HK1106463B - Fixed-dose syringe with limited aspiration - Google Patents

Description

Fixed dose syringe with limited aspiration

Background

1. Field of the invention

The present invention relates to medical devices, and more particularly to a fixed dose syringe designed to limit the amount of fluid drawn into the syringe to a predetermined maximum dose.

2. Description of the related Art

Diseases such as HIV and hepatitis continue to spread at alarming rates in less developed countries. The main reason for this spread is the reuse of syringes in mass immunization programs. Mass immunization programs are developed in third world countries to prevent the spread of infectious diseases, but vaccinators often use the same needle for sequential vaccinations to save time and money. For example, at a standard inoculation dose of 0.5ml per person, it is common during these mass immunization programs to fill 3ml of seedlings with a 3cc syringe and inoculate 6 persons with 0.5ml of seedlings each.

The synergy and fear of disease transmission caused by AIDS and hepatitis are due to the repeated use of needles in the mass immunization programs and have been of great interest to many. As a result, the syringe art has proposed several auto-disable syringes (designed as single use syringes) that become inoperable after a predetermined maximum dose has been injected, thereby reducing the risk of transmission of blood-borne pathogens. These devices include, for example, U.S. patent nos. 4,946,441, 4,961,728, 4,973,310, 5,000,737, 5,562,623, and 6,283,941. However, many prior art devices contain numerous complex parts that significantly increase the cost of production. Furthermore, the prior art has not produced a fixed dose syringe for mass production and assembly that is simple, reliable, low cost and easy to use, thereby allowing rapid, easy, precise and uniform completion of injections.

There is therefore a need for a fixed dose syringe that can be economically and reliably produced at high speeds, that fully protects users and others from accidental needle sticks and exposure to blood-borne pathogens, and that can be used more easily, quickly and accurately in mass immunization programs due to its limited maximum available capacity. These and other advantages are provided by the invention described below.

Disclosure of Invention

There is disclosed a fixed dose syringe which offers significant advantages over the prior art. The syringe of the present invention, if used properly, can be rendered unusable after a single injection is completed by means of a retractable needle. This feature of the syringe inhibits needle reuse, particularly in mass immunization programs, and reduces the likelihood of disease transmission in such programs. Furthermore, the syringe is designed for a defined amount of liquid to be withdrawn. The present invention includes a dose limiting structure that makes the syringe easier, faster and more accurate to use, particularly in mass immunization programs. However, it should be understood that the dose limiting advantages of the present invention are also applicable to non-retracting syringes.

The fixed dose syringe of the present invention comprises an elongate hollow syringe housing preferably having a retraction mechanism mounted in the forward end thereof. The retraction mechanism desirably includes a needle hub, a separable retainer and a spring. A retractable needle biased to retract axially rearwardly is secured in the needle mount. A plunger is disposed in the hollow housing, the plunger including a plunger seal in sliding sealing contact with an inner wall of the housing. The plunger also includes a tip shield for applying thumb pressure and a retraction cavity that receives the retracted needle when the retraction mechanism is actuated by forward movement of the plunger after fluid is drained during an injection.

In a preferred embodiment of the invention, the dose limiting structure comprises an inwardly directed projection on the inner wall of the housing, which projection is located behind a certain point corresponding to the desired maximum dose. The dose limiting structure further comprises a stop-ring member disposed on the plunger behind and adjacent to the plunger seal. During aspiration, an approximately nominal fixed dose is withdrawn when the stop-ring member contacts the inward projection, thereby limiting further withdrawal of the plunger. Under normal pressure, the plunger head does not move beyond the protrusion. However, if the user attempts to forcibly pull the plunger head back over the protrusion, the stop-ring member will not move over the protrusion without disengaging or removing the plunger seal, thereby preventing more fluid from being aspirated even if the needle is not retracted and preventing reuse of the syringe.

Drawings

The apparatus of the present invention will be further described and illustrated in conjunction with the following drawings, in which:

FIG. 1 is a front view of the syringe appearance in a pre-use condition;

FIG. 2 is a longitudinal cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 3-3 of FIG. 1, showing the plunger drawn to a correspondingly nominal fixed dose position;

FIG. 4 is a longitudinal cross-sectional view, partially broken away, of FIG. 3 showing the plunger head being withdrawn rearwardly to a point where the plunger seal is disengaged from the plunger and the retainer ring is still on the plunger; and

fig. 5 is a fragmentary detail taken from fig. 3 showing the plunger with the stop-ring member positioned behind the plunger seal adjacent the plunger seal and in contact with the dose limiting projection in the housing wall.

