WO2000041494A2

WO2000041494A2 - Safety syringe assembly

Info

Publication number: WO2000041494A2
Application number: PCT/IB2000/000030
Authority: WO
Inventors: Peter Balfour Dugmore; Anthony Eric Bull; Stanford William Gladwin Reynolds
Original assignee: Peter Balfour Dugmore; Anthony Eric Bull; Reynolds Stanford William Glad
Priority date: 1999-01-11
Filing date: 2000-01-11
Publication date: 2000-07-20
Also published as: WO2000041494A3; AU2000218862A1

Abstract

A hypodermic safety syringe assembly (120) comprises a cylindrical barrel (12A) having a front opening (18A) and a rear opening (26A). A piston assembly (28A) is arranged to travel reciprocally within the barrel. The piston assembly includes a retractor (124) which terminates in a front piston formation (122). A closure member (132) is formed with a central spigot formation (134) extending from a skirt (136) which is provided with an outer peripheral lip (138), just inwardly of which is formed an inner lip (140) for engaging a complemental channel formation (142) defined towards the outer periphery of the piston formation (122). The rib (138) locates within a complemental foremost groove (144) formed in the inner face of the barrel (12A). The lip (140) is arranged to engage with the channel formation (142) to disengage the closure member from the front end of the barrel so that the spigot and the needle attached thereto can be withdrawn into a locked safe position within the barrel after use.

Description

SAFETY SYRINGE ASSEMBLY

BACKGROUND OF THE INVENTION

This invention relates to a hypodermic safety syringe assembly

The needles of used hypodermic syringes pose an increasing threat of the transmissibility of potentially lethal infections such as HIV⁺ and hepatitis B viruses, not only to persons administering the injection, but also to persons who are charged with handling such equipment immediately after use, to others who are exposed to the possibility of accidental, post-injection contact in environments in which hypodermic procedures are routinely administered, and to still others who might come into contact with used syringes which have been inadequately disposed of

Various safety hypodermic syringes have been designed which attempt to minimise these risks These include various forms of needle containment and needle disposal units which respectively seek to encapsulate a used needle or allow such used needle to be destroyed by incineration or the like In order to be effective, needle destroying devices have to be available in situ at all locations where such procedures are undertaken The effectiveness of needle destroying devices is further reduced by the fact that the sharp end of the used needle may typically be exposed for an appreciable period of time before it is destroyed

Another arrangement which is available comprises a cylindrical sleeve which fits around the barrel of a syringe, and which can be extended forward over the needle attached to the syringe after use When the sleeve is fully extended, locking formations on the sleeve engage complemental locking formations formed on or adjacent the end of the syringe barrel so that the sleeve cannot be retracted

Drawbacks of protective sleeve arrangements include the fact that in a number of such devices the shield has an open end, which is large enough to allow a user's finger to enter and to contact the needle A directly concomitant disadvantage is the fact that in order to obviate this danger, the needle used has to be substantially shorter than the length of the syringe barrel and shield The extended and locked syringe/sleeve assembly is relatively long and bulky, and uses a substantial additional mass of plastic material compared with the syringe alone Arrangements of this type are also relatively complicated to manufacture, frequently involving a complete re-engineering of the syringe in order for it to co-operate in secure locking engagement with the sleeve Examples are provided by the disclosures in US Patents 5,053,018 and 5,304,149, both of which teach a hypodermic syringe and needle assembly on which is mounted a shield which is movable between a retracted position in which the needle point is exposed and an extended position in which the needle point is covered

User resistance has been encountered to the added bulk and overall diameter of the assembly contributed by the sleeve, which is particularly disadvantageous when the needle point needs to be acutely tangential to the surface of the skin of the patient The fact that the contents and the graduations on the syringe must be viewed through the material of the shield has also proved inconvenient and can lead to errors in use

An alternative arrangement where the syringe is substantially re-engineered typically proposes a device having a barrel, sheath and piston, the piston being provided with a liquid passageway interconnectable with the barrel The injection of fluid is accomplished by moving the barrel relative to the sheath (as opposed to the more familiar approach of moving the piston relative to the barrel, in conventional hypodermic syringe assemblies) An example of this approach is provided by South African Patent 93/5302, which teaches the automatic and non-discretionary single use safe rendition of a needle

Three disadvantages of this approach have manifested themselves in practice The first is the fact that the procedure represents a significant departure from the operation of a conventional syringe Nursing staff have shown resistance to the required adjustment from what is a comfortable and familiar routine A further disadvantage is the fact that this approach requires a large number of component parts, which adds significantly to the cost of both the moulds and mould operations required and of the materials used A final disadvantage is the impression left with the practitioner that the precise point when the device is rendered needle-safe is no longer a matter of professional choice, but is rather a matter of when the manufacturer has prescribed that it is advisable or necessary

The highest incidence of the HIV⁺ and hepatitis viruses generally occur in poor, third world countries which can ill afford devices reliant on significant re-engineering, which do not take into account the high level of the capital invested world-wide in manufacturing facilities for and stocks of conventional hypodermic syringes and needles

