A Torsion Spring Driven Injection Device

The invention relates to a torsion spring driven injection device for apportioning individually set doses of a liquid drug. The injection device has a needle cannula (35) for multiple uses and a cleaning chamber (56) for cleaning the tip of the needle cannula between subsequent injections. The cleaning chamber is filled with preservative containing liquid drug directly from the cartridge (30) in a filling sequence which is executed when the user initiates first use of the injection device. The sequence comprises the step of securing the piston rod guide in an inrotatable position and thereafter moving the cartridge in a proximal direction. Such axial movement of the cartridge without a similar movement of the plunger automatically pumps liquid drug from the cartridge and into the cleaning chamber via the lumen of the needle cannula.

THE TECHNICAL FIELD OF THE INVENTION

The invention relates to a medical injection device for injecting a liquid drug and especially to a pre-filled injection device for apportioning a multiple number of doses. The invention especially relates to such pre-filled injection device wherein the same needle cannula is used for a number of injections and wherein the tip of the needle cannula is cleaned between subsequent injections.

DESCRIPTION OF RELATED ART

WO2015/062845 discloses an injection device in which the same needle cannula is used for multiple injections. The needle cannula is covered by a telescopically movable needle shield which also carries a cleaning chamber for cleaning the tip of the needle cannula between subsequent injections. The cleaning solvent inside the cleaning chamber is a quantum of the liquid drug contained in the cartridge of the injection device. The quantum of liquid drug is in one example (FIG. 8-9) transferred from the cartridge to the cleaning chamber by moving the cartridge axially a distance relatively to the plunger of the cartridge. This is done by maintaining the piston rod, the piston rod foot and thus the plunger in a fixed position while moving the cartridge in the proximal direction.

WO2014/060369 discloses an injection device in which the piston rod is able to move in either direction between injections in order to relief any pressure build up inside the cartridge. Such “pressure relief system” usually comprises a piston rod guide which is decoupled from the drive mechanism when an injection is not being performed.

However since the drive system is not locked, it is not possible to build up pressure inside the cartridge to transfer liquid drug to the cleaning chamber as the piston rod guide is decoupled and thus free to rotate.

DESCRIPTION OF THE INVENTION

It is henceforth an object of the present invention to provide an injection device having a pressure relief system which can be disabled to transfer a quantum of liquid drug from the cartridge to the cleaning chamber.

It is further an object of a further invention to provide a mechanism which prevents the user form removing the cap from the injection device and thus perform an injection before the cleaning chamber has actually been correctly filled with liquid drug from the cartridge.

The invention is defined in claim1. Accordingly, in a first aspect the present invention relates to a torsion spring driven injection device for automatically apportioning individually set doses of a liquid drug. The main components of such injection device are:A housing storing a cartridge,A needle cannula,A movable needle shield,A cleaning chamber,A piston rod,A piston rod guide,A drive tube, andA torsion spring.

The housing stores the cartridge containing the liquid drug to be ejected. The cartridge is mounted such that it can slide axially inside the housing,

The needle cannula, which is to be used for multiple injections, is connectable with the interior of the cartridge such that liquid drug can flow through the lumen of the needle cannula and the needle cannula further has a distal tip for penetrating the skin of a user during an injection.

The needle shield which in one preferred example is telescopically slidable or movable covers at least the distal tip of the needle cannula between injections. The movable needle shield further carries a cleaning chamber for cleaning the distal tip of the needle cannula between subsequent injections. The cleaning chamber can either be an integral part of the movable needle shield or coupled to the movable needle shield to form a movable needle shield assembly. The cleaning chamber is preferably filled with liquid drug from the cartridge.

Since the liquid drug contains a preservative, this preservative cleans the tip of the needle cannula between injections.

The piston rod has an outer surface with a thread and a not-circular cross-section. The not-circular cross section can be formed in many different ways, e.g. as a track or as a flattened longitudinal surface.

The rotatable piston rod guide either mates with the not-circular cross-section of the piston rod or has an inner thread mating the outer thread of the piston rod.

The drive tube is rotatable by the torsion spring at least during ejection of the dose and the torsion spring is operational provided between the housing and the drive tube to rotate the drive tube during ejection.

The multiple doses to ejected can either be predetermined by the manufacture of the injection device or the doses can be individually set by the user prior to performing the ejection.

