WO2011026932A1

WO2011026932A1 - Cupped piston for a cartridge for drug delivery devices

Info

Publication number: WO2011026932A1
Application number: PCT/EP2010/062932
Authority: WO
Inventors: Michael Jugl; Günther SENDATZKI; Axel Teucher; Martin Otten
Original assignee: Sanofi-Aventis Deutschland Gmbh
Priority date: 2009-09-07
Filing date: 2010-09-03
Publication date: 2011-03-10

Abstract

Cupped Piston for a Cartridge for Drug Delivery Devices The present invention relates to a cartridge for a drug delivery device (13) comprising a housing having a distal end portion and a proximal end portion, wherein said proximal end portion is sealed with a piston (12) slidably disposed therein, wherein said piston comprises: - at least one annular sealing surface (20, 24) to radially abut against an inner side wall (15) of the cartridge, - a distal surface (28) to confine a drug receiving volume of the cartridge (16), - a thrust receiving surface (23) to engage with a plunger (11) of a drug delivery device (13) for displacing the piston in a proximal direction relative to the side wall (15), wherein the distal surface (28) and the thrust receiving surface (23) are disposed on opposite sides of a bottom portion (18), - a side wall portion (17) of tubular shape and being integrally formed with the bottom portion (18), wherein at least one sealing surface (24) is disposed distally with respect to the thrust receiving surface (23), and wherein the axial thickness of the bottom portion (18) and/or the radial thickness of the side wall section (17) is between 1 mm and 2 mm, preferably around 1 mm or less.

Description

Cupped Piston for a Cartridge for Drug Delivery Devices Field of the Invention

The present invention generally relates to pistons to be slidably disposed in cartridges containing a medicinal product to be disposed by means of drug delivery devices, such as pen-type injectors.

Background and Prior Art

User operated drug delivery devices are as such known in the prior art. They are typically applicable in circumstances, in which persons without formal medical training, i.e., patients, need to administer an accurate and predefined dose of a medicinal product, such as heparin or insulin. In particular, such devices have application, where a medicinal product is administered on a regular or irregular basis over a short term or long-term period. In order to accommodate with these demands, such devices have to fulfil a number of requirements. First of all, the device must be robust in construction, yet easy to use in terms of handling and in understanding by the user of its operation and the delivery of the required dose or medicament. The dose setting must be easy and unambiguous. Where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose. Moreover, the device should be suitable for recycling. To meet these requirements, the number of parts required to assemble the device and the number of material types the device is made from need to be kept to a minimum.

Such pen-type injectors are typically adapted to receive a replaceable or disposable cartridge containing the medicinal product to be disposed by the device. The cartridge comprises an outlet to be coupled with a piercing element, e.g. an injection needle, cannula or the like in a fluid transferring way. Further and in order to expel a

predefined dose of the medicinal product, a plunger of a drug delivery device is adapted to act on the piston for displacing said piston by a predefined distance in distal, thus dose-dispensing direction.

Figure 1 shows a cross sectional illustration of a piston 2 operably engaged with a drive mechanism 3 of a drug delivery device 1 according to the prior art. The drive mechanism 1 acts on a proximal and thrust receiving surface of the piston 2 by means of a pressure piece 4. In response to this force effect, the piston 2 moves in distal direction, that is downwards in Figure 1 . Due to its elastic properties, the piston 2 becomes subject to axial squeezing being accompanied by radial expansion. Such radial expansion contributes to an increase of friction forces between the piston and the side walls 5 of the cartridge 6, which is disadvantageous for a smooth running and easy displacement of the piston in the cartridge.

On the one hand, the piston has to provide a durable and leak-proof seal in order to prevent any uncontrolled discharge of medicinal product. On the other hand, the piston also has to prevent ingress of foreign substances into the drug receiving volume of the cartridge. Apart from its sealing capability, the piston has to be displaceable with respect to the side walls of the cartridge. Friction forces inherently present at the contact surfaces of cartridge side walls and piston should be kept to a minimum.

Document US 2002/0032413 A1 for instance discloses a plunger stopper for syringe barrels that has one or more constrictions at a first and a second end. Further, first and second ends of this plunger stopper are of tapered design. Since pistons as they are known in the prior art are typically made of an elastic material, they become subject of an at least marginal compression during dose dispensing. After dose dispensing, said elastic material reconstitutes to its original dimensions, which is accompanied by elastic relaxation of the piston. Since at the end of a dose dispensing action, the proximal surface of a cartridge's piston commonly remains in contact with a plunger of the drug delivery device, the inevitable elastic relaxation of the piston may lead to a pressure increase inside the drug receiving volume of the cartridge. Such pressure enhancement may in turn result in an uncontrolled dispensing or expelling of the medicinal product even after a drug dispensing procedure has terminated. The elastic properties, in fact the elastic relaxation of a cartridge's piston therefore contributes to the development of droplets of the medicinal product at the tip of a needle or cannula being coupled with the container in a fluid-transferring way.

