Injector for delivering liquid medication

Abstract

To provide a pre-filled injection device with a non-removable cartridge embedded in a housing structure.SOLUTION: The invention relates to a pre-filled injection device in which a piston rod drive mechanism comprises a threaded piston rod 60 which is moved helically in a nut secured to a housing structure 10. During assembly of the injection device, it is possible to eliminate the air-gap between a plunger 7 in a cartridge 5 and piston rod means 60 by moving the nut element for the drive mechanism axially during assembly. In an alternative solution, the piston rod 60 comprises a telescopic element which can slide axially in relation to the piston rod 60 to obtain the zero position.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pre-filled injection device for delivering a liquid agent, preferably in the form of one or more doses of the liquid agent. In particular, the present invention relates to such an injection device in which the distance that occurs between the piston rod moving the plunger forward inside the container and the plunger itself is minimized during the assembly of the injection device.

[0002] In a second aspect, the present invention relates to a method for assembling such an injection device.

[0003] Furthermore, the present invention relates to an alternative solution and a method for performing this alternative solution.

Background Art

[0004] Injection devices are widely known and are used for the treatment of a wide variety of different diseases, particularly within the area of diabetes. A very common type of injection device is the so-called disposable or pre-filled injection device. This type of injection device typically houses a cartridge that holds a predetermined amount of the liquid agent to be injected, and the cartridge is non-removably embedded within the injection device. Thus, when the content volume contained within the enclosed cartridge has been used, the user preferably discards the entire device for recycling. A more or less classical pre-filled injection device is the FlexPen® from Novo Nordisk A / S, which is described in more detail in [Patent Document 1] and is disclosed in detail in FIGS. 11 to 17 of [Patent Document 1]. This injection device comprises a housing structure that includes a cartridge holder for securing a cartridge that holds 3 ml of the liquid agent.

[0005] When producing such pre-filled injection devices, a relatively large number of different tolerances apply. There are various tolerances when molding the different parts that make up the injection device. There are tolerances in the various click-and-snap connections that permanently connect the individual parts, and there are tolerances when filling the liquid agent into the cartridge.

[0006] As a result of all these tolerances, assembled injectors are typically delivered to the end user with an individual distance between the plunger and piston rod inside the cartridge. This distance is called the air gap. Before starting to use the injector to inject a dose of liquid, the user must eliminate the air gap, which is usually done by dispensing a small dose, thereby allowing the piston rod to move forward without actually dispensing any liquid thereafter. This process is often called the initial priming of the injector. Thus, the first few empty doses allow the piston rod to move and come into contact with the plunger, and only when physical contact is established between the plunger and the piston rod will the liquid actually be dispensed, and the set dose size will be dispensed correctly.

[0007] Recently, a new type of pre-filled injector has been developed. These new injectors can dispense a limited, predetermined number of dose volumes, the dose volumes being predetermined and equal in volume by the injector manufacturer. This new type of injector is called a “multiple-use fixed-dose” injector. When using such a fixed-dose injector, it is impossible for the user to set and dispense small doses, as all dose volumes are predetermined and set by the fixed-dose injector manufacturer. An example of such a multiple-use fixed-dose injector is provided in [Patent Document 2]. Such injectors are very suitable for injecting liquid GLP-1 drugs, which are usually injected in fixed dose volumes, typically once daily or once weekly.

[0008] A wide variety of solutions have been proposed to avoid the process of priming injection devices.

[0009] [Patent Document 3] proposes providing a piston rod foot that slides axially against the piston rod during the assembly of the injection device and can be physically connected to the piston rod at a position where contact between the piston rod foot and the plunger is established during the assembly process. The present publication further describes a method in which the housing structure comprises two parts, the two parts sliding axially in a first state and permanently fixed to each other in a second state. The first state is the state during the assembly of the injection device, and the second state is the final unused delivery state of the injection device.

[0010] [Patent Document 4] describes a method in which an adjusting member screwed onto a piston rod rotates relative to a housing structure during the assembly of the injection, thereby causing the piston rod to move forward and contact a plunger. Once contact is established between the piston rod and the plunger, the adjusting member is physically fixed to the housing structure. Subsequently, when injection is performed, the adjusting member acts as a conventional nut element for helically advancing the rotatable piston rod during rotation.

[0011] A similar method involves moving the nut element to the correct position and physically securing it to the housing structure in that position. [Patent Document 5] This is disclosed in [publication name]. In this solution, the piston rod and nut member are pre-assembled after the nut element is axially positioned with the piston rod relative to the cartridge holder component of the housing structure. When the piston rod is in the correct contact position, the nut member is permanently connected to the cartridge holder component, for example, by welding.

[0012] However, all of these prior art methods are quite cumbersome and require highly specialized assembly processes. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] International Publication No. 1999 / 38554 [Patent Document 2] International Publication No. 2018 / 007259 [Patent Document 3] International Publication No. 2009 / 095332 [Patent Document 4] European Patent No. 2,968,777 [Patent Document 5] International Publication No. 2017 / 001694 [Overview of the Initiative]

[0014] The objective of this invention is to provide an injection device that can minimize the air gap in a very simple manner, suitable for mass production.

[0015] Therefore, in a first aspect of the present invention, a pre-filled injection device is provided for delivering a liquid agent, preferably in a dose. The pre-filled injection device is A housing structure extending along longitudinal axes defining distal and proximal directions, in which a cartridge is permanently embedded, wherein the cartridge is further provided with a movable plunger, A piston rod means for advancing a movable plunger during dispensing, wherein the piston rod means has an external thread and a longitudinal track structure, A rotatable drive element that engages with the longitudinal track structure of a piston rod means, thereby transmitting the rotation of the drive element to the rotation of the piston rod, The piston rod means comprises a nut element having an internal thread for engaging with the external thread, • Nut elements are in the following two different states: • A first state in which the nut element is positioned to slide axially relative to the housing structure, and · It has a second state in which the nut element abuts against a movable plunger and is permanently fixed to the housing structure.

[0016] In the first state, the nut element engages with the housing structure via an elastic joint surface that can axially bias the nut element, and thus the piston rod means, with respect to the housing structure, so that the piston rod means abuts against the movable plunger. In the second state, the nut element is permanently fixed to the housing structure, so that the piston rod moves spirally with respect to the nut member and the housing structure during rotation.

[0017] Therefore, it is possible to first pre-assemble the nut element and the piston rod means and then slide the nut element with respect to the housing structure until the correct position is obtained and maintained.

[0018] In this correct position, i.e., the position where the piston rod means abuts against the plunger inside the cartridge, the nut element is fixed to the housing.

[0019] Thereafter, during the assembly of the injection device, it is ensured that physical contact between the piston rod foot and the plunger is obtained individually for each injection device.

[0020] The above principle can be used for any type of pre-filled injection device in which the threaded piston rod advances inside the cartridge by rotating the piston rod with respect to the threaded nut element carried with the housing structure or otherwise associated with the housing structure.

[0021] Throughout this application, and in particular in the more detailed parts of the description, many of the examples used relate to so-called pre-filled multiple-use fixed-dose injection devices, but it should be particularly noted that the general teachings of this application are suitable for a wide range of different pre-filled injection devices and are in no way limited to specific examples. More specifically, the invention claimed in the appended claims is in no way limited to the examples used.

[0022] The wide range of pre-filled injection devices covered by the appended claims are also pre-filled injection devices having a dose setting mechanism by which the user can set the various individual dose sizes to be discharged each time the expelling action is performed.

[0023] A permanent connection between the nut element and the housing can be obtained in many different ways, but welding, and in particular laser welding, is preferred.

[0024] The resilient joint surface preferably includes one or more flexible arms having radial resilience and operable between the nut element and the housing structure.

[0025] The flexible arms are preferably provided on the nut element and abut against the inner surface of the housing structure.

[0026] Furthermore, the flexible arms abut against the inner surface within the housing structure, and the inner surface is provided with several grooves, one or more of which may be provided with an inclined bottom angled in the distal direction. The angle is preferably such that the piston rod means engaged by the internal thread inside the nut member is pressed against the movable plunger inside the cartridge.

[0027] When the pre-assembled nut element and piston rod are pushed in the proximal direction, the elasticity of the flexible arms combines with the inclined bottom surface of at least one of the grooves to bias the nut element in the distal direction.

[0028] Once contact is made with the plunger inside the cartridge, this flexible connection subsequently biases the nut element distally together with the piston rod means, thus ensuring that physical contact is maintained.

[0029] In the above, it should be understood that the piston rod means, in one embodiment, comprises both an actual piston rod and a piston rod foot. The piston rod may be rotatable relative to the piston rod or fixed to the piston rod in a rotational direction to rotate in harmony with it. Thus, the piston rod foot may be a separate part or integrally molded with the piston rod.

[0030] The connection between the nut element and the housing structure is preferably a weld created by directing a laser beam through an opening in the housing structure onto the surface connecting the nut element and the housing structure.

[0031] The present invention further relates to a method for assembling an injection device as defined herein.

