WO1990008565A1

WO1990008565A1 - Disposable syringe

Info

Publication number: WO1990008565A1
Application number: PCT/GB1990/000124
Authority: WO
Inventors: Richard Kiteley Power; John David Yair
Original assignee: R & R Inventions Limited
Priority date: 1989-02-01
Filing date: 1990-01-29
Publication date: 1990-08-09

Abstract

A medical syringe for once-only use has the piston (26) connected to the rod (10) by lugs (24) trapped in the piston. At the end of an initial factory assembly operation, formation (32) in the barrel (30) shears the lugs from the rod and they then remain effective in a first filling stroke by extending as abutments between a shoulder behind head (22) and the opposite end of the internal chamber in the piston. In a first syringe contents ejection stroke, the piston rod moves relative to the piston so that disc (12) contacts the piston to push it along the barrel, and the conical formation (20) on the rod forces the lugs out to the limits of the piston chamber radially, so that they become wedged in that chamber out of position for abutment with the rod. Suction refilling is prevented because the rod draws through the piston, and back-filling is prevented because the rod is displaced out of the piston.

Description

DISPOSABLE SYRINGE

This invention relates to medical syringes of the kind intended to be used once only, so as to prevent cross-infection for example amongst drug abusers. Many designs have been suggested, but hitherto, so far as me are aware, all have suffered from one or other of a number of disadvantages.

Thus, for a once-only syringe, a low cost is particularly important and many satisfactory designs are ruled out for economic reasons.

Some designs need to be factory-filled with the vaccine or like, which is inconvenient if successive patients need different doses especially of different vaccines.

The problem tuith other designs may be due to the increasing sophistication of those who seek re-use, or to a need for the first user to adopt some special procedure if the once-only intention is to be effective.

Thus for example in the design of Figures 5-8 of EP 300694 the disabling (to prevent second use) takes place when a conventional and second suction filling operation occurs. But this can be circumvented by the user back¬ filling the syringe by inserting the needle into a flexible ampoule and squeezing the ampoule so as to fill the barrel via the needle. Whilst the first user may be able to prevent this by deliberately commencing a second conventional suction filling operation so as to go through the Figures 7 and B positions which would - only then - prevent back-filling being possible, this is a special procedure which the busy practitioner may omit. If the syringe is discarded immediately after the first injection stroke, the unintended second use by back¬ filling can be carried out to return the parts to the Figure 5 position without going through the Figures 7 and 8 positions, and moreover this might be possible an infinite number of times. The objection of the present invention is to solve these problems and provide a syringe which is completely disabled in a manner preventing re-use after a mere single cycle.

According to the invention considered broadly, a medical syringe comprises a barrel having a needle at one end (or being adapted to be connected to a needle at one end), a tubular piston, a piston rod arranged to extend through the piston and having a shoulder to abut one end of the piston for displacing it in a barrel-contents ejection stroke when the piston is in one axial position relative to the piston rod, the opposite end of the piston being held to the rod when the piston is in a second axially displaced position on said rod by one or more lugs engaged between an abutment on the rod and a formation of the piston, characterised in that said lugs are separate entities at least after initial assembly and before the syringe is first filled, said lugs being retained in engagement during filling by the said formation and the arrangement being such that the lugs cease to be retained and become disengaged when the piston and rod move relative to one another from said second axial position.

This arrangement can be suction filled in a first cycle of operations whilst the lugs are in the engaged position, but as soon as the rod travel direction is reversed, e.g. the ejection stroke begins, the lugs can be expected to fall out of position or be displaced out of position and cannot effectively be re-inserted subsequently. This means that suction filling for a second cycle of operations is impossible. Back-filling for the second cycle may be prevented even if the syringe is discarded at the end of the ejection stroke because the lugs may also be used (in the first cycle) to hold the piston and abutment in one sealed condition, and the subsequent disengagement of the lugs permits relative movement so that the seal is disabled. Back-filling then results in flow through the piston which is of no avail in preparing the syringe for use. Initial assembly may be achieved by locating the rod, piston and lugs in an assembled condition, and displacing them in required positions along the length of the barrel by an air blast.

Two embodiments of the invention are illustrated in the accompanying drawing in which:-

Figures 1 - 8 show successive stages in the life of a once-only syringe.

Figure 9 shows a modification.

Turning now to Figs. 1-8 of the drawings, the syringe has a cruciform section piston rod terminating in a disc 12. A rod extension has a first circular cross sectional part 18, a second generally conical part 20 and a cylindrical head 22. A pair of lugs 24 extend for example at right angles to the axis of the rod in original manufacture, and all of these mentioned parts are moulded unitarily as a single piece from a relatively brittle material for example polystyrene.

The piston 26 is of a soft rubber or like and is tubular with an enlarged diameter chamber between its ends which are constituted by cylindrical axially aligned passages of a common diameter.

The piston is assembled to the rod by folding the lugs backwardly so as to lie closely adjacent to the conical part which is of a suitably reduced dimension to permit this as well as having a certain minimum dimension smaller than that of the head 22 for the purpose explained hereinafter. In the so-folded condition generally similar to that seen in Figure 1 , the rod extension is pushed through the bore of the piston for example by deforming the soft resilient material of the piston into an ellipse having its major axis coincident with a plane diametric of the piston rod and containing the lugs. After the lugs have passed through the one small end of the piston and entered the chamber the deformation of the piston can be relaxed and the resilience will return the piston to a circular shape. It will be noted that the lugs are of the same length as the chamber so that they are accommodated wholly therein as a close fit in the chamber. The so-assembled piston and rod are pushed into the barrel as generally shown in Figure 1. The movement is continued through the Figure 2 and Figure 3 positions. The Figure 3 position may be the one in which the syringe leaves the factory ready for use.

