IMPROVEMENTS IN RETRACTABLE SYRINGES

Technical Field

The present invention relates to improvements in retractable syringes.

Background of the Invention Retractable syringes are disclosed in the Applicant's international PCT patent application no. PCT/AU2004/001743 (WO 2005/058398) ("the PCT application"). The contents of the PCT application are incorporated herein by cross reference.

Object of the Invention

It is the object of the present invention to provide improvements in the manufacture and operation of the retractable syringes disclosed in the PCT application.

Summary of the Invention

Accordingly, in a first aspect, the present invention provides a retractable syringe including: a barrel having a front end, a rear end and defining a receptacle for containing a liquid for injection; a needle mounted at the front end of the barrel; a hollow plunger movable within the barrel from the rear end to the front end to expel fluid out of the barrel through the needle, said plunger having an inner chamber, an axial hole at the front end of the chamber and means blocking the axial hole; resilient means adapted to urge the needle in a rearward direction; and an expandable annular member having substantially planar, parallel, front and rear facing annular surfaces, wherein the annular member is adapted to provide a seal at the front end of the barrel, and restrain the resilient means until the expandable annular member is engaged by a forward part of the plunger when the plunger reaches the front end of the barrel, such that the expandable annular member moves towards the front end of the barrel and expands to release the resilient means, whereby the axial hole is unblocked and the needle is automatically retracted through the axial hole into the inner chamber of the plunger.

In a second aspect, the present invention provides a retractable syringe having: a barrel having a front end, a rear end and defining a receptacle for containing a liquid for injection; a needle mounted at the front end of the barrel;

a hollow plunger movable within the barrel from the rear end to the front end to expel fluid out of the barrel through the needle, said plunger having an inner chamber, an axial hole at the front end of the chamber and means blocking the axial hole; resilient means adapted to urge the needle in a rearward direction into the barrel; and an expandable annular member having substantially planar, parallel, front and rear facing annular surfaces, the annular member being adapted to provide a seal at the front end of the receptacle of the barrel, wherein the needle is adapted to engage and at least partially dislodge the means blocking the axial hole to unblock the axial hole when the plunger approaches the front end of the barrel, whereafter continued movement of the plunger towards the front end causes the expandable annular member to move along a surface at the front end of the barrel and expand to release the resilient means, whereby the needle is automatically retracted through the unblocked axial hole into the inner chamber of the plunger. The annular member preferably also has a substantially cylindrical outer wall.

The annular member preferably also has an inwardly convex curved inner wall. The annular member preferably has a substantially D shaped cross section.

In a third aspect, the present invention provides a barrel assembly for a retractable syringe, the barrel assembly including: a barrel adapted for movement of a plunger therein and having first and second ends; and a cap adapted for connection with the barrel at said first end, wherein the barrel includes a substantially flat, internal, annular shoulder facing said first end for receiving and locating an expandable annular member. In one form, the cap is adapted for snap engaging connection with the barrel at said first end. In another form, the cap is adapted for screw engaging connection with the barrel at said first end. The shoulder is preferably near said first end. The barrel preferably also includes at least one internal protuberance between the shoulder and said first end, the protuberance(s) adapted to assist in locating and retaining the annular member against the shoulder. The barrel preferably includes four circumferentially spaced apart protuberances, most preferably spaced away from the shoulder by the longitudinal dimension of the annular member.

The barrel preferably includes an external circumferential recess adapted to snap engagingly receive one or more inwardly facing barbs on the cap.

The cap is preferably adapted for housing a retractable needle assembly, prior to retraction.

In a fourth aspect, the present invention provides a retractable syringe including: a barrel having a front end, a rear end and defining a receptacle for containing a liquid for injection, the barrel including an inwardly facing shoulder at its front end; a plunger having a front end and a rear end, the plunger being movable within the barrel from the rear end to the front end of the receptacle to expel fluid out of the barrel through the needle; a plunger gasket substantially adjacent the front end of the plunger, the plunger being adapted to, upon at least partially abutting the barrel shoulder, deform towards the shoulder to thereby decrease the dead space of the syringe.

