WO2004045683A1

WO2004045683A1 - Hypodermic safety syringe

Info

Publication number: WO2004045683A1
Application number: PCT/IB2003/005238
Authority: WO
Inventors: Peter Balfour Dugmore; Stanford William Gladwin Reynolds; Anthony Eric Bull; Paul Maxwell Bunn
Original assignee: Peter Balfour Dugmore; Reynolds Stanford William Glad; Anthony Eric Bull; Paul Maxwell Bunn
Priority date: 2002-11-19
Filing date: 2003-11-19
Publication date: 2004-06-03
Also published as: AU2003283620A1

Abstract

A syringe (10) is provided, including a barrel (12) with a slideable piston (30) and a closure (22) closing off a front opening (16) of the barrel (12), in part. The needle (28) is attached to the closure (22). The closure (22) is releasably attached to the barrel (12) by a barrel engaging formation (52), engaged with closure engagement means (54,55) of the barrel (12). When fluid has been discharged from the barrel (12) through the closure (22) and needle (28), by moving the piston (30) towards the front end (14) of the barrel (12), the piston (30) urges the closure (22) towards a narrow zone (63), defined adjacent the closure engagement means (54,55), and the closure (22) is deformed and is released from engagement with the barrel (12). The piston (30) engages the closure (22) by means of resilient complemental engagement formations, and the engaged piston (30) and closure (20) can be withdrawn into the barrel (12), thus withdrawing the needle into a safe position within the barrel (12).

Description

HYPODERMIC SAFETY SYRINGE

BACKGROUND OF THE INVENTION

Potentially lethal infections such as human immune deficiency virus (HIV), hepatitis B. or the like, can be transferred by needle sticks from needles of used hypodermic syringes. The risk of needle stick extends to medical practitioners, persons responsible for handling equipment used in these procedures after use, and the like.

There is a need for a safety hypodermic syringe which approximates the simplicity and cost of manufacture and assembly of a conventional disposable syringe, in which the needle carrier resists premature dislodgement under increasing pressure in the barrel at any time during the injection procedure and retracts freely into a needle safe position when the procedure is completed, which ensures progressive seal integrity between the needle carrier, closure member and barrel, as pressure increases in the barrel during the injection procedure, and which minimises hydraulic pressure buildup in injection fluid trapped between the piston head and needle carrier as the two are urged into locking engagement at the end of the procedure. SUMMARY OF THE INVENTION

According to the invention there is provided a hypodermic safety syringe, which includes: a barrel having a rear end defining a rear opening, a front end defining a front opening, and having an inner wall defining closure engagement means adjacent the front opening, and defining a narrow zone between the closure engagement means and the front opening, which has an internal diameter smaller than an internal diameter of the closure engagement means; a closure, receivable in the barrel adjacent the front opening, and including hypodermic needle receiving means on a front of the closure, a piston engaging formation on a rear of the closure, and a peripheral resilient barrel engaging formation; and a piston, reciprocally movable within the barrel, and including a closure engaging formation at a front end of the piston, wherein the barrel engaging formation is shaped to be resiliently engageable with the closure engagement means of the barrel, when the closure is in an operational position, and to be resiliently deformable to disengage the closure engagement means, when urged towards the narrow zone, and wherein the closure engaging formation of the piston is shaped to engage the piston engaging formation, when the closure is urged towards the narrow zone, so that the engaged closure and piston can be withdrawn towards the rear end of the barrel, to a safe position. The barrel may define a frusto-conical release surface in the narrow zone, which may be inclined at an angle smaller than 45° relative to an axis of the barrel, to provide a mechanical advantage when the closure is urged against the release surface. In a preferred embodiment of the invention, the release surface is inclined at approximately 12° relative to the axis.

The closure engagement means of the barrel may include a recess defined in the inner periphery of the barrel, and/or an inwardly protruding ridge, which may be disposed on a rear side of the recess.

The closure may include a body and a circumferentially extending skirt and may define a displacement groove between the body and the skirt, so that a narrow, resiliently flexible zone is defined adjacent the displacement groove, between the skirt and the body, allowing the skirt to be displaceable relative to the body, when the closure is urged towards the narrow zone.