Objects of the Invention

It is therefore an object of the present invention to provide an improved piston for a cartridge containing a medicinal product to be dispensed by means of a drug delivery device. The piston should be easily displaceable in the cartridge yet maintaining a suffiecent air- and liquid proof seal with the walls of the cartridge to prevent any fluid leakage.

It is a further object of the present invention, to provide a piston having a diminished impact on the development and generation of post-dispensing droplets.

Summary of the Invention

The present invention relates to a cartridge for a drug delivery device, typically designed as an ampoule- or carpule, which is to be coupled with or which is disposed in the drug delivery device for dispensing of a predefined dose of a medicinal product contained in the cartridge. The cartridge comprises a housing having a distal and a proximal end portion, wherein at least said proximal end portion is sealed with a piston. The piston comprises at least one annular sealing surface to radially abut against an inner side wall of the cartridge. Said piston comprises a distal surface to confine a drug receiving volume of the cartridge. The piston which is adapted to be slidably disposed in axial, preferably in distal direction with respect to the cartridge's side walls, further comprises a thrust receiving surface to become operably engaged with a plunger of the drug delivery device. By means of the plunger, the piston can be displaced in distal direction relative to the cartridge's side wall in order to expel and to dispense a predefined amount of a liquid drug contained in the drug receiving volume of the cartridge.

At least one of the annular sealing surfaces of the piston is disposed proximally with respect to the thrust receiving surface. In other words, and with respect to the dose- dispensing movement of the piston, the thrust receiving surface is disposed upstream compared to the at least one sealing surface. Hence, at least one annular sealing surface of the piston is disposed downstream or on a downstream side compared to the thrust receiving surface in relation to a dose-dispensing movement of the piston.

The piston comprises a substantially cylindrical or tubular side wall section integrally formed with a bottom portion. The distal surface of the piston, confining a drug receiving volume of the cartridge and the proximal thrust receiving surface to engage with the plunger, are disposed on respective opposite distal and proximal faces of the piston's bottom portion. The axial extension of the bottom portion is preferably in the range of a few millimetres, preferably between 1 and 2 mm or even below 1 mm. Due to this comparatively small, disk-like bottom portion, elastic deformation and relaxation of the bottom portion can be kept in a low range. The piston according to the present invention comprises such a shape and geometry that, under the effect of a distally directed thrust acting on the thrust receiving surface leads to a respective axial displacement of at least one annular sealing surface. This axial, preferably distal displacement of the sealing surface is predominately governed by dragging rather than pushing. The sealing surface therefore trails the movement of the thrust receiving surface of the piston. Since at least one annular sealing surface is rearwardly and proximally disposed compared to the thrust receiving surface, application of force to the thrust receiving surface transfers to a drag and/or trailing force leading to a respective displacement of the at least one annular sealing surface.

Having the sealing surface disposed closer to the drive mechanism than the thrust receiving surface of the piston, the piston may become subject to an axial and elastic elongation during a dose dispensing action. Since an annular sealing surface of the piston is disposed downstream compared to the thrust receiving surface, an elastic relaxation process does substantially not affect the axial distance between a distal surface and a thrust receiving surface of a piston. Even though for some reason, axial distance between sealing surface and thrust receiving surface should become subject to a variation, the bottom portion of the piston or its thrust receiving surface by no way further displaces in distal direction. Since during a dose dispensing procedure, the piston may become subject to axial elongation, after termination of dose dispensing, the thrust receiving surface and/or the distal surface of the piston's bottom portion may become subject to a proximally directed displacement, which tends to generate a negative pressure in the drug receiving volume of the cartridge.

The thrust receiving surface is preferably arranged in a transverse plane of the substantially cylindrical housing or barrel of the cartridge. Hence, the surface normal of the thrust receiving surface substantially extends in axial direction.

According to a first preferred embodiment of the invention, the relative position of the thrust receiving surface and at least one annular sealing surface is such, that the axial distance between said sealing surface and thrust receiving surface at least temporaly increases under the effect of a distally directed thrust acting on the thrust receiving surface. In other words, the piston comprises such a contour, shape and/or geometry, that an elastic deformation and expansion of the piston may predominately affect only the relative axial position of the at least one sealing surface and the thrust receiving surface. However, the elastic properties of the piston does no longer noticeably has influence on the axial distance of a piston's distal end face and/or its thrust receiving surface. In a further preferred embodiment, the piston comprises a receptacle opened to the proximal direction for receiving the plunger of the drug delivery device. Generally, the piston comprises a cupped geometry with a bore or receptacle being open to the proximal direction.

