Reusable auto-injector

Abstract

Described herein is an auto-injector for receiving and operating a cassette, which includes a medicinal container, needle, and needle cover. The auto-injector features a main body and a lever that can move between open and closed positions. In the open position, the cassette can be inserted or removed. The auto-injector also has a latch system holding a plunger rod in a retracted position to accommodate the cassette. A linkage system, coupled to the plunger rod, releases the plunger rod when pressed against the skin, using energy from a main drive spring to deliver the medication via the needle of the cassette. After delivery, opening the lever slides the plunger rod distally to recharge the spring.

Description

REUSABLE AUTO-INJECTORBackground

[0001] Auto-injectors are widely used medical devices designed to deliver a fixed dose of medication, typically for self-administration by patients requiring frequent injections. Conventional auto-injectors are often single-use, combining a pre-filled medicinal container and needle assembly within a plastic body that houses a spring-driven mechanism for injecting the drug. These devices contribute significantly to medical waste due to their singleuse nature.

[0002] To address environmental and cost concerns, some reusable auto-injectors have been developed, separating the single use medicinal container from the reusable mechanism. These systems aim to reduce waste by allowing the replacement of the single use medical container while retaining the main body of the injector. However, challenges remain, including expensive reusable mechanisms, complex drug container assemblies, large form factors and additional user steps.

[0003] The embodiments described below are provided by way of example only and are not limiting of implementations which solve any or all of the disadvantages of known autoinjectors.Summary

[0004] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0005] A first aspect provides an auto-injector for receiving and operating a cassette, the cassette comprising at least a medicinal container, needle, and needle cover; the autoinjector comprising: a main body; a lever connected to the main body, that can be moved between an open position and a closed position, wherein upon reaching the open position, allows the cassette to be inserted or removed from the auto-injector; a latch system that holds a plunger rod in a fully retracted position, providing space for the cassette; and a linkage system mechanically coupled to the plunger rod (265), such that when a cassette (105) is inserted into the auto-injector (100), the needle cover (415) of the cassette (105) is pressed onto the skin of a user, the plunger rod is released from the latch system and advanced into the bore of the medicinal container by means of energy stored within a main drive spring to deliver contents of the medicinal container through the needle; wherein, after delivery, whenthe assembly is removed from the users skin the needle cover automatically slides in the proximal direction to cover the needle and when the plunger rod is in the proximal position, opening the lever results in a slidable movement of the plunger rod in the distal direction which recharges the main drive spring.

[0006] The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.Brief Description of the Drawings

[0007] Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which:

[0008] Figure 1 is an external view of the cassette and an auto-injector with the insert assembly removed;

[0009] Figure 2 is an exploded diagram showing some internal components of the autoinjector;

[0010] Figure 3 is an exploded diagram showing internal components of the insert assembly;

[0011] Figure 4 is an exploded diagram showing internal components of the cassette;

[0012] Figure 5 shows a series of steps taken by a user in order to operate the auto-injector;

[0013] Figure 6 shows a cross sectional diagram demonstrating a recharging step of a main drive spring;

[0014] Figure 7 shows the mechanical interaction of the lever, linkage rods, and yoke component within the auto-injector;

[0015] Figure 8 shows an interface between the yoke and the plunger rod;

[0016] Figure 9 shows the drive spring configuration;

[0017] Figure 10 shows a lever damping system;

[0018] Figure 11 shows an interface between the cassette needle cover and the autoinjector;

[0019] Figure 12 shows a pair of clamp jaws; and

[0020] Figure 13 shows an example of an alternative cassette arrangement.

[0021] Common reference numerals are used throughout the figures to indicate similar features.Detailed Description

[0022] Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0023] Described herein is an improved auto-injector that comprises a reusable device for receiving and operating a cassette, the cassette comprising at least a medicinal container, needle, stopper, and sliding needle cover. The medicinal container may be in the form of a pre-filled syringe. This arrangement offers improved sustainability and cost benefits by reducing waste through the use of reusable and disposable elements. The auto-injector also features a lever mechanism that provides mechanical advantage, making it easier for users to energise the main drive spring and operate the device efficiently, thereby accommodating a wide range of drug viscosities and improving overall usability.

[0024] Figure 1 is an external view of the cassette 105 and a reusable auto-injector 100 with an insert assembly 110 removed. The auto-injector 100 is designed to operate with the cassette 105, which is single use, and the insert assembly 110. The insert assembly 110 is part of the auto-injector 100, but may be manufactured separately to allow for maintenance, improved structural integrity, and customization for different applications.

[0025] The auto-injector 100 serves as the primary device housing and mechanism that facilitates the injection process, providing a sustainable and cost-effective alternative to fully single use systems. The cassette 105 is a single use assembly of components that includes a medicinal container, a needle, and a sliding needle cover. The cassette 105 is designed to be a straightforward and cost-effective component, which functions exclusively when integrated with the auto-injector 100. This design ensures that the cassette remains an economical and efficient element, without any unnecessary complexity or additional standalone functionality. As a result, the cassette 105 can only operate effectively when it is properly inserted into the auto-injector 100, ensuring compatibility within the complete system. The auto-injector 100 includes an insert assembly 110 as a guiding structure to accept the cassette that is purposely designed to ensure proper alignment and secure placement of cassette 105 within the device.

