US20080152507A1 - Infusion pump with a capacitive displacement position sensor - Google Patents

Abstract

Various methods and devices are provided for an electrokinetic infusion pump. In one embodiment of the invention, the infusion pump includes an infusion pump module, which can be configured to dispense an insulin containing infusion liquid, and an electrokinetic engine. The infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module. The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing. The capacitive displacement sensor is configured for measuring capacitance between the first capacitive plate and the second capacitive plate and can send a feedback signal to a closed loop controller that is indicative of the capacitance between the first and second capacitive plates.

Description

FIELD OF THE INVENTION
• The present invention relates, in general, to a medical devices and systems and, in particular, to infusion pumps, infusion pump systems and associated methods.
BACKGROUND
• Electrokinetic (EK) pumps provide for liquid displacement by applying an electric potential across a porous dielectric media that is filled with an ion-containing electrokinetic solution. Properties of the porous dielectric media and ion-containing solution (e.g., permittivity of the ion-containing solution and zeta potential of the solid-liquid interface between the porous dielectric media and the ion-containing solution) are predetermined such that an electrical double-layer is formed at the solid-liquid interface. Thereafter, ions of the electrokinetic solution within the electrical double-layer migrate in response to the electric potential, transporting the bulk electrokinetic solution with them via viscous interaction. The resulting electrokinetic flow (also known as electroosmotic flow) of the bulk electrokinetic solution is employed to displace (i.e., “pump”) a liquid. Further details regarding electrokinetic pumps, including materials, designs, and methods of manufacturing are included in U.S. patent application Ser. No. 10/322,083 (United States Published Application No. 2004/0074784) filed on Dec. 17, 2002, which is hereby incorporated in full by reference.
SUMMARY
• The present invention provides various methods and devices for an electrokinetic infusion pump. In one embodiment, the electrokinetic infusion pump includes an infusion pump module, which can be configured to dispense a medicament or another treatment agent (e.g., an insulin containing infusion liquid), and an electrokinetic engine. The infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module. The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The capacitive displacement sensor includes a first capacitive element, such as a capacitive plate, disposed on the moveable partition and a second element, such as a capacitive plate, disposed on the infusion module housing. The capacitive displacement sensor is configured for measuring capacitance between the first capacitive element and the second capacitive element and can send a feedback signal to a closed loop controller that is indicative of the capacitance between the first and second capacitive plates. In one exemplary embodiment, the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm. A gap between the first capacitive plate and the second capacitive plate can have a dimension in the range of approximately 10-1000 micrometers.
• In another embodiment, the electrokinetic engine includes a moveable partition and the infusion pump includes an infusion housing, and the capacitive displacement sensor is a dual capacitive displacement sensor. The dual capacitive displacement sensor includes a first capacitive plate and a second capacitive plate disposed on the moveable partition and a third capacitive plate and a fourth capacitive plate disposed on the infusion housing. The first, second, third, and fourth capacitive plates are in operative electrical contact. An overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.
• In another exemplary embodiment, an infusion pump system is provided that includes an infusion pump, for example, an electrokinetic pump, having a capacitive displacement position sensor and a closed loop controller. The infusion pump and closed loop controller are in operative communication and configured such that the closed loop controller can determine and control a dispensing state of the infusion pump based on a feedback signal received from the capacitive displacement position sensor. The infusion pump further includes an infusion pump module and an electrokinetic engine. The capacitive displacement sensor is configured for sensing a dispensing state of the infusion pump module. The infusion pump can be configured to dispense, for example, an insulin-containing infusion liquid.
• The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The electrokinetic engine can also include an electrokinetic supply reservoir that is at least partially collapsible. The capacitive displacement sensor can include a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing, and the capacitive displacement sensor can be configured for sensing a dispensing state by measuring capacitance between the first capacitive plate and the second capacitive plate. In one embodiment, the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm, and a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.
