WO2009029974A1

WO2009029974A1 - A vented plunger and piston for a syringe

Info

Publication number: WO2009029974A1
Application number: PCT/AU2008/001108
Authority: WO
Inventors: Bruce Leigh Kiehne
Original assignee: Occupational & Medical Innovations Ltd
Priority date: 2007-09-04
Filing date: 2008-07-31
Publication date: 2009-03-12

Abstract

A syringe is disclosed which has a barrel for containing a fluid, the barrel having an internal wall, a rear end opening, a front end opening and a chamber therein extending between said openings, a plunger mounted or mountable in the chamber of the barrel and axially moveable back and forth between the front and rear end openings of the barrel for the intake and expulsion of fluid from the chamber, and the plunger having a rear end portion which extends out of the rear end opening of the barrel when the plunger is mounted in the barrel, a piston with a pair of sealing means extending around the periphery of the plunger which are adapted to engage the internal wall of the barrel within the chamber to prevent fluid from leaking out of the rear end of the barrel, there being an area between the pair of sealing means, wherein the piston is further provided with at least one opening in communication with the area between the pair of sealing means and with the rear end opening of the barrel.

Description

A VENTED PLUNGER AND PISTON FOR A SYRINGE Field of the Invention.

The present invention relates to syringes, particularly medical syringes of the type that have a containing portion for holding a fluid and a plunger with a piston to evacuate the containing portion.

Background Art.

Hypodermic syringes are generally supplied in a fully packaged, sterile condition. Syringes are manufactured in clean rooms. However, to ensure the syringe is sterile, the packaged syringe generally undergoes a further process of (post- packaging) sterilisation. There are 3 main methods used for sterilisation

1) Moist Heat - otherwise known as steam sterilising. This form of sterilisation is less preferred for most syringes as the temperatures required for sterilisation can sometimes damage/warp the syringe, which normally includes at least some plastic components. 2) Irradiation - E-beam or Gamma rays can be used to irradiate the product. Again, this form of sterilisation is less preferred for most syringes as it can degrade some plastics in appearance and/or function, for example by yellowing or embrittlement.

3) Ethylene Oxide Gas sterilisation - commonly referred to as EO or EtO sterilisation, which requires gaseous communication into all assembled parts of the product and packaging.

The scope of this invention covers syringes and syringe plungers which are adapted to undergo the EO sterilisation process. EO Sterilisation Process EO is a highly toxic gas which also forms toxic by-products. Any instruments treated using the EO process must be properly aerated post-sterilisation to ensure residues in the product are kept to a minimum. The process is further complicated by the fact that the EO sterilisation process is typically performed on fully assembled instruments (including syringes) which are also sealed in the packaging ready for transport.

The packaging used must therefore be porous to gases, in order that the EO gas be communicated to all parts/surfaces of the syringe. Typically, the packaging used (commonly referred to as "peel pouches") has a paper side or breather panel that allows the EO molecules to pass through at a minimum rate. Once inside the packaging, the EO gas must be able to reach all surfaces of the product which could conceivably come into contact with any part of the patient, either directly or indirectly, for example by contacting the fluid carried in the syringe, which subsequently contacts the patient.

The EO sterilisation cycle normally proceeds as follows:

1) Preconditioning - sometimes skipped. The packaged product on pallets sits in a room adjacent to the EO chamber for a period in order to equalise in temperature and humidity.

2) The pallets are loaded into the treatment chamber and the chamber is sealed. The air is removed to a partial vacuum of between 50 to 9OkPa below atmospheric pressure and the load heated to approximately 50⁰C. Water is usually introduced as steam, which flash vaporises due to the lowered pressure.

3) The EO gas is then injected under pressure to 5OkPa above atmospheric pressure and left to dwell for a predetermined period of time.

4) The EO gas is then evacuated from the chamber and the chamber pressure is cycled through a number (usually 5) of changes of atmosphere, to fully evacuate any remaining EO gas from the chamber.

5) The pallets with the products are then left to air. Aeration can take 5-7 days for the residual levels of gas from inside the packaging to drop to below an acceptable level.