[0026] A lever mechanism of the auto-injector 100 allows for insertion and removal of cassette 105 when in the open position. After use, while the lever is being opened, the internal spring mechanism necessary for delivering the medicinal product is recharged. The interaction between these components ensures a streamlined, user-friendly process for administering injections. Upon insertion of cassette 105 into auto-injector 100, facilitated by the guiding structure of insert assembly 110, and the subsequent closure of the lever, the system is prepared for use.

[0027] The length of the lever of the auto-injector 100 of this example is approximately equal to the full length of the device. The length of the device may be 135mm. The lever articulates around a pivot positioned near a distal end of the body structure. The distal end of the body structure may be considered the end of the auto-injector 100 further from the needle when in use, and a proximal end of the body structure may be considered the end of the auto-injector 100 closer to the needle when in use. Therefore, it is the proximal end of the auto-injector 100 which is adjacent an injection site in the skin of the user when a dose of medication is being given.

[0028] From a fully closed state, where the lever is positioned against the device body, to a fully open state, the total angular lever travel of this example is approximately 125 degrees. The lever's length and angle of travel have been selected to increase the distance over which a user is able to apply a force to the lever during use. The longer the distance travelled, the more energy the user is able to provide for a given peak force level. This mechanical advantage enables the device to be compatible with drug viscosities and needle gauges that require large amounts of energy to deliver the drug in an acceptable time. Further, the mechanical advantage significantly reduces the effort required by the user, making the device accessible and easy to use for individuals with reduced strength, such as the elderly or those with physical limitations.

[0029] Moving the lever from the closed position to either a fully or partially open position enables access to a chamber into which the cassette 105 can be inserted. On closing the lever, access to the chamber is blocked and the cassette 105 remains secure within the autoinjector 105. This improves the system usability as it combines the spring recharge, as described in greater detail below, and the cassette removal / insertion into the same user action. The user therefore has only to consider inserting and removing the cassette and does not need to be aware that they are also recharging the spring. The cassette 105 may be inserted into the body using a substantially linear trajectory perpendicular to the longitudinal axis of the medicinal container encased within the cassette 105. This sideways loading and unloading direction provides usability advantages as it is a simple action that permits easycommunication of the task to the user, which would be more difficult if a more complex articulation were required.

[0030] Optionally, the chamber into which the cassette 105 is inserted includes a continuous framing contour whose colour contrasts with the colour of the inner surfaces of the chamber to enhance the visual impact of the chamber shape through a silhouette effect. The shape of the chamber may match the external shape of the cassette 105 to assist with indicating the correct insertion orientation to the user. In one example, two compliant bump features (not shown) located within the cassette chamber provide an interference fit to the cassette, retaining it in the auto-injector 100 after it is pushed in by the user. In other examples, a clamping jaw mechanism is held within the insert assembly and protrudes into the cassette cavity on closing the lever to provide an interference fit, as described in greater detail in relation to Figure 12.

[0031] Figure 2 is an exploded diagram showing some internal components of the autoinjector 100. As shown in this figure, the auto-injector 100 comprises a body 215 and a lever 210 that includes an optional magnet 205, which interacts with a corresponding optional magnet 220 on the body 215 to secure the lever 210 in the closed position. The lever 210 pivots around the lever pivot and is connected to the yoke 235 through the linkage rods 230, lever pivot pins 225 and yoke pivot pins 245, which in combination translate the lever's pivoting motion into linear movement of the yoke 235.

[0032] The drive spring 240, positioned coaxial to the drive spring rod 255, and optionally substantially surrounding the drive spring rod 225, provides the necessary force to advance the plunger rod 265 into the cassette 105, delivering the medicinal product. The yoke 235, connected by the yoke pivot pin 245, moves along with the lever 210, enabling the retraction and advancement of the plunger rod 265. The O-ring 250 and friction rod 260 work together to provide a damping effect, controlling the speed of the lever's movement and preventing sudden snaps. The yoke 235 of this example is U-shaped, meaning it has a configuration resembling the letter "U" with two parallel arms extending from a base. This design allows the yoke to straddle the plunger rod 265 and cassette chamber, ensuring stable and balanced movement within the auto-injector mechanism. The U-shape provides space for long linkage rods 230 to be integrated into the mechanism without requiring additional device length. Long linkage rods enhance the mechanical advantage provided by the mechanism by reducing lateral forces on the yoke 235 that could cause increased friction, wear, misalignment or binding. This structural arrangement ensures that the lever 210 can efficiently translate angular motion into linear motion, lowering the force requirements on the user.

[0033] When the lever 210 is opened, for example after delivery of a drug into a user, the plunger rod 265 is retracted out of the bore of the medicinal container 420, allowing for the removal of the cassette 105 and future insertion of a new cassette 105, recharging of the drive spring 240 and latching of the plunger rod 265 in the fully retracted position. This process involves multiple coordinated movements of the internal components. Specifically, the yoke 235, connected to the lever 210, moves to reposition the plunger rod 265 into its retracted position, thereby compressing the drive spring 240. This compression stores the necessary potential energy in the drive spring 240 for the next injection cycle.