Like reference numerals are used to designate like parts throughout the drawings.

Detailed Description

The structure and operation of the base injector and retraction mechanism used in the present invention is disclosed, for example, in U.S. patent nos. 5,385,551, 5,578,011, 5,632,733, 6,015,438, and 6,090,077, which are hereby incorporated by reference. The present invention also improves upon the syringes disclosed in these patents to control the amount of liquid drawn into the syringe. Although the figures show a 1cc syringe modified to deliver a maximum dose of 0.5ml/cc syringe, it should be understood that the invention is not limited to a particular dose or size syringe. For example, a 3cc syringe may be used to limit the dosage to 0.1 ml/cc.

Referring to fig. 1 and 2, fixed-dose syringe 10 preferably includes a tubular housing 12, a retraction mechanism 14, and a plunger 16. The housing 12 includes a front end 18 and an open rear end 20, and a longitudinally extending wall 22 therebetween. The cover 12 is preferably molded from a substantially transparent polymeric resin such as polypropylene and may be marked on its exterior with a conventional volume scale or only an optimal predetermined dose indicia scale, shown as "0.5 cc/ml" in FIG. 1.

As best seen in fig. 5, the wall 22 preferably has an inwardly directed projection 24 within the syringe housing 12, the projection 24 having chamfered side surfaces 26, 28 and a flat surface 30. The projections 24 desirably reduce the inside diameter of the housing 12 by about 0.007 inches on each side and are annular restraints. Those skilled in the art will appreciate, upon reading this disclosure, that other configurations of the restraint are possible. For example, the restraint may be configured as a circumferentially intermittent projection. The protrusion 24 is desirably formed as an integral part of the wall 22 during the molding process, but the protrusion 24 could be formed in or inserted into the housing 12 in other ways known to those skilled in the art after reading this disclosure. The projection 24 is spaced from the front end 18 of the housing 12 a set distance so that a user can draw a desired predetermined maximum dose.

The preferred chamfer angle for side 26 is between about 15 degrees and about 45 degrees, and more preferably about 30 degrees. The chamfer angle of the side 28 is preferably between about 5 degrees and 10 degrees, and more preferably about 10 degrees. The values of these angles will be discussed below in connection with the operation of the appliance.

As shown in FIGS. 2 and 3, retraction mechanism 14 is mounted within forward end 18 of housing 12 and preferably includes an elongated needle mount 32, a separable retainer 34, a spring 36, and a needle 38. Needle 38 is preferably secured in needle mount 32 by adhesive 40 which extends through forward end portion 18 in the non-retracted position and is covered by a removable protective cover 42. Separable retaining member 34 is preferably an annular structure that detachably frictionally engages needle mount 32 to retain needle 38 against the retraction force applied by compression spring 36.

Referring to fig. 2, 3 and 4, the plunger 16 preferably includes a substantially cylindrical sidewall 46 with a lower end 48 and an upper end 50. The lower end 48 of the plunger 16 includes a plunger head 52 with a reduced diameter portion 54 surrounded by annular shoulders 56, 58. An elastomeric plunger seal 60 and a retainer ring member 62 are mounted on the reduced diameter portion 54 between the first and second shoulders 56, 58. Seal 60 is compressed between first shoulder 56 and retainer ring member 62 in slidable sealing contact with an inner wall 64 of housing 12 and has a groove 66 along an outer wall 68. Stop-ring member 62 is compressed between plunger seal 60 and second shoulder 58 and may be configured as a circular member, a broken circular member, or any other similar configuration. In the preferred embodiment, stop-ring member 62 is formed of a suitable medical grade polymeric material that is less compressible than plunger seal 60. One such preferred polymeric material is an acetal resin marketed under the trademark DELRIN by DuPont. Stop-ring member 62 can also be formed from a suitable medical grade metal such as stainless steel, in which case stop-ring member 62 can be formed as a broken ring if desired so that it can be mounted on annular shoulder 56 during assembly of syringe 10. Stop-ring member 62 may also be formed from a ceramic material.

