Patent Publication Number: US-2022218893-A1

Title: Linear activated drug dosing pump system

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 63/135,857, filed Jan. 11, 2021, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Many conventional drug delivery systems, including, for example, wearable drug delivery devices, include a drug container, often referred to as a reservoir, that stores a liquid drug. A liquid drug stored in the reservoir may be delivered to the user by expelling the drug from the reservoir using a driven plunger, for example, a leadscrew driven plunger. In present known embodiments, the plunger is typically disposed directly within the reservoir such that the reservoir and the drive comprise a single unit. As result, the reservoir requires a large cross-sectional area, such as to be able to hold the device&#39;s entire supply of the drug. The large cross-sectional area has the disadvantage of increasing the minimum dosing increment for a given axial displacement of the plunger. In addition, the larger cross-sectional area requires a larger diameter plunger which leads to more drag and friction on the interior sealing surfaces of the reservoir, thereby increasing the force required to achieve a given pressure and, as a result, requiring a larger, more powerful motor to drive the plunger. A need therefore exists for a configuration which achieves the same effective delivery of the drug, but with a container having a smaller cross-sectional area to overcome the identified deficiencies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of the pump chamber of a first embodiment of the invention in which dual plungers are used. 
         FIG. 2  is a schematic view of the pump system of the present invention in a first state in which the pump chamber is empty and the plungers are in a touching, face-to-face configuration. 
         FIG. 3  is a schematic view of the pump system of the present invention in a second state in which the plungers have moved away from each other to draw a liquid from the reservoir into the pump chamber. 
         FIG. 4  is a schematic view of the pump system of the present invention in a third state in which the plungers are moving toward each other to force the liquid from the pump chamber to the patient interface. 
         FIG. 5  is a schematic view of the pump system of the present invention in a fourth state in which all the liquid has been forced from the pump chamber toward the patient interface. 
         FIGS. 6 (A-C) show three variations of the pump system of the present invention in which sensors are used to determine the volume of the liquid which has been drawn into the pump chamber. 
         FIG. 7  is a flowchart showing the process by which one or multiple units of the liquid are moved from the reservoir to the patient interface. 
         FIG. 8  is a cross-sectional view of the pump chamber of a second embodiment of the invention in which a single plunger is used. 
         FIG. 9  is a schematic view of the second embodiment of the pump system of the present invention in a first state in which the pump chamber is empty and the plunger is touching the end wall of the pump chamber. 
         FIG. 10  is a schematic view of the second embodiment of the pump system of the present invention in a second state in which the plunger has moved away from the end wall to draw a liquid from the reservoir into the pump chamber. 
         FIG. 11  is a schematic view of the second embodiment of the pump system of the present invention in a third state in which the plunger is moving toward the end wall to force the liquid from the pump chamber to the patient interface. 
         FIG. 12  is a schematic view of the second embodiment of the pump system of the present invention in a fourth state in which all the liquid has been forced from the pump chamber toward the patient interface. 
         FIG. 13  is a flowchart showing the process of the second embodiment of the invention in which one or multiple units of the liquid are moved from the reservoir to the patient interface. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure presents various systems, components and methods for moving a liquid, typically a liquid drug, such as insulin, from a liquid reservoir to a patient interface, typically a needle or cannula. Each of the systems, components and methods disclosed herein provides one or more advantages over conventional, prior art systems components and methods. 
     In various embodiments of the invention, the reservoir is separated from the pump chamber but connected thereto via a first conduit having a one-way valve such as to allow flow of the liquid from the reservoir into the pump chamber but not from the pump chamber back into the reservoir. In preferred embodiments of the invention, the reservoir may be a collapsible container; however, in other embodiments, the reservoir may be rigid. 
     In one embodiment of the invention, the pump chamber has disposed therein a pair of plungers driven by a leadscrew having both left-hand and right-hand threads such that, when the leadscrew rotates in one direction, the plungers move toward each other and, when the leadscrew is rotated in the opposite direction, the plungers move away from each other. 
     The first conduit connecting the pump chamber to the reservoir connects to the pump chamber between the plungers, preferably in the middle of the pump chamber. Thereby, the movement of the plungers away from each other creates a negative pressure in the pump chamber which draws the liquid from the reservoir through the first conduit and into the pump chamber. The leadscrew is thus rotated in a direction such as to move the plungers away from each other to draw the liquid into the pump chamber. The liquid is prevented from returning to the reservoir by the one-way valve disposed in the conduit between the reservoir and the pump chamber. 
