Abstract:
A micropump according to the invention uses an eccentric cam member rotating within a pump housing to sequentially open and close valves in the pump housing to withdraw fluid from a reservoir and provide metered amounts of the fluid to a cannula port for administration to a patient. The micropump may be used in a disposable pump for continuous infusion of medication such as insulin.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is directed to a micropump adapted for the continuous delivery of a liquid medication by infusion such as may be used in the delivery of insulin for the treatment of diabetes. 
         [0003]    2. Description of the Related Art 
         [0004]    Micropumps for the subcutaneous delivery of drugs are known, for example, from U.S. Pat. Nos. 7,726,955 and 8,282,366. This prior art describes, in various embodiments, a pump having a rotor mounted in a stator, or housing. Sealing rings situated at an angle on axial extensions on the rotor cooperate with channels formed between the rotor and the stator to move liquid in precise amounts through a rotor housing. However, these embodiments are relatively complex and not cost effective. The user keeps the pump when the infusion patch is changed, for several weeks. As the art continues to evolve toward fully disposable pumps, the need for compact and economical micropump designs remains acute. 
         [0005]    Another infusion pump known in the prior art comprises a rigid reservoir with a lead screw engaged in the reservoir to dispense medication through the cannula as the lead screw advances. In this arrangement, the actuator for delivery of the medication is directly connected to the lead screw and must therefore be very precise. Moreover, the device requires the rigid reservoir to provide calibrated dosages. Thus it is impossible to use a flexible reservoir, and the number of possible layouts for the pump is limited. 
       SUMMARY OF THE INVENTION 
       [0006]    In one aspect, the present invention is a micropump for delivery of medication by infusion, comprising: a pump housing; a piston positioned in the pump housing having a longitudinal piston axis; and a motor adapted to rotate the piston about the piston axis. The pump housing has an axial opening receiving the piston, a first aperture positioned radially with respect to the piston axis in fluid communication with a reservoir, and a second aperture radially positioned with respect to the piston axis in fluid communication with a cannula. The piston has an eccentric cam surface at one end thereof, said cam surface adapted to open and close the first aperture and the second aperture at respective rotational positions of the piston. The axial position of the piston inside the pump housing determines a pump volume space. 
         [0007]    In embodiments, the pump housing is stationary and the piston comprises an axial position cam surface, between the motor and the eccentric cam surface, engaging a stationary member on the pump housing, adapted to translate the piston axially within the pump housing when the piston rotates. 
         [0008]    In another aspect, the invention is a method for delivering medication by infusion with the above-described pump, including the steps of providing instructions to a microprocessor to deploy the cannula, and to cause the piston to rotate, drawing a volume of medication into the pump volume space from the reservoir and expelling the volume of medication through the cannula for infusion to a patient. In embodiments, the medication is insulin and the infusion dosage comprises an infusion over one to five days, and the method further comprises disposing of the pump after delivery of the infusion dosage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic overview of the fluid metering and delivery systems according to the invention. 
           [0010]      FIG. 2  is a view of the assembled fluid metering and delivery systems. 
           [0011]      FIG. 3  is an exploded view of the fluid metering system. 
           [0012]      FIG. 4A  and  FIG. 4B  are top and end views of the pump piston element of the fluid metering system. 
           [0013]      FIG. 5  and  FIG. 6  are cross sectional views of the metering system. 
           [0014]      FIG. 7  is a cross sectional view of the pump housing in the starting position of the pump cycle.  FIG. 7A  and  FIG. 7B  are corresponding partial cutaway views of the fluid delivery system in the stage depicted in  FIG. 7 , from different angles. 
           [0015]      FIG. 8  is a cross sectional view of the pump housing in the early stages of a pump cycle, before the start of the intake stroke. 
           [0016]      FIG. 9  is a cross sectional view of the pump housing during the intake stroke.  FIG. 9A  and  FIG. 9B  are corresponding partial cutaway views from different angles. 
