Patent Publication Number: US-2022233777-A1

Title: Cartridge fixation for a drug delivery device

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to International Patent Application No. PCT/EP2020/078700, filed Oct. 13, 2020, entitled “ CARTRIDGE FIXATION FOR A DRUG DELIVERY DEVICE,” which claims priority to European Application No. 19203413.0, filed Oct. 15, 2019, entitled “CARTRIDGE FIXATION FOR A DRUG DELIVERY DEVICE”, each of which is incorporated by reference herein, in their entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     Disclosed are medicament delivery devices for delivering, administering, dispensing, injecting, or infusing substances and/or liquids such as insulin or hormone preparations that include a housing and a cartridge holder connectable to the housing for holding a cartridge within the housing and the cartridge holder. 
     BACKGROUND 
     A variety of diseases exist that require regular treatment by parenteral subcutaneous or intramuscular administration of a drug or medicament, and a number of drug delivery devices have been developed to support a patient in accurately and controllably delivering an amount of drug in a self-administration process. 
     Injection devices for self-administration typically include a dosing and dispensing mechanism allowing a user to dial a desired dose and subsequently administer or dispense the dialed dose. The dispensing mechanism includes a piston rod, which is movable relative to a housing of the injection device. The piston rod is adapted to move a plug inside the cartridge in a distal direction in order to dispense the drug through a distal opening of the cartridge. 
     Such an injection device further includes the cartridge containing the liquid drug or medicament. The cartridge is usually held by a cartridge holder and a housing of the injection device accommodating the dose and dispensing mechanism. To hold the cartridge, a distal portion of the cartridge is accommodated in the sleeve-shaped cartridge holder and a proximal portion of the cartridge is accommodated in a recess of the housing. During assembly, the cartridge is either first inserted with its proximal portion in the recess of the housing or it is first inserted with its distal portion in the cartridge holder. Subsequently, the cartridge holder is connected with its proximal end with a distal end of the housing. For dosing and dispensing accuracy, it is important to rigidly and precisely hold the cartridge relative to the housing and the piston rod, in particular in an axial or dispensing direction. 
     Means for holding the cartridge within a housing are known in the art. For example, U.S. Pat. 9,867,945 B2 discloses a cartridge holder having inwardly and outwardly movable tongues on a proximal portion of the holder. The movable tongues include an inwardly directed protrusion adapted to engage with a proximal rim portion of the cartridge. During insertion of the cartridge into the holder the tongues elastically bend outwards and flex back when the cartridge is inserted. Accordingly, in an assembled state, the cartridge may be clamped between a distal end stop face of the holder and the protrusions such that the cartridge is secured against distal and proximal displacement with respect to the cartridge holder. 
     U.S. Pat. No. 9,149,580 B2 discloses a cartridge holder including a tensioning member connected to a compression spring positioned at a shoulder portion of a bottle-necked body of a cartridge. The cartridge holder is further equipped with at least one counter-bearing element adapted to provide a proximal end stop for the cartridge. Therefore, the cartridge can be effectively clamped between the tensioning member and the counter bearing element. 
     US 2007/0021718 A1 discloses holding means for a cartridge including a spring inserted into a recess of a housing of a pen injector. A proximal end of the spring is held by a snap-fit connection in a bottom of the recess. When a cartridge is inserted with its proximal portion into the recess the spring is compressed. In the assembled state, the compressed spring holds and biases the cartridge to a distal inner wall of the cartridge holder. The cartridge is thus axially held relative to the housing and the cartridge holder. 
     These prior art approaches suffer from the fact that the holding means for holding the cartridge relative to the housing may exert a biasing force or holding force to the cartridge when inserting the cartridge into the housing which may unintentionally increase. Such a high holding force may occur if the cartridge is longer than expected (e.g., due to manufacturing tolerances) or if the cartridge is inserted during assembly too deeply into the housing and thus the biasing element is overly compressed. If the holding force is too high the cartridge may be damaged or even break. On the other hand, if the holding force is too low the cartridge may move within the housing, such as after a storage period when material relaxation has been occurred. 
     SUMMARY 
     It is thus an objective of the present disclosure to reliably and precisely hold the cartridge relative to a housing of the drug delivery device or, more generally, to provide an easy to manufacture alternative holding means with improved assembling capabilities. 
     This objective is achieved by providing a housing for a cartridge unit for a drug delivery device according to the disclosure and claims. 
     According to certain implementations, a housing for a drug delivery device for administrating a liquid drug from a cartridge may include a recess for accommodating at least a proximal portion of the cartridge. The recess has an axis defining a longitudinal direction. The housing may further include a deformable member arranged inside the recess, where the deformable member may include a proximal end attached to the housing, such as to a sidewall of the recess, and a distal end movable within the recess relative to the housing and relative to the sidewall. The deformable member may deformable from a non-deformed state or an initial state to a deformed state by a displacement of its distal end. In the deformed state the deformable member may be adapted to limit a movement, such as a proximal movement, of a cartridge that may be present in the recess in the longitudinal direction relative to the housing. The deformable member may include a first arch between the proximal end and the distal end in the non-deformed state and in the deformed state. In the deformed state, the first arch may be deformed both elastically and plastically. 