     Once the pump chamber is filled with an appropriate quantity of the liquid, the leadscrew is rotated in a second, opposite direction, thereby driving the plungers toward each other. A second conduit connected to the pump chamber between the plungers connects the pump chamber to a patient interface, typically a needle. Thus, motion of the plungers toward each other causes a movement of the liquid through the second conduit to the patient. The second conduit is also fitted with a one-way valve such that the suction created by the motion of the plungers away from each other to draw the liquid from the reservoir into the pump chamber does not also draw fluids from the patient through the patient interface and into the pump chamber. 
     In a second embodiment of the invention, the pump chamber is fitted with a single plunger driven by a leadscrew. Suction is created to draw the liquid into the pump chamber by motion of the plunger away from a closed end of the pump chamber by rotation of the leadscrew in a first direction. In this embodiment, it can be seen that the first conduit connecting the reservoir to the pump chamber must be connected to the pump chamber near, if not directly adjacent to or through, the closed end of the pump chamber. 
     The liquid is then pushed out to the second conduit to the patient interface by motion of the plunger toward the closed end, caused by rotation of the leadscrew in the opposite direction. It should also be realized that the second conduit connecting the pump chamber to the patient interface must be connected to the pump chamber near or through the closed end. In the second embodiment of the invention, both the first and second conduits are also fitted with a one-way valve so as to prevent the liquid in the pump chamber from returning to the reservoir and to prevent fluids from the patient from entering the pump chamber. 
     In one embodiment of the invention, the rotation of the leadscrew can be driven by a drive coupled to the leadscrew either directly or via gearing. 
     The improved liquid delivery system disclosed herein thus addresses the problems identified in the Background section. By separating the reservoir from the pump chamber, the pump chamber can be configured with a cross-sectional area of any size, preferably small enough to overcome the difficulties associated with the larger diameter cross-sectional areas of conventional, prior art devices. 
       FIG. 1  is a cross-sectional view of a first embodiment of the pump chamber  104  of the present invention. Pump chamber  104  consists of an open-ended container comprising sidewall  103  and endcap  105 . Sidewall  103  may comprise a tube-like structure having a cross-sectional shape. In some instances, sidewall  103  and endcap  105  may be formed as an integral unit, however, in other instances, sidewall  103  and endcap  105  may be formed separately and joined together. Sidewall  103  and endcap  105  may be composed of, for example, glass, polypropylene or any other bio- or drug-compatible material. In certain embodiments, endcap  105  may be absent, with pump chamber  104  being open at both ends. 
     Sidewall  103  has formed therein inlet port  113  and outlet port  117 . Inlet port  113  may connect, via a conduit, to a reservoir which may hold a quantity of a liquid. Outlet port  117  may connect to a patient interface for delivery of the liquid to a patient. Preferably, inlet port  113  and outlet port  117  will be located midway between plungers  106   a ,  106   b , such that when plungers  106   a ,  106   b  are in a touching, face-to-face configuration, access to both inlet port  113  and outlet port  117  are fully or partially blocked. This serves as a safety feature to prevent free-flow of the liquid from the reservoir to the patient interface in the event of valve failure. In preferred embodiments of the invention, inlet port  113  and outlet port  117  are located opposite each other along sidewall  103 ; however, in other embodiments, inlet port  113  and outlet port  117  may be positioned at any convenient location along sidewall  103 . 
     Disposed within pump chamber  104  are plungers  106   a ,  106   b . In some embodiments, plungers  106   a ,  106   b  may be composed of, for example, a butyl rubber or silicon rubber material or any other commonly known drug-compatible material. In other embodiments, plungers  106   a ,  106   b  may be composed of a polycarbonate derivative or cyclic olefin polymer (COP), in which case, plungers  106   a ,  106   b  may be surrounded by one or more O-rings composed of butyl rubber or silicon rubber. In some embodiments, plungers  106   a ,  106   b  are configured with flat facing surfaces. In other embodiments, other shapes may be used but preferably the plungers  106   a ,  106   b  will have mating shapes, for example, one concave and one convex, such that when plungers  106   a ,  106   b  are together, no volume remains therebetween. The faces of plungers  106   a ,  106   b  may be configured with channels to direct the movement of the liquid in a desired direction. 