           [0017]      FIG. 10  is a cross sectional view of the pump housing after the intake stroke.  FIG. 10A  and  FIG. 10B  are corresponding partial cutaway views from different angles. 
           [0018]      FIG. 11  is a cross sectional view of the pump housing prior to initiation of the discharge stroke.  FIG. 11A  and  FIG. 11B  are corresponding partial cutaway views from different angles. 
           [0019]      FIG. 12  is a cross sectional view of the pump housing during the discharge stroke.  FIG. 12A  and  FIG. 12B  are corresponding partial cutaway views of the fluid delivery system during the discharge stroke from different angles. 
           [0020]      FIG. 13  depicts the rotational position of the piston at the end of the pump cycle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  provides a schematic overview of a fluid delivery system  100 , comprising a reservoir  120  in fluid communication with metering subsystem  200  for drawing a precise amount of fluid from the reservoir. A cannula mechanism  122  is provided for delivering medication from the metering subsystem  200  to the user  101 . The fluid delivery system, including metering subsystem  200 , is preferably lightweight and wearable and assembled in a compact form as shown in  FIG. 2 , so that the elements may be included in a single housing. The cannula mechanism  122  may be connected to the infusion site by an infusion set comprising tubing and a patch, or alternatively a cannula insertion mechanism may be incorporated into the housing along with the metering subsystem  200 . 
         [0022]    In embodiments, the pump is adapted to provide a continuous infusion dosage over 1 to 5 days. For example, in the case of insulin infusion, the pump may be worn and disposed of after 84 hours and the reservoir is sized to provide a dosage regimen in basal and bolus segments as a time varying series of fixed volume pulses. The infusion profile is split between the basal and bolus segments. For example, the basal segment may be a quasi-continuous flow of 5 μl pulses with a time lag that ranges from 0.17 to 1.2 hours/pulse, while the bolus segments comprise discrete volumes that generally occur around meal times, typically in a range of 10 to 500 μl, delivered at the maximum pump flow rate (minimum pump cycle time). In the case of insulin infusion, the reservoir  120  may be adapted to hold 1 ml to 5 ml of medication, preferably about 3 ml. However, this value is not critical. Although the invention is not limited to any specific reservoir embodiment, the reservoir  120  is preferably flexible and is not engaged with a plunger and lead screw, as is the case with many prior art insulin pumps. The flexible reservoir does not have an internal actuator mechanism for delivering fluid, which permits the overall pump to have a smaller footprint and more compact design. A suitable flexible reservoir may comprise a pouch made of medical grade flexible polyvinylchloride (PVC) or the like. Alternatively, a single rigid wall of medical grade plastic may be bonded to a flexible wall to form the reservoir. Reservoir  120  may be filled via a fill port  123  by syringe  121 , for example, or a prefilled reservoir or cartridge may be used. Metering subsystem  200  may be configured in fluid communication with the fill port  123 , so that metering subsystem  200  can be used to fill the reservoir  120  from an external source of medication via fill port  123 . 
         [0023]    Microcontroller  30  is provided on a printed circuit board (PCB) or the like and interfaces with sensors and circuitry  11 ,  12 ,  13 ,  14 ,  15 ,  17  and with actuators  16  and  18 , to control the pump and cannula. Power is provided by one or more batteries  19  in the housing. Display and user operable controls (not shown) may be provided on the unit, operatively connected to the PCB, or on a remote programming unit, to set and initiate basal and bolus segments of the dosage, as is known in the prior art. 
         [0024]    The embodiment of the metering system according to the invention depicted in the figures comprises a positive displacement pump with integrated flow control valves and a mechanical actuator and drive system. In the embodiment shown in  FIG. 2 , the actuator is a DC gear motor  24  powered by batteries  19 , however, other motor systems may be adapted for use with the invention, including a solenoid, nitinol (nickel-titanium alloy) wire motor, voice coil actuator motor, piezoelectric motor, or wax motor. The elements are arranged on support  21  received in a housing (not shown) to be worn on the patient&#39;s body. 
