HK1077237B - One-use retracting syringe with positive needle retention - Google Patents

Description

Disposable retractable syringe with reliably retractable needle after single use

Technical Field

1. Field of the invention

The present invention relates to medical devices for fluids and in particular to syringes having retractable needles which cannot be reused after an injection has been made.

2. Background of the prior art

In recent years, the technology of single use syringes has developed rapidly as the treatment of aids and other infectious diseases has made it difficult to protect the person providing the treatment services from accidental needle sticks with the used injection needles for the patients with the infectious disease. Used syringes with extended needle tips present a risk to medical personnel, health system employees, and others in the medical waste disposal chain. The prior art has disclosed a number of syringes and other medical devices with retractable needles, which are typically retracted into the syringe barrel or into a needle-receiving chamber in the barrel. U.S. patent 5,385,551, which is owned by each inventor of the present invention; 5,578,011, respectively; 5,632,733, respectively; 6,015,438; and 6,090,077, which are incorporated herein by reference, disclose the most advanced retractable syringes. The syringes disclosed in each of the above patents allow for automatic retraction of the needle by continuing to push on the plunger handle at the end of the injection, but also provide for a single manual retraction of the needle which prevents the healthcare worker from being exposed to a contaminated needle. The plunger-driven automatic retraction of these devices occurs prior to the needle being withdrawn from the patient. These retractable syringes are suitable for mass production at low cost and have high reliability and repeatability of action. They are suitable for automated production and assembly of parts for a variety of syringes of different barrel sizes, needle sizes, and different uses.

While the above-described syringes and other retractable syringes have eliminated or greatly reduced the problem of accidental needle sticks, certain aspects have indicated the need for a single use syringe that cannot be reused under any circumstances. Most, if not all, retractable syringes require the user to take some action to cause retraction of the needle after administration of the injection, and if the user does not retract the needle after a single use, then that retractable syringe has the potential to be reused. For non-retractable syringes, a solution to this problem has been proposed by mechanically locking the plunger handle after the first use of the syringe by various means, none of which have a retractable needle. Therefore, even if the syringe cannot be reused, there is a potential risk of an exposed needle stick as the plunger cannot be withdrawn a second time. Examples of syringes that can lock the plunger handle but which cannot be retracted include: free et al, U.S. patent 5,000,737 entitled Single Use Disposable Syringe; allison et al U.S. patent 5,205,825, it is entitled "Insertable Element for presenting Reuse of Plastic syringes"; U.S. Pat. No. 4,973,310 to Kosinski, its title is "Single-Use syringee"; U.S. Pat. No. 4,961,728 to Kosinski, its title is "Single Use Syring bathing Resistant syringes (Single Use syringes with structure Features to prevent Misuse)"; U.S. patent 5,531,691 to Shonfeld et al, entitled "Single Use Syring Assembly"; U.S. patent No. 5,562,623, entitled "Single-Use System assembling spring clip Lock and Plunger" the contents of these patents are hereby incorporated by reference.

The single use syringe described above cannot be reused after an injection is made, but its contaminated needle is still extended and must be covered or removed or otherwise disposed of to render the syringe safe and harmless. Accordingly, there is a need for an improved single use syringe in which the needle is retractable into the syringe barrel after use and which cannot be reused regardless of whether the needle is retracted.

Summary of The Invention

According to one aspect of the present invention there is provided a single use retractable syringe having a handle operated needle retention chamber which cannot be removed from the syringe barrel, the syringe comprising: an elongated hollow syringe barrel having a forward end and an open rearward end; a retractable needle mounted in a retracted configuration within the forward end of said syringe barrel and biased to retract rearwardly; movable parts including a handle connected to the needle retention chamber which is sealingly and slidably mounted for movement within the syringe barrel by means of the handle projecting from the open rear end of the barrel, the front end of the needle retention chamber having an opening which is sealed but openable to receive a retracted needle; retraction of the needle into the needle retention chamber is triggered by forward movement of the needle retention chamber against the retraction mechanism in response to movement of the handle after completion of an injection; (ii) a positive lock structure disposed within said syringe barrel capable of restricting rearward movement of said needle retention chamber and preventing it from being pulled out of said syringe barrel after a single use of said syringe; so that the retracted needle is safely stored in the needle retention chamber in the syringe barrel after a single use and is not easily removed by pushing or pulling on the handle.

According to another aspect of the present invention there is provided a single use syringe having a syringe barrel in which the syringe barrel has an injection needle extending from its forward end for injecting fluid and a movable handle extending from its rearward end and mounted for limited reciprocation therein, said movable handle including a forward end portion having a piston in sliding sealing contact with the inner surface of said barrel, wherein said piston establishes a variable injection fluid chamber within said barrel; in a further aspect, the invention provides a movable handle including a rear portion having a thumb cap for applying thumb thrust to said handle and a positive locking structure disposed in said barrel for limiting a second rearward movement of said handle after a first rearward movement of said handle to draw injection fluid into said variable fluid chamber and a first forward movement of said handle to inject fluid, the improvement comprising: said needle is a retractable needle mounted in a retracted configuration within the forward end of said barrel, the needle extending from its unretracted position and being biased to retract in a retracted position; the front end part of the handle is configured to trigger the retraction structure to act so as to retract the injection needle, and the front end part is provided with a needle retention chamber for accommodating the retracted injection needle and the piston positioned behind the variable fluid chamber; the needle retention chamber has a front end and a diametrically enlarged portion; said positive locking structure is a stop positioned to limit rearward movement of said needle retention chamber to within the confines of said barrel by contact with said enlarged portion of said needle retention chamber; if an attempt is made to pull the needle retention chamber past the stop by pulling on the rear portion of the handle, the rear portion of the handle disengages from the front portion; and wherein the syringe cannot be reused even if the injection needle is not retracted after one use.

According to another aspect of the present invention, there is provided a retractable syringe for single use having an operating handle which cannot be pulled out of a syringe barrel after a single use of the syringe, the syringe comprising: an elongated hollow syringe barrel having a forward end and an open rearward end; a retractable needle mounted in a retracted configuration within the forward end of said syringe barrel and biased in a rearward retraction direction; a plunger, comprising: a movable handle within said syringe barrel, said handle having: a front end portion having a piston in sliding sealing contact with the inner surface of the barrel; a rear end portion having a thumb cap at a rearmost end thereof for applying a pushing force to the handle by a thumb; and, a needle retention chamber within the forward end portion of the handle for receiving a retractable needle; (ii) a positive locking structure disposed within said syringe barrel capable of restricting rearward movement of said handle and preventing it from being pulled out of said syringe barrel after a single use of said syringe; so that the needle after use is safely stored in the needle storage chamber in the syringe barrel and can not be pushed or pulled to move any more.

