An injection device for delivering a liquid agent

Abstract

The present invention relates to a pre-filled injection device having a non-removable cartridge embedded in a housing structure, wherein the piston rod drive mechanism comprises a threaded piston rod that moves helically in a nut fixed to the housing structure. During assembly of the injection device, it is possible to eliminate the air gap between the plunger in the cartridge and the piston rod means by axially moving the nut element of the drive mechanism during assembly. In an alternative solution, the piston rod comprises a telescopic element that can slide axially relative to the piston rod to obtain a zero position.

Description

Technical Field

[0001] The present invention relates to a pre-filled injection device for delivering a liquid formulation, preferably in the form of one or more doses of the liquid formulation. In particular, the present invention relates to such an injection device in which the distance that occurs between the piston rod that moves 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 field 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 contains a cartridge that holds a predetermined amount of the liquid formulation 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 nearly classical pre-filled injection device is the FlexPen® from Novo Nordisk A / S, which is described in more detail in [Patent Document 1] and 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 formulation.

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

[0006] As a result of all these tolerances, the assembled injection device is typically delivered to the end user with the individual distance between the plunger inside the cartridge and the piston rod. This distance is called the air gap. Before starting to use the injection device to inject a dose of the medicament, the user needs to remove the air gap, and the removal of the air gap is typically done by setting and ejecting a small dose, whereby, thereafter, the piston rod moves forward without actually ejecting any medicament. This process is often called the initial priming of the injection device. Thus, only when the piston rod has moved into contact with the plunger and physical contact has been established between the plunger and the piston rod by means of the first few empty dose ejections, is the medicament actually ejected and the set dose size is correctly ejected.

[0007] Recently, a new type of pre-filled injection device has been developed. These new injection devices are capable of discharging a limited pre-defined number of dose volumes, the dose volumes being pre-determined by the manufacturer of the injection device and being equal in volume. This new type of injection device is called a "multiple-use fixed-dose" injection device. When using such a fixed-dose injection device, the user cannot set and eject a small dose since all dose volumes are pre-determined and pre-set by the manufacturer of the fixed-dose device. Examples of such multiple-use fixed-dose devices are provided in [Patent Document 2]. Such injection devices are very suitable for injecting liquid GLP-1 medicaments, which are usually injected in a fixed dose volume and are typically administered once a day or once a week.

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

[0009] [Patent Document 3] proposes providing a piston rod foot, which can be axially slid relative to the piston rod during the assembly of the injection device and physically connected to the piston rod at a position where contact between the piston rod foot and the plunger is established in the assembly process. This disclosure further describes a method in which the housing structure comprises two parts that are axially slid 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 adjustment member screwed onto the piston rod rotates relative to the housing structure during the assembly of the injection, so that the piston rod moves forward to contact the plunger. When contact is established between the piston rod and the plunger, this adjustment member is physically fixed to the housing structure. Thereafter, when injection is performed, the adjustment member operates as a conventional nut element for spirally advancing the rotatable piston rod during rotation.

[0011] A similar method in which the nut element moves to the correct position and is physically fixed to the housing structure at that position is disclosed in

Patent Document 5

[0012] However, all of these prior art methods are quite complicated and require a very specialized assembly process.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

[0014] It is an object of the present invention to provide an injection device that can minimize the air gap in a very simple manner suitable for mass production.

[0015] Accordingly, in a first aspect of the present invention, there is provided a pre-filled injection device for delivering a liquid agent, preferably in a dose. The pre-filled injection device comprises · a housing structure that extends along a longitudinal axis defining a distal direction and a proximal direction, in which a cartridge is permanently embedded, the cartridge being further provided with a movable plunger; · piston rod means for advancing a movable plunger during dispensing, the piston rod means having an external thread and a longitudinal track structure; · a rotatable drive element that engages with the longitudinal track structure of the piston rod means, such that rotation of the drive element is transmitted to the rotation of the piston rod; · a nut element having an internal thread for engaging with the external thread of the piston rod means, · the nut element is in the following two different states: · a first state in which the nut element is axially slidably disposed 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, against 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 relative 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 relative 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 individual injection device.

[0020] The above principle can be used for any type of pre-filled injection device in which the screw-in piston rod advances inside the cartridge by rotating the piston rod relative to a screw-in nut element that is 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 dispensed with each dispensing act.

[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 an inner surface within the housing structure, which inner surface is provided with several grooves, and one or more of these grooves 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 presses against the movable plunger inside the cartridge.

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

[0028] Once contact with the plunger inside the cartridge is obtained, thereafter, due to this flexible connection, the nut element is biased distally together with the piston rod means, thus ensuring that physical contact is maintained.

[0029] In the above, it should be understood that in one embodiment, the piston rod means comprises both an actual piston rod and a piston rod foot. The piston rod can rotate relative to the piston rod or can be fixedly provided in the rotational direction to the piston rod so as to rotate in harmony. Thus, the piston rod foot may be a separate part or may be integrally formed 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 the injection device defined herein.

[0032] The method comprises 1. a step of threadedly 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 relative to the housing structure; 3. a step of inserting at least the proximal component 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 abuts against the piston rod means; 5. at this position, a step of fixing the nut element to the housing structure.

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

[0034] Thereafter, the general concept of the method is to slide the nut element to the position of the first state and, when in the correct position, permanently connect the nut element to the housing structure (e.g., by laser welding).

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

[0036] In an alternative embodiment, the pre-filled injection device · a housing structure in which a cartridge having a movable plunger permanently embedded extends along a longitudinal axis (X) defining a distal direction and a proximal direction, and · a piston rod having a piston rod foot for advancing the movable plunger during dispensing, the piston rod having an external thread and a longitudinal track structure, and · a rotatable drive element that engages with the longitudinal track structure of the piston rod, so that the rotation of the rotatable drive element is transmitted to the rotation of the piston rod, and · 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 a telescopic element and axially fixed, and the telescopic element operates in the following two different states: - a first state in which the telescopic element is axially slidably arranged with respect to the piston rod, and - a second state in which the telescopic element is permanently fixed to the piston rod. The telescopic element non-rotatably engages a longitudinal passage within the piston rod extending along the longitudinal axis (X) in a first state, and the telescopic element is permanently fixed to the piston rod in a second state.

[0038] Thereafter, the piston rod foot is connected to the telescopic element, the telescopic element slides axially relative to the piston rod, and is permanently connected to the piston rod when physical contact is established between the piston rod foot fixed to the telescopic element and the plunger inside the cartridge.