     During assembly, the cartridge may be inserted into the drug delivery device, and a proximal portion of the cartridge may be inserted into the recess of the housing of the drug delivery device. During insertion of the cartridge into the housing recess, the deformable member may be deformed from the non-deformed state to the deformed state. The deformable member may be deformable by a displacement of the distal end. This distal end may be displaced by a proximal end of the cartridge when the cartridge is inserted into the housing recess. When the cartridge has been inserted into a final axial position into the housing recess, the arch of the deformable member may be elastically deformed and at the same time plastically deformed. In this deformed state, the housing with the deformable member may be adapted to limit a movement of the cartridge relative to the housing in the proximal, longitudinal direction. Additionally, if the cartridge is inserted into its final axial position the deformable member together with a cartridge holder or with any counter element connected to a distal end of the housing may be adapted to hold the cartridge relative to housing such that the cartridge is prevented from further movement relative to the housing. 
     During insertion of the cartridge, a resisting force or reaction force exerted by the deformed deformable member may act on the proximal end, such as on a rim portion, of the cartridge. There may be no resisting force in the non-deformed state when the cartridge does not abut the deformable member. The force initiates and may continuously increase at least in a first part during insertion of the cartridge into the recess because the arch of the deformable member may be deforming and some portions of the deformable member may be compressed. When the insertion of the cartridge is complete and the deformable member is in its deformed state there may still be a force exerted by the deformable member acting on the cartridge because the deformable member is in the deformed state not only plastically deformed but also elastically deformed. 
     The deformable member may be adapted to limit a movement of the cartridge in the recess in the longitudinal direction relative to the housing. Therefore, the cartridge may be held in the housing in a predefined, final axial position or in a predefined final axial positional range in the recess. Due to the arch-shaped member the force progression in relation to the deflection or to the deforming path during deformation of the arch may be optimally configured. For example, the arch may be configured such that the force progression is nearly linear or such that it follows a suitable mathematic function. Thus, the force acting on the cartridge may be predictable. Therefore, the deformable member may be adapted to reliably limit the axial movement of an inserted cartridge. In the assembled state, when a counter element, for example a cartridge holder, is mounted to the housing the cartridge may be reliably and precisely held such that the cartridge is secured against distal and proximal displacement. 
     Since the force acting on the cartridge may be adjustable by configuring the deformable member with an arch, the inserted cartridge may be held with a predefined force within a predefined force range. This may provide the ability to hold cartridges with different lengths, which may be caused due to manufacturing tolerances. Hence, the arch may be configured such that a short as well as a long cartridge may be optimally held by the deformable member relative to the housing. 
     The elastic deformation of the arch may cause a force acting on the proximal end of the inserted cartridge in a distal and longitudinal direction. The deformed arch may bias the cartridge in a distal direction against a stop element in a cartridge holder or against any counter element in an assembled state. 
     During storage, material relaxation may occur. Due to the elastic deformation of the arch there may still be a remaining force acting on the cartridge and a movement of the cartridge may be reliably limited even if the initial force is reduced due to any such material relaxation. 
     Besides the elastic deformation, the deformable member may be further plastically deformed in the deformed state such that a further movement of the cartridge may limited by the deformable member. The effect of the plastic deformation may be that, depending on the configuration of the arch, the exerted force on the cartridge by the member may be limited to a specific maximum value. Thus, the plastic deformation of the deformable member may limit the exerted (reaction) force acting on the cartridge and may thus prevent damage or even breakage of the cartridge. 
     In an assembled state when a holding means (e.g., a cartridge holder) is mounted the cartridge may be prevented from movement or the cartridge may only move in a very restricted range (e.g., several micrometers) relative to the housing and relative to any dosing element such as a plunger rod accommodated in the housing. Thus, the accuracy of the dosing and dispensing may be ensured. 
     In certain implementations, a sleeve shaped cartridge holder may include a recess adapted to accommodate a distal portion of the cartridge and may be mounted to the housing for completion of mounting of the cartridge into the drug delivery device. For instance, the opening of the recess of the cartridge holder may be configured to slide over a distal end of the cartridge. The cartridge may, as previously described, have its proximal end inserted into the housing. Alternatively, the cartridge may first be inserted with its distal portion in the cartridge holder and then the proximal portion of the cartridge may be inserted into the housing as described previously. In both variants, the proximal end of the cartridge holder may then be fixed to the distal end of the housing, for example, by a snap fit connection. The cartridge may thus be held by the cartridge holder and the housing relative to the housing inside the drug delivery device. 
     The term “plastic deformation” means that the deformation is irreversible and thus the deformation stays even after removal of the applied force. The term “elastic deformation” means that the deformation is recoverable as it disappears after the removal of the applied force. 
     The term “arch” means that the member has a curved shape between the proximal end and the distal end. The arch or the curved shape may form an arc of, for example, ranging between 30° to 190°, such as between 70° and 120°. The arch may be directed in any direction. The deformable member may include one or more arches between the two ends. 
