GB2246297A

GB2246297A - Non-reusable syringe

Info

Publication number: GB2246297A
Application number: GB9016375A
Authority: GB
Inventors: Colin Townsend-Rose; Kevin Earnshaw; John Earnest Andrews; Frances Drummond
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-07-25
Filing date: 1990-07-25
Publication date: 1992-01-29
Also published as: GB9016375D0

Abstract

In a hypodermic syringe 1 having a syringe barrel 2 with a piston 4 slidably retractable within the barrel 2 by a piston drive means 6 from an initial position in proximity to a needle mounting portion 7 to a retracted position remote therefrom for charging of said syringe 1 with a liquid to be dispensed therefrom, the syringe barrel 2 and piston 4 are provided with first and second interlocking engagement members 12, 20 for locking interengagement in a substantially discharged position of said syringe piston 4, whereby subsequent retraction of the piston 4 for re-use of the syringe 1 is substantially prevented. <IMAGE>

Description

SYRINGE The present invention relates to a non-reusable hypodermic syringe.

Many establishments make use of disposable hypodermic syringes, which are intended to be used once only and then discarded. By using a new sterile syringe for each application the risk of cross-infection is substantially avoided. However it is possible that used, discarded syringes may be cleaned and reused by unscrupulous persons and/or come into the hands of intravenous drug users, for instance, or even be re-used unintentionally with the consequential problem of cross-infection.

It is an object of the present invention to avoid or minimise one or more of-the above disadvantages by providing a hypodermic syringe capable of use only once before the syringe is rendered inoperable.

The present invention provides a hypodermic syringe having a syringe barrel having a first end with a hypodermic needle mounting portion, a syringe piston slidably retractable within said syringe barrel, in use of the syringe, by a piston drive means, from an initial position in proximity to said needle mounting portion to a retracted position remote from said needle mounting portion for charging of said syringe with a liquid to be dispensed therefrom, and then slidably drivable by said piston drive means towards said needle mounting portion to a substantially discharged position for discharge of a said liquid, characterised in that said syringe barrel and piston are provided with respective ones of first and second members of an interlocking engagement means formed and arranged for locking interengagement in said substantially discharged position of said syringe piston, whereby subsequent retraction of the piston for re-use of said syringe is substantially prevented.

Desirably said first and second members of said interlocking engagement means comprise flexible pawl means formed and arranged for fitting into and captive interlocking with an undercut recess, detent, lip or the like.

The first and second members of the interlocking engagement means may be provided at any convenient points on the respective ones of the syringe barrel and the piston but preferably said first member of said interlocking engagement means is provided at or in proximity to an end wall at said first end of said syringe barrel and said second member of said interlocking engagement means is provided on the piston crown, whereby in use of the syringe of the invention the piston becomes locked into the syringe barrel as said piston moves from said retracted position to said substantially discharged position.

Advantageously, the syringe barrel is provided with a piston retaining portion in the form of an overlapping lip on the syringe cylinder formed and arranged to prevent the accidental or otherwise removal of the piston from the syringe cylinder prior to use and thereby also to prevent tampering with and/or damage to the interlocking engagement means.

In order to frustrate any attempts at forcing open the interlocked members of the interlocking engagement means, piston drive means and/or the connection between it and the piston are conveniently provided with one or more frangible portions whereby forced retraction of the piston drive means simply results in disconnection from the locked piston. Additionally or alternatively the mounting of the second member of the interlocking engagement means in the barrel wall includes one or more frangible portions in the wall so that application of a piston retracting force to the locked piston results in breaking open of the barrel wall.