It is an object of the invention to provide an alternative safety syringe assembly which allows for an administering procedure which does not depart significantly from that of a conventional syringe, and which does not utilise an additional outer sheath or shield SUMMARY OF THE INVENTION

According to the invention there is provided a hypodermic safety syringe assembly comprising:

a cylindrical barrel having a front end defining a first aperture and a rear end defining a second aperture;

a closure member shaped to engage the barrel at or adjacent the front end thereof to seal the first aperture, and including a hypodermic needle spigot;

a piston assembly reciprocally movable within the barrel and including a retractor terminating in a piston formation engageable with the closure member to disengage the closure member from the front end of the barrel so that the spigot and a hypodermic needle attached thereto can be withdrawn into a locked safe position within the barrel after use; and

detaining means for detaining the spigot and needle in the locked safe position.

Preferably, the closure member includes a barrel engaging formation releasably engageable within a complemental closure member engaging formation at the front end of the barrel, the barrel engaging formation and the complemental engaging formation being arranged in an operating engaged position to prevent pressure exerted on the needle spigot while mounting the needle thereon, or on the needle point in use, from forcing the closure member backwards into the barrel.

Advantageously, the closure member includes a piston coupling formation for engaging a complemental coupling formation on the piston to facilitate disengagement of the barrel engaging and complemental closure member engaging formations from one another by withdrawal of the retractor

Conveniently, the piston coupling formation and complemental coupling formation are arranged to at least partly disengage the barrel engaging and complemental closure member engaging formations as the piston coupling and complemental coupling formations are urged into engagement with one another so as to facilitate the disengagement of the closure member from the front end of the barrel for withdrawal, together with the piston formation, into the locked safe position within the barrel

Typically, the engaging and coupling formations are shaped to allow the engaging and disengaging process to be effected during axial reciprocation of the piston assembly within the barrel

In a preferred form of the invention, the coupling and complemental coupling formations, as they are engaged, present an outer diameter which is materially greater than the inner diameter of the barrel, resulting in outward elastic deformation of the wall of the barrel at the front end thereof, and concomitant outward releasing distortion on the complemental closure member engaging formation defined in the inner wall of the barrel for facilitating the disengagement of the barrel engaging formation therefrom

Typically, compressive hoop stress arising from the outward elastic deformation of the wall of the barrel is arranged to enhance the interengagement of the coupling and complemental coupling formations

Conveniently, the barrel engaging formation comprises at least one circumferential lip or channel on the closure member acting in sealing cooperative click fit engagement with at least one corresponding respective channel or lip comprising the complemental closure member engaging formation defined in the inner wall of the barrel

In an alternative form of the invention, the barrel engaging formation and complemental closure member engaging formation comprise a bayonet-type fitting, with the first aperture being shaped to receive the fitting, with the piston coupling formation and complemental coupling formation including rotational locking engagement means for allowing the bayonet-type fitting to be rotatably disengaged

Any of the above described combinations of barrel engaging and complemental closure member engaging formations may be used to supplement any one or more of the others

Advantageously, the first aperture constitutes or is defined within a finger barrier extending inwardly from the front end of the barrel

Advantageously, the rotational locking engagement means extends to a locating formation designed to ensure automatic co-operating location of the piston coupling and complemental closure member coupling formations The said rotational locking engagement means may comprise one or more splines and complemental locking keyways forming the rotational locking interface between the piston coupling and complemental closure member coupling formations The splines and keyways preferably form complemental coronae with the keyways conveniently being provided with fairleads to ensure automatic location of the splines when the piston coupling and complemental coupling formations are brought together

The rotational locking interface may alternatively be provided by a friction fit which may be further enhanced by keying or roughening the co-operating surfaces of the piston coupling and complemental coupling formations Alternatively, the piston coupling and complemental coupling formations are non-circular in configuration to allow rotational locking engagement of one within the other

The barrel engaging formation may include a safety formation to prevent accidental disengagement of the engaging formation whilst the syringe is in use, the safety formation comprising a plurality of bosses or detents in the outer face of a front wall of the barrel alternating with a plurality of slots radiating outwardly from the outer periphery of the first aperture, the bayonet fitting being designed to engage in a click and/or compression fit with the bosses or detents in the engaged position, and to be rotated out of locking engagement therewith in order to be retracted backwardly through the slots

Conveniently, the safety formation is provided with rotation delimiting means comprising at least one stop alternating with the bosses described in the outer face of the front wall of the barrel to prevent over-rotation of the bayonet fitting into the operating, locked position in assembly, and to ensure the precise degree of counter-rotation out of locking engagement after the hypodermic procedure has been completed in order to align lugs of the bayonet fitting with the slots prior to retraction therethrough

Preferably, the piston coupling formation comprises a radially outwardly projecting peripheral lip and/or channel, and the complemental coupling formation comprises a complemental radially inwardly projecting peripheral lip and/or channel