     In the deformed state, the deformable member may be adapted to limit a movement of the cartridge in the longitudinal direction. That means movement of the cartridge may not be stopped or blocked in any case, but a restricted movement of the cartridge may only be possible. For example, the insertion force required for a movement of the cartridge in the proximal direction may be higher than in the non-deformed state. 
     The term “non-deformed state” means the deformable member is in its initial state after the manufacturing. The arch or any other portion of the deformable member is not yet deformed by a user or by an assembly process, such as by an insertion of the cartridge into the housing. The distal end of the member may not be moved from its initial position. 
     In contrast, the term “deformed state” means at least a section of the deformable member, such as the shape of the arch has been altered from an initial shape to a new shape. In the deformed state the distal end of the deformable member may be moved away from its initial position, for example, from a distal position to a proximal position relative to the housing. The term “deformed state” is not limited to a specific deformation of the arch but the deformed state includes all positions and orientations of the deformable member and of the arch that is different from their initial positions and in the deformed state the arch is deformed both elastically and plastically. In order to fulfill this limitation the deformation of the material of the deformable member must be in the so-called strain hardening region of the stress-strain curve of the material. That means the deformable member is in the deformed state as soon as the deformation of the material exceeds the pure (linear) elastic region and an irreversible plastic deformation occurs. 
     In the present context, the terms “substance”, “drug”, “medicament” and “medication” are to be understood to include any flowable medical formulation suitable for controlled administration through a means such as, for example, a cannula or a hollow needle, and includes a liquid, a solution, a gel or a fine suspension containing one or more medical active ingredients. A medicament may be a composition comprising a single active ingredient or a pre-mixed or co-formulated composition with more than one active ingredient present in a single container. Medication includes drugs such as peptides (e.g., insulin, insulin-containing drugs, GLP-1 containing drugs or derived or analogous preparations), proteins and hormones, active ingredients derived from, or harvested by, biological sources, active ingredients based on hormones or genes, nutritional formulations, enzymes and other substances in both solid (suspended) or liquid form but also polysaccharides, vaccines, DNA, RNA, oligonucleotides, antibodies or parts of antibodies but also appropriate basic, auxiliary and carrier substances 
     The term “distal” is meant to refer to the direction or the end of the drug delivery device carrying an injection needle or an injection cannula, whereas the term “proximal” is meant to refer to the opposite direction or end pointing away from the needle or cannula. 
     The term “injection system” or “injector” refers to a device that is removed from the injection site after each medication event or drug delivery process, whereas the term “infusion system” refers to a device with a cannula or needle that remains in the skin of the patient for a prolonged period of time, for example, several hours. 
     In certain implementations, the deformable member is arm-shaped and the arch of the deformable member may be located between the proximal end and distal end of the arm-shaped member. The term “arm-shaped” means the member has preferably a longitudinal shape or form between the proximal end and the distal end of the member. Hence, the length is longer than the width of the member. However, the arm-shaped member must not be extending along the longitudinal direction of the housing but it may extend along any other direction or the whole member can have a curved form, which does not extend along a specific direction. The arm-shaped member enables configuration of an advantageous force procession of the force acting on the cartridge when the cartridge is inserted into the housing. Furthermore, the arm-shape may allow for an efficient production of the deformable member. Where the deformable member is made of plastic, the arm-shape may be easy to demold or remove from an injection molding tool. 
     The deformable member may be deformable in the area of the arch. However, during deformation from the non-deformed state to the deformed state, other portions of the member may also be deformed. 
     The deformable member may be deformable from the non-deformed state to the deformed state by a displacement of the distal end of the member in the longitudinal direction relative to the housing, such as by a proximal displacement. The displacement may be caused when the cartridge is inserted into the recess of the housing with its proximal portion and moved in the proximal direction parallel to the longitudinal axis. That means, during insertion of the cartridge along the longitudinal direction the distal end of the member may also be moved substantially along the longitudinal direction. This may allow for an easy and quick deformation of the deformable member and may thus allow for an easy and quick limitation of a movement of the cartridge relative to the housing. 
     Alternatively, the deformable member may be deformable from the non-deformed state to the deformed state by moving the distal end in a direction perpendicular to the longitudinal direction or in any other direction. 
     In certain implementations, the distance between the proximal end and the distal end of the deformable member defines a length of the member in the longitudinal direction, where in the deformed state, the length is reduced compared to the non-deformed state. For instance, the deformable member such as the arch may be bent or deformed such that the length of the deformable member is reduced during deformation. Due to the deformation at least a portion of the arch may be compressed and/or stretched. The strain of the material due to the deformation may cause a force acting at least partially in the longitudinal direction and may thus be adapted to bias the inserted cartridge against a cartridge holder or any counter element at a distal end of the cartridge in an assembled state. 
     Alternatively, the length of the member may be enlarged in the deformed state compared to the non-deformed state. This may occur, for example, if the arch of the member is stretched during deformation. 