The skirt may define a radially outwardly extending lip, forming the barrel engaging formation, a skirt groove disposed inwardly from the lip, and a piston engagement formation in the form of a skirt protuberance disposed between the skirt groove and the displacement groove. The skirt protuberance may be generally circumferentially continuous or may be crenellated to form a plurality of segmented arcs. An outer diameter of the lip may be reducible, when the closure is urged towards the narrow zone and the skirt is displaced relative to the body.

The closure may define a piston engaging formation in the form of a clip recess extending forward ly from a rear face of the body. The clip recess may form a rearmost part of a fluid passage extending axially through the body to the needle receiving means.

The closure may define a piston engaging formation in the form of an annular recess, defined radially inwardly from the displacement groove, and extending forwardly from the rear face of the body.

The syringe may include a piston assembly comprising the piston and an elongate retractor, attached to a rear of the piston. The retractor may define a rupture zone near the piston, where the retractor may be ruptured to remove a rear part of the retractor.

The piston may include a circumferential piston protuberance extending from a front face of the piston and forming the closure engaging formation. The piston protuberance may be shaped to engage the piston engaging formation, when the closure has been urged towards the narrow zone and has been deformed. The piston may include a clip, complemental in shape to the clip recess, and extending from a front face of the piston. The clip may include a tapered head, allowing the clip to be inserted into the clip recess with ease, and may define a ridge at a rear of the head, allowing the clip to engage a complemental circumferential recess, defined in the clip recess, when the clip is engaged in the clip recess. Instead, or in addition, the clip may be in the form of an annular rib extending from the front face of the piston, and may include a circumferential detent ridge, engageable with a complemental detent ridge defined in the annular recess of the body. The annular rib may be broached to provide fluid venting means, for allowing fluid which would otherwise be trapped between the circumference of the rib and the closure engagement formation, to be vented via the fluid passage defined through the closure. The closure may include fluid venting means in the form of venting grooves defined in the rear of the closure for allowing fluid which would otherwise be trapped between the piston and the closure to be vented into the fluid passage.

The syringe may include biasing means urging the closure towards the safe position, for moving the closure from the operating position towards the safe position when the barrel engaging formation is disengaged from the recess defined in the barrel. The biasing means may comprise a compression helical coil spring, arranged to act between an inner face of the barrel, defined adjacent the front opening, and the front face of the closure, adjacent the needle receiving means. The barrel may include a closure retention formation, configured for retaining the closure in the safe position, within the barrel.

The invention will now be described, by way of non-limiting example, with reference to the accompanying diagrammatic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross-sectional side view of a syringe according to a first embodiment of the invention;

Figure 2 shows an enlarged cross-sectional side view of part of the syringe of Figure 1 ;

Figures 3 to 8 illustrate steps involved in engaging a piston of the syringe of Figure 1 with a closure of the syringe;

Figure 9 shows a cross-sectional side view of the syringe of Figure 1 , in its safe condition;

Figures 10 to 13 illustrate the forces involved in the steps of Figures 3 to 8, in engaging the piston with the closure;

Figure 14 shows a cross-sectional side view of part of a syringe according to a second embodiment of the invention;

Figure 15 shows a cross-sectional side view of a syringe according to a third embodiment of the invention; Figure 16 shows an enlarged cross-sectional side view of part of the syringe of Figure 15;

Figures 17A to 17C illustrate the steps involved in engaging the piston of the syringe of Figure 15, with the closure;

Figures 18A and 18B show perspective and under plan views of a closure in accordance with a fourth embodiment of the invention;

Figure 19 shows a cross-sectional side view of the syringe of Figure 15, with the closure in its safe condition;

Figure 20 shows an enlarged cross-sectional side view of part of the syringe of Figure 19;

Figure 21 shows an enlarged cross-sectional side view of a syringe in accordance with a fifth embodiment of the invention, in its safe condition;

Figures 22A and 22B show enlarged cross-sectional side views of part of a syringe in accordance with a sixth embodiment of the invention, with a closure and piston of the syringe in unengaged and engaged states respectively;

Figure 23 shows a plan view of a front face of the piston of Figures 22A and 22B; and