     Plungers  106   a ,  106   b  are connected by leadscrew  108 . In certain embodiments, leadscrew  108  may be composed of stainless steel, polypropylene, or any other well-known bio- or drug-compatible material. In preferred embodiments, leadscrew  108  comprises both left-handed threading  101   a  and right-handed threading  101   b  as an interface with plungers  106   a ,  106   b , such that rotation of leadscrew  108  in a first direction will cause plungers  106   a ,  106   b  to move toward each other along the longitudinal axis of pump chamber  104  until touching, and such that rotation of leadscrew  108  in a second, opposite direction will cause plungers  106   a ,  106   b  to move away from each other along the longitudinal axis of pump chamber  104 . 
       FIG. 2  is a schematic representation of the first embodiment of the invention in which a linear-actuated drug dosing system  100  comprises two plungers  106   a ,  106   b  disposed in pump chamber  104 . Reservoir  102  may contain a quantity of a liquid  103 , for example, a drug in liquid form. In some embodiments of the invention, reservoir  102  may be rigid, while, in other embodiments, the reservoir  102  may be flexible and collapsible to eliminate the need for a vent in the reservoir to prevent a vacuum performing therein as liquid  103  is drawn from reservoir  102  into pump chamber  104 . In some embodiments, reservoir  102  may be composed of high-density polyethylene or, in other embodiments, ACLAR®. 
     Reservoir  102  is fluidly coupled to pump chamber  104  through inlet port  113  via inlet conduit  112 . Likewise, pump chamber  104  is fluidly coupled to a patient interface through outlet port  117  via outlet conduit  116 . Inlet conduit  112  and outlet conduit  116  may be composed of, for example, stainless steel or Teflon and may be, for example, tubing of the type of which hypodermic needles are constructed. One-way valve  114  prevents liquid  103 , which has entered the pump chamber  104 , from returning to reservoir  102 . The patient interface may be, for example, a needle, a needle conduit or tubing that can be used as a fluid path to deliver the liquid  103  to a patient. One-way valve  118  prevents fluids from the patient from being drawn into pump chamber  104  as liquid  103  is being drawn into pump chamber  104  from reservoir  102 . 
     Plungers  106   a ,  106   b  are disposed within the pump chamber  104  and may be sealed against the inner surface of sidewall  103  of pump chamber  104 . It should be noted that the cross-sectional shape of pump chamber  104  may be any shape, including circular; however, in preferred embodiments, the cross-sectional shape of pump chamber  104  may be any one of a number of non-circular shapes, preferred examples of which are shown as reference number  124  in  FIG. 2 . The non-circular, cross-sectional shape of pump chamber  104  is desirable to prevent plungers  106   a ,  106   b  from rotating within pump chamber  104  when leadscrew  108  is rotated. Non-rotation of plungers  106   a ,  106   b  is necessary to enable the movement of the plungers  106   a ,  106   b  along the longitudinal axis of pump chamber  104  driven by the rotation of leadscrew  108  as it rotates in either direction. 
     Leadscrew  108  may be driven by any one of a number of known methods. In one embodiment, the drive source may be motor  120 , which may be coupled to leadscrew  108  via gearing  122 . Leadscrew  108  is, in this embodiment of the invention, configured with both left-hand and right-hand threads, as shown in the figure. Thus, rotation of leadscrew  108  in a first direction (e.g. clockwise) will cause plungers  106   a ,  106   b  to move toward each other, while rotation of leadscrew  108  in an opposite direction (e.g. counter-clockwise) will cause plungers  106   a ,  106   b  to move away from each other. 
     Motor  120  may be coupled to leadscrew  108  via gearing  122 . In some embodiments of the invention, gearing  122  may be a planetary gear system, but any configuration of coupling between the motor  120  and leadscrew  108  may be used, including a direct connection. Motor  120  may be a continuous motion motor or stepper motor and is preferably controlled by a software-driven controller. 
     In alternate embodiments of the invention, a nitinol wire drive (not shown) may be used to drive gearing  122  in lieu of motor  120  and may be coupled to leadscrew  108  via gearing  122 . 
       FIG. 2  shows the device in a static state, with plungers  106   a ,  106   b  shown together. This is a likely state of the device just subsequent to the delivery of one or more units of liquid  103  and in ready state for filling of the pump chamber  104  with additional liquid  103  from reservoir  102 . 