     In some examples, in the deformed state a first portion of the arch may be elongated and a second portion of the arch may be compressed compared to the non-deformed state. Hence, the arch may be deformed in such a way that an initial curve of the arch may be further bent. For example, an inner radius defining an inner curvature of the arch may be decreased in the deformed state compared to the non-deformed shape. Such a deformation may allow for a space-saving configuration of the deformable member. Furthermore, such a deformation may allow for a continuous and predicable force progression in relation to the deforming path. 
     Alternatively, the arch may be deformed in any other way, such as a deformation only by elongation or only by compression. 
     The deformable member may include a second arch between the proximal end and the distal end, and the previously described first arch and the second arch may constitute an s-shaped form in the non-deformed state and in the deformed state. The term “s-shaped” means the deformable member has more or less of an s-form. That means the first arch is preferably arranged adjacent to the second arch along a continuous line of the form of the deformable member. The two arches of the deformable member may not need to exactly and completely form an s-curve. The s-shape form may allow for a further compact design. In the s-shaped member strain and stress within the body of the member may be advantageously and widely dispersed within the body of the member and thus local strain peaks and local stress peaks may be avoided. Furthermore, during deformation the s-shape form of the deformable member may allow for a continuous and optimal force progression in relation the deflection of the member. 
     The second arch may allow for a configuration of the deformable member such that the resisting force or holding force of the deformable member during its deformation may be smooth, continuous and may be held in an optimal range. Namely, the force in relation to the deflection (deforming path) of the s-shaped member may in a first section rapidly increase and in a second section be very low or almost constant. The almost constant section may be desirable because a cartridge with a minimum length and a cartridge with a maximum length of a tolerance range may be held with almost the same predetermined force. 
     The deformable member may be deformable in the first and the second arch, such as exclusively deformable in the first and the second arch. The portions of the deformable member not belonging to the first or second arch may thus not be deformed. Therefore, during deformation from the non-deformed state to the deformed state only the first arch and the second may be deformed and the rest of the deformable member may not be deformed, and may be unable to be deformed. 
     In an alternative embodiment the deformable member may be configured such that only one of the two or more arches is deformed and the other arches may not be deformed in the deformed state of the deformable member. 
     A plane area of the cross-section of the deformable member may vary between the proximal end and the distal end. The plane area of the cross-section lies in a plane perpendicular to the center line of the deformable member. In some implementations, the deformable member may be tapered or the deformable member may include tapered portions. The varying plane area of the cross-section may permit the location of the deformable arch portion to be optimally defined. Hence, the plane area in the deformable portion in the arch may be reduced compared with the non-deformable portion of the deformable member such that the location of the deformation may be precisely defined and predicable. Furthermore, the plane area in the deformable portion may be configured such that the deformable portion is easily and optimally deformable. 
     In some implementations, the deformable member may be unitarily formed with the housing. The deformable member may be formed in one piece and for instance by the same material as the housing. This may allow for an efficient production of the housing with the deformable member. 
     The deformable member may be a separate and single part, which may be connected, for example, by bonding, e.g., an adhesive bond, or by a snap-fit connection. 
     The deformable member may be made of a polymer such as a polyoxymethylene, polypropylene, polyethylene, polycarbonate-acrylonitrile-butadiene-styrene, polybutylenterephthalate, a polyester or a polyamide. These polymers, such as polyethylene, may be easily deformable and may have an advantageous value for the elongation at break. That means the deformable member may be deformed both plastically and elastically in a specific deformation range without risk of breakage. For instance, polypropylene is very ductile, which means the deformable member is easy to stretch or easy to deform. 
     According to certain implementations, the housing may include at least two deformable members and may be arranged inside the recess of the housing. The two or more members may be arranged circumferentially and may be spaced apart evenly and/or symmetrically from each other. Thus an insertion movement of a cartridge into the recess of the housing may be limited by two or more deformable members and the insertion movement may thus be limited in a safe and optimal manner. 
     The proximal end of the deformable member may be attached to a connecting surface of the housing located inside the recess and may substantially extend along the longitudinal direction and in the distal direction. That means the deformable member may extend from the connecting surface perpendicular to the insertion direction of the cartridge, which is along the longitudinal direction. The term “substantially” means that the connecting surface may not exactly be orientated in the longitudinal direction but may be orientated from about −10° to +10° different from the longitudinal direction. 
     The proximal end of the deformable member may be attached to the connecting surface on the sidewall of the recess and may not be arranged in the space filled by the inserted cartridge. If the cartridge is inserted deeper into the recess than the final axial end position, then the deformable member may be deflected and the arch may be further deformed but the movement of the cartridge may not be blocked by the deformable member. 
     For instance, the cartridge, if further moved into the housing, may abut an axial end stop element inside the housing, which may be separated from the deformable member. Since the deformable member may be attached to a surface extending along the longitudinal direction or to a sidewall of the recess, the resisting force of the deformable member may increase only to a specific maximum value. Hence, the cartridge may not be damaged or broken by the deformable member because the force acting on the cartridge cannot exceed the maximum value or a predefined threshold. 
