Abstract:
An injection device  1  comprises a plunger ( 60 ) for expressing medicament from a syringe ( 20 ). An actuation mechanism ( 40 ) is arranged in use to provide a biasing force to urge the plunger ( 60 ) from a first rearward position to a second forward position to express a dose from the syringe ( 20 ). The device further comprises a latch member ( 50 ) comprising an aperture ( 54 ) through which the rearward end of the plunger ( 60 ) extends in its rearward position so as to be retained against the force of the actuation mechanism ( 40 ). A trigger ( 70 ) is provided for releasing the plunger ( 60 ) from the latch member ( 50 ). The rearward end of the plunger is provided with an enlarged head ( 66 ) and the latch member ( 50 ) is arranged to at least partially radially displace such that the aperture ( 54 ) may expand to release the enlarged head. The trigger ( 70 ) is moveable between ( 1 ) a primed position in which it prevents displacement of the latch member ( 50 ) and a release position in which it allows displacement of the latch ( 50 ).

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to injection devices and in particular, but not exclusively to a pen injector device. 
       BACKGROUND OF THE INVENTION 
       [0002]    Injection devices are used for the convenient administration of medicaments. For example, pen injectors may be used for providing a single metered dose of a medicament, such as Epinephrine, in an emergency or for providing regular metered doses of a medicament, such as insulin. 
         [0003]    One such injector device has been proposed in the applicants co-pending International Patent Application No. PCT/GB2011/051950 (the contents of which is incorporated herein by reference). The injector device of this patent application includes an elongate housing; a syringe disposed in said housing and having an internal piston to express a dose from a needle at its front end; a trigger device for, in use, activating the internal piston. A cap is provided that, in a fitted configuration, fits over at least part of the elongate housing and prevents activation of the trigger device. 
         [0004]    One particular advantage of this prior art injector device is that the overall size of the injector may be reduced since, in the forward (delivery) position, the drive spring at least partially surrounds the plunger and extends into the inner of the syringe. It is desirable for pen injectors to be of a compact form so that they can be carried around and used unobtrusively. Further compact injectors may be simple to manufacture, assemble and use with consequent savings in manufacturing and assembly costs, and a lower environmental impact. 
         [0005]    In some injectors it may be necessary use high force springs (for example due to high viscosity drugs or small needle diameters). As such there may be a need for an injector having a more resilient mechanism. Additionally, the applicant has now recognised that there may be a risk that the spring could catch on the neck of the aperture or within a spring coil at the rear of the syringe which could delay or prevent firing of the injection mechanism. 
         [0006]    Embodiments of the present invention are intended to address at least some of the abovementioned problems. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, in one aspect, this invention provides an injection device comprising: 
         [0008]    a plunger for expressing medicament from a syringe; 
         [0009]    an actuation mechanism arranged in use to provide a biasing force to urge the plunger from a first rearward position to a second forward position to express a dose from the syringe; 
         [0010]    a latch member comprising an aperture through which the rearward end of the plunger extends in its rearward position so as to be retained against the force of the actuation mechanism; and 
         [0011]    a trigger for releasing the plunger from the latch member; characterised in that 
         [0012]    the rearward end of the plunger is provided with an enlarged head and the latch member is arranged to at least partially radially displace such that the aperture may expand to release the enlarged head; and 
         [0013]    wherein the trigger is moveable between a primed position in which it prevents displacement of the latch member and a release position in which it allows displacement of the latch. 
         [0014]    The latch member may be axially fixed. The radial displacement of the latch member may be provided by a portion of the latch member flexing or hinging. For example the latch member may resiliently flex. 
         [0015]    The plunger may have a forward end sized and shaped to be received within the internal bore of a syringe. The actuation mechanism may provide a forward biasing force on the plunger. The actuation mechanism may comprise at least one biasing member (for example a compression spring). 
         [0016]    At least a portion of the trigger may be disposed radially outside of the latch member. 
         [0017]    The trigger may be slidably mounted within the housing. The trigger may be biased or held against the activation direction. For example, the trigger may be rearwardly biased and may, for example, be urged forwards against said bias to activate the injector device. The trigger device can be biased by means of at least one sprung member. The at least one sprung member can include a cam surface which, in use when sliding in the activation direction, rides over an abutment inside the housing. The trigger may conveniently be an axially moveable button (for example provided at an end of the injection device). 
         [0018]    The trigger may comprise a forwardly extending portion which is disposed radially outside of the latch member. 
         [0019]    The forwardly extending portion may substantially surround the latch member. For example the forwardly extending portion of the trigger may be generally cylindrical. 
