Flexible sealing member for injection device

Abstract: The invention relates to a flexible sealing member (1) for an injection device, comprising a neck (2), enclosing a channel (3) which is open at one end (4) and is closed at the other end by a diaphragm (5) and having an annular flange (6) at its closed end for a clamping connection of the sealing member in the injection device, wherein said diaphragm (5) is at least substantially in the shape of a spherical cap, its convex outer surface being remote from the open end (4) of the channel (3) in said neck (2). The invention further relates to an injection device comprising said sealing member.

Description: The invention relates to a flexible sealing member for an injection device, which includes a needle holder for sealingly gripping an injection needle and a chamber, said sealing member comprises a neck, enclosing a channel which is open at one end and is closed at the other end by a diaphragm and having an annular flange at its closed end for a clamping connection of the sealing member in the injection device. Such a sealing member is disclosed in British Patent Specification 1,318,803 and can be used in an injection device to separate the injection liquid in the barrel of said injection device from the injection needle. It is known to effect the communication between the barrel and the injection needle by causing the diaphragm to burst as a result of the fluid pressure exerted on the diaphragm after actuation of the device. As a result of this communication, the injection liquid in the barrel can reach the injection needle and will be injected. Such sealing members can be used not only in manually operated injection devices, e.g. in prefilled injection devices, but also in automatic injection devices or auto-injectors, e.g. in an autoinjector as disclosed in British Patent Specification 1,449,986. In fact, automatic injection devices are also pre-filled with injection liquid; they are, however, intended for use by unqualified persons. For that purpose they are constructed so that the injection liquid can be administered automatically by a person not trained in giving injections. Consequently, automatic injection devices are designed first of all for use by persons who at a given instant, which is not known beforehand, have to administer an injection into their own body. These persons include, for example, soldiers after they have been exposed to an enemy warfare gas, for example, a nerve gas. However, many of the medicaments used in automatic injection devices show undesired side effects or are insufficiently or incompletely active in therapeutic dosages. Therefore, the activity of said medicaments is often made up with benzodiazepines, for example diazepam, which is known to have a muscle-relaxing activity. In addition to said therapeutic activity, diazepam also has a sedative effect, as a result of which the fighting value of the soldiers at the front is restored. For this latter purpose the soldier in the field is preferably provided with a separate automatic injection device which is filled with a liquid diazepam formulation. Such an injector is especially intended for appeasing a buddy in the battle field who has panicked as a result of war acts or injuries: that is "buddy aid". It will be obvious from the above that high requirements regarding reliability have to be imposed upon automatic injection devices. Such injectors are usually stored for many years at a time and, moreover, will be kept by the potential users for long periods of time under varying conditions. Despite these facts, the reliability of the injector must be sufficiently ensured at the critical instant when the injection is required. In fact, at said critical instant the user's life may depend on the ready operation of the injection device. Therefore, high demands should be made upon the mechanical properties of a sealing member having a centrally positioned diaphragm which bursts under pressure and then permits the injection liquid to reach the injection needle. It will be obvious that said diaphragm should retain its sealing function prior to use of the injection device, but should burst open at the proper instant to allow passage of the injection liquid. These properties of the diaphragm should last, even under extreme conditions which may occur upon use of the device. The authorities even require a proper functioning of the injection device in the temperature range from -10°C up + 50°C, to permit use of the device under both arctic and tropical conditions. It has been found, however, that an automatic injection device, provided with a sealing member as disclosed in British Patent Specification 1,318,803 mentioned hereinbefore, does not meet this requirement, in that at a temperature of -10°C the time required for ejecting the injection liquid is generally too long. The total time of ejection can be divided into the delay time, i.e. the time between actuation of the device and the start of liquid flow, and the real ejection time, i.e. the time between the start of liquid flow and the moment