[0032] This method, 1. A step of screw-engaging the nut member and the piston rod means by rotating the nut member and the piston rod means relative to each other, 2. A step of translating the nut member together with the piston rod means with respect to the housing structure, 3. The process of inserting at least the proximal components of the cartridge together with the plunger into the housing structure, 4. A step of moving the cartridge together with the plunger relative to the piston rod means to a position where the plunger inside the cartridge contacts the piston rod means, 5. This includes the step of fixing the nut element to the housing structure at this position.

[0033] In one embodiment, the method further includes welding at least one flexible arm of a nut element to a housing structure, preferably by laser welding, at a position where the plunger inside the cartridge contacts the piston rod means.

[0034] From this point forward, the general concept of this method is to slide the nut element into the position of the first state and, when in the correct position, permanently connect the nut element to the housing structure (for example, by laser welding).

[0035] Therefore, in the second state, the nut member is permanently connected to the housing structure and acts as a well-known nut element for this type of injection device.

[0036] In an alternative embodiment, the pre-filled injection device is A housing structure in which a cartridge having a movable plunger extending along a longitudinal axis (X) defining the distal and proximal directions is permanently embedded, A piston rod having a piston rod foot for advancing a movable plunger during dispensing, wherein the piston rod has an external thread and a longitudinal track structure. A rotatable drive element that engages with the longitudinal track structure of a piston rod, thereby transmitting the rotation of the rotatable drive element to the rotation of the piston rod, It comprises a nut element having an internal thread for engaging with the external thread of the piston rod.

[0037] In this embodiment, the piston rod foot is connected to an extendable element and fixed axially, and the extendable element is in the following two different states: - A first state in which an extendable element is positioned to slide axially relative to the piston rod, and - In a second state, the extendable element is permanently fixed to the piston rod, In the first state, the retractable element is non-rotatably engaged with a longitudinal passage in the piston rod that extends along the longitudinal axis (X), and in the second state, the retractable element is permanently fixed to the piston rod.

[0038] From this point onward, the piston rod foot is connected to an extendable element, which slides axially relative to the piston rod and becomes permanently connected to the piston rod when physical contact is established between the piston rod foot, which is fixed to the extendable element, and the plunger inside the cartridge.

[0039] The permanent connection is preferably made by welding the expandable element directly to the piston rod (for example, by laser welding).

[0040] The present invention further includes a method for assembling such an injection device. This method is 1. The process of engaging the extendable element and the piston rod foot at the axial connection portion, 2. The process of inserting an expandable and retractable element into the longitudinal passage within the piston rod (60), 3. A process to establish physical contact between the plunger inside the cartridge and the piston rod foot, 4. This includes the step of fixing the extendable element to the piston rod at this position, for example, by welding.

[0041] Definition: An "injection pen" is typically an injection device that has an oval or elongated shape, somewhat similar to a writing pen. Such pens usually have a tubular cross-section, but can easily have different cross-sections, such as triangular, rectangular, or square shapes, or any variation of these or other geometric shapes.

[0042] The term "needle cannula" is used to describe the actual conduit that penetrates the skin during injection. Needle cannulas are typically made from a metallic material, such as stainless steel, and are preferably connected to a hub made of a suitable material, such as a polymer. However, needle cannulas can also be made from polymeric or glass materials. For example, the needle cannula, which is fitted into the hub, can be attached to the injection device either replaceably or permanently.

[0043] As used herein, the term “liquid formulation” means any drug-containing fluid pharmaceutical that can pass through a delivery means such as a hollow needle cannula in a controlled manner, such as a liquid, solution, gel, or microsuspension. Typical pharmaceuticals may include peptides, proteins (e.g., insulin, insulin analogs, and C-peptides), as well as other pharmaceuticals such as hormones, bioactive or activating agents, hormone and gene-based drugs, nutritional prescriptions, and other substances in solid (compound) or liquid form.

[0044] The term "cartridge" is used to describe the primary container that actually holds the liquid. Cartridges are usually made from glass, but can also be molded from any suitable polymer. The cartridge or ampoule is preferably sealed at one end by a punctureable membrane called a "septum," which can be punctured, for example, by the non-patient end of a needle cannula. Such a septum is usually self-sealing, meaning that when the needle cannula is removed from the septum, the opening created during penetration is automatically sealed by its inherent elasticity. The opposite end of the cartridge is typically closed by a plunger or piston made from a rubber composition or a suitable polymer. The plunger or piston can slide within the cartridge. The space between the punctureable membrane and the movable plunger holds the liquid that is pushed out as the plunger reduces the volume of the space that holds the liquid.

[0045] Since cartridges typically have a narrow distal neck portion into which the plunger cannot move, not all of the liquid contained within the cartridge can actually be discharged. Therefore, the terms “initial volume” or “substantially used” refer to the injectable volume contained within the cartridge, and not necessarily the total volume. The injectable volume within the cartridge must be at least equal to the volume that constitutes multiple predetermined sized dose volumes to be discharged. In one embodiment, if a multi-use fixed-dose injector is intended to contain, for example, three fixed doses, each having a volume of 0.3 ml, then the injectable volume of the cartridge must be at least 0.9 ml, and the total volume of the cartridge must be larger to include the volume that cannot be discharged by the narrow neck portion.

[0046] The term "pre-filled" injector refers to an injector in which a cartridge containing the liquid is permanently embedded within the injector so that it cannot be removed without permanently damaging the injector. Once the predetermined amount of liquid in the cartridge is used, the user typically discards the entire injector. Typically, the cartridge, pre-filled with a specific amount of liquid by the manufacturer, is fixed in a cartridge holder that is later permanently connected to the housing structure so that the cartridge cannot be replaced.

[0047] This is in contrast to "durable" syringes, which can be replaced by the user themselves with a new cartridge containing the liquid whenever it becomes empty. Pre-filled syringes are usually sold in packages containing two or more syringes, while durable syringes are usually sold one at a time. When using pre-filled syringes, the average user may need 50 to 100 syringes per year, whereas with durable syringes, a single syringe may last for several years, but the average user will still need 50 to 100 new cartridges per year.

[0048] The term "multiple-use fixed-dose" injector means an injector capable of delivering a predetermined number of (i.e., two or more) doses of substantially identical volume. Thus, the liquid contained in the cartridge is dispensed in several substantially identical dose volumes. In one embodiment, the cartridge may contain, for example, 3 ml of liquid, which can be dispensed in six identical doses, each of which is 0.5 ml. The number of equally sized doses is often 2 to 8, and preferably 4 to 6, identical dose volumes. The multiple-use fixed-dose injector may be either pre-filled so that the entire injector is discarded after a predetermined number of dose volumes have been dispensed, or it may be a durable injector that allows the user to replace the cartridge and dispense a new set of equally sized dose volumes from a new cartridge.

[0049] When the term "automatic" is used in conjunction with an injection device, it means that the injection device can administer the injection without the user of the injection device having to deliver the force required for the injection device to expel the liquid during administration. The force is typically delivered (automatically) by an electric motor drive or a spring drive. The actual spring for the spring drive is pulled by the user, for example, during dose setting, but such a spring is usually pre-pulled with a low force to avoid problems when delivering very small doses. Alternatively, the spring may be fully pre-loaded by the manufacturer with a pre-loaded force sufficient to expel the initial total volume of the liquid contained in the cartridge (i.e., the entire injectable volume) through several doses. Typically, when administering an injection, the user partially releases some of the force stored in the spring by activating a release mechanism provided either on the surface of the injection device housing or at the proximal end of the injection device. Alternatively, the injection device may be shield-triggered, with the operation of a movable shield releasing the force required to expel the dose.

[0050] As used in this description, the terms “permanently connected” or “permanently embedded” are intended to mean that the use of tools is required to separate components permanently embedded within the housing structure, and in particular the cartridge, and that if these components are separated, at least one of these components will be permanently damaged, and consequently the injector will become inoperable.

[0051] All reference materials cited herein, including publications, patent applications, and patents, are incorporated by reference to the same extent as they are incorporated by reference in whole, as if each reference material were individually and specifically indicated to be incorporated by reference in whole.

[0052] All headings and subheadings in this specification are for convenience only and should not be construed as limiting the invention.

[0053] The use of any examples or illustrative phrases presented herein (e.g., "such as") is solely intended to clarify the invention and, unless otherwise specified, does not limit the scope of the invention. Nothing in this specification should be construed as indicating that any non-claimed element is essential for the practice of the invention.

[0054] The references and incorporations of patent documents in this specification are for convenience only and do not reflect any consideration of the validity, patentability, and / or enforceability of such patent documents.

[0055] To the extent permitted by applicable law, this invention includes all modifications and equivalents of the subject matter described in the appended claims. [Brief explanation of the drawing]

[0056] The present invention will be described in more detail below in relation to preferred embodiments and with reference to the drawings.