The housing, or a housing element, is further operational provided with an internal opening either shaped as a thread mating the outer thread of the piston rod or as a key mating the not-circular cross-section of the piston rod. The piston rod is thus moved forward with or without rotation whenever the piston rod guide and the housing are rotated relatively.

The piston rod guide is axially movable at least between two positions;a first position in which the piston rod guide operates independently of the drive tube e.g. by being decoupled from the drive tube, anda second position in which the piston rod guide operates together with the drive tube e.g. by being coupled to the drive tube.

In the first position, the piston rod guide is operational decoupled from the drive tube such that the piston rod guide is free to rotate should the piston rod move axially. The pressure release mechanism is thus activated and axial movement of the plunger in the cartridge is conveyed to an axial movement of the piston rod and thus to a rotation of the piston rod guide.

In the second position, the pressure release mechanism is disabled by moving the piston rod guide axially into operational engagement with the drive tube which in this position is blocked. The piston rod guide is thus locked by the drive tube and unable to rotate.

Sliding the cartridge in the proximal direction when the piston rod guide is in the second position will thus create a pressure inside the cartridge since the piston rod, the piston rod foot and the plunger does not move axially. This pressure will thus force a quantum of the liquid drug contained inside the cartridge to flow through the lumen of the needle cannula and into the cleaning chamber.

Further, if the drive tube is released in the second position, the torsion spring will force the drive tube and the piston rod guide to rotate thus moving the piston rod forward toward the distal end of the cartridge.

The injection device is preferably a pre-filled injection device. Pre-filled injection devices are also often referred to as disposable injection device and means that the injection device is pre-filled with a specific amount of liquid drug. Once the liquid drug contained in the injection device has been used, the user discharges the entire injection device.

The pre-filled amount of liquid drug is usually contained in a cartridge which is permanently and non-removable embedded in the housing of the injection device such that both the housing and the cartridge are discarded together when the pre-filled injection device is disposed of.

In order to move the piston rod guide in the proximally direction from the first position to the second position, a release element is provided which release element preferably is operational by the movable needle shield, such that manipulation of the movable needle shield moves the release element proximally

The release element is preferably activated by a user during initiation of the injection device such that the piston rod guide is moved from the first position and into the second position in which the pressure release mechanism is disabled as the user makes the injection device ready for first use.

The piston rod guide is further moved in the distal direction from the second position to the first position by a resilient element.

Further, the release element is axially guided in the housing and connected to the movable needle shield by a thread. The release element is thus restricted to purely axial movement whereas the movable needle shield can be rotated preferably by the user. The movement here indicated shall be seen as being relatively to the housing.

As the movable needle shield is rotated it moves helically due to the threaded engagement with the release element which during initiation is temporarily locked to the housing.

In a further embodiment, the needle hub carrying the needle cannula is guided by the movable needle shield to move with the movable needle shield as the movable needle shield rotates. The needle hub is further guided helically such that the needle hub applies an axial pressure on the cartridge during its helical movement.

The pressure is preferably applied by having a tube-like structure on the needle hub in abutment with the distal end of the cartridge which is thereby pushed proximally as the needle hub is guided proximally.

The hub is preferably guided by an engagement with a helical track or the like such that the needle hub moves helically when pushed axially.

This axial pressure further moves the cartridge in the proximal direction and since the pressure relief mechanism is disabled thus preventing the piston rod guide from rotating, liquid drug will flow through the lumen of the needle cannula and into the cleaning chamber.

In a further aspect of the invention a mechanical user guiding mechanism is provided to guide the user correctly through a number of user steps required to transfer liquid drug from the cartridge and into the cleaning chamber. More specifically, the guiding mechanism comprises means preventing the user for removing the protective cap before a certain action has been done.

In one embodiment, the injection device comprises:

a housing having a first part and a removable cap at least partly covering the first part and removable in an axial direction of the injection device. Such cap is often referred to as a protective cap as it protects the distal end of the injection device.

The protective cap is internally provided with a first track extending substantially perpendicular to the axial direction, and the first part of the housing carries an outwardly pointing protrusion engaging the first track to prevent axial removal of the cap.

