Patent Publication Number: US-2023158244-A1

Title: Injection devices with automatic priming

Description:
TECHNICAL FIELD 
     The invention relates to medical devices for injecting a fluid from a vial, through a needle, into the skin of a subject. 
     The fluid is typically but not exclusively a biologically active substance such as a pharmaceutical. The subject may be human or animal. 
     BACKGROUND OF THE INVENTION 
     Many injector devices are known, which are used to deliver a fluid into the skin of a subject, while providing additional functionality compared with a manually operated hypodermic syringe. For example, some devices allow a variable dose to be pre-set and others allow the dose to be automatically delivered, for example using compressed air or the stored energy of a spring. In its broadest aspect, the present invention relates to the priming of injector devices prior to their use and is not incompatible with such additional functionality. However, the present invention is normally intended for devices that are single-use, in the sense that an empty vial cannot be replaced with a new one. This does not necessarily exclude using the device, after it has been primed, to deliver multiple doses of the fluid from a single vial. 
     Biologically active fluids such as pharmaceuticals are frequently packaged in cylindrical vials, which contain an axially sliding plunger. As the plunger moves from the proximal end (closer to the operator) to the distal end (closer to the subject), it displaces fluid from the distal end of the vial. Prior to use, for example during transport and storage, the distal end of the vial is normally sealed by a septum to maintain the sterility of the interior of the vial. Immediately before use, the septum must be ruptured to release the fluid, for example by piercing it with a hollow needle, through which the fluid can be delivered from the vial to the subject. The needle is typically double-ended and is held in a needle hub, which is moved towards the vial until the proximal end of the needle pierces the septum. The distal end of the needle is then available for injection into the skin of the subject. In the present specification, the engagement of the needle hub with the vial so that the needle pierces the septum is referred to as priming the device. 
     According to the prior art, the needle hub may be manually primed, for example by screwing the needle hub onto a threaded vial holder. It is also known to prime a device semi-automatically with a mechanism that moves the vial towards the needle hub as a result of pressing the device against the skin of the subject. 
     It is a requirement of injector devices that the distal end of the needle should be shielded from accidental contact before and after use. Many such devices include a retractable shield that surrounds the needle until the device is pressed against the skin of a patient. It is desirable that is should be possible to lock the shield against being retracted accidentally. 
     Many injection devices have the general form of a hypodermic syringe but on a larger scale to accommodate the additional mechanisms that they contain. The appearance of such “giant syringe” designs can be off-putting for patients who have a fear of injections. They can also cause problems for patients with limited dexterity who need to self-administer injections, who must align the device and support it against the skin, while performing whatever action the particular device requires to cause the delivery of the fluid. 
     SUMMARY OF THE INVENTION 
     The invention provides an injection device as defined in claim  1 . 
     The invention further provides a method of operating such an injection device, as defined in claim  15 . 
     Features of the invention that are preferred but not essential are defined in the dependent claims. 
    
    
     
       THE DRAWINGS 
         FIG.  1    is a perspective view of an injector device according to the invention. 
         FIG.  2    is the same view as  FIG.  1    with the air tank removed. 
         FIG.  3    is a longitudinal cross section through the injector device of  FIG.  1    after it has been primed. 
         FIG.  4    is a perspective view from above, showing the relationship between the rotary actuator and the needle holder. 
         FIG.  5    is a longitudinal cross section, showing the relationship between the rotary actuator and the needle holder in the latched condition of the device. 
         FIG.  6    is a perspective view from above, showing the relationship between the rotary actuator and the vial holder. 
         FIG.  7    is a longitudinal section through the vial holder on plane A-A of  FIG.  6   . 
         FIG.  8    is a longitudinal cross section similar to  FIG.  3   , showing the needle of the injector device in an advanced position. 
     
    
    
       FIG.  1    shows an injector device in accordance with the present invention. The upper part of the device comprises a domed compressed air tank  2 . The lower part of the device comprises a rotary actuator  4  having a wide base  3  and a central upstanding boss  5 . As will be described below, the device may be primed by gripping the actuator  4  on its knurled rim  6  and rotating it through a predetermined angle relative to the air tank  2 . The base  3  of the actuator  4  may then be rested against the skin of a subject and an injection can be performed by applying pressure to the broad upper surface  7  of the air tank  2  to move the tank towards the base  3  against the force of a compression spring  8 . A needle  9  on the axis of the device (not seen in  FIG.  1   ) is thereby lowered through an aperture in the base  3  to penetrate the surface of the skin. 