According to another aspect of the present invention, there is provided a single use syringe comprising: an elongated hollow syringe barrel having a forward end and an open rearward end; an injection needle mounted to a forward end portion of said barrel; a two-piece movable handle mounted for reciprocal movement within said barrel, said handle having a forward head portion and a handle portion detachably connected to said head portion, said forward head portion having a piston in sliding sealing contact with the inner surface of said barrel; a lock mounted in said barrel to permit said head portion to move through said lock when said head portion and said handle portion are inserted into said open rear end and a forward force is applied to said handle portion; after having passed the lock forward, the handle portion may be separated from the head portion when the handle portion is pulled back, the separation occurring by virtue of the head portion releasing the handle portion under the locking force of the lock rather than breaking of the separating element.

Thus, the single use retractable syringe of the present invention has a handle operated needle retention chamber that is not likely to be pulled out of the syringe barrel. The retractable structure prevents the exposed needle from being potentially dangerous after an injection is made. The positive locking structure of the present invention ensures that the syringe is truly a single use syringe and cannot be reused. In various embodiments, the movable parts including the handle and the needle retention chamber are prevented from moving rearward and are received within the syringe barrel after a rearward movement of the handle to fill the syringe and a forward movement to expel fluid from the syringe. The present invention eliminates the risk that even if a retractable syringe is retracted after a single use, it may still be reused because the user may have intentionally or inadvertently left the retraction mechanism untouched to leave the needle exposed for a second use. This does not occur with the syringe of the present invention because the positive locking feature of the present invention prevents the needle retention chamber from being removed again by preventing it from being removed. The needle retention chamber is secured within the barrel regardless of whether the retraction mechanism is activated or the needle is retracted. This means that the advantages of the invention can also be applied to non-retractable syringes where the injection needle is fixed at the front end of the barrel. This should be considered as a further aspect of the invention. In the application to non-retractable syringes, the present invention limits or prevents the handle (plunger) from being pulled back within the barrel in the same working principle. The syringe is of course not refillable since the handle cannot be pulled back a second time.

An elongated syringe barrel having a forward end and an open rearward end preferably has a retractable needle mounted in a retracted configuration within the forward end of the syringe barrel and biased in a rearward retraction direction. Movable parts including a handle and a needle retention chamber associated therewith perform the function of a conventional syringe plunger within the barrel. The forward end portion of the needle retention chamber has a piston mounted in sliding sealing contact with the inside surface of the barrel, and the movable member is movable by a handle extending out of the open rearward end of the barrel. At the rearmost end of the handle is a thumb cap for applying a thumb pushing force to the handle. The forward end of the needle retention chamber has an openable sealed opening for allowing the retracted needle to enter the needle retention chamber when further forward movement of the plunger triggers the retraction mechanism after injection of fluid into the patient. After the injection is completed, retraction of the needle into the needle retention chamber is triggered by forward movement of the needle retention chamber under the force of the handle against the retraction mechanism.

A positive locking structure disposed within the syringe barrel limits rearward movement of the needle retention chamber and prevents it from being pulled out of the syringe barrel after a single use of the syringe. The positive locking structure is configured so as not to interfere with one rearward movement and one forward movement of the movable member to the fullest extent, but to limit subsequent rearward movement of the needle retention chamber while maintaining the needle retention chamber within the syringe barrel. In a first embodiment, the positive locking structure is fixed in a fixed position within the barrel. The positive locking feature includes a reduced diameter portion of the inner diameter of the barrel forming a first stop and the needle retention chamber has an enlarged diameter portion forming a second stop which is urged forward past the first stop by pushing on the handle but which prevents rearward movement of the pull handle. The first embodiment also has a handle portion that is detachably connected to the needle retention chamber so that they separate with a separation force that is less than the force required to force the second stop back past the first stop. Preferably, the handle is released from the needle retention chamber by release of the separate parts rather than by their breaking.

The first embodiment also preferably includes a catch on the forward end portion that can be forced forward past the first stop by pushing on the handle before the second stop moves past the first stop. As long as the second stop does not move forward past the first stop, the handle can be pulled back to fill the syringe. This shoulder on the forward end portion of the needle retention chamber limits the amount of rearward movement of the movable member to establish the maximum designed fill volume of the syringe. This catch shoulder can be in contact with the first stop. However, the second stop at the rear of the needle retention chamber or some intermediate position during injection by pushing on the plunger moves past the first stop to provide the previously described limiting feature which allows the two part plunger to be separated by pulling the handle rearwardly. Once the handle is pushed forward so that all stops exceed the first stop in the barrel, the syringe can be emptied and the retraction mechanism will be triggered by continued forward movement of the handle.

A second embodiment of the present invention has an elongated syringe barrel preferably having a retractable needle mounted in a retracted configuration within the forward end of the syringe barrel and biased in a rearward retraction direction. A movable plunger within the syringe barrel has a forward end portion with a piston in sliding sealing contact with the inside surface of the barrel and a needle retention chamber behind the piston for receiving the retractable needle, and a rearward end portion with a thumb cap at the rearward end for applying a biasing force to the handle. In this second embodiment, positive locking structure is also provided in the syringe barrel which limits rearward movement of the handle after a single use of the syringe and prevents it from being pulled out of the syringe barrel.

The handle is provided with a positive locking structure which is movable in only one direction, from a first position near the rear end of the handle to a second position closer to the front end of the handle. The positive locking feature is configured to positively engage the syringe barrel after it has been moved forward of the first position to limit rearward movement of the needle retention chamber. The needle retention chamber is preferably located just prior to the second position of the positive locking feature. The handle preferably has a plurality of stepped teeth and the positive locking structure is preferably a clip having a tab bent inwardly relative to the stepped teeth, the tab allowing forward movement of the clip on the handle while preventing rearward movement of the clip. The clip has at least one rearwardly and outwardly bent tine which engages the syringe barrel to prevent rearward movement of the handle. The tines slide along the surface of the handle as they are rearward, but if rearward movement is desired, the tines dig into the inner surface of the barrel and are stopped. Preferably, the band surrounds a portion of the stepped teeth of the handle rear end portion, but not all of them, slightly more than half of the circumference in the circumferential direction.