       FIG. 3  is a schematic diagram showing the process of drawing liquid  103  from reservoir  102  into pump chamber  104 . Motor  120  may be activated in a direction such as to cause plungers  106   a ,  106   b  to move away from each other as shown by the arrows in pump chamber  104 . Movement of plungers  106   a ,  106   b  away from each other causes a negative pressure to form in the volume  104   a  between the plungers  106   a ,  106   b , which serves to draw liquid  103  through conduit  112 , into pump chamber  104  and, more specifically, into volume  104   a  between plungers  106   a ,  106   b . One-way valve  118  prevents fluids from the patient from being drawn through conduit  116  and into volume  104   a  of pump chamber  104  as plungers  106   a ,  106   b  create the negative pressure within volume  104   a  as they move away from each other. 
     Pump chamber  104  may be configured with a vent  107  on end wall  105  of pump chamber  104  to allow air between plunger  106   b  and end wall  105  of pump chamber  104  to escape as plunger  106   b  is moved toward end wall  105 , and to allow air to enter the space between end wall  105  and plunger  106   b  when plunger  106   b  is moved in the opposite direction, away from end wall  105 . 
       FIG. 4  is a schematic diagram illustrating the process of pumping liquid  103  from volume  104   a  through conduit  116  to the patient interface. Motor  120  may be rotated in a direction opposite the direction of rotation used to draw liquid  103  into volume  104   a  such as to move plungers  106   a ,  106   b  toward each other as shown by the arrows in  FIG. 4 , thereby creating a positive pressure within volume  104   a . The movement of plungers  106   a ,  106   b  toward each other reduces the size of volume  104   a  and forces liquid  103  into the conduit  116  and out to the patient through the patient interface. One-way valve  114  prevents liquid  103  from returning to reservoir  102  as plungers  106   a ,  106   b  move toward each other, ensuring that all of liquid  103  within volume  104   a  is forced into conduit  116 . 
     Once plungers  106   a ,  106   b  have reached a position where they are touching one another, as shown in  FIG. 5 , all, or most of liquid  103  within volume  104   a  will have been forced into conduit  116  to the patient interface. Plungers  106   a ,  106   b  do not necessarily need to touch each other to complete a cycle of liquid delivery. However, to reduce the amount of residual liquid within the system, and hence reduce the amount of wasted liquid at the end of usage of system  100 , plungers  106   a ,  106   b  preferably come into contact at the end of each cycle of liquid delivery, or alternatively, at a final cycle of drug delivery when all or nearly all of liquid drug has been dispensed from reservoir  102 . Having plungers  106   a ,  106   b  come into contact only at a final cycle of drug delivery will reduce the impact that plungers  106   a ,  106   b  have on constituents of the liquid (e.g., molecules of insulin) during each cycle of liquid delivery, thereby prolonging the life or effectiveness of the liquid (e.g., protein molecules within the liquid). 
     It should be noted that conduits  112 ,  116  interface with pump chamber  104  in the volume  104   a  between plunger  106   a ,  106   b . In preferred embodiments of the invention, conduits  112  and  116  will connect to volume  104   a  midway between the largest distance that plunger  106   a ,  106   b  can travel from each other, or, in other words, at the point where plungers  106   a ,  106   b  meet when they are touching each other or at the end of a cycle, such that when plungers  106   a ,  106   b  are in the position shown in  FIG. 2 , both inlet port  113  and outlet port  117  are blocked. 
     It should be noted that multiple units of liquid  103  may be drawn into volume  104   a  at a single time and may be dispensed in separate units to the patient. It is not necessary that volume  104   a  be emptied each time that a unit of liquid  103  is delivered to the patient. 
     It should be further noted that the quantity of liquid  103  drawn into volume  104   a  is dependent upon the distance between plungers  106   a ,  106   b  at their furthest point of travel away from each other. Thus, the quantity of liquid  103  drawn into volume  104   a  can be controlled by varying the distance between plungers  106   a ,  106   b . Larger distances between plungers  106   a ,  106   b  will result in a larger volume  104   a  and, thus, a larger quantity of liquid  103 , while smaller distances will result a smaller volume  104   a  and a smaller quantity of liquid  103  being drawn into volume  104   a.    
     One advantage of the dual-plunger design is that the system is balanced axially such that it does not induce a thrust onto the bearing support (i.e. the portion where the leadscrew  108  interfaces with end wall  105  of pump chamber  104 . This translates into less frictional losses in the system. One further advantage is that the design prevents the free flow of liquid  103  directly from reservoir  102  to the patient when plungers  106   a ,  106  block inlet port  113  and outlet port  117 . This can be a safety mechanism in the case of an over-pressure situation or if squeezing of the device forces liquid  103  out of reservoir  102 . 