• In one embodiment, the electrokinetic engine includes a moveable partition and the capacitive displacement sensor is a dual capacitive displacement sensor that includes first, second, third, and fourth capacitive plates. The first, second, third, and fourth capacitive plates are in operative electrical contact and an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.
• Methods for the closed loop control of an infusion pump are also provided, and in one embodiment the method can include sensing a dispensing state of an infusion pump, for example, an electrokinetic infusion pump, with a capacitive displacement position sensor and signaling the sensed dispensing state of the infusion pump to a closed loop controller via a feedback signal. The closed loop controller determines the dispensing state of the infusion pump based feedback signal and controls the dispensing state of the infusion pump by sending command signals from the closed loop controller to an engine driving the infusion pump. These steps can be repeated to maintain control of the electrokinetic infusion pump.
• Sensing the dispensing state can include sensing a position of a moveable partition of the electrokinetic infusion pump by the capacitive displacement sensor. Sensing the dispensing state can also include sensing the position of the moveable partition due to a change in overlap between capacitive plates of the capacitive displacement sensor. The dispensing state can be an infusion liquid displacement rate or an infusion liquid volume. The step of controlling the dispensing state can include controlling the dispensing state of an insulin containing infusion liquid. The capacitive displacement position sensor can be a dual capacitive displacement sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
• FIG. 1 is an exploded schematic illustration of an electrokinetic infusion pump system with closed loop control according to an exemplary embodiment of the present invention in a first dispense state;
• FIG. 2 is an exploded schematic illustration of the electrokinetic infusion pump system shown inFIG. 1 in a second dispense state;
• FIG. 3 is a perspective illustration of an electrokinetic infusion pump system according to another exemplary embodiment of the present invention being manually manipulated;
• FIG. 4 is a cross-sectional depiction of an electrokinetic infusion pump system according to a further exemplary embodiment of the present invention in a first dispense state;
• FIG. 5 is a cross-sectional depiction of the electrokinetic infusion pump system shown inFIG. 4 in a second dispense state;
• FIG. 6 is a perspective depiction of a portion of the electrokinetic infusion pump of the EK infusion pump system shown inFIG. 4;
• FIG. 7 is a perspective depiction of a portion of the electrokinetic infusion pump of the EK infusion pump system shown inFIG. 5;
• FIG. 8 is a perspective depiction of a portion of an electrokinetic infusion pump with capacitive displacement position sensors according to another exemplary embodiment of the present invention in a first dispense state;
• FIG. 9 is a perspective depiction of the portion of an electrokinetic infusion pump shown inFIG. 8 in a second dispense state;
• FIG. 10 is a schematic drawing depicting a capacitive plate configuration of the electrokinetic infusion pump shown inFIG. 8;
• FIG. 11 is a schematic drawing depicting a capacitive plate configuration of the electrokinetic infusion pump shown inFIG. 9;
• FIG. 12 is an electrical circuit schematic depicting the analog electric circuit formed by the capacitive displacement position sensor shown inFIGS. 8-11; and
• FIG. 13 is a flow diagram illustrating a method for the closed loop control of an electrokinetic infusion pump according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION
• Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.
• Various exemplary methods and devices are provided for controlling the dispensing state of an infusion pump system. In particular, the methods and devices provide a capacitive displacement position sensor coupled with an infusion pump to control the dispensing of an infusion liquid from the infusion pump.
• FIGS. 1-2 are exploded schematic illustrations of an electrokinetic (EK)infusion pump system100 with closed loop control according to an exemplary embodiment of the present invention.FIG. 1. illustrates the EKinfusion pump system100 in a first dispense state, whileFIG. 2 depicts the EKinfusion pump system100 in a second dispense state.
• Referring toFIGS. 1 and 2, the EKinfusion pump system100 includes an electrokinetic (EK)infusion pump102 and aclosed loop controller104. TheEK infusion pump102 can include a capacitive displacement position sensor (not shown inFIGS. 1 and 2). As is described in further detail below, theEK infusion pump102 and theclosed loop controller104 are in operative communication such that theclosed loop controller104 can determine and control the dispensing state of theEK infusion pump102 based on one or more feedback signals FB from the capacitive displacement position sensor. TheEK infusion pump102 and theclosed loop controller104 can be configured in a variety of ways. For example, theinfusion pump102 and theclosed loop controller104 can be entirely separate units, partially integrated (for example, predetermined components of theEK infusion pump102 can be integrated within the closed loop controller104), or a single integrated unit.