[0039] The permanent connection is preferably made by welding the telescopic element directly to the piston rod (e.g., by laser welding).

[0040] The present invention further includes a method for assembling such an injection device. The method comprises 1. Engaging the telescopic element and the piston rod foot at the axial connection part; 2. Inserting the telescopic element into the longitudinal passage within the piston rod (60); 3. Establishing physical contact between the plunger inside the cartridge and the piston rod foot; 4. Fixing the telescopic element to the piston rod, e.g., by welding, at this position.

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

[0042] The term "needle cannula" is used to describe the actual conduit that penetrates the skin during injection. The needle cannula is typically made of a metallic material such as stainless steel, for example, and is preferably connected to a hub made of a suitable material such as a polymer. However, the needle cannula can also be made of a polymeric material or a glass material. For example, the needle cannula that is mounted within the hub can be either replaceable or permanently attached to the injection device.

[0043] As used herein, the term "agent" means any pharmaceutically active, flowable pharmaceutical composition containing a drug that can pass through a delivery means such as a hollow needle cannula in a controlled manner, such as a liquid, solution, gel, or fine suspension. Representative drugs can include pharmaceuticals such as peptides, proteins (e.g., insulin, insulin analogs, and C-peptides), as well as hormones, biologically derived active agents or actives, hormone and gene-based drugs, nutritional formulations, and other substances in solid (formulations) or liquid form.

[0044] The term "cartridge" is used to describe the primary container that actually holds the agent. The cartridge is typically made of glass, but can also be molded from any suitable polymer. The cartridge or ampoule is preferably sealed at one end by a pierceable membrane called a "septum" that can be pierced, for example, by the non-patient side end of the needle cannula. Such a septum is typically self-sealing, which means 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 of a rubber composition or a suitable polymer. The plunger or piston can move slidably inside the cartridge. The space between the pierceable membrane and the movable plunger holds the agent that is pushed out when the plunger reduces the volume of the space holding the agent.

[0045] The cartridge usually has a narrow distal neck portion within which a plunger cannot move, so not all of the agent contained within the cartridge can actually be discharged. Thus, the term "initial amount" or "substantially used" refers to the injectable volume contained within the cartridge and, therefore, does not necessarily refer to the entire volume. The injectable volume within the cartridge must be at least equal to the volume that constitutes a plurality of predetermined sized dose volumes to be discharged. In one example, if a multi-use fixed-dose injection device is configured to accommodate three fixed doses each having a volume of, for example, 0.3 ml, the injectable volume of the cartridge must be at least 0.9 ml and the overall volume of the cartridge must be larger to include the volume that cannot be discharged by the narrow neck component.

[0046] The term "pre-filled" injection device means an injection device in which the cartridge containing the agent is permanently embedded within the injection device such that the cartridge cannot be removed without permanently destroying the injection device. When a predetermined amount of agent within the cartridge has been used, the user typically discards the entire injection device. Usually, cartridges filled with a specific amount of agent by the manufacturer are fixed within a cartridge holder that is later permanently connected within the housing structure such that the cartridge cannot be replaced.

[0047] This is contrary to a "durable" injection device which can always be replaced by the user himself with a cartridge containing the agent when empty. Pre-filled injection devices are usually sold in packages containing two or more injection devices, while durable injection devices are usually sold one at a time. When using a pre-filled injection device, the average user may require 50 to 100 injection devices per year, while when using a durable injection device, a single injection device can potentially be used for several years, however, the average user will need 50 to 100 new cartridges per year.

[0048] A "multiple-use fixed-dose" injection device means an injection device capable of delivering a plurality (i.e., two or more) of pre-defined doses that are substantially the same in volume. Thus, the medicament contained within the cartridge is discharged in several substantially identical dose volumes. In one example, the cartridge can contain, for example, 3 ml of medicament that can be discharged in six identical doses, each being 0.5 ml. The number of equally sized doses is often from 2 to 8, and preferably 4 to 6, identical dose volumes. The multiple-use fixed-dose injection device can be pre-filled such that the entire injection device is discarded after a pre-defined number of dose volumes have been discharged, or the user can replace the cartridge to enable a new series of equally sized dose volumes to be discharged from a new cartridge.

[0049] When the term "automatic" is used in conjunction with an injection device, this means that the injection device can perform the injection without the user of the injection device delivering the force required to discharge the medicament during dosing. The force is typically delivered (automatically) by an electric motor drive or a spring drive. The actual spring for a spring drive is, for example, pulled by the user during dose setting, but such a spring is usually pre-tensioned with a low force to avoid problems with delivering very small doses. Alternatively, the spring can be fully pre-loaded by the manufacturer with a pre-load force sufficient to discharge the initial total content (i.e., the entire injectable content) of the medicament contained within the cartridge over several doses. Typically, when performing an injection, the user operates a release mechanism provided either on the surface of the housing of the injection device or at the proximal end of the injection device to partially release some of the force accumulated within the spring. Alternatively, the injection device can be shield-triggered such that operation of a movable shield releases the force required to discharge the dose.

[0050] As used herein, the terms "permanently connected" or "permanently embedded" are intended to mean that separating components permanently embedded within a housing structure, and particularly a cartridge, requires the use of tools, and that if these components are separated, at least one of these components will be permanently damaged, and as a result, the injection device will no longer be able to operate.

[0051] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference in their entirety as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0052] All headings and subheadings are used herein for convenience only and should not be construed as limiting the invention in any way.

[0053] The use of any examples or illustrative language (e.g., "such as") presented herein is for the sole purpose of clarifying the invention and does not limit the scope of the invention unless otherwise specifically noted. No language in this specification should be construed as indicating that any non-claimed element is essential to the practice of the invention.

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

[0055] The invention includes all modifications and equivalents of the subject matter recited in the appended claims to the extent permitted by applicable law. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0057]

Figure 1

Figures 2A-2B

Figure 3

Figure 4

Figures 5A-5B

Figures 6A-6B

Figures 7A-7B

Figure 8

Figure 9

Figure 10

Figures 11A-11C

Figure 12

Figure 13

Figures 14A-14B

Figure 15

Figure 16

Figures 17A-17B

Figures 18A-18C

Figure 19

Figure 20

Figure 21

Figures 22A-22B

[0058] The figures are schematic and simplified for clarity, and they show only the details essential for understanding the present invention while omitting other details. Throughout, the same reference numerals are used for identical or corresponding parts.

