WO1995003845A1

WO1995003845A1 - Safety hypodermic syringe

Info

Publication number: WO1995003845A1
Application number: PCT/AU1994/000436
Authority: WO
Inventors: Antony James Lake
Original assignee: Antony James Lake
Priority date: 1993-07-30
Filing date: 1994-08-01
Publication date: 1995-02-09

Abstract

The invention provides a safety hypodermic syringe (10) including: an elongate barrel (11) defining a chamber (13) for holding injectable medicament or the like between a front end (14) thereof and a rear end (15) thereof; a plunger (12) having an elongate stem (22) slidable longitudinally in said barrel chamber (13) at its rear end; a needle-carrying needle assembly (34) at the front end of the barrel chamber (13) where it may be locked in forward position or unlocked by the operator; the plunger (12) being movable forwardly with the needle assembly (34) locked in said forward position to inject medicament from the chamber (13) through a fluid passage (20) through the needle assembly (34) and through the needle (16), the parts being so made and arranged that, following a forward injection action of the plunger (12) with the needle asembly (34) locked in said forward position (1) the needle assembly (34) can be rendered unlocked by the operator, (2) the fluid passage (20) through the needle assembly and needle to the barrel chamber (13) can be rendered sealed by the operator, and (3) when said needle assembly (34) has been rendered unlocked and said fluid passage (20) has been rendered sealed, subsequent withdrawal of the plunger (12) causes the needle assembly (34) to be withdrawn by suction into the barrel chamber (13) as the plunger is withdrawn rearwardly.

Description

"SAFETY HYPODERMIC SYRINGE" TECHNICAL FIELD OF THE INVENTION THIS INVENTION relates to a safety hypodermic syringe, and more particularly to a syringe designed to be used once and then rendered safe to prevent the possibility of so-called "needle stick" injuries in the medical environment.

BACKGROUND ART

In recent times, particularly during the last six years, with AIDS being so widely discussed and publicised, many inventions have been devised so that a single use syringe will incorporate means for retraction of the used hypodermic needle into either the barrel or the plunger of the syringe which can then be disposed of in a safe disposition. Two such inventions of Australian origin were the subject of International Patent Applications Nos. PCT/AU90/00426 and PCT/AU92/00178, both of which contain extensive discussions on specific prior art proposals ■ and contain the results of their International Search Reports identifying eight "documents considered to be relevant" to varying degrees in the first case and five in the other. The prior syringes embody a wide range of different constructions and complexities. Having studied many of the prior proposals for a syringe which will have the characteristics of being usable once only, able to be rendered safe against needle stick accidents, and able to be disposed of with maximum ease and safety, I have come to consider that there remains a need for a novel approach to the matter of achieving such characteristics, it being my view that most of the prior proposals are very expensive to manufacture, generally using integral, purpose-designed needles, while some are at least a little complicated to use, while in many cases there would seem to be some serious practical limitations which could detract from efficiency and cause lack of confidence among the people concerned. It follows from the aforegoing that my invention has been devised with the principal object in mind of providing a novel form of safety syringe which will prove to have advantages over current constructions in achieving the required characteristics as previously mentioned, namely, being able to be used once only in simple and effective manner; being able to be rendered safe by simple and efficient retraction of the needle into the "body" of the syringe; and being able to be disposed of with maximum ease and safety. The invention has a number of other objects bound up with specific refinements in preferred embodiments which I have in mind for achieving the aforementioned principal objects, as will be hereinafter apparent.

DISCLOSURE OF THE INVENTION With the foregoing and other objects in view, my invention resides broadly, according to one aspect, in a safety hypodermic syringe including: an elongate barrel defining a chamber for holding injectable medicament or the like between a front end thereof and a rear end thereof; a plunger having an elongate stem slidable longitudinally in said barrel chamber at its rear end; a needle-carrying needle assembly at the front end of the barrel chamber where it may be locked in forward position or unlocked by the operator; the plunger being movable forwardly with the needle assembly locked in said forward position to inject medicament from the chamber through a fluid passage through the needle assembly and through the needle, the parts being so made and arranged that, following a forward injection action of the plunger with the needle assembly locked in said forward position

(1) the needle assembly can be rendered unlocked by the operator,

(2) the fluid passage through the needle assembly and needle to the barrel chamber can be rendered sealed by the operator, and

(3) when said needle assembly has been rendered unlocked and said fluid passage has been rendered sealed, subsequent withdrawal of the plunger causes the needle assembly to be withdrawn by suction into the barrel chamber as the plunger is withdrawn rearwardly.