• The EK infusion pump systems according to embodiments of the present invention, including the EKinfusion pump system100, can be employed to deliver a variety of medically useful infusion liquids such as, for example, insulin for diabetes; morphine and other analgesics for pain; barbiturates and ketamine for anesthesia; anti-infective and antiviral therapies for Acquired Immune Deficiency Syndrome (AIDS); antibiotic therapies for preventing infection; bone marrow for immunodeficiency disorders, blood-borne malignancies, and solid tumors; chemotherapy for cancer; dobutamine for congestive heart failure; monoclonal antibodies and vaccines for cancer, brain natriuretic peptide for congestive heart failure, and vascular endothelial growth factor for preeclampsia. The delivery of such infusion liquids can be accomplished via any suitable route including subcutaneously, intravenously or intraspinally.
• TheEK infusion pump102 can also include an electrokinetic (EK)engine106 and aninfusion module108. TheEK engine106 can include an electrokinetic (EK)supply reservoir110, an electrokinetic (EK)porous media112, an electrokinetic (EK)solution receiving chamber114, afirst electrode116, asecond electrode118, and an electrokinetic (EK) solution120 (depicted as upwardly pointing chevrons).
• The pore size of theporous media112 can be, for example, in the range of 100 nm to 200 nm. A person skilled in the art will appreciate that theporous media112 can have any number of pores with any pore size that allows the appropriate amount ofelectrokinetic solution120 to flow through it. Moreover, theporous media112 can be formed of any suitable material including, by way of non-limiting example, Durapore Z PVDF membrane material available from Millipore, Inc. USA.EK solution120 can be any suitable EK solution including, but not limited to, 10 mM TRIS/HCl at a neutral pH.
• Theinfusion module108 can include the EK solution receiving chamber114 (which is also considered part of the EK engine106), aninfusion module housing122, amovable partition124, aninfusion reservoir126, aninfusion reservoir outlet128, and an infusion liquid130 (depicted as dotted shading). Although the capacitive displacement position sensor of theinfusion module108 is not depicted inFIGS. 1 and 2, the feedback signal FB between the capacitive displacement position sensor and theclosed loop controller104 is shown.
• Theclosed loop controller104 can include avoltage source132 and is configured to receive the feedback signal FB from the capacitive displacement sensor and to be in electrical communication with the first andsecond electrodes116 and118. TheEK engine106, theinfusion module108, and theclosed loop controller104 can be integrated into a single assembly, into multiple assemblies, or can be separate units.
• During operation of the EKinfusion pump system100, theEK engine106 provides the driving force for displacing (pumping) the infusion liquid130 from theinfusion module108. To do so, a voltage difference is established across the EKporous media112 by the application of an electrical potential between thefirst electrode116 and thesecond electrode118. This electrical potential results in an electrokinetic pumping of theEK solution120 from theEK supply reservoir110, through the EKporous media112, and into the EKsolution receiving chamber114.
• As the electrokineticsolution receiving chamber114 receives theEK solution120, themoveable partition124 is forced to move in the direction of arrows μl, shown inFIGS. 1-2. Such movement is evident by a comparison of the first dispense state shown inFIG. 1 to the second dispense state shown inFIG. 2. As themoveable partition124 moves in the direction of μl, theinfusion liquid130 is displaced (i.e., “pumped”) out of theinfusion reservoir126 and through theinfusion reservoir outlet128 in the direction of arrow μl. TheEK engine106 can continue to displace theEK solution120 until themoveable partition124 reaches a predetermined point near theinfusion reservoir outlet128, for example, a point just proximal of theinfusion reservoir outlet128, thereby displacing a predetermined amount (e.g., essentially all) of the infusion liquid130 from theinfusion reservoir126.
• It is evident from the description above and a comparison ofFIGS. 1 and 2, that the second dispensing state represented byFIG. 2 is achieved by electrokinetically displacing (i.e., pumping or dispelling) a portion of theinfusion liquid130 that is present within theinfusion reservoir126 in the first dispensing state represented byFIG. 1.
• The rate of displacement of the infusion liquid130 from theinfusion reservoir126 is directly proportional to the rate at which theEK solution120 is pumped from theEK supply reservoir110 into the EKsolution receiving chamber114. The proportionality between the rate of displacement of the infusion liquid130 (such as an insulin containing infusion liquid) and the rate at which theEK solution120 is pumped can be, for example, in the range of 1:1 to 4:1. Furthermore, the rate at which theEK solution120 is pumped from theEK supply reservoir110 is a function of the voltage and current applied by thefirst electrode116 and thesecond electrode118 and various electro-physical properties of the EKporous media112 and the EK solution120 (such as, for example, zeta potential, permittivity of the EK solution and viscosity of the EK solution).