In a further alternative form of the invention, the barrel engaging formation and complemental closure member engaging formation comprise a threaded screw-type fitting Preferably, the detaining means comprises a circumferential channel defined in the inner wall of the barrel at or adjacent its rear end, and an outer peripheral portion of the piston formation and/or closure member which is designed to be held captive within the circumferential channel to lock the needle in the needle safe position the channel being defined between front and rear raised detents or ribs projecting radially inwardly into the barrel cylinder

Advantageously, the closure member includes sealing means comprising a sealing disk or flange which acts in sealing engagement with the inner walls of the barrel at or adjacent its front end, with sealing engagement being reinforced by the addition of an upstanding wall or skirt to the flange of the closure member, and sealing engagement extending to the interface between the front face of the disk or flange and the rear face of the front end wall of the barrel

Conveniently, the closure member is provided with compression means designed to enhance sealing engagement and locking engagement within the front wall of the barrel, the compression means being provided by the sealing disk being defined as a forwardly tapering cone, the outer periphery of which has a nominally greater diameter than the internal diameter of the barrel, resulting in an outwardly biased disk spring compression which has the effect of holding the outer periphery of the closure member in sealing engagement with the inner circumference of the barrel side wall

The angle of the forwardly tapering cone of the sealing disk may be shallower than a rear face of the first aperture-defining front end wall of the barrel resulting in an axially directed disk spring compression for enhancing sealing engagement of the closure member against the barrel front end wall and inner circumference of the barrel side wall Typically, second sealing means are provided comprising a first O-ring designed to act in compressive sealing engagement between a front wall of the disk of the closure member and the front end wall of the barrel.

Conveniently, supplemental piston sealing means are provided in the form of a second O-ring seated on a rebated annular land defined within the piston formation.

One or more of the above means of sealing may advantageously be employed.

The retractor portion of the piston assembly typically comprises a shaft consisting of one or more radially tapered vanes or ribs and being provided with a finger disk at its rear end.

The shaft may be provided with a torque resisting formation, the torque resisting formation typically provided by one or more of the vanes having an axial lattice, preferably in the form of a single ribbed repeating Z-section, along the retractor shaft so as to increase resistance to torque applied thereto where rotational unlocking of the closure assembly is necessary prior to retraction of the needle.

Advantageously, the stop means of the safety formation of the first aperture is defined to allow only one direction of rotation of the closure member, thus permitting the axially latticed retractor vanes to be arranged so as to provide positively tensioned resistance to torque at the commencement of rotation of the shaft and thus facilitate rotational unlocking of the closure member.

The piston is typically designed as an annular disk or flange at the forward end of the piston assembly being designed to act in sealing engagement with the inner walls of the barrel

Advantageously, sealing engagement is enhanced by the provision of a wiper ring constituting an outwardly projecting peripheral lip on the skirt or flange of the piston

Preferably, distortion limiting means are provided to limit the distortion of the relative mass of the piston in moulding and also to enhance cooling time of the piston assembly as a whole in the mould

The distortion limiting means may comprise a webbed lattice formation defined in a space between a bulkhead or rear piston at the forward end of the retractor shaft and the back face of the piston, thus contributing to a thin and substantially uniform material thickness throughout the piston assembly, with thermally bulky sections eliminated and with cooling times in the mould concomitantly enhanced

Advantageously, the webbed lattice formation and the space thereby defined between the piston and the bulkhead may accommodate a sealing formation designed to enhance the sealing capability of the piston in cooperation with the inner walls of the barrel

In a preferred form of the invention, the hypodermic safety syringe assembly includes breakout means for facilitating separation of the retractor from the piston or closure member formation once the closure member and piston have been retracted into the locked needle safe position within the barrel

The breakout means may include retractor shear means for ensuring that the retractor shears laterally from the rear face of the piston

Alternatively, the breakout means is arranged to facilitate disengagement of the piston coupling formation from the complemental coupling formation, the breakout means being provided by a captive fulcrum defined by a heel of the outer periphery of the piston acting upon any peripheral point on the face of an inlet taper provided at the rear opening of the barrel

Advantageously, the retractor includes limiting means to limit the movement of the piston forwardly into the barrel to a position where it is functionally and accurately able to draw up the fluid to be injected but where it is constrained from accidentally engaging the closure member before the hypodermic procedure is completed

The limiting means also allows the practitioner discretionally to use the syringe assembly more than once for example when a "cocktail" of drugs is administered consecutively to the same patient without the necessity of using a fresh syringe for each injection

Typically, the limiting means comprises at least one axial rib or vane of the retractor which is formed with a ridged or expanded shoulder adjacent the rear end thereof, the shoulder being designed to abut against an edge defined by the rear end of the barrel

Typically, the safety syringe assembly includes at least one fluid venting channel for enabling the escape of fluid entrapped between the piston coupling formation and complemental coupling formation during engagement thereof

The safety syringe assembly is typically injection moulded from thermoplastic materials such as polypropylene, or the like BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a top plan view of a first embodiment of a safety syringe assembly according to the invention;