[0034] Figure 3 is an exploded diagram showing internal components of the insert assembly 110, particularly a plunger latch system which comprises the plunger rod 265, latch housing 330, latch collar 305, latch collar springs 325 and ball bearings 315. The latch system automatically secures the plunger rod 265 in its retracted position when the lever 210 is opened and subsequently holds plunger rod 265 in its retracted position when the lever is closed, preparing the system for the next injection.

[0035] When latched in its retracted position the plunger rod 265 is held in position by two or more ball bearings 315 that partially protrude into the circumferential latch groove feature 320 on the plunger rod 265. This groove 320 may have a sharp, filleted or chamfered edge. Each ball bearing 315 sits within a cylindrical hole in the latch housing 330, with the axis of these holes running perpendicular to the plunger rod axis and spaced evenly around the bore of the latch housing 330. The latch housing 330 is rigidly fixed within the upper 340 and lower 335 body structure of the insert 110, preventing the ball bearings 315 from moving along the plunger rod axis. The ball bearings 315 are constrained radially by the circumferential latch groove feature 320 on the plunger rod 265, which prevents inward movement, and by the bore of the latch collar 305, which prevents outward movement.

[0036] The latch collar 305 in this example features a bore diameter that varies along its length. This means that the internal opening of the latch collar 305 is not uniform but changes in diameter along its length. In a latched state, the latch collar 305 is positioned in such a way that a specific section of its bore, which has a smaller diameter, is aligned with the ball bearings 315. This smaller diameter section effectively restricts the movement of the ball bearings, causing them to protrude into the circumferential latch groove feature 320 on the plunger rod 265. This engagement between the ball bearings 315 and the latch groove 320 securely holds the plunger rod 265 in place. The latch collar 305 is biased into this position by the latch springs 325 ensuring the latch system remains engaged and the plunger rod 265 remains in a retracted position until the latch is intentionally disengaged.

[0037] To enhance the capability of the latch system, at least three ball bearings may be used to distribute radial forces evenly around the circumference of the latch collar. This even distribution minimizes deformation, allowing the latch collar 305 to be made from lower-cost materials like standard engineering plastics or lower-grade metals. These materials are characterised by their adequate strength, ease of manufacturing, and cost-effectiveness compared to high-grade metals or advanced composites.

[0038] The operation of disengaging the latch system begins when the latch collar 305 is moved distally after contact with one or more activation rods 310. This movement increases the effective bore diameter of the latch collar 305, creating additional space for the ball bearings 315 to move radially outward, away from the plunger rod 265 axis. Sufficient radial movement of the ball bearings 315 results in them disengaging from the circumferential latch groove feature 320 after which the plunger rod 265 is then free to move along the longitudinal axis of the medicinal container 420, forcing a dose of medication out through the needle and into a user. The ball bearings 315 are forced outward owing to the plunger force acting on their curved surfaces within the filleted or chamfered groove 320, creating a radial force component on the ball bearings 315.

[0039] The movement of the latch collar 305 is initiated when the needle cover guides 350 are moved until the activation rods 310 contact the latch collar 305. Further movement of the activation rods 310 provokes axial movement in the latch collar 305. Two latch springs 325 provide a biasing force on the latch collar 305. In an inactive state, the combination of the latch spring forces and the tapered section of the latch collar 305 exerts an inward radial force on the ball bearings 315. The ball bearings cannot move inward unless the circumferential latch groove feature on the plunger rod aligns with them, forcing the latch collar to remain inactive. When the plunger rod 265 is moved to the fully retracted position, the circumferential latch groove feature 320 align with the ball bearings 315 and the stored energy in the latch springs 325 forces the ball bearings 315 to move until they partially protrude into the circumferential latch groove feature 320, allowing the latch collar 305 to move, activating the latch system. In an active state, the force from the drive spring 240 is supported by the latch system and therefore there is no significant net forces acting on the lever 210 such that it remains in the fully open position, which allows user access to the cassette chamber.

[0040] The spring guide rod 255 and cylindrical bore of the plunger rod 265 provide guidance for the drive spring 240 during compression and decompression cycles, ensuring smooth operation and preventing the spring from bending or misalignment.

[0041] Figure 4 is an exploded diagram showing internal components of the cassette 105, designed to house and deliver medication to a user. The cassette body, substantially formedfrom a front 405 part and a back 425 part, provides structural support for the other components. It is designed to protect the medicinal container 420 and the needle (not shown), ensuring that they remain sterile and secure before use, provide a feature to aid removal of the rigid needle shield 450 by a user, obscure the needle form the user during use, provide a needle protection system that prevents access to the needle after use and remains in place until disposal and provides a mechanism that initiates activation of the autoinjector when it is pressed on the injection site by the user,

[0042] The cassette 105 of this example is symmetrical such that it can be inserted into the device body in one of two orientations, 180 degrees apart when rotated along the longitudinal axis of the medicinal container 420, in other embodiments the cassette may be inserted into the device body in one of four orientations, 90 degrees apart when rotated along the longitudinal axis of the medicinal container 420. The cassette 105 has a non-round cross section to assist in communicating the correct insertion orientation to the user and enable it to resist rolling when on a flat surface. The cassette 105 of this example is deeper than it is wide such that it is only possible for the user to insert the cassette 105 in one of the two correct rotational orientations.