• The features disclosed herein are applicable to a variety of electrokinetic infusion pump systems, including, for example, the electrokinetic infusion pumps and electrokinetic infusion pump systems of the type disclosed in U.S. patent application Ser. No. 11/532,587, filed Sep. 18, 2006, entitled “Electrokinetic Infusion Pump System,” which is incorporated herein in its entirety. In addition, features disclosed herein can be used in combination with electrokinetic infusion pump systems of the type disclosed in U.S. patent application Ser. No. 11/532,587, as well as with features of electrokinetic infusion pumps as disclosed in U.S. patent application Ser. No. 11/532,691, filed Sep. 18, 2006, entitled “Malfunction Detection With Derivative Calculation,” and U.S. patent application Ser. No. 11/614,211, filed Dec. 21, 2006, entitled “Malfunction Detection In Infusion Pumps,” both of which are likewise incorporated herein in their entirety.
• Further details regarding EK engines, including materials, designs, operation and methods of manufacturing, are included in U.S. patent application Ser. No. 10/322,083 (United States Published Application No. 2004/0074784) filed on Dec. 17, 2002, which has been incorporated by reference. Although a particular EK engine is depicted in a simplified manner inFIGS. 1 and 2, any suitable EK engine can be employed in embodiments of the present invention including, but not limited to, the EK engines described in the aforementioned U.S. patent application Ser. No. 10/322,083 and EK engines that substitute a media with a microchannel(s) for the aforementioned porous media.
• The capacitive displacement position sensor ofEK infusion pump102 is configured to sense (determine) the position of themoveable partition124. Based on the sensed position of the moveable partition124 (as communicated by feedback signal FB), theclosed loop controller104 can determine the dispensing state (e.g., the displacement position of themoveable partition124 at any given time and/or as a function of time, the rate of displacement of the infusion liquid130 frominfusion reservoir126, the rate at which theEK solution120 is pumped from theEK supply reservoir110 to the EKsolution receiving chamber114, and the volume of dispensed EK solution).
• Based on such a determination of dispensing state, theclosed loop controller104 controls (i.e., can command and manage) the dispensing state by, for example, (i) adjusting the voltage and/or current applied between thefirst electrode116 and thesecond electrode118 or (ii) maintaining the voltage between thefirst electrode116 and thesecond electrode118 constant while adjusting the duration during which power is applied between thefirst electrode116 and thesecond electrode118. For example, by adjusting the voltage and/or current applied across thefirst electrode116 and thesecond electrode118, the rate at which theEK solution120 is displaced from theEK supply reservoir110 to the EKsolution receiving chamber114 and, therefore, the rate at which theinfusion liquid130 is displaced through theinfusion reservoir outlet128, can be accurately and beneficially controlled.
• The closed loop control of EK infusion pumps described above beneficially compensates for variations that may cause inconsistent displacement (i.e., dispensing) of theinfusion liquid130 including, but not limited to, variations in temperature, downstream resistance, and mechanical friction.
• TheEK supply reservoir110 can have a variety of configurations. In one embodiment, theEK supply reservoir110 can be partially or wholly collapsible. For example, theEK supply reservoir110 can be configured as a collapsible sack. Such collapsibility provides for the volume of theEK supply reservoir110 to decrease as theEK solution120 is displaced therefrom. Such a collapsibleEK supply reservoir110 can also assist in the prevention of undesirable bubble formation within theEK supply reservoir110.
• Theinfusion module housing122 can also be configured in a variety of additional ways, and can be, for example, at least partially rigid to facilitate the movement of themoveable partition124 and the reception of theEK solution120 pumped from theEK supply reservoir110.
• Themoveable partition124 can be configured to prevent migration of theEK solution120 into theinfusion liquid130, while minimizing resistance to its own movement (displacement) as the EKsolution receiving chamber114 receives theEK solution120 pumped from theEK supply reservoir110. Themoveable partition124 can, for example, include elastomeric seals that provide intimate, yet movable, contact between themoveable partition124 and theinfusion module housing122. Themoveable partition124 can have a variety of configurations, such as, for example, a piston-like configuration, or themoveable partition124 can be configured as a moveable membrane and/or bellows.
