GB2622883A

GB2622883A - Plunger and injection device

Info

Publication number: GB2622883A
Application number: GB2214450.5A
Authority: GB
Inventors: Ken Cowe Toby; Mollie Katie Moore Aylish
Original assignee: Owen Mumford Ltd
Current assignee: Owen Mumford Ltd
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2024-04-03
Also published as: GB202214450D0; WO2024068955A1

Abstract

A plunger 70 for an injection device comprises two components or portions, the first portion 71 having two configurations. In its first configuration, the first portion engages the second portion 79 to prevent or restrict their relative movement. In a second configuration, they are disengaged to allow relative movement. The first component may have flexible arms (78, fig. 2; 178, fig. 5) with teeth or abutments engaging a receiving part (79a, fig. 3; 181, fig. 5) of the second component, and may be deflected radially inward or outward to disengage the components and allow axial collapse or shortening of the plunger. The relative movement may be damped or speed-limited via complementary screw threads or by foam or viscous fluid, e.g. flowing between chambers in the two components. A sleeve 100 may hold the first component in engagement with the second component, and either the flexible arms or the sleeve may be disengaged by a medicament container as the plunger is driven along the injection device.

Description

PLUNGER AND INJECTION DEVICE

Technical field

The present disclosure relates to plunger and an injection device.

Background

One of the most common routes of administration for medications is by injection, such as intravenous, subcutaneous or intramuscular injection. A syringe containing the medication is used for the injection, which typically is carried out by trained medical personnel. In certain instances, a patient is trained in the use of the syringe to allow for self-injection. Moreover, certain medications are formulated in pre-filled syringes for patient use, to avoid the need for the patient to fill the syringe. Some patients, however, may be averse to carrying out self-injection, particularly if the patient has a fear of needles. Automatic injection devices offer an alternative to a syringe for delivering a medication.

Summary of the Invention

Aspects and embodiments of the invention provide a plunger and an injection device as claimed in the appended claims.

According to an aspect of the present invention there is provided a plunger for an injection device comprising a first portion and a second portion. The first portion having a first configuration and a second configuration; wherein, in the first configuration, the first portion engages the second portion such that relative motion of the first and second portions is prevented and in the second configuration the first portion is disengaged from the second portion such that the first and second portions can move relative to one another.

In this way, the true end of dose notification can occur because a part of the plunger continues moving after the front of the plunger reaches the front of the medicament container. The continued movement allows a delay to the end of dose notification to be equivalent to the amount of time to allow for drug dispersal in the injection site.

The first portion may include flexible arms configured to engage with the second portion.

The second portion may include a receiving portion configured to receive at least a portion of the flexible arms. The receiving portion may be an abutment surface arranged to be contacted by an abutment surface of the flexible arms or a groove configured to receive a projection on the flexible arms.

The flexible arms may be arranged to flex towards the central axis of the first portion thereby to move the abutment surface of the flexible arms away from the abutment surface of the second portion thereby disengaging the first and second portions.

Alternatively the flexible arms may be arranged to flex away from the central axis of the first portion to move the projection away from the groove thereby disengaging the first and second portions.

The plunger may also include a third portion configured to maintain the first portion in the first configuration.

The third portion may be a sleeve disposed around one of the first and second portions, the sleeve being slideable between a position in which it surrounds the first portion such that the flexible arms cannot move away from the central axis, and a position in which it does not surround the first portion, permitting the flexible arms to move outwardly so as not to engage the second portion. The first portion may include a ramped latch and the second portion may include a groove.

The third portion may be an insert disposed within one of the first and second portions, the insert being slideable between a position in which it prevents the flexible arms of the first portion from moving towards the central axis, and a position in which it does not prevent the flexible arms of the first portion movig towards the central axis. This permits the flexible arms to move inwardly so the abutment portions are no longer in contact allowing relative movement of the first and second portions.

The plunger may include means to control the speed of relative movement of the first and second portion.

For example, the first and second portions may have complementary screw threads. The pitch of the thread may be selected to provide the optimal speed of collapse. The optimal speed of collapse may be determined by the delay required to signal the true end of dose.