The outwardly pointing protrusion is however provided on a flexible arm which is able to bend, and a second part or element is provided adjacent the first part. Further, the second element is provided with a surface positioned radially to the flexible arm and which surface has at least to different levels;

a first level preventing radial movement of the flexible arm, and a second level allowing radial movement of the flexible arm. Further, means are provided to shift the two levels into position adjacent the flexible arm.

When the first level of the surface is placed radially to the flexible arm radial movement of the flexible arm is thus prevented and the outwardly poiting protrusion remains inside the first track thus preventing axial movement of the protective cap. However, when the second level is moved into position underneath the flexible arm, the arm is allowed to flex in the radial direction and so are the outwardly pointing protrusion such that the protective cap can be removed.

The second level is preferably a deepened surface area which lies lower than the first level such that the flexible arm is allowed to flex radially when the deepened area underlies the flexible arm which then is allowed to bend inwardly towards a centre line of the injection device. The protective cap is thus only able to slide off the injection device when the deepened area is located beneath the flexible arm.

In a pen-shaped injection device, the first track in the cap in which the outwardly pointing protrusion is axially blocked is preferably formed as a circumferentially track on an inside of the protective cap.

In a preferred example of this invention, the first part is hollow and the second element is rotatable contained at least partly within the first part. The first part being the housing and the second part e.g. being a rotatable movable needle shield. The deepened surface area of the second part can thus be brought into the radial proximity of the flexible arm carrying the outwardly protrusion by rotating the second part and the first hollow part relatively to each other.

Definitions

An “injection pen” is typically an injection apparatus having an oblong or elongated shape somewhat like a pen for writing. Although such pens usually have a tubular cross-section, they could easily have a different cross-section such as triangular, rectangular or square or any variation around these geometries.

The term “Needle Cannula” is used to describe the actual conduit performing the penetration of the skin during injection. A needle cannula is usually made from a metallic material such as e.g. stainless steel and connected to a needle hub to form a complete injection needle all though the needle cannula could also be connected directly to the housing structure without a hub. A needle cannula could however also be made from a polymeric material or a glass material.

As used herein, the term “drug” is meant to encompass any drug-containing flowable medicine capable of being passed through a delivery means such as a hollow needle in a controlled manner, such as a liquid, solution, gel or fine suspension. Representative drugs includes pharmaceuticals such as peptides, proteins (e.g. insulin, insulin analogues and C-peptide), and hormones, biologically derived or active agents, hormonal and gene based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form.

“Cartridge” is the term used to describe the container actually containing the drug. Cartridges are usually made from glass but could also be moulded from any suitable polymer. A cartridge or ampoule is preferably sealed at one end by a pierceable membrane referred to as the “septum” which can be pierced e.g. by the non-patient end of a needle cannula. Such septum is usually self-sealing which means that the opening created during penetration seals automatically by the inherent resiliency once the needle cannula is removed from the septum. The opposite end is typically closed by a plunger or piston made from rubber or a suitable polymer. The plunger or piston can be slidable moved inside the cartridge. The space between the pierceable membrane and the movable plunger holds the drug which is pressed out as the plunger decreased the volume of the space holding the drug. However, any kind of container—rigid or flexible—can be used to contain the drug.

“Cleaning chamber” is in the present description broadly meant to be any kind of reservoir containing a cleaning solvent to clean at least the distal tip of the needle cannula between subsequent injections. Such cleaning chamber is preferably both distally and proximally sealed by a pierceable septum. However, the proximal septum could be replaced by any kind of sealing which would seal against the outer surface of the needle cannula. The distal septum and the proximal septum or seal of the cleaning chamber defines a confinement containing the cleaning solvent which cleaning solvent in a preferred embodiment is identical to the preservatives contained in the liquid drug used in the specific injection device. In a most preferred solution, the same preservative containing liquid drug is present in both the cleaning chamber and in the cartridge of the injection device thereby avoiding contamination of the preservative containing drug inside the cartridge.

Since a cartridge usually has a narrower distal neck portion into which the plunger cannot be moved not all of the liquid drug contained inside the cartridge can actually be expelled. The term “initial quantum” or “substantially used” therefore refers to the injectable content contained in the cartridge and thus not necessarily to the entire content.