[0043] The cassette embodiment contains a medicinal container 420 with a needle that remains stationary relative to the front 405 and back 425 body components as the medicinal container flange 435 engages on features on the front 405 and back 425 body components. In this example, the front 405 and back 425 body components are very similar apart from complementary rod-and-socket fittings 455 around their exterior to ensure a precise alignment and firm connection, enhancing the structural integrity and stability of the assembled cassette.

[0044] A cassette cap 430 engages with a rigid needle shield 450 that comes preinstalled on the medicinal container 420 using two hooking elements that grip the rigid needle shield 450 as the cap is removed, simultaneously removing it from the medicinal container 420. The cap 430, when installed, is also to prevent unintended activation of the sliding needle cover 415.

[0045] When inserted into the auto-injector 100, the needle cover 415 and cap 430 protrude from the proximal end of the auto-injector 100. This feature allows unobstructed access to the cap 430, and once the cap 430 is removed, enables the needle cover 415 to be pushed against the skin of the user. This action inserts the needle into the skin of a user and activates the drug delivery system. After use, the protruding locked needle cover 415 provides a feature by which the user can grip the cassette 105 to remove it from the auto-injector 100. This simplifies the auto-injector 100 by not requiring any other features or mechanisms to aid cassette 105 removal. The assembled front 405 and back 425 body components provide a further surface for a user to grip when inserting or removing the cassette 105 from the auto-injector 100, and assist in ensuring that the cassette 105 remains properly aligned and engaged with the auto-injector's mechanisms. The distal face of the cassette chamber is angled such that if the cassette 105 is rotated during removal from the chamber by means of a removal force in the vicinity of the needle cover 415, which results in a moment acting on the cassette 105, it does not become lodged against the distal face of the chamber. This improves the usability of the device.

[0046] The cassette 105 may include a viewing window 445 on both the front 405 and back 425 body components that enables light to pass through the medicinal container 420 for the user to easily inspect the contents of the medicinal container 420 prior to use. When the cassette 105 is installed in the autoinjector 100, the viewing windows 445 on the cassette 105 may be arranged to align with the viewing windows on the lower insert 335 and the viewing window on the lever 210 to allow the user to inspect the contents of the drug contained prior to use while it is assembled in the autoinjector 100.

[0047] In use, the sliding needle cover 415 is permitted to move distally such that the needle becomes exposed only once. This may be achieved with a sliding indicator flag 410 component. Initially, the flag 410 is in the distal position and acts as a ramp which deforms two protruding elements on the needle cover such that they clear a ledge feature in the body structure 405, 440. On its return, the needle cover moves the indicator flag 410 such that the two protruding elements on the needle cover are no longer able to pass the ledge 440. The indicator flag 410 has a secondary function of acting as an indicator to show the cassette 105 is in a “safe mode” by obscuring a section of the viewing window 445 indicating that it can no longer be used after one cycle of the needle cover 415.

[0048] This example of the cassette 105 does not contain sprung loaded energy and uses the stored energy in the auto-injector 100 to return the sliding needle cover 415. This reduces the component count and improves the sustainability credentials of the cassette 105 itself.

[0049] Figure 5 shows a series of steps taken by a user in order to operate the autoinjector 100. In the first step, the user begins by moving the lever 210 to the open position. This action, facilitated by the lever pivot 705, allows the chamber feature within the insert assembly 110 to become accessible for loading. During this process, the drive spring 240 is fully energized.

[0050] Next, in the second step, the user loads the cassette 105 into the chamber feature within the insert assembly 110. The cassette consists of several components including the cassette body front 405 and back 425 components, the medicinal container 420, and the needle cover 415. As the cassette 105 is inserted, it aligns with the chamber within the body 215 which holds it securely in place.

[0051] In the third step, the user moves the lever 210 to the closed position. The magnet on the lever 205 and the magnet on the body 220 ensure a firm closure. After closing the lever, the user removes the cassette cap 430, which exposes the needle cover 415 and prepares the needle for injection.

[0052] To administer the injection, in the fourth step, the user presses the auto-injector 100 firmly against their skin 505. This pressure causes the needle cover 415 to retract, exposing the needle and allowing it to penetrate the skin and then subsequently causing the energized drive spring 240 to propel the plunger rod 265 forward and push the medication through the needle. In this example, pressing for approximately 10 seconds allows for the full dose of medication to be delivered.

[0053] In the fifth step, after the injection, the user may remove the autoinjector 100 from the skin which causes the needle cover 415 to move proximally and lock in the fully extended position to provide protection to the used needle to prevent subsequent needle stick injuries. On removal the user may also check to ensure that the plunger rod 265, which may be of a contrasting colour to the medication in the medicinal container, has filled the viewing window. This visual confirmation indicates that the full dose has been delivered.

[0054] In the final sixth step, the user moves the lever 210 back to the open position, which retracts the plunger rod 265 and re-energizes the drive spring 240. With the plunger rod clear of the cassette the user can then unload and safely dispose of the used cassette 105 following proper disposal protocols. Throughout this process the needle cover 415 remains locked in the extended position to provide protection to the used needle.

[0055] Figure 6 shows a cross sectional diagram demonstrating a recharging step of a main drive spring. When a used cassette 105 is within the auto-injector 100 and the lever is moved from the closed position to the open position, access is provided to the used cassette 105. As the lever 210 moves, it actuates the yoke 235, which in turn retracts the plunger rod 265 from the medicinal container 420. This action simultaneously withdraws the plunger rod 265 fully from the cassette 105, fully energizes the main drive spring 240, and latches the plunger rod 265 in preparation for the next use of the device.