         [0025]    As shown in the exploded view of  FIG. 3 , the motor  24  is received in stationary motor casing  23 . Connector  25  receives the motor shaft  22  of the motor  24  and transmits torque from the motor to pump piston  27 . As used herein, the “axial” direction is along the axis of the motor shaft and the “radial” direction is the perpendicular direction. Unless the context clearly requires otherwise, the “clockwise” direction means clockwise looking down the axis of the motor shaft toward the motor. Slots  39  on piston  27  receive tabs  26  on connector  25  so that piston  27  rotates in unison with the motor shaft, but remains free to move axially. Alternatively, the piston may have rotational freedom but an axially fixed position, and the pump housing may be rotationally fixed but connected to the piston to allow for axial translation. In either case, the pump volume is determined by the axial position of a piston within the pump housing. 
         [0026]    In the embodiment shown, pump piston  27  is received in an axial opening in a stationary pump housing  29  and encloses pump volume space  47  in the pump housing behind elastomeric seal  37 . As shown in  FIG. 4A , piston  27  is configured with an axial position cam surface  32 . As described below, axial cam surface  32  engages a member on stationary pump housing  29  and causes piston  27  to translate axially within housing  29  when motor shaft  22  rotates. For example, in the embodiment shown, the member engaging the cam surface is a pin  31  inserted through the pump housing. 
         [0027]    The metering subsystem  200  is adapted to pull a precise volume of fluid from flexible reservoir  120  into pump volume  47 , and then expel the fluid through cannula  122  to an infusion site in small, discrete doses. A suitable pump volume space  47  may have a volume of 1 μl to 10 μl, preferably about 5 μl, so that two rotations of pump piston  27  deliver a unit (U) of insulin. Importantly, the position of pump piston  27  inside pump housing  29  determines the stroke, and the internal diameter of the pump housing determines the nominal size and accuracy of the dose. Therefore dosage accuracy is not determined by a specific rotational position of the motor shaft to deliver a corresponding amount of medication and the start/stop point for the rotational pump cycle need not be precise. The pump volume  47  may be altered by changing the diameter of piston  27  and/or pump housing  29 . In embodiments, cannula deployment is triggered by rotation of motor  24 , in a one-step deployment and infusion operation. 
         [0028]    In order to pull fluid into pump volume  47  during the intake stroke, and expel fluid during the discharge stroke, piston  27  is provided with an eccentric cam surface  33 , as shown in  FIG. 4B , to actuate valves to sequentially open and close reservoir fluid port  42  and cannula fluid port  41  at each end of the pump stroke to ensure that fluid flow is unidirectional from the reservoir to the patient and that there is no possibility of flow from the patient to the reservoir. As shown in the cross-sectional view of  FIG. 5 , the pump housing is provided with first and second apertures  43 ,  44  positioned radially with respect to the pump piston axis. Aperture  44  provides fluid communication between pump volume  47  and reservoir port  42 , while aperture  43  provides fluid communication between pump volume  47  and cannula port  41 . In this embodiment, apertures  43 ,  44  are positioned on opposite sides of pump housing  29 , 180 degrees apart with respect to piston  27 . The angular allocation for each segment of the pump cycle may be adjusted as needed to optimize performance of the pump, by altering the size and slope of the eccentric cam surface  33 , to increase or decrease the angular allocation for a particular portion of the pump cycle, or by changing the radial position of apertures  43 ,  44 . 