     The device in this embodiment of the invention has the overall appearance and function of a large push-button. Its rounded shape, being very different in appearance from a conventional hypodermic syringe or injector pen, is less threatening to many subjects who have a fear of needles. It is also very easy and reliable to use in a “twist and press” action. After the device has been primed by twisting the base  3  relative to the air tank  2 , the injection can then be performed with one hand. Operating the push-button requires little dexterity, and the wide base  3  keeps the device stable, ensuring that its axis remains perpendicular to the skin. 
       FIG.  2    is a similar view to  FIG.  1    but with the air tank  2  removed to reveal more details of the device. It can be seen that the spring  8  acts between the actuator  4  and a vial holder  10 , which can move axially relative to the actuator  4 . The vial holder  10  can move through a predetermined distance before a distal edge  11  of the vial holder butts against the base  3  of the actuator  4 . The vial holder  10  supports a vial  12  of the fluid that is to be delivered by the device. The upper (proximal) end of the vial  12  is exposed by the vial holder  10  and is closed by a vial cap  14 . The lower (distal) end of the vial  12  (not seen in  FIG.  2   ) is sealed by a septum  16  to maintain the contents of the vial sterile during transportation and storage. When pressure is applied to a plunger  18  within the vial  12 , it can slide axially in the distal direction to displace fluid from the distal end of the vial  12 . 
       FIG.  3    shows a cross section on the axis of the injector device of  FIGS.  1  and  2   . It shows how the vial holder  10  slides axially on an outer surface of the boss  5 . It also shows how an inner wall  20  of the air tank  2  is shaped to surround the vial  12  and to be capable of sliding axially on the periphery of the vial holder  10 . A valve  22  pierces an upper end of the inner wall  20  and provides a conduit for the selective release of compressed air from the tank  2  when a valve seal  24  is ruptured. The valve  22  is connected to an aperture in the vial cap  14  so that it can deliver compressed air into a space between the vial cap  14  and the plunger  18 , which will drive the plunger in the distal direction. When the air tank  2  slides on the vial holder  10  and moves axially relative to the vial  12 , the valve remains fixed in relation to the vial cap  14 . This relative movement between the air tank  2  and the valve  22  is capable of rupturing the valve seal  24  and releasing compressed air from the tank  2  into the vial  12 . A compression spring  26  acting between the air tank  2  and the valve  22  offers resistance to the relative movement between them. This valve spring  26  has a higher spring constant than the actuator spring  8 , whereby, when a given force is applied to the proximal surface  7  of the air tank  2 , the vial holder  10  will move fully through the predetermined axial distance before there is sufficient relative movement between the air tank  2  and the valve  22  to rupture the valve seal  24 . 
       FIG.  3    also shows a needle holder  32 . The needle holder  32  supports the needle  9 , which is aligned with the axis of the device. A distal end of the needle  9  can be moved along the axis to penetrate the skin of a subject, as previously described. A proximal end of the needle  9  can be moved in the proximal direction to pierce the septum  16  of the vial  12 , as seen in  FIG.  3   . The hollow needle  9  thereby provides a conduit for fluid to flow from the vial  12  into the skin of the subject. In this embodiment, the needle  9  is supported directly by the needle holder  32 . It would also be possible for the needle  9  to be supported in a needle hub (not shown), which is in turn mounted on the needle holder. For example, the needle hub could be generally cup-shaped, being concave in the proximal direction, and push-fitted onto a complementary structure at the distal end of the needle holder  32 . 
     The needle holder  32  is in turn supported by the vial holder  10 . The needle holder  32  comprises four hub arms  34  (seen in  FIGS.  4  and  5   ) that are circumferentially spaced and extend axially from the needle holder  32  in the proximal direction. The needle holder  32  comprises four hub arms  34  (seen in  FIGS.  4  and  5   ) that are circumferentially spaced and extend in the proximal direction from the needle holder  32 . The vial holder  10  comprises four complementary vial arms  36  that are circumferentially spaced and extend in the distal direction from the proximal end of the vial holder  10 . (The vial arms  36  can be seen through openings in the proximal end of the vial holder  10  in  FIG.  2   .) The hub arms  34  and the vial arms  36  interdigitate to form between them a complete collar around the vial  12  in the region where they overlap. They thus prevent relative rotational movement between the needle holder  32  and the vial holder  10  but they permit a degree of relative axial movement as the arms  34 , 36  slide past one another. It will be understood that the number of hub arms  34  and the number of vial arms  36  could be different from four. 