According to further embodiment, the substantially cylindrical or tubular side wall section of the piston is substantially plane and even shaped in axial direction and allows to removably receive a piston rod of a drive mechanism of a drug delivery device. The receptacle and in particular its side wall portion designed not to become mechanically connected or otherwise engaged with the piston rod of the drive mechanism of the drug delivery device. Mechanical engagement of piston and piston rod exclusively occurs through an abutment of thrust receiving surface and piston rod.

In a further preferred embodiment, the axial depth of the receptacle corresponds to at least 50 %, preferably at least 70 % and most preferably at least 80 % of the piston's axial elongation. In this way, the axial distance between a thrust receiving or proximal surface of the piston and its distal surface is smaller than 50 %, 30 % or 20 % of the piston's axial elongation. By reducing the axial distance between the piston's distal surface and thrust receiving surface, droplet-inducing impact of the piston's elastic deformation and relaxation can be advantageously diminished.

In another preferred embodiment, the side wall section of the piston at least sectionally comprises a concave shaped outer contour between adjacent, axially separated sealing surfaces. In a typical embodiment, the piston comprises at least two annular sealing surfaces, wherein a first sealing surface is disposed close to a distal end of the piston and a second annular sealing surface is disposed near a proximal end of the piston. Due to the concave shaped side wall section, the contact surface between piston and side walls of a cartridge can be advantageously reduced allowing for a smooth-running axial dose-dispensing displacement of the piston with respect to the cartridge's side walls. According to another preferred embodiment of the invention, also the bottom portion comprises at least one annular sealing surface adapted to provide a liquid-proof seal between piston and inner side walls of a cartridge. According to a further embodiment, the axial thickness of the bottom portion and/or radial thickness of the side wall section may also exceed 2 mm. Thickness of said portions may range between 1 mm and 5 mm or between 1 mm and 3 mm. Depending on the material used for the piston and depending on its intrinsic elastic properties, axial and/or radial thickness of bottom portion and side wall section of the piston may even be in a range around 1 mm or less.

In another embodiment, the piston is pre-assembled in the housing or barrel of the cartridge prior to mechanical engagement with the piston rod of the drug delivery device. This allows to fill the cartridge with the medicinal product before it is

commercially distributed and/or used. According to further embodiments, it is therefore intended that the drug receiving volume of the cartridge is at least partially filled or pre- filled with the injectable medicament.

While the distal end portion of the cartridge is typically to be coupled with a cannula, an injection needle or the like in a fluid-transferring way, the proximal end portion is sealed with the slidably disposed piston as described above. The cartridge may be of disposable or reusable type and may be used in conjunction with drug delivery devices, typically of pen-injector type, e.g. for administering numerous pre-defined doses of a medicinal product, in particular of insulin or heparin.

In a further independent aspect, the invention also reflects in a drug delivery device for dispensing of a dose of a liquid drug, which is contained in and provided by a cartridge as previously described. The drug delivery device comprises a plunger or piston rod, which is adapted to operably engage with a thrust receiving surface of the piston as described above. Hence, the plunger comprises a geometry that allows for insertion into the piston's receptacle until the plunger, which might be equipped with a thrust piece, operably engages with the piston's thrust receiving surface. Brief Description of the Drawings

Without limitation, the present invention will be explained in greater detail below in connection with preferred embodiments and with reference to the drawings in which:

Figure 1 depicts a drug delivery device in cross-sectional illustration with a cartridge according to the prior art, Figure 2 shows in cross-sectional illustration a drug delivery device with a cartridge and a piston according to the present invention and

Figure 3 illustrates an enlarged cross-sectional schematic illustration of the piston accordgin to the invention.

Detailed Description

The cartridge 16 as illustrated in Figure 2 comprises a cylindrical side wall 15 being adapted to slidingly receive the piston 12 having a cupped or at least partially hollow shape. The piston 12 has a bottom portion 18, which is integrally formed with the side wall section 17 of tubular or substantially cylindrical shape.

As further illustrated in Figures 2 and 3, the piston 12 comprises a first annular sealing surface 20 at its bottom portion 18 as well as a second annular sealing surface 24 at its upper, proximal end section. The bottom portion 18 comprises a thrust receiving surface 23 confining a receptacle 21 of the piston 20. The thrust receiving surface 23 is adapted to receive axial thrust exerted by a plunger 1 1 of a drug delivery device's 13 drive mechanism 1 . As illustrated in Figure 2, the plunger 1 1 at its distal and

downwardly directed end comprises a radially extended flange-like thrust piece 14, which abuts against the thrust receiving surface 23 of the piston 12. Opposite to the thrust receiving surface, the bottom portion 18 comprises a distal surface 28, which confines a drug receiving volume of the cartridge 16. Due to the cupped-like contour and shape of the piston 12, axial thickness or width of the bottom portion 18 is comparatively small, which provides a beneficial and advantageous reduced impact of any elastic deformation and relaxation processes on post- dispensing droplet generation. In typical embodiments, axial distance between the first annular sealing surface 20 and the thrust receiving surface 23 can be as small as 1 mm. Furthermore, also the side wall thickness 25 as depicted in Figure 3 might be as small as 1 mm. Moreover, the overall axial extension of the entire piston might be in the range of about 2 mm or less.