Figure 2 shows a partly cross-sectional side view of the safety syringe assembly along the lines 2-2 of Figure 1 ;

Figure 3A shows a top plan view of a closure member forming part of the safety syringe assembly of Figures 1 and 2;

Figure 3B shows a cross-sectional side view of the closure member along the lines 3B-3B of Figure 3A;

Figure 3C shows an underplan view of the closure member;

Figure 3D shows an underplan view of a piston assembly forming part of the safety syringe assembly of Figure 2;

Figure 4 shows a detailed cross-sectional side view of a front portion of the safety syringe assembly of Figure 2 with the closure member and piston assembly in the engaged position;

Figures 5A to 5C show end-on views in the direction of arrow A of

Figure 4 of the closure member in the respective disengaged, partly engaged and fully engaged positions at the front end of the barrel;

Figure 6A shows a partly cross-sectional side view of the safety syringe assembly with the closure member and needle in the fully retracted engaged position within the barrel;

Figure 6B shows a partly cross-sectional side view of the safety syringe assembly with the piston assembly being broken away from the closure member;

Figure 7 shows a cross-sectional detail of part of the piston and the rear end of the barrel;

Figure 8 shows a partly cross-sectional side view of a front end of a second embodiment of a hypodermic safety syringe assembly of the invention;

Figure 9 shows a party cross-sectional side view of a front end of a third embodiment of a safety syringe assembly of the invention;

Figure 10 shows a partly cross-sectional side view of a fourth embodiment of a safety syringe assembly of the invention;

Figures 11A to 11D show partly cross-sectional side views of the respective forward disengaged, retracted disengaged, forward engaged and retracted engaged positions illustrating a typical injection administering cycle;

Figures 12A to 12D show cross-sectional details illustrating, stepwise, the manner in which the front end of the piston engages the rear end of the closure member in a click fit; Figure 13 shows a cross-sectional detail of a rear end of the safety syringe assembly in the Figure 1 1 D retracted engaged position,

Figure 14 shows a cross-sectional side view of a front end of a fifth embodiment of a safety syringe assembly of the invention, and

Figure 15 shows a cross-sectional side view of a front end of a sixth eccentric embodiment of a safety syringe assembly of the invention

DESCRIPTION OF EMBODIMENTS

Referring first to Figures 1 and 2, a hypodermic safety syringe assembly 10 comprises a cylindrical barrel 12 having a front end 14 and a rear end 16 The front end 14 defines an opening 18 within a finger barrier 20 which is arranged to receive a bayonet fitting 22 on a closure member 24 in the manner described below A second aperture 26 is defined at the rear end of the barrel for receiving a piston assembly 28 which is reciprocally movable within the barrel The piston assembly comprises a front generally disc-shaped piston formation 30, a retractor 32 comprising an array of cruciform vanes 34, 35 and 36 and a rear finger-engageable retractor disc 38 The rearmost face of the retractor disc 38 is formed with a series of ribs 40, and the outer circumference of the disc is provided with crenellations 42 for providing gripping assistance The vane 35 and opposed vane 36 have a zig-zag profile to provide the retractor 32 with torsional stability and resistance during twisting thereof A pair of opposed finger-engageable tabs 46 extend outwardly on either side of the aperture 26

The closure member 24 is clearly illustrated in Figures 3A to 3C, and comprises a hypodermic needle spigot 48 extending from a disc-shaped skirt 50 A pair of opposed bayonet lugs 52 intermediate the spigot 48 and the skirt 50 are sized to be received within complemental recesses 54 which are more clearly visible in Figures 5A to 5C An O-πng 56 is fitted between the skirt 50 and the lugs 52 to enhance the seal between the skirt 50 and the inner front face 58 of the finger barrier 20

A spigot or press stud formation 60 extends rearwardly from the centre of the closure member, and is divided into quadrants 62 by a series of drainage channels 64 Each of the quadrants is formed with circumferential overhanging sawtooth splines 66 which engage in a click fit with a corresponding array of sawtooth splines 68 formed within a socket formation 70 in the front face of the piston formation 30

The manner in which the closure member 24 and the piston formation 30 are held in co-operative engagement at the front end of the barrel 12 is clearly shown in Figures 4 and 5A to 5C The O-rιng 56 has been omitted from Figure 4 for the sake of clarity, and can in fact be omitted completely in cases where an outer peripheral lip 72 of the sealing skirt 50 forms a sufficiently liquid tight seal with the barrel 12 During manufacture of the syringe assembly, the closure member 24 is passed through the opening 26 and the bayonet lugs 52 are passed through the apertures 54 to a position in which the outer peripheral rib or lip 72 of the sealing skirt locates in a sealing compression fit within a channel 74 formed within the inner wall of the barrel 12 adjacent its front inner face