Optionally, the means to control the speed may also include a damping means. The damping means may be a viscous fluid such as a smart grease disposed on the screw threads. Alternatively, the damping means may be a foam disposed between the first and second portions such that the foam is compressed during relative movement of the first and second portions. Alternatively, the damping means may comprise fluid means. The fluid means being disposed initially between the first portion and the second portion.

The second portion being provided with a compartment into which the fluid can enter via an aperture. Movement of fluid into the compartment acting to damp the speed of relative motion between the first and second portions.

In another embodiment there is provided an injection device including a housing, a medicament container configured to hold a substance to be injected, a plunger as described above and a drive means for exerting a force on the plunger.

In use, the drive means moves the plunger in the first configuration forward to dispense medicament. Forward movement of the plunger causes the flexible arms to come into contact with the medicament container. This contact moves the flexible arms towards the central axis of the first portion thereby moving the flexible arms out of engagement with the abutment surface moving the first portion into the second configuration.

Alternatively, in use the drive means moves the plunger in the first configuration forward.

The third portion, on contact with the slides medicament container moving from a position in which it surrounds the first portion such that the flexible arms cannot move away from the central axis, and a position in which it does not surround the first portion, permitting the flexible arms to move outwardly so as not to engage the second portion.

According to another aspect, there is provided a method of injecting a substance into an injection site using an injection device, the method comprising exerting a force on a syringe via a plunger as described above to urge the substance in a container of the syringe out through the needle.

The skilled person will understand that any one of the above features described above may be incorporated into any of the other aspects of the invention either separately or together.

Brief description of the drawings

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an exploded illustration of the collapsible plunger according to a first embodiment Figure 2 shows two different exterior views of a first part of the collapsible plunger; Figure 3 shows two different exterior views of a second part of the collapsible plunger; Figure 4 shows the sleeve;Figure 5 illustrates an alternative embodiment of a collapsible plunger; Figure 6 shows two different cross sections (orthogonal to each other) through an injection device according to the present invention, in a default state (unactuated); Figure 7 shows the two different cross sections through the injection device with the needle cap removed; Figure 8 shows the two different cross sections through the injection device with the actuator (firing) cap removed; Figure 9 shows the two different cross sections through the injection device immediately after the device has been fired; Figure 10 shows the two different cross sections through the injection device with the needle extended; Figure 11 shows the two different cross sections through the injection device mid substance delivery; Figure 12 shows the two different cross sections through the injection device towards the end of delivery, as the plunger starts to collapse; Figure 13 shows the two different cross sections through the injection device with the plunger collapsed; Figure 14 shows the two different cross sections through the injection device with the driver released; Figure 15 shows the two different cross sections through the injection device with the shroud extended; and Figure 16 shows the intermediate driver and the shroud;

Detailed description

The present invention relates to a plunger for an injection device, an injection device, components thereof, and methods for injecting a substance, such as a liquid drug or vaccine, into a patient to manage or cure a medical condition. In one embodiment, the automatic injection device is a pen, i.e., an autoinjector pen or autoinjection pen (used interchangeably herein).

Figure 1 illustrates an embodiment of the plunger according to the present invention. The plunger 70 is a collapsible plunger which includes a first portion 71 and a second portion 76, each having a generally elongate form, and being movable linearly and coaxially with respect to each other to vary the total length of the plunger 70. As will be explained below, the plunger 70 is configured, in use, to collapse during delivery of the substance from a cartridge or syringe 53. The first and second portions 71, 76 of the plunger 70 are shown in Figures 2 and 3 respectively.

Referring first to Figure 2, the first portion 71 of the plunger is shown. This can be seen to have a first end 71a which may be integral with, connected to or in communication with a bung 54 in a cartridge or syringe. The first end 71a may selectively apply pressure to the bung 54 to expel the dose from syringe through the needle 55. The first portion 71 comprises an internally (screw/helically) threaded barrel 77, and a pair of opposed ramped latches 78. The first portion 71 of the plunger 70, and particularly the barrel 77, comprises a through bore to receive a portion of the second portion 76 of the plunger 70.

Each latch 78 comprises a flexible arm and a projection which is directed internally into the through bore of the barrel 77.