     Various other methods are possible in this embodiment of the invention for measuring the size of the volume  104   a  between plungers  106   a ,  106   b , and thus the quantity of liquid  103  which is drawn into volume  104   a . In one embodiment of the invention, the size of volume  104   a  may be determined algorithmically by calculation based on the number of turns of leadscrew  108  and the known distance that plungers  106   a ,  106   b  travel based on the determined number of turns. Other embodiments of determining the size of volume  104   a  utilizing sensors will now be discussed. 
       FIG. 6A  shows one embodiment using a pressure gauge to calculate a volume change in the pump chamber  104  using the ideal gas law equation PV=nRT. A gas pressure gauge  601  may be configured to interface with pump chamber  104  through vent  107  in end wall  105 . Using air pressure in area  602  as measured by pressure gauge  601 , the change in the position of the plungers, and thus changes in the quantity of liquid  103  in volume  104   a , can be derived from a measurement of the change in air pressure within area  602 . The actual quantity of liquid  103  drawn into volume  104   a  may be further dependent on other factors, for example, the size of conduit  112 . 
       FIG. 6B  shows a second embodiment utilizing a three-segment custom linear encoder using simple analog techniques. In this embodiment, change in the length (length=l 1 +l 2 +l 3 ) of conductive bar or wire  604  can alter its resistance/current and can be calibrated to the position of plunger  106   b . The position of plunger  106   a  can thereafter be inferred from the position of plunger  106   b.    
       FIG. 6C  shows yet another embodiment utilizing an ultrasonic sensor. An ultrasonic source  606  may direct a beam of ultrasonic sound through vent  107 . The speed of sound through various media (i.e., air→plastic→aqueous spolution→plastic→air) is known and, as such, based on timing, with the known distance between the ultrasonic source  606  and an ultrasonic detector  608 , a quantity of the liquid  103  can be inferred. 
       FIG. 7  shows a flowchart showing process  700  for delivery of liquid  103  from the reservoir  102  to the patient interface. The system  100  begins from a start position  702 . The start position is preferably the position wherein the plungers  106   a ,  106   b  are in a touching, face-to-face configuration such that volume  104   a  is reduced to virtually zero. 
     At block  704 , the plungers are moved apart by turning of leadscrew  108  and liquid  103  is drawn from reservoir  102  into the volume  104   a  between plungers  106   a  and  106   b . At block  706 , it is determined whether the desired quantity of liquid  103  has been drawn into volume  104   a  of pump chamber  104  and, if not, control is returned to block  704 , where the plungers  106   a ,  106   b  continue to move away from each other until the desired quantity of liquid  103  is present in volume  104   a . The determination of whether the desired quantity of liquid  103  has been drawn into volume  104   a  may be made algorithmically by calculating, for example, the number of turns of leadscrew  108  and its relationship to the size of volume  104   a  or with the assistance of one of the sensor arrangements shown in  FIGS. 6 (A-C), or through the use of any other sensor arrangement. 
     At block  716  it is determined if it is time for the delivery of the additional units of liquid  103  to the patient. If so, control is sent to block  708  and if not, system  100  loops at decision point  716  until triggered. The delivery of additional units of liquid  103  could be triggered automatically, for example, by a periodic timer, by manual initiation of the delivery by the patient, or by any other means, such as through an analysis of input received from sensors regarding the current condition of the patient. 
     At block  708 , the movement of plungers  106   a ,  106   b  toward each other is initiated by rotation of leadscrew  108  in an opposite direction, such as to force a quantity of liquid  103  from volume  104   a  and into conduit  116 , and from there to the patient interface. At  710  it is determined if the quantity so far delivered to the patient interface comprises the desired quantity and, if not, control returns to  708 , where the plungers continue to move toward each other to push a further quantity of liquid  103  to the patient interface. At  710 , if the desired quantity of liquid  103  has been delivered to the patient interface, the process is complete at  712 . 
     At decision point  714 , it is determined if the volume  104   a  is empty, that is, the last quantity of liquid  103  has been delivered to the patient. If volume  104   a  is empty, control returns to start position  702  and the process repeats with the loading of an additional quantity of liquid  103  from reservoir  102  to volume  104   a . If volume  104   a  is not empty, control returns to decision point  716 , where the process loops until the delivery of the next unit of liquid  103  is triggered. 