A third embodiment of the present invention includes all of the features of the syringes of the first and second embodiments, except for the optional locking feature. In a third embodiment, positive locking structure which limits rearward movement of the handle is provided in the syringe barrel in a fixed position relative to the barrel. More specifically, the positive locking structure is disposed inside the open rear end of the barrel. This optional locking structure mounted in a fixed position within the open rearward end of the barrel relative to the barrel is preferably a resilient clip having one or more forwardly and inwardly bent tines that are spaced from the handle by a sliding collar mounted over the handle during initial rearward movement of the handle to draw fluid into the barrel, which allows a rearward movement of the handle from an initial forward position within the barrel without the resilient tines engaging the handle. When the plunger is pushed forward, the sliding collar moves forward out of contact with the resilient tines to allow the resilient tines to engage the handle and thereby prevent rearward movement of the handle. In a third embodiment, as in the second embodiment, the rear end portion of the handle has a plurality of stepped teeth over which the sliding collar is fitted. The sliding collar has a conical inner surface which allows the plunger handle to move rearwardly relative to the collar, but the collar has a catch which catches on the edge of one of the stepped teeth, which catch causes the collar to move away from the resilient clip as the handle is moved forwardly. The resilient clip allows the stepped teeth of the handle to slide through it as the handle is pushed forward, but if the handle is moved rearward, the resilient tines of the clip dig into the handle and prevent any rearward movement of the handle. After the handle is pulled back to the maximum extent, a stop surface at the back end of the needle retention chamber will contact the end surface of the collar to prevent the handle from being pulled back further. The ferrule is captured within the barrel.

Although the present invention is most effective in combination with a retractable needle mounted in a retraction structure in the forward end of the barrel, the present invention is primarily concerned with the problem of single use of the syringe, and therefore the present invention is applicable not only to syringes having a retractable needle, but also to syringes having a fixed needle.

Brief description of the drawings

FIG. 1 is a longitudinal cross-sectional view of a first embodiment of the syringe of the present invention having a needle retention chamber and a detachable handle, the syringe being shown in a ready-to-fill position;

FIG. 2 is a cross-sectional view of the handle and thumb cap of the first embodiment taken along line 2-2 in FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of the first embodiment of FIG. 1, wherein the plunger has been pulled back to the maximum charge position and stopped;

FIG. 4 is a longitudinal cross-sectional view of the syringe of the previous figures, wherein the handle has been pushed to an injection end position;

fig. 5 is a longitudinal cross-sectional view of the syringe of the previous figures, showing: if the handle is pulled back from the position shown in FIG. 4 to the position shown in FIG. 5, the handle is disengaged but retraction has not been actuated;

FIG. 5A is an enlarged longitudinal cross-sectional view of the middle portion of the first embodiment shown in FIG. 5, showing the needle retention chamber and the plunger seal in the position shown in FIG. 5 before retraction occurs;

FIG. 5B shows the motion stop in the barrel as seen in the direction of line 5B-5B in FIG. 5A;

FIG. 5C is an alternative to the stop of FIG. 5B, showing that the stop can be one or more radial projections;

FIG. 5D shows an alternative position of the stop of FIGS. 5B and 5C which assists in setting the stroke of the syringe;

FIG. 6 is a longitudinal cross-sectional view of the syringe of the previous figures with the needle retracted into the needle retention chamber and the handle in its fully forward position with the thumb cap entering the opening in the rear of the syringe barrel;

FIG. 7 is a longitudinal cross-sectional view of FIG. 6 showing how the handle separates from the needle retention chamber in the syringe of FIG. 6 when the handle is pulled rearwardly after the needle has been retracted into the needle retention chamber;

FIG. 8 is a longitudinal cross-sectional view of a second embodiment of the present invention having a retractably mounted needle, a needle retention chamber, a stepped handle having a plurality of stepped teeth, and a positive locking mechanism including a clip, now in its first position near the rear of the handle;

FIG. 9 is a perspective view of an exemplary construction of the clip of FIGS. 8-14;

FIG. 10 is a longitudinal cross-sectional view of the syringe of FIG. 8 with the handle pulled rearwardly to draw fluid into the syringe and the clip moved to a second position closer to the front of the handle;

FIG. 11 is a longitudinal cross-sectional view of the single use retractable syringe of FIGS. 8 and 10 with the handle pushed sufficiently forward to complete the injection;

FIG. 12 is a longitudinal cross-sectional view of the syringe of FIG. 11 with the handle pushed forwardly to a maximum extent beyond the full injection position to retract the needle into the needle retention chamber;

FIG. 13 is a longitudinal cross-sectional view of an alternative configuration of the second embodiment of the present invention wherein the handle is detachably secured to the rear of the needle retention chamber and the plunger is in a full end-of-injection position in a manner similar to the first embodiment;

FIG. 14 is the syringe of FIG. 13 with the plunger having been pushed further forward from the position shown in FIG. 13 to retract the needle into the needle retention chamber;

FIG. 15 is a longitudinal cross-sectional view of a third embodiment of the present invention having the same retractable needle and needle retention chamber as in the previous figures, but showing a different positive lock configuration that allows the handle to be pulled back once to fill the syringe;

FIG. 16 is a perspective view of the spring clip of FIG. 15 showing a preferred plurality of resilient tines;

FIG. 17 is a longitudinal cross-sectional view of the third embodiment of FIG. 15, showing the handle pulled back to a position corresponding to that of the embodiment of FIG. 10;

FIG. 18 is a longitudinal cross-sectional view showing how the resilient clip is released to engage the handle as the handle begins to move forward during injection, thereby preventing any significant rearward movement of the handle;

fig. 19 is a longitudinal cross-sectional view of the syringe of the third embodiment shown in fig. 18, wherein the handle has been pushed forward to an injection complete position.

Detailed description of the invention

In the following description, like parts are given the same reference numerals. Preferably, the parts shown in the various figures are circular or cylindrical in nature.

Figures 1-7 disclose a first embodiment of a single use retractable syringe which is related to a modification of the retractable syringe shown in figures 1-3 of us patent 5,632,733. Although a detailed description of the preferred retractable syringe is found in this reference, as well as in other documents listed in the prior art summary, the main features thereof will be briefly described herein in connection with the present invention. The present invention provides a plunger handle positive lock that prevents the syringe from being reused even if the needle is not retracted after the first use. It should be understood that: the present invention is not limited to a particular retraction device or structure, but rather it may be used with other retractable needle devices, particularly those that trigger a retraction action by pushing forward on a plunger handle after completion of an injection. There are a number of means by which the needle can be retracted back into the bore in the plunger. For example, U.S. patent 5,407,436 to Toft or 5,713,952 to Pressly, Sr. may be modified by the present invention. In the latter case, although the plunger handle does have a structure that prevents secondary use, it does so only after the syringe has been actually retracted.