• FIG. 3 is a perspective illustration of an electrokinetic (EK)infusion pump system200 according to another exemplary embodiment of the present invention being manipulated by a user's hands (H). The EKinfusion pump system200 can include an electrokinetic (EK)infusion pump202 and aclosed loop controller204.
• TheEK infusion pump202 and theclosed loop controller204 can be handheld, and/or mounted to a user by way of clips, adhesives or non-adhesive removable fasteners. For example, the EKinfusion pump system200 can be configured to be worn on a user's belt, thereby providing an ambulatory EK infusion pump system. In addition, theclosed loop controller204 can be directly or wirelessly connected to a remote controller or other auxiliary equipment (not shown inFIG. 3) that provide analyte monitoring capabilities and/or additional data processing capabilities.
• TheEK infusion pump202 and theclosed loop controller204 can include components that are essentially equivalent to those described above with respect to theEK infusion pump102 and theclosed loop controller104. In addition, theclosed loop controller204 can include a variety of features, including adisplay240,input keys242aand242b, and aninsertion port244.
• Thedisplay240 can be configured, for example, to display a variety of information, including infusion rates, error messages and logbook information. During use of the EKinfusion pump system200, and subsequent to theEK infusion pump202 having been filled with infusion liquid, theEK infusion pump202 can be inserted into theinsertion port244. Upon such insertion, operative electrical communication is established between theclosed loop controller204 and theEK infusion pump202. Such electrical communication includes the ability for theclosed loop controller204 to receive a feedback signal FB from a capacitive displacement position sensor of theEK infusion pump202 and operative electrical contact with first and second electrodes of theEK infusion pump202.
• One skilled in the art will recognize that an infusion set (not shown but typically including, for example, a connector, tubing, needle and/or cannula and an adhesive patch) can be connected to the infusion reservoir outlet of theEK infusion pump202 and, thereafter, primed. As may be suitable for a particular infusion set, such attachment and priming can occur before or afterEK infusion pump202 is inserted intoinsertion port244. After determining the position of a movable partition ofEK infusion pump202, voltage and current are applied across the EK porous media ofEK infusion pump202, thereby dispensing (pumping) infusion liquid.
• FIG. 4 is a cross-sectional depiction of an electrokinetic (EK)infusion pump system300 according to a further exemplary embodiment of the present invention in a first dispense state, whileFIG. 5 depicts the EKinfusion pump system300 in second dispense state.FIG. 6 is a further perspective depiction of a portion of the EKinfusion pump system300 in the first dispense state ofFIG. 4, whileFIG. 7 is in the second dispense state ofFIG. 5. As will be evident from the discussion below, the focus ofFIGS. 6 and 7 is the capacitive displacement position sensor of the EKinfusion pump system300. Therefore,FIGS. 6 and 7 are further simplified versions ofFIGS. 4 and 5 that serve to highlight the capacitive displacement position sensor.
• Referring toFIGS. 4-7, the EKinfusion pump system300 includes an electrokinetic (EK)infusion pump302 and aclosed loop controller304. As will be clear to one skilled in the art from the following description, theEK infusion pump302 includes an integrated electrokinetic (EK) engine and infusion module (collectively element306) and a capacitivedisplacement position sensor307.
• The integrated EK engine andinfusion module306 includes an electrokinetic (EK)supply reservoir310, an electrokinetic (EK)porous media312, an electrokinetic (EK)solution receiving chamber314, afirst electrode316, asecond electrode318, and an electrokinetic (EK) solution320 (depicted as upwardly pointing chevrons). The integrated EK engine andinfusion module306 also includes aninfusion module housing322, amovable partition324, aninfusion reservoir326, aninfusion reservoir outlet328, and an infusion liquid330 (depicted as dotted shading).
• Themoveable partition324 can have a variety of configurations, but in the illustrated embodiment can include afirst infusion seal348, aspacer349, and asecond infusion seal350. Thespacer349 is positioned between the first and second infusion seals348,350, with the first infusion seal positioned proximal of thespacer349 and thesecond infusion seal350 positioned distal of thespacer349. Thespacer349 of themoveable partition324 is at a position B in the first dispense state a shown inFIG. 4, and is at a position C in the second dispense state as shown inFIG. 5. The distance between position B and position C is labeled D inFIG. 5.
• In an exemplary embodiment, the capacitivedisplacement position sensor307 includes a firstcapacitive element352, such as a capacitive plate, a secondcapacitive element354, such as a capacitive plate, a firstelectrical contact356, a secondelectrical contact358, and acapacitance measurement module360.