According to one preferred embodiment, I provide a syringe of the above type, wherein the plunger has at its front end a plunger piston sealably slidable in the barrel chamber, and wherein the needle assembly is slidable longitudinally in the barrel forwardly of the plunger and has a needle carrier piston sealably slidable in the front end of the chamber, the needle carrier including a foremost portion to receive the needle and retain same in use, the needle carrier and needle thereon being so dimensioned as to be withdrawable rearwardly as an assembly through a front end opening to the barrel.

In this embodiment, suitably the plunger piston and needle carrier piston are mounted separately of ' one another and are unconnected except that the carrier piston is subject to suction or pressure effects in the space therebetween upon reciprocation of the plunger, the barrel chamber being of uniform circular cross-section throughout its length and the plunger piston and needle carrier piston being of equal outside diameters.

Suitably, the needle assembly is adapted to be held and locked in forward operative position by means including releasable clip means normally preventing withdrawal of the needle assembly but adapted to be released by the operator so that the needle assembly will be rendered unlocked. As later described, it is preferred that the front end of the barrel chamber be adapted to accommodate an external cap or internal plug in fixed relationship thereto for sealing purposes after the needle assembly and needle thereof have been withdrawn by suction into the barrel chamber.

Either the needle passage can be rendered sealed so that the needle assembly will be drawn by the plunger or the passage through the needle carrier can be sealed. In an embodiment of the first type, the fluid passage to be rendered sealed by the operator is the needle passage which is of such diameter that a suitable clogging material, such as viscous petroleum jelly, may be drawn therein to a limited but clogging content upon initial withdrawal of the plunger, the fluid passage through the needle then being effectively rendered sealed so that suction effects are exerted on the needle assembly as the plunger is withdrawn further rearwardly. In the alternative construction, the fluid passage to be rendered sealed by the operator may comprise a flow passage through the needle assembly rearwardly of the needle and between the needle and a connecting opening to the chamber, said flow passage having an intermediate enlarged opening accommodating a valve member adapted to seat sealably on a valve seat about the rear end of the enlarged opening or to be supported non-sealably at the front end of the enlarged opening, whereby the fluid passage through the needle assembly can be rendered sealed by the operator when the latter causes the syringe to be disposed with its needle assembly to the chamber uppermost, or the fluid passage will be rendered and maintained unsealed when the syringe is disposed with the needle assembly lower than the plunger. In that instance, preferably the valve member is a ball valve such as a stainless steel ball of small diameter to minimise restriction of the passage past the valve member in the enlarged opening, the end of the latter remote from the chamber having centering flutes therearound to support the ball valve in non-sealing relationship when the ball contacts same gravitationally or when held there under pressure during an injection action of the plunger. It is preferred that, in each embodiment of the invention, the plunger stem will have a weakened neck portion enabling it to be snapped off when it has reached a withdrawn position. Thus, the rear end of the barrel may be open and unobstructed to facilitate breaking of the plunger stem, in which case an unthinking operator might withdraw the plunger completely before taking the opportunity of utilising the facility for breaking off the stem at the weakened neck portion. However, this will do no harm since the partial vacuum will be broken and thus the plunger will separate from the needle carrier and still leave the latter and its retained needle within the barrel.

For extra safety at the other or front end of the barrel when the needle has been withdrawn therein, I prefer to provide, as aforementioned, a snap-action closure cap to be pushed on and lock over the front opening (or an effective plug for the opening) so that there would be no way that accidental access could be achieved to either end of the barrel in any manner that could cause contact to be made with the retained needle. The appropriately closed barrel, containing the needle in the safest possible arrangement, can then be disposed of together with the broken-off stem according to established procedures. However, the cap could be replaced by any type of plug or equivalent sealing means, as mentioned above.