The single use retractable syringe of the present invention is generally indicated by the numeral 10 in fig. 1. Syringe 10 has an elongated hollow syringe barrel 12 having a front end portion 14 and an open rear end portion 16. The retractable needle 18 is mounted to the retraction structure 20. the retraction structure 20 includes an elongated needle holder 22. the needle holder 22 has a shoulder on the front that fits within an opening 24 in the front of the front portion 14 to prevent forward movement of the needle holder 22. As can be seen in FIG. 1, a small portion of needle holder 22 extends forwardly from the barrel. A releasable ring-like structure retainer 26 releasably and frictionally engages an enlarged head 30 of the needle holder 22 along an interface 28. The interface 28 is oriented in the retracted direction. The positioning member 26, together with the head 30 of the needle holder 22, is preferably press fitted against the inner side walls of the front part 14, against which they are immobilized against the retraction force exerted by the compression spring 34. The front end of spring 34 rests against the rearward facing shoulder of front part 14 and the rear end thereof bears against the forward facing shoulder of head 30 of needle holder 22, rather than against the movable retainer 26. The needle 18 is secured within the needle holder 22 with an adhesive 36.

The syringe is operated by a movable part including a handle 38, handle 38 being releasably connected to needle retention chamber 40 by means of a bayonet connection 42, preferably by a snap-fit engagement formed between a forward end 44 of handle 38 and a rearward end of needle retention chamber 40. The handle 38 preferably has a stem 76 with a guide rib 78 and a thumb cap 70, as shown in FIG. 2. The mating of the finger grip 80 and thumb cap 70 allows the syringe user to operate with a single hand. As seen in FIG. 7, forward end 44 of handle 38 has a circumferential groove 46 that releasably mates with one or more circumferential projections 48 at the rearward end of needle retention chamber 40 to form bayonet connection 42. The force required to withdraw handle 38 from needle retention chamber 40 is less than the force required to pull needle retention chamber 40 past stop 66 in the barrel. When the handle is pulled strongly, the handle is separated from the needle retention chamber and the needle retention chamber is left in the cylinder body.

The movable parts 38, 40 act together as a plunger that reciprocates within the barrel 12 with a piston-type seal in sliding contact with the inner surface of the barrel 12. The forward end 50 of needle retention chamber 40 has a piston seal 52 mounted thereon. Seal 52 sealingly slides in contact with the inner surface of barrel 12 to create a variable fluid chamber 56 located forward of forward end 50 of needle retention chamber 40. The forward end of needle retention chamber 40 has an opening sealed with a removable plug or other seal 60, which is preferably held in a friction fit within the opening.

Needle retention chamber 40 has a retention space 58 in which the retracted needle may be retained and a movable stopper 60, which stopper 60 slidably seals the opening of chamber 58. The forwardmost end of the nose portion 50 has a head 62 for contacting the locating member 26 and urging it away from the head 30 to a space 64 located in the nose portion 14 in front of the head 30 of the needle holder 22. This action will be automatically completed when the handle (movable part) is pushed further from the full "end of injection position" shown in fig. 4. Further pushing on the handle from the position of the movable parts shown in fig. 4 will cause the annular retainer 26 to move further forward and the bung 60 to move back out of position, thus opening the holding space 58 and releasing the needle 18 so that it can be retracted into the space 58 under the action of the spring 34, as shown in fig. 6. The construction described thus far provides a retractable needle syringe which is resistant to needle stick accidents and is not easily reused because the parts have been disconnected from each other after the needle is retracted and the thumb cap has been tightly inserted into the rear end 16 of the barrel 12. The invention ensures that it is no longer possible to touch the needle or other parts if the needle is retracted, and prevents the syringe from being refilled if the needle is not retracted.

Most importantly, the inner surface 54 of syringe barrel 12 is provided with positive locking structure 66 which includes one or more tabs projecting radially inwardly and designed to limit the rearward movement of needle retention chamber 40 and prevent its removal from the syringe barrel after a single use of the syringe. Needle retention chamber 40 preferably has an enlarged rearward end 68 which cooperates with optional locking structure 66 on the inside wall of the barrel. The gap is such that: the thumb cap 70 is forced to slide forward past the positive locking structure 66 when depressed hard by the thumb, but once the syringe handle 38 and needle retention chamber 40 are pushed forward so that the rear end 68 of the needle retention chamber 40 passes the positive locking structure tab 66, any attempt to reverse this movement is impossible because the handle 38 will disengage the needle retention chamber 40, as shown in figures 5 and 7.

Figure 1 shows the syringe in a ready-to-fill position. Handle 38 and needle retention chamber 40 have been pushed to bring the rear end 68 of needle retention chamber 40 into contact with a first stop 66 (hereinafter referred to) formed by a small protrusion in a fixed position on the inside wall of the barrel. The rearward end 68 of needle retention chamber 40 preferably includes a second stop (hereinafter referred to as "stop") that cooperates with the first stop to prevent further forward movement of the moving parts unless a much greater force is applied. The second stop is preferably a partial increase in diameter at the rearward end of the cylindrical needle retention chamber which is most suitably located at the rearward end of the needle retention chamber as shown in figure 1. However, the enlarged diameter portion may be moved forward from the rear end of the needle retention chamber as required by the geometry. The different diameter enlargement at different positions of the needle retention chamber is provided to vary the filling stroke to establish different filling volumes for different doses. The first and second stops 66, 68 constitute positive locking features.

Although the variable fluid chamber 56 appears somewhat large in the ready-to-fill position, in practice it is only a relatively small fraction of the maximum volume of the syringe and is, by definition, very small for 1cc or 1/2cc syringes. It can be seen that: the position of stop 66 and the length and diameter of needle retention chamber 40 and barrel 12 will determine the volume of the fluid filled. Needle retention chamber 40 is sized and positioned to fully retract the entire needle 18 so that there is no exposed needle tip after the needle is retracted.

Figure 3 shows the next step in the filling process in which the user optionally pulls back on the syringe handle until the shoulder 72 on the forward end of the needle retention chamber 40 abuts the first stop 66, which gives the user a tactile feel indicating that the syringe is full of injection fluid.

