Abstract:
An injection device  110  is described having a housing  112  and a cap  130 . The injection device  110  houses a syringe  114  having a needle which is sealed by a boot  118 . The cap  130  is arranged so that the boot  118  can be connected to the cap  130  while exerting a minimal force on the syringe, but cannot be removed from the cap  130  without applying a significantly greater force to the syringe. The housing  112  and cap  130  are arranged so that upon removal of the cap  130  from the housing  112 , the boot  118  is removed from the syringe  114.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an injection device of the type that receives a syringe, extends it, discharges its contents and then retracts it automatically. 
     BACKGROUND OF THE INVENTION 
     Devices of this general description are shown in WO 95/35126 and EP-A-0 516 473 and tend to employ a drive spring and some form of release mechanism that releases the syringe from the influence of the drive spring once its contents are supposed to have been discharged, to allow it to be retracted by a return spring. 
     Often, such injection devices are required to work with sealed hypodermic syringes which typically have a hermetically sealed cover or “boot” that covers the hypodermic needle and maintains the sterility of the syringe contents. The boot may be formed from a rubber material. Naturally, it is necessary to maintain the sterility of the syringe contents up to the point of administration, which means that the boot must be removed with the syringe inside the injection device. 
     Typically, the action required to remove the boot from the syringe entails either pulling the boot away from the syringe or twisting the boot and pulling it away from the syringe. If a filled syringe has been around for quite a while before it is used, it is often difficult to remove the boot from the syringe; a substantial force is often required. 
     The injection device may be designed so that removal of a cap of the injection device also removes the boot from the syringe. In such cases, the boot must be connected to the cap in such a way that the force required to remove the boot from the syringe is less than the force required to disconnect the boot from the cap. In order to connect the boot to the cap, an “insertion” force is exerted on the syringe. If this insertion force is too high, damage to the syringe and/or boot will occur, and the injection device will fail to operate correctly. The force required to remove a boot from a syringe is generally an order of magnitude greater than the maximum insertion force that can be exerted on the syringe via the boot without causing damage to the boot and/or syringe. 
     Therefore, there is a need for a means for connecting a cap of an injection device to a boot of a syringe in such a way that removal of the cap from the injection device causes removal of the boot from the syringe, and connection of the cap to the boot exerts a minimal force on the syringe and/or boot. 
     SUMMARY OF THE INVENTION 
     The methods and apparatus of the present invention are designed to address this need. 
     The present invention provides a cap for an injection device, the cap comprising: 
     a first part having a first end for receiving an injection device and a second end, the first part defining a first axis and having grip means for gripping the boot of a syringe, wherein the grip means is movable from a first position to a second position, the second position being further from the first axis than the first position; and 
     a second part having retention means arranged such that movement of the retention means from a third position to a fourth position prevents the grip means from moving from the first position to the second position. 
     The first part may include a pair of arms, each arm having a first end and a second end, wherein the grip means is formed at a first end of each arm, the first ends of the arms being closer to the first end of the cap than the second ends of the arms. The grip means may comprise a hooked end portion. Each arm may be formed from a segment of a cylinder. When the grip means is in the first position, the first ends of the arms may be closer to the first axis than when the grip means is in the second position. The arms may be arranged so that the axis of the cylinder from which each arm is formed is substantially parallel to the first axis when the grip means is in the first position. 
     The movement of the retention means from the third position to the fourth position may be in a direction substantially parallel to the first axis. The retention means may comprise a ring shaped portion. The internal diameter of the ring shaped portion may be less than the distance between the first ends of the arms when the grip means is in the second position. When the retention means is positioned in the fourth position, the ring shaped portion may surround the first ends of the arms. Once the retention means has been moved from the third position to the fourth position, the retention means may prevent the grip means from moving from the first position to the second position. The ring shaped portion may have one of a groove and a ridge formed on an inner surface thereof. The arms of the first part may have the other of the groove and the ridge formed on an external surface and proximal to the first end thereof, such that when the retention means is positioned in the fourth position, the ridge on one of the first and second parts of the cap is positioned within the groove on the other of the first and second parts of the cap. 
     In a first embodiment, the second part may comprise a pair of legs, wherein a first end of each of the pair of legs is connected to the ring shaped portion. Each of the pair of legs may have a foot at a second end thereof. The second end of the first part of the cap may be provided with one or more apertures therethrough. When the retention means is in the third position, each leg may extend through one of the apertures. When the retention means is in the fourth position, each of the feet may be positioned within one of the apertures. The retention means may be moved from the third position to the fourth position by applying a force to the foot of each leg, thus forcing the legs through the apertures, the ring shaped portion from the third position to the fourth position and the grip means from the first position to the second position. 