The barrel 30 is an appropriate diameter for the piston and has an attached needle 35 or means for attaching the same. The barrel also has an anvil formation 32 on its interior bottom end and this projects upwardly about a recess 34 shaped and dimensioned to accept the head 22 fairly closely. The rim of that recess, which is an operative anvil face may be square or acutely angled. The adjacent face of the piston s of complementary shape to the end of the barrel. The anvil will contact the root of each lug, that is to say a thin portion immediately adjacent to the head, at a point where the plastic is already stressed by the folding operation.

In going from the Figure 1 position to the Figure 2 position the piston bottoms in the barrel and the head starts to enter the recess, this movement terminating when the lugs come to rest on the anvil. Continued movement of the piston rod in the same direction as the Figure 3 position leaves the lugs resting on the anvil and takes the head into the recess, that is to say it separates the lugs from the head by a shearing operation. The lugs become trapped in the Figure 3 position being gripped between resilient material of the piston and their contact with the rod extension and this wedge-locks the parts together in that position. The resilience of the piston material forces the lugs towards one another so as to engage them with the reduced diameter portion of the rod extension immediately behind the head._.

The syringe may now be charged with fluid in the usual way. Figure 4 shows the beginning of the operation, when the resistance to movement of the piston causes it to lag as the piston rod is retracted until the lugs have moved with the piston rod, because of their abutment behind the head, and have come into engagement with the top end of the chamber in the piston. The Figure 4 position of piston and rod represents the relative positions of these parts during the whole of the filling cycle.

Ejection of syringe contents occurs when the piston is again moved towards the needle (Fig.5) which takes the disc 12 into abutment with the piston. This causes the cylindrical first part of the rod extension 18 to act as a cam to separate the lugs and push them firmly against the chamber wall. The dimensional match between the lugs and chamber and their cooperating shapes causes the lugs to be trapped in this final position relative to the piston.

The ejection stroke is completed in Figure 6 when the head again enters the recess and it will be noted that there is very little space internally of the piston for undischarged fluid, making this syringe design particularly economical in use of vaccine and the like.

Any attempt to re-use the syringe by pulling the piston rod leads to the Figures 7 and 8 positions. That is the piston rod pulls through the piston and separates therefrom.

It will be appreciated that sealing against leakage in syringe filling is provided by the fit between the completely cylindrical portion of the first part 18 of the piston rod and the bore of the piston above the chamber, and in ejection by the same formations plus the disc/piston end contact.

If any attempt is made to re-use by inserting the needle into an ampoule and squeezing the ampoule so as to force fluid into the barrel and displace the piston along the barrel, this is frustrated because the fluid can flow through the piston and along grove 36 which, in the Fig B position extends through the upper part of the piston. Hence the piston does not move. Alternatively the applied pressure may simply force the rod through the piston, that is leaving the piston in the Figure 7 position and displacing the rod to the Figure 8 position, to like effect.

In the modification of Figure 9, the lugs 24 are trapped between the head 22 at the end of the piston rod 18 and an internal shoulder in the piston. The same shearing effect occurs on completion of the factory assembly steps by contact with anvil 32, and the lugs remain wedged in the illustrated position during the first filling cycle, to fall-out during the first ejection stroke. The difference between this and Figures 1 - 8 is that after the ejection stroke commences the lugs are not trapped in the piston, but become loose in the barrel 30. The effect, in terms of the syringe being unusable is the same whether re-filling is by suction or back-filling.

Claims

CLA IMS

1. A medical syringe comprising a barrel having a needle at one (or being adapted to be connected to a needle at one end), a tubular piston, a piston rod • arranged to extend through the piston and having a shoulder to abut one end of the piston for displacing it in a barrel-contents ejection stroke when the piston is in one axial position relative to the piston rod, the opposite end of the piston being held to the rod when the piston is in a second axially displaced position on said rod by one or more lugs engaged between an abutment on the rod and a formation of the piston, characterised in that said lugs are separate entities at least after initial assembly and before the syringe is first filled, said lugs being retained in engagement during filling by the said formation and the arrangement being such that the lugs cease to be retained and become disengaged when the piston and rod move relative to one another from said second axial position.

2. A syringe as claimed in Claim 1 characterised in that said lugs and rod are moulded from a brittle plastics material and in that the interior needle end of the barrel has an anvil formation arranged to contact and shear the lugs at the end of the initial assembly movement.

3. A syringe as claimed in Claim 1 characterised in that the piston is sealed to the rod to prevent flow of fluid therethrough by two alternate seals, the first of which is between said one end of the piston and said shoulder, and the second of which is between an internal zone of the tubular piston and a complementary zone on the rod arranged so that the said zones are adjacent in the assembled and ready to fill position but spaced apart in the ejection position.

4. A syringe as claimed in Claim 1 characterised in that the lugs are made as separate components assembled in position.

5. A syringe as claimed in any of Claims 1 - 4 wherein the lugs are located wholly within the piston and the latter -is provided with an internal chamber to receive and locate the lugs, one end of said chamber providing said formation on the piston, and said rod is provided

- with a f usto-conical portion to force the lugs radially outwardly to wedge in said chamber out of said engagement when the piston and rod are moved relative to one another in a syringe contents ejection stroke.

6. A syringe as claimed in any of claims 1 - 4 wherein the lugs extend outwardly of the piston between said formation and said abutment when engaged as aforesaid, and when disengaged become free for total disengagement from said piston.

7. A syringe substantially as described with reference to Figures 1 - 8 of the accompanying drawing.

8. A syringe substantially as described with reference to Figure 9 of the accompanying drawing.