Fig. 4 shows the next step in the operation of the syringe in which the needle has been inserted into the patient (not shown) and the plunger has been depressed to the end-of-injection position. At this point, the forward portion of needle retention chamber 40 is in a position such that forward movement of tip 62 can in turn begin to withdraw stopper 60 from the opening at forward end 50 of needle retention chamber 40 and slide positioning member 26 forward over head 30 of needle holder 22 in retraction mechanism 20. This is accomplished by depressing the thumb cap 70 until the thumb cap 70 is snugly received within the opening 74 of the enlarged rear end 16 of the barrel 12. This is the needle retraction position of figure 6 in which the retractable needle has been retracted into the needle retention chamber with the stopper 60 at its rear end. The thumb cap 70 has entered the opening 74. In this position, the needle is safely retracted and the handle is flush into the opening in the rearward end of the syringe barrel, preventing further use.

However, if the user does not retract the needle after the position of FIG. 4 is reached (we see FIG. 5 instead of FIG. 6), attempting to move the movable part further by pulling on handle 38, as shown in FIG. 5, will only cause second stop 68 located behind needle retention chamber 40 to contact first stop 66, so that it cannot be moved further. The handle portion 38 is released from the needle retention chamber 40 by the release of the detent connection 42, leaving no means of access to the internal parts of the syringe. The groove 46 on the front portion 44 of the handle 38 is disengaged from one or more protrusions 48. During release, the parts may deform slightly. As can be seen from fig. 4 and 5, even if the handle 38 is reinserted into the barrel in order to reuse the syringe, the fill volume of the variable chamber will not be sufficient.

Fig. 5A is an enlarged view of the middle portion between the fracture lines shown in fig. 5. In which the catch 72 is more clearly visible, which is preferably formed as a ring of castellated radial projections on the nose portion 50. The rear end portion 68 of needle retention chamber 40 has an enlarged diameter end surface 82 with an edge that abuts against first stop 66. It can be seen that: at the rear end of the needle retention chamber is a catch projection 48 which engages with a groove 46 in the handle 38 as seen in figure 5, but now the handle has been disengaged. Fig. 5B is a cross-sectional view showing that first stop 66 may be a continuous small protrusion around the inner diameter of barrel 12. Figure 5C shows that first stop 66 can be a plurality of larger radially inward projections positioned to contact and block the rearward end 68 of needle retention chamber 40, preventing it from being pulled further by handle 38. Similarly, if the stop 66 is continuous, the rearward end of the needle retention chamber including the second stop 68 may be discontinuous. It is not necessary that the needle retention chamber be angularly oriented in the circumferential direction so long as one or the other is continuous, and if so, the needle retention chamber may be pulled out of the barrel by the handle.

Figure 5D shows that the rear end of the needle retention chamber can be modified to have a straight rear end portion 68' sized to fit through the through-hole between the tabs of stop 66. Instead, a protrusion 69 is provided on the outside surface of the needle retention chamber at a different location in the diametrical direction to act as a stop against the positive locking protrusion 66. Diametrical projection 69 may be considered a second stop that cooperates with first stop 66 to limit rearward movement of needle retention chamber 40. The second stop 69 functions in exactly the same manner as the enlarged rear end portion 68 of the needle retention chamber of the previous figures, and is forced through the through-hole between the projections 66 when moved forward by the force applied to the thumb cap 70. The user then attempts to pull the handle backward with the diametrically disposed projection 69 in contact with projection 66 and requires a force greater than the force required to disengage handle 38 from needle retention chamber 40. This is an alternative method of providing different travel of the handle relative to the barrel. This method is useful in setting the stroke of a particular syringe to inject a desired dose.

Figures 8-14 illustrate a second embodiment of the single use retractable syringe of the present invention having the preferred retraction structure disclosed in the previous figures and designated by the same reference numerals. Parts modified from those in the previous figures will be given prime notation. The syringe of the second embodiment is generally designated by the reference numeral 10'. Retractable syringe 10' has the exact same retractably mounted needle 18 and retraction structure 20 as the first embodiment. It has a modified syringe barrel 12' relative to the first embodiment but it does not have the same positive locking structure nor the enlarged rear end portion 16. Barrel 12' has a front end portion 14 and an open rear end 84. A movable handle 38 ' is reciprocally mounted within barrel 12 ', and barrel 12 ' also has a needle retention chamber 40 ' connected to handle 38 '. The front end portion 50 of the plunger includes the same piston seal 52 and slidably urged stopper 60 as discussed in the first embodiment. The rear end portion of the movable handle has a thumb cap 86 for applying force to the handle. Needle retention chamber 40 'is either fixedly or detachably connected to handle 38', but is merely for ease of manufacture. If the two movable parts are made separately, they should be joined and it is ensured that they cannot be separated, for example by welding, gluing or other permanent fixing methods, or they may be moulded in one piece.

The second embodiment is different from the first embodiment in that: the positive locking feature is a preferred metal clip 88, as shown in FIG. 9. The clip 88 has a tab 90 and one or more pairs of locking teeth 92 on a body 94. Tongue 90 is slightly bent inward to interact with a plurality of stepped teeth 96 on handle 38 'behind needle retention chamber 40'.

Fig. 8 shows the initial position of the single use retractable syringe of the second embodiment. In this initial position, the handle is pushed forward sufficiently within the syringe barrel to slightly contact the retraction mechanism but not cause retraction. This is judged by the type of touch that the operator touches the stopper 60 against the needle holder head 30. The positive locking structure 88 fits over the handle 38' and is movable from a first position 98, fig. 8, to a second position 100, which can be accomplished in a simple manner by pulling the handle back relative to the syringe barrel. The positive locking structure, including clip 88, can only move in one direction from a first position near the rear of the handle to a second position closer to the front of the handle. The tines 92 are configured to engage the inner surface 102 of the barrel 12' if an attempt is made to move the clip rearwardly with the handle. Because the tines 92 are pointed rearward, the tines 92 are free to slide along the barrel inner surface 102 as the clip moves forward within the barrel 12'. The tongue 90 will abut the edge of the step tooth 96 as the handle is moved rearwardly relative to the yoke 88. Thus, when the handle is pulled rearwardly, the step teeth 96 slide relative to the clip 88, and the clip 88 can move from the first position 98 of FIG. 8 to the second position 100 of FIG. 10. Fig. 10 illustrates the position of the handle 38' relative to the clip 88 after a maximum amount of fluid has been drawn into the fluid chamber 56 by the injection needle 18. Needle retention chamber 40' is just forward of the second position of positive locking structure 88. Thus, it can be seen that the clip constitutes an optional locking structure.