From Figure 4, it is apparent that, in the relaxed position, the sealing skirt 50 extends rearwardly at an angle which is less acute or shallower than the rearwardly extending angle of the inner face 58 of the finger barrier 20, thereby providing a relief area 78 In assembly, advancing the closure member to occupy this relief area constitutes a disk spring traverse, to effect a compressive return bias of the sprung skirt 50 The front face of the finger barrier is formed with a pair of chamfered bosses 80 over which the lugs are able to ride in the manner illustrated in Figure 5B when the closure member is pushed forward and twisted in the direction of arrow 82 through 90° to the Figure 5C position, in which the lugs 52 locate against stop formations 84 similarly extending from the front face of the finger barrier 20 In the Figure 4 and 5C positions, the lugs are located in a compression fit with sufficient axial force to seal the front end of the syringe, and sufficient rotational restraint to prevent accidental disengagement of the bayonet lugs 52 during the hypodermic procedure

The piston assembly 28 is then inserted through the rear opening 26 of the barrel to the position shown in Figure 2 in which the piston formation 30 contacts but does not engage with the closure member 24 and is therefore free to be urged reciprocally backwards and forwards within the barrel 12, and the syringe assembly 10 is then sterilized and packaged In use, the piston assembly 28 is conventionally drawn back by the practitioner to draw the fluid to be injected into the barrel 12, and the injection is administered in the normal fashion, save only that at the end of the procedure the piston formation 30 is fully advanced to a position in which the socket formation 70 defined in the front face of the piston is urged in a snap fit over the press stud formation 60 The final position is that illustrated in Figure 4, in which all of the fluid is evacuated from the syringe A supplementary O-rιng 86 may be provided for supplementing the seal between an outer peripheral lip 88 of the piston and the inner face of the barrel 12 The piston formation 30 is partly hollow, in that it is provided with an H-shaped lattice 90 between a rear piston disc 92 and the front piston disc 31 In order to disengage the closure member 24, additional pressure is applied on the piston assembly to compress the skirt 50 of the closure member 24 and rotate the lugs 52 through 90° back from the Figure 5C to the Figure 5A positions Thereafter, the closure member 24 and accompanying needle hub assembly 94 is retracted back into the barrel 12 of the syringe to a retracted engaged position illustrated in Figure 6A As is apparent from Figure 7, the rear end of the barrel 12 is formed with a retaining channel 96 defined between a front retaining rib 98 and a rear retaining rib 100 The front retaining rib 98 is dimensioned to allow passage of both the outer lip 88 of the front piston disc 31 and a fulcrum lip 102 formed at the outer periphery of the rear piston disc 92 The rear retaining rib 100 is more pronounced, to the extent that it allows passage of the smaller diameter fulcrum lip 102, whilst preventing passage of the larger diameter piston lip 88, thereby effectively holding the front piston disk 31 and the accompanying closure member 24 and needle hub assembly 94 captive within the barrel

Once the piston formation 30 has been retracted to the Figure 6A position, the piston assembly 28 is broken away from the closure member 24 This is achieved by tilting the piston assembly to one side so that the fulcrum lip 102 locates between one of a series of fulcrum ridges 104 located at the rear opening 26 of the barrel After the piston assembly has been broken away in the manner illustrated in Figure 6B, both portions of the syringe can be safely disposed of with the needle hub assembly 94 being located safely within the barrel in such a way that the possibility of needlestick is avoided

Referring now to Figure 8, an alternative embodiment of a safety syringe assembly 106 is shown in which a single size closure member 24A can be used to seal off the front end of a first syringe barrel 108 having a larger diameter and a second syringe barrel, which is indicated in broken outline at 1 10 having a smaller diameter, without the need to change the dimensions of the closure member

In Figure 9 a closure member 24B is shown formed with an integral needle 1 12 with the entire closure member 24B and integral needle 12 being dimensioned so that it can be retracted into the barrel 12, which would not be the case with a conventional separate needle hub assembly, part of which is indicated in broken outline at 114

In Figures 10 to 13, a fourth preferred embodiment of a safety syringe assembly 120 of the invention is shown Those components which are similar or identical to the components of the first embodiment are indicated with the same numerals suffixed by an A The barrel 12A has a front opening 18A and a rear opening 26A, with a piston assembly 28A arranged to travel reciprocally within the barrel and terminating in a front piston formation 122 with a front piston disc 123 and a sealing lip or wiper ring 145 projecting outwardly from the forward edge of a piston skirt 147 An intermediate retractor 124 comprising a pair of cruciform vanes 126 and 128 extends rearwardly from the front piston formation and terminates in a rear finger disc 130 A closure member 132 is formed with a central spigot formation 134 extending from a skirt 136 which is provided with an outer peripheral lip or rib 138, just inwardly of which is formed an inner lip or nb 140 for engaging a complemental channel formation 142 defined towards the outer periphery of the piston formation 122 The rib 138 locates within a complemental foremost groove 144 formed in the inner face of the barrel 12A adjacent the finger barrier 20A