The inner diameter of stop-ring member 62 is preferably sized to receive plunger head 52 therethrough with a slight clearance sufficient to allow stop-ring member 62 to freely move over plunger head 52 when plunger seal 60 is not mounted on reduced diameter portion 54 of plunger head 52. However, the inner diameter of stop-ring member 62 is not large enough to allow stop-ring member 62 to move past first and second shoulders 56, 58 without deforming sufficiently. Stop-ring member 62 preferably has an outer diameter sized to allow stop-ring member 62 to slide within fluid chamber 44 of housing 12 when plunger 16 is installed in syringe 10 with plunger seal 60, but large enough to restrict movement of ring 62 past protrusion 24 during aspiration, as described below.

Plunger head 52 also has a distal end portion 70 that forms an opening into a retraction cavity 72. Removable plug member 74 is preferably held in the opening of retraction cavity 72 by frictional engagement and cooperates with plunger head 52 to seal the opening of retraction cavity 72. Removable plug member 74 also has a front portion 76 extending beyond end 70. Retraction cavity 72 at least partially retains retracted needle 36, needle hub 32, plug member 74, and spring 36 when retracted.

The upper end 50 of the plunger 16 includes an end cap 78 for the thumb to depress the plunger. The end cap 78 includes a circular end wall with an opening 80 for a closure cap 82. The closure cap 82 has a cap head 84 connected to a longitudinally extending annular skirt 86. The head 84 of the closure 82 fits snugly within the opening 80 effectively sealing the opening 80 so that liquid particles do not escape. The annular skirt 86 frictionally engages the inner wall of the plunger 16. A vent (not shown) may be provided in end cap 78 for venting retraction cavity 72, however, the vent may also be provided on the wall of plunger 16.

The rear end 20 of the housing 12 includes laterally extending lateral wings 88 and a collar 90. Laterally extending wings 88 work in conjunction with end cap 78 to allow one-handed operation of the syringe. Collar 90 extends behind laterally extending shoulders 88 and includes an opening 92 that closely receives the outer periphery of end cap 78 when plunger 16 is compressed to the retracted position. After retraction has occurred, plunger 16 is no longer grasped because end cap 78 is fully inserted into opening 92.

Turning now to the operation of the syringe 10, fig. 1 and 2 show the syringe in a ready-to-fill position. To draw fluid into fluid chamber 44, needle 38 is inserted into a fluid container (e.g., a vial) and head 52 of plunger 16 is pulled toward open rear end 20 of housing 12 until stop-ring member 62 contacts inward projection 24. The user will feel the contact between the stop-ring member 62 and the inward projection 24. At this point the best defined maximum available capacity of the syringe has been achieved. Fig. 3 shows the plunger reaching a position corresponding to the nominal capacity of the syringe 10. As used herein, "nominal capacity" refers to the desired fixed dose as set by the manufacturer. As used herein, the term "defined maximum available volume" of a syringe refers to a volume sufficient to aspirate a desired nominal volume. For example, as will be appreciated by those skilled in the art, when the stop-ring member 62 contacts the projection 24, preferably about 10 to about 20 percent of the liquid in excess of the desired fixed dose is drawn into the syringe 10, thereby allowing the user to remove air bubbles or account for wear if desired.

Referring to fig. 2 and 3, after the predetermined nominal maximum dose has been obtained, needle 38 is then inserted into the patient (not shown) and plunger 16 is pressed toward front end 18 to the end-of-injection position. When the end-of-injection position is reached, where some liquid is still being ejected from the needle, the plunger is forced further down into the housing 12. When this is done, plunger tip 70 contacts and moves separable retaining member 34, reducing the frictional engagement between needle mount 32 and separable retaining member 34. Further depression of plunger 16 also moves plug member 74 away from the opening of retraction cavity 72. When the frictional engagement between needle mount 32 and separable retainer 34 is less than the retraction force of spring 36, spring 36 snaps out causing needle mount 32 to advance upwardly into open retraction cavity 72, while at least withdrawing needle 38 into position in housing 12 and completely plugging end cap 78 into open rear end 20 of housing 12 to prevent reuse.