[0057] [Figure 1] Figure 1 shows an exploded assembly diagram of a spring-driven injection device according to one embodiment of the present invention. [Figure 2A-2B] Figures 2A and 2B show cross-sectional views of the spring-driven injection device shown in Figure 1. Figure 2B is a view rotated 90° from Figure 2A. [Figure 3] Figure 3 shows a cross-sectional view of the proximal components of a spring-driven injection device, with the piston rod positioned in its initial position. Figure 3 is rotated 90° relative to Figure 4. [Figure 4] Figure 4 shows a cross-sectional view of the proximal components of a spring-driven injection device, with the piston rod in the stopped position. Figure 4 is rotated 90° from Figure 3. [Figure 5A-5B] Figures 5A and 5B show more detailed cross-sectional views of the proximal components of a spring-driven injection device. Figure 5B is rotated 90° relative to Figure 5A. [Figure 6A-6B] Figures 6A and 6B show perspective views of the drive tube from different angles. [Figures 7A-7B] Figures 7A and 7B show perspective views of the connector as seen from the opposite end. [Figure 8] Figure 8 shows a perspective view of the piston rod. [Figure 9] Figure 9 shows a side view of the joint surface between the drive tube and the bridge structure inside the housing structure. [Figure 10] Figure 10 shows a cutaway view of the joint surface between the drive tube and the housing structure. [Figure 11A-11C] Figures 11A to 11C show the attachment of the torsion spring to the spring base of the housing structure. [Figure 12] Figure 12 shows an exploded assembly diagram of the piston rod and nut member for zero-point adjustment according to the first embodiment. [Figure 13] Figure 13 shows the zero-point adjustment in the first embodiment. [Figures 14A-14B] Figures 14A and 14B show perspective views of the zero-point adjustment nut member as seen from the opposite end. [Figure 15] Figure 15 shows a perspective view of the housing component. [Figure 16] Figure 16 shows the cut-out part of the housing component for zero-point adjustment. [Figures 17A-17B] Figures 17A and 17B show two dissected images of the joint surface between the nut member and the housing component for zero-point adjustment. [Figure 18A-18C] Figures 18A to 18C show cross-sectional views of alternative zero-point adjustments. [Figure 19] Figure 19 shows a nut component for the alternative solution shown in Figures 18A to 18C. [Figure 20] Figure 20 shows an alternative piston rod for a second alternative zero-point adjustment. [Figure 21] Figure 21 shows an extendable connection between the piston rod and the piston rod foot for a second alternative zero-point adjustment. [Figures 22A-22B] Figures 22A and 22B show cross-sectional views of a second alternative zero-point adjustment. Figure 22B is rotated 90° relative to Figure 22A.

[0058] The figures are schematic diagrams, simplified for clarity, and show only the details essential to understanding the invention, while omitting other details. Throughout, the same reference numerals are used for the same or corresponding parts. [Modes for carrying out the invention]

[0059] Where the terms “up” and “down,” “right” and “left,” “horizontal” and “vertical,” “clockwise” and “counterclockwise,” or similar relative expressions are used below, they are merely references to the attached diagrams and do not represent actual usage. The diagrams shown are schematic, and therefore, their relative dimensions, as well as the configurations of different structures, are intended to serve only as illustrative purposes.

[0060] In that context, it may be convenient to define the term “distal end” in the attached diagram as referring to the end of the injection device to which the needle cannula is fixed and which is pointed toward the user during injection, while the term “proximal end” refers to the opposite end, as shown in Figures 2A and 2B. Distal and proximal mean along the axial orientation extending along the longitudinal axis (X) of the injection device, as similarly disclosed in Figures 2A and 2B.

[0061] In the following embodiments, when referring to clockwise and counterclockwise directions, it is understood that the injection device is being viewed from a position distal to the injection device. Therefore, clockwise is a rotation toward the right, like the arm of a clock, and counterclockwise is a rotation toward the left.

[0062] The following terms will be used throughout the detailed description below to explain the various movements performed by the injection device described.

[0063] "Translational motion" refers to strictly linear motion that does not involve any rotation.

[0064] "Rotational motion" refers to any rotational motion centered on a central point, which may be the center point of a planar axis or central axis having a longitudinal extension.

[0065] "Axial motion" refers to any motion along an axial direction. Such motion can be strictly translational motion, or it may include rotational motion, and thus become "helical motion." This is because helical motion is a combination of axial motion and rotational motion.

[0066] "Stretchable" means encompassing situations in which a movable element moves outward from and / or inward from its base element. Stretchable motion can be translational or rotational, and therefore stretchable motion is spiral-like.

[0067] Figure 1 discloses an exploded assembly diagram of a spring injection device according to one embodiment of the present invention. In the disclosed embodiment, the injection device is pen-shaped, and is often also called an injection pen.

[0068] The dispensed liquid is contained within a cartridge 5, which is a generally hollow glass ampoule, sealed distally by a puncturable partition 6 and proximal by a movable plunger 7. The movable plunger 7 is positioned to move distally by a piston rod 60. To properly distribute force from the piston rod 60 to the plunger 7, a piston rod foot 85 can be provided between the piston rod 60 and the plunger 7, as shown in Figure 13.

[0069] Cartridge 5 is typically filled with a liquid by the manufacturer and permanently and irreplaceably fixed within the housing structure of the injector, so that the injector becomes a pre-filled injector. The disclosed housing structure comprises a housing component 10, a cartridge holder 20, a spring base 25, and a shield guide 30. However, the housing structure may comprise any number of components or, alternatively, may be molded as a single housing unit.

[0070] The housing component 10 (also shown in Figure 15), cartridge holder 20, spring base 25, and shield guide 30 are preferably permanently fixed to each other so that the cartridge 5 is permanently sealed within the housing structure, thereby constituting a pre-filled injection device. Proximal to the housing component 10, the housing component 10 is closed by the spring base 25, which clicks into the housing component 10 during assembly of the pre-filled injection device. Distal to the housing component 10, the shield guide 30 also clicks into the housing component 10. The cartridge holder 20 is preferably permanently fixed to the housing component 10 by a pair of elastic click arms 21, or alternatively, by being molded integrally with the housing component 10.

[0071] The figure depicts a pair of elastic click arms 21, but any number of arms can be provided. Since the embodiments herein refer to pen-shaped injection devices having a tubular cross-section, many of the various protrusions, arms, guide trajectories, and other mechanical elements are provided in pairs. However, for many of these attributes, any random number can be provided.

[0072] The shield guide 30 guides the retractable and movable shield 40, the function of which will be described later. At the distal end, the shield guide 30 is provided with a peripheral track 31 having an axial opening 32 on its outer surface. This peripheral track 31 guides a radially pointed projection 36 located on the inner surface of the protective cap 35, as disclosed in Figure 2B (and shown by the dashed line in Figure 1). From this point onward, the user needs to rotate the protective cap 35 counterclockwise (when viewed from the distal position) relative to the shield guide 30 and, consequently, the housing structure, before the radially pointed projection 36 can move axially outward through the axial opening 32 and the protective cap 35 can be removed.

[0073] At the distal end, the cartridge holder 20 is provided with a needle hub 45 that carries the needle cannula 46, at least during use. Alternatively, a needle magazine having multiple needle cannulas can be integrated into the injection device.

[0074] For example, as disclosed in Figures 2A and 2B, the needle cannula 46 has a distal end for penetrating the user's skin during injection and a proximal end 47, the proximal end 47 penetrating through the septum 6 of the cartridge 5 so that the liquid can be pushed out of the cartridge 5 and flow through the lumen of the needle cannula 46 and through the user's skin.

[0075] The needle hub 45 is fixed to the cartridge holder 20 by a mating surface that is operated during the starting process. During this starting process, the needle hub 45 moves axially in the proximal direction so that the proximal end 47 of the needle cannula 46 penetrates through the partition wall 6 of the cartridge 5. Also, in the sequence of moving the needle hub 45, the proximal locking arm 48 provided on the needle hub 45 irreversibly engages with the distal mating surface 22 on the cartridge holder 20 and locks to the distal mating surface 22, so that the needle hub 45 is subsequently irreversibly locked to the cartridge holder 20.

[0076] The needle hub 45 is preferably moved proximal by the rotation of a retractable shield 40, which allows the needle hub 45 to be moved proximal via a helical joint surface. Once the starting process is complete, a locking arm 48 on the needle hub 45 is locked to the cartridge holder 20, and a click arm 43 provided on the retractable shield 40 engages with the housing structure to prevent the user from rotating the retractable shield 40 back to its previous position. The engagement of the click arm 43 is preferably with the axial inner surface of a shield guide 30 fixed to the housing component 10. From this point onward, the starting process may be performed only once.

[0077] After the startup process is complete, the injection device is ready for use, as disclosed in Figures 2A and 2B, and the user can use the injection device for multiple injections as described. As further described, the injection of the liquid is driven by a spring, which in embodiments of this disclosure is a torsion spring that delivers a torsional force. However, any type of spring can be used in the injection process.

[0078] The retractable and movable shield 40 carries a cleaning assembly 50, which is disclosed in more detail in WO2019 / 101670. The cleaning assembly 50 keeps the distal end of the needle cannula 46 biologically clean between injections and is fixed to the retractable and movable shield 40 by a shield tip 55 that clicks into the retractable and movable shield 40, by which an elastic arm 56 engages with the retractable and movable shield 40, so that the cleaning assembly 50 follows all the movements of the retractable and movable shield 40, namely rotational, translational, and helical movements.

[0079] The cleaning assembly 50 preferably contains a liquid cleaning agent, which in one embodiment may be the same preservative contained in the liquid in the cartridge 5. In a preferred embodiment, the cleaning agent is a liquid pharmaceutical preparation containing the same preservative as the one contained in the cartridge 5, which is filled into the cleaning assembly 50 when the injection device is started.