[0056] The movement of the lever 210 continues until the necessary travel to recharge the drive spring 240 is completed and the plunger latch system becomes active. The lever angle, at this point, ensures that the plunger rod 265 is fully withdrawn from the medicinal container 420, enabling the removal of the cassette 105. This ensures that the cassette cannot be removed until the drive spring 240 has been successfully energized and the plunger rod 265 is latched in place.

[0057] Figure 7 shows the mechanical interaction of the lever 210, linkage rods 230, and yoke 235 within the auto-injector 100. The lever pivot 705 is located at the distal end of the body, also positioned away from the central plane of the device, close to the external surface of the body, opposite to the lever side. The pivot position and the form of the distal end of the lever enables the overall length of the device to be reduced by allowing sufficient internal space within the device such that the distal end of the drive spring is positioned distally from the lever pivot axis.

[0058] The lever motion is connected to the plunger motion by means of two solid linkage rods 230, which, in this example, are approximately 56mm in length, and a sliding yoke 235. The linkage rods 230 translate the angular motion of the lever to linear motion of the yoke 235 that is contained within the body structure. The solid linkage rods 230 are connected by means of pin joint interfaces 710 to fixed points on the lever 210. In this example, these points are located approximately 27mm from the lever pivot axis on the lever skirt 715 that protrudes down each side of the lever 210 and extends from the end of the lever 210 to past the linkage pin location. The lever skirt 715 has the secondary function of increasing the second moment of area of the lever 210 in the area between the pivot 705 and linkage pin interface, thus increasing lever stiffness and durability.

[0059] One end of the linkage rods 230 is connected by means of a pin joint 720 interface to the yoke 235. The yoke 235 of this example is shaped such that the pivot points are located approximately 32mm from a face stepped bore 725 in the yoke 235 which engages with a lip feature 730 at the distal end of the plunger rod 265. The relative positioning of the stepped bore feature 725 and the pivot pin locations on the yoke 235 enables longer linkage rods to be packaged in the device that act to reduce side loading of the yoke 235 and loading through the linkage rods and pivots while also enabling the overall device length to stay more compact.

[0060] The relative geometry of the lever pivot location, lever linkage pivot, linkage length, yoke pivot, and body surfaces, reduces the maximum size of the exposed opening 735 between the linkage, body, and lever. This helps reduce the risk of finger entrapment in the mechanism during lever articulation.

[0061] Figure 8 shows an interface between the yoke 235 and the plunger rod 265. The yoke 235 can travel linearly within the body of the device, with its position at any time being a function of the lever position. In this example, the total yoke travel is set to approximately 49mm as this is equivalent to the distance the plunger rod 265 needs to move to clear the proximal end of the medicinal container 420 after it has fully delivered a dose within a standard 1 ml long or 2.25ml prefilled syringe.

[0062] The plunger rod 265 includes an external lip feature 730 at the distal end, which engages with a stepped bore 725 in the yoke 235. In this example, the plunger rod lip feature 730 diameter is approximately 7mm and its depth is 3mm. This configuration enables the yoke 235 to apply a force to the plunger rod 265 in the distal direction but does not enable the yoke 235 to apply a force to the plunger rod 265 in the proximal direction. This characteristic allows the yoke 235 to move the plunger rod 265 from its proximal position, after dose delivery when the lever is in the fully closed position, to the fully distal position, when the drive spring is fully energised, and the plunger rod latch system is active when the lever is in the fully open position. This feature also allows the yoke 235 to travel freely when the plunger rod 265 is latched in its fully distal position. This is necessary for allowing the user to close the lever after a cassette has been removed, then allow it to be opened again for insertion of a new cassette, then allow it to be closed in preparation for delivering the drug in the medicinal container 420, all while the plunger rod 265 remains in the latched position.

[0063] Figure 9 shows more detail regarding the drive spring 240 configuration. The plunger rod 265 can move linearly within the device along the axis of the medicinal container 420. The main drive spring 240 is positioned within the plunger rod 265 and remains in a compressed state in all positions, such that the spring force always acts on the plunger in the proximal direction via the end face of the spring cavity. The plunger rod 265 diameter may be increased as far as possible within the constraints associated with the internal bore geometry of the medicinal container, after allowable tolerances are considered. The plunger rod 265 inner spring cavity diameter may be increased based on the external diameter and the constraints due to a predetermined minimum wall thickness required to withstand material stress levels for the material, hence a high strength polymer or metal such as stainless steel may be required with an exemplary thickness of 0.5-1 mm. The internal spring cavity of the plunger rod 265 may extend from the distal end of the plunger rod to within 5mm of the circumferential latch groove feature 320, thereby increasing the length of the internal spring cavity.

[0064] A high strength spring may therefore be packaged inside the plunger rod 265. The free length of the spring may be maximized in order that the highest average spring force across the plunger travel is achieved while also maximizing the force at the maximum working length to prevent plunger stall risk, and minimizing the force at the minimum working length to prevent excessively high forces acting on the latch system. Optionally, the drive spring 240 has a 4.5mm diameter, music wire material, 200mm length, and 0.12 N / mm spring constant. In some examples, the drive spring 240 may be replaced with any number of springs arranged in a series that would have the same effect as a single spring.