Before needle 38 is inserted into the patient, the user encounters resistance if the user attempts to move plunger 16 in a rearward direction (labeled 57 in fig. 4) and past a position corresponding to the desired maximum dose. This resistance is caused by stop-ring member 62 colliding with projection 24. To move the plunger 16 beyond the position associated with the desired maximum dose, the user must preferably exert about 20 pounds of force on the plunger 16. This amount of resistance is provided by the preferred dimensions of the retainer ring member 62 and the projection 24 and the materials used for them. For example, while the bevel angle of side 28 is small so that stop-ring member 62 can easily move over projection 24 when plunger 16 is loaded during assembly, a larger bevel angle of side 26 may help achieve a force value that moves stop-ring member 62 over projection 24. Additionally, stop-ring member 62 should be relatively thin but rigid enough to allow plunger seal 60 to disengage plunger head 52 if a user pulls plunger 16 past a position corresponding to a nominal fixed dose of force. If stop-ring member 62 is too thick or stop-ring member 62 is too deformable, excessive pressure may be placed on plunger seal 60 or plunger seal 60 may not resist movement past projection 24, respectively, when a user attempts to pull plunger 16 to the position corresponding to the nominal fixed dose.

As is apparent in fig. 4, further pulling of plunger head 52 beyond projection 24 will not draw more fluid into syringe 10 because stop-ring member 62 will not move beyond projection 24 without disengaging or disengaging plunger seal 60 from plunger head 52. Without plunger seal 60, plunger 16 will no longer create suction to draw more fluid into syringe 10, and the syringe will no longer be operable because plunger seal 60 is no longer properly mounted on plunger head 52 to create suction. Thus, disengagement of plunger seal 60 from plunger 16 prevents reuse of syringe 10 even if the needle is not retracted after use.

After the plunger seal 60 is removed from the plunger 16, the plunger seal 60 is preferably left between the inward projection 24 and the front end 18 in the housing 12. With plunger seal 60 disengaged from plunger head 52, stop-ring member 62 preferably remains on and is free to float about plunger head 52.

One skilled in the art will appreciate based on this disclosure that the protrusion 24 may extend further into the housing such that contact of the plunger seal 60 and the protrusion 24 alerts the user that the plunger 60 has reached the desired maximum movement, and that if the user attempts to move the plunger 16 further rearward, the plunger seal 60 will disengage or disengage from the plunger 16 without the aid of the ring 62.

Other variations and modifications will become apparent to those skilled in the art upon reading the present disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled.

Claims (29)

1. A retractable syringe having a defined maximum usable capacity, comprising:

an elongated hollow syringe housing having a front end, a rear end with an opening, and a longitudinally extending wall between said front and rear ends;

an elongate plunger disposed for reciprocal movement in sliding sealing contact with the longitudinally extending wall of the housing, said plunger having a tubular wall defining a forward end portion having a plunger head with a plunger seal thereon, a rearward end portion with an end cap, and a hollow interior having a retraction cavity;

a retractable needle disposed at the forward end of said housing, said retractable needle preventing reuse of the syringe by retracting into a retraction cavity after injection;

a fluid chamber disposed in the housing between the retractable needle and the plunger head; and

a dose defining structure, the structure comprising: an inwardly directed projection integrally formed on said longitudinally extending wall within said housing, said projection being spaced rearwardly from the forward end of said housing at a location corresponding to a defined maximum available capacity of said syringe; and a stop-ring member disposed on said plunger head behind said plunger seal, said stop-ring member cooperating with said inward projection on said longitudinally extending wall in said housing to limit rearward movement of said plunger in said housing while said plunger seal is retained on said plunger.

2. The retractable syringe of claim 1 wherein the plunger head has a first annular shoulder spaced from a second annular shoulder by a reduced diameter portion therebetween.

3. The retractable syringe of claim 2 wherein the stop-ring member and the plunger seal are disposed on a reduced diameter portion of the plunger head.

4. A retractable syringe as claimed in claim 3 wherein continued rearward movement of said plunger within said housing to a position in which said stop-ring member is spaced rearwardly of said inward projection on said longitudinally extending wall within said housing causes said inward projection to disengage said plunger seal from said plunger.

5. The retractable syringe of claim 4 wherein at the end of aspiration, the stop-ring member contacts the protrusion to alert a user that the defined maximum available volume has been reached.

6. The retractable syringe of claim 4 wherein the inwardly directed projection has a first chamfered side closer to the front end of the housing and a second chamfered side closer to the rear end of the housing.

7. The retractable syringe of claim 6 wherein the first chamfered side has a chamfer angle between 15 degrees and 45 degrees.