Figure 24 shows an enlarged cross-sectional side view of part of a syringe in accordance with a seventh embodiment of the invention, including closure-biasing means. DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Figures 1 to 13 of the drawings, a syringe in accordance with the first embodiment of the invention is generally indicated by reference numeral 10, and includes a cylindrical barrel 12 having a front end 14 defining a front opening 16 and a rear end 18 defining a rear opening 20. A closure 22 fits inside the barrel 12, adjacent the front opening 16, and closes the front opening. The closure 22 includes hypodermic needle receiving means in the form of a hollow spigot 24 on which a needle hub 26 is attached. A hypodermic needle 28 extends from the needle hub 26.

The syringe 10 includes a piston assembly comprising a piston 30, slideably disposed within the barrel 12, and a piston retractor 32 extending from a rear of the piston 30 and terminating in a finger disc 34. The piston 30 has a front disc 36 spaced from a rear disc 38 by a circumferentially extending O-ring groove 40 within which an O-ring 42 is located.

As can be seen in Figure 2, the closure 22 has a body 44 connected to a peripherally extending skirt 46 by a flexible zone forming a hinge 48. A displacement groove 50 is defined between the body 44 and the skirt 46. The skirt 46 has a barrel engaging formation in the form of a lip 52, which engages closure engagement means of the barrel, in the form of a circumferentially extending ridge 54 on the bore 56 of the barrel 12 to form a fluid seal between the closure 22 and the barrel 12. A circumferential recess 55 is defined to the front of the ridge 54.

The skirt 46 also includes a skirt protuberance 58 and a skirt groove 60, for engaging a closure engaging formation of the piston, in the form of a piston protuberance 62. In Figure 2, an undeformed position of the skirt 46 is shown in dashed lines, for illustrative purposes.

A narrow zone is defined by an inner wall of the barrel, in the form of an inclined release surface 63, located between the ridge 54 and a front section 64 of the barrel. The inclined release surface 63 is frustro- conically shaped.

In Figure 3, the piston protuberance 62 is shown abutting the skirt protuberance 58, while the closure 22 is in its operational position. As the piston 30 is pushed forward ly in the barrel 12 by the retractor 32, the piston protuberance 62, pushing against the skirt protuberance 58, urges the lip 52 slideably forward along the release surface 63 to the position shown in Figure 4, in which the diameter of the closure 22 is reduced and the skirt protuberance 58 is hinged inwardly relative to the piston protuberance 62. Further force applied on the piston 30 causes the piston protuberance 62 to move along the skirt protuberance 58 and to locate within the skirt groove 60 as shown in Figures 5 and 6. In Figure 6 it can be seen that the piston 30 abuts the ridge 54 which limits any further forward motion of the piston 30. With the piston protuberance 62 located in the skirt groove 60, the piston protuberance 62 and the skirt protuberance 58 are engaged with one another, and the diameter of closure 22 has been reduced to a point where, as shown in Figures 7 and 8, the lip 52 can clear the ridge 54 thereby allowing piston 30 and the closure 22 to be freely retracted into the barrel 12, while engaged, with a clearly defined clearance gap 53 between the lip 52 and the bore of the barrel 12.

Referring now to Figure 9, the piston 30 and the closure 22 are shown in a safe position, after having been retracted to the rear end 18 of the barrel 12 until the lip 52 has passed beyond a circumferentially extending locking ridge 64 with the piston 30 abutting a retaining ridge 66. In this position the hypodermic needle 28 is safely stored within the barrel 12 and the piston 30 and closure 22 are locked between the locking and retaining ridges 64 and 66. The piston retractor 32 can then be severed by rupturing a rupture zone comprising a frangible connection 68, to remove a rear part of the retractor 32 from the piston 30.