The barrel shoulder preferably tapers inwardly towards the barrel front end. The end surface of the plunger gasket facing the barrel shoulder preferably deforms from being substantially normal to the longitudinal axis of the barrel to tapering inwardly towards the barrel front end.

The plunger gasket, in uncompressed form, preferably has substantially planar, parallel, front and rear facing annular surfaces joined by an inwardly curved side wall. hi a fifth aspect, the present invention provides a method of assembling a retractable syringe, the method including the following steps: inserting a needle into a cap with a resilient means therebetween; positioning the needle relative to the cap so as to compress the resilient means; clamping the needle against movement relative to the cap; engaging the cap with a barrel having an expandable annular member therein such that the expandable annular member engages the needle; and releasing the clamp of the needle relative to the cap, whereby the expandable annular member maintains the position of the needle relative to the cap until the expandable annular member is dislodged relative to the barrel.

Li one form, the method preferably also includes the step of the cap being snap engaged with the barrel. In another form, the method preferably also includes the step of the cap being screw engaged with the barrel.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings wherein:

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Fig. 1 is a perspective view of an embodiment of a 3 millilitre syringe; Fig. 2 is a perspective view of an embodiment of a 1 millilitre syringe; Fig. 3a is a cross sectional perspective view of the syringe shown in Fig. 2, near the end of the plunger stroke; Fig. 3b is an enlarged detailed view of the syringe shown in Fig. 3 a;

Fig. 4a is a cross sectional, perspective view of the syringe shown in Fig. 2, at the end of the plunger stroke;

Fig. 4b is an enlarged detailed view of the syringe shown in Fig. 4a; Fig. 5 is a perspective view of the expandable annular member used in the syringe of Fig. 2;

Fig. 6 is a cross sectional, side view of the expandable annular member shown in Fig. 5;

Figs. 7 to 9 are sequential, cross sectional, side views of steps involved in the assembly of the barrel and cap of the syringe shown in Fig. 2; Fig. 10 is a cross sectional, perspective view of the syringe shown in Fig. 1; during the plunger strokes;

Fig. 11a is a cross sectional, perspective view of the syringe shown in Fig. 1 near the end of the plunger stroke;

Fig. 1 Ib is an enlarged detailed view of the syringe shown in Fig. 11a; Fig. 12a is cross sectional, perspective view of the syringe shown in Fig. 1, at the end of the plunger stroke;

Fig. 12b is an enlarged detailed view of the syringe shown in Fig. 12a; Fig. 13 is cross sectional, perspective view of the syringe shown in Fig. 1, after needle retraction; Fig. 14 is a perspective view of the plunger gasket used in the syringe of Fig. 1; and

Fig. 15 is a cross sectional, side view of the plunger gasket shown in Fig. 14.

Detailed Description of the Preferred Embodiments Figs. 1 and 2 show first and second embodiments of syringes 20 and 22, having 3 and 1 millilitre sizes, respectively. The construction, assembly and operation of the syringes 20 and 22 is substantially identical to the syringes described in the PCT application, with the exception of the improvements which shall be described below.

Figs. 3a to 4b show the (1 millilitre) syringe 22 which, like the syringes shown in the PCT application, includes a barrel 24 having a front end 24a, a rear end 24b and

Figs. 3a to 4b show the (1 millilitre) syringe 22 which, like the syringes shown in the PCT application, includes a barrel 24 having a front end 24a, a rear end 24b and defining a receptacle for containing a liquid for injection therein. The rear end 24b has a flange 26 for supporting a user's fingers during injection. A needle 30 having a hub 32 mounted thereto is mounted at the front end 24a of the barrel 24. The hub 32 has an enlarged base part 32a.