Most syringes have a piston with two radially extending rubber seals. The front seal creates a fluid chamber inside the barrel. The rear seal serves to stabilise against sideways rotation and to keep debris and biological contamination away from the front seal. According to the relevant governing standard for safety, the seals must have minimum performance criteria which affect the assembly tolerances between piston seal diameter and barrel internal diameter. The minimum criteria are that the seals must not leak:

1) under partial vacuum of 88kPa below ambient pressure, and 2) no fluid leak from the fluid chamber when the internal pressure in the fluid chamber is increased to 30OkPa, and the plunger is located in a disadvantageous position in the barrel (pulled out and cocked to one side).

The problem faced in subjecting syringes which meet these minimum criteria to EO sterilisation is that the area located between the seals cannot be effectively treated with EO gas due to the fact that the EO treatment is undertaken at a much lower pressure (50 kPa above atmospheric) than that required to force the EO past the seals (in excess of 30OkPa above atmospheric for a syringe which meets the minimum criteria) and into the area between the seals. Attempts have been made to create syringes in which gases can reach the area located between the piston seals. For instance, in British Patent No 1212565 the rear piston seal has a notch cut into it. The notch effectively creates a break in the seal which allows gas to communicate from behind the piston into the space between the seals. However, the broken seal in GB 1212565 is undesirable because it significantly reduces the effectiveness of the seal in performing the above-mentioned stabilisation and other functions. International Patent Application No PCT/FR2006/002007 describes a syringe in which the open rear end of the barrel has a number of passages indented into the barrel's internal bore. The passages function such that, when the plunger is retracted far enough for the piston to become positioned in the open rear end of the barrel, the passages form gaps between the internal bore of the barrel and the piston seals. These gaps allow gas to reach the area located between the piston seals. However, one major problem with this arrangement arises from the fact that, as explained above, syringes generally undergo a sterilisation process after they are sealed within the packaging. Typically, the syringe will be packaged with the plunger inserted most of the way into the barrel so that the syringe occupies the minimum amount of room. This enables the smallest possible packaging to be used. However, as noted immediately above, the syringe design in PCT/FR2006/002007 only permits gas to reach the area located between the piston seals when the plunger is withdrawn almost all the way out of the barrel. Consequently, the syringe design in PCT/FR2006/002007 is not suitable for use with most post-packaging sterilisation processes where the syringe is packaged with the plunger inserted most or all of the way into the barrel. It will be clearly understood that any reference herein to previous or conventional products, methods, apparatuses, practices or other information does not constitute an acknowledgement or admission that any products, methods, apparatuses, practices or other information (including publications), or any possible combination thereof, formed part of the common general knowledge in the field, or is otherwise admissible prior art, whether in Australia or in any other country.

Summary of the Invention.

The present invention is directed to a vented plunger and piston for a syringe, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

With the foregoing in view, the present invention in one form, resides broadly in a vented piston for a syringe of the general type including a containing portion and a plunger with a piston portion for evacuation of the containing portion, the vented piston including a pair of spaced apart sealing portions for sealing the piston relative to the containing portion of the syringe and at least one vent in communication with a portion located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled.

In an alternative embodiment, the present invention resides in a vented piston for a syringe, the syringe including a plunger and a barrel with an internal bore, the piston fixed to the plunger and having a pair of spaced apart sealing portions each adapted to create an unbroken seal against the internal bore, and at least one vent in communication with a portion of the piston located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled.

In a further alternative embodiment, the present invention resides in a vented plunger and piston for a syringe of the general type including a containing portion and a plunger with a piston portion for evacuation of the containing portion, the vented piston including a pair of spaced apart sealing portions for sealing the piston relative to the containing portion of the syringe and at least one vent in communication with a portion located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled.

In another alternative embodiment, the present invention resides in a vented plunger and piston for a syringe, the syringe including a barrel with an internal bore, the piston fixed to the plunger and having a pair of spaced apart sealing portions each adapted to create an unbroken seal against the internal bore, and at least one vent in communication with a portion of the piston located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled. In a further alternative embodiment, the present invention resides in a syringe with a vented plunger and piston, the syringe including a containing portion and a plunger with a piston portion for evacuation of the containing portion, the vented piston including a pair of spaced apart sealing portions for sealing the piston relative to the containing portion of the syringe and at least one vent in communication with a portion located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled.