[0065] A polymer or metallic spring rod 255 is positioned coaxially within the drive spring 240 and plunger rod 265. Other suitable materials may be used to form the spring rod 255. The distal end of the rod 255 is fixed into the device body structure or it may be part of the body component. The spring rod 255 extends such that there is always an overlap between the spring rod 255 and the plunger rod 265 even when the plunger rod 265 is in the fully proximal position. The purpose of the spring rod 255 is to help reduce spring snaking during use. The proximal end of the spring rod 255 includes a conical point that assists engagement with the plunger rod 265 through hole and enables it to engage with a spring compression assembly tool.

[0066] The plunger rod 265 has a through hole along its axis that is visible as an opening at the proximal end, and in this example the hole is approximately 1.7mm in diameter. This is helps enable successful assembly by allowing an approximately 1 ,5mm diameter spring compression assembly tool to be inserted through the proximal end of the plunger rod 265 that temporarily extends the effective length of the spring rod during assembly. This may help to prevent spring snaking during assembly, where there would otherwise be no overlap between the plunger rod 265 and spring rod. The assembly rod is a straight rod at least 150mm long that includes a conical cavity feature at one end that locates against the spring rod to maintain coaxial alignment during use. After completion of the spring compression stage during the assembly process, the spring compression tool is removed in the distal direction.

[0067] Figure 10 shows a lever damping system. This motion damping system controls the speed of the yoke 235 movement. This helps to prevent the lever 210 snapping back too quickly in the case that the main drive spring 240 is partially compressed during lever opening, but not compressed sufficiently such that the plunger rod latch becomes active. In this example, the main drive spring 240 acts on the yoke 235 through the plunger rod 265, biasing the lever 210 to the closed position. If this occurs in an uncontrolled manner, the lever 210 may impact the fingers of the user and injure or startle them.

[0068] An elastomer element in the form of an O-ring 250 is positioned within a groove feature 1005 within the yoke 235 adjacent to the stepped bore 725 feature. A friction rod 260, optionally made from either a metal or a polymer, is affixed to the distal end of the device body and runs parallel to the drive spring rod 255. The friction rod 260 passes through the hole in the elastomer element and the friction rod 260 is sized such that there is a radial interference between the elastomer element and the friction rod 260. The friction rod 260 is sufficiently long that the rod remains in interference with the elastomer element over the full extent of the yoke 235 travel.

[0069] The damping force is generated by the frictional drag forces of the elastomeric element that is moved via the yoke 235, sliding back and forth along the stationary friction rod 260. In another example, the damping force may be varied as a function of yoke 235 position by varying the diameter of the friction rod 260 across its length. In another example the geometry of the elastomer element may result in the damping force magnitude being dependant on the direction in which the yoke 235 is moving.

[0070] Figure 11 shows an interface between the cassette needle cover 415 and the autoinjector 100. When the cassette 105 is positioned correctly within the chamber 1105, a pair of protruding features 460 on the side of the cassette needle cover 415 align with a pair of features on the needle cover guides 350 that protrude from the walls of the cassette chamber 1105. The needle cover guides 350 are spring-loaded using springs 1110 contained within the device body and provide the force necessary to provide a biasing force to the needle cover that can return it to its fully proximal position after activation. Including the needle cover spring 1110 in the reusable device allows the cassette to be designed without containing a component or set of features that provide the needle cover 415 return force, reducing the cost of this element.

[0071] The figure also depicts a non-linear needle cover return force versus needle cover travel profile 1120. This force profile helps users to fully press the auto-injector 100, which in use contains a cassette 105, against the injection site, ensuring that the needle 605 is properly inserted and the medication is injected. Initially, as the user presses the device, the force required increases, creating a force ramp. Once this initial force ramp is overcome, the reaction force suddenly drops off, causing the auto-injector 100 to accelerate forward due to the potential energy stored in the user's arm. This acceleration happens before the user can react to stop it, ensuring that the needle 605 is inserted deeply enough to activate the medication delivery. This mechanism is designed to help prevent user errors where the needle 605 might not be inserted far enough if the force profile were linear, thereby ensuring reliable and consistent activation of the auto-injector 100.

[0072] The needle cover guides 350 provide the secondary function of providing a mechanical linkage between the cassette needle cover 415 and the plunger latch system. When the needle cover travel enables the desired needle penetration depth, the associated travel of the needle cover guides 350 provides a mechanical signal, via the guide rods 1115, that lifts the latch collar 305, unlatching the plunger rod and initiating dose delivery via the drive spring rod 255.

[0073] As shown in Figure 12, in some examples, a cassette 105 is secured in the body chamber 1105 by means of two translating clamp jaws 1205', 1205" that move inwards tofirmly hold the cassette 105 as the lever 210 is moved into its fully closed position. This movement is achieved through the linear motion of the yoke 235 contacting the rear face of the translating clamp jaws 1205', 1205" and pushing them on a diagonal path that runs both towards the proximal end of the device and inwardly towards the centre line of the cassette 105. The inner surfaces of the translating clamp jaws 1205', 1205" engage with the cassette 105. These surfaces have a deep undercut 1210 such that they are sufficiently compliant to accommodate for manufacturing tolerances in the cassette. The translating clamp jaws 1205', 1205" are spring loaded by means of clamp jaw springs 1215', 1215" each acting on a respective translating clamp jaw 1205', 1205" which causes them to retract clear of the cassette 105 when the lever is opened. As there is clearance between the cassette and device, little to no force may be required to seat the cassette 105 correctly, and the user is only required to overcome the weight of the cassette 105 during removal. The system also allows the cassette to be removed by inverting the device body and allowing the cassette 105 to fall out of the device.