The barrel may suitably be a simple inexpensive cylinder so that the contained plunger piston and needle carrier piston are of equal diameters. However, the front end of the barrel can conveniently have a peripheral inner flange which acts to retain the needle carrier and its piston from passing forwardly of the front extremity through the opening defined by the inner flange. However, the front end of the needle carrier extends through and forwardly of that opening and is dimensioned to receive the needle fitment thereon, the total needle and carrier assembly being able to pass through the opening upon removal of the aforementioned retaining clip means.

The clip means may suitably be a plastic or equivalent member, of resilient or bendable material and of plate-like form, adapted to be clipped or snapped into a groove or recess at a retaining position where its laterally projecting edges will extend beyond and thus engage the front end of the barrel, so that the needle carrier assembly cannot pass through the opening defined by the flange. However, after the needle has been used and the plunger is foremost, the operator can grasp and forcibly pull away the retaining clip so that the needle carrier becomes free of protrusions and is unlocked so that it can enter the barrel when the plunger is withdrawn rearwardly provided that the needle passage or needle assembly passage has been closed off to create a partial vacuum. Other features of the invention will be apparent from the following descriptions of suitable preferred forms of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, wherein:- Fig. 1 shows in part-sectional elevation a typical prior art syringe as currently employed;

Figs. 2A, 2B, 2C and 2D show diagrammatically the prior art syringe of Fig. 1 at its various stages progressively in normal use; Fig. 3 is a view similar to that of Fig. 1 showing one illustrative embodiment of safety syringe according to my invention;

Fig. 4 is an enlarged sectional view in respect of the components in Detail A of Fig. 3; Figs. 5A, 5B, 5C, 5D, 5E and 5F show in greater detail and in separated relationships certain components of my syringe of Figs. 3 and 4, namely the barrel, the plunger, the needle carrier, the needle, the cap, and the needle carrier clip, respectively;

Figs. 6A, 6B, 6C, 6D, 6E, 6F and 6G show diagrammatically the manner of using my illustrative embodiment as shown in Figs. 3, 4 and 5 hereof;

Fig. 7 shows in enlarged sectional detail view another embodiment of my syringe invention having a modified form of needle carrier incorporating a ball valve in the liquid or fluid passage therethrough, the syringe being held to face downwards so that the valve is in inoperative position;

Fig. 8 is similar to Fig. 7 but with the syringe held to face upwards so that the valve is in operative position, and Figs. 9A, 9B, 9C and 9D show the manner of using the modified embodiment of the invention shown in Figs. 7 and 8.

Referring initially to the prior art illustrations of Fig. 1 and Figs. 2 to 2D, this known type of syringe 110 is of very basic construction and has a cylindrical barrel 111 defining a chamber 113 between its front end 114 and its rear end 115. The contents of the chamber 113 are expressed through a passage in a needle 116 communicating through the hollow interior of a mounting adaptor 117 having a rear socket end 118 to wedge over a tapered needle carrier protrusion 119 which has a front opening 120 to the chamber 113. Thus, the contents of the chamber 113 are expressed through the opening 120 and the needle 116 by a plunger 112 which has a front plunger piston 121 connected by a stem 122 of cruciform cross- section to a rearmost thumb plate 123 to be pulled or pushed by the operator. Four flat thin plastic plates 124 make up the stem 122, it being convenient to make as many components as possible from plastics materials for economical reasons. Any desired design details may be used in the plunger piston 121 provided that its exterior makes close sealably slidable contact within the chamber 113, suitably being of rubber or the like with at least two peripheral ridges 125 and 126 spaced by a groove 127. With the plunger piston 121 suitably moulded of rubber, it may contain a retaining recess 128 for the connector head 129 of the stem 122 of the plunger 112 passed through a restricted opening 130 to the recess 128.

