WO2006066963A1

WO2006066963A1 - Segmented piston rod

Info

Publication number: WO2006066963A1
Application number: PCT/EP2005/013986
Authority: WO
Inventors: Bo Radmer
Original assignee: Novo Nordisk A/S
Priority date: 2004-12-23
Filing date: 2005-12-23
Publication date: 2006-06-29
Also published as: JP2008525070A; EP1830906A1

Abstract

The present application relates to a piston rod for a syringe device, the piston rod comprising a plurality of axially arranged segments (1) forming a stack of segments having a base length, the plurality of segments (1) being rotatable relative to each other. In the stack of segments at least two of the plurality of segments (1) each comprises an inclined surface (5) relative to the axial direction of the piston rod so that a relative rotation between these two segments causes the length of the stack of segments to change.

Description

SEGMENTED PISTON ROD

FIELD OF THE INVENTION

The present invention relates to a segmented piston rod. In particular, the present invention relates to a segmented piston rod for use in syringe devices such as in medication or injection delivery devices.

BACKGROUND OF THE INVENTION

US 5,514,097 discloses a medicament injection apparatus for subcutaneous or intramuscular delivery of a medicament. The apparatus conceals a needle behind a needle shroud. On apparatus activation, the needle is trust forward, pushing the needle tip outside the needle shroud with enough force to puncture the skin. The needle is thus automatically introduced into the tissue at the proper needle skin orientation. In the same action, the apparatus automatically dispenses an accurate pre-set dose of medicament. The dose can be set by a manual, variable dosing assembly or by an automatic dosing assembly.

US 2002/0016571 relates to a device for administering an injectable medicament in doses. The device according to US 2002/0016571 comprises among other elements a reservoir for the medicament and a piston which forces the medicament out of the reservoir when moved in a feed direction towards a reservoir outlet.

In both US 5,514,097 and US 2002/0016571 the piston for forcing the medicament out of its reservoir is a stiff and rigid element having a constant and thereby non-variable length.

US 6,508,788 discloses a medication delivery device comprising a container containing a fluid medicament. The medicament is expelled from the container by moving forward an elastomeric piston inside a cartridge. The piston is moved forward by a telescopic piston rod, which can either be centrally located in the container or eccentric located. One end of the telescopic piston rod abuts the elastomeric piston either by itself or through an additional plate. The abutment proves a friction large enough to prevent a lower part of the telescopic rod from rotating. In order to prevent the elastomeric piston from rotating inside the container a second telescopic piston rod is provided parallel with the first telescopic piston rod Other references, such as WO 03/062672 and WO 01/78811, also disclose telescopic- based piston rods.

However, in telescopic-based systems it is difficult to maintain full control over the outermost element of the telescopic rod whereby exact control over a dose to the ejected from e.g. a syringe device is lost. This lack of controllability is a major drawback of such telescopic-based syringe devices.

Thus, it is an object of the present invention to provide a piston rod arrangement offering full control over each element constituting the piston rod.

It is a further object of the present invention to provide an expandable piston rod arrangement that in a non-expanded state takes up as little space as possible. By reducing the space required by the non-expanded piston rod, the overall size of a syringe device housing the piston rod may be reduced.

SUMMARY OF THE INVENTION

The above-mentioned objects are complied with by providing, in a first aspect, a piston rod for a syringe device, the piston rod comprising a plurality of axially arranged segments forming a stack of segments having a base length, the plurality of segments being rotatable relative to each other, wherein at least two of the plurality of segments each comprises at least one inclined surface relative to the axial direction of the piston rod so that a relative rotation between these two segments causes the length of the stack of segments to change.

One or more segments may be adapted to be rotated between an initial and an end position. The angle of rotation between the initial and the end position may in principle be from just a few degrees and up to 360 degrees.

In order to keep control of the plurality of segments, a first locking arrangement may be provided. The first locking mechanism may be adapted to fixate any of the plurality of segments in a position between a segment's initial and end position so as to provide a infinitely expendable piston rod. The first locking mechanism is applied during the expansion of the length of the stack of segments. This first locking mechanism may be implemented as a key/keyway connection between the segments and an interior surface part of an associated syringe device. A second locking arrangement may be provided. This second locking mechanism may be implemented as mechanism working directly between two neighbouring segments when a segment is brought into its outer most position relative an abutting segment. The second locking mechanism may be implemented in various ways, such as ripples formed as microstructures on a surface part of the segments, edges or indentations formed on a surface part of the segments.

Each segment may, in a plane substantially perpendicular to the axial direction of the piston rod, be constituted by at least two substantially identical portions. In one embodiment, each segment is constituted by two substantially identical portions each having at least one inclined surface. In another embodiment, each segment may, in a plane substantially perpendicular to the axial direction of the piston rod, have a helical- formed inclined surface.

The stack of segments may comprise between 5 and 30 segments, such as between 10 and 20 segments. Each or just some of the segments may be made of metal or made of a polymer-based material, such as plastic. In case a number of segments are made of metal the segments could be fabricated using a stamping process, or alternatively, the segments could be sintered from a metal powder.