     In a second embodiment, the second part may comprise a cylindrical member having the retention means at a first end thereof, and a foot at a second end thereof. The cylindrical member may be provided with a pair of opposing apertures through which the arms of the first part may extend. The second end of the first part of the cap may be provided with a central aperture therethrough. When the retention means is in the third position, the foot of the second part may protrude through the central aperture, and when the retention means is in the fourth position, the foot may be positioned within the first part of the cap or flush with the second end of the first part of the cap. 
     In either embodiment, the second part of the cap may further be provided with a movable protrusion which can communicate with a corresponding ridge proximal to the second end of the first part of the cap. The movable protrusion and the ridge function to maintain the second part in the third position until a force is applied to the foot or feet of the second part. The movable protrusion may be positioned proximal to the second end of the second part of the cap. 
     The cap may further comprise an external feature with which a user can grip the cap. 
     The present invention also provides an injection device comprising: 
     a housing containing a syringe having a discharge nozzle and a boot that covers its discharge nozzle, wherein the boot extends from a first end of the housing through an exit aperture; and 
     a cap as recited above. 
     When the first part of the cap includes a pair of arms, each arm having a first end and a second end, and when the grip means is formed at a first end of each arm, the first ends of the arms being closer to the first end of the cap than the second ends of the arms, then the diameter of the boot may be more than the distance between the grip means at the first end of each arm when the grip means is in the first position so that movement of the grip means from the second position to the first position causes the cap to be connected to the boot, and removal of the cap from the housing when the grip means is in the second position causes removal of the boot from the syringe. 
     The force required to remove the boot from the syringe may be less than the force required to disconnect the boot from the cap when the grip means is in the first position and the retention means is in the fourth position. 
     The force required to disconnect the boot from the cap when the grip means is in the first position and the retention means is in the fourth position may be an order of magnitude greater than the force required to insert the boot into the cap when the grip means is in the first position and the retention means is in the third position. 
     The present invention also provides a method of attaching a cap to a boot of a syringe comprising: 
     providing a cap comprising: 
     a first part having a first end for receiving an injection device and a second end, the first part defining a first axis and having grip means for gripping the boot of a syringe, and 
     a second part having retention means, wherein 
     the grip means is arranged in a first position and the retention means is arranged in a third position; 
     inserting a boot of a syringe into the cap so that the grip means moves from the first position to a second position, the second position being further from the first axis than the first position, 
     inserting the boot of the syringe further into the cap so that the grip means moves from the second position to the first position, and the boot is gripped by the grip means; and 
     moving the retention means from the third position to a fourth position, thus preventing the grip means from moving from the first position to the second position, such that the boot cannot be removed from the cap. 
     When the first part includes a pair of arms, each arm having a first end and a second end, and the grip means is formed at a first end of each arm, the step of inserting the boot into the cap may comprise positioning the boot between the grip means at the first ends of each arm. 
     The first part and the grip means may be moulded as a single item. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a plan view of an injection device including a cap according to a first embodiment of the present invention; 
         FIG. 2  shows a perspective view of the injection device of  FIG. 1 ; 
         FIG. 3  shows a perspective view of a syringe for use in an injection device according to the present invention; 
         FIG. 4  shows a perspective view of the syringe of  FIG. 3  when connected to a cap according to a first or a second embodiment of the present invention; 
         FIG. 5  shows a perspective view from a first direction of a cap according to a first embodiment of the present invention; 
         FIG. 6  shows a perspective view from a second direction of a cap according to a first or a second embodiment of the present invention; 
         FIG. 7  shows a perspective view of a second part of a cap according to a first embodiment of the present invention. 
         FIG. 8  shows a perspective view from a first direction of a cap according to a second embodiment of the present invention; 
         FIG. 9  shows a perspective view of a second part of a cap according to a second embodiment of the present invention; 
         FIGS. 10   a  and  10   b  show cut-away views of a cap according to a second embodiment of the present invention with the second part of the cap positioned in third and fourth positions respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an injection device  110  according to the present invention. The injection device has an injection device housing  112 . 