Fig. 2A shows diagrammatically the prior art syringe 110 as supplied ready for use, with the plunger 112 inserted and the needle 116 fitted ready for use. When the needle 116 is inserted in injectable material and the plunger 112 is withdrawn, the chamber 113 will receive the injectable material 131 through the needle 116 and the front opening 120 so that the syringe 110 becomes "charged ready for use" as in Fig. 2B. The operator then injects the patient so that the plunger 112 is foremost and the components resume the initial positions of Fig. 2A except that the needle 116 and other passages to the chamber including the front opening 120 will contain residual injectable materials as shown in the "following injection" view of Fig. 2C. Since the used syringe 110 must now be disposed of and rendered non-usable, it is necessary to remove the needle 116 and deposit it in a "sharps container", the other components also being disposed of, namely the plunger 112 and the barrel 111. As will be apparent from Fig. 2D, there will be a high possibility of accidents occurring, and this has led others and myself towards devising suitable safety syringes. A first form of my invention has been illustrated in Figs. 3 and 4, Figs. 5A to 5F, and Figs. 6A to 6G, using one embodiment which may or may not prove to be a preferred form and which is given by way of example only, following as closely as possible the corresponding features of the prior art syringe of Figs. 1 and 2A to 2D. Thus the drawings of my embodiment employ numerals 10 through 31 for features corresponding to those marked 110 through 131, respectively, in the prior art syringe.

According to this embodiment of my invention, the safety hypodermic syringe 10 has an elongate barrel 11 of cylindrical form defining a cylindrical chamber 13 for holding injectable material 31 between a front end 14 and a rear end 15. The plunger 12 is longitudinally slidable in the barrel 11 and has at its front end a plunger piston 21 sealably slidable in the chamber 13, the plunger 12 having a stem 22 behind the plunger piston 21 to permit digital reciprocation using a thumb plate 23. It will be seen that the plunger 12, piston 21 and stem 22 are the same as in the prior art except that the four thin _'plastic plates 24 making up the stem 22 are each cut away at recesses 32 for weakening purposes. As before, the piston 21 has peripheral ridges 25 and 26 with a groove 27 therebetween, and it has an internal recess 28 for the connector head 29 of the stem, the restricted opening 30 defining shoulders 33 to retain said head 29 when the stem 22 is fitted and the plunger is installed.

A feature of my invention is that I provide a needle carrier 34 mounted so as to be longitudinally slidable in the barrel 11 forwardly of the plunger 12 and having a needle carrier piston 35 sealably slidable in the front end 14 of the chamber 13, the needle carrier 34 including a front carrier protrusion and core portion 19 to receive a needle 16 and retain it in use. In this regard, I can use a needle 16 as in the known embodiment, with a mounting adaptor 17, and a rear socket end 18 to fit over and wedge suitably on the needle carrier core portion 19. In my invention, the front opening 20 to the chamber is located axially through the carrier 34 which is slidable within the barrel 11, whereas in the prior form the front opening 120 was through the front end of the barrel 111 itself.

It will be noted that the needle carrier 34 and needle 16 thereon are so dimensioned laterally of the main axis that they could be withdrawn rearwardly as an assembly through the front end of the chamber where there is a front opening 36 to the barrel 11. However, the needle carrier 34 is normally held in forward operative position by bearing against the rear face of an internal flange 37 to limit the forward position and by having a clip member 38 which normally prevents withdrawal rearwardly of the carrier 34 and needle 16 through the opening 36, but which is a manually releasable clip adapted to be rendered inoperative after the needle has been used.

A feature of the invention is that the plunger piston 21 and needle carrier piston 35 are mounted separately of one another and are unconnected except that the carrier piston 35 is subject to suction or pressure effects in the space 39 between the two pistons upon reciprocation of the plunger 12. A further feature is that the parts are so made and arranged that the plunger piston 21 can be withdrawn to "suck" the needle carrier 34 along with it under the conditions where (1) the plunger 12 has been moved by the operator to complete a forward stroke and thus is lying foremost, (2) the manually releasable clip means 38 has then been released by the operator, and (3) the operator has caused the passage through the needle 16 and hence the needle carrier to be sealed by a clogging material, or by some other clogging agent, or by a clogging object or member as instigated by the operator. In the drawings, there is shown a blob 51 of petroleum jelly or other viscous liquid sucked into the needle so that a small content will seal the needle passage and adhere to the outside also. Under these conditions, withdrawal of the plunger 12 rearwardly will cause the needle carrier piston 35 to follow the plunger piston 21 under the partial vacuum conditions existing in the space 39 therebetween so that the assembly of needle carrier 34 and needle 16 will be withdrawn rearwardly into the chamber 13 within the barrel 11.