Referring now to Figures 10 to 13, the forces involved in engaging the closure 22 with the piston 30 are described. It will be appreciated that the skirt 46 of the closure 22 is in effect a flexible conical plastic spring washer in hinged engagement with a resilient body 44. The actual stress analysis of a conical plastic spring washer is complex. It will be readily appreciated, however, that progressive backward pressure on the closure 22 (for example, when a practitioner affixes a needle hub to the closure 22 or when the needle 28 is urged into a patient in the process of administering an injection) will have the effect of progressively expanding the lip 52 relative to the bore of the barrel 12, thereby preventing the closure 22 from being prematurely pushed backwards into the barrel 12, before the injection has been administered. For the sake of simplicity, but without compromising the integrity of the illustration, the forces involved in coupling the piston 30 and the closure 22 are here considered as acting in two dimensions instead of in three dimensions. It is assumed that the skirt 46 of the closure 22 bends around the point "a" of the hinge 48. It is also assumed that the barrel 12 and the piston 30 are rigid and that the only flexible component is the closure 22. At the point where the piston 30 is brought into locking engagement within the closure 22, this is largely true, since deformation of the barrel 12 is curtailed at this position by the wall 15 of the front end 14 of the barrel. In addition to simplifying the analysis of the forces involved, there is a commercial advantage in manufacture, where interactive deformation of the barrel, piston and closure is not a prerequisite to effective engagement of the piston 30 with the closure 22.

For the sake of simplicity it is also assumed that there is no friction. This is of course not true. The polypropylene for manufacture of the components has a friction coefficient somewhere between 0.1 to 0.2 but the exclusion of friction will not compromise the explanation. In any event, in line with common practice, the bore of the barrel may be coated with a silicon lubricant to reduce the friction.

The horizontal forces "H" shown in an axial direction in each of Figures 10 to 13, are the same in value and represent the force applied by the operator's thumb, on the finger disc 34 of the retractor 32, and transferred to the piston 30.

In Figure 10, the horizontal force "H" is applied on the piston 30, which, in turn, pushes the closure 22 at point "c". The force at point "c" is at right angles to the line of contact which is represented by a broken line. The force at point "c" has a vector value of "S" which can be represented by a vertical component "Q" and a horizontal component "H".

At point "b", the lip 52 or lobe exerts a force at right angles (normal) to the dotted line of contact at "b" which is equal and opposite to the reaction force "R" exerted by the barrel 12, as shown.

This resultant force "R" can be represented by a horizontal force "H" and a vertical force "P". The horizontal force "H" is the same in all instances.

The net result of all these forces on the skirt 46 is to bend it inwards around the point "a" of the hinge 48. Analysis of the moments about point "a" provides an appreciation of the effectiveness of the various forces acting on the skirt 46. The moment contribution is the vector value of the force which is represented by its length and direction multiplied by the perpendicular distance from the pivot point to the line of action of the force. Considering only the resultant vectors "R" and "S" it will be seen that there is a, large moment contribution from "R". The inclination of the release surface 63 results in a significant contribution to the bending of the skirt 46. The shallower the angle of inclination, the greater the contribution. By contrast the contribution of "S" is small.

Referring now to Figure 11 , the closure 22 has been pushed forwardly along the release surface 63 which has had the effect described above, of bending the skirt 46 into a suitable position for clipping engagement with the piston protuberance 62. This provides a high degree of flexibility in the manufacturing tolerances of the piston protuberance 62 and the skirt protuberance 58 because one has only to continue pushing the piston 30 until a suitable clipping configuration between the piston and skirt protuberance is achieved. At this stage the vector "S" exerts a sizeable contribution towards the bending moment.

Referring now to Figure 12, the skirt 46 has reached the steeper front wall 15 of the barrel and "R's" contribution has diminished somewhat. However, the wedging action at "c" takes over as "S" becomes very large. Further forward motion of the piston 30 concludes the engaging or clipping action between the piston protuberance 62 and the skirt protuberance 58.

As can be seen from Figure 13, the skirt 46 is firmly retained by the piston 30, the diameter of the closure 22 has been reduced to the point where the lip 52 can clear the ridge 54 on the bore of the barrel, and the piston 30 and the closure 22 can be freely retracted into the barrel 12.

Referring now to Figure 14 of the drawings, in a second embodiment of the invention, a closure 22.1 with an offset spigot 24.1 is shown. Such an arrangement is generally used with relatively large barrel diameters, to allow the hypodermic needle to be introduced into a vein substantially parallel to a patient's skin.

