WO2003051435A1

WO2003051435A1 - Pneumatically retractable safety syringe

Info

Publication number: WO2003051435A1
Application number: PCT/AU2002/001672
Authority: WO
Inventors: John Thomas Mcdonald
Original assignee: John Thomas Mcdonald
Priority date: 2001-12-18
Filing date: 2002-12-11
Publication date: 2003-06-26
Also published as: AUPR960001A0

Abstract

A syringe including a holding means (12) for supporting a needle (11) in an operative position at one end of the syringe; a syringe chamber (5); a plunger (1) operable to discharge the contents of the syringe chamber (5); and a gas generating means (30) located externally of the syringe chamber (5) and in fluid communication (14) with the holding means (12), wherein actuation of the gas generating means (30) moves the holding means (12) and withdraws the needle (11) into the syringe chamber (5) following discharge of the contents of the syringe.

Description

"PNEUMATICALLY RETRACTABLE SAFETY SYRINGE"

TECHNICAL FIELD OF THE INVENTION

The invention relates to syringes. In particular, the invention concerns syringes that may be used in the medical field or by intravenous drug users.

BACKGROUND TO THE INVENTION

In the medical field, there is always a risk of doctors, nurses and other medical staff being injured by pricks from used syringes. Aside from the risk of immediate physical injury there is also the risk of transmission of a disease, bacteria or virus through the contaminated syringe. There is also the similar risk that persons may be pricked by contaminated syringes discarded by drug users.

Accordingly, a number of devices have been developed to ensure that needles from syringes are safely secured to prevent such injury. Some of these devices employ a protective overcap to cover the needle sharp after use of the syringe. Such devices have the disadvantage in that the protective overcap must be manually applied to the needle after use before being effective to protect against injury. Other devices employ a complex mechanical arrangement that retracts the needle into the syringe body after use.

One problem with these previous syringes have been the complexity of design. When the internal diameter of the most commonly used disposable syringe is less than 6mm the cost of the micro engineering required to reliably construct these syringes is prohibitive. For example, the syringe proposed in WO 98/44971 is quite complex such that it would be unlikely to operate at any practical size, much less at less than 6 mm diameter.

The other problem with previous syringes has been safety. With a gas operated syringe there has been the danger of operating gas leaking past a seal and being directly injected into a patient via the needle. For example, the syringe proposed in WO 98/34659 has an option of gas operation (Fig. 5). This syringe relies on an uncontrolled amount of the injecting fluid leaking past a seal to activate a substance and produce a gas to operate the syringe. Considering the variety of liquids that can be injected, the patient may adversely react to the mixture of liquid and gas. In addition, an unknown quantity of the fluid being injected is also lost, making it difficult to determine the amount of fluid received by the patient.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention provides a syringe including: a holding means for supporting a needle in an operative position at one end of the syringe; a syringe chamber; a plunger operable to discharge the contents of the syringe chamber; and a gas generating means located externally of the syringe chamber and in fluid communication with said holding means, wherein actuation of the gas generating means moves the holding means and withdraws the needle into the syringe chamber following discharge of the contents of the syringe.

The activation of the gas generating means by the plunger provides for the safe withdrawal of the needle into the syringe body immediately after use.

Preferably, the holding means and the gas generating means are in fluid communication via a passage extending therebetween. The gas generating means is preferably located in a first chamber adjacent the syringe chamber. A second chamber may be defined by the holding means and the syringe to receive gas from the gas generating means.

In one preferred embodiment, the gas generating means is activated after the syringe has been emptied by depressing a button or further plunger. In another preferred embodiment, the gas generation means is activated by operation of the plunger to empty the syringe. This may be done by the plunger having a lateral extension to depress the button or further plunger in conjunction with operation of the plunger.

Preferably, the gas generating means includes two separated substances which generate a gas upon mixing. It is preferred that one substance is located within the first chamber. The other substance is preferably located on or in the button or further plunger. The two substances are preferably separated by a frangible barrier. The gas generating means preferably has means for rupturing the frangible barrier. The means for rupturing the frangible barrier may be located within the first chamber. In a preferred embodiment the rupturing means is a sharp protrusion or spike. The type of substances chosen to react with each other will vary the gas generation time.

It is preferred that the button or further plunger activates the gas generating means by moving the button or further plunger so that the rupturing means ruptures the frangible barrier for mixing the two substances.

A retaining means is preferably provided for inhibiting movement of the holding means. The retaining means can permit the holding means to move upon activation of the gas generating means. Preferably, the retaining means is formed integrally with the syringe chamber.

In one preferred embodiment, the retaining means is a ridge located on the syringe chamber which releasably engages the holding means. In this form of the invention suitable for use in the medical field, fast acting substances are used to shorten gas generation time so as to retract the needle into the syringe chamber rapidly. In another preferred embodiment suitable for use by drug users, a slow or delayed reaction between the gas generating substances is used so that the injection can be completed before the needle retracts into the syringe chamber. This slow or delayed reaction is preferably done by coating the solid substance, forming the solid substance as a tablet or using slow reacting substances.