With regard to the recesses 32 in the stem 22 as previously described, these are provided in the stem 22 adjacent the rear of the plunger piston 21 to afford a weakened neck portion 40 at which the stem 22 may be snapped off by manual pressure in a lateral lever action when the weakened neck portion 40 reaches the rear end 15 of the barrel 11 on completion of withdrawal of the plunger 12. The rear end 15 is open and unobstructed to facilitate breaking off, and it follows that an unthinking operator might withdraw the plunger 12 completely before taking the opportunity to break it off at the weakened portion 40. However, this will do no harm since the partial vacuum will be broken and the needle carrier 34 will cease to follow the plunger, the needle carrier and needle still being retained in the barrel.

For extra safety at the other or front end 14 of the barrel 11 after the needle 16 has been withdrawn therein, I provide a snap-action closure cap 41 as shown in Fig. 5E to be pushed on and lock over the open front end at the opening 36 defined by the flange 37. The cap 41 has annular teeth 42 around its inner mouth 43 and which engage in ratchet-like manner with external annular teeth 44 moulded in the front end of the barrel 11 as shown. This will encapsulate the needle completely for the desired purposes, with all components being able to be disposed of with maximum safety. Any suitable internal plug could be used instead.

The aforementioned clip means 38 could take any desired form, but as shown in Fig. 5F, it may suitably be a plastic sheet-like member 45 adapted to be clipped or snapped into a groove or recess 46 (see Fig. 4) in the needle carrier 34, there being laterally protruding edge portions 47 and 48 of the clip member 45 to engage the front end of the barrel to prevent the needle carrier assembly from sliding back into the chamber. However, after the needle has been used and the plunger is foremost, the operator can grasp and forcibly pull away the retaining clip 45 so that the shoulder portions 49 about the opening 50 are pulled out of the groove 46, ridding the needle carrier 34 of protrusions and clip means whereby the carrier 34 can enter the barrel 11 when the plunger 12 is withdrawn rearwardly provided that the needle passage and needle carrier fluid passage have been closed off to create a partial vacuum in the space 39. The steps involved in using my syringe as aforedescribed will be clear from Figs. 6A to 6G which afford useful comparison with the usage steps for the prior syringe as shown in Figs. 2A to 2D. It will be seen that Figs. 6A, 6B and 6C correspond to Figs. 2A, 2B and 2C except that the needle 16 is mounted on the front core portion 19 of the needle carrier 34 which is fitted with a needle carrier piston 35, sliding movement thereof being prevented by the attachment of the clip means 38 in the form of a sheet-like plate 45 having edge protrusions. Instead of removing the needle as in Fig. 2D, my syringe is then used as in Fig. 6D to cause clogging of the needle 16 with viscous petroleum jelly, the plunger being withdrawn slightly for that purpose after the clip means have been removed and the needle tip has been inserted into the petroleum jelly.

As apparent from Fig. 6E, with the needle blocked, continued withdrawal of the plunger causes retraction of the needle carrier and needle into the syringe barrel, whereafter as shown in Fig. 6F, with the plunger fully withdrawn, it may be broken off at the weakened neck portion and then disposed of. Finally as in Fig. 6G, the cap 41 is placed over the end of the barrel and pushed firmly to snap into locked position so that the needle is totally encapsulated and the residual assembly can be disposed of. Should the plunger be accidentally fully withdrawn from the barrel, the partial vacuum between the plunger piston and the needle carrier piston is broken so that the needle and carrier remain safely inside the barrel. Thus, the cap can be placed over the end of the barrel as before.

While the syringe as illustrated and described to this point will thus be found very effective in achieving the objects for which the invention has been devised, this has been given by way of example only and can be altered as to design in numerous respects. Also, in certain cases I understand it is medical practice to charge a syringe by drawing material from a rubber topped bottle using a large bore needle and then exchanging this needle for a smaller bore needle before injecting the patient, and in such cases my system would allow the first needle to be placed inside the barrel very carefully from the needle end before locking the cap in place to encapsulate both needles after use. It would also seem that the principles of the syringe could be incorporated in blood-taking syringes, it being thus understood that the invention is not limited solely to syringes for the injecting of drugs but also embraces blood-collecting syringes. In certain cases, the stem breakage feature may be optional as an addition to the other features described, and of course any manner of closing off the needle opening may be employed, with the word "clogging" embracing all means for sealing off the opening.