• Thefirst capacitive plate352 is mounted on themovable partition324, and moves parallel to the longitudinal axis of theinfusion module housing322 along with themovable partition324. Thesecond capacitive plate354 remains stationary and is mounted on theinfusion module housing322 such that there is a gap G (also referred to as a separation) between thefirst capacitive plate352 and thesecond capacitive plate354. The gap G can be filled with any suitable material including, for example, air, a wall of the infusion module housing322 (which is formed of plastic or other suitable electrically insulating material), other suitable electrically insulating material, and combinations thereof.
• The firstelectrical contact356 provides electrical contact between thefirst capacitive plate352 and thecapacitance measurement module360, while secondelectrical contact358 provides electrical contact between secondcapacitive plate354 andcapacitance measurement module360. In the first dispense state depicted inFIGS. 4 and 6, themoveable partition324 is in a first position, and thefirst capacitive plate352 partially overlaps thesecond capacitive plate354. Thecapacitance measurement module360 is configured to provide a feedback signal FB to theclosed loop controller304 which is indicative of the capacitance between the first and secondcapacitive plates352,354. As themoveable partition324 and thefirst capacitive plate354 move and the capacitance between the first and secondcapacitive plates352,354 changes, theclosed loop controller304 uses the feedback signal FB to control the dispense state, as will be described in more detail below.
• As the capacitance between two capacitive plates is proportional to their overlapping area divided by the distance between the plates, a measured capacitance between thefirst capacitive plate352 and thesecond capacitive plate354 can be readily correlated to the extent of their overlap. Since thefirst capacitive plate352 is attached to themoveable partition324, the extent of overlap and/or any change in overlap can be employed to determine the position (i.e., displacement position) of themoveable partition324. For example, inFIGS. 5 and 7, themoveable partition324 has moved relative to its position inFIGS. 4 and 6, and the overlap between thefirst capacitive plate352 and thesecond capacitive plate354 has increased. This increase in overlap will result in an increase in the capacitance that is measured by thecapacitance measurement module360.
• The position of themovable partition324 can then be readily derived from the change in capacitance between the twocapacitive plates352,354 since the measured capacitance C is proportional to A/G where A is the area of plate overlap and G is the gap dimension. In this regard, the first and secondcapacitive plates352,354 have typical dimensions, for example, of 10 mm (width) by 20 mm (length). The area of overlap between the first and secondcapacitive plates352,354 can vary depending on the placement of the first and secondcapacitive plates352,354 on themoveable partition324 and theinfusion module housing322. For example, the largest overlap between the first and secondcapacitive plates352,354 can be a substantially complete overlap of the first and secondcapacitive plates352,354, and the smallest overlap between the first and secondcapacitive plates352,354 has typical dimensions, for example, of 10 mm (in width) by 5 mm (in length). In addition, the gap dimension G can have a range between 10 and 1000 micrometers, and, for example, it can be 0.5 mm.
• In the embodiments shown inFIGS. 4-7, both the first and secondcapacitive plates352,354 are in direct electrical connection with thecapacitance measurement module360. However, providing a direct electrical connection to thefirst capacitive plate352 can raise the cost and complexity of manufacturing.FIG. 8 is a perspective depiction of a portion of an electrokinetic (EK)infusion pump400 according to another embodiment of the present invention in a first dispense state. As is explained in more detail below, theEK infusion pump400 employs a dual capacitive coupling configuration to address the issue of manufacturing cost and complexity.FIG. 9 is a perspective depiction of the portion of theEK infusion pump400 in a second dispense state.FIGS. 8 and 9 are simplified in a similar manner to the simplified depictions ofFIGS. 6 and 7.
• FIG. 10 is a schematic drawing depicting acapacitive plate configuration500 of the first dispense state ofFIG. 8, whileFIG. 11 is a schematic drawing depicting acapacitive plate configuration600 of the second dispense state ofFIG. 9.
• Referring toFIGS. 8-11, theEK infusion pump400 includes an integrated electrokinetic (EK) engine andinfusion module406, and a dualcapacitive displacement sensor407. The integrated EK engine andinfusion module406 includes aninfusion module housing422 and amoveable partition424.
• The dualcapacitive displacement sensor407 includes afirst capacitive plate482, a second capacitive plate484 (configured as an extension of first capacitive plate482), athird capacitive plate486, afourth capacitive plate488, a firstelectrical contact490, and a secondelectrical contact492.