Best Mode for Carrying Out the Invention

[0059] When the following terms are used: "up" and "down", "right" and "left", "horizontal" and "vertical", "clockwise" and "counterclockwise", or similar relative expressions, these are merely for reference to the attached drawings and do not indicate the actual usage situation. The figures shown are schematic, and thus, not only their relative dimensions but also the configurations of different structures are intended to function only for illustrative purposes.

[0060] In that context, it may be convenient to define that, in the appended figures, the term "distal end" means the end of the injection device that secures the needle cannula and is pointed towards the user during injection, whereas the term "proximal end" means the opposite end, as shown in FIGS. 2A and 2B. Distal and proximal mean along an axial direction extending along the longitudinal axis (X) of the injection device, as also disclosed in FIGS. 2A and 2B.

[0061] In the following examples, when referring to clockwise and counterclockwise or anticlockwise directions, it is understood that the injection device is being viewed from a position distal to the injection device. Thus, clockwise direction is a rotation towards the right like the arm of a clock, and counterclockwise direction is a rotation towards the left.

[0062] To describe the various movements performed with the described injection device, the following terms are used throughout the following detailed description.

[0063] "Translational movement" means a strictly linear movement without any rotation.

[0064] "Rotational movement" means any rotational movement about a center, which center may be, i.e., the center point of a longitudinal extension, i.e., one planar axis or central axis.

[0065] "Axial movement" means any movement in the axial direction. Such movement may be strictly translational or may include rotational movement and thus be a "helical movement". This is because a helical movement is a combination of an axial movement and a rotational movement.

[0066] "Extensible" means covering the situation where a movable element moves out of and / or into a base element. An extensible movement may be translational or may include rotation and thus be helical.

[0067] Figure 1 discloses an exploded view of a spring injection device according to an embodiment of the present invention. In the disclosed embodiment, the injection device is in the shape of a pen, which is often also referred to as an injection pen.

[0068] The dispensed medicament is contained within a cartridge 5, which is generally a hollow glass ampoule sealed at the distal end by a pierceable septum 6 and at the proximal end by a movable plunger 7. The movable plunger 7 is arranged to move distally by a piston rod 60. To appropriately distribute the 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 depicted in Figure 13.

[0069] The cartridge 5 is typically filled with the medicament by the manufacturer and is permanently and irreplaceably fixed within the housing structure of the injection device, and thus the injection device is a pre-filled injection device. The disclosed housing structure comprises a housing part 10, a cartridge holder 20, a spring base 25, and a shield guide 30. However, the housing structure can comprise any number of components or, alternatively, can be formed as a single unitary housing unit.

[0070] The housing part 10 (also shown in Figure 15), the cartridge holder 20, the spring base 25, and the shield guide 30 are preferably permanently fixed to each other such that the cartridge 5 is permanently enclosed within the housing structure, thereby constituting a pre-filled injection device. Proximally, the housing part 10 is closed by a spring base 25 that click-fits onto the housing part 10 during assembly of the pre-filled injection device. Distally of the housing part 10, the shield guide 30 is also click-fitted onto the housing part 10. The cartridge holder 20 is preferably permanently fixed to the housing part 10 by a pair of resilient click arms 21 or, alternatively, by being integrally formed with the housing part 10.

[0071] The figure depicts a pair of elastic click arms 21, although any number of arms can be provided. In the examples of this specification, since the injection device is pen-shaped with a tubular cross-section, many of the various protrusions, arms, guide tracks, and other mechanical elements are provided in pairs of two. However, for many of these attributes, any arbitrary number can be provided.

[0072] The shield guide 30 guides a telescopically movable shield 40, which will be described later in terms of its function. Distally, 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 protrusion 36 located on the inner surface of the protective cap 35, as disclosed in FIG. 2B (and shown by the dashed line in FIG. 1). Thereafter, the user needs to rotate the protective cap 35 counterclockwise (when viewed from the distal position) with respect to the shield guide 30 and thus the housing structure before the radially pointed protrusion 36 can move axially out through the axial opening 32 and the protective cap 35 can be removed.

[0073] Distally, 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 a plurality of needle cannulas can be integrated into the injection device.

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

[0075] The needle hub 45 is fixedly attached to the cartridge holder 20 by a joint surface that operates in the starting process. During this starting process, the needle hub 45 moves axially in the proximal direction such that the proximal end 47 of the needle cannula 46 passes through the partition wall 6 of the cartridge 5. Also, in the order of moving the needle hub 45, an arm 48 that latches on the proximal side provided on the needle hub 45 irreversibly engages with the distal joint surface 22 on the cartridge holder 20 and is locked to the distal joint surface 22. Therefore, thereafter, the needle hub 45 is irreversibly locked to the cartridge holder 20.

[0076] The needle hub 45 preferably moves in the proximal direction by the rotation of a telescopically movable shield 40 that can move the needle hub 45 proximally via a helical joint surface. When the starting process is completed, the locking arm 48 on the needle hub 45 is locked to the cartridge holder 20, and a click arm 43 provided on the telescopically movable shield 40 engages with the housing structure to prevent the user from rotating the telescopically movable shield 40 back to its previous position. The engagement of the click arm 43 is preferably an engagement with the axial inner surface of a shield guide 30 fixedly attached to the housing part 10. Thereafter, the starting process can only be performed once.

[0077] After the starting process is completed, the injection device is in a ready-to-use state as disclosed in FIGS. 2A and 2B, and the user can use the injection device for multiple injections as described. As further described, the injection of the liquid agent is driven by a spring, which in the embodiments of the present disclosure is a torsion spring that delivers a torsional force. However, any type of spring can be used in the injection process.

[0078] The telescopically movable shield 40 carries a cleaning assembly 50, which is disclosed in more detail in WO2019 / 101670. This cleaning assembly 50 keeps the distal end of the needle cannula 46 biologically clean during injection, and is click-fitted to the telescopically movable shield 40 by a shield tip 55 fixed to the telescopically movable shield 40 by engaging the elastic arm 56 with the telescopically movable shield 40. Therefore, the cleaning assembly 50 follows all movements of the telescopically movable shield 40, namely both rotational movement, translational movement, and helical movement.

[0079] The cleaning assembly 50 preferably contains a liquid cleaning agent, which may be the same preservative as that contained in the liquid in the cartridge 5 in one embodiment. In a preferred embodiment, the cleaning agent is a liquid agent of the same preservative-containing pharmaceutical as that contained in the cartridge 5 and filled into the cleaning assembly 50 during the start-up of the injection device.