         [0020]    One of the latch member and the trigger may be provided with a substantially radially projecting member which is arranged to engage an opposing surface of the other of the trigger and latch member. At least one pair of radially opposed projecting members may be provided. The, or each, radially projecting member may comprise a boss. When the trigger is in the primed position the radially projecting member may abut the opposing surface to prevent radial movement of the latch member. When the trigger is in the release position the radially projecting member may move clear of the opposing surface. For example, the surface of the trigger or latch member which opposes the radially projecting member may comprise at least one cut out sized and shaped to receive the at least one outwardly projecting member. The cut out may be arranged to be moved into alignment with the boss when the trigger is in the release position. 
         [0021]    The latch member may be provided with at least one radially outwardly projecting boss on an exterior surface. The at least one radially outwardly projecting boss may be arranged to abut an interior surface of the trigger when the trigger is in the primed position. 
         [0022]    The trigger may comprise at least one cut out sized and shaped to receive the at least one outwardly projecting boss. The cut out may be arranged to be moved into alignment with the boss when the trigger is in the release position. The cut out may, for example, be provided on the forwardly projecting portion of the trigger. 
         [0023]    It will be appreciated that prior to the movement of the trigger to the release position the radially projecting member or boss may abut the opposing surface so as to inhibit radially expansion of the latch member. Upon movement of the trigger to the release position the member or boss may move into alignment such that the boss or member and surface no longer abut and the latch is free to expand. Advantageously, such an arrangement can be used to enable more accurate control of the point of release of the plunger from the latch member. For example, the alignment of a member or boss with a corresponding cut out may provide an arrangement where the latch will only release the plunger upon full alignment of the boss or member and cut-out. 
         [0024]    The enlarged head may comprise a rearwardly outwardly tapering surface. For example the outwardly tapering surface may be substantially frustoconical. The tapering surface may act to cam the flexible portions of the latch member outward as the plunger passes through the aperture. 
         [0025]    A rear portion of the enlarged head may comprise a rearwardly inwardly tapering surface. The inwardly tapering surface may be frustoconical. The inwardly tapering rear portion may help prevent the plunger catching as it exits the aperture and may allow any return flexure of the latch member to help push the plunger through the aperture.
   Forward movement of the trigger towards the actuation position may be arranged to engage the rearward end of the plunger such that the trigger may physically urge the plunger through the aperture. Thus, the trigger may be arranged to aid the release of the plunger from the latch member.   
 
         [0027]    This arrangement may, for example, be particularly advantageous in injectors utilising high stiffness springs and is considered novel and inventive in its own right. Thus, according to a further aspect the invention provides an injector comprising: 
         [0028]    a plunger for expressing medicament from a syringe; 
         [0029]    an actuation mechanism arranged in use to provide a forward biasing force to urge the plunger from a first rearward position to a second forward position to express a dose from the syringe; 
         [0030]    a latch member arranged to retain the plunger against the force of the actuation mechanism; and 
         [0031]    a trigger for releasing the plunger from the latch member; and wherein the trigger is further arranged to physically engage (for example abut) a portion of the plunger to reinforce the forward biasing force of the actuation member to overcome the retaining force of the latch member. 
         [0032]    The trigger may reinforce the forward biasing force by being arranged to transmit a forward axial force on the plunger during depression of the trigger. 
         [0033]    This aspect may be combined with any of the features referred to above with respect to the first aspect of the invention. 
         [0034]    The trigger may comprise an axially moveable button disposed at the rear of the injector and comprising a rearward facing surface for engagement by a user and an opposing forward facing surface and wherein the forward facing surface is arranged to engage the rearward portion (for example an end face) of the plunger as the trigger is moved from the primed position to the release position. 
         [0035]    The trigger and plunger may be provided with interconnecting features. For example, the forward facing surface may be provided with an inwardly extending projection for engaging rearward tip of the plunger. The tip of the plunger may be provided with a recess or depression sized and shaped to receive the projection. 
         [0036]    The latch member is formed integrally with the housing. For example, the latch member may be an inner housing member provided within a rearward portion of the housing. 
         [0037]    The latch member may comprise at least one axially extending slot. The latch may be an axially split member. The latch member may comprise a radially segmented member, for example a cylindrical member. The at least one axially extending slot may be arranged to allow the latch member to flex radially. Advantageously, the stiffness of the latch member (and the resulting force required to release the plunger) may be easily tailored for example by adjusting any of the material stiffness, the dimensions of the slot, the number of slots, the latch face angle and the thickness of the walls of the latch member. 