The side wall section 17 further comprises a concave shaped contour 22 between first and second annular sealing surfaces 20, 24. Further, the side wall section 17 comprises another concave-shaped constriction 29 at its proximal, upper end.

Axial extension of the entire piston 12 may range between 2 mm and 5 mm, preferably between 2 mm and 4 mm or even between 2 mm and 3 mm. In particular, axial distance 27 between thrust receiving surface 23 and the waste line of the concave side wall section 22 may be as small as about 1 mm or less.

Since the at least one sealing surface 24 is separated from the thrust receiving surface in proximal direction, a distally directed force effect acting on the thrust receiving surface 23 leads to a radial force transmission in the bottom portion and finally to a correspondingly distally directed dragging and/or trailing of the second sealing surface 24. In effect, the entire piston may become subject to axial elongation during a dose dispensing procedure. In this way, a smooth-running axial displacement of the piston can be provided and development of post-dispensing droplets can be counteracted. List of Reference Numerals

1 drive mechanism

2 piston

3 drug delivery device

4 pressure piece

5 side wall

6 cartridge

1 1 plunger

12 piston

13 drug delivery device

14 pressure piece

15 side wall

16 cartridge

17 side wall

18 bottom portion

20 sealing surface

21 receptacle

22 outer contour

23 thrust receiving surface

24 annular sealing surface

25 wall thickness

26 axial thickness

27 axial extension

28 distal surface

29 constriction

Claims

A cartridge for a drug delivery device (13) comprising a housing having a distal end portion and a proximal end portion, wherein said proximal end portion is sealed with a piston (12) slidably disposed therein, wherein said piston comprises: at least one annular sealing surface (20, 24) to radially abut against an inner side wall (15) of the cartridge , a distal surface (28) to confine a drug receiving volume of the cartridge (16), - a thrust receiving surface (23) to engage with a plunger (1 1 ) of a drug delivery device (13) for displacing the piston in a proximal direction relative to the side wall (15), wherein the distal surface (28) and the thrust receiving surface (23) are disposed on opposite sides of a bottom portion (18), - a side wall portion (1 7) of tubular shape and being integrally formed with the bottom portion (18), wherein at least one sealing surface (24) is disposed distally with respect to the thrust receiving surface (23), and wherein the axial thickness of the bottom portion (18) and/or the radial thickness of the side wall section (17) is between 1 mm and 2 mm, preferably around 1 mm or less. 2. The cartridge according to claim 1 , wherein the relative position of the thrust receiving surface (23) and the at least one sealing surface (24) of the piston (12) is such, that the axial distance between said sealing surface (24) and thrust receiving surface (23) at least temporally increases under the effect of a distally directed thrust acting on the thrust receiving surface (23).

The cartridge according to any one of the preceding claims 1 or 2, wherein the piston (12) further comprises a proximally opened receptacle (21 ) adapted to receive the plunger (1 1 ) of the drug delivery device (13).

The cartridge according to claim 3, wherein the axial depth of the receptacle (21 ) is at least 50 %, preferably at least 70%, most preferably at least 80% of the piston's axial elongation.

The cartridge according to any one of the preceding claims, wherein the substantially cylindrical or tubular side wall section (1 7) of the piston (12) is substantially plane and even shaped in axial direction adapted to removably receive a piston rod (1 1 ) of a drive mechanism (1 ) of a drug delivery device.

The cartridge according to any one of the preceding claims, wherein the piston (12) is pre-assmebled in the housing (15) prior to mechanical engagement with the piston rod (1 1 ).

The cartridge according to any one of the preceding claims, wherein the drug receiving volume is at least partially filled with an injectable

medicament.

The cartridge according to claims 6 or 7 , wherein the side wall section (17) of the piston (12) at least sectionally comprises a concave shaped outer contour between adjacent, axially separated sealing surfaces (20, 24).

The cartridge according to any one of the preceding claims, wherein the bottom portion (18) comprises at least one annular sealing surface (20). A drug delivery device for dispensing of a dose of a liquid drug contained in a cartridge according to any one of the preceding claims and comprising a plunger (1 1 ) adapted to operably engage with a thrust receiving surface (23) of a piston (12) of the cartridge (12).