[0080] A torsion spring arrangement is provided to move the piston rod 60 distally during dose ejection. 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 an embodiment of the present disclosure, the torsion spring 65 is a metal spring with wires wound spirally. In the longitudinal direction, the torsion spring 65 can be divided into different zones or areas. In some of these zones, the wires of the coil have no or very little distance between the coils, and in other zones, the coils have a fairly large longitudinal distance between the coils. These zones are called compression zones 66 (see, for example, FIG. 1). Such compression zones 66 with a distance between the coils provide a compressive force, so that the torsion spring 65 can apply both torsional force and compressive force. When the two ends of the torsion spring 65 are compressed towards each other, the torsion spring 65 returns a longitudinally directed force and biases the two ends away from 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 more distal end on the opposite side 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 attached by passing the hooks through the axial openings of the respective parts 25, 70 such that the hooks are captured by the edges of the axial openings, and then performing a relative rotation of the respective parts 25, 70 and the torsion spring 65. The torsion spring 65 is preferably first engaged with the drive tube 70 and then, in the assembly process, engaged with the spring base 25. Both the drive tube and the spring base can be provided with snap protrusions as described in one embodiment.

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

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

[0086] The inner 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 component that is fixed to the housing component 10, for example, by gluing or welding, during the assembly of the injection device. The nut member 11 is provided with an internal thread 12 on its inner surface that engages with the 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 FIGS. 12 to 17A and 17B, in a further embodiment, as described, it is possible to utilize the nut member 11 to eliminate the air gap during the assembly of the injection device.

[0088] The longitudinal track structure 62 on the piston rod 60 is engaged by the inwardly pointed protrusions 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 helically in the distal direction within the internal thread 12 of the nut member 11. The inwardly pointed protrusions 75 disclosed in FIGS. 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, and thus 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 the drive tube 70 at its distal end and the spring base 25 at its proximal end. The torsion spring 65 is in a tensioned state during the manufacture of the injection device, i.e., during assembly of the injection device, so that when the injection device is delivered to the user, a relatively high torque is stored in the torsion spring 65. The torque stored in the unused delivery state of the injection device is preferably sufficient to expel the entire initial content volume of the cartridge 5, which means that the torque is sufficient to drive the piston rod 60 and thus the plunger 7 towards or near the distal end of the cartridge 5. In a preferred embodiment, such a multi - use fixed - dose injection device will have a torsion spring 65, which is in a tensioned state and is ready to expel approximately two to eight predetermined and equally sized dose volumes, so that the user does not need to tension the torsion spring 65 between each of these two to eight injections.

[0090] The drive tube 70 disclosed in FIGS. 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 of a sleeve that decreases gradually and circumferentially apart. The first helical shape 71 extends axially and terminates within the first axially driving flange 72.

[0091] Furthermore, the most distal part of the drive tube 70 has an outer surface that is radially offset with respect to the rest of the drive tube 70. This radial indentation on the outer surface of the drive tube 70 defines a second axially driving flange 78 that is parallel to the first axially driving flange 72 but is 180° offset in the rotational direction, as best seen in FIG. 6A. These two axially driving flanges 72, 78 define the stopping points of the rotation of the drive tube 70 as described.

[0092] Until it connects to the second axially driven flange 78, the radial indentation has a helical structure that forms a helical surface that abuts against a similar helical surface provided inside the housing structure. This helical surface has the same configuration as the housing helix 16, but is longitudinally offset in the proximal direction as best seen in FIG. 17B. The joining surface between these two surfaces has the same effect as the joining surface between the first helical shape 71 and the housing helix 16. By having two such helical joining surfaces, the operation of the injection device is more stable.

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

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

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

[0096] The first helical shape 71 at the distal end of the drive tube 70 extends axially and engages a similar helical shape 16 (see, e.g., FIG. 10) provided within a bridge structure 15 inside a housing part 10 of a 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 tapers circumferentially away and terminates within a first axial housing flange 17 that can engage a first axial drive flange 72 of the drive tube 70.

[0097] FIG. 9 discloses the interface between the drive tube 70 and the bridge structure 15 located inside the housing part 10. That is, the housing part 10 is visually cut away. FIG. 10 discloses the interface between the drive tube 70 and the housing structure including the bridge structure 15. In the view of FIG. 10, it is the housing structure, rather than the drive tube 70, that is cut radially along line “A” of FIG. 5A and viewed from the distal position. Thus, the cut is made through the first axial housing flange 17. The housing part 10 is further visually cut open in a longitudinal plane along the centerline “X”.

[0098] The internal bridge structure 15 is provided with a further second axial housing flange 18 as seen in FIGS. 9 and 17B, and the second axial housing flange 18 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 of the second axial drive flange 78 and the second axial housing flange 18 in addition to the abutment of the first axial drive flange 72 and the first axial housing flange 17, as best seen in FIGS. 9 and 10. All four flanges 72, 17; 78, 18 are preferably parallel to each other and to the longitudinal central axis “X” of the injection device. Further, as will be explained, the axial lengths (the “dl” shown in FIGS. 6A and 6B) of these four flanges 72, 17; 78, 18 are the same.

[0099] Since the torsion spring 65 constantly applies a torsional force to the drive tube 70, the drive tube 70 will rotate in the counterclockwise direction (in the embodiment) when viewed from the distal end of the injection device. However, the engagement between the first axially driven flange 72 and the first axially housing flange 17, and the engagement between the second axially driven flange 78 and the second axially 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 the tooting 26 inside the spring base 25, so that the drive tube 70 rotates in only one direction, which is the counterclockwise direction when viewing the injection device from the distal position in the disclosed embodiment. This will be described, for example, in FIG. 5B.

[0101] The telescopically movable shield 40 is rotatable relative to the housing structure and can rotate between a locked position and an unlocked position. As shown in FIG. 1, the telescopically movable shield 40 is provided with a spiral structure 41 that terminates within the radial ends 44a, b on its outer surface, and the radial ends 44a, b are positioned at an angular distance from each other such that these radial ends 44a, b together define an axial opening. On the inner surface of the housing part 10, inwardly pointed protrusions are provided, and the inwardly pointed protrusions can slide through the axial opening of the spiral structure 41 when the telescopically movable shield 40 rotates to the unlocked position. At any other position, this inwardly pointed protrusion will contact the spiral structure 41 when attempting to move the telescopically movable shield 40 in the proximal direction in a translational direction, which will hereafter define the locked position.

[0102] Due to the spiral structure 41, the needle shield 40 is forced to move spirally when rotating. Therefore, when the needle shield 40 is unlocked, 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.