         [0029]    In the embodiment shown, the first and second apertures  43 ,  44  each receive a valve structure. Each valve structure includes respective O-ring seal  34 ,  34 ′ surrounding the aperture and a respective valve actuator  28 ,  28 ′ which compresses a respective O-ring seal  34 ,  34 ′ under force of respective spring  35 ,  35 ′ to close the respective aperture  43 ,  44  when cam surface  33  is not pressing against actuator  28 ,  28 ′. When cam surface  33  is rotated into position and depresses a valve actuator  28  or  28 ′, the fluid line to the cannula port  41  or reservoir port  42  is opened. The springs  35 ,  35 ′ are maintained in a biased state in the valve seat by respective valve caps  36 ,  36 ′ and must ensure sufficient spring force to prevent back flow at back pressures encountered during use of the device. Although O-rings are depicted in this embodiment, other sealing systems known in the art could be adapted for this purpose, such as an elastomeric ball in a V-shaped seat, an overmolded V-shaped poppet, or an overmolded membrane which can be biased to provide fluid entry through apertures  43 ,  44 . In general, components of the metering subsystem are made of a rigid medical grade plastic, such as acrylonitrile butadiene styrene (ABS) for all of the pump components, while liquid silicone rubber (LSR) with shore A hardness between 20 and 50 is used for the seals. If desired, the LSR seals may be molded directly onto the hard plastic substrates, in which case the substrate parts should be made of a plastic material with a higher softening temperature such as polyetherimide (PEI) or polysulfone (PS). 
         [0030]    In the embodiment depicted, pump housing  29  is stationary and piston  27  is translated inside the pump housing  29 . For this purpose, piston  27  comprises an axial position cam surface in the form of a groove  32 . As seen in  FIG. 4A , groove  32  includes proximal ledge  32   b  located toward the motor  24  and a distal ledge  32   a  located toward eccentric cam surface  33  on the opposite end of piston  27  from motor  24 . A stationary member, such as pin  31 , is received through an opening in the pump housing and constrains the piston to move axially back and forth between the position of proximal ledge  32   b  and axial ledge  32   a , guided along an axial translation portion of the groove  32 , as motor shaft  22  rotates. One of ordinary skill in the art will appreciate that an axial cam surface on piston  27  engaging pump housing  29  may be embodied in various ways to provide for axial movement of piston  27 . For example, a groove may be located on the pump housing instead of on the piston. 
         [0031]    A complete pump cycle requires 360 degrees of rotation in one direction. Rotating motor shaft  22  in the reverse direction will cause fluid to flow in the opposite direction. In embodiments, the pump may be placed in fluid communication with fill port  123  to fill reservoir from an external source such as a vial by rotating the motor shaft in the reverse direction. 
         [0032]    The pump cycle will be described with reference to a complete clockwise rotation (viewed looking down the piston toward the motor). The rotation of eccentric cam surface  33  about the piston axis, accompanied by the reciprocating action of piston  27  in this embodiment is understood by referring to the following sequential steps of the pump cycle described in  FIG. 7  through  FIG. 13 : ( 1 ) reservoir valve open state, ( 2 ) pump intake stroke; ( 3 ) reservoir valve closed state; ( 4 ) cannula valve open state; ( 5 ) pump discharge stroke; and ( 6 ) cannula valve closed state. 
         [0033]      FIG. 7  is a cross sectional view from the end of the pump housing, looking down the piston toward the motor, showing the metering system in its starting position. The pump piston  27  is fully extended. As shown in  FIG. 7A  and  FIG. 7B , pin  31  rests on proximal ledge  32   b  in this position and the piston does not translate axially. Cam surface  33  is not engaged with either valve actuator  28  or  28 ′, and a slight clearance is provided between cam surface  33  and actuators  28  and  28 ′ on radially opposite sides of the pump housing. The cam surface  33  is said to be “in clearance” with the actuator tips in this state. In this state, the valves are closed by the force of springs acting on O-ring seals  34 ,  34 ′ through valve actuators  28  and  28 ′. In the initial state, valve actuators  28  and  28 ′ are spring loaded against valve caps  36  and  36 ′ so that they have a permanent bias sufficient to prevent leakage at the operating back pressures of the device. The valve actuator may rest on a shoulder in the pump housing around apertures  43 ,  44 . In this way, compression of O-ring seals  34  or  34 ′ is determined by the geometry of the valve actuator cooperating with the surfaces of the pump housing around the apertures  43 ,  44 , rather than solely on the spring force. 