     The tips of the hub arms  34  project radially outwards to form a hub spring seat  38  and the tips of the vial arms  36  project radially outwards to form a vial spring seat  40 . A compression spring  42  acts between the two spring seats  38 , 40  and urges them axially apart. By urging the tips of the interdigitating hub arms  34  and vial arms  36  further apart, the tendency of the spring  42  is to increase the length of overlap between the arms  34 , 36 . If the needle holder  32  is free to move, the spring  42  therefore draws it in the proximal direction until the needle holder  32  abuts the vial holder  10  and the proximal end of the needle  9  has pierced the septum  16  of the vial  12 . The spring  42  thereafter holds the needle holder  32  and the vial holder  10  in abutment and they are effectively become locked together both axially and rotationally. 
     However, in accordance with the invention, it is required that the needle  9  should be prevented from piercing the septum  16  until the device is primed immediately before use. Accordingly, a latch mechanism is provided to restrain the axial movement of the needle holder  32  until the latch is released. 
     In the illustrated embodiment of the invention, the latch is provided by the rotary actuator  4 .  FIG.  4    shows how the needle holder  32  sits in a central aperture  44  of the boss  5  of the actuator  4 . Four circumferentially spaced hub holder lugs  46  project radially outwards from the needle holder  32 . Four circumferentially spaced actuator lugs  48  project radially inwards from the actuator  4 . When the actuator  4  is in a first angular position, as shown in  FIG.  4   , the actuator lugs  48  interfere with the hub holder lugs  46  to obstruct the passage of the needle holder  32  through the aperture  44 . Therefore, despite the action of the spring  42  urging the needle holder  32  in the proximal direction, it is restrained at the axial position shown in  FIG.  5   . When the needle holder  32  is latched in this position, the proximal end of the needle  9  does not pierce the septum  16  and the distal end of the needle  9  does not project beyond the base  3  of the actuator  4  so the device can remain safe and sterile during transport and storage. When the actuator  4  is manually rotated through a sufficient angle for the respective lugs  46 , 48  to pass each other, the needle holder  32  becomes free to move automatically under the influence of the spring  42 . This causes the needle  9  to pierce the septum  16  and prime the device for use. 
     It will be understood that the number of holder lugs  46  and the number of actuator lugs  48  does not have to be four; and it is not strictly essential that the numbers should be equal, provided that there are some rotary positions where the respective lugs  46 , 48  interfere to prevent the passage of the needle holder  32  through the aperture  42 . More generally, the aperture  42  can have almost any non-circular cross-section and it will be possible to design a profile of the needle holder  32  that will fit through it in certain angular positions but not in other angular positions. (Neither the aperture nor the profile can have circular symmetry about the axis.) It is preferred that the actuator  4  should not need to be rotated through a large angle to release the latch. For example, the angle is preferably less than 45° and more preferably 15° to 20°. 
     Rotation of the actuator  4  relative to the needle holder  32  is permitted by the engagement between the actuator  4  and the vial holder  10 . (It will be recalled that the vial holder  10  and the needle holder  32  are rotationally locked together by their respective interdigitating arms  34 , 36 .) As seen in  FIG.  4   , four circumferentially spaced protrusions  50  project radially outwards from the periphery of the boss  5  of the actuator  4 . Each protrusion  50  is located in a guide track  52  on a cylindrical inner surface of the vial holder  10 .  FIGS.  6  and  7    show that each guide track  52  follows a substantially L-shaped course, comprising a linear part  54  that is parallel to the axis and a circumferential part  56  that intersects with the distal end of the linear part  54 . When the protrusions  50  of the actuator  4  follow the circumferential parts  56  of the guide tracks, they permit relative rotation but not relative axial movement between the actuator  4  and the vial holder  10 . When the protrusions  50  of the actuator  4  follow the linear parts  54  of the guide tracks, they permit relative axial movement but not relative rotation between the actuator  4  and the vial holder  10 . 
