WO2012115560A1

WO2012115560A1 - Piston and container for a medical syringe

Info

Publication number: WO2012115560A1
Application number: PCT/SE2012/000016
Authority: WO
Inventors: Jan Svensson
Original assignee: Intradrug Medical Systems Ab
Priority date: 2011-02-21
Filing date: 2012-02-10
Publication date: 2012-08-30
Also published as: SE1100111A1; SE535700C2

Abstract

The invention relates to a piston (4) for a container (1) with a cylindrical inner surface, where the container is provided with a sealing upper seal (3, 6) through which at least one piston rod (5) extends in a slideable fashion. The piston is attached to the lower end of the piston rod and the container has a lower sealable opening (2). The main portion of the upper surface of the piston is convex, while the main portion of the lower surface of the piston is less convex than the upper surface. This makes the piston act as a check valve, which lets liquid pass only when the piston is moved in the container in one direction. In one embodiment the upper surface of the piston extends to the piston rod (5) and is attached at it. This gives the piston a more pronounced check valve characteristic. In another embodiment, a recessed channel (9) may extend on the upper surface of the piston from the periphery of the piston towards its centre. This channel further enhances the check valve characteristics of the piston. The invention further relates to a container (1) with a cylindrical inner surface, typically a syringe, with such a piston.

Description

Piston and container for a medical syringe

The present invention relates to a piston for a container and a container with such a piston according to the introductory portions of the independent claims.

In particular, it relates to such a piston for a container and a container with such a piston where the container is constituted by a syringe.

Background of the invention

WO2008150208 discloses a two chamber syringe where various substances may be stored separated from each other and then be mixed at a selected time for dispensing of the mixture. The substances are kept separated from each other by a piston with a penetrable seal that, when opened allows substances to flow from one chamber to another. The penetrable seal is bidirectional, which is suitable for mixing of certain kinds of substances, but less suitable for other kinds of substances where the penetrable seal should be unidirectional.

An object of the invention is therefore to provide a piston for a container and a container with such a piston where the piston is able to allow liquid to flow past it in one direction but not in the opposite direction.

These and other objects are attained by a piston for a container and a container with such a piston according to the characterising portions of the independent claims.

Summary of the invention

The invention relates to a piston 4 for a container 1 with a cylindrical inner surface, where the container is provided with a sealing upper seal 3, 6 through which at least one piston rod 5 extends in a slideable fashion. The piston is attached to the lower end of the piston rod and the container has a lower sealable opening 2. The main portion of the upper surface of the piston is convex, while the main portion of the lower surface of the piston is less convex than the upper surface, such that the lower surface of the piston may be flat or concave. This makes the piston act as a check valve, which lets liquid pass only when the piston is moved in the container in one direction. In this way, two different chambers with different substances may be kept separated, but allows them to be mixed when needed.

In a particularly advantageous embodiment the upper surface of the piston extends to the piston rod 5 and is attached at it. This gives the piston a more pronounced check valve characteristic.

In yet another advantageous embodiment, a recessed channel 9 may extend on the upper surface of the piston from the periphery of the piston towards its centre. This channel further enhances the check valve characteristics of the piston.

The invention further relates to a container 1 with a cylindrical inner surface, typically a syringe, with such a piston.

Brief description of the drawings

Fig. 1 shows a syringe with a piston according to the invention in a first usage step

Fig. 2 shows a syringe with a piston according to the invention in a second usage step

Fig. 3 shows a syringe with a piston according to the invention in a third usage step

Fig. 4 shows a syringe with a first embodiment of a piston in a first usage step

Fig. 5 shows the syringe in greater detail with the first embodiment of the piston

Fig. 6 shows the syringe with the first embodiment of the piston in a second usage step

Fig. 7 shows the syringe in greater detail with the first embodiment of the piston

Fig. 8 shows a side view of the first embodiment of the piston

Fig. 9 shows the first embodiment of the piston in an angled view from above

Fig. 10 shows the first embodiment of the piston from below

Fig. 11 shows a syringe with a second embodiment of a piston in a first usage step

Fig. 12 shows the syringe in greater detail with the second embodiment of the piston Fig. 13 shows the syringe with the second embodiment of the piston in a second usage step

Fig. 14 shows the syringe in greater detail with the second embodiment of the piston

Fig. 15 shows a side view of the second embodiment of the piston

Fig. 16 shows the second embodiment of the piston in an angled view from above

Fig. 17 shows the second embodiment of the piston from below

Description of preferred embodiments

Figs. 1-3 show a simplified illustration of a syringe with a piston according to the invention in a first, a second and a third usage step. Fig. 1 shows the syringe with the piston in a storage position, fig. 2 shows the syringe with the piston during mixing and fig. 3 shows the syringe with the piston in its lowermost position during dispensing.