     The housing  112  contains a hypodermic syringe  114  of conventional type as shown in  FIG. 3 . The syringe includes a syringe body  116  defining a reservoir and terminating at one end in a hypodermic needle. The syringe  114  has a hermetically sealed cover or “boot”  118  that covers the hypodermic needle and maintains the sterility of the syringe contents. The boot is generally formed of a soft rubber or plastics material. Whilst the syringe illustrated is of hypodermic type, this need not necessarily be so. Transcutaneous or ballistic dermal and subcutaneous syringes may also be used with the injection device of the present invention. 
     The injection device is further provided with a cap  130 . The cap comprises a first part  132  and a second part  134 . 
     According to a first embodiment of the invention, as shown in  FIGS. 1 ,  2  and  4  to  7 , the first part  132  has a first end  136  for attachment to the housing  112  of the injection device  110 . The first part  132  also includes grip means  139  for gripping the boot  118  of the syringe  114 . The first part  132  includes a pair of arms  138 , each having a first end and a second end. The grip means  139  are formed at the first end of each arm  138 . Each arm  138  is formed from the segment of a cylinder. The arms  138  and grip means  139  are movable from a first position to a second position wherein the second position is further away than the first position from a first axis A-A defined by the first part  132  of the cap  130 . 
     The second part  134  includes retention means for retaining the grip means  139  in the first position. The retention means comprises a ring-shaped portion  140 . The internal diameter of the ring shaped portion  140  is less than the distance between the first ends of the arms  138  when the arms  138  are in the second position. The retention means is movable in a direction parallel to the axis A-A from a third position to a fourth position. When the retention means is in the third position, the ring shaped portion  140  surrounds the second end of the arms  138 . When the retention means is in the fourth position, as shown in  FIGS. 1 to 6 , the ring shaped portion  140  is proximal to the grip means  139  and prevents the arms  138  from moving into the second position. 
     The second part  134  also includes a pair of legs  142 . A first end of each leg  142  is connected to the ring shaped portion  140 . Each leg has a foot  144  at a second end thereof. 
     The second end of the first part  132  of the cap  130  is provided with a pair of apertures  146 . When the retention means is in the fourth position, as shown in  FIGS. 1 to 6 , the feet  144  are positioned within the apertures  146 . When the retention means is in the third position, the legs  142  extend through the apertures  146  and the ring shaped portion  140  is close to the second end of the first part  132  of the cap. In order to move the second part  134  from the third position to the fourth position, a force is applied to each foot  144 . The legs move through the apertures  146  until the feet are positioned within the apertures  146 . With this movement, the ring shaped portion  140  slides along the arms  138  until it is proximal to the first end of the arms  138 , thus preventing the arms  138  from moving from the first position, away from the axis A-A, towards the second position. 
     During manufacture of the injection device  110 , the syringe  114  and boot  118  are inserted into the housing as a single piece. In order to attach the cap  130  to the boot  118 , the cap  130  is provided with the arms  138  in the first position and the ring shaped portion  140  in the third position, such that the legs  142  extend through the apertures  146 . The cap  130  is then placed on the housing  110 . As the cap  130  is pushed onto the housing, the boot  118  forces the arms  138  from the first position to the second position until the grip means reach the end of the boot  118  at which point the arms  138  spring from the second position to the first position. Consequently, the boot ends up positioned between the legs  138  of the first part  132 . A force is then applied to the feet  144 , which, in turn, pushes the ring shaped portion  140  down the outside of the arms  138 , until the ring shaped portion is proximal to the first end of the arms  138 , thus preventing the arms  138  from moving from the first position, away from the axis A-A, towards the second position. 
     According to a second embodiment of the invention, as shown in  FIGS. 1 ,  4 ,  6  and  8  to  10 , the first part  132  has a first end  136  for attachment to the housing  112  of the injection device  110 . The first part  132  also includes grip means  139  for gripping the boot  118  of the syringe  114 . The first part  132  includes a pair of arms  138 , each having a first end and a second end. The grip means  139  are formed at the first end of each arm  138 . Each arm  138  is formed from the segment of a cylinder. The arms  138  and grip means  139  are movable from a first position to a second position wherein the second position is further away than the first position from a first axis A-A defined by the first part  132  of the cap  130 . 