Turning to Figure 3, the second portion 76 of the plunger 70 can be seen to include a flanged second end 72. The second portion 76 also comprises an externally (screw/helically) threaded shaft 79, for complementary engagement with the barrel 77 of the first portion 71. The screw threading need only be provided along a portion of the shaft 79, and need not extend continuously around the shaft 79. At one end of the shaft 79 a groove 79a is provided, as part of a retaining mechanism along with the ramped latches 78, for retaining the first and second portions 71, 79 together. Adjacent to the shaft 79, the second portion 76 is provided with a main body having a proximal portion 73 and a distal portion 74 having differing external diameters and connected by an angled portion 75. Optionally, the external diameter of the proximal portion 73 is greater than the distal portion 74 of the second portion 76.

In use, in a first configuration the projection on each of the ramped latches 78 engages with the groove 79a of the second portion 76. When the ramped latches 78 are engaged with the groove 79a relative movement of the first and second portions 71, 76 is prevented when force is exerted on the plunger. When the ramped latches 78 disengage from the groove 79a the force exerted on the plunger 70 causes the first and second portions 71, 76 to collapse towards each other under certain conditions which will be explained below. The collapse takes the form in the present embodiment of the first and second portions 71, 76 rotating with respect to each other about their common longitudinal axis as the threaded shaft 79 screws into the threaded barrel 77.

Optionally, the speed with which the first and second portions move relative to each other may be moderated. For example, the screw threading of the barrel 77 and shaft 79 may be provided with a coating of a viscous fluid such as a smart grease. The viscous fluid acts to damp the speed at which the two threads move relative to one another. Alternatively, or additionally the angle of pitch of the threads of the first and second portions may be selected to provide the desired speed of collapse of the plunger.

In another embodiment the end 71a of the first portion may be provided with an end wall and foam may be placed abutting within the through bore adjacent to or near the end wall. The foam is compressed by the forward motion of the second portion when the first and second portions are moving relative to one another thereby retarding the forward motion of the second portion.

In yet another embodiment the end 71a of the first portion is provided with an end wall. Additionally, the front end 79a of the second portion is provided with an aperture and within the second portion there is provided a compartment. Fluid is placed within front end of the first portion. Release of the projections allowing forward motion of the second portion causes fluid to pass from the first portion to the second portion through the aperture in the front end 79a of the second portion. This movement of fluid may be used to moderate the velocity of the forward movement of the second portion. Further moderation may be attained by selection of a fluid of desired viscosity.

A sleeve 100, illustrated in Figure 4, serves to maintain the engagement of the ramped latches and the groove 79a by preventing outward movement of the flexible arms. This prevents the first and second portions 71, 76 of the plunger 70 from collapsing. When the plunger 70 reaches a predetermined point in in delivery, and then permits the collapse. The sleeve can be seen to comprise a main, hollow, body 102, and a lip or flange 104. The sleeve 100 is disposed, in use, around the first portion 76, and initially (as shown in Figures 1 to 6) around and over the ramped latches 78. This causes the ramped latches 78 to engage with the groove 79a on the second portion 76, thereby inhibiting the flexible arms from moving outwards thereby maintaining engagement of the projections with the groove thus inhibiting the first and second portions from moving with respect to each other.

In use, the sleeve 100 moves with the plunger 70 during delivery of the medication shown and described in Figures 6 to 11 below, until the lip 104 comes into contact with the flange 56 of the syringe or cartridge. The contact of the lip 104 with the flange 56 prevents any further forward movement of the sleeve 100. Further forward movement of the plunger 70 moves the the ramped latches 78 out of engagement with the sleeve 100. This allows the ramped latches 78 to move outwardly and disengage from the groove 79a. Disengagement of the ramped latches 78 and the groove 79a allows relative movement of the first and second portions of the plunger 70 and thereby allowing collapse of the plunger 70 to commence.

It will be appreciated that, in order for the plunger 70 to collapse, the force required to cause the first and second portions 71, 76 to move towards to each other via a screwing action is required to be less than the force required to expel the substance from the syringe 50.