A syringe in accordance with a third embodiment of the invention is illustrated in Figures 15 to 17 of the drawings, wherein component parts operating in a similar way to those shown in Figures 1 to 14, have been given the same reference numbers, while those whose function or operation differs, have been given reference numbers qualified with the suffix " 2"

Referring first to Figure 15, a syringe 10 includes a cylindrical barrel 12.2 having a front end 14 with a front opening 16 and a rear end 18.2 with a rear opening 20. A closure 22.2 closes the front opening 16. The closure 22.2 has a spigot 24.2 on which a needle hub 26 is attached. A hypodermic needle 28 extends from the needle hub 26.

A piston 30.2 is slideably located within the barrel 12.2. A piston retractor 32.2 extends from the rear of the piston 30.2 and terminates in a finger disc 34.

Referring to Figure 16, the closure 22.2 has a body 44.2 connected to a peripherally extending skirt 46.2 by a hinge 48.2. A displacement groove 50.2 is defined between the body 44.2 and the skirt 46.2. The skirt 46.2 has a lip 52.2, which engages a circumferentially extending ridge 54 on the bore 56 of the barrel 12.2 to form a fluid seal between the closure 22.2 and the barrel 12.2.

The skirt 46.2 also includes a skirt protuberance 58.2 and a skirt groove 60.2 in which a first piston protuberance 62.2 can nest slideably. In Figure 16 the undeformed position of the skirt 46.2 is shown in dashed lines, for illustrative purposes.

An inwardly tapering cylindrical clip recess 70 having a clip detent or land 72, is defined in the rear opening of a fluid passage or bore 74 extending through the spigot 24.2, lockably to engage a complementally and forwardly tapering circumferential ridge 76 defined on the tip of a second piston protuberance 78 or clip and having the form of a cylindrical nib 80.

An inclined release surface 63 is located between the ridge 54 and a front section 64 of the barrel. The inclined release surface 63 is frustro-conical in shape.

In Figures 16 and 17A, the angled inner surface of the lip 65.2 of the first piston protuberance 62.2 is shown at the point where it first tangentially contacts the outer angled surface of the lip 82 of the skirt protuberance 58.2, and where the ridge 76 of the second piston protuberance 78 is in position to be forwardly urged into clipping engagement with a recess or clip detent 72 in clip recess 70. As the piston 30.2 is pushed further forwardly in the barrel 12.2, the angled inner surface of the first piston protuberance 62.2, pushing against the angled outer surface of the skirt protuberance 58.2 hinges the skirt protuberance 58.2 inwardly around the hinge 48.2 thereby closing up the displacement groove 50.2. At the same time, the closure lip 52.2 is urged slideably forward along the release surface 63 to the position shown in Figure 17B in which the first piston protuberance 62.2 is fully and complementally nested in the skirt groove 60.2, where the diameter of the closure 22.2 is commensurately reduced and where the second piston protuberance 78 is lockably engaged in the clip recess 70. In Figure 17B it can also be seen that the piston 30.2 abuts the ridge 54 which limits any further forward motion. With the first piston protuberance 62.2 nested in the skirt groove 60.2, the diameter of closure 22.2 has been reduced to a point where, as shown in Figure 17C, the lip 52.2 can clear the ridge 54 thereby allowing engaged piston 30.2 and closure 22.2 to be freely retracted into the barrel 12 to its safe position, with a clearly defined clearance gap 53.2 between the lip 52.2 and the bore of the barrel 12.2.

Referring to Figures 18A and 18B of the drawings, a closure in accordance with a third embodiment of the invention is generally indicated by reference numeral 22.3, and includes a skirt protuberance 58.3, broached at points a, b, c, and d, which is crenellated to form a plurality of circumferentially spaced, segmented arcs, so as to reduce hoop stress, and so facilitate inward hinging of skirt protuberance 58.3 around hinge 48.3. Fluid venting grooves 82 are also provided to relieve hydraulic pressure and vent injection fluid trapped between the front face of the piston 30.2 and the rear face of the closure 22.3, as they come into locking engagement after an injection has been given.