• The first and secondcapacitive plates482,484 are mounted on themovable partition424, and move parallel to the longitudinal axis of theinfusion module housing422 together with the movable partition424 (for example, in the direction of arrow A6 as shown inFIG. 11). The third and fourthcapacitive plates486,488 are mounted on theinfusion module housing422 such that there is a gap between thefirst capacitive plate482 and thethird capacitive plate486, as well as a gap between thesecond capacitive plate484 and thefourth capacitive plate488. The gaps can be filled with any suitable material including, for example, air, a wall of the infusion module housing422 (which is formed of plastic or other suitable electrically insulating material), other suitable electrically insulating material, and combinations thereof.
• The firstelectrical contact490 provides electrical contact between thefourth capacitive plate488 and thecapacitance measurement module460, while the secondelectrical contact492 provides electrical contact between thethird capacitive plate486 and thecapacitance measurement module460.
• The extent of overlap between thefirst capacitive plate482 and thethird capacitive plate486 is variable as themoveable partition424 moves, as evidenced by a comparison ofFIGS. 8 and 9 orFIGS. 10 and 11. However, the extent of overlap between thesecond capacitive plate484 and thefourth capacitive plate488 is constant asmoveable partition424 moves, as evidenced by a comparison ofFIGS. 8 and 9 orFIGS. 10 and 11. The position of themovable partition424 can then be derived from a change in capacitance as measured by thecapacitance measurement module460. The position of themoveable partition424 can be readily derived since the total measured capacitance is the result of two capacitances in series, of which one is constant and one is variable with moveable partition position. In other words, 1/C_totis equal to the sum of 1/C_cand 1/C_v(where C_totis the measured total capacitance, C_cis the constant capacitance between the second and fourthcapacitive plates484,488 and C_vis the variable capacitance between first and thirdcapacitive plates482,486).
• FIG. 12 is an electrical circuit schematic depicting anelectric circuit700 that is essentially equivalent to the circuit formed by the capacitive plates depicted inFIGS. 8-11. As depicted inFIG. 12, the circuit includes one variable capacitor that includes the first and third capacitive plates (i.e.,capacitive plates482 and486) and one fixed capacitor that includes the second and third capacitive plates (i.e.,capacitive plates484 and488).
• FIG. 13 is a flow diagram illustrating amethod800 for the closed loop control of an electrokinetic (EK) infusion pump according to an exemplary embodiment of the present invention. Themethod800 includes, atstep810, sensing a dispensing state of an EK infusion pump with a capacitive displacement position sensor. The capacitive displacement position sensor and the EK infusion pump can be any such sensor and EK infusion pump as described herein with respect to embodiments of the present invention.
• Subsequently, the sensed dispensing state of the EK infusion pump is signaled to a closed loop controller via a feedback signal, as set forth instep820. The closed loop controller then determines the dispensing state of the electrokinetic infusion pump based on the feedback signal, as set forth instep830.
• Subsequently, atstep840, the dispensing state of the EK infusion pump (e.g., infusion liquid displacement rate) is controlled by the closed loop controller by the sending command signals from the closed loop controller to an electrokinetic engine of the EK infusion pump. The command signal can be, for example, based on a comparison of the determined dispensing state and a predetermined desired dispensing state and be a command signal that adjusts for any differences between the determined dispensing state and the predetermined desired dispensing state.
• Themethod800 can be practiced using EK infusion pump systems according to the present invention including the embodiments ofFIGS. 1-12. Moreover, steps810 through840 can be repeated as necessary to establish and maintain accurate control of the EK infusion pump dispensing state.
• EK infusion pumps and EK infusion pump systems according to embodiments of the present invention are economical to manufacture since the capacitive plates of their capacitive displacement position sensors can be formed using conventional economical techniques such as laser ablation of thin metal layers, screen printing and offset printing. Moreover, since the plates can be manufactured economically, the capacitive displacement position sensors described herein can be included as a component within a disposable EK infusion pump.
• In addition, capacitance can be measured using techniques with beneficially low power consumption, thus enabling EK infusion pumps and EK infusion systems with extended lifetimes. For example, capacitance-to-digital converter device AD7745 (commercially available from Analog Devices Inc., U.S.A.) can directly measure capacitance and convert the measured capacitance to a digital signal at an indicated power consumption of approximately 1 mW.
• It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods within the scope of these claims and their equivalents be covered thereby
• One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims (20)