Although the present invention has been described with reference to the first portion 71 of the plunger 70 being received within the second portion 76 of the plunger 70 the skilled person would understand that alternative configurations are possible for example the second portion 76 of the plunger 70may be situated within the first portion 71 of the plunger 70 An alternative embodiment of the present invention will now be described with reference to Figure 5. In this embodiment like features are provided with like reference numbers.

In the alternative embodiment the second portion 176 of the plunger 170 is provided with two rearwardly extending flexible arms 178. Each of the flexible arms 178 is provided with an abutment surface 180 that engages with a corresponding abutment surface 181 on a first portion 171 of the plunger 170. Relative movement of the first and second portions 171, 176 of the plunger 170 is prevented when the abutment surfaces 179, 181 are engaged with one another.

The second portion 176 is further provided with a head 177a and an elongate body 177. The head 177a has a diameter greater than the body 177 of the second portion 176. The head 177a is further provided with an external screw thread 177b.

The first portion 171 of the plunger 170 is provided with a wall 173 defining an aperture.

The internal surface of the aperture is provided with a complementary screw thread 173b to the screw thread 177b of the head 177a of the second portion 176.

In use, the plunger is in an initial configuration where the first and second abutment surfaces are engaged with one another. As the plunger moves forward the flexible arms come into contact with the body of the syringe or cartridge. This moves the flexible arms inwards and out of engagement with the abutment surface of the first portion. This allows relative movement of the first and second portions and thus, collapse of the plunger.

As described with reference to the first embodiment the speed with which the collapse occurs may be varied using one or more of a viscous fluid, pitch angle of the screw thread or any other suitable means.

The skilled person will understand that although the first portion 71, 176 of the plunger has been described as having a pair of opposed latches or flexible arms, any suitable number of latches may be provided on either of the above embodiments. Further although relative movement of the first and second portions has been described as being prevented through the use of the latches the skilled person will understand that other suitable mechanisms for selectively preventing relative movement of the first and second portions may be provided.

An injection device including a plunger according to the first embodiment described above is described herein with reference to Figures 6 to 15. Figures 6 to 15 show the injection device as a whole, in cross sections (two different orthogonal cross sections per Figure), at various different stages of an actuation sequence of the device. Figure 1 is provided with reference numerals labelling the parts. In the interests of clarity the same parts are not labelled in Figures 7 to 15, but are readily discernible.

With reference to Figure 6, which shows the device in a default, unactuated state with protective caps disposed thereon, the injection device 10 includes a housing 12 for housing a container, such as a syringe, containing a dose of a substance to be injected.

The housing 12 preferably has a tubular configuration, though the housing 12 may have any suitable size, shape and configuration for housing a syringe or other container of a substance to be injected. While the invention will be described with respect to a syringe mounted in the housing 12, one skilled in the art will recognize that the automatic injection device 10 may employ any suitable container for storing and dispensing a substance.

References to radial and axial in this specification should be taken in relation to the longitudinal axis unless otherwise stated. The term axis can be taken to be the longitudinal axis of the device unless otherwise stated or obvious from the context. The normal of the longitudinal axis is taken to be perpendicular to the longitudinal axis.

The syringe is preferably slidably mounted in the housing 12, as described in detail below. In an inactivated position, the syringe is sheathed and retracted within the housing 12. When the device is actuated, a needle of the syringe projects from a first (proximal) end 20 of the housing 12 to allow ejection of a substance from the syringe into a patient.

As shown, the first end of the housing 20, i.e., the proximal end, includes an opening through which the needle of the syringe projects during actuation of the device 10.

A second (distal) end 30 of the housing 12, i.e., the distal end, includes an activation button 32 for actuating the syringe to move from a sheathed position within the housing 12 to a projecting position, and subsequently to expel the substance from the needle into the patient. The housing 12 houses one or more actuators that perform the functions of moving the syringe and expelling the substance from the syringe.

A first removable cap 24 (or needle cap) for covering the first end 20 of the housing 12, to prevent exposure of the needle in the syringe prior to use. A second removable cap 34 (or actuator cap) covers the second end 30 of the housing 12 to prevent accidental actuation of the activation button 32.