The skirt 136 of the closure member 132 and the face of the front piston disc 123 are respectively constituted as backwardly and nominally complemental forwardly inverted cones In assembly, the closure member 132 is expected to be introduced into the rear aperture 26A of the barrel 12A on a mandrel with a distal pin locating within the fluid channel running centrally through the needle spigot 134, the conical configuration of the closure member 132 allowing forward pressure from the mandrel to cause a nominal decrease in diameter of the skirt 136 during insertion Conversely, backward pressure_on the closure member 132 when a needle assembly 94A is urged onto the needle spigot 134 or brought into use will tend to expand the skirt 136 thereby enhancing locking and sealing interengagement of the nb 138 in the foremost complemental groove 144 In order to minimize material and consequent risk of deformation during moulding in the front piston disc 123, the angles of the cones defined by the skirt 136 of the closure member 132 and the face of the piston disc 123 are shallow (typically of the order of 10 5° in the case of the face of the closure member and 10° on the angled face of the front piston disc)

In the advanced disengaged position of Figure 11 A, which corresponds to the detail of Figure 12A, the piston formation 122 contacts but does not interengage with the closure member 132, with the result that the piston assembly 28A is able to reciprocate within the barrel 12A Before administering an injection, the practitioner fits a needle hub assembly 94A onto the spigot 134 and retracts the piston assembly 28A with the sealing lip or wiper ring 145 in close circumferential sealing engagement with the inner wall of the barrel 12A in order to introduce fluid into the barrel chamber 135 with the result that the safety syringe assembly is now in the Figure 11 B position The injection is then administered, so that the piston assembly reverts to the advanced disengaged position of Figure 1 1A

If a second or a series of injections is to be administered to the same patient, the procedure so far described may be repeated, using the same syringe Thereafter, additional pressure is applied by urging the finger disc 130 towards the barrel finger tabs 46A, thereby causing interengagement of the respective complemental channels and lips or ribs 142 and 140 on the respective piston formation 122 and closure member 132 in the manner illustrated in Figure 11 C In order to minimize fluid loss in the interengaging space 125 defined between the channels and ribs 142 and 140 radial fluid venting grooves 127, which are shown in broken outline in Figure 12C, are provided to allow fluid to escape under compression between the spaces 125 and 129 The clipping stroke of the interengagement is also made very short (typically of the order of 0 75mm), which is made possible by the accurate alignment of the piston formation 122 relative to the closure member 132 provided by the interference fit in the barrel chamber 135 itself The closure member 132 and needle hub assembly 94A is then retracted within the barrel chamber 135 to the position illustrated in Figure 1 1 D, with the piston formation 122 being locked in position at the rear end of the barrel, after which the retractor 124 is snapped off at a weakened zone 137 between the retractor 124 and the piston assembly, which is constituted by the front piston disc 123 and the rear piston disc 92A

In Figure 12A, the disengaged advanced position of Figure 1 1A is illustrated in more detail The outermost peripheral rib 138 is shown in firm engagement with the complemental channel or groove 144, the rearmost part of which is bordered by a ridge 148 having an outwardly relieving taper of approximately 12° The rear portion of the inner channel 143 is bounded by the radially outwardly directed nb 140 Similarly, the front part of the channel 142 of the piston formation 122 is bounded by a radially inwardly directed rib 152 The nb 140 is formed with a trailing face 154 which is angled at 20° relative to the main axis of the syringe barrel The nb 152 is similarly formed with a leading face 156 which is angled at 30° relative to the main axis of the barrel It is clear from Figures 12A and 12B that the distance d2 between the inner face of the barrel wall 12A where it is in sealing engagement with the sealing lip 145 and the innermost projecting portion of the rib 152 is significantly greater than the distance d1 defined by the gap between the outermost portion of the rib 140 and the inner face of the wall 12A As a result, forward urging of the piston formation 122 will cause the barrel wall 12A to deform outwardly, with the interaction of the respective faces 154 and 156 simultaneously causing slight inward deformation of the skirt 136 of the closure member

The barrel wall, which is typically formed from a softer grade of polypropylene than the piston formation 122 and closure member 132, consequently deforms progressively outwardly in the manner illustrated at 160A, 160B and 160C in Figures 12B to 12D respectively This has the effect of creating a gradually widening gap 162 between the rib 138 and the channel 144, by distorting the ridge 148 radially outwardly in the direction of arrow 164 It is also clear from Figure 12D that, once the interengaging rib or lip and channel formations of the closure member 132 and piston formation 122 have fully mterengaged, the resultant outward deformation in the wall of the barrel is sufficient to allow the mated piston formation and closure member to be retracted

It is important to note the series of positively reinforcing release and interengagement effects which are achieved during and as a result of the interengagement of the piston formation 122 and the closure member 132 The net effect of inducing tensile hoop stress in the skirt of the piston assembly 122 and compressive hoop stress in the skirt 136 of the closure member 132, in combination with a superimposed and selective compressive hoop stress provided by the barrel wall 12A, is to expand the barrel 12A, contract the skirt 136, relieve the lip or rib 138 of the closure member 132 in the foremost complemental groove 144, and then allow the closure_member 132 to be drawn backwardly through the barrel in enhanced compressive locking interengagement with the piston assembly 122 Release of the closure member 132 backwardly through the barrel 12A is initially further enhanced by the relieving 12° outward taper of the ridge 148