[0080] A torsion spring arrangement is provided to move the piston rod 60 distally during dose discharge. The torsion spring arrangement comprises a torsion spring 65, a drive tube 70, and an internal nut member 11 for driving the piston rod 60 distally, as described.

[0081] In embodiments of the present disclosure, the torsion spring 65 is a metal spring in which a wire is wound in a spiral. In the longitudinal direction, the torsion spring 65 may be divided into different zones or areas. In some of these zones, the wires of the coil have little to no distance between them, while in other zones, the coils have a fairly large longitudinal distance between them. These zones are called compression zones 66 (see, for example, Figure 1). Such compression zones 66, where there is distance between the coils, provide a compressive force, and thus the torsion spring 65 can exert both torsional and compressive forces. When the two ends of the torsion spring 65 are compressed toward each other, the torsion spring 65 releases a longitudinally oriented force, biasing the two ends toward each other.

[0082] The two ends of the torsion spring 65 are bent into hooks. One hook is attached to the housing structure via a spring base 25 at the proximal end of the injection device, and the other hook is attached to the drive tube 70 at the opposite, more distal end of the injection device. Thus, a torsional force can be provided between the housing structure and the drive tube 70, and this torsional force can be used to rotate the drive tube 70.

[0083] The torsion spring 65 is preferably mounted by passing the hook through the axial openings of each component 25, 70 such that the hook is captured by the edge of the axial opening, followed by relative rotation of each component 25, 70 and the torsion spring 65. The torsion spring 65 preferably first engages with the drive tube 70 and then, in the assembly process, engages with the spring base 25. Both the drive tube and the spring base may be provided with snap projections as described in one embodiment.

[0084] The piston rod 60, disclosed in detail in Figure 8, is provided with an external thread 61 on its outer surface and further comprises a longitudinal raceway structure 62 that is open at the distal end but terminates in a stop surface 63 at the proximal end. The longitudinal raceway structure 62 has a free length referred to as "L". The free length "L" is the measured length from the engagement of the piston rod 60 with an inwardly pointed projection 75 on the drive tube 70 to the stop surface 63 at the proximal end of the raceway structure 62, as best seen and described in Figures 3 and 5A. Thus, the free length "L" is a representation of the axial length that the piston rod 60 can move distally before the stop surface 63 engages with the inwardly pointed projection 75. Therefore, as can also be seen in Figure 3, the free length "L" is shorter than the actual length of the raceway structure 62.

[0085] The longitudinal raceway structure 62 refers to any type of structure provided in or on the piston rod 60 that can define the longitudinal free length "L". For example, it may be any type of raceway, groove, or similar recess.

[0086] The internal nut member 11 is fixed to the housing structure in both the rotational and axial directions. In one embodiment, the nut member 11 is an integral part of the housing component 10. Alternatively, the nut member 11 may be a separate part that is fixed to the housing component 10 during the assembly of the injection device, for example, by gluing or welding. The nut member 11 is provided with an internal thread 12 on its inner surface that engages with an external thread 61 on the piston rod 60, so that the piston rod 60 moves helically when it rotates relative to the housing structure.

[0087] As disclosed in Figures 12 to 17A and Figure 17B, in further embodiments, as described, the nut member 11 can be used to eliminate an air gap during assembly of the injection device.

[0088] The longitudinal track structure 62 on the piston rod 60 is engaged by inwardly pointed projections 75 provided on the inner surface of the drive tube 70, so that each time the drive tube 70 rotates, the piston rod 60 rotates simultaneously and therefore moves distally helically within the internal thread 12 of the nut member 11. The inwardly pointed projections 75 disclosed in Figures 6A and 6B are preferably provided in pairs, but can be provided singly or in any random number.

[0089] The torsion spring 65 is enclosed between the housing structure and the drive tube 70, so that the torque stored in the torsion spring 65 can rotate the drive tube 70 relative to the housing structure. In the disclosed embodiment, the torsion spring 65 engages with the drive tube 70 at its distal end and with the spring base 25 at its proximal end. The torsion spring 65 is tensed during the manufacturing of the injection device, i.e., during its assembly, so that a relatively high torque is stored in the torsion spring 65 when the injection device is delivered to the user. The torque stored in the unused delivery state of the injection device is preferably sufficient to discharge the entire initial volume of cartridge 5, meaning that the torque is sufficient to drive the piston rod 60 and, consequently, the plunger 7, to the distal end or near the distal end of cartridge 5. In a preferred embodiment, such a multi-use fixed-dose injector has a torsion spring 65 that is stretched and ready to dispense approximately 2 to 8 predetermined and equally sized dose volumes, so that the user does not need to stretch the torsion spring 65 between each of these 2 to 8 injections.

[0090] The drive tube 70 disclosed in Figures 6A and 6B has a first helical shape 71 at its distal end. That is, the distal end of the drive tube 70 is made from a sleeve that gradually decreases in the circumferential direction. The first helical shape 71 extends axially and terminates within a first axial drive flange 72.

[0091] Furthermore, the distal end of the drive tube 70 has an outer surface that is radially offset relative to the rest of the drive tube 70. This radial recess on the outer surface of the drive tube 70 defines a second axial drive flange 78, which is parallel to the first axial drive flange 72 but offset by 180° in the rotational direction, as is best seen in Figure 6A. These two axial flanges 72, 78 define the stopping point of rotation of the drive tube 70, as will be described.

[0092] Up to the second axial drive flange 78, the radial recess has a helical structure that forms a helical surface that abuts against a similar helical surface provided on the inside of the housing structure. This helical surface has the same configuration as the housing helical shape 16, but is offset longitudinally in the proximal direction, as is best seen in Figure 17B. The joint surface between these two surfaces has the same effect as the joint surface between the first helical shape 71 and the housing helical shape 16, as described. Having two such helical joint surfaces makes the operation of the injection device more stable.

[0093] Furthermore, two outwardly pointed projections 73, 74 are provided on the outer surface of the drive tube 70. In the disclosed embodiment, these two projections 73, 74 are also offset 180° from each other and also offset longitudinally by a certain distance.

[0094] As described, one or more inwardly pointed projections 75 on the inside of the drive tube 70 engage with the longitudinal track structure 62 in the piston rod 60. On its outer surface, the drive tube 70 is provided with a helical flange 76, the use of which will be described later.

[0095] The housing component 10 of the housing structure is molded internally with an internal bridge structure 15 having an axial opening through which a piston rod 60 can move. On the inner surface, the bridge structure 15 guides and supports the distal component of the drive tube 70. This guide is depicted in Figure 6A, with the contour of the bridge structure 15 indicated by a dashed line. The bridge structure 15, which also carries the nut member 11, can, in one embodiment, be molded separately and attached to the housing component 10. In either case, the bridge component 15 contacts the housing component 10 only through a radial bearing component 19, through which only a limited angular space is obtained such that the axial opening exists around the bridge component 15. This is best seen in Figures 17A and 17B.

[0096] The first helical shape 71 at the distal end of the drive tube 70 extends axially and engages with a similar helical shape 16 (see, for example, Figure 10) provided within a bridge structure 15 located inside the housing component 10 of the housing structure (hereinafter referred to as the housing helical shape 16). This housing helical shape 16 as the first helical shape 71 is a sleeve that gradually decreases away in the circumferential direction and terminates within a first axial housing flange 17, which can engage with the first axial drive flange 72 of the drive tube 70.

[0097] Figure 9 discloses the joint surface between the drive tube 70 and the bridge structure 15 located inside the housing component 10. That is, the housing component 10 is visually cut open. Figure 10 discloses the joint surface between the drive tube 70 and the housing structure including the bridge structure 15. In the diagram of Figure 10, it is the housing structure, not the drive tube 70, that is radially cut along line "A" in Figure 5A and viewed from a distal position. Thus, the cut is made through the first axial housing flange 17. The housing component 10 is further visually cut open in the longitudinal plane along the center line "X".

[0098] The internal bridge structure 15 is further provided with a second axial housing flange 18, as seen in Figures 9 and 17B, which can abut against a second axial drive flange 78. Thus, the rotational engagement between the drive tube 70 and the housing structure is defined by the abutment between the first axial drive flange 72 and the first axial housing flange 17, in addition to the abutment between the second axial drive flange 78 and the second axial housing flange 18, as is best shown in Figures 9 and 10. It is preferable that all four flanges 72, 17; 78, 18 are parallel to each other and to the longitudinal central axis "X" of the injection device. Furthermore, as will be described, the axial lengths ("dl" shown in Figures 6A and 6B) of these four flanges 72, 17; 78, 18 are the same.

[0099] Because the torsion spring 65 constantly applies a torsional force to the drive tube 70, the drive tube 70 rotates counterclockwise (in this embodiment) when viewed from the distal end of the injection device. However, the engagement between the first axial drive flange 72 and the first axial housing flange 17, and the engagement between the second axial drive flange 78 and the second axial housing flange 18, prevent the drive tube 70 from rotating relative to the housing structure.

[0100] Furthermore, several ratchet arms 77 provided on the drive tube 70 engage with a tooting 26 inside the spring base 25, so that the drive tube 70 rotates in only one direction, which in the disclosed embodiment is counterclockwise when the injection device is viewed from a distal position. This is illustrated, for example, in Figure 5B.