Referring now to Figures 19 and 20 of the drawings, the piston 30.2 and closure 22.2, engaged in accordance with the third embodiment of the invention, are retracted to the rear end 18.2 of the barrel 12.2 until the lip 84 of the piston 30.2 has passed rearwardly into a locking detent groove 86 defined by a circumferentially extending locking ridge 64.2 and a circumferentially extending retaining ridge 66.2 on the bore of the barrel 12.2. In this safe position, the hypodermic needle 28 is safely stored within the barrel 12.2 and the piston 30.2 in coupled engagement with the closure 22.2 is securely held in locking groove 86 between the locking and retaining ridges 64.2 and 66.2 respectively. The piston retractor 32.2 can then be severed from the piston 30.2 by rupturing a rupture zone comprising a frangible connection 68.2.

Figure 21 of the drawings shows a syringe in accordance with a fifth embodiment of the invention, which offers an alternative to the piston retractor 32.2 and the safe locking arrangement of Figures 19 and 20. In the fifth embodiment of the invention, an annular flange locking formation 88 with a diameter smaller than the diameter of the piston 30.4, is provided on the piston retractor 32.4, approximately 5 mm rearwardly of the piston 30.4. A circumferentially extending locking ridge 64.4 and a pair of retaining ridges 66.4 and 67.4 defining a locking detent groove 86.4, are formed on the bore of the barrel 12.4, proximate the rear end 18 of the barrel 12.4. When the piston 30.4 and closure 22.2 are retracted rearwardly into the barrel 12.4, the flange locking formation 88 clears the locking ridge 64.4 and is then urged past a tapering fairlead 90, until it clicks into locked nesting arrangement within detent locking groove 86.4. At this point the lip 84.4 of the piston 30.4 is held by locking ridge 64.4, against being retracted further rearwardly into the barrel. The piston retractor 32.4 can then be severed from the piston 30.4 by rupturing a rupture zone comprising a frangible connection 68.4 and since not only the piston and closure, but also the distal portion of the retractor 32.4 itself, are held firmly and securely in the barrel, the chance of accidental retraction of the needle 28 out of the rear opening of the barrel 20, is considerably minimised.

Figures 22A and 22B and Figure 23 of the drawings, show a part of a syringe in accordance with a sixth embodiment of the invention, illustrating the closure and piston engagement arrangement. Figure 22A and 22B show the closure 22.5 and piston 30.5 in an unengaged or operative state, and in an engaged or inoperative state, respectively, with the closure in its operative, and safe positions, respectively.

The piston 30.5 includes on its front face 92 a second piston protuberance 78.5 comprising a forwardly extending annular rib 94 having an outwardly projecting circumferential detent ridge in the form of a lip 96. As shown in Figure 22B, when the piston 30.5 has been urged forwardly to engage the closure 22.5, the annular rib 94 is brought into engagement with the clip recess 70.5, defined by annular recess or groove 98, and the circumferential lip 96 is brought into locked clipping engagement behind an inwardly projecting detent ridge 100 within the groove 98. The closure 22.5 may include fluid venting means in the form of venting grooves (not shown), defined in the rear of the closure 22.5, for allowing fluid which would otherwise be trapped between the piston 30.5 and the closure 22.5, to be vented into the fluid passage. Referring now to Figure 23 of the drawings, the front face 92 of the piston 30.5 is provided with fluid venting channels 102 which broach the walls of annular rib 94 so that injection fluid is able to vent out of the space 104 defined by the rib 94 in which said fluid would otherwise be trapped as the piston 30.5 is brought into engagement with the closure 22.5.

Referring to Figure 24 of the drawings, in a seventh embodiment of the invention, closure biasing means is provided by a compression helical coil spring 108 biased in the direction of arrow A. The coil spring 108 is characterised by spring coils 110 of progressively increasing diameter, such that when the spring 108 is compressed, the coils 110 nest one within the other in the manner of a clock spring, thereby taking up the minimum of space. The base 112 of the spring is held in compression against an inner front face 114 of the barrel 12, and the apex 116 of the spring 108 encircles and is held in compression against the spigot 24, at its base. In practice, when the closure 22 is brought into coupled engagement with the piston 30, and the diameter of the lip 52 of the closure 22 is thereby reduced sufficiently to clear ridge 54 on the bore of the barrel 12, compression exerted by the spring 108 in the direction of arrow A has the effect of urging the closure 22 and needle (not shown) backwardly into the barrel 12 from its operating position towards its safe position. In the event that the practitioner neglects to retract the closure 22 into a fully locked safe position immediately after using the syringe, e.g. when he only has one hand available for operating the syringe, once manual pressure on the finger tab 34 is relaxed, the spring 108 moves the needle back into a position where the point is effectively shielded until it can be rendered permanently safe.