that said liquid flow has completely stopped. It has been observed that in particular the delay time of this known injection device is completely unpredictable and varies between broad limits; therefore the "ejection-behaviour" is not reproducible. This also applies when sealing members of bromobutyl rubber are used. This is the material of choice for injection devices comprising liquid diazepam formulations, as is described in European Patent Application 0390244. As mentioned in the above British Patent Specification 1,318,803, the injection device includes a needle holder for sealingly gripping an injection needle having in addition to a forward tip preferably also a backward tip, said needle holder including a chamber wherein the sharp backward tip of the needle extends and which allows a diaphragm - upon use of the injection device - to expand and to be ruptured by contact with said tip (Figures 3 and 4; page 3, left column, lines 32-62). It is the object of the present invention to provide a flexible sealing member for an injection device as defined in the opening paragraph, in which the above disadvantages do not occur. This object can be achieved according to the characterising part of claim 1 in that the diaphragm is at least substantially in the shape of a spherical cap, its convex outer surface being remote from the open end of the channel in said neck. It has been found surprisingly that by using the above sealing member of the invention in an injection device, in particular an automatic injection device, the above requirement is completely met. At low temperatures, e.g. at a temperature of -10°C, the injection liquid can be ejected with a considerably reduced delay time, providing a total ejection time within the required specifications. Moreover the "ejection-behaviour" is completely reproducible in that injection devices provided with the sealing member of the invention function well within acceptable time limits at low temperatures, e.g. at -10°C, and thus can be used conveniently under arctic conditions. The favourable properties of the sealing member of the invention are particularly prominent if the special shape of the diaphragm is combined with the shape of the flange as disclosed in British Patent Specification 1,318,803, mentioned hereinbefore, viz. having a substantially quadrangular cross-section, wherein both the front face and the rear face of said flange are acutely angled to the neck and extend in approximately the same direction, the outer edge of said front face projecting away from the neck. By using a sealing member with a flange as defined above, the diaphragm is prestretched during the clamping operation of the flange in the injection device. This prestretched condition of the diaphragm in the injection device guarantees an optimum "ejection behaviour", since after the bursting incident the flow aperture for the injection liquid can never be obstructed, so that the injection liquid behind the sealing stopper can then always freely reach the injection needle. When using a sealing member provided with a flange as defined above, said sealing member of the present invention is in a preferred embodiment dimensioned in such manner, that the front of the convex outer surface of the diaphragm projects forward from the neck over an at most substantially equal distance as the outer edge of the front face of the flange. This preferred embodiment of the sealing member of the invention is described in greater detail hereinafter. The present invention further relates to an injection device, comprising (i) a barrel which is open at each end, the forward end having a narrowed end portion with an adjoining outwardly extending flange, (ii) a needle holder for sealingly gripping an injection needle, said needle holder including a chamber and an outwardly extending flange part near the end of the chamber remote from the needle, and (iii) a flexible sealing member, comprising a neck with an outward annular flange. The sealing member is to be accomodated in said injection device in such manner that the neck of the sealing member is inserted in the narrowed end portion of the barrel and that the annular flange of the sealing member is sealingly clamped between the flange of the barrel and the flange part of the needle holder. Said injection device is characterized according to the present invention in that a sealing member as defined hereinbefore is accomodated in the injection device in such manner that the convex outer surface of the diaphragm faces the injection needle. The invention will now be described in greater detail with reference to a preferred embodiment which is shown in the drawings, in which Figure 1 is a cross-sectional view of an embodiment of the sealing member according to the invention, in a condition prior to accomodating said member in an injection device, taken on the line I-I of Figure 2, and Figure 2 shows the same sealing member viewed in the axial direction taken on the line II-II of Figure 1. The sealing member denoted with reference numeral 1 comprises a neck 2, enclosing a channel 3 