The diameter of each segment may be adapted to fit within a cartridge of an associated syringe device meaning that the diameter of each segment may be within the range between 5 and 15 mm, such as approximately 10 mm.

In a second aspect, the present invention relates to a syringe device comprising a piston rod according to the first aspect. The syringe device may be a medication delivery device or any other kind of injection device.

In a third aspect, the present invention relates to a segment for a segmented piston rod for a syringe device, the segment comprising an inclined surface relative to an axial direction of the piston rod so that a relative rotation between the segment and another segment causes the length of the segmented piston rod to change.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in further details with reference to the accompanying drawings, in which Fig. 1 shows a first embodiment of the piston rod according to present invention,

Fig. 2 shows a second embodiment of the piston rod according to the present invention, and

Fig. 3 shows an example of the piston rod according to the present invention when said piston rod is installed in a medication delivery device.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In the most general aspect of the present invention, a piston rod is formed by a plurality of segments arranged to form a stack of segments. The segments forming the stack are rotatable relative to each other so that for example one or more segment may be kept at a fixed orientation whereas one or more other segments may be rotated relative to the one or more fixed segments. In order for the stack of segments to be expandable at least two of the segments must have an inclined surface so that a relative rotation between these two segments expands the overall length of the stack of segments forming the piston rod. The stack of segments may be formed by identical segments, or it may be formed by sets of segments, where each set of segments is formed by a base segment and a rotating segment. Alternatively, the stack of segments may be formed by a combination of a set or sets of segments and identical segments.

When expanding the length of the stack of segments the following procedure is generally followed: The segment to be separated from the stack of non-separated segments - i.e. the segment to be pushed forward - is kept fixed relative to a piston plate abutting the cartridge containing the medicament to be ejected from the syringe device. Thus, it is the segment or segments not abutting the piston plate that are rotated when a segment is to be pushed forward. The rotation of this or these segments pushes - via one or more inclined surfaces - the segment to be displaced in the direction of the cartridge causing a dose of medicament to be ejected from the cartridge. Figs. 1 and 2 show various of examples of segments suitable for implementing the present invention. As seen, the segments may take various forms and shapes, but in order to expand the stack length by rotating at least two segments must have at least one inclined surface.

The diameter of the segments forming the stack of segments may in principle be arbitrary. However, in order to use the stack of segments as a piston rod in a medication delivery device, the diameter of the segments must fit within the cartridge holding the medicament to be ejected from the mediation delivery device. Segments according to the present invention would preferably be within the range between 5 and 15 mm, such as approximately 10 mm.

Fig. 1 shows an embodiment of the present invention. Fig. Ia shows an isolated segment according to this embodiment, Fig. Ib shows a stack of segments in a non-expanded state, whereas Fig. Ic shows the stack of segment in an expanded state.

As seen in Fig. Ia the segment 1 according to this embodiment is constituted by two identical half's 2 and 3. Each half comprises a mechanical stop mechanism 4 and two oppositely inclining surfaces 5 and 6. The inclining surfaces incline over angle corresponding to 180 degrees and terminate at the mechanical stop 4. The inclining angle will depend on the number of segments forming the stack. In case 15 segments form the stack, and the stack should be capable of expanding a distance of 50 mm, each segment shall contribute to the expansion is within 3.3 mm.

Fig. Ib shows a stack formed by three segments 7, 8, and 9. By arranging two neighboring segments opposite to each other a perfect match between them is achieved. This perfect match is seen in Fig. Ib between segments 7 and 8, and between segments 8 and 9. It is also seen that the mechanical stop mechanism 4 sets the minimum length of the overall stack. Thus, when stop 4 of segment 7 abuts the corresponding stop of segment 8 the minimum length of the stack formed by segments 7 and 8 is achieved. Similar considerations apply between segments 8 and 9.

In case the overall length of the stack of segments is to be increased two of the segments, for example 8 and 9, need to be rotated relative to the third segment 7. During this rotation segments 8 and 9 are kept in a fixed relationship relative to each other. The relative rotation between segments 8 and 9 and segment 7 causes the length of segments 7 and 8 to increase whereby the overall length of the stack increases. When segments 7 and 8 reaches their, in relation to each other, outermost position segments 7 and 8 are fixed to each other by some sort of fixation means. Such fixation could involve click arrangements in the form of protrusions, rough surface parts of the inclined surface etc. At this outermost position between segments 7 and 8 no further expansion may be achieved via relative movements of segments 7 and 8. However, if segment 9 is rotated relative to segments 7 and 8 (which are now fixated to each other) a further expansion of the stack length is achievable. Fig. Ic shows an example where all three segments (7, 8, and 9) have been rotated relative to each other. However, none of the segments shown in Fig. Ic have reached their outermost positions which means that the overall length of the stack of segments shown in Fig. Ic may be further increased.