         [0038]    Whilst the invention has been described above, it extends to any inventive combination set out above, or in the following description or drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The invention may be performed in various ways, and an embodiment thereof will now be described by way of example only, reference being made to the accompanying drawings, in which: 
           [0040]      FIG. 1  is an exploded view of the first embodiment of an autoinjector in accordance with this invention; 
           [0041]      FIGS. 2( a ) and 2( b )  are respective side and top section views of the autoinjector of  FIG. 1  assembled and prior to use; 
           [0042]      FIG. 3  is a three dimensional view of the latch member of the autoinjector of  FIG. 1 ; and 
           [0043]      FIGS. 4( a ) to ( d )  are partial cross sectional views of the rearward portion of the autoinjector of  FIGS. 1 and 2  taken through the line of the boses on the latch member showing the activation sequence. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0044]    Front as used herein will be understood to refer to the end of the injector assembly (or components thereof) which, in use, are closest to the delivery needle delivery end of the injector (i.e. the end which is pointed at the skin). Rear as used herein will be understood to refer to the end of the pen injector assembly (or components thereof) which, in use, are furthest from the needle delivery end of the injector (i.e. the end which is pointed away from the skin). Forward and rearward will, likewise, be understood to refer to the directions orientated towards the front and rear of the injector assembly. 
         [0045]    Referring initially to  FIGS. 1 to 3 , the autoinjector  1  comprises an outer housing  10  of cylindrical form in the bore of which is disposed a syringe  20 . The syringe is formed of front  10   a  and rear  10   b  housing portions (split for convenience of manufacture). The syringe is of known form with a barrel  22 , a needle  24  extending from the forward end, and a flange  26  at its rear end. A medicament is contained within the syringe and can be expressed through the needle by a piston  28  inside the barrel. The syringe is supported and surrounded by a carrier assembly  30 . A biasing spring  32  is provided which, in the assembled state, biases the carrier  30  rearwardly such that the needle  24  of the syringe  20  is shrouded within the housing  10 . 
         [0046]    In the rear of the housing  10   b  is provided an actuation mechanism which is arranged such that when released it urges the plunger forward relative to the housing. The actuation mechanism includes a first, outer, spring  40  which acts between the front face of a transverse inner wall  52  which is formed as part of a latch member  50  (which is best seen in  FIG. 3  and described in further detail below) at the rear of the housing  10  and a forward flange  43  of a top hat-shaped intermediate member  42 . A second, inner, spring  44  is received within a cylindrical part of the intermediate member  42  and acts between an inner face of the rear end wall thereof and a circumferential rib  62  on the forward part of a plunger  60 . At the rear end, the plunger has a reduced diameter neck  64  with an enlarged head  66  (which will be described in further detail below). In the initial position shown in  FIG. 2 , the neck  64  is located within an aperture  54  in the transverse wall  52  of the housing latch member  50 . The enlarged head  66  retains the plunger in position within the aperture  54 . 
         [0047]    Projecting rearwardly from the rear end of the housing is a captive axially slideable trigger button  70  movable against a rearward bias from the initial position, shown for example in  FIG. 2 . The trigger button  70  includes a forwardly extending portion  78  which has a generally cylindrical profile. As best seen in the cross section of  FIG. 2 , the forwardly extending portion fits within the rear housing portion  10   b  and radially surrounds the rear portion of the latch member  50 . The forwardly extending portion  78  is provided with a plurality of cut-outs  76  (which are sized and dimensioned to receive bosses  56 , shown in  FIG. 3 , of the latch member as will be described below). The trigger button  70  is held in place by two integral forwardly extending arms  72  with cam surfaces  74  which ride over respective abutments  55  inside the rear of the housing. However, initially, forward movement of the trigger button is prevented by means of two rearwardly extending locking arms  82  which extend back from the rear end of a cap  80 . The arrangement and function of the cap is substantially as described in in the applicants co-pending International Patent Application No. PCT/GB2011/051950. 
         [0048]    The latch member  50  is shown in isolation in  FIG. 3  (although it will be appreciated that in some embodiments the latch member  50  may be formed as an inner portion of the rear housing  10   b  which is spaced apart from and within the housing  10   b ). The latch member  50  has a generally cylindrical body which is segmented at its rear end by a pair of opposing axially extending slots  58  such that the rear portion of the body provides two opposing segments (although it will be appreciated that further slots may be provided to define a greater number of segments). The slots  58  join at the transverse inner wall  52  at the rear of the latch member and are conjoined with the aperture  54 . As such the aperture  54  may be considered to be a split aperture. Thus, it will be appreciated that the slot  58  enables the segments of the latch member to resiliently flex radially outwardly to enable the aperture  54  to be expanded. Proximal to the rearward end of the latch member  50  radially outwardly projecting bosses  56  are provided spaced circumferentially around the latch member. For example, the boses may be arranged in pairs which are substantially radially opposed (so as to constrain in the radial direction in which they oppose one another), The forward end of the latch member  50  is provided with two outwardly radially projecting abutments  55  over which the arms  72  ride when the button is depressed. It may be noted that  FIG. 3  appears to show 4 such abutments but the other outward projections  57  are, in fact, connecting portions which extend between the latch member  50  and the rear housing  10   b.    