     Note that the end position of the plungers when the pump chamber is empty at block  712  is the same as start position at  702 , wherein the plungers are in a touching, face-to-face configuration and are thereby ready to draw the next quantity of liquid  103  into volume  104   a.    
     The second embodiment of the invention has components similar to the first embodiment in configuration and composition and operates in a similar manner. As such, the description of the second embodiment has been condensed for brevity and like reference numerals have been used for like components. 
       FIG. 8  is a cross-sectional view of a second embodiment of the pump chamber  104  of the present invention in which only a single plunger  106  is used. Rotation of leadscrew  108  in a first direction moves plunger  106  toward end wall  105 , while movement of the leadscrew  108  in a second, opposite direction moves plunger  106  away from end wall  105 . Inlet port  113  and outlet port  117  are preferably located adjacent end wall  105 , such that movement of the plunger  106  toward the end wall forces any liquid within the pump chamber  104  into the output conduit  117 . Otherwise, the components and materials of the second embodiment of the pump chamber are identical to that of the first embodiment shown in  FIG. 1 . 
       FIG. 9  is a schematic representation of the second embodiment of the invention in which a linear-actuated drug dosing system  100  comprises a single plunger  106  disposed in pump chamber  104 . 
     Reservoir  102  is fluidly coupled to pump chamber  104  through inlet port  113  via inlet conduit  112 . Likewise, pump chamber  104  is fluidly coupled to a patient interface through outlet port  117  via outlet conduit  116 . One-way valve  114  prevents liquid  103  which has entered the pump chamber  104 , from returning to reservoir  102 . 
     One-way valve  118  prevents fluids from the patient from being drawn into pump chamber  104  as liquid  103  as being drawn into pump chamber  104  from reservoir  102 . 
     Plunger  106  is disposed within the pump chamber  104  and may be sealed against the inner surface sidewall  103  of pump chamber  104 . Leadscrew  108  may be driven by any one of a number of known methods. In one embodiment, the drive source may be motor  120 , which is coupled to leadscrew  108  via gearing  122 . Leadscrew  108  is, in this embodiment of the invention, configured with a single threading, as shown in the figure. Thus, rotation of leadscrew  108  in a first direction (e.g. clockwise) will cause plunger  106  to move toward end wall  105 , while rotation of leadscrew  108  in an opposite direction (e.g. counter-clockwise) will cause plunger  106  to move away from end wall  105 . 
     Motor  120  may be coupled to leadscrew  108  via gearing  122  to drive leadscrew  108  in either rotational direction. 
       FIG. 9  shows the device in a static state, with plunger  106  shown adjacent end wall  105  and blocking inlet port  113  and outlet port  117 . 
       FIG. 10  is a schematic diagram showing the process of drawing liquid  103  from reservoir  102  into pump chamber  104 . Motor  120  may be activated in a direction such as to cause plunger  106  to move away from end wall  105  as shown by the arrow in pump chamber  104 . Movement of plunger  106  away from end wall  105  causes a negative pressure to form in the volume  104   a  between the plunger and end wall  105 , which serves to draw liquid  103  through conduit  112 , into pump chamber  104  and, more specifically, into volume  104   a  between plunger  106  and end wall  105 . One-way valve  118  prevents fluids from the patient from being drawn through conduit  116  and into volume  104   a  as plunger  106  creates the negative pressure within volume  104   a  as it moves away from end wall  105 . 
       FIG. 11  is a schematic diagram illustrating the process of pumping liquid  103  from volume  104   a  through conduit  116  to the patient interface. Motor  120  may be rotated in a direction opposite the direction of rotation used to draw liquid  103  into volume  104   a  such as to move plunger  106  toward end wall  105  as shown by the arrow in  FIG. 11 , thereby creating a positive pressure within volume  104   a . The movement of plunger  106  toward end wall  105  reduces the size of volume  104   a  and forces liquid  103  into the conduit  116  and out to the patient through the patient interface. One-way valve  114  prevents liquid  103  from returning to reservoir  102  as plunger  106  moves toward end wall  105 , ensuring that all of liquid  103  within volume  104   a  is forced into conduit  116 . 