The piston assembly, closure member and needle hub assembly are subsequently retracted to the Figures 11 D and 13 position In this position, it can clearly be seen that a channel 166 is defined between a front nb 168 and a rear rib 170, with the rear rib 170 being sufficiently prominent to prevent both the front and rear piston discs 123 and 92A from being retracted out of the barrel chamber 135 The frangible connection 137 is designed so that it has both tensile and compressive strength, but is weak in a shear vector, which can then be relied on in breaking off the retractor 124

The lower edges of the vanes 126 and 128 are formed with rectangular notches 172 having respective transverse and axial faces 174 and 176 The faces are dimensioned so that, during break off, initial contact adjacent the rearmost rib 170 is made by the axial face 176 and not the transverse face 174 Leverage using the transverse face 174 as the fulcrum will result in an extracting moment tending to pull the piston out of the barrel rather than a sliding/wedging contact on the axial face 176 in which a transverse shear component will predominate at the point of weakness 137

In assembly, it is expected that the piston assembly will be guided and urged through a tubular jig forwardly into the rear opening 26A of the barrel 12A, with the forward end of the jig being flared to locate within and effect a nominal widening of the inner diameter of the rear of the barrel during insertion and the tubular configuration of the jig itself being designed to protect the frangible connection 137 of the piston assembly 28A from inadvertent shear stress

Referring now to Figure 14, an alternative embodiment of a safety syringe assembly is shown in which an O-rιng seal 180 is provided within a channel 182 formed in the closure member 132 to provide an additional seal between the closure member and the finger barrier 20A

In Figure 15, a still further embodiment of a safety syringe assembly is shown in which a closure member 132 is formed with an eccentric spigot 184 and a corresponding eccentric finger barrier 20B and eccentric aperture 18B An arrangement of this type lends itself to the preferred snap-fit embodiment of Figure 10

The syringe assembly of the invention meets the objectives of providing a safety syringe which in use conforms closely to conventional and familiar procedures, and which dispenses with the need for a separate needle shield Further, in the preferred embodiment, the assembly can be optionally produced with a central or eccentric needle spigot to meet differing practitioner needs and preferences Because the syringe assembly uses nominally the same material content as standard disposable syringes, it is relatively economical and cost competitive to produce

Claims

A hypodermic safety syringe assembly comprising

a cylindrical barrel having a front end defining a first aperture and a rear end defining a second aperture,

a closure member shaped to engage the barrel at or adjacent the front end thereof to seal the first aperture, and including a hypodermic needle spigot,

a piston assembly reciprocally movable within the barrel and including a retractor terminating in a piston formation engageable with the closure member to disengage the closure member from the front end of the barrel so that the spigot and a hypodermic needle attached thereto can be withdrawn into a locked safe position within the barrel after use, and

detaining means for detaining the spigot and needle in the locked safe position

A hypodermic safety syringe assembly according to claim 1 in which the closure member includes a barrel engaging formation releasably engageable within a complemental closure member engaging formation at the front end of the barrel, the barrel engaging formation and the complemental engaging formation being arranged in an operating engaged position to prevent pressure exerted on the needle spigot while mounting the needle thereon, or on the needle point in use, from forcing the closure member backwards into the barrel A hypodermic safety syringe assembly according to claim 2 in which the closure member includes a piston coupling formation for engaging a complemental coupling formation on the piston to facilitate disengagement of the barrel engaging and complemental closure member engaging formations from one another by withdrawal of the retractor

A hypodermic safety syringe assembly according to claim 3 in which the piston coupling formation and complemental coupling formation are arranged to at least partly disengage the barrel engaging and complemental closure member engaging formations as the piston coupling and complemental coupling formations are urged into engagement with one another so as to facilitate the disengagement of the closure member from the front end of the barrel for withdrawal, together with the piston formation, into the locked safe position within the barrel

A hypodermic safety syringe assembly according to claim 4 in which the engaging and coupling formations are shaped to allow the engaging and disengaging process to be effected during axial reciprocation of the piston assembly within the barrel

A hypodermic safety syringe assembly according to claim 5 in which the coupling and complemental coupling formations, as they are engaged, present an outer diameter which is materially greater than the inner diameter of the barrel, resulting in outward elastic deformation of the wall of the barrel at the front end thereof, and concomitant outward releasing distortion on the complemental closure member engaging formation defined in the inner wall of the barrel for facilitating the disengagement of the barrel engaging formation therefrom A hypodermic safety syringe assembly according to claim 6 in which compressive hoop stress arising from the outward elastic deformation of the wall of the barrel is arranged to enhance the interengagement of the coupling and complemental coupling formations

A hypodermic safety syringe assembly according to any one of the preceding claims 3 to 7 in which the barrel engaging formation comprises at least one circumferential lip or channel on the closure member acting in sealing co-operative click fit engagement with at least one corresponding respective channel or lip comprising the complemental closure member engaging formation defined in the inner wall of the barrel