which is open at one end 4 and is closed at the other end by a diaphragm 5. The thin-walled diaphragm is in the form of a spherical cap; the convex outer surface of said cap is remote to the open end 4 of the channel. At its closed end the sealing member has an annular flange 6 for a clamping connection of the sealing member in an injection device (not shown). The neck 2 is provided with four strengthening ribs 7. As will be obvious from Figure 1, the annular flange has a substantially quadrangular cross-section, wherein both the front face 8 and the rear face 9 are acutely angled to the neck and extend in approximately the same direction. The outer edge 10 of said front face, provided with a plurality of anti-adhesion bumps 12, projects away from the neck. The front 11 of the convex outer surface of the diaphragm projects forward form the neck over a substantialy equal distance as the outer edge 10 of the front face of the flange, aside from said anti-adhesion bumps. Upon accomodation of the sealing member in an injection device, the diaphragm is prestretched when the annular flange 6 is clamped between a flange part of the needle holder of said injection device and a flange of the barrel of said device, exactly as described in British Patent Specification 1,318,803 mentioned hereinbefore. The above-described sealing member is used in an automatic injection device as described in British Patent Specification 1,449,986, mentioned hereinbefore, and compared with a sealing member as known from British patent Specification 1,318,803. At a temperature of -10°C the total ejection time as well as the delay time, as defined above, are determined by actuating the injection device and measuring the time period up to the start of liquid flow and till the liquid flow has completely stopped. Fifty injection devices provided with sealing members as described above are compared with 50 equal devices, wherein known sealing members have been incorporated. For the injection devices according to the invention the average delay time at -10°C determined as described above, is 0, the average ejection time is 1.66 sec. The variation (standard deviation) in ejection time is 0.33. Under the same conditions for the known injection devices an average delay time of 1.16 sec. is found, said delay time varying between 0 and 7.35 seconds. The total ejection time for these known devices is 3.05 with a variation (standard deviation) of 1.64.

Claims: A flexible sealing member for an injection device which includes a needle holder for sealingly gripping an injection needle and a chamber - which sealing member (1) comprises a neck (2), enclosing a channel (3) which is open at one end (4) and is closed at the other end by a diaphragm (5) and having an annular flange (6) at its closed end for a clamping connection of the sealing member in the injection device, said sealing member being characterized in that the diaphragm (5) is at least substantially in the shape of a spherical cap, its convex outer surface (11) being remote from the open end (4) of the channel (3) in said neck (2). A sealing member as claimed in claim 1, characterized in that the annular flange (6) has a substantially quadrangular cross-section, wherein both the front face (8) and the rear face (9) of said flange are acutely angled to the neck and extend in approximately the same direction, the outer edge (10) of said front face projecting away from the neck, so that during the clamping operation of the flange in the injection device the diaphragm is prestretched. A sealing member as claimed in claim 2, characterized in that the front (11) of the convex outer surface of the diaphragm (5) projects forward from the neck (2) over an at most substantially equal distance as the outer edge (10) of the front face (8) of the flange (6). An injection device, comprising (i) a barrel which is open at each end, the forward end having a narrowed end portion with an adjoining outwardly extending flange, (ii) a needle holder for sealingly gripping an injection needle, said needle holder including a chamber, said needle holder further including an outwardly extending flange part near the end of the chamber remote from the needle, and (iii) a flexible sealing member, comprising a neck (2) with an outward annular flange (6); said sealing member to be accomodated in said injection device in such manner that the neck of the sealing member is inserted in the narrowed end portion of the barrel and that the annular flange of the sealing member is sealingly clamped between the flange of the barrel and the flange part of the needle holder; said injection device being characterized in that a sealing member as claimed in any of the preceding Claims is accomodated in the injection device in such manner, that the convex outer surface (11) of the diaphragm (5) faces the injection needle.

Inventors: RIS JACOBUS, VAN SCHOONHOVEN HENDRIK A, RIS, JACOBUS, VAN SCHOONHOVEN, HENDRIK A.
Applicants: DUPHAR INT RES, DUPHAR INTERNATIONAL RESEARCH B.V
Application year: 1991
Main classification: A61M5
IPC codes: A61M39, B65D51, A61M5