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

[0104] The housing part 10 is provided with a pair of longitudinal windows 13. These longitudinal windows 13 are aligned with similar windows 23 provided in the cartridge holder 20 so that the user can visually inspect the content volume of the cartridge 5. The telescopically movable shield 40 radially sandwiched between the housing part 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 content volume of the cartridge 5 only when the telescopically movable shield 40 rotates to the unlocked position of the shield 40. When the telescopically movable shield 40 is in the locked position, the solid part of the telescopically movable shield 40 prevents the user from visually seeing the cartridge 5. Therefore, this rotation of the set of windows 49 in the telescopically movable 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 part 10 can be provided with a scale indicating a plurality of doses of the injection device. In the embodiments of FIGS. 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 thereafter see how many doses have been taken and how many remain in the cartridge 5.

[0106] The telescopically movable shield 40 also releases the torque stored in the torsion spring 65 when moved translationally in the proximal direction, thereby being used to discharge a predetermined dose volume. During injection, the user presses the shield tip 55 and thereafter the telescopically movable shield 40 against the skin, whereby the telescopically movable shield 40 moves in the proximal direction.

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

[0108] One of the two inwardly pointed protrusions 81, 82 (shown as "81") cannot be directly seen in the enclosed figure but is shown by a puncture line in FIG. 7B. The two protrusions 81, 82 are offset 180° from each other in the disclosed embodiment.

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

[0110] The hooks 83 on the connector element 80 are provided distally on a pair of axially extending parts 84. These axially extending parts 84 allow the connector part 80 to surround the bridge part 15 of the housing part 10 and operate through the axial opening between the radial bearings 19 in the connection between the bridge part 15 and the housing part 10, as best seen in FIGS. 2A, 5A, and 17A.

[0111] Spring Attachment As disclosed in FIGS. 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 FIGS. 11A - 11C, the torsion spring 65 is provided with a hook 67 at the end of the torsion spring 65. To illustrate the spring attachment, FIGS. 11A - 11C show only the proximal end of the torsion spring 65 and also only a part of an alternative spring base 25. FIGS. 11A - 11C disclose only one end of the torsion spring 65, but it is clear that both ends are provided with such hooks 67 and can be attached in the same way.

[0113] To attach the torsion spring 65, first pass one hook 67, for example, through the axial passage 26 in the spring base 25 in a translational direction. This translational movement is indicated by the arrow "A" in FIG. 11A, indicating that the movement between the spring base 25 and the torsion spring 65 is relative movement, i.e., one or both of the elements can move in the translational direction.

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

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

[0116] When the torsion spring 65 and the spring base 25 rotate relative to each other, the hook 67 of the torsion spring 65 passes over this radial snap protrusion 28 and is thus irreversibly locked to the spring base 25 as shown in FIG. 11C.

[0117] The radial snap protrusion 28 has two sides provided in the rotational direction. The side that first encounters the hook 67 during rotation has an inclined surface 29a to make it easier for the hook 67 of the torsion spring 65 to slide over the radial snap protrusion 28. The side opposite to the snap protrusion 28 is preferably provided with a steep surface 29b to prevent the hook 67 of the torsion spring 65 from rotating in the opposite direction after being 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 protrusion 28 without being pushed forward by an assembly tool. In such an embodiment, it is not sufficient to simply rotate the spring base 25 and the torsion spring 65 relative to each other. This is particularly the case when the torsion spring 65 has an open winding such that it cannot transmit sufficient torque to the proximal end that carries the hook 67 when rotating the torsion spring 65. In such a case, 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 protrusion.

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

[0120] The radial snap projection 28 is disclosed in relation to the spring base 25, but such a radial snap projection 28 can also be provided on the fixed drive tube 70 so as to secure the other end of the torsion spring 65. Hereinafter, the snap projection 28 can be provided on either the spring base 25, the drive tube 70, or 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 movement and, for example, by 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 becoming separated from either the spring base 25 or the drive tube 70.

[0122] At a later stage during the assembly process, the torsion spring 65 can also be attached to other parts of the spring base 25 or 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. When this pre-assembled unit is positioned inside the housing part 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 part 10 by engaging with a pair of flexible connecting arms 9 (most clearly seen in FIGS. 15 and 16) provided on the housing part 10. In one embodiment, the radial snap protrusion 28 is provided only on the drive tube 70 and not on the spring base 25.

[0124] Injection When the telescopically movable shield 40 rotates to the unlocked position, the user presses the distal shield tip 55 of the telescopically movable shield 40 against the skin, whereby a predetermined dose volume is discharged as the telescopically movable shield 40 moves translationally in the proximal direction. This translational movement is transmitted to a similar translational movement of the connector element 80.

[0125] The connector element 80, depicted in more detail in FIGS. 7A and 7B, is guided translationally relative to the housing part 10 during dosing, and the two inwardly pointed protrusions 81, 82 abut against the outwardly pointed protrusions 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 be moved 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 in the distal direction.

[0126] The translational movement of the drive tube 70 in the proximal direction slides the first axial drive flange 72 and the second axial drive flange 78 on the drive tube 70 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 protrusion 75 on the drive tube 70 slides a certain axial distance within the longitudinal track structure 62 on the piston rod 60.

[0127] Thereafter, the size of the predetermined dose volume prepared by this translational movement of the drive tube 70 correlates with the longitudinal distance that the drive tube 70 moves, that is, the axial length of the engagement between the first axial drive flange 72 and the first axial housing flange 17, and the axial length of the engagement between the second axial drive flange 78 and the second axial housing flange 18, as well as the pitch of the screw connections 12, 61 between the piston rod 60 and the nut member 11. The translational distance that the drive tube 70 moves when a predetermined dose volume is prepared is called "dl" (operating distance).

[0128] When the first axial drive flange 72 and the second axial drive flange 78 disengage from the engagement with the first axial housing flange 17 and the second axial housing flange 18 and move in the translational direction, the drive tube 70 will be forced to rotate by the torque stored in the torsion spring 65. Therefore, the spiral shape 71 on the drive tube 70 rotates downward below the housing spiral shape 16 inside the housing component 10 until the first axial drive flange 72 and the second axial drive flange 78 contact the first axial housing flange 17 and the second axial housing flange 18 again. The spiral movement can be supported by an additional spiral joint surface as described above. In the disclosed embodiment, this rotation is 360°. That is, every time the drive tube 70 translates a distance of "dl" in the proximal direction, it rotates one full revolution. Thereafter, the piston rod 60 also rotates 360° and thus moves to the distal direction 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] Thus, each of the predetermined dose volumes is prepared when the drive sleeve 70 is translated in the proximal direction by the operating distance "dl", and is discharged when the drive sleeve 70 is rotated in the distal direction and returned to the initial position.