The syringe does in regular fashion comprise an essentially cylindrical container 1 with a spout 2 at its lower end, and a top portion at its upper end. Inside the cylindrical container extends a piston 4 attached to a piston rod 5. The piston rod extends from the piston towards the top and extends through an upper seal 6. On top of the spout sits a spout lid 7 such that a chamber forms between the spout lid and the upper seal. The chamber is divided in two, one upper and one lower, by the piston and the chamber portions are approximately equal in size. The piston keeps substances stored in the two chamber portion separated in a fashion that is water tight, such that with the piston in the position illustrated in fig. 1, the two substances may be held fully separated for an unlimited period of time. The syringe thus constitutes a two chamber syringe where, for example, a dry substance may be stored in the lower chamber portion while a solvent is stored in the upper chamber portion.

The piston is embodied such that it acts as a check valve, as is further described in connection with figs. 4-17. If the piston is pulled towards the top of the syringe, it allows liquids to pass, while if it is pushed towards the spout of the syringe, it does not allow liquids to pass and forces it to follow the piston. In fig. 2 the piston has been pushed towards the top of the syringe and liquid from the upper chamber portion has been forced beyond the piston and has been dispensed into the lower chamber portion. In the figure, the two substances are illustrated as being separated only in order to explain the functionality, but in reality the liquid flows out under pressure and is mixed, which is the purpose of the design. When the substances have been fully mixed, the piston is pushed down towards the spout as illustrated by the arrow in fig. 3. In order to empty the contents through the spout, the spout lid has to be remove and in the figure it is removed.

Fig. 4 shows a syringe with a first embodiment of a piston in a first usage step, where the substances in the two chamber portions are kept separated by the piston for storage. Fig. 5 shows the syringe in greater detail with the first embodiment of the piston in the first usage step. The figure illustrates the lower end of the piston rod, where a widened end portion 8 is arranged. The end portion locks the piston to the piston rod and it is arranged near the centre of the piston.

The piston extends a short distance up the sides of the piston rod and creates a cylindrically symmetrical portion with a diameter slightly larger than the piston rod. The piston widens downwards and finally reaches the cylindrical inner wall of the syringe. At its widest, the piston has a diameter that slightly exceeds the inner wall diameter, such that it aligns against the inner wall with a certain pressure. The lower end of the piston is sharply cut off and forms an essentially flat, circular surface. Around the upper and lower circular edges of the widest portions of the piston, the piston is rounded to facilitate movement in either direction.

That the elastic piston extends up along the lower end of the piston rod, and thus reaches the piston differentiates it from regular seals for pistons. Pistons are typically designed as a rigid cylinder element, and an elastic seal is arranged around its periphery, such that the seal do not reach the piston rod. As the piston, which in the illustrated embodiment essentially corresponds to both the rigid cylinder element and the seal ring in a regular piston, on its upper side extends all the way into the piston rod, gives the piston the ability to be stetched out downwards from the piston rod and along its periphery such that it gives in to liquid pressure from above. The piston according to the invention is, with the exception of the widened end portion 8 of the piston rod and a short piece if the piston rod near the end portion, in its entirety constituted by an elastic substance such as rubber, silicone or similar.

As can be directly measured in fig. 5, the ratio between the height, h, of the part of the piston extending from its lower surface to the lower surface of the piston rod, and full height of the piston, H, extending to the top of the widened portion of the piston rod is 75%. Further, the ratio between the diameter of the piston rod, d, and the piston diameter, D, is 17%. These ratios have been shown to give the requested check valve properties of the valve, but obviously other ratios work too and h/H ratios in the interval 70%-80% are good, while h/H ratios in interval 50%-90% are acceptable. The basic idea is to position the piston rod end asymmetrically within the piston such that it tends to act differently while being slid upwards with respect to how it acts when slid downwards. Correspondingly d/D ratios in the interval 10%-30% are good, while d/D ratios in the interval 5%-50% are acceptable.

Fig. 6 shows the syringe with the first embodiment of the piston in a second usage step, where liquid from the upper chamber portion has flowed past the periphery of the piston and into the lower chamber portion. Fig. 7 shows the syringe in greater detail with the first embodiment of the piston in the second usage step. The piston is in movement upwards in the figure and liquid is passing the piston in a downwards direction as the arrows in the figure illustrates. As the piston is asymmetric, it exhibits different degrees of yield at movement upwards and downwards, respectively. When the piston is moved upwards as in the figure, the material around the periphery of the piston stretches downwards, which gives a very small movement of the material in the direction of the centre axis of the piston. This small movement or the diminished pressure that the piston exerts on the inside of the piston is sufficient to allow liquid to pass.