In a yet further alternative embodiment, the present invention resides broadly in a syringe with a vented plunger and piston, the syringe including a barrel with an internal bore, the piston fixed to the plunger and having a pair of spaced apart sealing portions each adapted to create an unbroken seal against the internal bore, and at least one vent in communication with a portion of the piston located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled. According to still a further aspect, the invention resides in a syringe

(which may be a safety syringe) comprising a barrel for containing a fluid having a cylindrical internal wall, a rear end opening and a front end opening and a chamber therein extending between said openings, a plunger mounted or mountable in the chamber of the barrel and axially moveable back and forth between the front and rear end opening of the barrel for the intake and expulsion of fluid from the chamber, and the plunger having a rear end portion extending out of the rear end opening of the barrel, a piston with a pair of sealing means extending around the periphery of the plunger engaging an inside surface of the wall of the barrel within the chamber to prevent fluid from leaking out of the rear end of the barrel with an area between the pair of sealing means, wherein the piston is further provided with at least one opening in communication with the area between the pair of sealing means and the rear end opening of the barrel.

According to a yet still further aspect, the invention resides in a syringe comprising a barrel for containing a fluid, the barrel having an internal wall, a rear end opening, a front end opening and a chamber therein extending between said openings, a plunger mounted or mountable in the chamber of the barrel and axially moveable back and forth between the front and rear end openings of the barrel for the intake and expulsion of fluid from the chamber, and the plunger having a rear end portion which extends out of the rear end opening of the barrel when the plunger is mounted in the barrel, a piston with a pair of sealing means extending around the periphery of the plunger which are adapted to engage the internal wall of the barrel within the chamber to prevent fluid from leaking out of the rear end of the barrel, there being an area between the pair of sealing means, wherein the piston is further provided with at least one opening in communication with the area between the pair of sealing means and with the rear end opening of the barrel.

For clarity, the following terms are used in this specification: Barrel - the containing portion of the syringe with a forward, needle-attaching portion and one or more extensions at the rear in order to grip the barrel and against which force is applied during depression of the plunger.

Plunger - the moveable portion used to fill and evacuate the barrel. Normally the plunger is slideable in the barrel. Typical plungers include a plunger head portion to which the piston in mounted, an elongate stem with one or more ribs to assist with alignment of the stem in the barrel and a thumb pad at the end opposite the plunger head portion. The ribs of the stem normally configured to form an X-shaped cross- section. Plungers are available in different types, for example, single use syringes of certain types have a cavity located in the stem of the plunger to contain the needle once the syringe has been used. Piston - portion including seals, which is normally located at the head end of the plunger. Normally manufactured of a resilient material such as rubber or a substitute and functions to seal the fluid chamber from the rest of the barrel.

The vented piston and/or plunger of the present invention may be used with any type of syringe. It is particularly well adapted to be used in association with syringes of the type described in United States Patent Nos. 6,994,690 or 7,147,621, or International Application No PCT/AU2007/001009.

Pistons of syringes, and the vented piston of the invention in particular, are normally provided with a pair of seals, normally a forward seal located closer to the needle end of the barrel and a rear, "wiping" seal. The piston is typically an open body portion having a forward face with at least one sidewall extending therefrom to define a cavity in the piston. The cavity is normally located over at least a portion of the plunger head and is secured thereon. The seals usually extend outwardly from the sidewall of the piston about the sidewall. The piston is usually circular (as are most of the components of the syringe) and the seals therefore preferably extend circumferentially to abut an inner surface of the barrel to form the seal.

The vented piston of the invention includes at least one vent in communication with a portion located between the sealing portions. The vent is located in/through a sidewall of the piston between the forward and rear seals. The vent will preferably be an opening and there may be a single vent opening or multiple openings spaced about the sidewall.

The vent openings may have any shape such as slots or simple circular openings. The vent opening(s) may be partially formed in/through the rear wiping seal. However, this configuration is less preferred as it allows fluid to easily escape from the rear of the barrel if the front seal is compromised.