Fig. 11 shows the position of the handle after the fluid in the variable fluid chamber 56 is maximally expelled, i.e. at the end of the injection. It can be seen that: the inwardly angled tabs 90 of clip 88 snap over the lower edges of the stepped teeth 96 and move forward with handle 38 'and needle retention chamber 40'. The rearward pointed tines 92 slide along the inner surface of the barrel 12' without interfering with the forward movement of the handle.

Fig. 12 shows how the syringe 10' of the second embodiment retracts its needle by simply pushing on the thumb cap 86 and moving the handle from the end-of-injection position of fig. 11 to the retracted position of fig. 12. It can be seen that: the positioning member 26 has been pushed down by the head 62 from the head 30 of the needle holder 22 into the space 64 and, as the plug 60 moves from the front end portion to the rear end portion of the needle retention chamber 40', the spring against the needle holder and needle has moved back to retract into the needle retention chamber and is retained there by the spring 34. These features are sized to allow the entire needle, including its sharpened tip, to be retracted into the barrel 12'. It has been described above that the positive locking structure located within the barrel does not affect one rearward and one forward movement of the handle. Now, however, with the positive lock mechanism 88 in its second position of FIG. 12, any reverse or rearward movement of the needle retention chamber is prevented by the clip 88 because the sliding tines 92 are now in the position to penetrate the inner surface 102 of the barrel 12 'and the rear end 104 of the needle retention chamber 40' contacts the bottom surface of the clip 88, thereby preventing rearward movement of the handle and needle retention chamber. Since clip 88 cannot move rearward and prevents rearward movement of needle retention chamber 40', it will be appreciated that: it is not possible to pull the handle back out of the syringe barrel after a single use. Comparing the position of the clip 88 in fig. 11 and 12, it will be appreciated that: the handle cannot be pulled out regardless of whether the needle is retracted or not. The handle is therefore locked within the barrel after a single use. It is also clear that: the fill volume can be adjusted by changing the initial position of the clip 88 relative to the handle 38', as illustrated in U.S. patent nos. 5531,691 and 5,562,623 to Shonfeld et al, both of which are mentioned in the background section above.

Fig. 13 and 14 correspond to fig. 11 and 12, respectively. The syringe 10 "of them differs from the syringe 10' of figures 11 and 12 only in that: the handle 38 "is detachably connected to the needle retention chamber 40" in a detachable connection. The rearward portion of needle retention chamber 40 "preferably has a circumferential groove 108, and the forward end of handle 38" has an annular radial projection 110 secured thereto which corresponds to groove 108 and engages therewith. The separable connection 106 allows the movable parts, including the handle 38 "and needle retention chamber 40", to be a two-part structure, which facilitates their separate molding and assembly, and also allows one of the parts to be changed while maintaining a standard size, e.g., the handle may be made longer or shorter for the same needle retention chamber 40 ", or the length of the needle retention chamber may be changed for a standard handle 38". One reason for changing the needle retention chamber may be to use different length needles. Varying the stroke is also another way to vary the maximum dose. The length of the barrel can vary but is not critical as the clip 88 prevents the handle 38 "and needle retention chamber 40" from backing after the first injection has been made, and the clip functions in exactly the same manner as described above in connection with figures 8-12. Retraction of the handle is prevented regardless of whether the retraction mechanism is actuated.

Fig. 15-19 illustrate a third embodiment of the present invention. The syringe of this embodiment is designated by the reference numeral 11. The syringe 11 is the retractable syringe of fig. 1-7, but with the following differences. The parts shown in figures 15-19 up to the rear end of the needle retention chamber are considered identical to those of the first embodiment and the rear end portion 112 of the barrel 12 has been modified to accommodate the resilient clip arrangement 114 shown in figure 16. The portion of the barrel 12 behind the finger grips 80 is thickened, much like the rear portion 16 of the first embodiment. It also has an opening 74 for receiving the thumb cap 70 at the rear end of the handle 116, but a reduced diameter seating surface 118 just forward of the opening 74. The abutment 118 is preceded by an annular groove 120 in the enlarged rear end portion 112 of the barrel 12 in which the resilient clip 114 is mounted and fixed relative to the barrel. It will be seen that: the resilient clip 114 includes structure on the inside of the barrel that limits the continued rearward movement of the needle retention chamber after the first use of the syringe.

Handle 116 is located behind needle retention chamber 122 (fig. 17) and is formed with a plurality of stepped teeth 124 along its length, as are stepped teeth 96 of the second embodiment. The handle 116 has a slide in the form of a collar 126, the collar 126 including a catch 128 configured to catch an edge 130 of any of the stepped teeth 124, the collar 126 being a split annular part to enable it to be fitted to the handle. The thumb cap 70 may be installed and secured in place after the collar is installed on the shaft of the handle 116, or the handle may be two piece.

The spring clip 114 preferably has an annular body 132 and an open gap 134 that allows the annular body to be slightly compressed to allow it to be seated in the groove 120 by the reduced diameter abutment 118. The springing clip 114 has a plurality of springing tines 136 that are spaced from the handle by the rear end portion of the sliding collar 126 in an initial installation state, as shown in fig. 15. This is the initial position of the handle, which corresponds to the starting position of fig. 1 or 8. A slight reduction 138 in barrel 12 prevents ferrule 126 from moving back as handle 116 is pulled back to the fig. 17 position, pulling handle 116 back to draw fluid into variable volume fluid chamber 156 (not shown in fig. 17, see fig. 3). For clarity of illustration, the stepped teeth 124 and catch shoulders 128 are slightly exaggerated, in effect they allow the handle to be pulled back unobstructed to the ready to inject position of fig. 17. This is the first pull back of the handle 116 and needle retention chamber 122. The back end of the needle retention chamber 122 has a stop surface 140 that abuts the end surface of the collar 126 when the handle is fully retracted, as shown in figure 17. The collar 126 in fig. 17 still keeps the resilient tines out of contact with the handle 116.

Fig. 18 shows: what happens when the handle 116 of the syringe 11 is pushed forward from the position of fig. 17, towards the position of fig. 18 and finally to the position of fig. 19 by the force of the thumb cap 70. What will happen is that: the sliding element, i.e., the shoulder 128 of the collar 126, will catch on the edge 130 of the step tooth 124 and disengage from the resilient clip 114 as it moves forward, which causes the resilient tines 136 to ride over the step tooth 124 as the handle 116 moves forward and pass the teeth one by one until the handle 116 reaches the position of fig. 19.