     Once plunger  106  has reached a position where it is touching end wall  105 , as shown in  FIG. 12 , all, or most of liquid  103  within volume  104   a  will have been forced into conduit  116  to the patient interface. Plunger  106  does not necessarily need to touch end wall  105  to complete a cycle of liquid delivery. However, to reduce the amount of residual liquid within the system, and hence reduce the amount of wasted liquid at the end of usage of system  100 , plunger  106  preferably comes into contact with end wall  105  at the end of each cycle of liquid delivery, or alternatively, at a final cycle of drug delivery when all or nearly all of liquid drug has been dispensed from reservoir  102 . Having plunger  106  come into contact with end wall  105  only at a final cycle of drug delivery will reduce the impact that plunger  106  has on constituents of the liquid (e.g., molecules of insulin) during each cycle of liquid delivery, thereby prolonging the life or effectiveness of the liquid (e.g., protein molecules within the liquid). 
     It should be noted that conduits  112 ,  116  must interface with pump chamber  104  in the volume  104   a  between plunger  106  and end wall  105 . In preferred embodiments of the invention, conduits  112  and  116  will connect to volume  104   a  directly adjacent end wall  105 , such that when plunger  106  is in the position shown in  FIG. 12 , both inlet port  113  and outlet port  117  are blocked. 
       FIG. 13  shows a flowchart showing process  1300  for delivery of liquid  103  from the reservoir  102  to the patient interface. The system  100  begins from a start position  1302 . The start position is preferably the position wherein plunger  106  is in contact with end wall  105  such that volume  104   a  is reduced to virtually zero. 
     At block  1304 , the plunger  106  is moved away from end wall  105  by turning of leadscrew  108  and liquid  103  is drawn from reservoir  102  into the volume  104   a  between plunger  106  and end wall  105 . At block  1306 , it is determined whether the desired quantity of liquid  103  has been drawn into volume  104   a  and, if not, control is returned to block  1304 , where the plunger  106  continues to move away from end wall  105  until the desired quantity of liquid  103  is present in volume  104   a.    
     At block  1316  it is determined if it is time for the delivery of the additional units of liquid  103  to the patient. If so, control is sent to block  1308  and if not, system  100  loops at decision point  1316  until triggered. 
     At block  1308 , the movement of plunger  106  toward end wall  106  is initiated by rotation of leadscrew  108  in an opposite direction, such as to force a quantity of liquid  103  from volume  104   a  and into conduit  116 , and from there to the patient interface. At  1310  it is determined if the quantity so far delivered to the patient interface comprises the desired quantity and, if not, control returns to  1308 , where the plunger  106  continues to move toward end wall  105  to push a further quantity of liquid  103  to the patient interface. 
     At  1310 , if the desired quantity of liquid  103  has been delivered to the patient interface, the process is complete at  1312 . 
     At decision point  1314 , it is determined if the volume  104   a  is empty and, if so, control returns to start position  1302  and the process repeats with the loading of an additional quantity of liquid  103  from reservoir  102  to volume  104   a . If volume  104   a  is not empty, control returns to decision point  1316 , where the process loops until the delivery the next unit of liquid  103  is triggered. 
     The embodiments described herein provide numerous benefits over existing prior art systems. As will be appreciated by a person of ordinary skill in the art, and, in particular with wearable devices, the comfort of the patient can be enhanced by reducing the size of the device. The above described embodiments accomplish this by allowing for a pump mechanism having a smaller cross-sectional area and, in addition, utilizing non-circular cross-sectional shapes that could, for instance, be provided as a flattened rectangular shape, thereby reducing the profile of the device. In addition, the smaller cross-sectional area of the pump mechanism, in addition to the fact that only a portion of the quantity of liquid in the reservoir is drawn into the pump chamber at any one time, allows for the use of a smaller, less powerful motor to drive the plungers. 
     The following examples pertain to further embodiments: 
     Example 1 is a pump system comprising a pump chamber, a leadscrew having both left-hand threading and right-hand threading disposed along the longitudinal axis of the pump chamber and two plungers coupled to the leadscrew such that rotation of the leadscrew in a first direction causes the plungers to move together and a rotation of the leadscrew in the other direction causes the plungers to move apart. 
     Example 2 is an extension of Example 1, or any other example disclosed herein, wherein the pump chamber has a non-circular cross-sectional shape. 
     Example 3 is an extension of Example 1, or any other example disclosed herein, wherein the pump chamber is configured with an inlet port and an outlet port. 
     Example 4 is an extension of Example 3, or any other example disclosed herein, wherein the inlet port and an outlet port are located in an area of the sidewall between the two plungers. 
