from silver, titanium, platinum, or another corrosion stable metal.
- the active metal anode 36 may also include a conventional current collector, such as a screen, mesh or wire current collector fabricated from the same metal as that of the active metal anode; or it may be fabricated from other metals such as brass, which is coated with the same metal as is the active anode metal. While specific examples of electrode materials and current collectors have been disclosed, for illustrative purposes, it is to be understood that other electrode materials known to those with ordinary skill in the art having the present disclosure before them are likewise contemplated for use.
- the anion exchange membrane 34 is positioned between the first electrode 32 and the second electrode 36.
- the anion exchange materials from which the membrane 34 may be made are well known in the art and do not require extensive elaboration. In brief, these materials are cross-linked polymer resins of the strong base type. Preferred resins are the copolymers of styrene and di-vinyl benzene having quaternary ammonium ion as the charge group, which have a high selectivity for chloride ions and high resistance to organic fouling.
- Such anionic membranes are, for example, Neosepta-type membranes, which are commercially available from AMERIDIA (www, ameridia. com) .
- the auxiliary electrode 32, the cationic exchange membrane 34, and the active electrode 36 are respectively positioned adjacent to the protective porous separator 28.
- the auxiliary electrode 32 is a solid pellet, mesh, or metal powder type electrode that is fabricated from zinc, iron, magnesium, aluminum, or another corrosion stable metal or alloy.
- the active metal anode 36 is a porous cathode pellet that can be readily reduced when coupled with the active metal anode 36.
- the auxiliary electrode 32 may be fabricated from porous silver chloride, manganese dioxide, or other materials that can be readily reduced, or may catalyze reduction reaction — e.g., reduction of oxygen or evolution of gaseous hydrogen from water — when coupled with the active metal anode.
- the auxiliary metal anode 32 may also include a conventional current collector, such as screen, mesh, or wire current collectors fabricated from the same metal as that of the active metal anode 36; or it may be fabricated from other metals such as brass, which is coated with the same metal as is the active anode metal.
- the active electrode 36 may include a conventional current collector such as screen, mesh, or wire current collectors fabricated from silver, titanium, platinum, or another corrosion stable metal. While specific examples of electrode materials and current collectors have been disclosed for illustrative purposes, it is to be understood that other electrode materials known to those with ordinary skill in the art having the present disclosure before them are likewise contemplated for use.
- the cation exchange membrane 34 is positioned between the first electrode 32 and the second electrode 36.
- the cation exchange materials from which the membrane 34 may be constructed are well known in the art and do not require extensive elaboration. In brief, these materials are cross-linked polymer resins of the strong base type. Some preferred resins include copolymers of styrene and di-vinyl benzene having sulfonate ion as the charge group, which have a high selectivity for sodium ions. Such commercial cationic membranes, e.g., National type membranes, are available from Dupont ® .
- the electrical control circuit 38 is connected to the electrodes via conventional electrical conduit and as will be discussed in greater detail below, directly controls the rate of water transfer from the external source 46 to the electrical pump product chamber 16.
- the support members 42 are highly porous solid disk materials that provide mechanical rigidity for the ion exchange membrane and allow water to transport through it.
- the support members 42 can be made of hard plastic; ceramic; glass or corrosion stable metals, e.g., titanium; or a combination thereof.
- the fluid delivery device 10 can deliver fluid 22 in accordance with the following process.
- the activation switch 40 is actuated, whereupon an electrical circuit is complete and causes electrode reactions to take place at the electrodes 32, 36, and water to be extracted from the external environment 46; and, ultimately to be driven across ion exchange membrane 34 into the electrical pump product chamber 16.
- water from the external environment 46 such as a human body — diffuses through the protective porous separator 28 and into the first electrode compartment 30.
- the first electrode 32 is made of silver chloride and the second electrode 36 is made of zinc
- the following reactions occur.
- the electrode silver chloride is reduced to metallic silver, thus releasing chloride ions into solution according to the equation:
- the osmotic flux is the result of the electro-osmotic flux, which establishes the necessary concentration gradient. Therefore, the osmotic flux can be modified by virtue of modifying the electroosmotic driving force. This is not possible with osmosis based devices and so their delivery rate is not adjustable.
- the water molecules transported into the electrochemical pump product chamber 16 generate pressure within the electrochemical pump product chamber. The pressure build-up causes some back transport of water from the electrochemical pump product chamber 16 to the auxiliary electrode compartment 30.
- Jeof electroosmotic flux
- J O f osmotic flux
- Jbdf back diffusion flux
- Jhf hydraulic flux
- the first electrode 32 is made of zinc and the second electrode 36 is made of silver chloride
- the following reactions take place.
- the electrode zinc is dissolved according to the equation:
- the osmotic flux is the result of the electro-osmotic flux, which establishes the necessary concentration gradient. Therefore, the osmotic flux can be modified by virtue of modifying the electroosmotic driving force. This is not possible with osmosis based devices and so their delivery rate is not adjustable.
- the water molecules transported into the electrochemical pump product chamber 16 generate pressure within the electrochemical pump product chamber 16. The pressure build-up causes some back transport of water from the electrochemical pump product chamber 16 to the auxiliary electrode compartment 30.
- the steady state flux obtained for a given ion-exchange membrane can be expressed in terms of the same mathematical equation I shown above.
- Both embodiments of the present invention discussed above are capable of generating high pressure within the electrochemical pump product chamber 16. High pressure is desired to deliver viscous formulations and to also produce delivery that is less sensitive to the ambient pressure changes.
- Fig. 6 The pressure generated by the first embodiment of the present invention discussed above is shown in Fig. 6 wherein the maximum pressure (P max , the pressure at which the flux becomes zero) that can be achieved is 20 psi at 0.136 mA/cm 2 . Operation at 3.8 times the current density (0.525 mA/cm 2 ) provided a P max of 700 psi. In the case of the second embodiment of the present invention, Fig. 7 shows P max to be 350 psi at 0.136 mA/cm 2 .
- the generated pressure imparts a force upon displaceable member 14 — the only movable component.
- the displaceable member 14 is displaced laterally away from electrochemical pump product chamber 16, which controllably expels fluid from the reservoir 12.
- fluid delivery rate or a fluid delivery rate profile, e.g., pulsing
- pulsing can be facilely varied by other means, including, but not limited to, selecting resistors with different resistance values or by changing the signal output from the electrical controller.
- volume flux and current density were obtained at high and low volume fluxes. This is illustrated in the case of first embodiment in Fig. 2 for volume flux ranging from 2.0 to 10.0 ⁇ L h '1 cm '2 ; and in Fig. 3 for volume flux ranging from 0.1 to 2.5 ⁇ L h "1 cm “ 2 .
- the current density required to produce such volume fluxes depends on the membrane type used and may be as low as 20 ⁇ A cm "2 to produce a volume flux of 0.5 ⁇ L h "1 cm “2 , as shown in Fig. 4.
- Another feature of the embodiment shown in Fig. 1 is high stability operation over more than 1000 hours of operation.
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Abstract
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Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US10/908,804 US7458965B2 (en) | 2002-05-01 | 2005-05-26 | Fluid delivery device having an electrochemical pump with an ion-exchange membrane and associated method |
PCT/US2006/020570 WO2006128039A2 (en) | 2002-05-01 | 2006-05-26 | Fluid delivery device having an electrochemical pump with an ion-exchange membrane and associated method |
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US20150258273A1 (en) * | 2011-08-31 | 2015-09-17 | Forrest W. Payne | Electrochemically-Actuated Microfluidic Devices |
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