So far as the clogging material is concerned, instead of using a volume of petroleum jelly or the like from an "external jar", the blocking material could be in an accessible cavity in the syringe cap or in some part of the syringe itself. Then again the needle carrier 34 could incorporate a chamber containing a viscous blocking medium, the chamber being able to be ruptured by external pressure applied by the operator after the syringe has been used, as for example by squeezing a rupturable membrane between the thumb and forefinger, so that the blocking medium enters and clogs the passage through the needle carrier.

Yet another way of sealing the fluid passage to the chamber is shown in the further embodiment of the invention illustrated in Figs. 7, 8 and 9A to 9D, the modified syringe 10a therein having substantially the same features as in Fig. 3, corresponding parts having the same numerals suffixed by the letter "a", but sealing of the opening 20. through the needle carrier body 34a is effected by a stainless steel valve ball 52 disposed in an enlarged opening 53 having a valve seat 54 at the end adjacent the chamber 13a and centering flutes 55 at the other end, the flutes 55 ensuring that fluid flow is at all times unimpeded to and from the needle 16a, the syringe 10a being held to face downwards as in Fig. 7 when charging the chamber 13a (see Fig. 9A) or when injecting a patient (see Fig. 9B).

However, when the syringe 10a is held facing upwards as in Fig. 8, discharge is possible but the valve ball 52 gravitationally seats on its valve seat 54. This means that fluids (including air) can be expelled from the syringe 10a. but the passage 20a will be sealed against the inflow of fluids when the plunger 12a is withdrawn. Thus the syringe 10a is shown in Fig. 9C facing upwards after being full discharged, the carrier clip (shown at 38a in Figs. 9A and 9B) then being removed and discarded. Withdrawal of the plunger 12a then causes the valve ball 52 to block the ingress of air or other fluids, and as shown in Fig. 9D, further withdrawal of the plunger retracts the carrier 34a and needle 16a into the syringe barrel 11-a, and the procedures can be continued to achieve the same results as are illustrated by Figs. 6E to 6G in respect of the first embodiment, the principal difference being that the operator causes the needle carrier passage to be sealed by a valve instead of causing the needle passage to be sealed by a viscous blocking material.

Many other modifications of constructional detail and design may be made as will be readily apparent to persons skilled in the art and without departing from the broad scope and ambit of the invention, as defined by the appended claims.

Claims

1. A safety hypodermic syringe including: an elongate barrel defining a chamber for holding injectable medicament or the like between a front end thereof and a rear end thereof; a plunger having an elongate stem slidable longitudinally in said barrel chamber at its rear end; a needle-carrying needle assembly at the front end of the barrel chamber where it may be locked in forward position or unlocked by the operator; the plunger being movable forwardly with the needle assembly locked in said forward position to inject medicament from the chamber through a fluid passage through the needle assembly and through the needle, the parts being so made and arranged that, following a forward injection action of the plunger with the needle assembly locked in said forward position

(1) the needle assembly can be rendered unlocked by the operator,

2. A safety hypodermic syringe according to Claim

1, wherein the plunger has at its front end a plunger piston sealably slidable in the barrel chamber, and wherein the needle assembly is slidable longitudinally in the barrel forwardly of the plunger and has a needle carrier piston sealably slidable in the front end of the chamber, the needle carrier including a foremost portion to receive the needle and retain same in use, the needle carrier and needle thereon being so dimensioned as to be withdrawable rearwardly as an assembly through a front end opening to the barrel.

3. A safety hypodermic syringe according to Claim

2, wherein the plunger piston and needle carrier piston are mounted separately of one another and are unconnected except that the carrier piston is subject to suction or pressure effects in the space therebetween upon reciprocation of the plunger, the barrel chamber being of uniform circular cross-section throughout its length and the plunger piston and needle carrier piston being of equal outside diameters.

4. A safety hypodermic syringe according to any one of the preceding claims, wherein the needle assembly is adapted to be held and locked in forward operative position by means including releasable clip means normally preventing withdrawal of the needle assembly but adapted to be released by the operator so that the needle assembly will be rendered unlocked.