The piston is normally a unitary member but may be formed from two or more parts, each part located relative to the plunger to form a piston functioning substantially similar to a unitary piston. According to one possible multi-part configuration, a rear ring with a sealing portion may be provided and mounted on the plunger head towards the rear of the plunger head and a forward cap may be provided with a circumferential seal and a cover portion to cover the front end of the plunger head. The piston is typically attached to the plunger. An adhesive is one manner in which the attachment may be formed. However, the piston may be co- molded with the plunger or plunger head. In order to achieve this, the plunger is normally formed first, after which it is typically placed into a second mold with the piston then molded about the plunger head. In the course of the molding, the surface of the plunger head typically undergoes a small degree of melting as the molten piston material is injected into the mold, causing the piston material to fuse to the plunger head.

The flow path which is formed using the vented piston of the present invention exists when the syringe is assembled, that is, when the piston is located with both sealing portions in the barrel. The flow path allows gaseous communication of gas located outside the syringe with the portion located between the two piston seals, allowing both ingress and egress of EO gas in particular.

The plunger of a particularly preferred embodiment of the invention may also preferably be provided with a bore to assist with the definition of a flow path for the gas. In particular, the plunger may be provided with a longitudinal bore and at least one, typically a number of lateral openings communicating with the bore and the vents located in the piston. In this configuration, the longitudinal bore of the plunger may provide a dedicated flow path for the gas or the bore may form a part of another mechanism of the syringe such as for example, part of a retractable or "shoot back" needle assembly.

In configurations where the bore is provided as a dedicated flow path for the gas, the bore will typically be approximately centrally located through at least a portion of the plunger. Preferably, the bore may be provided as a tubular central member of the stem of the plunger from which the ribs extend. The bore may extend substantially over the length of the plunger from the thumb pad to a location near the piston.

According to one embodiment, the bore may extend through the thumb pad of the plunger. This configuration will typically allow flow through the bore to the area between the seals of the piston even if the plunger is fully depressed. This may be important in single use syringes whereby use of the syringe requires full depression of the plunger which thereby locks the plunger in the barrel and the thumb pad abuts the rear opening of the barrel to cover the opening.

Alternatively, the bore may be provided only over part of the length of the plunger, typically at a portion of the plunger located adjacent the head end of the plunger. Provision of the bore close to the plunger head and not completely through the length of the plunger allows an activated syringe (fully depressed plunger) to form a sealed unit in contrast to the full length bore embodiment in which a gas flow path will typically exist at all times.

According to the alternative, shortened plunger bore configuration, there will typically be at least one opening provided in the shortened bore to allow gas flow from outside the barrel to the at least one vent. According to this embodiment, the ribs of the stem of the plunger are normally spaced such that the gas can flow into the barrel between the ribs to communicate with the shortened bore and the vents in the piston. The bore opening may be located along or adjacent, to a longitudinal midline of the plunger or as a side entry opening to a longitudinal bore.

Where the bore is provided, it is preferably provided with a plug means allowing the flow of gas therethrough but preventing the flow of other media. It is particularly preferred that the plug means be gas permeable but impermeable to liquids and biologic material. The plug may also be referred to as gauze or similar.

The plug will preferably be associated with the bore and preferably located at least partially within the bore. For example, where the bore extends through the thumb pad of the plunger, the plug may be provided at the outer end of the bore, recessed into the thumb pad to cover the opening to the bore. Alternatively, the plug may be provided fully within the bore itself. One or more plugs may be provided.

Materials used for the plug will typically include those currently in use in catheters and intravenous introducing sets. Any material with the functional characteristics, namely gas permeability/liquid and biologic impermeability may be used. Typically the plug will be partially resilient such that it is closely received within the bore and material or fluid is not able to pass through the bore except through the plug. The plunger bore is typically in fluid communication with the at least one vent in the piston through the provision of one or more lateral openings in the plunger. Typically, a number of lateral openings will be provided spaced about the circumference of the plunger head. The openings in the plunger head will preferably be slot openings. A major advantage of providing slot openings is that at least one opening provided in the piston will typically always be aligned with at least a portion of at least one of the slot openings in the plunger in order to provide the flow path.

Where the bore is provided as a part of a retractable or "shoot back" syringe construction, there may be one or more openings provided in the bore, typically towards an outer end of the bore. For example, where a bore is provided as a needle-receiving chamber of a single use syringe, one or more openings will preferably be provided in the walls of the chamber between the ribs of the plunger, towards the thumb pad of the plunger.