         [0049]    In operation, the user pulls the cap  80  off forwardly which arms the device by rendering the trigger button  70  operational (and which may typically also remove a needle shield, not shown, from the syringe). In this primed state, as shown in  FIG. 4( a ) , the trigger button  70  is biased to its rearward position and the reduced diameter neck  64  at the rear of the plunger  60  is positioned within the aperture  54  of the latch member  50 . The plunger  60  is subject to a biasing force in the forward direction from the springs  40 ,  44  of the actuation mechanism but is held captive in its rearward position as the enlarged head  66  cannot pass through the aperture  54  without the segmented sections of the latch member  50  being flexed radially outwardly. Such outward movement is prevented since the bosses  56  abut the inner surface of the forwardly extending portion  78  of the trigger button  70 . 
         [0050]    Following removal of the cap, the user offers the injection device up to the injection site and presses the trigger button  70 . The trigger button slides forwardly from the position shown in  FIG. 4( a )  to the position shown in  FIG. 4( b ) . As the button  70  moves forward the cut outs  76  in the forward portion of the trigger button  70  are brought into alignment with the bosses  56  of the latch member  50 . In this position (shown in  FIG. 4( b ) ) the latch member is no longer constrained against radial expansion by the trigger button. It will be noted that in this position the forwardly projecting member  79  provided on the internal surface of the trigger button  70  which may engage the rearward end of the plunger. The rearward end of the plunger  60  may be provided with correspondingly profiled recess  69  into which the member  79  may locate. This enables a portion of the actuating force provided by the user to be directly transferred into a forward force upon the plunger  60 . This arrangement may be particularly useful in providing a “fail safe” arrangement in which the member  79  of the trigger button  70  only engages the plunger recess  69  if the plunger does not immediately release upon the trigger moving towards the forward position. In other words, the plunger may normally be expected to be released by the driving force of the springs  40 ,  42  and the member  79  may provide a reinforcing action in the event of any stiction in the syringe or mechanism or the need to design the latch mechanism to be very resilient to forward movement of the springs (as may be required when high force springs are used for high viscosity drugs or small needle diameters). 
         [0051]    Thus, under the forward driving force of the springs  40 ,  42  of the actuation mechanism (possibly reinforced by direct force from the trigger button  70  on the end of the plunger  60 ) the enlarged head  66  may be forced through the aperture  54  by flexing the segments of the latch member  50  radially outwardly. Advantageously, the enlarged head  66  is profiled along its axial length to assist its transition through the aperture  54 . In particular, the forward portion  67  of the enlarged head  66  has a rearwardly outwardly tapering profile which acts to cam the segments of the latch  50  radially outwardly as the plunger moves forward. The rearward portion  68  of the enlarged head has a rearwardly inwardly tapering profile which helps to ensure that the head  66  will smoothly leave the aperture  54  without being caught by any resilient spring back of the latch member  50  (which would instead only act to cam the head through the aperture). 
         [0052]    Once the plunger is released (as shown in  FIGS. 4( c ) and 4( d ) ), the first spring  40  expands to extend the syringe  20  so that the needle  24  penetrates the flesh. Initially, the second spring  44  typically remains substantially fully compressed, with the plunger  28  bearing against the piston  20  within the syringe but not moving it relative to the syringe (for example due to the compressibility of the medicament therein). Once the syringe has been moved to its fully forward position the second spring  44  may act between the a circumferential rib  62  on the forward part of a plunger  60  and the intermediate member  42  to drive the plunger  28  forward and dispense the medicament through the needle  24 . It may be noted that during this second phase the second spring  44  extends into the barrel  22  of the syringe  20  along with the plunger  60 , this is advantageous in reducing the overall size of the injector device. The taper leading to the enlarged latching head of the plunger ensures that the plunger does not catch on the second spring at this point. 
         [0053]    Although the invention has been described above with reference to a preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, the latch member may be split into any convenient number of segments and, for example at least one boss may be provided on each section. Alternatively or additionally, the bosses may be omitted from the latch member and the trigger may simply abut a portion of the latch surface in the primed position. Alternatively, the boses and cut-outs may for example be reversed without substantially altering their function of blocking/freeing the radial movement of the latch member. Thus in some embodiments inwardly extending projections (such as boses) could be formed on the trigger which abut a surface of the latch member in the primed position and move out of alignment (for example by moving into alignment with a cut-out on outer surface of the latch) with in the release position. In some embodiments the device may be a single use device and, for example, the syringe may be integrally formed with the housing.