     In contrast, a spring or any deformable element which may be attached to a connecting surface perpendicular to the longitudinal direction (and thus perpendicular to the movement of an inserting cartridge) or a deformable element which is arranged on a proximal front end side of the inserted cartridge may only be deformed to a specific maximum and the resisting force caused by the element may abruptly increase to a breaking force when the cartridge is inserted too deeply into the recess. 
     According to certain implementations, the connecting surface may be an outer wall of an element inside the recess of the housing. 
     Such an outer wall may be, for example, an outer surface of an insert element arranged coaxially inside the recess, where the outer wall of the insert extends along the longitudinal direction. In this case, the deformable member may extend preferably radially outward from the outer wall in the direction to the inner sidewall of the recess. 
     In an alternative embodiment the connecting surface may be an inner sidewall of the recess. In this case, the deformable member(s) may extend radially inward from the inner sidewall to a center of the recess. 
     The housing may include a stop element adapted to prevent a movement of the cartridge in the longitudinal direction beyond the stop element. The stop element may be separate from the deformable member. That means the stop element may not be a part or a portion of the deformable member. The stop element may be unitarily formed with the housing or it may be a separate element connectable to the housing. 
     The stop element may be adapted to stop or block any movement of the cartridge in the proximal and longitudinal direction. In contrast, the deformable member may be adapted to limit a movement of the cartridge in the proximal and longitudinal direction, which means a movement may not be prevented per se, but may be restricted and may be dependent on forces acting on the cartridge in the longitudinal direction. 
     Since the stop element is separated from the deformable member the two may separately function to limit a movement (and/or bias the cartridge) and provide an axial end stop. This may enable each function to be carried out optimally. For instance, the deformable member may be configured such that the resisting force or holding force (caused by the deformed member) in relation of the deflection of the deformable member may be adjusted to a specific cartridge length or range of lengths. Additionally, a stop end adapted to block a proximal movement of the cartridge inside the housing beyond a specific axial position may be provided independent of the deformable member in a space-saving design. 
     Implementations further relate to providing a cartridge unit including a housing as described herein, the cartridge containing the liquid drug, a cartridge holder for accommodating a distal portion of the cartridge and connectable to a distal end of the housing such that the cartridge may be held relative to the housing by the cartridge holder and the housing. The deformable member may be deformable from the non-deformed state to the deformed state by a displacement of the distal end of the deformable member. The displacement may be caused by an insertion of a proximal portion of the cartridge into the housing, for instance where a proximal end of the cartridge abuts the distal end of the deformable member. Therefore, in the deformed state the proximal end of the cartridge may abut the distal end of the deformable member. 
     In an assembled state, the distal portion of the cartridge may be within the cartridge holder and the proximal portion of the cartridge may be within the housing. Furthermore, a proximal end of the cartridge holder may be connected to a distal end of the housing. Thus, the cartridge may be held within the cartridge holder and the housing because the deformable member may be in the deformed state and the deformed deformable member may limit a movement of the cartridge relative to the housing and the cartridge holder. 
     Further implementations provide a drug delivery device for administrating a liquid drug from the cartridge comprising the cartridge unit as described previously, and a dosing and dispensing mechanism. 
     Methods for assembling a cartridge unit for a drug delivery device are also provided, and may involve the steps of:
         a. Providing a housing including a recess for accommodating a proximal portion of the cartridge, the recess having an axis defining a longitudinal direction, a deformable member being arranged inside the recess, where the deformable member includes a proximal end attached to the housing and a distal end movable within the recess relative to the housing, the deformable member further including an arch;   b. Inserting a distal portion of the cartridge into an opening of a sleeve-shaped cartridge holder;   c. Inserting a proximal end portion of the cartridge holder with the cartridge into the recess of the housing in the longitudinal direction;   d. Deforming, by a proximal end of the cartridge, the deformable member of the housing from a non-deformed state to a deformed state by a displacement of a distal end of the deformable member in the proximal and longitudinal direction and thereby deforming the arch both elastically and plastically;   e. Connecting the proximal end portion of the cartridge holder with a distal end portion of the housing, in particular by a snap lock.       

     The cartridge may be firstly inserted with its distal portion into the opening of the cartridge holder and secondly the cartridge holder with the inserted cartridge can be connected with the proximal end of the cartridge holder to the housing. Alternatively, the cartridge can be firstly inserted with its proximal portion into the opening of the housing and secondly the cartridge holder can be pulled over the distal portion of the cartridge and thirdly the proximal end of the cartridge holder can be connected to the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure will be explained in more detail in the following text with reference to the disclosed embodiments, which are illustrated in the attached drawings, in which: 
         FIG. 1  depicts an isometric view of an injection pen that may be used in connection with implementations of the present disclosure; 
         FIG. 2 a    depicts a cross-sectional view of an injection pen assembly including components of  FIG. 1  taken along the longitudinal axis of the injection pen housing, according to implementations of the present disclosure; 
         FIG. 2 b    depicts a front view of the housing of the injection pen assembly of  FIG. 2 a   , without cartridge and cartridge holder; 
         FIGS. 3 a , 3 b , 3 c , and 3 d    depict cross-sectional views of the deformable member as the deformable member moves from the non-deformed to the deformed state, according to implementations of the present disclosure; 
         FIG. 4  depicts a diagram showing the force progression in relation to the deflection of the deformable member; 
         FIG. 5  depicts a cross-sectional view of a housing for a smaller cartridge taken along the longitudinal axils of an injection pen. 