By the term “Pre-filled” injection device is meant an injection device in which the cartridge containing the liquid drug is permanently embedded in the injection device such that it cannot be removed without permanent destruction of the injection device. Once the pre-filled amount of liquid drug in the cartridge is used, the user normally discards the entire injection device. This is in opposition to a “Durable” injection device in which the user can himself change the cartridge containing the liquid drug whenever it is empty. Pre-filled injection devices are usually sold in packages containing more than one injection device whereas durable injection devices are usually sold one at a time. When using pre-filled injection devices an average user might require as many as 50 to 100 injection devices per year whereas when using durable injection devices one single injection device could last for several years, however, the average user would require 50 to 100 new cartridges per year.

“Scale drum” is meant to be a cylinder shaped element carrying indicia indicating the size of the selected dose to the user of the injection pen. The cylinder shaped element making up the scale drum can be either solid or hollow. “Indicia” is meant to incorporate any kind of printing or otherwise provided symbols e.g. engraved or adhered symbols. These symbols are preferably, but not exclusively, Arabian numbers from “0” to “9”. In a traditional injection pen configuration the indicia is viewable through a window provided in the housing.

Using the term “Automatic” in conjunction with injection device means that, the injection device is able to perform the injection without the user of the injection device delivering the force needed to expel the drug during dosing. The force is typically delivered—automatically—by an electric motor or by a spring drive. The spring for the spring drive is usually strained by the user during dose setting, however, such springs are usually prestrained in order to avoid problems of delivering very small doses. Alternatively, the spring can be fully preloaded by the manufacturer with a preload sufficient to empty the entire drug cartridge though a number of doses. Typically, the user activates a latch mechanism e.g. in the form of a button on, e.g. on the proximal end, of the injection device to release—fully or partially—the force accumulated in the spring when carrying out the injection.

The term “Permanently connected” as used in this description is intended to mean that the parts, which in this application is embodied as a cartridge and a needle assembly, requires the use of tools in order to be separated and should the parts be separated it would permanently damage at least one of the parts.

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

All headings and sub-headings are used herein for convenience only and should not be constructed as limiting the invention in any way.

The use of any and all examples, or exemplary language (e.g. such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.

The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

DETAILED DESCRIPTION OF EMBODIMENT

When in the following terms as “upper” and “lower”, “right” and “left”, “horizontal” and “vertical”, “clockwise” and “counter clockwise” or similar relative expressions are used, these only refer to the appended figures and not to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as there relative dimensions are intended to serve illustrative purposes only.

In that context it may be convenient to define that the term “distal end” in the appended figures is meant to refer to the end of the injection device which usually carries the injection needle whereas the term “proximal end” is meant to refer to the opposite end pointing away from the injection needle and usually carrying the dose dial button.

Distal and proximal are meant to be along an axial orientation extending along the longitudinal axis “X” of the injection device and is further indicated in the figures.

FIGS. 1 to 4discloses the injection device according a first embodiment.

Proximally the injection device1is provided with a dose setting button5rotatable by a user to set a dose to be ejected. The dose setting button5is axially secured to the housing10such that the dose setting button5does not translate axially when rotated in either direction. The dose set by this rotation is visually shown on a scale drum65appearing in a dose window2provided in the housing10.

The distal end of the injection device1is inFIGS. 1 to 3covered by a removable protective cap75which can be manipulated by a user as will be explained.

FIG. 4depicts the injection device1with the protective cap75removed. Distally a telescopically movable movable needle shield20covers the needle cannula35. Further inFIG. 4, the protective cap75when mounted covers a longitudinal window11in the housing10, through which longitudinal window11, the user is able to visually inspect the drug contained in a cartridge30carried in the injection device1.

The movable movable needle shield20is able to move telescopically and the distal end has an opening21through which the needle cannula35protrudes and is further provided with longitudinal tracks22which are engaged by gripping means provided internally in the protective cap75.

The housing10is divided into a number of housing parts10A,10B,10C,10D which are click-fitted together to form one housing10. In the embodiment disclosed inFIG. 1, four such housings parts10A,10B,10C,10D are shown. A distal housing part10A, a proximal housing part10D, a first intermediate housing part10B and a second intermediate housing part10C. Some of the housing parts10A,10B,10C,10D or all the parts could alternatively be moulded to form one or more unitary parts.