According to a further possible embodiment, the flow path may be defined through a "breather" member or assembly which is separate from the piston and plunger. The breather member or assembly will preferably be located between the piston and plunger and be attachable to each of the piston and plunger.

This configuration leaves the plunger with its original function as the part mainly responsible for evacuating/loading the fluid chamber substantially without any modification except for the attachment portion to attach the breather member or assembly.

According to this embodiment, the forward end of the plunger is provided with an attachment portion and a corresponding attachment portion is provided on the breather member. This attachment will preferably be accomplished using a snap fitting mechanism.

The breather member is preferably a cylindrical member having internal openings forming a flow path therethrough and having lateral openings which are preferably in communication with openings provided in the piston between the forward and rear seals. This configuration may similarly be provided with gauze or filter paper which is gas permeable but impermeable to liquids and biological material. Preferably the gauze will be provided between the forward end of the plunger and the rear end of the breather member and will suitably cover the openings to the breather member.

The forward end of the breather member will typically attach the piston by deforming the piston to cover the breather member. Again, providing the openings in the breather member as slots typically ensures that at least one of the openings in the piston sidewall is in communication with at least a portion of one of the slot openings to create the flow path.

According to this embodiment, the forward end of the plunger only makes contact with the "filter paper" or "gauze" part and the breather part. There may be some contact on the periphery of the fins of the plunger or not. Assembly of the plunger, breather member and piston is typically as follows: plunger to "plug" to breather to piston, or alternately plunger to breather to piston with the "gauze" part provided as a plug and offset to one side.

Brief Description of the Drawings. Various embodiments of the invention will be described with reference to the following drawings, in which:

Figure 1 is a sectional side elevation view of an assembled prior art "shoot back" style syringe with a vented plunger and showing the flow path of EO gas during the sterilization process. Figure 2 is a side elevation view of a piston with multiple openings according to an aspect of the present invention.

Figure 3 is a sectional side elevation view of the piston illustrated in Figure 2.

Figure 4 is a side elevation view of a piston with a single opening according to an aspect of the present invention.

Figure 5 is a sectional side elevation view of the piston illustrated in Figure 4.

Figure 6 is a side elevation view of a vented plunger according to an aspect of the invention prior to addition of the piston seal cap. Figure 7 is a sectional side elevation view of the vented plunger illustrated in Figure 6.

Figure 8 is a sectional side elevation view of an assembled syringe of the retractable type with vented plunger and piston according to a preferred embodiment of the present invention.

Figure 9 is a sectional side elevation view of the vented plunger and piston illustrated in Figure 8. Figure 10 is a sectional side elevation view of an assembled syringe of a standard type with vented plunger and piston according to a preferred embodiment of the present invention.

Figure 11 is a sectional side elevation view of an assembled syringe of an alternative type with vented plunger and piston according to a preferred embodiment of the present invention.

Figure 12 is a sectional side elevation view of an assembled syringe with vented plunger and piston of an alternative configuration.

Figure 13 is a sectional side elevation view of the syringe of Figure 12 in the activated or used condition. Figure 14 is a sectional side view of an end of a vented plunger with a piston having a pair of separate seals.

Figure 15 is a sectional side view of an end of a vented plunger with a piston co-molded with the plunger.

Figure 16 is a sectional side view of an end of a vented piston according to a particularly preferred embodiment.

Figure 17 is a perspective view from the rear of the vented piston illustrated in Figure 16.

Figure 18 is a perspective view of a standard plunger with the vented piston illustrated in Figures 16 and 17. Figure 19 is a detailed perspective view of the plunger and piston illustrated in Figure 18 showing the flow pathway of the EO gas during sterilization.

Figure 20 is a partially sectional perspective view of a plunger and piston configuration according to a preferred embodiment of the present invention.

Figure 21 is an exploded view of a plunger and piston configuration according to an embodiment of the present invention.

Figure 22 is an exploded view of a plunger and piston configuration according to an alternative embodiment of the present invention. Figure 23 is a partially sectional perspective view of the plunger and piston illustrated in Figure 20.