     
    
    
     The reference symbols used in the drawings, and their primary meanings, are listed in summary form in the list of designations. In principle, identical parts are provided with the same reference symbols in the figures. 
     DETAILED DESCRIPTION 
     The following describes a drug delivery device with a cartridge unit and a housing according to the present disclosure. The drug delivery device may be in the form of an injection pen, as described herein.  FIG. 1  shows an isometric view of certain components of the injection pen, namely a housing  40 , a cartridge  30 , a cartridge holder  20  and a pen cap  10 . The injection pen may further include a dosing and dispensing mechanism. The housing  40 , the cartridge  30  and the cartridge holder  20  may form a cartridge unit. In the following disclosure, the cartridge unit is described in detail. Firstly, the structural features are described, and secondly, the functional features are depicted in detail. 
       FIG. 2 a    depicts a cross-sectional view of the cartridge unit, where the cross-sectional view is taken along the longitudinal axis of the housing  40 . The housing  40  is illustrated as having a sleeve shape and may be made of polypropylene. In a proximal portion of the housing  40 , a dosing and dispensing mechanism may be accommodated. The housing  40  may include a recess  48  at a distal end portion, which recess  48  may be adapted to accommodate a proximal portion of the cartridge  30 . The recess  48  may have a substantially cylindrical shape. An opening forms a distal end of the recess  48  while a bottom portion may be made of four struts  49  circumferentially spaced apart from each other (see  FIG. 2 b   ) and may form the proximal end of the recess  48 . The struts  49  may support an insert  45  with a through hole in the center of the recess  48 . The through hole may serve as a guide for an axially moveable piston rod of the dosing and dispensing mechanism. An axis extending from the distal end to the proximal end of the recess  48  defines a longitudinal direction. 
     As shown in  FIGS. 2 a  and 2 b    two deformable members in the form of arms  41 . 1 ,  41 . 2  are attached to an outer circumferential wall of the insert  45 . The two arms  41 . 1 ,  41 . 2  may be circumferentially spaced apart from each other. A distal end  52  of each arm  41 . 1 ,  41 . 2  may be moveable within the recess  48  relative to the housing  40  and a proximal end of each arm  41 . 1 ,  41 . 2  may be inextricably (e.g., non-removably) attached to the outer wall  46  of the insert  45 , e.g., may be integrally formed therewith. Each arm  41 . 1 ,  41 . 2  may include a first arch  42  and a second arch  43  (see  FIGS. 3 a -3 d   ) which may be arranged such that the arm has an s-shape. Starting from the attached proximal end of the arm, the arm  41 . 1 ,  41 . 2  may include a bend or curve by the first arch  42  from the wall of the insert  45  in the proximal direction. The second arch  43  may be adjacent the first arch and thus the arm  41 . 1 ,  41 . 2  may have a bend or curve back in the distal direction by the second arch  43 . Each arm  41 . 1 ,  41 . 2  may further include a straight section  44  at a distal portion of the arm  41 . 1 ,  41 . 2 . In  FIGS. 2 a  and 2 b   , the straight section  44  extends substantially along the longitudinal direction. The straight section  44  may include a rib on its outer side such that the cross-section of the straight section is not rectangular. The distal end  52  of the arm may be moveable relative to an inner sidewall of the recess  48 . 
     The plane area of the cross-section of each arm  41 . 1 ,  41 . 2  may vary between the distal end and the proximal end of the arm. Namely, the plane area of the cross-section may decrease from the distal end of the arm  41 . 1 ,  41 . 2  to the arches  42 ,  43  of the arm such that the plane area of the cross-section in the s-shaped portion may be reduced compared to the plane area of the cross-section in a distal portion of the arm  41 . 1 ,  41 . 2 . 
     On an inner sidewall of the recess  48  two sliding surfaces  47  may be arranged along the longitudinal direction and circumferentially spaced apart from each other such that the sliding surfaces  47  are next to the distal end  52  of each arm  41 . 1 ,  41 . 2 . 
     The housing  40  may further include an end stop  53 , which may stop or block a proximal movement of the cartridge  30  beyond an end stop position. The end stop  53  may include a stop surface that is arranged perpendicular to an insertion direction and which may be arranged on each strut  49  at the bottom of the recess  48 . When the cartridge is moved proximally beyond its final axial position it abuts the end stop  53  after a short movement in the proximal direction. Hence, the end stop  53  may prevent further insertion in the proximal direction. 
     The cartridge holder  20  as shown in  FIG. 1  may be sleeve-shaped and may also include a recess, but may be adapted to accommodate a distal portion of the cartridge  30 . The cartridge holder  20  may include latches or hooks  21  at its proximal end, which may be configured to engage with apertures  51  or counter elements arranged on a distal end of the housing  40 . In the embodiment shown, the cartridge holder  20  may be connected with its proximal end to the distal end of the housing  40  by a snap lock connection. Alternatively, the cartridge holder  20  may be connected with the housing  40  by any other connecting means, for example, by adhesive bonding, by plastic welding, by a thread or by a bayonet fitting. 