The invention illustrated holds the advantage of reducing the risk of needle stick from needles 28 of used hypodermic syringes 10, which could lead to the transmission of infections, including potentially lethal infections such as HIV and hepatitis B viruses, while avoiding the need for equipment external to the syringe 10, to render the syringe safe. It also holds the advantage of simplicity and low cost of manufacture and assembly. It further holds the advantage that use of the syringe 10 is substantially similar to use of conventional syringes, with which practitioners are familiar, making provision for single-handed operation in some cases. It further holds the advantage that a user of the syringe 10 has a choice of when the needle is retracted into the safe position, thereby allowing the syringe 10 to be used more than once at the discretion of the practitioner before it is rendered safe and inoperable - for example, when it is desirable to administer a sequential "cocktail" of drugs to the same patient without the necessity of using a new syringe for each injection.

The construction of the invention illustrated also holds the advantage that premature dislodgement of the closure 22 from the barrel 12, whether as a result of rearward pressure on the spigot (for example, when a needle hub is affixed thereto) or of increasing hydraulic pressure in the barrel, is resisted, and that the seal integrity between the closure 22 and the barrel 12 does not deteriorate as the hydraulic pressure within the barrel 12 increases.

Claims

1. A hypodermic safety syringe (10), which includes: a barrel (12) having a rear end (18) defining a rear opening (20), a front end (14) defining a front opening (16), and having an inner wall defining closure engagement means (54,55) adjacent the front opening (16), and defining a narrow zone (63) between the closure engagement means (54,55) and the front opening (16), which has an internal diameter smaller than an internal diameter of the closure engagement means (54,55); a closure (22), receivable in the barrel (12) adjacent the front opening (16), and including hypodermic needle receiving means (24) on a front of the closure (22), a piston engaging formation (58) on a rear of the closure, and a peripheral resilient barrel engaging formation (52); and a piston (30), reciprocally movable within the barrel (12), and including a closure engaging formation (62) at a front end of the piston (30), characterised in that the barrel engaging formation (52) is shaped to be resiliently engageable with the closure engagement means (54,55) of the barrel (12), when the closure (22) is in an operational position, and to be resiliently deformable to disengage the closure engagement means (54,55), when urged towards the narrow zone (63), and in that the closure engaging formation (62) of the piston (30) is shaped to engage the piston engaging formation (58), when the closure (22) is urged towards the narrow zone (63), so that the engaged closure (22) and piston (30) can be withdrawn towards the rear end (18) of the barrel (12), to a safe position.

2. A syringe (10) as claimed in Claim 1 , characterised in that the barrel (12) defines a frusto-conical release surface (63) in the narrow zone, which is inclined at an angle smaller than 45° relative to an axis of the barrel (12).

3. A syringe (10) as claimed in Claim 2, characterised in that the release surface (63) is inclined at approximately 12° relative to the axis.

4. A syringe (10) as claimed in Claim 1 , characterised in that the closure engagement means of the barrel includes a recess (55), defined in the inner periphery of the barrel (12).

5. A syringe (10) as claimed in Claim 1 , characterised in that the closure engagement means of the barrel (12) includes an inwardly protruding ridge (54).

6. A syringe (10) as claimed in Claim 1 , characterised in that the closure (22) includes a body (44) and a circumferentially extending skirt (46), and defines a displacement groove (50) between the body (44) and the skirt (46), so that a narrow, resiliently flexible zone (48) is defined adjacent the displacement groove (50), between the skirt (46) and the body (44), allowing the skirt (46) to be displaceable relative to the body (44), when the closure (22) is urged towards the narrow zone (63).