[0074] There is shown in Figure 13 an alternate cassette embodiment, which has rotational symmetry and an approximately square cross-section such that it can be inserted into the device body in one of four orientations, 90 degrees apart when viewed from an axial direction. The non-round profile of the cassette body 405, 425 and needle shield 430 may resist rolling when placed on a flat surface. This cassette embodiment comprises a pre-use needle shield lock-out function that is intended to prevent users inadvertently retracting the needle shield 430, thereby preventing subsequent use of the cassette prior to inserting it into the reusable device. This functionality is achieved by a pair of cantilevered hook features 1340 on the body that sit against a ledge on the needle shield to prevent it moving proximally and exposing the needle.

[0075] When inserted into the reusable device, the pre-use needle shield lock is deactivated when the needle shield guides (not shown) apply a force to the distal face of the needle shield 430 which concertinas the needle shield, by compressing the living spring features. The lip of the needle shield moves over the angled face of the cantilevered hook 1340 which pushes it clear of the needle shield ledge. This functionality requires the position of the needle shield guides to be linked to the position of the reusable system lever, such that the action of closing the lever causes the needle shield guides to move proximally, and in doing so apply a load to the distal face of the needle shield. Alongside unlocking the cassette prior to use, the shield guides provide the force necessary to bias the needle shield in the proximal direction. Once the pre-use lock function has been deactivated the sliding needle cover 430 is permitted to move distally such that the needle becomes exposed only once. This is achieved by the interaction between two pips that protrude from the inside face of the locking ring 1305 and aset of cut out features on the body 1330 into which the pips are constrained to run within, the locking ring 1305 is free to rotate within the needle shield 430.

[0076] In the initial state the proximal motion of the needle shield is prevented by the interaction of the locking ring pips and the proximal end of a pocket 1335 in the body cut out feature. When the needle shield is pressed against the user's skin and the needle shield is pushed distally in relation to the body, the pips travel up an angled and then axial channel, resulting in a rotational movement of the locking ring. As the needle shield is removed from the user's skin and the needle shield guides bias the needle shield proximally, the pips follow an alternate path in the cut-out feature, coming to rest in the lock out location 1345. In this position the geometry of the cut out restricts the allowable movement of the pips which results in the permanent lock out of the needle shield offset between the pre and post use states assists in improving the protection to the user from a used needle as the needle tip is positioned further in from the needle shield face reducing the risk of finger access to the needle tip. It also allows the relative position change of the needle shield to uncover a safe mode indicator 1350 when in the post use lock out state, that is not visible in the pre-use state. The safe mode indicator flag is a coloured feature at the proximal end of the body component, optionally applied using either a decal or printing.

[0077] Prior to entering safe mode this indicator is fully concealed from view by the opaque needle shield insert 1310, and when in safe mode the indicator feature is exposed such that, it can be viewed through the locking ring 1305 and needle shield 430 which in this example are both manufactured in an optically transparent material. The opaque needle shield insert 1310 has multiple functions beyond shrouding the safe model indicator feature. It also communicates needle end to user through its colour, reduces internal diameter of skin contact element for improved injection depth control, provides feature to prevent cap rotation, and control the axial position on the locking ring.

[0078] The cap element comprises two components 1315, 1325 that may be arranged to snap together. The lower cap 1325 provides an ergonomic tab feature for the user to grip and pull during cap removal. A through cut in the lower cap 1325 both reduces the volume of material in the part and provides a feature that a tool could be inserted into to aid cap removal if necessary. The lower cap 1325 may include two serrated rigid needle shield (RNS) grip features 1320 which care intended to interact with the planar serrated features on the medicinal container RNS 450. The RNS grip features may be constructed such that they can flex and therefore are able to move axially within the tapered bore feature in the upper cap 1315 component when subject to external forces. During assembly of the medicinal container RNS 450 into the cap assembly the force applied to the RNS grip features move them in the proximal direction where the taper permits them to open outwardly, providingsufficient clearance for the medicinal container RNS to be fully pushed into the cap assembly. During cap removal the forces between the medicinal container RNS and the RNS grip features pushes the RNS grip features in the distal direction where the taper forces them inwards, further increasing the friction levels on the PFS RNS. This effectively locks the cap to the RNS during cap removal, preventing any usability issues relating to the cap and medicinal container RNS becoming detached. This exemplary cassette comprises a medicinal container 420 with a needle that remains stationary relative to the body 405, 425 throughout use. The medicinal container flange engages within an undercut flange retention feature in the body that prevents any axial relative movement. To assemble the medicinal container into the body a long cut feature in the body allows the flange retention feature to splay to permit insertion.