A syringe 50 or other suitable container for a substance is disposed within the interior of the housing 12. The illustrative syringe 50 includes a hollow barrel portion 53 for holding a dose of a liquid substance to be injected. The illustrative barrel portion 53 is substantially cylindrical in shape, though one skilled in the art will recognize that the barrel portion 53 may have any suitable shape or configuration. A seal, illustrated as a bung 54, seals the dose within the barrel portion 53. The syringe 50 may further include a hollow needle 55 connected to and in fluid communication with the barrel portion 53, through which the dose can be ejected by applying pressure to the bung 54. The hollow needle 55 extends from a proximal end of the barrel portion 53. The distal end of the barrel portion 53 includes a flange 56. The skilled person will recognize that the invention is not limited to the illustrative embodiment of the syringe 50 and that any suitable container for containing a dose of a substance to be injected may be used in accordance with the teachings of the invention.

The syringe 50 is received within a syringe carrier 40 which is slidably disposed within the housing 12. The syringe carrier 40, at its distal end, is provided with an abutment surface arranged to engage with the flange 56 of the syringe. At its proximal end the syringe carrier is provided with one or more flexible projections 44. The syringe 50 rests in the carrier 40, and both are contained in the housing 12. The syringe carrier 400 may have any suitable configuration and size suitable for carrying or guiding the syringe 50 within the housing 12.

The injection device further includes an actuation mechanism, including a plunger 70, an intermediate driver 80 and biasing means. In the present invention the biasing means is a compression spring 88, although it will be understood that any suitable means for biasing the plunger and intermediate driver 80 distally.

The actuation mechanism selectively moves and actuates the syringe 50 to inject the dose contained in the syringe 50 into a user.

The intermediate driver 80 is provided with a cylindrical inner portion 81 and an outer portion 82 connected by a connecting portion 83. The circumference of the outer portion 81 is greater than that of the inner portion 81 and the outer portion 81 extends further distally than the inner portion. The connecting portion 83 and the compression spring 88 are configured such that, prior to use of the injection device, 10, the compression spring is engaged with the connecting portion 83 and biases the intermediate driver 80 distally. Additionally, prior to use the connecting portion 83 is situated such that it is in communication with the angled portion 75 of the plunger 70 such that any biasing force exerted on the intermediate driver 80 by the compression spring 88 is communicated to the plunger 70 and distally biases the plunger 70.

The activation button of the present embodiment retains the plunger 70 and first biasing means 88 in a retracted, latched position. In the illustrative embodiment, the flanged second end 72 of the plunger 70 extends through an opening in the distal end of the housing 12 and the flanges abut the external distal wall of the housing. The flanges are configured such that proximal pressure on the flanges causes the flanged end of the plunger to flex inwards and move through the opening in the distal end of the housing 12 thereby allowing the coil spring 72 to move the intermediate driver 80 and plunger distally. For example, the second flanged end 72 of the plunger 70 may comprise one or more proximally extending fingers provided with one or more flanges.

Any suitable alternative method of releasably retaining the distal end of the plunger 70 distally may be used. The activation means which may have any suitable size, shape, configuration and location suitable for releasing the plunger 70 or otherwise activating the device 10. The activation means may be an activation button 32 formed on a distal end 30 of the housing 12, or may comprise another suitable device, such as a latch, twist-activated switch and other devices known in the art. While the illustrative activation means is located towards a distal end 30 of the device 10, one skilled in the art will recognize that the activation means may be positioned in any suitable location on the device 10.

Figures 6 and 7 respectively illustrate the proximal end 20 of the injection device 10 before and after the first removeable cap 24 is removed from the device. In Figure 6 the first removeable cap 24 is engaged with the proximal end 20 of the injection device. An interior needle cover 22 sheaths the syringe needle 55.

The housing 12 is provided with at least one radial projection or abutment feature 14 which extends inwards towards the central longitudinal axis of the injection device 10.

The proximal end the syringe carrier is provided with one or more flexible projections 44 which engage the at least one radial projection 14 before the injection device 10 is activated. The engagement of the at least one radial projection 14 and the proximal ends of the one or more flexible projections 44 acts to retain the syringe carrier in its distal, pre-activation, position.