If the piston is then pushed downwards, the periphery of the piston is stretched upwards, and the conical upper portion of the piston then makes the piston expand radially such that the pressure the piston applies to the inner surface of the syringe instead increases and blocks passage of liquid in the opposite direction.

Figs. 8-10 show the first embodiment of the piston in a side view, in an angled view from above and from below, respectively. The figures illustrated five channels 9 on the upper side of the piston that extend radially from the centre of the piston. The channels are constituted by recessed tracks that extend from the narrower upper portion of the piston towards the periphery of the piston, but do in an unloaded state not reach all the way to the periphery. If the piston is pushed upwards, the periphery of the piston will be stretched somewhat downwards, and those of the end portions of the channels that are situated closest to the piston periphery will then be stretched out such that they reach closer to or all the way to the periphery. In this way the channels further facilitates passage of liquid past the periphery of the piston, as the piston is pulled upwards. If the piston on the other hand is pulled downwards, the periphery of the piston will on the contrary be stretched upwards, such that the channels are removed from the periphery and the piston continues to block flow of liquid past the piston despite the channels.

Fig. 11 shows a syringe with a second embodiment of a piston in the first usage step, that is when the piston seals the upper from the lower chamber portions. Fig. 12 shows the syringe in greater detail with the second embodiment of the piston in the first usage step. The piston is largely identical to the one according to the first embodiment, but does comprise a recess 10 on the lower surface of the piston that extends cylindrically symmetrically with respect to the centre axis of the piston rod. The lower surface, which in the first embodiment is flat, has a recess that extends upwards towards the piston rod but does not reach all the way to the end portion 8 of the piston rod.

The recess 10 is intended to further weakening the piston, such that it becomes more yielding as the piston moves upwards in the syringe, but with a nearly unchanged behaviour when the piston is pushed downwards. Alternatively the recess, which is deepest at the centre of the lower side of the piston, may be replaced by a shallow, annular recess that extends circularly symmetrically around the centre axis of the piston rod at the lower side of the piston near its periphery.

Fig. 13 shows the syringe with the second embodiment of the piston in the second usage step and fig. 14 shows the syringe in greater detail with the second embodiment of the piston in the second usage step. In figs. 13-14 the piston is moving upwards and the periphery of the piston then stretches downwards. The downward stretching of the periphery gives a diminished outwards directed pressure of the piston against the inner surface of the syringe, and this is sufficient to allow liquid to pass beyond the piston in a downwards direction.

In the second embodiment of the piston, the asymmetry between its upper and lower sides is more pronounced than in the first embodiment. Here, the upper portion of the piston extends upwards in a conical fashion, while on the lower portion it is provided with an essentially conical recess with the tip of the cone directed upwards.

Fig. 15-17 show the second embodiment of the piston in a side view, in an angled view from above and from below, respectively. The second embodiment of the piston is also provided with five channels that further facilitate passage of liquid when the piston is pushed upwards. The recess on the lower side of the piston increases the tendency of the piston to allow its periphery to stretch as it is pushed upwards, as compared to the first embodiment.

In the illustrated embodiments the container is exemplified as having a pipe shaped inner surface and a needle, but obviously the syringe may be any form of such a container, where the piston according to the invention divides its internal volume into two portions, and where liquid can pass the piston only when the piston is moved in one direction. The two embodiments of the piston constitute well working examples of a more generalized form that has a convex upper surface and a lower surface which is less convex that the upper, being flat as in the first embodiment or concave as in the second embodiment. Both embodiments are illustrated with channels, but this only constitutes an example and they are not necessary for the function.

The concepts of concave and concave, respectively, are typically used for spherical or near spherical objects, but the concepts here means the more generalized concepts of increasing towards the centre and decreasing towards the centre. The container with a tubular inner surface does in both embodiments have a circular cross section through the inner surface, but it may obviously be elliptical, rectangular or have any chosen shape. The concepts if increasing towards the centre then refers to a more arbitrarily selected centre point such as for example the centre of gravity of the cross section. The illustrated two chamber syringe may obviously be provided with further pistons that separate the storage volume into three of more chamber portions.

In both illustrated embodiments, the piston does at its upper side extend all the way to the piston rod and is attached to it as the whole piston is cast around the piston rod. The purpose of this is that the upper portion of the piston should be forced to stretch outwards as the piston is pushed upwards, while the more yielding lower portion, which is not attached to any central element, tends to move outwards in a radial direction when the piston is pushed downwards. A corresponding effect is also achieved if the piston is more voluminous on the upper side than on the lower side, but obviously the attachment to the piston rod give a larger such effect.