The second intermediate housing part10C is internally provided with a thread12as best seen inFIG. 6Bwhich depicts the injection device1as delivered to the user. An exploded view of the injection device1is disclosed inFIG. 5. The main components which are also identified onFIG. 6Aare:Dose setting button:5Housing:10Needle shield:20Cartridge:30Needle cannula:35Needle hub:40Piston rod:45Piston rod foot:50Cleaning capsule:55Piston rod guide:60Scale drum:65Drive tube:70Protective cap:75Ratchet element:80Spring base:85Release element:90Torsion spring:100

The movable needle shield20is distally provided with a cleaning capsule55in which a cleaning chamber56is distally sealed by a distal septum57and proximally by a movable piston58. The interior of the cleaning chamber56is, at least in a situation of use, filled with liquid drug from the cartridge30stored in the first intermediate housing part10B as will be explained.

Further, a needle cannula35is provided. A distal end36of the needle cannula35is maintained inside the cleaning chamber56between injections and a proximal end37projects proximally from a hub40to which the needle cannula35is attached. The needle cannula35is hollow and a longitudinal lumen38connects the distal end36and the proximal end37.

The first intermediate housing part10B supports the cartridge30containing the liquid drug to be injected. The cartridge30is able to slide inside the first intermediate housing part10B as will be explained. The distal end of the cartridge30is sealed by a pierceable septum31and the proximal end is sealed by a movable plunger32. To expel liquid drug from the cartridge30, a piston rod45carrying a piston rod foot50is moved distally inside the cartridge30. The piston rod foot50abuts the plunger32inside the cartridge30thus forcing the plunger32forward such that the volume of the cartridge30containing the liquid drug is reduced and the liquid drug flows out through the lumen38of the needle cannula35.

The piston rod foot50is provided with a spike51which connects the piston rod foot50to the plunger32such that the piston rod foot50and the plunger32move in unison. Proximally, the piston rod foot50is provided with connection means52connecting the piston rod foot50to the piston rod45. The result being that the piston rod45, the piston rod foot50and the plunger32move together in the axial direction

The piston rod45has an outer thread46which engages a corresponding thread12in the second intermediate housing part10C such that whenever the piston rod45is rotated it screws forward or backwards. In order to rotate the piston rod45a piston rod guide60is provided which has an internal key61engaging a longitudinal track47provided in the piston rod45.

To rotate the piston rod guide60a drive assembly is provided. This drive assembly comprises a drive tube70and a torsion spring100which is operable between the drive tube70and a spring base85. The spring base85is firmly attached to the housing10in a non-movable manner, but could alternatively be moulded as an integral part of the housing10. The torsion spring100is distally connected to the drive tube70such that the torsion spring100is strained when the drive tube70is rotated relatively to the housing10and the spring base85.

The drive tube70is rotational connected to a scale drum65by having a protrusion71slidable engaged in a longitudinal track66provided inside the scale drum65. The scale drum65further has a helical outer track67which travels in a corresponding thread inside the housing10such that scale drum65travels helically when rotated by the drive tube70.

In order to strain the torsion spring100, a ratchet element80connects the drive tube70with the dose setting button5. Rotation of the dose setting button5is thus via a gearing wheel6transferred to a rotation of the drive tube70and thus a straining of the torsion spring100. The connection between the dose setting button5and the ratchet element80is provided such that the dose setting button5and the drive tube70can be rotated in both rotational directions.

The dose dial button5is connected to the ratchet element80via a ratchet mechanism as described in WO 2013/178372 which allows the dose setting button5to be rotated in both directions while the ratchet mechanism holds the torque of the torsion spring100until the set torque is released. The ratchet mechanism essentially comprises ratchet arms81operating in a toothed ring86of the spring base85, such that the ratchet element80is held in its position when the torsion spring100is strained. For that purpose, the ratchet element80is distally provided with a plurality of teeth82engaging a toothing provided internally in the drive tube70. Further, the dose setting button5is internally provided with teeth which are able to move the ratchet arms81radially whenever the dose setting button5is rotated in the dose reducing direction. This allows the ratchet element80to move rotational backward in relation to the toothed ring86such that the set dose can be incrementally reduced.

