Syringe plunger and syringe

Embodiments of the invention relate to a plunger for a syringe and to a syringe.

BACKGROUND

Figure 1 illustrates a syringe 10 as known in the prior art. The syringe 10 comprises a chamber in the form of a cylinder 12 and a plunger 14 arranged so that the plunger 14 reciprocates within the cylinder 12. A needle 16 is attached to the cylinder 12 by means of an applicator 18. The plunger 14 has a head 26. A seal 20 is attached to the head 26 of the plunger 14.

During use, the needle 16 is inserted into the medication to be administered which is dissolved in, or in suspension in, a liquid. The plunger is then drawn backwards (in the direction of arrow 22), thereby drawing the seal 20 backwards creating an under-pressure between the seal and the liquid. This, in turn, draws liquid into the cylinder 12.

During administration, the needle 16 is inserted into a vein or subcutaneously, the plunger 14 is depressed (pushed forwards in the direction of arrow 24), thereby forcing the seal 20 downwards which expels the liquid out of the needle 16 and into the patient.

As designated by reference numeral 30, a space exists between the seal 20 and the tip of the needle 16. Generally, when the syringe 10 is filled, it is inverted so that the needle points upwards and the liquid is then drawn into the cylinder 12.

- 1 The space 30 is filled with air prior to administration and this air, when the needle is inverted for administration, will be situated adjacent the tip of the needle. Therefore, unless any action is taken to avoid this, the aim would be injected first, prior to the liquid.

For these reasons, action of purging a syringe a well-known whereby the plunger 14 is depressed until the air has been expelled.

However, a user does not know that all of the air has been expelled until they observe liquid being expelled from the tip of the needle. Depending on the skill and dexterity of the user, this can lead to a lesser or greater expulsion of liquid. However, in each case, some of the liquid containing the medication will be expelled.

Besides that, re-usable needles like Insulin Pens keep on compiling air bubbles that are very hard to purge or get rid of totally.

This results in a significant waste of medication. Not only does this result in wasted costs, but there is an associated uncertainty regarding the dosage provided.

It is desirable to avoid or minimize the necessity to purge syringes of unwanted air.

SUMMARY

According to a first aspect, the invention provides a plunger for a syringe comprising a head for reciprocating within a chamber of the syringe to thereby deliver a shot of liquid contained within the piston, the head further comprising a seal which is impermeable to liquid, but permeable to gas to allow gas to pass the head, but prevent liquid from doing so.

-2The seal may comprise a membrane which may be a semi-permeable membrane.

The plunger according to claim 1 wherein the head comprises a chamber in fluid communication with the seal to accommodate gas passing through the seal.

A further embodiment of the invention extends to a syringe comprising a chamber for accommodating a liquid to be dispensed and a piston for reciprocating with the chamber so that liquid contained within the chamber is expelled by movement of the piston, the piston comprising a plunger as herein described.

The membrane may be dimensioned in accordance with a size of the chamber to accommodate gas which may be stored in the chamber together with the liquid.

DESCRIPTION OF ACCOMPANYING FIGURES

Embodiments of the invention are described with reference to the accompanying schematic diagrams in which:

Figure 1 is an illustration of a syringe as known in the art;

Figures 2 and 3 are illustrations of syringes according to embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are described hereafter with reference to the accompanying diagrams.

Figure 2 illustrates a syringe 100 according to a first embodiment. In this embodiment of the invention, the seal 20 is replaced by a seal 40 which is permeable to gas, but not to liquid. Suitable materials are known in the art. In one

-3embodiment, the seal 40 is provided by a membrane which is permeable to gas but not to liquid. For example, the material sold by Proctor will under the trade name Roofshield may be used.

During use of the syringe, when the syringe is inverted after having filled, the air will be located adjacent to the seal 40. When a user depresses the plunger 14, the action causes the seal 22 press against the air located in space 30. This force creates the force necessary for the gas to pass through the membrane of the seal 40. In this manner, all the gas may be removed without having to purge the syringe and thereby avoiding the waste of any of the medication involved.

Figure 3 illustrates a further embodiment of the invention. In this embodiment, syringe 102 includes a reservoir 42 located adjacent to the seal 44.

The seal 40 of the embodiment of Figure 2 is dimensioned to accommodate the air which may be located between the seal 40 and the liquid in the chamber 12. The embodiment of Figure 3 differs from that of Figure 2 in that any excess a passes through the seal 44 and is then contained within reservoir 42. The seal 44 is also comprised of a material which is permeable to gas, but not to liquid.

The Rubber plunger 40 could also be made of Hard Foamed Rubber to host the air that passes through the membrane and into its voids.

It is to be realised that the dimensions of the seal 40 as illustrated in Figure 2 may be chosen independence on the diameter and length of the piston 14 and chamber 12 to accommodate the typical air volumes which may be involved in normal administration of the medication.