BRIEF DESCRIPTION OF THE DRAWING

To assist the understanding of the invention, a preferred embodiment of the invention will now be described, by way of example only, with reference to Figure 1, which is a cross-sectional view of a syringe made in accordance with one preferred embodiment of the invention.

BEST MODE OF CARRYING OUT THE INVENTION

Figure 1 shows a safety syringe in accordance with one preferred embodiment of the invention suitable for use in the medical field. The syringe has a plunger 1, syringe chamber 5 and hollow needle 11. The needle 11 is mounted on a piston 12 for holding the needle 11 to the syringe. The gas generating means 30 is located externally of syringe chamber 5.

The plunger 1 has a seal 4 attached at one end for preventing leaking of fluid between the plunger 1 and syringe chamber 5. Piston 12 has seals 13 which engage retaining ridges 6, 8 that are formed integrally with syringe chamber 5. The piston 12 is spaced from the end of the syringe to define a chamber 25.

Gas generating means 30 is formed integrally with the syringe on its outer exterior. Gas generating means 30 has a push button or plunger 22, chamber 17 and a passage 14 to communicate gas from chamber 17 to chamber 25. Plunger 22 has a cavity for containing a substance 19 for generating a gas in chamber 17. The substance 19 may be a liquid or solid. Generally substance 19 is a liquid. Substance 19 is contained in the cavity by a frangible barrier 18. The frangible barrier 18 is a foil diaphragm bonded to plunger 22.

A second substance 15 is located on the floor of chamber 17 for reacting with substance 19 to generate a gas in chamber 17. The substance 15 can be a solid in powder, granulated or solid form. A sharp protrusion 16, which is moulded into the body 23 of chamber 17, is aligned above foil diaphragm 18 and cavity 26 to puncture the foil diaphragm 18 and release the liquid 19 when the syringe is activated. The sharp protrusion 16 may be a sharp spike or blade.

A port 7 is provided in the side of piston 12 between seals 13. Port 7 is connected to tube 10 through which port 7 directs any gas leaking past seals 13 to exhaust into the atmosphere. Port 7 reduces the risk of gas entering syringe chamber 5 and contaminating or reacting with the fluid to be discharged. A soft seal 9 may be provided between the needle 11 and chamber 25 to stop any gas from leaking around the needle 11.

A seal 20 is provided between plunger 22 and chamber body 23 to prevent gas leaking from chamber 17. Ridge 21 in body 23 prevents plunger 22 from being ejected from chamber body 23 when gas is produced in chamber 17.

The syringe has a barbed ridge 3 in side walls 2 for allowing the syringe to be assembled while preventing the plunger 1 and piston 12 from being ejected or removed from the syringe after activation.

In operation, the syringe when unsealed would have the plunger 1 touching the piston 12 and resting on ridge 8. The syringe would be filled in chamber 5 in the normal manner, either from a patient's vein or bottle. The ridges 6, 8 keeps the piston 12 and needle 11 in place during filling and injection.

After the syringe has emptied the contents of chamber 5 into the vein or sample container, the doctor, nurse or medical staff member pushes sharply on the plunger 22, forcing piston 22 and seal 21 towards spike 16. Spike 16 ruptures foil diaphragm 18 and the liquid 19 is released to mix with the solid activating substance 15. A gas is produced which escapes chamber 17 via passage 14 to chamber 25. The gas generated produces a gas pressure in chamber 25 to force the piston 12, needle 11 and plunger 1 up into the syringe chamber 5 entrapping the needle 11 in the syringe.

A slight offset in the needle mount in piston 12 ensures that even if the plunger 1 was forced back down the syringe, the needle 11 cannot protrude from the syringe body 2. That is, the needle mount in piston 12 is misaligned from the needle hole opening in chamber 25 at the end of the syringe. Thus, needle 11 is also misaligned from the needle opening when needle 11 is retracted into syringe chamber 5, thereby preventing reuse of needle 11 through the needle opening by pushing down on plunger 1.

Many substances could be used to produce the required amount of gas. The type of substance chosen will vary the gas generation time. Fast acting substances are used so that the needle 11 is retracted into syringe chamber 5 quickly, minimising the risk of needle stick injury. The fast acting ingredients can produce enough gas to force the needle piston 12 and plunger 1 up into the syringe chamber 5 as far as the barbed stop 3. In testing it was found that an organic acid (citric acid or dilute hydrochloric acid) mixed with bicarbonate of soda worked very well. The dilute hydrochloric acid plus granulated soda bicarbonate can produce 210 kPa of carbon dioxide in just three seconds. Similarly, 0.6 g of alka seltzer plus water produces 230 kPa in 40 seconds in a 5 cc syringe.