In other respects the hypodermic syringe of the invention is of generally known construction with the barrel and piston drive means made from plastics such as polystyrene or polypropylene or the like which can be readily moulded. The piston may be formed of similar materials and provided with suitable seal means e.g. 'O' rings or the like for sealing interengagement with the barrel side walls, or more conveniently, is made substantially wholly of a sealing material such as natural or synthetic rubber. Conveniently the members of the interlocking engagement means are formed integrally, e.g. by moulding, with respective ones of the piston and barrel.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings which: Fig. 1 is a sectional side elevation of a first syringe of the invention; Fig. 2 is an enlarged view of part of the syringe of Fig. 1; Fig. 3 is a sectional side view generally similar to Fig. 2 of a second embodiment of the invention with another type of interlocking engagement means; Figs. 4a-c are detail views of another embodiment similar to that of Figs. 1 and 2 showing interlocking of the first and second member of the interlocking engagement means in use of the syringe;; Figs. 5a-c are detail side or sectional side views showing some preferred methods of attachment of the piston drive member to the syring piston, and Fig. 6 is a detail sectional side view of a further form of interlocking engagement means.

Reference is first made to Fig. 1 which shows a non-reusable hypodermic syringe of the invention, generally indicated by reference number 1. The syringe 1 comprises a syringe barrel 2 containing a syringe piston 4, is provided with piston drive means in the form of a plunger 6. An interlocking interengagement means 8 comprises first members in the form of a plurality of flexible pawls 20 engagable with a second member in the form of an undercut recess 12 provided on the barrel 2 and the piston 4 respectively. A hypodermic needle 14 is attached 7 at a first end 18 of the cylinder 2 remote from a piston retaining collar 16 provided at the other end 17 of the barrel 2. The piston retainer 16 is arranged so as to prevent the piston 4 being removed prior to use and the interengagement means 8 being tampered with so as to render them inoperable.

Fig. 2 shows on an enlarged scale the interlocking engagement means 8 of the syringe of Fig. 1. The first end 18 of the barrel 2 is provided with a plurality of flexible pawls 20 integrally formed with the end wall 22 of the barrel 2. A closely fitting piston 4 is provided around its circumference with seals 24 to engage the barrel side wall 26, and its crown portion 27, with an undercut recess 12 formed and arranged for captively engaging said flexible pawls 20. When the piston 4 is driven to its substantially discharged position with the piston crown portion 27 more or less engaging the end wall 22 of the barrel 2, so as to discharge any liquid (not shown) contained in the syringe barrel 2, first and second members 20, 12 of the engagement means 8 lock together thereby rendering the syringe 1 useless for further use.

Fig. 2 also shows the connection of the piston plunger 6 to the piston 4. In normal use of the syringe 1 during the charging and discharge strokes - a thin neck portion 30 of the plunger 6 adjacent the piston 4 is sufficiently strong to more the piston 4 back and forth. On the discharge stroke when the piston recess 12 engages and locks with the pawls 20 on the end wall 22 of the syringe barrel 2, any attempt to withdraw the piston 4 will cause the neck 30 of the plunger 6 to break rendering the syringe 1 useless.

Fig. 3 shows another embodiment of the invention with a second type of locking interengagement means 8 and like parts corresponding to those in the embodiments in Figs.

1 and 2 are indicated by like reference numbers.

The piston crown portion 27 is provided with a number of flexible pawls 20 positioned around the periphery thereof. The syringe barrel 2 has proximally the first end 18 of the barrel 2 on the barrel side wall 26, a radially inwardly projecting flange 32 formed and arranged captively to engage the flexible pawls 20 of the piston 4 after the pawls 20 have returned to their normal position from radially inwardly deflected positions during traversal of the flange 32, thereby securing the piston 4 in its substantially fully discharged position in the syringe barrel 2.

Figs. 4a-4c show how the pawls 20 of the embodiments in Figs. 1 and 2 engage and lock with the undercut recess 12 in the piston crown. In Fig. 4a the rim 12a of the piston recess 12 engages the pawls 20, the angled contact surfaces thereof causing the pawls 20 to deflect inwardly as shown in Fig. 4b. As the piston 4 reache its substantially fully discharged position proximal the first end 18 of said barrel 2 the pawls 20 have fully entered the recess 12 and spring open as shown in Fig.

4c, captively engaging the rim 12a of the recess 12.

Attempting to pull back the plunger 6 against the locking action of the engagement means 8 causes the connection 30 between the piston 4 and plunger 6 to break.