5. A safety hypodermic syringe according to Claim 4, wherein the clip means is of plate-like form and so shaped as to be adapted to be clipped or snapped into a groove or recess at a retaining position on the needle assembly where its laterally projecting edges will extend beyond and thus engage the front of the barrel, the needle carrier being thereby prevented from passing through the opening at the front end of the barrel until the needle assembly is unlocked by the operator upon removal of the clip means.

6. A safety hypodermic syringe according to any one of the preceding claims, wherein the plunger stem has a weakened neck portion enabling the plunger stem to be snapped off when it has reached a withdrawn position.

7. A safety hypodermic syringe according to any one of the preceding claims, wherein the front end of the barrel chamber is adapted to accommodate an external cap or internal plug in fixed relationship thereto for sealing purposes after the needle assembly and needle thereof have been withdrawn by suction into the barrel chamber.

8. A safety hypodermic syringe according to any one of the preceding claims, wherein the fluid passage to be rendered sealed by the operator is the needle passage which is of such diameter that a suitable ^*clogging material, such as viscous petroleum jelly, may be drawn therein to a limited but clogging content upon initial withdrawal of the plunger, the fluid passage through the needle then being effectively rendered sealed so that suction effects are exerted on the needle assembly as the plunger is withdrawn further rearwardly.

9. A safety hypodermic syringe according to any one of Claims 1 to 7, wherein the fluid passage to be rendered sealed by the operator comprises a flow passage through the needle assembly rearwardly of the needle and between the needle and a connecting opening to the chamber, said flow passage having an intermediate enlarged opening accommodating a valve member adapted to seat sealably on a valve seat about the rear end of the enlarged opening or to be supported non-sealably at the front end of the enlarged opening, whereby the fluid passage through the needle assembly can be rendered sealed by the operator when the latter causes the syringe to be disposed with its needle assembly uppermost, or the fluid passage will be rendered and maintained unsealed when the syringe is disposed with the needle assembly lower than the plunger.

10. A safety hypodermic syringe according to Claim 9, wherein the valve member is a ball valve such as a stainless steel ball of small diameter to minimise restriction of the passage past the valve member in the enlarged opening, the end of the latter remote from the chamber having centering flutes therearound to support the ball valve in non-sealing relationship when the ball contacts same gravitationally or when held there under pressure during an injection action of the plunger.

11. A safety hypodermic syringe including: an elongate barrel defining a chamber for holding injectable medicament or the like between a front end thereof and a rear end thereof; a plunger slidable longitudinally in said barrel and having at its front end a plunger piston sealably slidable in said chamber, the plunger having stem means behind said plunger piston to permit digital reciprocation thereof, and a needle carrier slidable longitudinally in said barrel forwardly of said plunger and having a needle carrier piston sealably slidable in the front end of said chamber, the needle carrier including a foremost portion to receive a needle and retain same in use; and wherein

(a) said needle carrier and needle thereon are so dimensioned as to be withdrawable rearwardly as an assembly through a front end opening to the barrel;

(b) said needle carrier is adapted to be held in forward operative position by means including manually releasable clip means normally preventing withdrawal of the needle carrier and needle assembly through said front end opening of the barrel;

(c) said plunger piston and needle carrier piston are mounted separately of one another and are unconnected except that the carrier piston is subject to suction or pressure effects in the space therebetween upon reciprocation of the plunger;

(d) the parts are so made and arranged that after (i) the plunger has been moved by the operator to complete a forward stroke and occupy its foremost position, (ii) the manually releasable clip means has then been released by the operator, and (iii) the operator has then caused the fluid flow passage through the needle and needle carrier to be sealed, withdrawal of the plunger rearwardly will cause the needle carrier piston to follow the plunger piston under the partial vacuum conditions therebetween so that the assembly of needle carrier and needle will be withdrawn rearwardly into the chamber within the barrel, and

(e) the plunger stem adjacent the rear of the plunger piston has a weakened neck portion at which the plunger stem may be snapped off by manual pressure in a lateral lever action when the neck portion reaches the rear end of the barrel on completion of withdrawal of the plunger.