[0079] A label wrapped circumferentially around the proximal end of the body after the medicinal container has been inserted may prevent the body from splaying and holds the medical container securely in the body. If the medicinal container glass flange were to break during use, two internal bump features in the body may interfere with the medical container flange and provide sufficient friction such that the medicinal container barrel is prevented from falling out of the proximal end of the cassette.

[0080] Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person.

[0081] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages.

[0082] Any reference to 'an' item refers to one or more of those items. The term 'comprising' is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0083] The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

[0084] It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art.Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.

Claims

CLAIMS1 . An auto-injector (100) for receiving and operating a cassette (105), the cassette (105) comprising at least a medicinal container (420), a needle (605), and a needle cover (415); the auto-injector (100) comprising: a main body (215); a lever (210) connected to the main body (215), that can be moved between an open position and a closed position, and when in the open position allows the cassette (105) to be inserted or removed from the auto-injector (100); a latch system arranged to hold a plunger rod (265) in a fully retracted position; a main drive spring (240); and a linkage system mechanically coupled to the plunger rod (265), such that when a cassette (105) is inserted into the auto-injector (100), the needle cover (415) of the cassette (105) is pressed onto the skin of a user, the plunger rod (265) is released from the latch system and advanced into the medicinal container (420) by means of energy stored within the main drive spring (240) to deliver contents of the medicinal container (420) through the needle (605); wherein, after delivery, when the plunger rod (265) is in a proximal position, opening the lever (210) results in a slidable movement of the plunger rod (265) in a distal direction which recharges the main drive spring (240).

2. The auto-injector of claim 1 , wherein the peak force applied to the proximal tip of the lever is less than the peak force applied to the main drive spring during the lever opening stroke.

3. The auto-injector of any previous claim, wherein the cassette is removable from the main body when the lever is in the open position in one action along a path primarily perpendicular to the longitudinal axis of the needle.

4. The auto-injector of any previous claim, wherein the main drive spring is recharged by means of at least two linkage elements connected between the lever and at least one sliding element contained within the main body, where the connection point between the linkage elements and the sliding elements is proximal to a connection point between the sliding elements and the plunger rod.

5. The auto-injector of any previous claim, wherein, once inserted into the auto-injector, the medicinal container and needle of the cassette remain in a fixed position relative to the main body.

6. The auto-injector of any previous claim, wherein the linkage system comprises a sliding yoke component.

7. The auto-injector of claim 6, wherein the yoke is substantially “U” shaped.

8. The auto-injector of claim 6 or claim 7, wherein the linkage system comprises a dampening mechanism and / or a lead screw mechanism connected to the yoke.

9. The auto-injector of any previous claim, wherein after activation, a sliding of the needle cover in the proximal direction causes the needle cover to be locked in a position substantially covering the needle.

10. The auto-injector of any previous claim, wherein the auto-injector comprises a viewing window which, when the cassette is inserted into the auto-injector, aligns with a viewing window in the cassette such that the medicinal container is externally visible.11 . The auto-injector of claim 10 when dependent on claim 9, wherein a feature to indicate locking of the needle cover at least partially blocks the viewing window of the cassette.

12. The auto-injector of any previous claim, wherein the main drive spring is located coaxially with the plunger rod.

13. The auto-injector of any previous claim, further comprising a skirt adjacent the lever, which protrudes down each side of the lever and extends proximally from the distal end of the lever.

14. The auto-injector of any previous claim, further comprising one or more clamp jaws operable to grip the cassette when the lever is in the closed position.

15. The auto-injector of claim 14, further comprising a pair of clamp jaws, wherein, when a cassette is inserted into the auto-injector, each clamp jaw is positioned on an opposing side of the cassette.

16. The auto-injector of claim 15, wherein the pair of clamp jaws are spring loaded by means of a spring urging on each clamp jaw, and further wherein the spring urging on each clamp jaw causes the clamp jaw to retract when the lever is in the open position.

17. The auto-injector of any preceding claim, wherein the provided space for the cassette matches the profile of the cassette such that the cassette can be fitted within the main body in only one of four orientations.

18. The auto-injector of any previous claim, wherein the cassette needle cover is locked prior to insertion into the auto-injector to prevent exposure of the needle.

19. The auto-injector of claim 18, wherein the cassette needle cover is unlocked by means of one or more needle cover guides moving in a proximal direction after the cassette has been inserted into the auto-injector.

20. A kit of parts for an auto-injection assembly, comprising an auto-injector (100) and a cassette (105), the cassette (105) comprising at least a medicinal container (420), a needle (605), and a needle cover (415); the auto-injector (100) comprising: a main body (215); a lever (210) connected to the main body (215), that can be moved between an open position and a closed position, and when in the open position allows the cassette (105) to be inserted or removed from the auto-injector (100); a latch system arranged to hold a plunger rod (265) in a fully retracted position; a main drive spring (240); and a linkage system mechanically coupled to the plunger rod (265), such that when the cassette (105) is inserted into the auto-injector (100), the needle cover (415) of the cassette (105) is pressed onto the skin of a user, the plunger rod (265) is released from the latch system and advanced into the medicinal container (420) by means of energy stored within the main drive spring (240) to deliver contents of the medicinal container (420) through the needle (605); wherein, after delivery, when the plunger rod (265) is in a proximal position, opening the lever (210) results in a slidable movement of the plunger rod (265) in a distal direction which recharges the main drive spring (240).

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