     Example 5 is an extension of Example 4 or any other example disclosed herein, in which the pump system further comprises a reservoir connected to the pump chamber through the inlet conduit connected to the input port of the pump chamber, and a one-way valve disposed between the reservoir and the pump chamber which allows fluid flow in a direction from the reservoir into the pump chamber but not in the reverse direction. 
     Example 6 is an extension of Example 5, or any other example disclosed herein, wherein the reservoir is collapsible. 
     Example 7 is an extension of Example 5, or any other example disclosed herein, wherein the pump system further comprises a patient interface connected to the pump chamber through an outlet conduit connected to the outlet port of the pump chamber and a one-way valve allowing fluid to flow in a direction from the pump chamber to the patient interface but not in the reverse direction. 
     Example 8 is an extension of Example 7, or any other example disclosed herein, wherein the movement of the plungers away from each other causes a negative pressure in the space between the plungers, thereby drawing liquid in the reservoir into the pump chamber. 
     Example 9 is an extension of Example 8, or any other example disclosed herein, wherein movement of the plungers toward each other causes a positive pressure in the space between the plungers, thereby forcing liquid in the pump chamber into the outlet conduit. 
     Example 10 is an extension of Example 9, or any other example disclosed herein, wherein the volume of the space between the first and second plungers is algorithmically determined based on the number of turns of the leadscrew. 
     Example 11 is an extension of Example 9, or any other example disclosed herein, wherein the volume of the space between the first and second plungers is algorithmically determined based on input from a sensor. 
     Example 12 is an extension of Example 9, or any other example disclosed herein, wherein a quantity of a liquid disposed in the reservoir is drawn into the pump chamber as the plungers move away from each other. 
     Example 13 is an extension of Example 9, or any other example disclosed herein, wherein a single unit of the liquid may be forced into the patient interface by movement of the plungers such as to reduce the volume of the space therebetween by a predetermined amount corresponding to a single unit of the liquid. 
     Example 14 is an extension of Example 1, or any other example disclosed herein, wherein the pump system further comprises a drive for rotating the leadscrew in either direction. 
     Example 15 is extension of Example 14, or any other example disclosed herein, wherein the drive comprises a motor coupled to the leadscrew via one or more gears. 
     Example 16 is a method comprising moving two plungers away from each other within the pump chamber to draw a quantity of a liquid into the pump chamber and moving the plungers toward each other to deliver a desired quantity of the liquid to a patient interface. 
     Example 17 is an extension of the Example of 16, or any other example disclosed herein, wherein the liquid is stored in an external reservoir which is coupled to the pump chamber via an inlet conduit having a one-way valve to prevent the liquid from moving from the pump chamber to the reservoir. 
     Example 18 is an extension of Example 18, or any other example disclosed herein, wherein the patient interface is coupled to the pump chamber via an outlet conduit configured with a one-way valve to prevent fluids from moving from the outlet conduit into the pump chamber. 
     Example 19 is an extension of Example 17, or any other example disclosed herein, wherein the first and second plungers are coupled to a leadscrew having both left-hand and right-hand threading and wherein rotation the leadscrew in a first direction causes the plungers to move toward each other and in a second, opposite direction causes the plungers to move away from each other and further wherein the leadscrew is coupled to a motor to drive the leadscrew in either direction. 
     Example 20 is a pump system which comprises a pump chamber, a threaded leadscrew extending along a longitudinal axis of the pump chamber, a plunger coupled to the leadscrew, an inlet port coupled to a reservoir and an outlet port coupled to a patient interface, wherein rotation of the leadscrew causes the plunger to move away from the closed end of the pump chamber to draw liquid from the reservoir into the pump chamber and rotation of the leadscrew in a second, opposite direction causes the plunger to move toward the closed end of the pump chamber thereby forcing the liquid from the pump chamber to the patient interface. 
     Certain embodiments of the present invention were described above. It is, however, expressly noted that the present invention is not limited to those embodiments, but rather it is intended that additions and modifications to the expressly described embodiments herein are also to be included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express herein, without departing from the spirit and scope of the invention. In fact, variations, modifications, and other implementations of what was described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention. As such, the invention is not to be defined only by the preceding illustrative description. Future filed applications claiming priority to this application may claim the disclosed subject matter in a different manner and may generally include any set of one or more limitations as variously disclosed or otherwise demonstrated herein.