Drug delivery device

1. A drug delivery device for pumping liquid from a liquid reservoir comprising an elastic plunger sealingly slidable within a rigid container wall of the liquid reservoir for expelling liquid out of the liquid reservoir, the drug delivery device comprising:

a delivery system outlet fluidly connected to the liquid reservoir;

a piston pump comprising an electrically driven plunger actuator arranged to displace the plunger a predefined distance per pump cycle; and

a dosing unit arranged downstream of the liquid reservoir and fluidly connected to the liquid reservoir, the dosing unit comprising a chamber portion arranged between an inlet valve and an outlet valve, the chamber portion arranged to receive from the liquid reservoir a discrete pump cycle volume of liquid under an operational pressure generated by the piston pump greater than ambient pressure, and to the deliver the pump cycle volume of liquid to the delivery system outlet, the discrete pump cycle volume being dependent on the operational pressure,

wherein the chamber portion comprises a top wall and a bottom wall that lie against each other when the chamber portion is empty, and that separate apart as the chamber portion is filled with liquid, the bottom wall resting against a base of the dosing unit, and

wherein the bottom wall is bonded to the base, the bonding arranged along at least portions of a perimeter of the bottom wall such that when liquid is injected into the chamber portion and the top wall moves away from the bottom wall, an elastic tensile stress is generated in the top wall of the chamber portion.

2. The drug delivery device of claim 1 , wherein the operational pressure is in a range between 10 and 1600 millibars over ambient pressure.

3. The drug delivery device of claim 2 , wherein the operational pressure is in a range between 500 and 1000 millibars over ambient pressure.

4. The drug delivery device of claim 1 , wherein the chamber portion is elastically expandable at least in a state when filled with the pump cycle volume of liquid.

5. The drug delivery device of claim 4 , wherein an elastic property of the elastic expandable chamber portion defined by a volume change ΔV multiplied by an operational pressure greater than ambient pressure ΔP is in a range of:

5·10 −8 <ΔV×ΔP< 1·10 −3 [m 3 Pa].

6. The drug delivery device of claim 5 , wherein the elastic property of the elastic expandable chamber portion defined by the volume change ΔV multiplied by the operational pressure greater than ambient pressure ΔP is in a range of:

5·10 −6 <ΔV×ΔP< 1·10 −4 [m 3 Pa].

7. The drug delivery device of claim 1 , wherein the dosing unit comprises a flexible tube incorporating the chamber portion.

8. The drug delivery device of claim 1 , wherein the drug delivery device is a patch pump device configured to be mounted against a patient's skin for transcutaneous delivery of the liquid to the patient.

9. The drug delivery device of claim 8 , wherein the liquid transcutaneously delivered to the patient is insulin.

10. The drug delivery device of claim 1 , wherein the inlet and outlet valves are in the form of pinch valves.

11. The drug delivery device of claim 1 , comprising a pump chamber actuator arranged to bias against the chamber portion to expel liquid out of the chamber portion to deliver the pump cycle volume of liquid to the delivery system outlet.

12. The drug delivery device of claim 1 , wherein the plunger actuator comprises a linear actuator and a bent actuation rod coupled at a first end to the linear actuator and at a second end to the plunger, the linear actuator being arranged parallel and laterally adjacent to the liquid reservoir.

13. The drug delivery device of claim 12 , wherein the linear actuator comprises a linear screw and a nut blocked in rotation and slideably movable upon rotation of the screw.

14. The drug delivery device of claim 12 , wherein the actuation rod comprises a curved spring sheet beam, the actuation rod having a portion bent in a U-shape between straight sections.

15. The drug delivery device of claim 14 , wherein the U-shape bent portion of the actuation rod is slidably guided in a housing guide slot of a housing.

16. The drug delivery device of claim 15 , wherein a housing portion forming the housing guide slot in which the actuation rod slides, is made of a polymer.

17. The drug delivery device of claim 16 , wherein the polymer is Polytetrafluoroethylene (PTFE).

18. The drug delivery device of claim 16 , wherein the housing guide slot comprises roller bearings mounted along the guide slot on a convex side of the U-shape bent portion.

19. The drug delivery device of claim 16 , wherein the housing guide slot is made integrally with the housing of the polymer that is an injected polymer.

20. The drug delivery device of claim 12 , wherein the actuation rod is made of a tape of spring metal.

21. The drug delivery device of claim 20 , wherein the spring metal is a stainless steel alloy.

22. The drug delivery device of claim 1 , wherein the liquid reservoir, the dosing unit, and the delivery system outlet form part of a disposable part of the drug delivery device connectable and separable from a reusable part of the drug delivery device, the reusable part comprising the plunger actuator, a control system configured to control the piston pump, and an electrical drive unit coupled to the plunger actuator.

23. A method of operating the drug delivery device of claim 1 , the method comprising:

a) operating the plunger actuator to advance the plunger and create an overpressure in the liquid reservoir due to an elasticity of the plunger,

b) opening the inlet valve while the outlet valve is closed and operating the plunger actuator to advance the plunger and fill the chamber portion with the pump cycle volume of liquid thus creating the operational pressure in the chamber portion,

c) closing the inlet valve, opening the outlet valve, and emptying the chamber portion by actuation of the pump chamber actuator either passively or actively, and

d) closing the outlet valve.

24. The method of claim 23 , wherein the operational pressure is greater or smaller than a target pressure due to a predefined target volume of liquid being filled in the chamber portion, the target volume being considered as a fill volume of the chamber portion at the target pressure without any pressure exerted by a pump chamber actuator.

25. The method of claim 24 , wherein the target pressure is ambient pressure, in which case the operational pressure is always greater than the target pressure.

26. The method of claim 25 , wherein the pump cycle volume of liquid is in a range of 1% to 50% greater than a maximum volume of the chamber portion, the maximum volume being considered as the fill volume of the chamber portion at ambient pressure without any pressure exerted by a pump chamber actuator.

27. The method of claim 23 , wherein the operational pressure in the chamber portion in b) is in a range of between 10 and 1600 millibars over ambient pressure.

28. The method of claim 27 , wherein the operational pressure in the chamber portion in b) is in a range of between 500 and 1000 millibars over ambient pressure.