The first removeable cap 24 is provided with an inner wall 25 and an outer wall 26 having a greater diameter than the inner wall 25. The inner and outer walls 25,26 extend distally and are connected by a proximal end wall 27. The inner surface of the outer wall 26 is configured to engage with the outer surface of the proximal end of the housing 12 in any suitable manner. For example, the outer wall 25 may form a frictional engagement with the housing or be provided with a screw thread.

The inner wall 25 extends distally inside the proximal end of the housing and the proximal end of the syringe carrier. The outer surface of the inner wall 25 and the radial projection 14 are in contact when the first removeable cap 24 and housing 12 are engaged. The inner wall 25 is of sufficient rigidity to prevent the flexible projections of the syringe carrier flexing towards the central longitudinal axis of the injection device 10 and moving past the radial projection 14 when the first removeable cap 24 is engaged with the housing 12.This assists prevention of premature activation of the device by retaining the syringe carrier 24 in its distal pre-activation position.

The inner wall 25 may be provided with one or more projections 28 which extend inwardly towards the central longitudinal axis of the injection device 10. The projection(s) 28 are configured to engage with the a feature of the interior needle cover 22, for example, the distal end of the interior needle cover 22, such that removal of the first removeable cap 24 also causes removal of the interior needle cover 22 as shown in Figure 7. When the cap 24 is removed, the syringe needle 55 is exposed within the lumen 1012 of the housing 12. The cap 24 may also include an opening in a proximal end thereof.

Although the first removeable cap 24 has been described as having tubular walls the skilled person will understand that the cap may be any suitable shape to engage with the housing 12. Additionally the inner wall 25 may comprise one or more sections spatially separated. Further, although the first removeable cap 24 has been described as having an inner wall and an outer wall the skilled person will understand that the outer wall is optional.

To actuate the device the second removeable cap 34 is removed from the device, as shown in Figures. The injection device 10 can then be introduced to the injection site. Depressing the button 32 causes the flanged end of the plunger 70 to move inwards thereby causing the flanges to no longer be retained by distal wall of the housing 12.

This allows the spring 88, which has been retained in a compression state, to exert a proximal force on the intermediate driver 80.

As can be seen the connecting portion 83 of the intermediate driver 80 is provided with an inner angled surface on its proximal side which engages with the angled portion 74 of the plunger 70. The proximal end of the compression spring 88 is seated on the distal side of the flange and is received between the inner portion 81 and a part of the outer portion 82 which extends distally from the flange forming a seat for the proximal end of the compression spring 88.

As the compression spring 88 exerts a force on the distal side of the connecting portion 83 this force is transmitted through to the angled face of the connecting portion 83 which engages the angled portion 74 of the plunger rod 70 thereby moving the plunger rod 74 proximally. The force exerted on plunger 70 causes a force to be exerted on the syringe 50 via the bung 54 causing the flexible projections 44 of the syringe carrier 40 to be deflected inwardly and move past the abutment feature 14 and thus move proximally inserting the needle into the user.

Once the needle 55 has been inserted forward motion of the syringe carrier 40 and thus the syringe 50 is arrested by any suitable means meaning that further proximal movement of the plunger rod causes proximal movement of the bung 54 within the syringe 50 thereby causing medicament to be expelled from the container 18 through the needle 22.

In Figures 6 to 14 the intermediate driver 80 is held in a compressed formation by the housing 12. At least the outer portion is able to move from a compressed formation with a reduced diameter to a relaxed formation with an increased internal diameter. This may be achieved, for example, by providing one or more flexible fingers as the outer portion 82, at least part of the outer portion 82 being formed by a non-contiguous wall or by making the outer portion from at least two materials, one being more flexible than the other to allow the circumference of the outer portion to be reduced.

In the compressed formation the intermediate driver 80 has an inner circumference less than the outer circumference of the proximal portion 73 of the plunger rod 70 and thus engages the plunger rod 70 at the angled portion 75. In the relaxed formation the intermediate driver 80 has an inner circumference greater than the outer circumference of the proximal portion 73 of the plunger rod 70 and thus can move along the plunger rod, as shown in Figure 15.

The housing is provided with one or more supporting ribs (not shown) extending longitudinally down the inner surface of the housing. The ribs reduce the inner diameter of the housing thereby maintaining the intermediate driver 80 in the compressed configuration.