Fig. 2 shows another embodiment of the present invention. Fig. 2a shows an isolated segment, Fig. 2b shows three segments arranged in a stack in an unexpanded state, whereas Fig. 2c shows two segments arranged to form an expanded state of a stack.

Again, each segment 10 is constituted by two identical half's 11 and 12 - see Fig. 2a. Each half comprises a stop mechanism in form of a stop surface 13, and an inclined surface 14. Fig. 2b shows how three segments can form a stack in its unexpanded state.

Fig. 2c shows the expanded state of a stack formed by two segments. As seen the two segments 15 and 16 are rotated relative to each other whereby the overall length of the stack is significantly increased. In the illustration shown in Fig. 2c the segments 15 and 16 are close to their mutual outermost position and a fixation means will lock the two segments together if segment 16 is rotated further in the counterclockwise direction relative to segment 15.

Fig. 3 shows the segmented piston rod according to the present invention positioned in a medication delivery device 26. The segmented piston rod is operated as follows:

The dose to be ejected is set by rotating the scale drum 17 upwards in the inner housing threads 18. A rosette 19 between the scale drum and a connector pipe 20 is pushing the connector pipe 20 upwards. The connector pipe 20 is prevented from rotating by a dosage cup 21. The dosage cup 21 is locked by a one-way ratchet (not shown) with the housing of the medication delivery device.

When a dose is to be delivered from the medication delivery device the button 22 needs to be pushed down. When the button 22 is pushed down the scale drum 17 and the connector pipe 20 causes the dosage cup 21 to rotate. When the dosage cup 21 is rotating, the idle segments 23 (the segments closest to the dosage cup 21) will rotate with the dosage cup 21. The segment to be pushed forward 24 (towards the cartridge) is prevented from rotating. In order to prevent the segment 24 abutting the cartridge from rotating this segment 24 may have a key/keyway connection (not shown) with the housing of the medication delivery device. By keeping the segment 24 in a fixed relation with the housing a relative rotation between segments 23 and segment 24 is provided whereby segment 24 is pushed in a direction towards the cartridge.

When segment 24 has reached its end position it is released from the key/keyway connection (or other type of locking arrangement). In case another segment has previously pushed towards the cartridge, the segment just released from the locking arrangement is locked to that segment. This is in fact illustrated in Fig. 3 where segment 25 has previously been pushed towards the cartridge.

When segment 24 has been released, the next segment (the segment of segments 23 being closest to the cartridge) is locked to the housing and is now being pushed in the direction towards the cartridge upon rotation of the segment or segments between the locked segment and the dosage cup 21.

Claims

1. A piston rod for a syringe device, the piston rod comprising a plurality of axially arranged segments (1) forming a stack of segments having a base length, the plurality of segments (1) being rotatable relative to each other, wherein at least two of the plurality of segments (1) each comprises at least one inclined surface (5) relative to the axial direction of the piston rod so that a relative rotation between these two segments causes the length of the stack of segments to change.

2 A piston rod according to claim 1, wherein one or more segments are adapted to be rotated between an initial and an end position.

3. A piston rod according to claim 2, further comprising a first locking arrangement adapted to fixate any of the plurality of segments in a position between a segment's initial and end position so as to provide a infinitely expendable piston rod.

4. A piston rod according to claim 3, wherein the first locking arrangement is provided on an interior surface part of an associated syringe device.

5. A piston rod according to any of the preceding claims, further comprising a second locking arrangement adapted to fixate any of the plurality of segments in an outer most position relative an abutting segment.

6. A piston rod according to claim 5, wherein the second locking arrangement is provided on a surface portion of a number of the plurality of segments.

7. A piston rod according to any of the preceding claims, wherein each segment, in a plane substantially perpendicular to the axial direction of the piston rod, is constituted by at least two substantially identical portions.

8. A piston rod according to claim 7, wherein each segment is constituted by two substantially identical portions.

9. A piston rod according to claim 8, wherein each of the two substantially identical segments comprises at least one inclined surface.

10. A piston rod according to any of claims 1-6, wherein each segment, in a plane substantially perpendicular to the axial direction of the piston rod, has a helical-formed inclined surface.

11. A piston rod according to any of the preceding claims, wherein the stack of segments comprises at least 5 segments.

12. A piston rod according to claim 11, wherein the stack of segments comprises between 5 and 30 segments, such as between 10 and 20 segments.

13. A piston rod according to any of the preceding claims, wherein each segment is made of metal or made of a polymer-based material, such as plastic.

14. A piston rod according to any of the preceding claims, wherein the diameter of each segment is adapted to fit within a cartridge of an associated syringe device.

15. A piston rod according to claim 14, wherein the diameter of each segment is within the range between 5 and 15 mm, such as approximately 10 mm.

15. A syringe device comprising a piston rod according to any of the preceding claims.

16. A syringe device according to claim 15, wherein the syringe device is a medication delivery device.

17. A segment for a segmented piston rod for a syringe device, the segment comprising an inclined surface relative to an axial direction of the piston rod so that a relative rotation between the segment and another segment causes the length of the segmented piston rod to change.