FIG. 6Adiscloses the situation in which the injection device1has not been taken into use.FIG. 6Bis an enlarged picture of a part of the injection device1shown inFIG. 6A. In this situation, the piston rod guide60is decoupled from the drive tube70such that the piston rod guide60is free to rotate. The piston rod guide60rotates freely on a proximal extension of the housing part10C which proximal extension internally carries the thread12for the piston rod45.

Should the liquid drug inside the cartridge30e.g. be exposed to temperature changes, the volume will expand or retract and the plunger32will henceforth move axially. This axial movement of the plunger32is conveyed to the piston rod foot50which moves in unison with the plunger32. Due to the connection, via the connecting means57, between the piston rod foot50and the piston rod45, the piston rod45will also move axially. Since the piston rod45is threadely connected to the thread12of the housing part10C, the piston rod45will rotate as it is moved axially. This rotation of the piston rod45makes the piston rod guide60rotate as the key61provided inside the piston rod guide60engages the longitudinal track47of the piston rod45.

As the piston rod guide60in this situation is not rotational locked it rotates freely as the piston rod45move in either direction. Since the piston rod45and the piston rod foot50are secured to the plunger32, the piston rod45will follow any movement of the plunger32. The pressure inside the cartridge30will therefore automatically adjust to the temperature simply by rotation of the piston rod guide60. This principle is referred to as pressure relief.

To release the torsion spring100to rotate the piston rod guide60and thereby the piston rod45, a release element90is provided. As disclosed inFIG. 10, this release element90has a plurality of release arms91extending in a proximal direction and further a plurality of thread-arms92projecting in the distal direction. These thread-arms92are distally provided with a guiding thread93. At least one of the thread-arms92is divided such that a trigger arm94also pointing in the distal direction is provided. This trigger arm94carries a trigger knob95, the function of which will be explained latter. Further, the trigger-arm94is distally provided with a thread segment96that follows the pitch of the guiding thread93. The release element90is on a sidewall also provided with an outwardly pointing protrusion97, the function of which will be explained latter. The proximal ridge98of the guiding thread93further forms a basis for a compression spring101.

The compression spring101lies between the ridge98of the guiding thread93on the release element90and the first intermediate housing part10B urging the release element90in the distal direction. The compression spring101is slightly pre-tensed such that the guiding element90is constantly urged in the distal direction.

The release element90operates inside the first intermediate housing part10B and the guiding thread93is guided in a longitudinal track13provided in first intermediate housing part10B such that release element90only travels axially. The guiding thread93protrudes through the opening13and is engaged by the internal track25of the movable needle shield20which slides on an outside surface of the first intermediate housing part10B

When the injection device1is delivered to a user, the cap75is pre-mounted, the cleaning chamber56is empty and the proximal end37of the needle cannula35is not inserted into the cartridge30. This is the situation depicted inFIG. 1and inFIG. 6. The user initially has to prepare the injection device accordingly before an injection can be performed. During these preparations, the pierceable septum31of the cartridge30must be penetrated by the proximal end37of the needle cannula45and the cleaning chamber56must be filled with liquid drug from the cartridge30.

When initiating the injection device, the user first moves the protective cap75a distance “Y” in the proximal direction in a purely axial movement as depicted inFIG. 1. This axial movement also move the movable needle shield20in the proximal direction since the distal end of the movable needle shield20abut the interior of the protective cap75.

The movable needle shield20is on the interior surface provided with a longitudinal track23which track23is provided with a radial parking track24(seeFIG. 9). In the initial position of the needle shield30, a protrusion41provided on an outer wall of the hub40is parked in this radial parking track34such that the hub40follows axial movement of the needle shield30.

When delivered to the user as depicted inFIG. 6A-B, the internal thread25of the movable needle shield20is engaged with the distal end of the guide thread93of the thread arms92of the release element90such that the movable needle shield20and the guiding element90move axially together guided by the longitudinal opening13.

When the user initates use of the injection, the user pushes the protective cap75in the proximal direction. This purely axial movement is conveyed to the movable needle shield20which thus also moves axially together with guiding element90. This axial movement further tightens the compression101as disclosed inFIG. 7A.

As the guiding element90is moved axially, the trigger-knob95slides axially along the side of the longitudinal opening13and is caught by the indentation19provided in the side wall of the longitudinal opening13thus temporary securing the guiding element90in this position.