Any other suitable means may be used to reduce the inner diameter of the housing. For example, the thickness of the housing wall may be increased or annular projections or rings may be provided if the longitudinal distance between the annular projections is less than the length of the flexible part of the outer portion.

The inner diameter of the housing increases at a position where the intermediate driver 80 is to move to its relaxed formation and thus disengage from the plunger, as per Figure 15. This may be achieved by reaching the end of the inner supporting ribs, decreasing the thickness of the housing wall, ending the annular projections. In the present device the intermediate driver 80 disengages from the plunger 70 when the medicament has been delivered to the user i.e. when the bung 54 has reached the proximal end of the syringe 50. The skilled person will understand that any suitable position may be chosen.

Figure 14 shows the intermediate driver 80 reaching, for example, the end of the supporting ribs. When this occurs the outer portion can move outwards towards the relaxed position as illustrated in Figure 4b. The outer movement of the outer portion allows the angled surfaces of the plunger and the connecting portion to move past each other thereby disengaging the plunger 70 and intermediate driver 80. Thus the plunger 70 no longer has a proximal force being applied to it by the drive spring 88 and no longer moves forward. Additionally, drive spring 88 is still exerting a proximal force on the connecting portion of the intermediate driver 80 and thus the intermediate driver 80 continues to move proximally within the housing 12 of the injection device 10, to the position shown in Figure 15.

As the intermediate driver 80 continues to move proximally it contacts a shroud 90. As the intermediate driver is driven proximally by the drive spring 88 it also drives the shroud 90 proximally. The shroud and intermediate driver 80 are illustrated in more detail in Figure 11.

In Figure 16 it can be seen that the shroud 90 is provided with a shrouding portion 91 which has a contiguous wall to protect the user from the needle after the injection device has been used. The shroud is further provided with two rearwardly extending arms 92 configured to engage with the intermediate driver. Each of the two rearwardly extending arms 92 are provided with a recess 93 which receives the radial projection 14 or abutment feature and allows the shroud 90 to move proximally along the radial projection. The radial projection 14 may guide the direction of movement of the shroud 90; however, the skilled person would also understand that the arms 92 may be positioned in order that they do not engage with the radial projection 14.

The distal end of the shroud arms 92 and the proximal end of the outer portion 82 of the intermediate driver 80 are provided with engagement features 84, 94. The engagement features may be any suitable features designed to assist the engagement of the intermediate driver 80 and the shroud 90. For example, one of the intermediate driver 80 and the shroud 90 may be provided with a projection 84 and the other of the intermediate driver 80 and the shroud 90 is provided with a complementary recess 94 to receive the projection. As illustrated in Figure 10 the projections have a frusto-conical shape, however, the skilled person will understand any suitable shape may be used.

Additionally, in order to assist alignment of the distal end of the shroud arms 92 and the proximal end of the outer portion 82 an outer portion of the shroud arms and/or the outer portion may be received in a groove in the housing 12.

Each of the shroud arms 92 is further provided with flexible lateral arms 95. When the shroud 90 is at its proximal position the distal end of the lateral arms 95 abuts a feature in the housing 12 (not shown) thereby preventing the shroud 90 from being moved distally after the injection device has been used. The skilled person would understand that alternative methods of preventing the shroud from moving backwards may be The sequence of use shown in Figures 6 to 15 is now summarised. Starting from Figure 6, which shows a default state, firstly the needle cap is removed (Figure 7) and the actuator cap is removed (Figure 8). The injection device is then fired (Figure 9), with the result that the plunger is no longer locked in place and is able to move under the force applied by the compression spring 88. The plunger urged the syringe 50 forwards until the needle 55 projects from the housing 12 (and into an injection site), as shown in Figure 10. Once the needle is fully extended, the plunger continues to press against the syringe 50 (and more specifically the bung 54), which applies pressure to expel the substance in the syringe out through the needle 55, as shown in Figures 11 to 14. During this delivery of the substance, and as shown in Figures 11 to 14, the plunger 70 collapses.

Following the collapse of the plunger 70, delivery is complete, and the intermediate driver disengages from the plunger 70, to instead engage with the shroud 90, to urge it into place around the needle 50, as shown in Figure 15.