Figure 24 is an exploded view of a plunger and piston configuration according to still a further embodiment of the present invention. Figure 25 is an exploded view of a plunger and piston configuration according to yet a further embodiment of the present invention.

Figure 26 is a side view of the plunger and piston illustrated in Figure 25.

Figure 27 is a sectional side view of the plunger and piston illustrated in Figure 26 along line B-B.

Figure 28 is a detailed sectional side view of the piston and plunger illustrated in Figure 25.

Detailed Description of the Preferred Embodiment. According to a first preferred aspect of the present invention, a vented piston for a syringe is provided.

In order that the invention be more easily understood, Figure 1 provides a sectional side view of an assembled syringe 10 with a "shoot back" plunger 11 and showing the flow path of EO gas during the sterilization process.

Like most syringes, the syringe illustrated in Figure 1 has a barrel 12. The barrel 12 forms the containing portion of the syringe 10. It also has a forward portion 13 which houses the needle prior to "shoot-back", and one or more extensions 14 at the rear for gripping the barrel 12 and against which force is applied during depression of the plunger 11. The plunger 11 is the moveable portion used to fill and evacuate the barrel 12. Normally the plunger 11 is slideable in the barrel 12. Typical plungers 11 include a plunger head portion 15 to which a piston 16 is mounted, an elongate stem 17 with one or more ribs 18 to assist with alignment of the stem 17 in the barrel 12 and a thumb pad 19 at the end opposite the plunger head portion 16. The ribs 18 of the stem 17 are normally configured to form an X-shaped cross- section. Plungers 11 are available in different types, for example, single use syringes of certain types have a cavity located in the stem to contain the needle which is shot back once the syringe has been used, and Figure 1 illustrates a plunger of this type.

The piston typically includes seals, and is normally located at the head end of the plunger 11. The piston is normally manufactured of a resilient material such as rubber or a substitute and functions to form a seal between the plunger 11 and barrel 12.

Pistons 16 of syringes, and the vented piston of the invention in particular, are normally provided with a pair of seals, normally a forward seal 20 located closer to the needle end of the barrel 12 and a rear, "wiping" seal 21.

The plunger 11 of the "shoot back" syringe illustrated in Figure 1 is provided with a piston 16 having a pair of seals to seal the plunger relative to the barrel of the syringe. It can be seen from Figure 1 that the EO gas cannot reach the portion located between the seals.

Figures 2 to 5 then illustrates a pair of configurations of a vented piston including a pair of spaced apart seals 20, 21 for sealing the piston 16 relative to a syringe barrel 12. The piston 16 illustrated in Figures 2 and 3 has a multiplicity of vents 22 located between the seals 20, 21 such that a flow path exists to the portion located between the seals when the syringe is assembled. The piston illustrated in Figures 4 and 5 has only a single vent 22 located between the seals 20, 21.

Both types of illustrated piston have an open body portion having a forward portion 23 with a sidewall 24 extending therefrom to define a cavity in the piston 16. The cavity is normally located over the plunger head 15 and is secured thereon. The seals 20, 21 extend outwardly from the sidewall 24 of the piston 16.

The vents illustrated in Figures 2 to 5 are simple circular openings.

The plunger 11 of the preferred embodiments of the invention illustrated in Figures 6 to 13 in particular is provided with a bore 25 to assist with the definition of a flow path for the gas. As illustrated, the plunger 11 is provided with a longitudinal bore 25 and at least one, but typically a number of, lateral openings 26 communicating with the bore 25 and the vents 22 located in the piston 16. The longitudinal bore 25 of the plunger 11 may provide a dedicated flow path for the gas, as illustrated in Figures 10 to 13, or the bore 25 may form a part of another mechanism of the syringe such as for example, part of a retractable or "shoot back" needle assembly, as illustrated in Figures 6 to 9.

In configurations where the bore is provided as a dedicated flow path for the gas (Figures 10 to 13), the bore 25 is approximately centrally located through at least a portion of the plunger. The bore 25 is provided as a tubular central member of the stem 17 of the plunger 11 from which the ribs 18 extend.

According to a first embodiment of the dedicated flow path bore configuration as illustrated in Figures 10 and 11, the bore 25 extends substantially over the length of the plunger 11, extending through the thumb pad 19 to a location near the piston 16, communicating with lateral openings 26 in the plunger head portion 15 and the vents 22 in the piston 16. This configuration allows flow through the bore 25 even if the plunger 11 is fully depressed.