     The second part  134  includes retention means for retaining the grip means  139  in the first position. The retention means comprises a ring-shaped portion  140 . The internal diameter of the ring shaped portion  140  is less than the distance between the first ends of the arms  138  when the arms  138  are in the second position. The retention means is movable in a direction parallel to the axis A-A from a third position, as shown in  FIG. 10   a , to a fourth position, as shown in  FIG. 10   b . When the retention means is in the third position, as shown in  FIG. 10   a , the ring shaped portion  140  surrounds a central portion of the arms  138 . When the retention means is in the fourth position, as shown in  FIG. 10   b , the ring shaped portion  140  is proximal to the grip means  139  and prevents the arms  138  from moving into the second position. 
     The ring shaped portion  140  has a groove  150  formed on its inner surface. The arms  138  of the first part  132  have a corresponding ridge  152  formed on an external surface, proximal to the first end of the arms  138 . When the retention means is positioned in the fourth position, as shown in  FIG. 10   b , the ridge  152  on the arms  138  is positioned within the groove  150  on the ring shaped portion  140 . 
     The second part  134  comprises a cylindrical member with the retention means at a first end thereof, and a foot  144  at a second end thereof. The cylindrical member is provided with a pair of opposing apertures  160  through which the arms  138  of the first part extend. 
     The second end of the first part  132  of the cap  130  is provided with a central aperture  146 . When the retention means is in the third position, as shown in  FIG. 10   a , the foot  144  of the second part  134  protrudes through the central aperture  146 . When the retention means is in the fourth position, as shown in  FIG. 10   b , the foot  144  is positioned within the first part of the cap. 
     The second part  134  of the cap is further provided with a movable protrusion  154  which can communicate with a corresponding ridge  156  proximal to the second end of the first part  132  of the cap. The movable protrusion  154  and the ridge  156  function to maintain the second part  134  in the third position until a force is applied to the foot  144  of the second part  134 . 
     In order to move the second part  134  from the third position to the fourth position, a force is applied to the foot  144 . The movable protrusions  154  move towards the axis A-A and ride over the ridge  156 . The apertures  160  move over the arms  138  until the groove  150  on the ring-shaped portion  140  engages the ridge  152  on the arms  138  and the foot  144  is positioned within the first part  132  of the cap. With this movement, the ring shaped portion  140  slides along the arms  138  until it is proximal to the first end of the arms  138 , thus preventing the arms  138  from moving from the first position, away from the axis A-A, towards the second position. 
     During manufacture of the injection device  110 , the syringe  114  and boot  118  are inserted into the housing as a single piece. In order to attach the cap  130  to the boot  118 , the cap  130  is provided with the arms  138  in the first position and the ring shaped portion  140  in the third position, such that the foot  144  protrudes from the aperture  146 . The cap  130  is then placed on the housing  110 . As the cap  130  is pushed onto the housing, the boot  118  forces the arms  138  from the first position to the second position until the grip means reach the end of the boot  118  at which point the arms  138  spring from the second position to the first position. Consequently, the boot  118  ends up positioned between the legs  138  of the first part  132 . A force is then applied to the foot  144 , which, in turn, pushes the ring shaped portion  140  down the outside of the arms  138 , until the groove  150  and ridge  152  engage and the ring shaped portion  140  is proximal to the first end of the arms  138 , thus preventing the arms  138  from moving from the first position, away from the axis A-A, towards the second position. 
     In both embodiments, when the injection device  110  is to be used, the user holds the housing  112  with one hand, and grips the cap  130  with the other hand using the grip surfaces  170 . The user then pulls the cap  130  away from the housing  112 . The grip means  139  grip the boot  118  and, in pulling the cap  130  away from the housing  110 , the boot  118  is also removed from the syringe  114 . 
     The force required to remove the boot  118  from the syringe  114  is significantly less than the force required to disconnect the boot  118  from the cap  130  when the grip means is gripping the boot  118 . 
     The force required to disconnect the boot  118  from the cap  130  when the grip means is gripping the boot is significantly greater than the force required to insert the boot  118  into the cap  130  when the retention means is in the third position. For example, the force required to insert the boot between the arms  138  when the retention means is in the first position is less than 1N, whereas the force required to remove the cap  130  from the boot  118  when the retention means is in the fourth position is of the order of 60N. 
     The exterior of the cap  130  is provided with a pair of grip surfaces  170 . These grip surfaces  170  provide a surface through which the user can grip the cap  130 . 
     The present invention provides a simple and effective way of solving the problems of the prior art devices. Since no modifications need to be made to the syringe or boot, a standard syringe can be used, and manufacturing costs can be reduced. 
     It will of course be understood that the present invention has been described by way of example, and that modifications of detail can be made within the scope of the invention as defined by the following claims.