Considering Figures 11 to 14, detailing the collapse of the plunger, in more detail. In Figure 11, delivery of the substance is underway. At this stage the sleeve 100 around the plunger 70 is still in place and moving with the plunger 70, preventing collapse of the plunger. In Figure 12 the lip 104 of the sleeve 102 has come into contact with the flange 56, and is no longer covering the ramped latches 78. As a result, the latches 78 are not in engagement with the groove 79, and the plunger 70 has started to collapse. This commencement of collapse takes place prior to all of the substance having been expelled from the syringe 50. In Figures 13 and 14 the plunger 70 can be seen to continue to collapse, until the intermediate driver 80 disengages from the plunger 70 (to engage the shroud 90 instead) and no further force is applied to the plunger 70.

Certain terminology is used in the following description for convenience only and is not limiting. The word "proximal" refers to the front, or patient, end of the device. The word "distal" refers to the rear, or syringe user, end of the device. The term "longitudinal'', with or without axis, refers to a direction on an axis through the device in the direction of the longest extension of the device. The term "radial" or "transverse/transversal", with or without axis, refers to a direction generally perpendicular to the longitudinal direction, e.g. "radially outward" would refer to a direction pointing away from the longitudinal axis.

It should be understood that the detailed description and specific examples are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from the

description.

Claims

CLAIMS: 1. A plunger for an injection device comprising: a first portion and a second portion; the first portion having a first configuration and a second configuration; wherein, in the first configuration, the first portion engages the second portion such that relative motion of the first and second portions is prevented and in the second configuration the first portion is disengaged from the second portion such that the first and second portions can move relative to one another.
2. A plunger according to claim 1 wherein the first portion includes flexible arms configured to engage with the second portion.
3. A plunger according to claim 2 wherein the second portion includes a receiving portion configured to receive at least a portion of the flexible arms.
4. A plunger according to claim 3 wherein the receiving portion comprises an abutment surface arranged to be contacted by an abutment surface of the flexible arms.
5. A plunger according to claim 4 wherein the flexible arms are arranged to flex towards the central axis of the first portion thereby to move the abutment surface of the flexible arms away from the abutment surface of the second portion thereby disengaging the first and second portions.
6. A plunger according to claim 3 wherein the receiving portion comprises a groove configured to receive a projection on the flexible arms.
7. A plunger according to claim 6 wherein the flexible arms are arranged to flex away from the central axis of the first portion to move the projection away from the groove thereby disengaging the first and second portions.
8. A plunger according to any preceding claim further comprising a third portion configured to maintain the first portion in the first configuration.
9. A plunger according to any preceding claim further comprising means to control the speed of relative movement of the first and second portion.
10. A plunger according to claim 9 wherein the means to control the speed comprises complementary screw threads on the first and second portions.
11. A plunger according to claim 10 wherein the pitch of the thread is configured to obtain a desired speed of relative movement.
12. A plunger according to any one of claims 9 to 10 wherein the means to control the speed comprises or further comprises damping means.
13. A plunger according to claim 12 wherein the damping means comprises a viscous fluid or a foam.
14. A plunger according to claim 12 or 13 wherein the first portion and second portion are provided with chambers and movement of fluid from the first portion to the second portion controls the speed of relative movement of the first and second portions.
15. An injection device comprising: a housing; a medicament container configured to hold a substance to be injected; a plunger as claimed in any one of the preceding claims and a drive means for exerting a force on the plunger.
16. An injection device as claimed in claim 15 when dependent on claim 4 or claim 5 or any of claims 8 to 14 when dependent on claim 4 or claim 5 wherein, in use, the drive means moves the plunger in the first configuration forward; the flexible arms move out of engagement with the abutment surface due to contact with the medicament container thereby moving the first portion into the second configuration.
17. An injection device as claimed in claim 15 when dependent on claim 8 or any of claims 9 to 14 when dependent on claim 8 wherein, in use, the drive means moves the plunger in the first configuration forward; the third portion moves out of engagement with the abutment surface due to contact with the medicament container thereby disengaging from the flexible arms and allowing the first portion to move into the second configuration.