1. An electrokinetic infusion pump comprising:

an infusion pump module; and

an electrokinetic engine,

wherein the infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module.

2. The electrokinetic infusion pump ofclaim 1, wherein:

the infusion pump module includes an infusion module housing;

the electrokinetic engine includes a moveable partition; and

the capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing.

3. The electrokinetic infusion pump ofclaim 2, wherein the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm.

4. The electrokinetic infusion pump ofclaim 3, wherein a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.

5. The electrokinetic infusion pump ofclaim 2, wherein the capacitive displacement sensor is configured for measuring capacitance between the first capacitive plate and the second capacitive plate.

6. The electrokinetic infusion pump ofclaim 1, wherein the electrokinetic engine includes a moveable partition and the infusion pump includes an infusion housing, and wherein the capacitive displacement sensor is a dual capacitive displacement sensor that includes:

a first capacitive plate and a second capacitive plate disposed on the moveable partition; and

a third capacitive plate and a fourth capacitive plate disposed on the infusion housing;

wherein the first capacitive plate, the second capacitive plate, the third capacitive plate and the fourth capacitive plate are in operative electrical contact and wherein an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.

7. The electrokinetic infusion pump ofclaim 1, wherein the capacitive displacement sensor is configured to send a feedback signal to a closed loop controller, the feedback signal indicative of the capacitance between the first and second capacitive plates.

8. The electrokinetic infusion pump ofclaim 1, wherein the infusion pump is configured to dispense an insulin containing infusion liquid.

9. An infusion pump system, comprising:

an infusion pump that includes:

a capacitive displacement position sensor; and

a closed loop controller,

wherein the infusion pump and closed loop controller are in operative communication and configured such that the closed loop controller can determine and control a dispensing state of the infusion pump based on a feedback signal received from the capacitive displacement position sensor.

10. The system ofclaim 9, wherein the infusion pump is an electrokinetic pump.

11. The system ofclaim 10, wherein the electrokinetic infusion pump further includes

an infusion pump module; and

an electrokinetic engine,

and wherein the capacitive displacement sensor is configured for sensing a dispensing state of the infusion pump module.

12. The system ofclaim 11, wherein:

the infusion pump module includes an infusion module housing;

the electrokinetic engine includes a moveable partition; and

the capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing.

13. The system ofclaim 12, wherein the capacitive displacement sensor is configured for sensing a dispensing state by measuring capacitance between the first capacitive plate and the second capacitive plate.

14. The system ofclaim 13, wherein the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm.

15. The system ofclaim 14, wherein a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.

16. The system ofclaim 11, wherein the electrokinetic engine includes a moveable partition and wherein the capacitive displacement sensor is a dual capacitive displacement sensor that includes:

a first capacitive plate;

a second capacitive plate;

a third capacitive plate; and

a fourth capacitive plate,

and wherein the first capacitive plate, the second capacitive plate, the third capacitive plate and the fourth capacitive plate are in operative electrical contact and wherein an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.

17. The system ofclaim 11, wherein the electrokinetic engine includes an electrokinetic supply reservoir that is at least partially collapsible.

18. The system ofclaim 9, wherein the capacitive displacement sensor is configured to send the feedback signal to the closed loop controller.

19. The system ofclaim 9, wherein the infusion pump is configured to dispense an insulin-containing infusion liquid.

20. A method for the closed loop control of an infusion pump, comprising:

sensing a dispensing state of an infusion pump with a capacitive displacement position sensor;

signaling the sensed dispensing state of the infusion pump to a closed loop controller via a feedback signal;

determining, with the closed loop controller, the dispensing state of the infusion pump based feedback signal; and

controlling the dispensing state of the infusion pump with the closed loop controller by sending command signals from the closed loop controller to an engine driving the infusion pump.

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