A hypodermic safety syringe assembly according to either one of the preceding claims 3 or 4 in which the barrel engaging formation and complemental closure member engaging formation comprise a bayonet-type fitting, with the first aperture being shaped to receive the fitting

A hypodermic safety syringe assembly according to claim 9 in which the piston coupling formation and complemental coupling formation include rotational locking engagement means for allowing the bayonet-type fitting to be rotatably disengaged

A hypodermic safety syringe assembly according to either one of claims 9 or 10 in which the barrel engaging formation includes a safety formation to prevent accidental disengagement of the engaging formation whilst the syringe is in use, the safety formation comprising a plurality of bosses or detents in the outer face of a front wall of the barrel alternating with a plurality of slots radiating outwardly from the outer periphery of the first aperture, the bayonet fitting being designed to engage in a click and/or compression fit with the bosses or detents in the engaged position, and to be rotated out of locking engagement therewith in order to be retracted backwardly through the slots

A hypodermic safety syringe assembly according to claim 11 in which the safety formation is provided with rotation delimiting means comprising at least one stop alternating with the bosses described in the outer face of the front wall of the barrel to prevent over-rotation of the bayonet fitting into the operating, locked position in assembly, and to ensure the precise degree of counter-rotation out of locking engagement after the hypodermic procedure has been completed in order to align lugs of the bayonet fitting with the slots prior to retraction therethrough

A hypodermic safety syringe assembly according to any one of the preceding claims 3 to 12 in which the piston coupling formation comprises a radially outwardly projecting peripheral lip and/or channel, and the complemental coupling formation comprises a complemental radially inwardly projecting peripheral lip and/or channel

A hypodermic safety syringe assembly according to either one of claims 3 or 4 in which the barrel engaging formation and complemental closure member engaging formation comprise a threaded screw-type fitting

A hypodermic safety syringe assembly according to any one of the preceding claims in which the detaining means comprises a circumferential channel defined in the inner wall of the barrel at or adjacent its rear end, and an outer peripheral portion of the piston formation and/or closure member which is designed to be held captive within the circumferential channel to lock the needle in the needle safe position, the channel being defined between front and rear raised detents or ribs projecting radially inwardly into the barrel cylinder

A hypodermic safety syringe assembly according to any one of the preceding claims in which the closure member includes sealing means comprising a sealing disk or flange which acts in sealing engagement with the inner walls of the barrel at or adjacent its front end, with sealing engagement being reinforced by the addition of an upstanding wall or skirt to the flange of the closure member, and sealing engagement extending to the interface between the front face of the disk or flange and the rear face of the front end wall of the barrel

A hypodermic safety syringe assembly according to claim 16 in which the closure member is provided with compression means designed to enhance sealing engagement and locking engagement within the front wall of the barrel, the compression means being provided by the sealing disk being defined as a forwardly tapering cone, the outer periphery of which has a nominally greater diameter than the internal diameter of the barrel, resulting in an outwardly biased disk spring compression which has the effect of holding the outer periphery of the closure member in sealing engagement with the inner circumference of the barrel side wall

A hypodermic safety syringe assembly according to claim 17 in which the angle of the forwardly tapering cone of the sealing disk is shallower than a rear face of the first aperture-defining front end wall of the barrel, resulting in an axially directed disk spring compression for enhancing sealing engagement of the closure member against the barrel front end wall and inner circumference of the barrel side wall

A hypodermic safety syringe assembly according to any one of the preceding claims 16 to 18 in which second sealing means are provided comprising a first O-rιng designed to act in compressive sealing engagement between a front wall of the disk of the closure member and the front end wall of the barrel

A hypodermic safety syringe assembly according to any one of the preceding claims 16 to 19 in which supplemental piston sealing means are provided in the form of a second O-ring seated on a rebated annular land defined within the piston formation

A hypodermic safety syringe assembly according to any one of the preceding claims which includes breakout means for facilitating separation of the retractor from the piston or closure member formation once the closure member and piston have been retracted into the locked needle safe position within the barrel

A hypodermic safety syringe assembly according to claim 21 in which the breakout means includes retractor shear means for ensuring that the retractor shears laterally from the rear face of the piston

A hypodermic safety syringe assembly according to claim 21 in which the breakout means is arranged to facilitate disengagement of the piston coupling formation from the complemental coupling formation, the breakout means being provided by a captive fulcrum defined by a heel of the outer periphery of the piston acting upon any peripheral point on the face of an inlet taper provided at the rear opening of the barrel

A hypodermic safety syringe assembly according to any one of the preceding claims in which the retractor includes limiting means to limit the movement of the piston forwardly into the barrel to a position where it is functionally and accurately able to draw up the fluid to be injected but where it is constrained from accidentally engaging the closure member before the hypodermic procedure is completed

A hypodermic safety syringe assembly according to any one of claims 3 to 13 which includes at least one fluid venting channel for enabling the escape of fluid entrapped between the piston coupling formation and complemental coupling formation during engagement thereof