A hollow plunger 34 is moveable within the barrel 24 from the rear end 24b to the front end 24a to expel liquid out of the barrel 24 through the needle 30. The plunger 34 has an inner chamber 36, an axial hole 38 at the front end of the chamber 36 and means blocking the axial hole 38, in the form of a plug 40. The plug 40 has an enlarged head 40a facing the rear end 24b of the syringe 22, which locates against an inwardly facing flange 44 near the front end of the plunger 34. The rear end of the plunger 34 has a flange 34a, for supporting a user's thumb during injection, and a cap 34b to close the inner chamber 36. The syringe 22 also includes a resilient means, in the form of a coil spring 46, adapted to urge the needle 30 in a rearward direction. The needle 30 is retained in the position shown relative to the barrel 24 by the enlarged base part 32a of the needle hub 32 engaging with an expandable annular member 48, the latter being best shown in Figs. 5 and 6. The expandable annular member 48 is formed from isoprene (or silicone) rubber. The remainder of the syringe components are formed from plastics material.

The syringe shown in the PCT application had an expandable annular member in the form of an O-ring. However, the expandable annular member 48 has substantially planar, parallel, front and rear facing annular surfaces 50 and 52 respectively. The member 48 also has a substantially cylindrical outer wall 54 and an inwardly convex curved inner wall 56, which results in the member 48 having a substantially 'D-shaped' cross section.

The member 48 represents an improvement over the previously mentioned O- ring, as the flat surfaces 50 and 52 allow the assembled height and concentricity of the needle hub 32 to be more accurately positioned to ensure the sealing surfaces of the annular member 48 are not compromised with respect to the adjacent inner surface of the barrel 24 and the adjacent outer surface of the needle hub 32, particularly the enlarged part 32a. The assembled height of the needle hub 32 can be more accurately controlled by the 'D-shaped' member 48 than an O-ring as the flat surface 52 sits squarely on the barrel shoulder 24c, which is highly desirable.

In contrast, an 0-ring would rest on its circular profile on the edge of the shoulder 24c resulting in an assembled profile that is harder to accurately control and define. This then results in the assembled height of the needle hub also being harder to accurately control and define during design. An 0-ring may also be more prone to deformation by the compressed spring 46 than a D-shaped member 48 similar dimensions, which further complicated the control and design of the assembled height of the needle hub 32.

The expandable annular member 48 is also coated with a medical lubricant during assembly to reduce friction against the interior of the barrel 24, which lowers the activation force required to retract the needle 30.

The barrel 24 includes a substantially flat internal annular shoulder 24c, facing the first end 24a, which receives and locates the annular member 40 in an abutting relationship with the flat annular surface 52. The barrel 24 also includes four internal protuberances, in the form of barbs 24d, which are positioned forwardly from the shoulder 24c by the longitudinal dimension of the annular member 40. The annular member 40 passes over the barbs 24d during its assembly to the position shown (i.e. abutting against the shoulder 24c). The barbs 24d thereafter assist in locating and retaining the annular member 40 against the shoulder 24c, prior to needle retraction. The cylindrical surface between the shoulder 24c and the barbs 24d is slightly outwardly tapered towards the front end 24a of the barrel 24.

The syringe 22 also includes a cap 58 with a number of inwardly facing barbs 60 that snap engage with a groove 62 (see Fig. 9) near the end 26 of the barrel in order to snap engage the cap 58 to the barrel 24. The cap 58 also has a lid 64. Prior to the cap 58 being engaged with the barrel 24, the annular member 48 can be conveniently positioned against the forward facing annular shoulder 24c from the (open) front end 24a of the barrel 24.

The syringe shown in the PCT application has an internally formed cap and barrel and an annular insert with a shoulder equivalent to shoulder 24c. The insert is introduced from the rear end of the barrel and then positioned at the forward end of the barrel against the cap. Attempting to mould the syringe shown in the PCT application as a single component is very difficult and requires an undercut rim inside the barrel to locate the annual member. The arrangement in the syringe 22 described above advantageously produces the same end result, and whilst using the same number of components, but is far easier, and less risky, to mould. Further, the needle 30 and spring

32 can be accurately loaded in the cap 58 prior to its engagement with the barrel 24, as will be described in more detail below.

The retraction of the needle 30 at the end of the plunger stroke is otherwise similar to that of the syringe shown in the PCT application. Accordingly, as shown in 5 Figs. 3a and 3b and Figs. 4a and 4b, the annular member 48 initially prevents the spring 46 from retracting the needle 30 and the needle hub 32 into the plunger 34 until, at the end of the plunger stroke, the annular member 48 is forced forwardly out of engagement with the needle hub 32 by the forward end of the plunger 34. Simultaneously, the needle hub 32 forces the plug 40 out of engagement with the forward end of the plunger 34. As io a result, the spring 46 can retract the needle 30, the needle hub 32 and the plug 40 into the inner chamber 36 of the plunger 34.