     The function of the deformable arms  41 . 1 ,  41 . 2  and the interaction of the cartridge  30  with the housing  40  and the cartridge holder  20  is described in the following with reference to  FIGS. 3 a    to  3   d.    
       FIGS. 3 a  to 3 d    show a cross-sectional, detailed view of the deformable arms  41 . 1 ,  41 . 2  of the housing  40 . The cross-sectional view runs along the longitudinal direction of the housing  40  and shows only the upper part of the cross-section. In  FIG. 3 a   , an initial and non-deformed state of the deformable arms  41 . 1 ,  41 . 2  is depicted. When the cartridge  30  is inserted into the recess  48  via its proximal portion, a proximal end or rim portion  31  of the cartridge  30  abuts a distal end  52  of the arms  41 . 1 ,  41 . 2 . If the cartridge  30  is further inserted in proximal and in the longitudinal direction into the recess  48  of the housing  40  the rim portion  31  of the cartridge  30  moves the distal end  52  of the arm  41 . 1 ,  41 . 2  radially outward on a sliding surface  47  and slightly moves the distal end  52  in proximal direction, as shown in  FIG. 3 b   . Consequently, an outer distal edge of the arm  41 . 1 ,  41 . 2  abuts the sliding surface  47  on the inner sidewall of the recess  48  and the distal end  52  of each arm  41 . 1 ,  41 . 2  is further moved in the proximal direction sliding along the surface  47 . This movement deforms the two arches  42 ,  43  of each arm  41 . 1 ,  41 . 2 . Due to the elastic deformation of the deformable material (e.g., polypropylene) of the arms  41 . 1 ,  41 . 2  at this stage, a reaction force or resisting force is caused by the deformation. The reaction force or resisting force acts on the rim portion  31  of the cartridge  30  and is substantially directed in the distal direction. 
     Further insertion of the cartridge  30  in the proximal direction moves the distal ends  52  of the arms  41 . 1 ,  41 . 2  further along the sliding surface  47  of the sidewall of the recess  48  in the proximal direction and thereby further deforming the arches  42 ,  43  of each arm  41 . 1 ,  41 . 2 . In particular, the first arch  42  is bent towards a center line or center of the recess  48 . Due to that movement at least one of the two arches  42 ,  43  is deformed plastically. That means the deformation is irreversible and the deformation stays even after removal of the applied force by the cartridge insertion. From this instant, the arms  41 . 1 ,  41 . 2  are in the deformed state. That means in the deformed state the deformation of the material goes beyond a pure linear elastic deformation. 
     The position of the arms  41 . 1 ,  41 . 2  after the further insertion of the cartridge  30  in proximal direction is shown in  FIG. 3 c   . At this stage, the first and the second arch  42 ,  43  are significantly deformed. The first arch  42  is bent or pressed towards a rigid outer wall  46  of the insert  45 , whereas the second arch  43  is widened or stretched. 
       FIG. 3 d    shows the final inserted position of the cartridge  30 . The first and second arch  42 ,  43  of the arms  41 . 1 ,  41 . 2  are even more deformed than in the previous position shown in  FIGS. 3 a  to 3 c   . The deformation of the arms  41 . 1 ,  41 . 2  is still elastic and plastic, and the arms  41 . 1 ,  41 . 2  are still in the deformed state. In case the cartridge  30  would be inserted even further into the recess in the longitudinal direction, the reaction force would only slightly increase to a maximal value. However, the reaction force cannot exceed the maximal value due to the s-shape of the arms  41 . 1 ,  41 . 2 . That effect will be described in detail with respect to the force-deflection diagram of  FIG. 4 . In this final position, the rim portion  31  of the cartridge  30  is near the end stop  53  but does not yet abut the end stop  53 . 
     After the cartridge  30  is inserted into the recess  48  of the housing  40  up to a predefined axial position (inserted end position) the cartridge holder  20  is snapped with its latches or hooks  21  at the proximal end with the apertures  51  at the distal end of the housing  40 . The cartridge  30  may be either first inserted with its distal portion into the recess of the cartridge holder, and then the cartridge holder  20  with cartridge  30  may be connected to the housing  40 , or the cartridge  30  may be first inserted with its proximal portion into the recess  48  of the housing  40  and then the cartridge holder  20  may be put over the distal end of the cartridge  30  and subsequently connected to the housing  40 . 
     In  FIG. 4  a force-deflection diagram is depicted, which shows the force progression of the reaction force (resistant force) of the arms  41 . 1 ,  41 . 2  in relation the deflection or deforming path of the arms (force vs. deflection). 
     The horizontal axis (labeled s-axis) shows the amount of deflection or the deformation path of the arms  41 . 1 ,  41 . 2  in the proximal and longitudinal direction when the distal end  52  of the arms  41 . 1 ,  41 . 2  is displaced from an initial distal position to a proximal position in the deformed state. The vertical axis (labeled f-axis) shows the force progression of the reaction force or resisting force of the arms  41 . 1 ,  41 . 2 . 