Alternatively as illustrated in Figures 12 and 13, the bore 25 may be provided only over a partial length of the plunger 11, typically at a portion of the plunger 11 located adjacent the plunger head 15. Provision of the bore 25 close to the plunger head 15 and not completely through the length of the plunger 11 allows an activated syringe with a fully depressed plunger 11, as illustrated in Figure 13, to form a sealed unit in contrast to the full length bore embodiment in which a gas flow path will typically exist at all times.

According to the alternative plunger bore configuration illustrated in Figure 13, there is at least one opening 27 provided in the shortened bore to allow gas flow from outside the barrel 12 to the vents 22 in the piston 16. According to this embodiment, the ribs 18 of the stem 17 are normally spaced such that the gas can flow into the barrel 12 between the ribs 18 to communicate with the bore 25 and the vents 22. The bore opening 27 of the embodiment illustrated in Figure 12 and 13, is located as a side entry opening to the longitudinal bore 25.

Where the bore is provided as a part of a retractable or "shoot back" syringe construction, a form of which is illustrated in Figures 6 to 9, the bore is provided as dual use needle-receiving chamber and gas flow bore of a single use syringe. One or more openings 27 are provided in the walls of the chamber/bore 25 between the ribs of the plunger 11 towards the thumb pad 19 of the plunger 15.

Where a bore 25 is provided, it is preferably provided with a plug 28 allowing the flow of gas therethrough but preventing the flow of other media. The plug 28 is gas permeable but impermeable to liquids and biologic material.

The plug 28 of the illustrated embodiments is located in association with the bore and preferably at least partially within the bore. For example, where the bore extends through the thumb pad of the plunger, as illustrated in Figure 10, the plug 27 can be provided at the outer end of the bore 25, recessed into the thumb pad 19. Alternatively as illustrated in Figures 11 to 13, the plug can be provided fully within the bore 25 itself, whether the bore is a partial length (Figures 12 and 13) or full length bore (Figure 11).

A number of lateral openings 26 are provided and spaced about the circumference of the plunger head 15. The openings of the preferred embodiment are slot openings as illustrated in Figures 6 and 7. A major advantage of providing slot openings is that at least one opening provided in the piston will always be aligned with at least a portion of at least one of the slot openings in the plunger in order to provide the flow path.

According to alternative embodiments, the vents 22 may be partially formed in/through the rear wiping seal 21 such as is illustrated in Figures 16 to 19.

The piston 16 is normally a unitary member but may be formed from two or more parts, each part located relative to the plunger to form a piston functioning substantially similar to a unitary piston. According to the two part configuration, a form of which is illustrated in Figure 14, a rear ring 29 with a seal 21 is provided and mounted on the plunger head 15 towards the rear of the plunger head

15 and a forward cap 30 is provided with a circumferential seal 20 and a cover portion 31 to cover the front end of the plunger head 15.

The piston 16 may be co-molded with the plunger 11 or plunger head 15. In order to achieve this, the plunger 11 is formed first, after which it is placed into a second mold with the piston 16 then molded about the plunger head. In the course of the molding, the surface of the plunger head 15 undergoes a small degree of melting as the molten piston material is injected into the mold causing the piston material to fuse to the plunger head 15.

Various other views of embodiments described above have been included in Figures 20 to 24.

A further possible embodiment is illustrated in Figures 25 to 28, in which the flow path is defined through a "breather" member 35 which is separate from the piston 16 and plunger 11. The breather member 35 is located between the piston 16 and plunger 11 and be attachable to each of the piston 16 and plunger 11. This configuration leaves the plunger 16 with its original function as the component mainly responsible for evacuating/loading the barrel 12 substantially without any modification except for an attachment finger 36 to attach the breather member 35. According to the illustrated embodiment, the forward end of the plunger 16 is provided with an attachment finger 36 and a corresponding attachment opening 37 is provided on the rear of the breather member 35 forming a snap fitting mechanism.