The tapered surface 24e minimizes friction retention of the D-shaped member 48 as it is pushed off the barrel shoulder 24c (i.e. there is less friction retaining the D-shaped member 48 halfway through activation than at the beginning). This result in the syringe

I ₅ requiring a lower activation force than what would be required if the surface 24e was cylindrical.

The assembly advantage mentioned above shall now be described with reference to Figs. 7 to 9.

Fig. 7 shows the cap 58, spring 46 and needle 30 prior to assembly. Fig. 8 shows 0 the needle 30 forced into its extended position relative to the cap 58 with the spring 46 compressed to its minimum extent. This position is maintained by a clamp 70 gripping the needle 30. Fig. 9 shows the compressed cap, needle and spring assembly prior to engagement with the barrel 24. The cap 58 is then positioned over the end of the barrel 24 with its barbs 60 engaging the barrel groove 62 and the needle hub 32 being gripped, 5 and thereafter held against the edge of the spring 46, by the expandable annular member 48. The expandable annular 48 grips the needle hub 32 as its internal diameter is slightly smaller than the external diameter of the needle hub base part 32a. The clamp 70 can then be released as the needle 30 and the needle hub 32is restrained against moving away from the cap 58 by the expandable annular member 48. The assembly of the remainder of 0 the syringe 22 can then be completed by inserting the plunger 34 into the barrel 24. This arrangement and assembly method is advantageous as the compression of the spring 46 can be very accurately controlled with the clamp 70, which minimises assembly reject rates.

The syringe 20 is constructed and functions substantially in accordance with the syringe 22, aside from the differences that will be described below. Like features in the syringe 22 are indicated with the reference numerals to those used to describe the syringe 20.

5 At present, there is no ISO standard for syringe dead volume in automatically retractable syringes. However, ISO 7886 defines, for normal (i.e. non retractable) disposable syringes, a maximum 'dead volume' for a given syringe volume. As best seen in Figs. 3b and 4b, the exterior shape of the end of the plunger 34 is substantially complementary to the interior shape of the front end 24a of the barrel 24. When the o plunger 34 is fully depressed, as shown in Fig. 4b, the 1 millilitre syringe 22 meets the ISO 7886 standard.

As will be described below with reference to Figs. 12 to 15, the 3 millilitre syringe 20 includes a deformable plunger gasket 82 to minimise dead volume and thus meet ISO 7886. s As shown in Figs. 14 and 15, the plunger gasket 82 has substantially planar, annular front and rear services 84 and 86 joined by an inwardly curved side wall 88. The plunger gasket 82 is formed from isoprene (or silicone) rubber, which is compressible.

As best shown in Fig. 10, the interior surface near the front end 24a of the barrel 24 has a shoulder 80 which tapers inwardly towards the barrel front end 24a. The forward 0 facing annular surface 84 of the gasket 82 is initially orientated normal to the longitudinal axis of the syringe 20. As a result, when the plunger 34 is nearly at the end of its stroke, as shown in Fig. 1 Ib, there is a small gap of triangular cross section (see Fig. 1 Ib), between the interior of the barrel 24 and the plunger gasket 82, which represents the dead volume. When the depression of the plunger is continued, the outermost forward corner ₅ of the gasket 82 abuts the outermost corner of the plunger interior. This causes the curved side wall 88 of the gasket 82 to compress inwardly which results in its forward surface 84 tilting outwardly to substantially correspond in shape with the tapered surface of the barrel interior, as shown in Fig. 12b. This results in the gasket 82 filling the dead volume, which should allow the 3 millilitre syringe 20 to meet the ISO 7886 dead volume o requirements.

Although the invention has been described with reference to preferred embodiments, it will be appreciated that those persons skilled in the art that the invention is not limited to these particular embodiments and may be embodied in many other forms.