         [0034]      FIG. 8  depicts the reservoir valve open state ( 1 ) before the start of the intake stroke. Motor  24  is shown rotating in a clockwise direction so that cam surface  33  on piston  27  rotates to contact valve actuator  28  to bias spring  35  and open fluid communication with reservoir port  42 . In this position, pin  31  has not yet entered the sloped axial translation portion of groove  32 . 
         [0035]    During the pump intake stroke ( 2 ) depicted in  FIG. 9 ,  FIG. 9A  and  FIG. 9B , actuator  28  is fully depressed. Fluid flows into the pump volume space  47  through reservoir port  42  and aperture  44  while aperture  43  remains closed. As shown in  FIG. 9A  and  FIG. 9B , pin  31  engages the angled portion of axial cam surface  32  causing piston  27  to translate toward motor  24  in the direction indicated by arrow  99 . Fluid is drawn into pump volume space  47  as indicated by arrow  98 . The intake stroke is complete when pin  31  rests on distal ledge  32   a , stopping axial movement of piston  27 . Actuator  28  remains fully depressed and actuator  28 ′ remains in clearance with cam surface  33 . 
         [0036]      FIG. 10 ,  FIG. 10A  and  FIG. 10B  show reservoir port  42  closing. Rotation of piston  27  causes cam surface  33  to release actuator  28 , recompressing seal  34  due to bias of spring  35  and stopping fluid flow through aperture  44 . During this portion of the pump cycle, pin  31  rests on distal ledge  32   a  preventing axial translation of piston  27 . 
         [0037]      FIG. 11  shows cannula valve open state ( 4 ). Rotation of piston  27  causes cam surface  33  to engage actuator  28 ′, releasing compression on O-ring seal  34 ′ and opening fluid communication between pump volume  47  and cannula port  41  through aperture  43 .  FIG. 11A  and  FIG. 11B  show pin  31  resting on distal ledge  32   a  during this portion of the pump cycle, preventing axial translation of piston  27 . 
         [0038]    During the pump discharge stroke ( 5 ), depicted in  FIG. 12 ,  FIG. 12A , and  FIG. 12B , eccentric cam  33  holds open fluid communication with the cannula port  41  while reservoir port  42  remains closed.  FIG. 12A  shows piston  27  moved axially in a distal direction as indicated by the arrow. Pin  31  engages the angled axial translation portion of cam surface  32 , as shown in  FIG. 12B , causing piston  27  to translate away from motor  24  and causing fluid to be discharged from pump volume space  47  through cannula port  41  as indicated by the arrow. 
         [0039]    After the piston has completed 360 degrees of rotation, as depicted in  FIG. 13 , sensor  38  is engaged, indicating that the pump cycle is complete. With the pump returned to the cannula valve closed state ( 6 ), reservoir port  42  and cannula port  41  are blocked and pin  31  rests on proximal ledge  32   b . In the embodiment shown, sensor  38  is an ON/OFF switch that detects that the pump has completed a full cycle. However, other sensor systems, such as an encoder wheel and optical sensor, may be used to recognize intermediate states and communicate that information to microprocessor  30 . The use of a higher resolution sensor permits the discharge stroke to be incremented. In the embodiment described herein, the discharge stroke includes a complete rotation of piston  27 , emptying the contents of pump volume  47 , however, a finer resolution of infusion dosage could be implemented without departing from the scope of the invention. 
         [0040]    The foregoing description of the preferred embodiments is not to be deemed limiting of the invention, which is defined by the appended claims. The person of ordinary skill in the art, relying on the foregoing disclosure, may practice variants of the embodiments described without departing from the scope of the invention claimed. For example, although described in connection with continuous delivery of insulin for treatment of diabetes, it will be apparent to those of skill in the art that the infusion pump could be adapted to deliver other medications. A feature or dependent claim limitation described in connection with one embodiment or independent claim may be adapted for use with another embodiment or independent claim, without departing from the scope of the invention.