Fig. 5a shows a piston 4 and plunger 6 formed and arranged for screw threaded engagement. After the piston 4 is lock; into the syringe cylinder (not shown) the plunger 6 may-be unscrewed, thereby again rendering the syringe 1 inoperable. Further, the thread 34 of the plunger 6 and the piston 4 is formed and arranged to strip if the plunger 6 is pulled back when the piston 4 is locked in position with the cylinder 2 thereby releasing the piston 4 from the plunger 6.

Fig. 5b uses a 'T'-slot connection 36 between the piston 4 and the plunger 6. The plunger 6 may be removed after use and the interengagement of the piston 4 and the cylinder 2 thereof and should the syringe be the subject of attempted reuse, pulling the plunger 6 will cause the lugs 38 on the 'T' to break off and/or the retaining rim portion 40 of the slot to break again rendering the syringe inoperable.

Another means of connection between the piston 4 and the syringe 6 is via a strong rigid connection as seen in Fig. 5c. In this arrangement part of the first end wall 18 of the syringe barrel 2 and the pawls 20 are formed and arranged to break away from the cylinder 2 and remain attached to the piston 4 again rendering the syringe 1 inoperable.

It will of course be appreciated that various modifications may be made to the above described embodiments without departing from the scope of the present invention.

Thus for example by using a suitably shaped interlocking engagement means member on the barrel side wall, of generally similar nature to that of Fig.3, the other member on the piston may simply be constituted by the piston head itself, or a radially outwardly projecting seal which may be in the form of an integrally formed flange or a separately formed 'O'-ring or the like. In yet another form of the invention the interlocking engagement means could be in the form of radially outwardly or inwardly extending recess means in the barrel side wall or the piston side wall respectively, and radially inwardly or outwardly projecting, respectively pawl means or other resiliently biased projection means mounted in the other of piston side wall and barrel side wall as generally indicated in Fig.

Claims

1. A hypodermic syringe having a syringe barrel having a first end with a hypodermic needle mounting portion, a syringe piston slidably retractable within said syringe barrel, in use of the syringe, by a piston drive means, from an initialrposition in proximity to said needle mounting portion to a retracted position remote from said needle mounting portion for charging of said syringe with a liquid to be dispensed therefrom, and then slidably drivable by said piston drive means towards said needle mounting portion to a substantially discharged position for discharge of a said liquid, characterised in that said syringe barrel and piston are provided with respective ones of first and second members of an interlocking engagement means formed and arranged for locking interengagement in said substantially discharged position of said syringe piston, whereby subsequent retraction of the piston for re-use of said syringe is substantially prevented.

2. A syringe as claimed in claim 1 wherein the first and second members of said interlocking engagement means comprise flexible pawl means formed and arranged for fitting into and captive interlocking with an undercut recess, detent, or lip.

3. A syringe as claimed in claim 1 or claim 2 wherein the first and second members of the interlocking engagement means are disposed on respective ones of the crown of the piston, and the internal face of an end wall of the barrel in proximity to the hypodermic needle mounting portion.

4. A syringe as claimed in claim 1 or claim 2 wherein the first and second members of the interlocking engagement means are disposed on respective ones of the crown of the piston and the barrel side wall in proximity to said first end of the barrel.

5. A syringe as claimed in claim 1 or claim 2 wherein one of the first and second members of the interlocking engagement means comprises radially inwardly or radially outwardly extending recess means in the barrel side wall or the piston side wall respectively, and radially inwardly or outwardly projecting, respectively, pawl means or other resiliently biased projection means mounted in the other of the piston side wall and barrel side wall.

6. A syringe as claimed in any one of claims 1 to 5 wherein at least one of the piston drive means, the piston drive means connection to the piston, and a barrel wall means portion mounting a said interlocking engagement means member has a frangible portion so that subjecting the piston drive means to an excessive piston retracting force results in breakage of said frangible portion thereby preventing piston retraction. Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NPS IRH Funher copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPJ 7HZ. Pnnted by Multiplex techniques ltd. St Man Cray. i