[0101] The retractable shield 40 is rotatable relative to the housing structure and can rotate between a locked position and an unlocked position. As shown in Figure 1, the retractable shield 40 is provided on its outer surface with a helical structure 41 terminating in radial ends 44a, b, which are positioned at an angular distance apart such that together they define an axial opening. An inwardly pointed projection is provided on the inner surface of the housing component 10, which can slide through the axial opening of the helical structure 41 when the retractable shield 40 is rotated to the unlocked position. At any other position, this inwardly pointed projection will come into contact with the helical structure 41 when attempting to move the retractable shield 40 in the translational direction in the proximal direction, thereby defining a locked position.

[0102] The spiral structure 41 forces the needle shield 40 to move spirally when it rotates. Therefore, it is possible to move the needle shield 40 to a position where the distal tip of the needle cannula 46 is positioned just outside the cleaning assembly 50 when the needle shield 40 is released.

[0103] In the locked position, the retractable shield 40 is prevented from moving in the translational direction, but in the unlocked position, the retractable shield 40 can move in the translational direction. In this context, translation means axial motion along the central axis "X" without any rotation.

[0104] The housing component 10 is provided with a pair of longitudinal windows 13. These longitudinal windows 13 are aligned with similar windows 23 provided within the cartridge holder 20 so that the user can visually inspect the contents of the cartridge 5. A retractable shield 40, radially sandwiched between the housing component 10 and the cartridge holder 20, is rotatable between a locked position and an unlocked position and is provided with a further set of windows 49. These windows 49 are aligned with the other windows 13, 23 so that the user can see the contents of the cartridge 5 only when the retractable shield 40 is rotated to the unlocked position. When the retractable shield 40 is in the locked position, the solid parts of the retractable shield 40 prevent the user from visually viewing the cartridge 5. Thus, this rotation of the set of windows 49 within the retractable shield 40 also indicates when the injection device is ready for injection.

[0105] In one embodiment, a pair of longitudinal windows 13 provided within the housing component 10 may be provided with a scale indicating multiple doses of the injector. In the embodiments of Figures 1 and 15, this scale shows four sections, each representing one of a predetermined dose volume. Thus, the user can visually see the physical position of the plunger 7 within the section of the window 13 and see how many doses have been taken and how many remain in the cartridge 5.

[0106] The retractable and movable shield 40 is also used to release the torque stored in the torsion spring 65 when it moves in a translational direction in the proximal direction, thereby dispensing a predetermined dose volume. During injection, the user presses the shield tip 55, and thereafter the retractable and movable shield 40, against the skin, thereby causing the retractable and movable shield 40 to move proximal.

[0107] To transmit translational motion from the retractable shield 40 to the drive tube 70, a connector element 80, as disclosed in Figures 7A and 7B, is provided. The connector element 80 is provided with two inwardly pointed projections 81, 82 on its inner surface, which are guided relative to the housing component 10 in the translational direction, i.e., without any rotation, and which are also offset in both the rotational and axial directions.

[0108] One of the two inwardly pointed projections 81, 82 (indicated as "81") is not directly visible in the enclosed figure, but is indicated by a puncture line in Figure 7B. In the disclosed embodiment, the two projections 81, 82 are offset 180° from each other.

[0109] Both the retractable and movable shield 40 and the connector element 80 are provided with hooks 42 and 83. When the retractable and movable shield 40 rotates, the two hooks 42 on the retractable and movable shield 40 can be brought into engagement with the two hooks 83 provided on the connector element 80.

[0110] The hook 83 on the connector element 80 is provided distally on a pair of axially extending parts 84. These axially extending parts 84 allow the connector element 80 to surround the bridge element 15 of the housing element 10 and to operate through the axial opening between the radial bearings 19 in the connection between the bridge element 15 and the housing element 10.

[0111] Spring installation As disclosed in Figures 2A and 2B, the torsion spring 65 is located between the drive tube 70 and the spring base 25, so that the torsion spring 65 can rotate the drive tube 70 relative to the spring base 25, which is part of the housing structure.

[0112] In one embodiment disclosed in Figures 11A to 11C, the torsion spring 65 is provided with a hook 67 at one end. To illustrate the mounting of the spring, Figures 11A to 11C show only the proximal end of the torsion spring 65 and also only a portion of an alternative spring base 25. Although Figures 11A to 11C disclose only one end of the torsion spring 65, it is clear that both ends are provided with such hooks 67 and can be mounted in the same manner.

[0113] To mount the torsion spring 65, one hook 67 is first passed through the axial passage 26 in the translational direction, for example, at the spring base 25. This translational motion is indicated by the arrow "A" in Figure 11A, which shows that the motion between the spring base 25 and the torsion spring 65 is relative motion, meaning that one or both of the elements may move in the translational direction.

[0114] As disclosed in Figure 11B, when the hook 67 is passed axially through the axial passage 26, the torsion spring 65 and the spring base 25 rotate relative to each other, so that the hook 67 catches on the shelf 27 formed within the spring base 25, as shown in Figure 11C.

[0115] In order to irreversibly fix the torsion spring 65 to the spring base 25, the radial snap projection 28 is located on the spring base 25 within the axial passage 26.

[0116] As the torsion spring 65 and the spring base 25 rotate relative to each other, the hook 67 of the torsion spring 65 passes over the radial snap projection 28 and is subsequently irreversibly locked to the spring base 25, as shown in Figure 11C.

[0117] The radial snap projection 28 has two sides provided in the rotational direction. During rotation, the side that first encounters the hook 67 has an inclined surface 29a to make it easier for the hook 67 of the torsion spring 65 to slide over the radial snap projection 28. The opposite side of the snap projection 28 is preferably provided with a steeply sloped surface 29b to prevent the hook 67 of the torsion spring 65 from rotating in the opposite direction after it has been attached.

[0118] In one embodiment, the inclined surface 29a is angled so that the hook 67 of the torsion spring 65 cannot pass through the radial snap projection 28 without being pushed forward by an assembly tool. In such embodiments, it is not sufficient to simply rotate the spring base 25 and the torsion spring 65 relative to each other. This is especially true in cases where the torsion spring 65 has open windings so that sufficient torque cannot be transmitted to the proximal end carrying the hook 67 when the torsion spring 65 is rotated. In such cases, it is necessary to use an assembly tool that grasps the torsion spring 65 at the proximal end and pushes the hook 67 forward to pass through the radial projection.

[0119] In one embodiment, the assembly tool may be a support element that enters the axial passage when the torsion spring 65 is in the position disclosed in Figure 11B, and contacts the rear hook 67, thereby rotating the hook 67 onto the radial snap projection 28 and to the position disclosed in Figure 11C.

[0120] While the radial snap projection 28 is disclosed in relation to the spring base 25, such radial snap projection 28 may also be provided on the fixed drive tube 70 to secure the other end of the torsion spring 65. Thereafter, the snap projection 28 may be provided on the spring base 25, on the drive tube 70, or on both elements.

[0121] In one embodiment, the torsion spring 65 is initially attached to either the spring base 25 or the drive tube 70 by purely rotational motion and, for example, by the use of a tool. This forms a pre-assembled unit comprising either the spring base 25 or the drive tube 70 and the torsion spring 65. Since the torsion spring 65 is irreversibly attached for the radial snap projection 28, this pre-assembled unit can be moved around during the assembly process without the torsion spring 65 being separated from either the spring base 25 or the drive tube 70.

[0122] In a later stage of the assembly process, the torsion spring 65 can be attached to the spring base 25 or other parts of the drive tube 70 by rotating this part and the torsion spring 65 relative to each other.

[0123] Preferably, the pre-assembled unit consists of a torsion spring 65 and a drive tube 70. During the pre-assembly process, the torsion spring 65 is irreversibly attached to the drive tube 70 as described above. Once this pre-assembled unit is positioned inside the housing component 10, the spring base 25 rotates to engage with the proximal hook 67 of the torsion spring 65 and is axially fixed to the housing component 10 by engaging with a pair of flexible connecting arms 9 (most commonly shown in Figures 15 and 16) provided on the housing component 10. In one embodiment, the radial snap projection 28 is provided only on the drive tube 70 and not on the spring base 25.

[0124] injection When the retractable and movable shield 40 is rotated to the unlocked position, the user presses the distal shield tip 55 of the retractable and movable shield 40 against the skin, thereby causing the retractable and movable shield 40 to move in a translational direction in the proximal direction, thereby dispensing a predetermined dose volume. This translational motion is transmitted to a similar translational motion of the connector element 80.

[0125] The connector element 80, depicted in more detail in Figures 7A and 7B, is guided translationally relative to the housing component 10 during dispensing, and two inwardly pointed projections 81, 82 abut against outwardly pointed projections 73, 74 on the outer surface of the drive tube 70, so that the drive tube 70 also moves translationally together with the connector element 80. The compression zone 66 on the torsion spring 65 allows the drive tube 70 to move translationally in the proximal direction, and the compression of the torsion spring 65 further applies an axial force to the drive tube 70, biasing the drive tube 70 distally.