Fig. 19 shows the end-of-injection position, with the remaining parts corresponding to the positions of fig. 4 or 13. The needle retention chamber front portion 50, as in figure 1, has reached the retraction mechanism 20 at the front of the syringe and fluid has been expelled from the needle 18. The resilient tines 136 drop into the annular groove 142 in the rear end portion of the handle 116. However, from the acute angle of the resilient tine 136 relative to the stepped tooth 124, it should be appreciated that: it is not possible to pull back the handle 116 from the position of fig. 18 or from any intermediate position between the position of fig. 15 and the position of fig. 19 because the resilient tines 136 would dig into any step teeth in contact with them and trap the handle 116 within the barrel 12. Thus, the spring clip 114 provides an optional locking structure within the barrel by engaging the movable components in a fixed position, which does not interfere with the rearward and forward movement of the movable components (handle and needle retention chamber) to the fullest extent. However, since the handle cannot be pulled back a second time, continued rearward movement of the needle retention chamber is prevented and the needle retention chamber is retained within the barrel.

Finally, after the completion of the injection position of fig. 19, and finally pushing the thumb cap 70 forward from the position of fig. 19, movement of the handle will actuate the retraction action of the retractable parts, the result of which is shown in fig. 6, 12 and 14. The needle will retract into the needle retention chamber 122 and be retained in the barrel. Thus, in all three embodiments, the plunger-activated retraction action and retraction mechanism may be the same, with the exception of the positive lock structure for limiting rearward movement of the needle retention chamber.

Preferably, the parts are made of conventional injection moldable plastic, typically polypropylene. The piston seal is conventional and the band is preferably metal.

Although several embodiments of the present invention have been described above with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention.

Claims (35)

1. A single use retractable syringe having a handle operated needle retention chamber which cannot be removed from the syringe barrel, the syringe comprising:

an elongated hollow syringe barrel having a forward end and an open rearward end;

a retractable needle mounted in a retracted configuration within the forward end of said syringe barrel and biased to retract rearwardly;

movable parts including a handle connected to the needle retention chamber which is sealingly and slidably mounted for movement within the syringe barrel by means of the handle projecting from the open rear end of the barrel, the front end of the needle retention chamber having an opening which is sealed but openable to receive a retracted needle;

retraction of the needle into the needle retention chamber is triggered by forward movement of the needle retention chamber against the retraction mechanism in response to movement of the handle after completion of an injection;

(ii) a positive lock structure disposed within said syringe barrel capable of restricting rearward movement of said needle retention chamber and preventing it from being pulled out of said syringe barrel after a single use of said syringe; so that the retracted needle is safely stored in the needle retention chamber in the syringe barrel after a single use and is not easily removed by pushing or pulling on the handle.

2. The retracting syringe of one use of claim 1 wherein the needle retention chamber is connected to the handle.

3. The retracting syringe of one use of claim 1 wherein the needle retention chamber is detachably connected to the handle.

4. The retractable single use syringe of claim 1 wherein said positive locking structure comprises structure disposed in said barrel engageable with the movable element and configured to not interfere with a rearward and a forward movement of said movable element to the fullest extent, but to prevent subsequent rearward movement of said needle retention chamber to retain said needle retention chamber in said syringe barrel.

5. The retractable single use syringe of claim 4 wherein the structure disposed in the barrel to prevent subsequent rearward movement of the needle retention chamber is in a fixed position relative to the barrel during use of the syringe.

6. The retracting syringe of one use of claim 5 wherein the structure in the barrel at a fixed position relative to the barrel comprises a reduced diameter portion of the inner diameter of the barrel constituting a first stop and the needle retention chamber has a diametrically enlarged portion constituting a second stop, wherein the second stop is urged forward past the first stop when the handle is pushed but resists rearward movement caused by pulling the handle.

7. The retracting syringe of one use of claim 6 wherein the handle is detachably connected to the needle retention chamber such that their separation force is less than the force required to force the second stop back past the first stop so that their separation will leave the needle retention chamber in the barrel.

8. The retracting syringe of one use of claim 7 wherein the handle is separated from the needle retention chamber by release of the separating portion rather than by breaking of the separating portion.

9. The retracting syringe of single use of claim 8 wherein the needle retention chamber has a forward portion with a shoulder that can be forced past the first stop before the second stop moves past the first stop when the handle is depressed, the shoulder limiting the amount of rearward movement of the movable element to establish a maximum designed fill volume for the syringe.

10. The retracting syringe of one use of claim 5 wherein the structure disposed inside the barrel for limiting subsequent rearward movement of the needle retention chamber by remaining in a fixed position comprises a structure mounted within the open rearward end of the barrel.

11. The retracting syringe of one use of claim 5 wherein the structure includes a resilient clip which positively engages the handle after the handle is pushed forward to complete an injection, thereby preventing the handle from being pulled further rearward once the clip engages the handle.

12. The retracting syringe of one use of claim 11 wherein the handle includes a thumb cap for pushing the handle forward, the thumb cap being closely received within the open rearward end of the barrel when retraction of the needle is triggered by sufficient depression of the plunger.

13. The retracting syringe of one use of claim 11 wherein the handle extending behind the needle retention chamber is stepped along its length and includes a sliding feature thereon which in an initial installed condition spaces the spring clip from the handle to allow the plunger to be pulled back to draw the syringe into fluid and then when the handle is pushed the sliding feature moves forward to release the spring clip into contact with the handle.

14. The retracting syringe of one use of claim 5 wherein the structure disposed inside the barrel for limiting subsequent rearward movement of the needle retention chamber comprises a resilient clip mounted in a fixed position within the open rearward end of the barrel and a sliding member in contact with the handle, the sliding member holding the resilient clip away from the handle when the handle is pulled rearward and the sliding member releasing the resilient clip into contact with the handle by forward movement with the handle when the handle is pushed forward within the barrel.

15. The retracting syringe of one use of claim 4 wherein the structure disposed within the barrel for limiting said subsequent rearward movement of said needle retention chamber changes its position relative to said barrel during use of the syringe.

16. The retracting syringe of one use of claim 15 wherein the structure includes a resilient clip which positively engages the handle after the handle is pushed forward to complete an injection and which prevents the handle from being subsequently pulled rearward once the clip engages the handle.

17. The retracting syringe of one use of claim 15 wherein the handle includes a thumb cap for pushing the handle forward, the thumb cap being closely received within the open rearward end of the barrel when retraction of the needle is triggered by sufficient depression of the plunger.