8. The retractable syringe of claim 6 wherein the first chamfered side has a chamfer angle of about 30 degrees.

9. The retractable syringe of claim 6 wherein the second chamfered side has a chamfer angle between 5 degrees and 10 degrees.

10. The retractable syringe of claim 6 wherein the second chamfered side has a chamfer angle of about 10 degrees.

11. The retractable syringe of claim 3 wherein the stop-ring member is a polymer.

12. The retractable syringe of claim 3 wherein the stop-ring member is metal.

13. A retractable syringe as claimed in claim 1, characterised in that it has a nominal capacity of 0.5 ml.

14. The retractable syringe of claim 1 wherein said retractable needle is mounted in a retraction mechanism in the forward end of said housing and said needle is extended in its unretracted position.

15. The retractable syringe of claim 14 wherein the forward end of the plunger actuates the retraction mechanism to retract the needle.

16. The retractable syringe of claim 15 wherein said retraction mechanism includes a needle mount, a separable retaining member and a spring, said separable retaining member engaging said needle mount with a retaining force exceeding a retraction force applied to said needle mount by said spring when said spring is compressed.

17. The retractable syringe of claim 16 wherein the forward end portion of said plunger has a tip aligned to abut said separable retaining member and slide said retaining member longitudinally relative to said needle mount, thereby creating said retraction force in excess of said retaining force and causing at least a portion of said retraction mechanism to retract into said retraction cavity to prevent reuse of the syringe.

18. A retractable syringe having a defined maximum usable capacity, comprising:

an elongated hollow syringe housing having a front end, a rear end with an opening, and a longitudinally extending wall between said front and rear ends;

an elongate plunger disposed for reciprocal movement in sliding sealing contact with the interior of said housing, said plunger having a tubular wall defining a forward end portion having a plunger head with first and second annular shoulders separated by a reduced diameter portion therebetween, a rearward end portion having an end cap, and a hollow interior having a retraction cavity;

a plunger seal and a retainer ring member disposed on the reduced diameter portion of the plunger head and compressed between the two shoulders;

a retraction mechanism provided in a front end portion of the housing, the retraction mechanism being configured to be actuated by forward movement of the plunger;

an inwardly directed annular projection circumscribing said longitudinally extending wall within said housing and located at a defined point corresponding to said defined maximum available capacity;

wherein contact between said stop-ring member and said inwardly directed annular projection upon aspiration provides a tactile signal to the user that the plunger has reached a predetermined maximum amount of travel.

19. The retractable syringe of claim 18 wherein the plunger seal is a releasable plunger seal.

20. The retractable syringe of claim 19 wherein said releasable plunger seal disengages said plunger when said plunger is forced past said defined point corresponding to a defined maximum usable capacity.

21. The retractable syringe of claim 18 wherein the inward annular projection has a first chamfered side closer to the front end of the housing and a second chamfered side closer to the rear end of the housing.

22. The retractable syringe of claim 21 wherein the first chamfered side has a chamfer angle between 15 degrees and 45 degrees.

23. The retractable syringe of claim 21 wherein the first chamfered side has a chamfer angle of about 30 degrees.

24. The retractable syringe of claim 21 wherein the second chamfered side has a chamfer angle between 5 degrees and 10 degrees.

25. The retractable syringe of claim 21 wherein the second chamfered side has a chamfer angle of about 10 degrees.

26. The retractable syringe of claim 18 wherein said retraction mechanism includes a needle mount, a separable retaining member and a spring, said separable retaining member engaging said needle mount with a retaining force exceeding a retraction force applied to said needle mount by said spring when said spring is compressed.

27. The retractable syringe of claim 26 wherein the forward end portion of said plunger has a tip aligned to abut said separable retaining member and slide said retaining member longitudinally relative to said needle mount, thereby creating said retraction force in excess of said retaining force and causing at least a portion of said retraction mechanism to retract into said retraction cavity to prevent reuse of the syringe.

28. The retractable syringe of claim 27 wherein said retraction needle, said needle mount and said spring are at least partially retracted into said retraction cavity upon actuation of said retraction mechanism to prevent reuse of the syringe.

29. The retractable syringe of claim 28 wherein the end cap is inserted into an opening at the rear end of the housing when retracted to prevent reuse of the syringe.