Claims

1 A piston (4) for a container (1) with a cylindrical inner surface, where the piston and the container constitute parts of a syringe intended for medical applications, where the container is provided with a sealing upper seal (3, 6) through which at least one piston rod (5) is slideably extends, and where the container is provided with a lower closable opening (2), characterised in that the main portion of the upper surface of the piston is convex, while the main portion of the lower surface of the piston is less convex than the upper surface.

2 A piston according to claim 1, characterised in that the upper surface of the piston extends to the piston rod and is attached to it.

3 A piston according to claims 1 or 2, characterised in that the main portion of the lower surface of the piston is flat.

4 A piston according to claims 1 or 2, characterised in that the main portion of the lower surface of the piston is convex.

5 A piston according to any one of the preceding claims, characterised in that the upper surface of the piston is bevelled around its periphery.

6 A piston according to any one of the preceding claims, characterised in that the upper surface of the piston is provided with at least one recessed channel (9) that extends from the periphery of the piston towards its centre.

7 A piston according to claim 6, characterised in that the recessed channel extends from the piston bevel towards its centre.

8 A piston according to any one of the preceding claims, characterised in that the lower surface of the piston is bevelled around its periphery.

9 A piston according to any one of the preceding claims, characterised in that the upper surface of the piston inside the upper bevel is convex, while the lower surface of the piston inside the lower bevel is less convex than the upper surface. A piston according to claim 9, characterised in that the lower surface of the piston inside the lower bevel is flat. A piston according to claim 9, characterised in that the lower surface of the piston inside the lower bevel is convex. A piston according to any one of the preceding claims, characterised in that the ratio between the height of the part of the piston extending from its lower surface to the lower surface of the piston rod, and the full height of the piston extending to the top of the widened portion of the piston rod is in the interval 70%-80%. A piston according to any one of the preceding claims, characterised in that the ratio between the height of the part of the piston extending from its lower surface to the lower surface of the piston rod, and the full height of the piston extending to the top of the widened portion of the piston rod is in the interval 50%-90%. A piston according to any one of the preceding claims, characterised in that the ratio between the diameter of the piston rod and the piston diameter is in the interval 10%-30%. A piston according to any one of the preceding claims, characterised in that the ratio between the diameter of the piston rod and the piston diameter is in the interval 5%-50%. A container (1) with a cylindrical inner surface, where the container constitute part of a syringe intended for medical applications, where the container is provided with a sealing upper seal (3, 6) through which at least one piston rod (5) is slideably extends, and where a piston (4) is attached to the lower end of the piston rod, and where the container is provided with a lower closable opening (2), characterised in that the main portion of the upper surface of the piston is convex, while the main portion of the lower surface of the piston is less convex than the upper surface. A container according to claim 16, characterised in that the upper surface of the piston extends to the piston rod and is attached to it. A container according to claims 16 or 17, characterised in that the main portion of the lower surface of the piston is flat. A container according to claims 16 or 17, characterised in that the main portion of the lower surface of the piston is convex. A container according to one of the claims 16-19, characterised in that the upper surface of the piston is bevelled around its periphery. A container according to one of the claims 16-20, characterised in that the upper surface of the piston is provided with at least one recessed channel (9) that extends from the periphery of the piston towards its centre. A container according to claim 21, characterised in that the recessed channel extends from the piston bevel towards its centre. A container according to one of the claims 16-22, characterised in that the lower surface of the piston is bevelled around its periphery. A container according to one of the claims 16-23, characterised in that the upper surface of the piston inside the upper bevel is convex, while the lower surface of the piston inside the lower bevel is less convex than the upper surface. A container according to claim 24, characterised in that the lower surface of the piston inside the lower bevel is flat. A container according to claim 24, characterised in that the lower surface of the piston inside the lower bevel is convex. A container according to one of the claims 16-26, characterised in that the ratio between the height of the part of the piston extending from its lower surface to the lower surface of the piston rod, and the full height of the piston extending to the top of the widened portion of the piston rod is in the interval 70%-80%. A container according to one of the claims 16-27, characterised in that the ratio between the height of the part of the piston extending from its lower surface to the lower surface of the piston rod, and the full height of the piston extending to the top of the widened portion of the piston rod is in the interval 50%-90%. A container according to one of the claims 16-28, characterised in that the ratio between the diameter of the piston rod and the piston diameter is in the interval 10%-30%. A container according to one of the claims 16-29, characterised in that the ratio between the diameter of the piston rod and the piston diameter is in the interval 5%-50%.