[0130] The shield spring 90 in the form of a helical 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 translates proximally during dose preparation. By compressing the shield spring 90, the connector element 80 is biased in the distal direction.

[0131] As also seen in FIGS. 6A and 6B, the drive tube 70 is provided with a helical flange 76 on its outer surface, and the helical flange 76 engages with inwardly pointed protrusions 81, 82 inside the connector element 80 when the torsion spring 65 begins to rotate the drive tube 70. This engagement between the inwardly pointed protrusions 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" (FIGS. 6A and 6B), through which the inwardly pointed protrusions 81, 82 inside the connector element 80 can slide in the translational direction when the openings "d" are aligned with the inwardly pointed protrusions 81, 82 in the rotational direction. 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 abut again against the first axial housing flange 17 and the second axial housing flange 18 inside the housing part 10, which is when a predetermined dose volume has been discharged. Thus, the shield spring 90 will push the connector element 80 and the telescopically movable shield 40 in the distal direction when a predetermined dose size has been discharged, i.e., after the drive tube 70 has rotated 360° (in this embodiment) and reached the initial position.

[0133] Also, in this state, the inwardly pointed protrusions 81, 82 will align with the outwardly pointed protrusions 73, 74, and thus, the subsequent next dose volume can be released by repeating the procedure described herein.

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

[0135] During the movement of the telescopically movable shield 40 in the distal direction, the spiral structure 41 on the telescopically movable shield 40 abuts against a similar spiral path 33 provided inside the housing structure and preferably on the inner surface of the shield guide 30, thereby forcibly rotating the telescopically movable shield 40 to the locking position when the telescopically movable shield 40 moves back to the initial position.

[0136] End of content volume Accordingly, a predetermined dose volume is prepared by pressing the telescopically movable shield 40 against the user's skin and moving the drive tube 70 in the proximal direction. When the drive tube 70 moves a working distance "dl" in the proximal direction, the first spiral shape 71 on the drive tube 70 reaches the 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 spirally in the distal direction 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 protrusion 75 inside the drive tube 70. Since the piston rod 60 is screwed into the nut member 11 fixed in the housing structure (61, 12), the piston rod 60 moves spirally in the distal direction during rotation.

[0137] Each time the drive tube 70 moves proximally by the operating distance “dl” and is released, the piston rod 60 is forced to rotate, in this embodiment, 360°, i.e., one complete revolution, and thus moves forward by the axial distance determined by the pitch of the screw between the piston rod 60 and the nut member 11. When the remaining distance between the inwardly pointed protrusion 75 on the drive tube 70 and the stop surface 63 on the piston rod 60 becomes less than the length “dl” of the axial flanges 72, 78, 17, 18, it is impossible to move the drive tube 70 to the release position and release a further fixed dose.

[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 FIG. 3. However, for each discharge of a predetermined dose size, the piston rod 60 moves distally until the stop surface 63 on the piston rod 60 reaches a position where it cannot move the drive tube 70 proximally by the full operating distance “dl”. When this occurs, it is impossible to move the drive tube 70 to the release position and thus impossible to select a further predetermined dose size, thereby preventing the user from discharging a further predetermined dose.

[0139] In other words, if the remaining portion of the free length “L” of the track structure 62 of the piston rod 60 is shorter than the operating distance “dl”, it is impossible to move the axial drive flanges 72, 78 out of engagement with the axial housing flanges 17, 18 and thus impossible to release a further fixed dose volume.

[0140] Finally, each time the user prepares one of the predetermined dose volumes, the drive tube 70 moves translationally in the proximal direction by an operating distance “dl”, and rotates back to its initial position when the prepared predetermined dose volume is discharged. In this rotational movement, the drive tube 70 preferably rotates approximately 360°. If the time accumulated while the drive tube 70 moves by the operating distance “dl” and the distance accumulated while the piston rod 60 moves in the distal direction remain smaller than the length “dl” of the free length “L” of the available track structure 62 of the piston rod 60, the stop surface 63 on the piston rod 60 prevents the dose tube 70 from moving in the proximal direction by the full fixed dose setting (i.e., the full operating distance “dl”), and thus prevents the user from selecting the full predetermined dios size.

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

[0142] Example of end of content volume In one example, 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 protrusion 75 of the drive tube 70 with the piston rod 60 and the stop surface 63 within the piston rod 60 is set to 43 mm at the factory.

[0143] To release one of the fixed doses, the drive tube 70 moves a working distance “dl” in the proximal direction. In the example, “dl” may be 5 mm. When the drive tube 70 moves a working distance “dl” = 5 mm in the proximal direction, the torsion spring 65 causes the drive tube 70 to rotate one full revolution (i.e., 360°) and return to the initial position. During this rotation, the piston rod 60 also rotates compulsorily by the same number of degrees, 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 a given axial distance in the distal direction per full revolution. The pitch may be such that, for example, the distance the piston rod 60 moves is 10 mm per full revolution (360°) of the piston rod 60. This means that when four fixed doses are released (i.e., the drive tube 70 moves four times by the working distance “dl”), the piston rod 60 moves 40 mm in the distal direction, leaving only the 3 mm free length “L” of the track structure 62 before reaching the stop surface 63, and since the drive tube 70 requires an axial movement of “dl” = 5 mm to release a further fixed dose volume, the 3 mm free length “L” of the track structure 62 remains, but it is no longer possible to release a further fixed dose volume.

[0144] Zero point adjustment In one embodiment of the invention, mainly disclosed in FIGS. 12 to 17A and 17B, the nut member 11 may be a separate element fixedly attached to the housing part 10 of the housing structure during the assembly of the injection device. In such an embodiment, the nut member 11 can be fixedly installed within the housing structure without the use of physical attachment means such as gluing or welding. By using a dedicated assembly, in such an embodiment, the nut member 11 can 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 referred to as zero - point adjustment. The zero - point means the point at which the piston rod 60 (or the piston rod foot 85) abuts against the plunger 7 inside the cartridge 5. If such an abutment is achieved during the manufacture of the injection device, the user does not need to perform an initial priming of the injection device before discharging the first dose volume.

[0145] The nut member 11 for this purpose is disclosed in FIGS. 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 protrusions 95 provided on the proximal side of the nut member 11. These two angled thread protrusions 95 together form an external thread on the nut member 11. However, this external thread can be made from either one or more flanges or any number of the external thread protrusions 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 suitable number can be provided.