[0126] The translational motion of the drive tube 70 in the proximal direction causes the first axial drive flange 72 and the second axial drive flange 78 on the drive tube 70 to slide along the first axial housing flange 17 and the second axial housing flange 18 of the housing component 10, respectively. At the same time, the inwardly pointed projection 75 on the drive tube 70 slides a certain axial distance within the longitudinal track structure 62 on the piston rod 60.

[0127] From this point forward, the size of a predetermined volume prepared by this translational motion of the drive tube 70 correlates with the longitudinal distance the drive tube 70 travels, i.e., the axial length of the engagement between the first axial drive flange 72 and the first axial housing flange 17, the axial length of the engagement between the second axial drive flange 78 and the second axial housing flange 18, and the pitch of the screw connections 12, 61 between the piston rod 60 and the nut member 11. The translational distance the drive tube 70 travels when a predetermined volume is prepared is called "dl" (operating distance).

[0128] As the first axial drive flange 72 and the second axial drive flange 78 disengage from the first axial housing flange 17 and the second axial housing flange 18 and move in the translational direction, the torque stored in the torsion spring 65 forces the drive tube 70 to rotate, so that the helical shape 71 on the drive tube 70 rotates downwards toward the housing helical shape 16 inside the housing component 10 until the first axial drive flange 72 and the second axial drive flange 78 re-engage with the first axial housing flange 17 and the second axial housing flange 18. The helical motion may be supported by additional helical joint surfaces, as previously described. This rotation is 360° in the disclosed embodiment. That is, the drive tube 70 rotates in one complete revolution each time it translates proximal by a travel distance "dl". From this point onward, the piston rod 60 also rotates 360° and therefore moves to a distal distance determined by the pitch of the screw 61 on the piston rod 60 and the pitch 12 of the engaging nut member 11.

[0129] Therefore, each predetermined volume is prepared when the drive sleeve 70 is moved in the translational direction by a distance "dl" in the proximal direction, and is dispensed when the drive sleeve 70 is rotated distally and returned to its initial position.

[0130] A shield spring 90 in the form of a helical coil compression spring is provided between the connector element 80 and the housing structure, preferably between the connector element 80 and the spring base 25, and applies a compressive force to the connector element 80 when the connector element 80 is translated proximal during dose preparation. The compression of the shield spring 90 biases the connector element 80 distally.

[0131] As can be seen in Figures 6A and 6B, the drive tube 70 is provided with a helical flange 76 on its outer surface, which engages with inwardly pointed projections 81, 82 on the inside of the connector element 80 when the torsion wrench 65 begins to rotate the drive tube 70. This engagement between the inwardly pointed projections 81, 82 and the helical flange 76 supports the helical guide of the drive tube 70.

[0132] The helical flange 76 on the drive tube 70 is provided with two axial openings "d" (Figures 6A and 6B), through which the inwardly pointed projections 81, 82 on the inside of the connector element 80 can slide in the translational direction when the openings "d" are rotatably aligned with the inwardly pointed projections 81, 82. This alignment occurs when the first axial drive flange 72 and the second axial drive flange 78 on the drive tube 70 are about to contact the first axial housing flange 17 and the second axial housing flange 18 on the inside of the housing component 10, which is when a predetermined volume has been discharged. Thus, when a predetermined volume has been discharged, i.e., after the drive tube 70 has rotated 360° (in this embodiment) to reach its initial position, the shield spring 90 will push the connector element 80 and the retractable shield 40 distally.

[0133] Furthermore, in this state, the inwardly pointed projections 81 and 82 are aligned with the outwardly pointed projections 73 and 74, so that the next subsequent dose volume can be released by repeating the procedure described herein.

[0134] When the retractable and movable shield 40 moves to its initial position and then returns, the cleaning assembly 50 carried by the retractable and movable shield 40 is returned to its initial position, and the distal tip of the needle cannula 46 is positioned inside the cleaning chamber 50.

[0135] During the distal movement of the retractable shield 40, the helical structure 41 on the retractable shield 40 contacts a similar helical path 33 provided on the inside of the housing structure and preferably on the inner surface of the shield guide 30, thereby forcing the retractable shield 40 to rotate to a locked position as it moves to and from its initial position.

[0136] Contents run out Therefore, a predetermined dose volume is prepared by pressing the retractable and movable shield 40 against the user's skin, thereby moving the drive tube 70 proximal. When the drive tube 70 moves proximal by a travel distance "dl", the first helical shape 71 on the drive tube 70 reaches a release position, and the axial drive flanges 72, 78 are released from the axial housing flanges 17, 18. In this release position, the drive tube 70 can rotate under the influence of the torque stored in the torsion spring 65. As described, the drive tube 70 moves distally in a helical manner during rotation. Also during this rotation, the drive tube 70 rotates the piston rod 60 due to the engagement between the longitudinal track structure 62 of the piston rod 60 and the inwardly pointed projection 75 inside the drive tube 70. Since the piston rod 60 is screwed into nut members 11 fixed within the housing structure (61, 12), the piston rod 60 moves distally in a helical manner during rotation.

[0137] Each time the drive tube 70 moves proximal by a travel distance "dl" and is released, the piston rod 60 is forced to rotate 360°, i.e., in one complete revolution, and therefore move forward by an axial distance determined by the screw pitch between the piston rod 60 and the nut member 11. When the remaining distance between the inwardly pointed projection 75 on the drive tube 70 and the stop surface 63 on the piston rod 60 becomes smaller than the length "dl" of the axial flanges 72, 78, 17, 18, it is not possible to move the drive tube 70 to the released position and release any further fixed load.

[0138] When the injection device is delivered to the user, the stop surface 63 on the piston rod 60 is located at the proximal end of the injection device, as disclosed in Figure 3. However, for each predetermined dose size discharge, the piston rod 60 moves distally until the stop surface 63 on the piston rod 60 is in a position where the drive tube 70 cannot be moved proximal by its full operating distance "dl". Once this is done, it is impossible to move the drive tube 70 to the release position, and therefore it is not possible to select a further predetermined dose size, thereby preventing the user from dispensing an additional predetermined dose.

[0139] In other words, if the remaining portion of the free length "L" of the raceway structure 62 of the piston rod 60 is shorter than the operating distance "dl", it is not possible to move the axial drive flanges 72, 78 to disengage them from the axial housing flanges 17, 18, and therefore to release any further fixed volume.

[0140] Ultimately, the drive tube 70 moves translationally by a working distance "dl" proximal each time the user prepares one of the predetermined dose volumes, and rotates back to its initial position when the prepared predetermined dose volume is dispensed. In this rotational motion, the drive tube 70 preferably rotates approximately 360°. If the time accumulated while the drive tube 70 moves by a working distance "dl" and the distance accumulated while the piston rod 60 moves distally remains less than the length "dl" of the free length "L" of the available track structure "L" of the piston rod 60, the stop surface 63 on the piston rod 60 prevents the dose tube 70 from moving proximal by a full fixed dose setting (i.e., the total working distance "dl"), and therefore prevents the user from selecting the full predetermined dose size.

[0141] In different embodiments, the first helical shape 71 and the housing helical shape 16 may be divided into two or more surfaces so as to provide two or more axial flange contacts (72, 18; 78; 17). In such cases, the possible rotations of the drive tube 70 and piston rod 60 for each translational motion may differ from 360°. For example, if twice the number of axial flange contacts are provided, the rotation would be 180° so that the piston rod 60 rotates by half a full rotation with each dose release.

[0142] Examples of when the contents run out In one embodiment, the free length "L" of the track structure 62 may be, for example, 43 mm. That is, the translational distance between the engagement of the inwardly pointed projection 75 of the drive tube 70 with the piston rod 60 and the stop surface 63 in the piston rod 60 is set to 43 mm at the factory.

[0143] To release one of the fixed loads, the drive tube 70 moves proximal by a travel distance "dl". In this example, "dl" may be 5 mm. Once the drive tube 70 has moved proximal by a travel distance "dl" = 5 mm, the torsion spring 65 causes the drive tube 70 to rotate in one full revolution (i.e., 360°) back to its initial position. During this rotation, the piston rod 60 is also forced to rotate by the same degree, i.e., 360°. Depending on the pitch of the screw connection between the piston rod 60 and the nut member 11, the piston rod 60 moves distally by a given axial distance for each full revolution. The pitch may be such that, for example, the distance the piston rod 60 moves is 10 mm for each full revolution (360°) of the piston rod 60. This means that when the four fixed doses are released (i.e., the drive tube 70 moves four times by a distance "dl"), the piston rod 60 moves 40 mm distally, leaving only a free length "L" of 3 mm of the track structure 62 before reaching the stopping surface 63, and that the drive tube 70 requires an axial movement of "dl" = 5 mm to release further fixed dose volumes, so although a free length "L" of 3 mm of the track structure 62 remains, it is no longer possible to release further fixed dose volumes.