     A first section  61  of the curve in the diagram is nearly linear. This is at the very beginning of the deformation when the arm is bent radially outward (corresponding to the deformation shown in  FIG. 3 b   ) and the material of the arms  41 . 1 ,  41 . 2  is then in its linear elastic region. Further deflection of the arms—only axial movement of the distal end  52  of the arm  41 . 1 ,  41 . 2  in proximal direction is possible—abruptly increases the force. The curve in the diagram has a sharp bend and subsequently the curve rises strongly in the second section  62  which is non-linear. From this point, the behavior is non-linear and not only an elastic but also a plastic deformation of the arms  41 . 1 ,  41 . 2  occurs at this stage. Thus, the arms  41 . 1 ,  41 . 2  have been transformed from the non-deformed state to the deformed state. That means at that stage the material is deformed not only elastically but also plastically. 
     Due to the arch-shaped arms the force-deflection curve has a predefined optimal procession. Namely, the maximal value of the force is chosen such that the cartridge is not damaged. Even if the cartridge is longer than expected or even if the cartridge is inserted too deeply into the housing the resisting force or reaction force acting on the cartridge does not exceed a predefined maximum value. That means the force-deflection curve is flattened or nearly horizontal at a greater deflection of the arms (see end section of the diagram). 
     The uninterrupted or solid line of the graph shows the behavior deflection vs. force in with new molded polypropylene material. The dotted line of the graph shows the behavior if the polypropylene material is stored for 100,000 hours. Due to the material relaxation the resistant force is lower than with new material. However, with the s-shaped arms disclosed herein, the resisting force is still above a required minimum force to bias the cartridge against the cartridge holder in order to reliably hold the cartridge within the cartridge holder and the housing. 
     The vertical lines  63 ,  64  and  65  define the deflection range used for holding the cartridge. The range is broad in order to cover cartridges with different lengths. The left vertical line  63  defines the lower end of the range or a lower threshold with a minimum deflection if a short cartridge is held. The force generated by the deformed arms is still high enough to bias the short cartridge against the cartridge holder to reliably and safely hold the cartridge within the cartridge holder and the housing. The vertical line  64  in the middle of the deflection axis marks the nominal value  64  of deflection. The right vertical line  65  defines the upper end of the deflection for longer cartridges. The force generated by the deformed arms if inserted a long cartridge does not exceed a predefined value and thus even a long cartridge cannot be damaged. 
       FIG. 5  depicts a sectional view of a further implementation of the present disclosure. The housing  140  shown in  FIG. 5  is adapted for cartridges having a relatively smaller diameter, for example for a cartridge containing 1.5 ml of a drug, than the larger cartridges, for example for cartridges containing 3 ml of a drug, used for the housing  40  as described previously with reference to  FIGS. 1 to 3 . 
     In contrast to the previously described embodiments of  FIGS. 1 to 3 , the arms  141 , e.g.,  141 . 1 ,  141 . 2 , are attached to an inner wall of the recess and not to the insert of the housing  140 . Furthermore, the arms  141  may include only one arch  142 . The proximal end of the arm may be attached to the inner wall of the recess and a first proximal section  146  of the arm  141  may extend inclined in a proximal direction. The arch  142  may follow the proximal section  146  such that a distal and straight section  144  of the arm  141  may points in a distal direction. The straight section  144  of the arm  141  may include a radially inwardly directed ledge  143 , which may be adapted to support the rim portion  31  of the inserted cartridge. 
     The insertion of a cartridge into the housing  140  and the deformation of the arms  141  corresponds to the embodiment described previously with reference to  FIGS. 1 to 3 . Namely, when inserting a cartridge the proximal end or rim portion of the cartridge abuts the ledge  143 . Further insertion of the cartridge moves the distal end of the arms  141  in the proximal direction. This leads to a deformation of the arches  142  and the arms  141  are deformed from the non-deformed state to the deformed state as described previously with respect to the first embodiment. 
     While the embodiments have been described in detail in the drawings and foregoing description, such description is to be considered illustrative or exemplary and not restrictive. Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain elements or steps are recited in distinct claims does not indicate that a combination of these elements or steps cannot be used to advantage, specifically, in addition to the actual claim dependency, any further meaningful claim combination shall be considered disclosed. 
     LIST OF DESIGNATIONS 
     
         
           10  cap 
           20  cartridge holder 
           21  latch element 
           30  cartridge 
           31  rim portion 
           40  housing 
           41 . 1 ,  41 . 2  arms 
           42  first arch 
           43  second arch 
           44  straight section 
           45  insert 
           46  outer wall of insert 
           47  sliding surface 
           48  recess 
           49  struts 
           51  apertures 
           52  distal end 
           53  end stop 
           61  linear section 
           62  non-linear section 
           63  left vertical line 
           64  nominal value line 
           65  right vertical line 
           140  housing 
           141 . 1 ,  141 . 2  arm 
           142  arch 
           143  ledge 
           144  straight section 
           146  proximal end section