The protective cap75is internally provided with a first track76and a second track77. When the protective cap75is pushed proximally, the first track76engages a first protrusion14provided externally on the first housing part10A and the second track77engages a second protrusion15also provided on the first housing part10A. Both engagements provide tactile information to the user that the protective cap75has reached its correct proximal position.

Both the first protrusion14and the second protrusion15are provided on individual flexible arms which can be hindered in radial movement by placing a solid element under the flexible arms. The movable needle shield20is e.g. provided with a longitudinal recess26such that the flexible arm carrying the first protrusion14can only flex radially when the flexible arm is located above this recess26. The protective cap75can thus only be axially moved on the first housing part10A when the movable needle shield20is in a specific rotational position.

Further in the position disclosed inFIG. 7A-C, the protrusion97is positioned directly underneath the opening3in the first housing part10B. At the same time, the flexible arm carrying the protrusion15is located radially above the opening3. The result being that the arm carrying the protrusion15can only flex very limited. At the same time the track77is formed with a plurality of steep flanges in one rotational direction such that the protective cap75can only rotate in one rotational direction.

In the proximal position of the protective cap75as disclosed inFIG. 7A-C, the hub40has been moved together with the movable needle shield20and the proximal end37of the needle cannula35is now inserted into the cartridge30(seeFIG. 7C).

TheFIGS. 7B and 7Care partial enlargement of details inFIG. 7A. As the movable needle shield20moves proximally it brings along the release element90due to the engagement between the internal thread25of the movable needle shield20and the external thread93on the thread arms92. In the position shown inFIG. 7A-C, in which the protective cap75is correctly positioned in its proximal position, the knob95is engaged in the indentation19and the compression spring101is fully compressed.

The axial movement of the release element90is via the release arms91transferred to an axial movement of the piston rod guide60such that external teeth62provided externally on the piston rod guide60engages an internal toothing72inside the drive tube70(seeFIG. 7B). The piston rod guide60is hereafter rotational locked to drive tube70with the result that the piston rod45cannot rotate any longer. The pressure relief system is in this manner disabled and the piston rod45is unable to flow freely.

When moving the movable needle shield20and the release element90proximally, the needle hub40which is locked in the radial parking track24also moves proximally. As disclosed inFIG. 8, the hub40is internally provided with inner protrusions42which during the proximal movement of the needle hub40slides axially in axial tracks16provided in the first intermediate housing part10B. As long as the inner protrusions43is positioned in the axial tracks16, the hub40is unable to rotate.

Following the axial movement of the movable needle shield20which is finalized when the first track76engages with the first protrusion14as disclosed inFIG. 2, the user starts rotating the protective cap75as indicated by the arrow “R” inFIG. 3. The connection between the second protrusion15and the second track77is as previously explained formed such that the protective cap75can only rotate in one rotational direction. The rotational direction being one that screws the movable needle shield20in the proximal direction in the guiding thread93.

As the movable needle shield20is rotated and translated in the proximal direction the side surface of the longitudinal track23abuts the protrusion41of the needle hub40which is thereby also rotated. During the rotation of the hub40the internal protrusions42abut a sloping surface17in the axial track16which forces the hub40to move in the proximal direction.

The hub40is internally provided with an internal sleeve43which are best seen inFIG. 7C. The sleeve is hollow and surrounds the needle cannula35. The hollow sleeve43could alternatively be formed from a number of axially extending arms. The proximal end of the hollow sleeve43abut the distal end of the cartridge30and as the hub40travels in the proximal direction the sleeve43pushes the cartridge30also in the proximal direction.

For that purpose, the cartridge30is supported in the first intermediate housing part10B in a way allowing axial movement of the cartridge30.

As the movable needle shield20is rotated relatively to the guiding element90, the internal protrusion42slides along the slope17while the cartridge30moves a distance “Z” in the proximal direction as disclosed inFIG. 11. Once the cartridge has moved the distance “Z” in the proximal direction, the internal protrusions42enters into the circular track18which allows full rotation of the hub40.

Since the piston rod guide60is rotational locked to the drive tube70in this situation, the piston rod foot50and thus the plunger32is prevented from moving in the proximal direction. However, as the cartridge30is moved proximally a pressure will build up internally in the cartridge30which pressure will force liquid drug to be pressed through the lumen38of the needle cannula35.