[0144] Zero point adjustment In one embodiment of the present invention, primarily disclosed in Figures 12-17A and 17B, the nut member 11 may be a separate element fixed to the housing component 10 of the housing structure during the assembly of the injection device. In such an embodiment, the nut member 11 can be fixed within the housing structure without the use of physical mounting means such as gluing or welding. By using a dedicated assembly, in such an embodiment, the nut member 11 can also be used to completely eliminate, or at least sufficiently minimize, any air gaps resulting from different tolerances in the assembly process. Eliminating such air gaps is often also called zero-point adjustment. The zero point means the point where the piston rod 60 (or piston rod foot 85) contacts the plunger 7 inside the cartridge 5. If such contact is achieved during the manufacture of the injection device, the user does not need to perform initial priming of the injection device before discharging the first dose volume.

[0145] A nut member 11 for this purpose is disclosed in Figures 14A and 14B and comprises an internal thread 12 that engages with an external thread 61 on the piston rod 60, and two external thread projections 95 provided on the proximal side of the nut member 11. These two angled thread projections 95 together form an external thread on the nut member 11. However, this external thread may be made from one or more flanges or any number of external thread projections 95.

[0146] The nut member 11 is further provided with several ratchet arms 96 on its outer surface, and the use of the ratchet arms 96 will be described. In the disclosed embodiment, two ratchet arms 96 are disclosed on the distal side of the nut member 11, but any preferred number can be provided.

[0147] The bridge structure 15 inside the housing component 10, which supports the nut member 11, for example, as disclosed in Figure 16, is provided in this embodiment with axial teeth 97 that allow the nut member 11 to rotate in only one direction. The permitted direction of rotation is clockwise, meaning that the ratchet arm 96 and the teeth 97 are joined in such a way that rotation in the counterclockwise direction is prevented.

[0148] The bridge structure 15 inside the housing component 10 is further provided with an internal thread 98 having a orientation such that the nut member 11 is screwed in a proximal helical manner when rotated in the permitted clockwise direction.

[0149] During the assembly of the injection device, one important objective is to eliminate the distance between the piston rod 60 and the plunger 7 inside the cartridge 5, the so-called air gap. When the piston rod foot 85 is attached to the piston rod 60 as disclosed in Figure 13, this objective is to eliminate the physical distance between the distal surface of the piston rod foot 85 and the proximal surface of the plunger 7, so that the piston rod foot 85 and the plunger 7 come into contact when the injection device is delivered to the end user in an unused state.

[0150] During final assembly, if the nut member 11 rotates relative to the housing structure, the piston rod 60 advances distally until the piston rod 60 or the piston rod plunger 85 contacts the plunger 7 inside the cartridge 5.

[0151] The rotation of the nut member 11 is preferably performed by using a special tool on the production line that engages with the nut member 11 and can transmit rotation to the nut member 11. In one preferred embodiment, the piston rod 60 is first positioned at the engagement portion with the nut member 11, located within the bridge structure 15 of the housing component 15. Then, the position of the plunger 7 in the cartridge 5 used for that particular injection device is detected using electronically computerized equipment. If the position of the plunger 7 and the position of the piston rod 60 (or piston rod foot 85) are measured and known, the computer can determine how much the nut member 11 needs to be rotated in order to bring the piston rod foot 85 or piston rod 60 of a particular injection device into contact with the plunger 7 when the injection device is assembled.

[0152] Therefore, the position of the nearest end of the piston rod 60 or the piston rod foot 85 is finely adjusted by rotating the nut member 11 on a unidirectional contact surface with the bridge structure 15. Importantly, the nut member 11 can be rotated in a direction that advances the piston rod 60 (or piston rod foot 85) into contact with the plunger 7.

[0153] The piston rod 60 is further provided with an axial track structure 62 engaged by an inwardly pointed projection 75 on the drive tube 70, the axial track structure 62 is further provided with several ratchet arms 77 that engage with a tooting 26 inside the spring base 25, forming a unidirectional ratchet joint surface, so that the drive tube 70 rotates in only one direction, which in the disclosed embodiment is counterclockwise when the injection device is viewed from a distal position. Thus, these ratchet arms 77 prevent the piston rod 60 from rotating clockwise.

[0154] From this point onward, the engagement between the piston rod 60 and the drive tube 70 prevents the piston rod 60 from rotating clockwise. Therefore, when the nut member 11 is rotated clockwise, this rotation is transmitted to the translation of the piston rod 60 distally, because the piston rod 60 cannot follow the clockwise rotation of the nut member 11.

[0155] When the dose is discharged, the drive tube 70 and piston rod 60 rotate counterclockwise. The nut member 11 is prevented from rotating counterclockwise by the unidirectional ratchet joint surfaces 96, 97 between the nut member 11 and the housing component 10 (via the bridge structure 15), so the nut member 11 does not rotate and therefore supports the helical motion of the piston rod 60 distally.

[0156] To eliminate the air gap between the piston rod 11 (or piston rod foot 85) and the plunger 7 inside the cartridge 5, the nut member 11 rotates clockwise relative to the housing structure, translating the piston rod 60 distally.

[0157] If the piston rod 11 (or piston rod foot 85) is in contact with the plunger 7, it is impossible to further rotate the nut member 11 clockwise. However, in one embodiment, this is achieved by electronically measuring the position of the piston rod foot 85 before final assembly so that it is in the correct position when assembled with the cartridge holder component 20.

[0158] Due to the unidirectional joint surfaces 96 and 97 between the nut member 11 and the housing part 10, it is impossible to rotate the nut member 11 in a counterclockwise direction (when viewed from a distal position).

[0159] The results described above indicate that the nut member 11 self-locks to the housing structure, and there is no need to physically fix the nut member 11 to the housing structure. From this point onward, there is no need to weld or glue the nut member 11 to the housing structure, as described in the prior art.

[0160] Self-locking, as used herein, means that the piston rod 60 (or foot portion 85) abuts against the plunger 7, so that the nut member 11 cannot rotate clockwise, and that the unidirectional ratchet joint surfaces 96, 97 prevent the nut member 11 from rotating counterclockwise.

[0161] When the piston rod 60 rotates counterclockwise to discharge the prepared volume, the nut member 11 is also prevented from following this rotation by its unidirectional ratchet joint surfaces 96, 97, and when the nut member 11 rotates clockwise during assembly to eliminate the air gap, the piston rod 60 is prevented from following this rotation by its connection with the drive tube 70 (62, 75) and the engagement between the drive tube 70 and the housing structure (77, 26).

[0162] If the pitch of the first threaded connections 61, 12 between the piston rod 60 and the nut member 11 is high, i.e., if the piston rod 60 moves a long distance with each rotation, it is prudent to have second threaded connections 95, 98 between the threaded projection 95 on the nut member 11 and the threaded flange 98 inside the housing component 10, so that the nut member 11 can be helically screwed proximal to the housing structure during the rotation of the nut member 11.

[0163] As is most clearly shown in Figure 17B, the projection 95 constituting the external thread on the nut member 11 is fixed behind the thread flange 98 inside the bridge structure 15 of the housing component 10, so that it moves proximal as the nut member 11 rotates relative to the housing structure. Furthermore, Figure 16 depicts the thread flange 98 having an axial opening inside the bridge structure 15, which allows the thread projection 95 on the nut member 11 to engage proximal behind the thread flange 98.

[0164] This means that when the nut member 11 rotates clockwise, the nut member 11 moves proximal while moving the piston rod 60 distally. Therefore, the pitch of the second screw connections 95, 98 between the nut member 11 and the housing structure must be subtracted from the pitch of the first screw connections 61, 12 between the piston rod 60 and the nut member 11 in order to find the effective zero-point adjustment pitch.

[0165] The low effective pitch for zero-point adjustment makes fine-tuning the process of eliminating the air gap easier. Therefore, when operating with a piston rod 60 with a high pitch, it is beneficial to have second screw connections 95, 98 between the nut member 11 and the housing component 10, especially when a relatively large volume needs to be discharged with each rotation of the piston rod 60.

[0166] If the pitch of the first screw connections 61, 12 between the piston rod 60 and the nut member 11 is low, the second screw connections 95, 98 are not considered necessary, and therefore the nut member 11 only needs to rotate in one plane relative to the housing structure without the ability to move axially.

[0167] Alternative zero-point adjustment An alternative nut component for zero-point adjustment is disclosed in Figures 18A to 19B. This alternative nut component is assigned reference numeral 111, and the various elements added in this embodiment are preceded by the number "1". The remaining components of this embodiment are numbered in the same way as those used in the previous embodiment.

[0168] The nut element 111 is provided with an internal thread 112 on its inner surface and a pair of elastic arms 113 on its outer surface. In this embodiment, only two elastic arms 113 are disclosed, but any number of elastic arms 113 can be provided.

[0169] In this embodiment, the axial opening in the bridge structure 15 of the housing structure that guides the nut element 111 is provided with at least one, preferably two, axially extending grooves 115 that guide the elastic arm 113 in the translational direction. Thereafter, the engagement between the globe 115 and the flexible arm 113 ensures that the nut element 111 can only slide in the translational direction, i.e., without rotating relative to the housing structure.

[0170] The groove 115 is provided with an inclined bottom surface 116 (see Figure 18B) that slopes radially outward in the distal direction. This has the effect of exposing the elastic arm 113 to an increasing radial force when it moves proximal, and therefore biasing the nut element 111 distally with the increased force as it moves further proximal.

[0171] As shown in the figure, the flexible arm 113 is preferably inclined radially, and therefore the flexible arm 113 follows an angle with respect to the central axis that corresponds to the angle of the inclined base surface 116.