     When the protrusions  50  of the actuator  4  are located at the blind ends of the circumferential parts  56  of the guide tracks, this corresponds to the rotary actuator  4  being in its first position, in which the actuator lugs  48  obstruct the holder lugs  46  to restrain the needle holder  32  against axial movement. At the same time, the shape of the guide track  52  prevents relative axial movement between the actuator  4  and the vial holder  10 . Therefore, in the first position, not only is the needle holder  32  latched to prevent priming of the device but the operation of the “push-button” is also latched to prevent accidental deployment of the injector needle  9 . 
       FIG.  6    shows the profile of the linear parts  54  of the guide tracks  52 , which is complementary to the profile of the protrusions  50 . (In  FIG.  6   , the protrusions  50  are partly rotated out of view in the circumferential parts  56  of the guide tracks  52 .) It can be seen that the profile includes a “bump”  57 , which offers slight resistance when the actuator  4  is rotated to or from the first position and provides haptic and/or audible feedback in the form of a click when the device is latched or unlatched. 
     As the actuator  4  is rotated from its first position to its second position, the needle holder  32  becomes unlatched and moves under the influence of the spring  42  to prime the device for use. The same rotation causes the protrusions  50  to follow the circumferential parts  56  of the guide tracks  52  until they reach the intersection with the linear parts  54 . In this second position, the vial holder  10  becomes free to move axially relative to the actuator  4  and the device can be operated to inject the fluid into the skin of a subject. If desired, an intermediate angular position of the actuator  4  could be defined between the first and second positions, at which the device has been primed but the push-button has not yet been unlatched. A second bump could be provided in the profile of the circular parts  56  of the guide tracks to hold the actuator  4  in that intermediate position and provide further haptic and/or audible feedback to the user. 
     Note that it would be possible to invert the illustrated arrangement so that protrusions from the vial holder  10  follow guide tracks in the actuator  4 . 
     In the light of the foregoing explanation, the operation of the device should be apparent but will now be briefly described. 
     During manufacture, the device is assembled around a sealed and sterile vial  12 . The actuator  4  is rotated to the first position to latch the device against premature priming or operation during transport and storage. The needle holder  32  is restrained in the position shown in  FIG.  5   . 
     When it is desired to deliver the dose of fluid from the vial to a subject, the device is first primed by rotating the actuator  4  relative to the via holder  10  from its first position to its second position. This unlatches the needle holder  32 , which moves under the influence of the spring  42  to cause the proximal end of the needle  9  to pierce the septum  16  of the vial  12 . This is the position shown in  FIG.  3   . 
     The base  3  of the actuator is then placed against the skin of a subject and sufficient pressure is applied to the proximal surface  7  of the compressed air tank  2  to overcome the resistance of the actuator spring  8 . The air tank  2 , vial holder  10 , vial  12  and needle holder  32  move axially as a unit, sliding on the boss  5  of the actuator  4  until the bottom edge  11  of the vial holder  10  abuts the base  3  of the actuator  4  and the distal end of the needle  9  has penetrated the skin of the subject. In this position the vial holder  10  can move no further but, as shown in  FIG.  8   , there remains a small gap  58  between the bottom of the compressed air tank  2  and the base  3  of the actuator  4 . Further pressure applied to the proximal surface  7  of the air tank  2  can overcome the resistance of the valve spring  26  and cause further axial movement of the air tank  2  relative to the vial holder  10  and the valve  22 , to close the gap  58 . The relative movement between the air tank  2  and the valve  22  causes the valve seal  24  to rupture and releases compressed air from the tank  2  into the vial  12 , thereby driving the plunger  18  in the distal direction and displacing fluid from the vial  12  through the hollow needle  9  and into the skin of the subject. 
     The invention has been described with reference to a single embodiment but there is no intention to limit the scope of the invention to that embodiment of it. The reader will understand different ways of putting the invention into practice. It should also be understood that different aspects of the illustrated embodiment can be used independently of each other. In particular, the means for priming the device by unlatching it, to allow an internal spring  42  to drive the needle  9  to pierce the septum  16 , could be used with a different means for operating the device to deliver a dose of fluid to the subject.