7. A syringe (10) as claimed in Claim 6, characterised in that the skirt (46) defines a radially outwardly extending lip (52), forming the barrel engaging formation, a skirt groove (60) disposed inwardly from the lip (52), and a piston engagement formation in the form of a skirt protuberance (58) disposed between the skirt groove (60) and the displacement groove (50).

8. A syringe (10) as claimed in Claim 7, characterised in that the skirt protuberance (58) is generally circumferentially continuous.

9. A syringe (10) as claimed in Claim 7, characterised in that the skirt protuberance (58) is crenellated to form a plurality of segmented arcs (58.3).

10. A syringe (10) as claimed in Claim 7, characterised in that an outer diameter of the lip (52) is reducible, when the closure (22) is urged towards the narrow zone (63) and the skirt (46) is displaced relative to the body (44).

11. A syringe (10) as claimed in any one of Claims 6 to 10, characterised in that the closure (22) defines a piston engaging formation in the form of a clip recess (70) extending forwardly from a rear face of the body (44).

12. A syringe (10) as claimed in Claim 11 , characterised in that the clip recess (70) forms a rearmost part of a fluid passage (74) extending axially through the body (44) to the needle receiving means (24).

13. A syringe (10) as claimed in any one of Claims 6 to 12, characterised in that the closure (22) defines a piston engaging formation in the form of an annular recess (98), defined radially inwardly from the displacement groove (50), and extending forwardly from the rear face of the body (44).

14. A syringe (10) as claimed in any one of the preceding claims, characterised in that it includes a piston assembly comprising the piston (30) and an elongate retractor (32), attached to a rear of the piston (30).

15. A syringe (10) as claimed in Claim 14, characterised in that the retractor (32) defines a rupture zone (68) near the piston (30), where the retractor (32) can be ruptured to remove a rear part of the retractor (32).

16. A syringe (10) as claimed in any one of the preceding claims, characterised in that it includes a circumferential piston protuberance (62) extending from a front face of the piston (30) and forming the closure engaging formation.

17. A syringe (10) as claimed in Claim 16, characterised in that the piston protuberance (62) is shaped to engage the piston engaging formation (58), when the closure (22) has been urged towards the narrow zone (63) and has been deformed.

18. A syringe (10) as claimed in Claim 11 or Claim 12, characterised in that the piston (30) includes a clip (78), complemental in shape to the clip recess (70), and extending from a front face of the piston (30).

19. A syringe (10) as claimed in Claim 18, characterised in that the clip (78) includes a tapered head, allowing the clip (78) to be inserted into the clip recess (70) with ease, and defines a ridge (76) at a rear of the head, allowing the clip (78) to engage a complemental circumferential recess (72), defined in the clip recess (70), when the clip (78) is engaged in the clip recess (70).

20. A syringe (10) as claimed in Claim 18, characterised in that the clip (78) is in the form of an annular rib (94) extending from the front face of the piston, and includes a circumferential detent ridge (96), engageable with a complemental detent ridge (100) defined in an annular recess (98) of the body (44).

21. A syringe (10) as claimed in Claim 20, characterised in that the annular rib (94) is broached to provide fluid venting means, for allowing fluid to be vented via a fluid passage (74) defined through the closure (22).

22. A syringe (10) as claimed in any one of the preceding claims, characterised in that the closure (22) includes fluid venting means in the form of venting grooves (82) defined in the rear of the closure (22), for allowing fluid which would otherwise be trapped between the piston (30) and the closure (22) to be vented into a fluid passage (74).

23. A syringe (10) as claimed in any one of the preceding claims, characterised in that it includes biasing means (108), urging the closure (22) towards the safe position.

24. A syringe (10) as claimed in Claim 23, characterised in that the biasing means (108) comprises a compression helical coil spring, arranged to act between an inner face (114) of the barrel (12), defined adjacent the front opening (16), and the front face of the closure (22), adjacent the needle receiving means (24).

25. A syringe (10) as claimed in any one of the preceding claims, characterised in that the barrel (12) includes a closure retention formation (64,66), configured for retaining the closure (22) in the safe position, within the barrel (12).

26. A syringe (10) as claimed in Claim 1, substantially as herein described and illustrated.

27. A new syringe, substantially as herein described.