[0172] To assemble the injection device, the nut element 111 and the piston rod 60 are first pre-assembled by rotating the nut element 111 and the piston rod 60 relative to each other so that the nut element 111 is screwed onto the piston rod 60. The pre-assembled piston rod 60 and nut element 111 are then placed inside the opening in the bridge structure 15, as disclosed in Figure 18A.

[0173] When the injection device is fully assembled, as disclosed in Figure 18C, the piston rod 60 may be in direct contact with the plunger 7 inside the cartridge 5, or the piston rod foot 85 may be provided between the piston rod 60 and the plunger 5, such that there is contact between the piston rod foot 85 and the plunger 7.

[0174] In one embodiment, the piston rod foot 85 can be connected to the piston rod 60 at the same time as the piston rod 60 is pre-assembled with the nut element 111, or after the piston rod 60 has been pre-assembled with the nut element 111, as shown in Figure 18B.

[0175] In one embodiment, the piston rod foot 85 may click-fit to the piston rod 60 with a bearing-like connection so that the piston rod foot 85 can rotate relative to the piston rod 60. In another embodiment, the piston rod foot 85 is a separate or unconnected element positioned between the piston rod 60 and the plunger 7. Alternatively, the piston rod foot 85 may be rotatably connected to the piston rod 60 so that it can rotate together with the piston rod 60.

[0176] In the latter embodiment, the piston rod foot 85 may house an electronic sensor that can register the rotational speed of the piston rod 60 with respect to the cartridge 5 and thereafter the housing structure in order to determine the volume discharged.

[0177] Once the piston rod 60 and the nut element 111 are pre-assembled with or without the piston rod foot 85, the nut element 111 slides axially, so that the flexible arm 113 engages with the groove 115 provided in the opening of the bridge section 15 of the housing structure.

[0178] In the final stage of assembly, the cartridge 5 is placed inside the cartridge holder 20, and the cartridge holder 20 moves proximal to the cartridge 5, so that the plunger 7 inside the cartridge 5 contacts the piston rod 60 (or foot 85), and the cartridge holder 20 clicks into place with the housing component 10 of the housing structure.

[0179] Therefore, the plunger 7 inside the cartridge 5 contacts the piston rod 60 (or foot 85), thereby forcing the nut element 111 to slide in a translational direction in the proximal direction. Due to the elasticity of the flexible arm 113, when the flexible arm 113 is pressed against the inclined bottom surface 116 of the groove 99, the nut element 111, and thus the piston rod 60, are automatically biased distally, thereby maintaining contact between the plunger 7 and the piston rod 60 (or foot 85). Each time contact is obtained and maintained between the plunger 7 and the piston rod 60 (or foot 85), a laser beam (indicated as "L" in Figure 18C) is directed through an opening 14 in the housing structure onto the outer surface of the bridge structure 15. As disclosed in Figure 18C, two or more such openings 14 may be present, if necessary.

[0180] Preferably, the bridge structure 15 is molded from a polymer that is more transparent to laser light than the polymer from which the flexible arms 113 of the nut elements 111 are formed, so that the energy of the laser beam is converted into heat on the contact surface area between the bridge structure 15 and the flexible arms 113, i.e., on the inner surface of the bridge structure 15.

[0181] Therefore, the injection device according to this embodiment has a nut element 111 that can operate between two different states. A first state in which the nut element 111 is axially movable and preferably moves slightly proximal by collision with the plunger 7 in the cartridge 5. During this axial movement in the proximal direction, the elasticity of the nut element 111 causes it to bounce distally, thereby maintaining physical contact with the plunger 7.

[0182] At a position where physical contact is achieved between the plunger 7 and the piston rod 60 (or foot portion 85), the nut element 111 is welded to the housing structure or otherwise connected, which thereafter defines a second state of the nut element 111.

[0183] In this second state, the nut element 111 is fixed axially to the housing structure, and the piston rod 60 then moves helically when rotated relative to the nut element 111 and the housing structure.

[0184] The positioning of the pre-assembled nut element 111 and piston rod 60 can be determined electronically, so that welding can be performed before the cartridge is actually positioned.

[0185] Second alternative zero-point adjustment Figures 20 to 22B disclose an alternative solution in which an extendable element 100 is disposed between the piston rod foot 85 and the piston rod 60.

[0186] An alternative piston rod 60 is disclosed in Figure 20 and is provided with two claws 105 distal to it that can grip around the retractable element 100. Although only two gripping claws 105 are disclosed, any number of claws 105 can be provided.

[0187] The piston rod 60 is provided with an external thread 61 that engages with an internal thread 12 provided within the nut member 11, and in this alternative embodiment, it is preferably an integrated part of the housing structure. The piston rod 60 is further provided with a longitudinal track structure 62 that engages with the drive element 70.

[0188] The retractable element 100, shown in detail in Figure 21, is provided with a circular rib 101 on its distal side, and behind the circular rib 101, a click arm 86 provided on the piston rod foot 85 engages so that the retractable element 100 can be axially fixed to the piston rod foot 85. This click-fit connection allows the piston rod foot 85 to rotate relative to the retractable element 100.

[0189] The retractable element 100 is further provided with several outwardly pointed surfaces 102 on which a claw 105 can abut. Thereafter, the claw 105 is suitable for sliding on these outwardly pointed surfaces 102 so that the retractable element 100 can slide against the piston rod 60.

[0190] For this purpose, the retractable element 100 is slidably positioned within the axial opening 106 of the piston rod 60 so that the piston rod foot 85 can slide axially with respect to the piston rod 60 together with the retractable element 100.

[0191] As disclosed in Figures 22A and 22B, when the piston rod foot 85 (connected to the retractable element 100) slides and contacts the plunger 7 inside the cartridge 5, the retractable element 100 is welded to the piston rod 60 by directing a laser beam "L" through an opening 14 in the housing structure onto the claw 105 of the piston rod 60, thereby welding the claw 105 to the outwardly pointed surface 102 of the retractable element 100.

[0192] The expandable element 100 is preferably square in shape, having four outer surfaces 102, and the axial opening 106 is also preferably square in shape so that the expandable element 100 can only translate relative to the piston rod 60 in the first state.

[0193] While several preferred embodiments have been described above, it should be emphasized that the present invention is not limited thereto and can be embodied in other ways within the scope of the subject matter defined in the following claims.

Claims

1. A pre-filled injection device for delivering liquid medication, A housing structure in which a cartridge (5) having a movable plunger (7) extending along a longitudinal axis (X) defining the distal and proximal directions is permanently embedded, A piston rod means (60, 85) for advancing the movable plunger (7) during dispensing, wherein the piston rod means (60, 85) comprises a piston rod (60) and a piston rod foot (85), and the piston rod (60) has an external thread (61) and a longitudinal track structure (62), A rotatable drive element (70) that engages with the longitudinal track structure (62) of the piston rod means (60, 85), and so the rotation of the drive element (70) is transmitted to the rotation of the piston rod (60), The piston rod means (60, 85) comprises a nut element (111) having an internal thread (112) that engages with the external thread (61), The nut element (111) is in one of two different states: - A first state in which the nut element (111) is axially slidable relative to the housing structure, and - The piston rod foot (85) is in contact with the movable plunger (7), and the nut element (111) is permanently fixed to the housing structure, In the first state, the nut element (111) engages with the housing structure via an elastic joint surface (113, 116) which has several flexible arms (113) that are movable between the nut element (111) and the housing structure and can bias the nut element (111) axially relative to the housing structure, thereby causing the piston rod means (60, 85) to contact the movable plunger (7), A pre-filled injection device characterized in that, in the second state, the nut element (111) is permanently fixed to the housing structure, and therefore the piston rod means (60, 85) moves helically relative to the nut element (111) and the housing structure when rotated.

2. The injection device according to claim 1, wherein the nut element (111) is permanently fixed to the housing structure by welding.

3. The injection device according to claim 1 or 2, wherein the flexible arm (113) is provided on the nut element (111) and abuts against the inner surface of the housing structure.

4. The injection device according to claim 3, wherein the inner surface that contacts the flexible arm (113) is formed as a groove (116).

5. The injection device according to claim 4, wherein the groove (116) has an inclined bottom that is angled in the distal direction.

6. The injection device according to any one of claims 1 to 5, wherein the housing structure has a passage (14) for a laser beam ("L").

7. A method for assembling an injection device according to any one of claims 1 to 6, wherein the method is - A step of screw-engaging the nut element (111) and the piston rod means (60, 85) by rotating them relative to each other, - A step of translating the nut element (111) together with the piston rod means (60, 85) with respect to the housing structure, - A step of inserting at least the proximal component of the cartridge (5) together with the plunger (7) into the housing structure, - A step of moving the cartridge (5) together with the plunger (7) to a position where the plunger (7) inside the cartridge (5) contacts the piston rod means (60, 85), A method comprising the step of fixing the nut element (111) to the housing structure at this position.

8. A method for assembling an injection device according to claim 7, wherein at least one of the flexible arms (113) of the nut element (111) is welded to the housing structure at the position in which the plunger (7) inside the cartridge (5) contacts the piston rod means (60, 85).

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