[0147] The bridge structure 15 inside the housing part 10 that supports the nut member 11, for example, as disclosed in FIG. 16, is provided with an axial tooth part 97 that enables the nut member 11 to rotate only in one direction in this embodiment. The permitted rotation direction is the clockwise direction, which means that the ratchet arm 96 and the tooth part 97 are joined so as to prevent rotation in the counterclockwise direction.

[0148] The bridge structure 15 inside the housing part 10 is further provided with an internal thread 98 having a direction such that when the nut member 11 rotates in the permitted clockwise direction, it is screwed in a spiral shape in the proximal direction.

[0149] During the assembly of the injection device, one important purpose is to eliminate the distance existing between the piston rod 60 and the plunger 7 inside the cartridge 5, the so-called air gap. As disclosed in FIG. 13, when the piston rod foot 85 is attached to the piston rod 60, this purpose 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] When the nut member 11 rotates relative to the housing structure during final assembly, the piston rod 60 advances in the distal direction until the piston rod 60 or the piston rod plunger 85 abuts against the plunger 7 inside the cartridge 5.

[0151] The rotation of the nut member 11 is preferably done by using a special tool in the production line that engages with the nut member 11 and can transmit the 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, which is located within the bridge structure 15 of the housing part 15. Thereafter, an electronically computerized facility is used to detect the position of the plunger 7 within the cartridge 5 used for that particular injection device. When the position of the plunger 7 and the position of the piston rod 60 (or the 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 the piston rod 60 of the particular injection device into contact with the plunger 7 when the injection device is assembled.

[0152] Therefore, the position of the proximal end of the piston rod 60 or the piston rod foot 85 is finely adjusted by rotating the nut member 11 at the one-way joint surface with the bridge structure 15. What is important here is that the nut member 11 can be rotated in the rotational direction that advances the piston rod 60 (or the piston rod foot 85) into contact with the plunger 7.

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

[0154] Thereafter, the engagement between the piston rod 60 and the drive tube 70 prevents the piston rod 60 from rotating in the clockwise direction. Thus, when the nut member 11 is rotated in the clockwise direction, this rotation cannot be followed by the piston rod 60 because the piston rod 60 cannot follow the clockwise rotation of the nut member 11, and is transmitted to the translation of the piston rod 60 in the distal direction.

[0155] When the dose is discharged, the drive tube 70 and the piston rod 60 rotate in the counterclockwise direction. The nut member 11 is prevented from rotating in the counterclockwise direction by the one-way ratchet engagement surfaces 96, 97 between the nut member 11 and the housing part 10 (via the bridge structure 15), so the nut member 11 does not rotate and thus supports the helical movement of the piston rod 60 in the distal direction.

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

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

[0158] The one-way engagement surfaces 96, 97 between the nut member 11 and the housing part 10 prevent the nut member 11 from rotating in the counterclockwise direction (when viewed from the distal position).

[0159] The above results indicate that the nut member 11 self-locks with respect to the housing structure, eliminating the need to physically fix the nut member 11 to the housing structure. Henceforth, as described in the prior art, there is no need to weld or glue the nut member 11 to the housing structure.

[0160] By self-locking, as used herein, it means that the piston rod 60 (or the foot portion 85) abuts against the plunger 7, preventing the nut member 11 from rotating in the clockwise direction, and the one-way ratchet engagement surfaces 96, 97 prevent the nut member 11 from rotating in the counterclockwise direction.

[0161] When the piston rod 60 rotates counterclockwise to discharge the prepared dose volume, the nut member 11 similarly cannot follow this rotation due to the one-way ratchet engagement surfaces 96, 97. When the nut member 11 rotates clockwise to eliminate the air gap during assembly, the piston rod 60 is prevented from following this rotation by its engagement with the drive tube 70 (62, 75) and the engagement between the drive tube 70 and the housing structure (77, 26).

[0162] When the pitch of the first screw connection 61, 12 between the piston rod 60 and the nut member 11 is high, i.e., the piston rod 60 moves a long distance with each rotation, it is advisable to have a second screw connection 95, 98 between the screw protrusion 95 on the nut member 11 and the screw flange 98 inside the housing part 10 so that the nut member 11 can be spirally screwed proximally with respect to the housing structure during the rotation of the nut member 11.

[0163] As best seen in FIG. 17B, the protrusions 95 that form the external threads on the nut member 11 are fixed behind the screw flange 98 inside the bridge structure 15 of the housing part 10 so as to move proximally when the nut member 11 rotates relative to the housing structure. Further, FIG. 16 depicts that the screw flange 98 has an axial opening inside the bridge structure 15, and due to the axial opening, the screw protrusions 95 on the nut member 11 can engage proximally behind the screw flange 98.

[0164] This means that when the nut member 11 rotates in the clockwise direction, the nut member 11 moves proximally while moving the piston rod 60 in the distal direction. Therefore, the pitch of the second screw connection 95, 98 between the nut member 11 and the housing structure needs to be subtracted from the pitch of the first screw connection 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 of the zero - point adjustment makes the fine - tuning of the process of eliminating the air gap easier. Therefore, it is beneficial to have a second screw connection 95, 98 between the nut member 11 and the housing part 10 when operating with a piston rod 60 having a high pitch, which requires discharging a relatively large volume each time the piston rod 60 rotates.

[0166] When the pitch of the first screw connection 61, 12 between the piston rod 60 and the nut member 11 is low, the second screw connection 95, 98 is not considered necessary, and thus, 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 member for zero point adjustment is disclosed in FIGS. 18A - 19B. This alternative nut member is assigned the reference number 111, and various elements added in this embodiment are prefixed with "1". The remaining components of this embodiment are numbered with the same numbers as those used in the previous embodiment.

[0168] 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] The axial opening within the bridge structure 15 of the housing structure that guides nut element 111 is provided, in this embodiment, with at least one, preferably two, axially extending grooves 115 that guide elastic arms 113 in the translational direction. Henceforth, the engagement between groove 115 and flexible arm 113 ensures that nut element 111 can only slide in the translational direction, i.e., without rotating relative to the housing structure.

[0170] Groove 115 is provided with an inclined bottom surface 116 (see FIG. 18B) that slopes radially outward in the distal direction. This has the effect that when elastic arm 113 is moved in the proximal direction, it is exposed to an increasing radial force and, therefore, when nut element 111 moves further proximally, it is urged distally with an increasing force.