As with a soft drink bottle, once the pressure is built up to a certain level no further gas is released until the pressure is reduced.

The combination of organic acid plus soda bicarbonate has other advantages. First, the result of the reaction is carbon dioxide plus water plus salt. This ensures that by the time the syringe body degrades, the steel needle has corroded and is unusable. Second, the cost of active ingredients is less than one cent to operate a 5 cc syringe. The gas escapes through the needle opening in the syringe, leaving the needle 11 , salt and water in the syringe chamber 5.

In a modification of the preferred embodiment suitable for drug users the plunger 1 has a laterally extending pad 24 (shown in dashed lines in Fig. 1) such that it covers plunger 22. Thus, depressing plunger 1 depresses plunger 22, causing the gas generating means 30 to be activated as the contents of chamber 8 of syringe chamber 5 are discharged.

In the embodiment for drug users, a slow or delayed reaction between the gas generating substances 19 and 15 is used so that the injection could be completed before pressure builds up to force retraction of needle 11. This can be done by coating the solid substance or forming the solid substance as a tablet. The solid substance (coated or in tablet form) slows the reaction as it takes more time to dissolve than a powdered or granulated form. The reaction may also be delayed by using slow reacting substances. For example, a slow reaction can be generated by using kitchen variety citric acid as the liquid and soda bicarbonate in tablet form as the solid substance. This produces the same 210 kPa in around three minutes depending on the strength of the acid.

The actual size of a commonly used 1cc disposable syringe usually has an internal diameter of less than 6 mm. This diameter must be kept to this size to allow the accurate measurement of small volumes. To economically place a retracting mechanism, such as proposed in the prior art, in a disposable syringe of this diameter would be impractical. In contrast, the preferred embodiment of the present invention allows for syringes to be made with the gas generating means 30 which fulfil the above requirements of 6 mm syringes.

It is understood that various modifications, alterations, variations and additions to the construction and arrangement of the embodiment described herein are considered as falling within the ambit and scope of the present invention.

Claims

Claims:

1. A syringe including: a holding means for supporting a needle in an operative position at one end of the syringe; a syringe chamber; a plunger operable to discharge the contents of the syringe chamber; and a gas generating means located externally of the syringe chamber and in fluid communication with said holding means, wherein actuation of the gas generating means moves the holding means and withdraws the needle into the syringe chamber following discharge of the contents of the syringe.

2. A syringe according to claim 1 , wherein said holding means and said gas generating means are in fluid communication via a passage extending therebetween.

3. A syringe according to claim 1 or 2, wherein said gas generating means is located within a first chamber adjacent said syringe chamber.

4. A syringe according to claim 3, wherein a second chamber is defined by the holding means and the syringe to receive gas from the gas generating means.

5. A syringe according to any one of claims 1 to 4, wherein the gas generating means is activated by depressing a button or further plunger.

6. A syringe according to claim 5, wherein the plunger has a lateral extension to depress the button to activate the gas generating means.

7. A syringe according to claim 5, wherein the further plunger is operated in conjunction with operation of the plunger to activate the gas generating means.

8. A syringe according to any one of claims 3 to 7, wherein the gas generating means includes two separated substances which generate a gas upon mixing.

9. A syringe according to claim 8, wherein one substance is located within said first chamber.

10. A syringe according to claim 8 or 9, when dependent on claim 6 or 7, wherein the other substance is located on or in the button or further plunger.

11. A syringe according to any one of claims 8 to 10, wherein the two substances are separated by a frangible barrier.

12. A syringe according to claim 11, wherein the gas generating means has means for rupturing the frangible barrier.

13. A syringe according to claim 12, wherein the means for rupturing the frangible barrier is located within the first chamber.

14. A syringe according to claim 12 or 13, wherein the rupturing means is a sharp protrusion or spike.

15. A syringe according to any one of claims 12 to 14, when dependent on claim 6 or 7, wherein the button or further plunger activates the gas generating means by moving the button or further plunger so that the rupturing means ruptures the frangible barrier for mixing the two substances.

16. A syringe according to any one of claims 8 to 15, wherein the two substances are selectively chosen to vary the gas generation time.

17. A syringe according to claim 16, wherein said one substance is a solid and said other substance is a liquid.

18. A syringe according to claim 17, wherein said solid is bicarbonate soda and said liquid is an organic acid.

19. A syringe according to claim 17 or 18, wherein said bicarbonate soda is granulated or in tablet form.

20. A syringe according to claim 19, wherein said bicarbonate soda in tablet form is coated to delay generation of the gas.

21. A syringe according to any one of claims 1 to 19, wherein a retaining means releasably engages the holding means.

22. A syringe according to claim 19, wherein the retaining means releases the holding means to move under pressure from the gas produced by activation of the gas generating means.

23. A syringe according to claim 20, wherein the retaining means is formed integrally with the syringe chamber.

24. A syringe according to claim 20 or 21 , wherein the retaining means is a ridge.