18. A single use syringe having a syringe barrel in which the syringe barrel has an injection needle extending from its forward end for injecting fluid and a movable handle extending from its rearward end and mounted for limited reciprocal movement therein, said movable handle including a forward end portion having a piston in sliding sealing contact with the inner surface of said barrel, wherein said piston establishes a variable injection fluid chamber within said barrel; in a further aspect, the invention provides a movable handle including a rear portion having a thumb cap for applying thumb thrust to said handle and a positive locking structure disposed in said barrel for limiting a second rearward movement of said handle after a first rearward movement of said handle to draw injection fluid into said variable fluid chamber and a first forward movement of said handle to inject fluid, the improvement comprising:

said needle is a retractable needle mounted in a retracted configuration within the forward end of said barrel, the needle extending from its unretracted position and being biased to retract in a retracted position;

the front end part of the handle is configured to trigger the retraction structure to act so as to retract the injection needle, and the front end part is provided with a needle retention chamber for accommodating the retracted injection needle and the piston positioned behind the variable fluid chamber;

the needle retention chamber has a front end and a diametrically enlarged portion;

said positive locking structure is a stop positioned to limit rearward movement of said needle retention chamber to within the confines of said barrel by contact with said enlarged portion of said needle retention chamber;

if an attempt is made to pull the needle retention chamber past the stop by pulling on the rear portion of the handle, the rear portion of the handle disengages from the front portion; and

wherein the syringe cannot be used any more even if the injection needle is not retracted after one use.

19. A single use syringe as described in claim 18 wherein said stop is a structure formed in said barrel that allows said forward portion of said handle and said needle retention chamber to be pushed forward of said stop by pushing on a thumb cap; and

if the needle retention chamber is pulled rearwardly, it contacts the stop as it moves rearwardly and creates a resistance greater than the force required to disengage the handle, thereby ensuring that the needle will be retained within the barrel, preventing the syringe from being used a second time.

20. The retracting syringe of one use of claim 19 wherein the handle and the needle retention chamber are separated by release of the separating portion rather than breaking them.

21. The retracting syringe of one use of claim 19 wherein the rear end portion of the handle is detachably connected to the needle retention chamber with a snap fit.

22. The retracting syringe of one use of claim 19 wherein the needle retention chamber has a catch near its forward end that is forced forward past the stop when the handle is depressed, the catch being configured to move rearward against the stop when the handle is pulled rearward to establish the maximum volume of the variable fluid chamber.

23. A retractable syringe of the single use type having an operating handle which cannot be pulled out of the syringe barrel after a single use of the syringe, comprising:

an elongated hollow syringe barrel having a forward end and an open rearward end;

a retractable needle mounted in a retracted configuration within the forward end of said syringe barrel and biased in a rearward retraction direction;

a plunger, comprising:

a movable handle within said syringe barrel, said handle having: a front end portion having a piston in sliding sealing contact with the inner surface of the barrel;

a rear end portion having a thumb cap at a rearmost end thereof for applying a pushing force to the handle by a thumb; and the number of the first and second groups,

a needle retention chamber within the forward end portion of said handle for receiving a retractable needle;

(ii) a positive locking structure disposed within said syringe barrel capable of restricting rearward movement of said handle and preventing it from being pulled out of said syringe barrel after a single use of said syringe; so that the needle after use is safely stored in the needle storage chamber in the syringe barrel and can not be pushed or pulled to move any more.

24. The retracting syringe of single use of claim 23 wherein the handle carries the positive locking feature, the positive locking feature being movable in only one direction from a first position near the rear end of the handle to a second position closer to the front end of the handle, the positive locking feature being configured to positively engage the syringe barrel after it has been moved forward of the first position to limit rearward movement of the needle retention chamber.

25. The retracting syringe of one use of claim 24 wherein the needle retention chamber is located just forward of the second position of the positive lock.

26. The retracting syringe of one use of claim 25 wherein after the plunger is fully depressed to perform an injection, further thumb pressure on the thumb cap at the rearmost end of the plunger will cause the needle to retract.

27. The retracting syringe of one use of claim 25 wherein the rear portion of the handle has a plurality of stepped teeth and the positive locking structure comprises a clip having a tab bent inwardly relative to the stepped teeth, the tab allowing forward movement of the clip but preventing rearward movement thereof, the clip having at least one outwardly bent prong engageable with the syringe barrel to prevent withdrawal of the handle.

28. The retracting syringe of one use of claim 27 wherein the clip surrounds a portion of the stepped teeth of the handle rear portion but not all of them.

29. The retractable syringe of one use of claim 23 wherein said positive locking structure within said syringe barrel that limits rearward movement of said handle comprises a structure for mounting in a fixed position relative to said barrel.

30. The retracting syringe of one use of claim 29 wherein the structure mounted in a fixed position relative to the barrel is disposed within the open rearward end of the barrel.

31. The retracting syringe of one use of claim 30 wherein the handle includes a thumb cap for pushing forward on the handle, the thumb cap being closely received within the open rearward end of the barrel when sufficient depression of the plunger triggers retraction of the needle.

32. The retracting syringe of one use of claim 30 wherein the structure mounted in a fixed position relative to the barrel within the open rearward end of the barrel is a resilient clip having one or more forwardly turned prongs which are shielded from contact with the handle by a collar on the handle during initial rearward movement of the handle to draw injection fluid into the barrel, a rearward movement of the handle relative to the barrel from the initial forward position, and then a forward movement of the collar out of contact with the resilient clip as the plunger is depressed to effect an injection, whereupon the resilient clip engages the handle to prevent rearward movement thereof.

33. The retracting syringe of one use of claim 32 wherein the rear end portion of the handle has a plurality of stepped teeth over which the sliding collar fits, the tapered inner surface of the collar allowing rearward movement of the plunger handle relative to the sliding collar, the sliding collar being movable forward with the handle by its engagement of the inner surface with one of the stepped teeth of the handle.

34. A single use syringe comprising:

an elongated hollow syringe barrel having a forward end and an open rearward end;

an injection needle mounted to a forward end portion of said barrel;

a two-piece movable handle mounted for reciprocal movement within said barrel, said handle having a forward head portion and a handle portion detachably connected to said head portion, said forward head portion having a piston in sliding sealing contact with the inner surface of said barrel;

a lock mounted in said barrel to permit said head portion to move through said lock when said head portion and said handle portion are inserted into said open rear end and a forward force is applied to said handle portion;

after having passed the lock forward, the handle portion may be separated from the head portion when the handle portion is pulled back, the separation occurring by virtue of the head portion releasing the handle portion under the locking force of the lock rather than breaking of the separating element.

35. A single use syringe as described in claim 34 wherein said needle is a retractable needle retractably mounted to a forward portion of said barrel.