[0171] As seen in the figures, flexible arm 113 is preferably inclined radially, and thus, flexible arm 113 follows an angle with respect to the central axis corresponding to the angle of inclined bottom 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 such that the nut element 111 is screwed onto the piston rod 60. Thereafter, the pre-assembled piston rod 60 and nut element 111 are placed inside the opening within the bridge structure 15 as disclosed in FIG. 18A.

[0173] When the injection device is fully assembled, the piston rod 60 can directly abut against the plunger 7 inside the cartridge 5, or the piston rod foot 85 can be provided between the piston rod 60 and the plunger 5 such that there is an abutment between the piston rod foot 85 and the plunger 7 as disclosed in FIG. 18C.

[0174] In one embodiment, this piston rod foot 85 can be connected to the piston rod 60 either simultaneously before the piston rod 60 is pre-assembled with the nut element 111, or after the piston rod 60 is pre-assembled with the nut element 111 as shown in FIG. 18B.

[0175] In one embodiment, the piston rod foot 85 can be click-fitted to the piston rod 60 with a bearing-like connection such 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 can be connected to the piston rod 60 in a rotational direction and rotated together with the piston rod 60.

[0176] In the latter embodiment, the piston rod foot 85 can house an electronic sensor that can register the number of rotations of the piston rod 60 with respect to the cartridge 5 and, subsequently, the housing structure in order to determine the volume expelled.

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

[0178] In the final step of assembly, the cartridge 5 is placed inside the cartridge holder 20, and the cartridge holder 20 moves proximally together with the cartridge 5, so that the plunger 7 inside the cartridge 5 contacts the piston rod 60 (or the foot portion 85), and the cartridge holder 20 is snap-fitted to the housing part 10 of the housing structure.

[0179] Accordingly, the plunger 7 inside the cartridge 5 abuts against the piston rod 60 (or the foot portion 85), thereby forcing the nut element 111 to slide in the 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 in the distal direction, so that the contact between the plunger 7 and the piston rod 60 (or the foot portion 85) is maintained. Each time contact is obtained and maintained between the plunger 7 and the piston rod 60 (or the foot portion 85), a laser beam (indicated by "L" in FIG. 18C) is directed onto the outer surface of the bridge structure 15 through an opening 14 within the housing structure. As disclosed in FIG. 18C, two or more such openings 14 may be present as required.

[0180] The bridge structure 15 is preferably formed from a polymer that is more transmissive to laser light than the polymer in which the flexible arm 113 of the nut element 111 is 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 arm 113, i.e., on the inner surface of the bridge structure 15.

[0181] Accordingly, 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 the nut element 111 is slightly moved proximally by a collision with the plunger 7 in the cartridge 5. During this axial movement in the proximal direction, due to the elasticity of the nut element 111, the nut element 111 rebounds distally, thereby maintaining physical contact with the plunger 7.

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

[0183] In this second state, the nut element 111 is axially fixed to the housing structure, and then the piston rod 60 moves spirally 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 alternatively 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 a telescopic element 100 is disposed between the piston rod foot portion 85 and the piston rod 60.

[0186] An alternative piston rod 60 is disclosed in Figure 20 and is provided with two hooks 105 on the distal side that can grip around the telescopic element 100. Only two such hooks 105 are disclosed, but any number of hooks 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 is engaged by a drive element 70.

[0188] The telescopic element 100, shown in more detail by FIG. 21, is provided with a circular rib 101 on the distal side, and behind the circular rib 101, a click arm 86 provided on the piston rod foot 85 engages such that the telescopic element 100 can be axially fixed to the piston rod foot 85. By this click-fit connection, the piston rod foot 85 can rotate relative to the telescopic element 100.

[0189] The telescopic element 100 is further provided with several outwardly pointed surfaces 102 against which the hook 105 can abut, as disclosed in FIGS. 22A and 22B. Thereafter, the hook 105 is suitable for sliding on these outwardly pointed surfaces 102 such that the telescopic element 100 can slide relative to the piston rod 60.

[0190] For this purpose, the telescopic element 100 is slidably disposed within the axial opening 106 of the piston rod 60 such that the piston rod foot 85, together with the telescopic element 100, can slide axially relative to the piston rod 60.

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

[0192] The telescopic element 100 preferably has a square shape with four outer surfaces 102, and the axial opening 106 also preferably has a square shape such that the telescopic element 100 can only translate relative to the piston rod 60 in the first state.

[0193] Although several preferred embodiments have been shown above, it is 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

Claim 1 A pre-filled injection device for delivering a liquid formulation, comprising a housing structure in which a cartridge (5) having a movable plunger (7) extending along a longitudinal axis (X) defining distal and proximal directions is permanently embedded; piston rod means (60, 85) for advancing the movable plunger (7) during dispensing, said piston rod means (60, 85) comprising a piston rod (60) and a piston rod foot (85), said piston rod (60) having an external thread (61) and a longitudinal track structure (62); a rotatable drive element (70) engaging with the longitudinal track structure (62) of the piston rod means (60, 85) such that rotation of the drive element (70) is transmitted to rotation of the piston rod (60); a nut element (111) having an internal thread (112) engaging with the external thread (61) of the piston rod means (60, 85); wherein the nut element (111) operates in two different states: - a first state in which the nut element (111) is axially slidable relative to the housing structure; and - a second state in which the piston rod foot (85) abuts against the movable plunger (7) and the nut element (111) is permanently fixed to the housing structure; wherein, in the first state, the nut element (111) engages with the housing structure via an elastic joint surface (113, 116) having several flexible arms (113) with radial elasticity and operable between the nut element (111) and the housing structure and biasing the nut element (111) axially relative to the housing structure, whereby the piston rod means (60, 85) abuts against the movable plunger (7); and wherein, in the second state, the nut element (111) is permanently fixed to the housing structure, whereby the piston rod means (60, 85) moves helically relative to the nut element (111) and the housing structure during rotation. A pre-filled injection device as claimed in claim 1. Claim 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 abuts against 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 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, the method comprising: - a step of thread-engaging the nut element (111) and the piston rod means (60, 85) by rotating the nut element (111) and the piston rod means (60, 85) relative to each other; - a step of translating the nut element (111) together with the piston rod means (60, 85) relative to the housing structure; - a step of inserting at least the proximal part 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) proximally to a position where the plunger (7) inside the cartridge (5) abuts against the piston rod means (60, 85); - a 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 the at least one flexible arm (113) of the nut element (111) is welded to the housing structure at the position where the plunger (7) inside the cartridge (5) abuts against the piston rod means (60, 85).

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