Since the distal tip36of the needle cannula35is maintained inside the cleaning chamber56this chamber56will be filled with liquid drug and the piston58will move in the proximal direction thus allowing the cleaning chamber56to be filled.

As the cartridge30is moved the distance “Z” in the proximal direction, and the cleaning chamber56is filled an overpressure can be build inside the cartridge30. In order to equalize such overpressure, the user keeps rotating the protective cap75and thus the movable needle shield20due to the engagement between the track22and a corresponding axial ridge78provided inside the protective cap75. Due to this further rotation of the protective cap75and the movable needle shield20, the movable needle shield20screws proximally in the thread93of the guiding element90.

When the thread25internally in the needle shield reaches the end of the thread93of the guiding element90, the distal end36of the needle cannula35has penetrated through the septum57of the cleaning chamber56thus allowing an overpressure inside the cartridge30to escape. This is depicted inFIG. 12where it is seen that the movable needle shield20is moved to its proximal end position as the thread93has reached the end of the thread25.

As best seen inFIG. 9, the internal thread25of the movable needle shield20has an abrupt end27. Once the thread segment96on the trigger arm94abuts this abrupt end27, the trigger arm94will be forced to bend in the peripheral plane and thus be moved out of its engagement with the indentation19in the longitudinal opening13.

Once the trigger-knob95is moved radially free of the indentation19, the compression spring101will force the movable needle shield20and the release element90to move proximally into the position shown inFIGS. 13 and 14.

As the movable needle shield20and the release element90move distally, a spring arm83provided proximally on the ratchet element80will move both the ratchet element80and the piston rod guide60distally as also shown inFIG. 13andFIG. 14whereinFIG. 14is identical toFIG. 13however with the protective cap75removed. In this position, the injection device1is ready to perform an injection. The cleaning chamber56is filled and the piston rod guide60is in the pressure relief position i.e. the piston rod45floats freely inside the injection device to compensate for temperature changes.

Also in the position disclosed inFIG. 13, the first flexible arm carrying the first protrusion14is located radially above the26such that the flexible arm can flex and the protective cap can be axially removed.

With the injection device1in the position disclosed inFIG. 13, the user rotates the dose setting button5to set a dose to be injected. During this rotation, the torsion spring100is strained. The user then removes the protective cap75as shown inFIG. 14and presses the distal end of the movable needle shield20against the skin as indicted by the dotted line “S” inFIG. 15A.

As the movable needle shield20is locked to the guiding element90these two elements20,90translates axially in unison which tightened the compression spring101.

The axial movement of the guiding element90is translated to the piston rod guide60which also move axially as depicted inFIG. 15B. The teeth external62on the piston rod guide60thus engages the internal toothing72in the drive tube70which renders the piston rod guide60inrotatable in relation to the drive tube70.

At the same time the proximal end of the piston rod guide60pushes the ratchet element80in the proximal direction such that the teeth82provided distally on the ratchet tube slides out of its engagement with the drive tube70. As the drive tube70is no longer secured against rotation, the torsion spring100forces the drive tube70to rotate. Since the piston rod guide60in this position is inrotatable coupled to the drive tube70, the piston rod guide60rotates with the ratchet element80and this rotation is translated to a rotation of the piston rod45which is thus screwed forward in its threaded connection12/46with the housing10.

Once the liquid drug in the set dose has been delivered to the user, the needle cannula35is removed from the skin and the compression spring101urges the movable needle shield20and the guiding element90in the distal direction as shown inFIG. 16A-Bwhich is actually the same situation as disclosed inFIG. 14.

In this position the spring arm83provided proximally on the ratchet element80moves the ratchet element80distally such that the teeth82re-enters the engagement with the drive tube70thus securing the torsion spring100. This movement also moves the piston rod guide60into its pressure relief position wherein the piston rod guide60is free to rotate under influence of the axial movement of the plunger32.

As the movable needle shield20slides back to its initial position, the distal tip36of the needle cannula35re-enters the cleaning chamber56such that the distal tip36is contained submerged in the liquid drug contained in the cleaning chamber56until next injection.

Since the liquid drug both in the cartridge30and especially in the cleaning chamber56contains a preservative, the distal tip36of the needle cannula35is biological cleaned before the next injection.

Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.