The breather member 35 is a cylindrical member having internal openings forming a flow path therethrough (as illustrated in Figure 28 in particular) and having lateral openings 26 which communicate with the vents 22 provided in the piston 11 between the forward 20 and rear 21 seals.

The illustrated configuration is also provided with gauze or filter paper

38 which is gas permeable but impermeable to liquids and biological material. The gauze 38 is provided between the forward end of the plunger 11 and the rear end of the breather member 35 and is clamped there by the snap fit mechanism. The gauze

38 covers the openings to the breather member 35.

The piston 16 is attached over the breather member 35 by deforming the piston 16 to cover the breather member 35. Again, providing the lateral openings 26 in the breather member 35 as slots ensures that at least one of the vents 22 in the piston sidewall is in communication with at least a portion of one of the slot openings

26 to create the flow path.

According to this embodiment, the forward end of the plunger 11 only makes contact with the gauze 38 and the breather part 35. There may be some contact on the periphery of the ribs 18 of the plunger 11 or not.

In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

1. A syringe comprising a barrel for containing a fluid, the barrel having an internal wall, a rear end opening, a front end opening and a chamber therein extending between said openings, a plunger mounted or mountable in the chamber of the barrel and axially moveable back and forth between the front and rear end openings of the barrel for the intake and expulsion of fluid from the chamber, and the plunger having a rear end portion which extends out of the rear end opening of the barrel when the plunger is mounted in the barrel, a piston with a pair of sealing means extending around the periphery of the plunger which are adapted to engage the internal wall of the barrel within the chamber to prevent fluid from leaking out of the rear end of the barrel, there being an area between the pair of sealing means, wherein the piston is further provided with at least one opening in communication with the area between the pair of sealing means and with the rear end opening of the barrel.

2. A syringe as claimed in claim 1, wherein the pair of sealing means comprises a forward seal and a rear seal, the forward seal located closer to the forward end opening of the barrel and the rear seal located closer to the rear end opening of the barrel when the plunger is in the barrel.

3. A syringe as claimed in any one of the preceding claims, wherein the piston comprises a forward face, at least one sidewall and a cavity, the cavity being adapted for positioning on at least a portion of a head of the plunger.

4. A syringe as claimed in claim 2 or 3, wherein at least one opening comprises a vent in/through a sidewall between the forward and rear seals.

5. A syringe as claimed in any one of the preceding claims, wherein at least one opening creates a path for gas to flow between the sealing portions of the piston when the syringe is assembled with both sealing portions inside the barrel.

6. A syringe as claimed in claim 5, wherein the plunger is provided with a bore which helps to define the gas flow path.

7. A syringe as claimed in claim 6, wherein the bore comprises a longitudinal bore in the plunger having one or more lateral openings communicating with the bore and with the opening(s) in the piston.

8. A syringe as claimed in claim 6, wherein the bore provides a dedicated flow path for the gas.

9. A syringe as claimed in claim 8, wherein the bore extends approximately along the plunger's longitudinal axis the full-length of the plunger from a head portion of the plunger to the rear end portion of the plunger which includes a thumb pad.

10. A syringe as claimed in claim 8, wherein the bore extends along only part of the length of the plunger from a head portion of the plunger enabling the syringe to form a sealed unit when the plunger is completely depressed into the barrel.

11. A syringe as claimed in claim 6, wherein the syringe comprises a single use syringe with a retractable needle mechanism and the bore forms a receptacle for containing the needle after it is retracted.

12. A syringe as claimed in any one of claims 6-11, wherein the bore is provided with plug means allowing flow of gas therethrough but preventing flow of other media.

13. A syringe as claimed in claim 1 having a breather member which forms a path for gas to flow between the sealing portions of the piston when the syringe is assembled with both sealing portions inside the barrel.

14. A vented piston for a syringe, the syringe including a plunger and a barrel with an internal bore, the piston fixed to the plunger and having a pair of spaced apart sealing portions each adapted to create an unbroken seal against the internal bore, and at least one vent in communication with a portion of the piston located between the sealing portions such that a flow path exists to the portion located between the sealing portions when the syringe is assembled.

15. A syringe as claimed in claim 1 substantially as described with reference to the relevant drawings.

16. A vented piston for a syringe as claimed in claim 14 substantially as described with reference to the relevant drawings.