Hypodermic syringe with selectively retractable needle

[0002] The present invention is generally related to hypodermic syringes and more particularly to syringes that include a needle that is retractable after the intended use to substantially prevent inadvertent exposure to the needle and reuse of the syringe.

[0003] Hypodermic syringes are widely used in the medical arts for administering medicaments and for drawing body fluid samples. Generally, hypodermic syringes have a metal needle attached either fixedly or removably that has a sharpened distal point for penetrating vial stoppers or patient's skin. The hypodermic syringes and needles have been used for many years with few problems reported when the vast numbers and needles being used are considered. More recently, with the recognition of viral diseases that are transmitted by body fluids and greater sensitivity of the need to protect health care workers from inadvertent contact with previously used needles (commonly referred to as “sharps”) as well as the need to reduce criminal misuse of improperly disposed of needles and syringes, syringes and needles that include provisions to prevent reuse have been developed.

[0004] Provisions intended to prevent reuse of needles and syringes include a variety of sharps collector systems that are widely used in health care facilities. Other developments include needle attachments that may be readily broken off by practitioners once the syringe has completed its intended use. A variety of shielding mechanisms has been developed; some of which are currently commercially available. While many of these developments have reduced the incidence of inadvertent exposure of healthcare workers to sharps, most of these devices can readily be overcome by an individual determined to obtain and misuse a hypodermic syringe and needle. As a result of this problem, further developments in the art of hypodermic syringes have resulted in syringes with needles that withdraw into the body of the syringe once their intended use is completed.

[0005] U.S. Pat. No. 4,838,869 discloses a retractable hypodermic needle configured for one time use wherein the needle is spring loaded and automatically irretrievably retracted into the hypodermic syringe when the syringe plunger is fully depressed, whereby protrusions on the end of the plunger engage tabs holding the spring loaded needle to release the needle for retraction. A potential problem with the design disclosed in this patent is that many times a practitioner may draw and expel a fluid several times during preparation for administration of a medicament, with this design, the practitioner could inadvertently discharge the retraction mechanism. Further, the design would be very difficult to manufacture in large volumes.

[0006] U.S. Pat. No. 4,900,307 discloses a hypodermic needle with an enlarged hub that provides provisions for selectively withdrawing the needle into the hub once the syringe and needle have completed their intended usage. While this disclosed design does substantially eliminate the problem of premature discharge of the retraction mechanism, the enlarged hub has a considerable “dead volume” that would result in a significant undeliverable retention of the medicament. Additionally, although the needle is secured in the hub after discharge, the syringe itself is still fully functional after the hub with the needle inside is removed.

[0007] U.S. Pat. No. 4,994,034 discloses a hypodermic injection system with a retractable needle wherein the needle retracts within the interior cavity of a syringe plunger. The disclosed invention includes a cylindrical spring housing with resilient fingers which capture a coiled spring that biasly holds a needle holder against the retaining force of the resilient fingers. The plunger in this disclosure has a frangible end, which when engaging the resilient fingers under a pre-determined amount of force, dissociate which remaining inwardly-tapered shoulders spread the resilient fingers, allowing the coiled spring to eject the needle and its holder into the interior cavity of the syringe plunger. A syringe manufactured using this disclosure would be complex and difficult to assemble. It is believed that no successful commercial product has been produced using this disclosure.

[0008] U.S. Pat. No. 5,019,044 discloses a safety hypodermic syringe with a hypodermic needle fixed connected to a holder plate and constantly supported by a spring for making axial movement. The holder plate is normally retained by a clamp at a ready position for injection. When the plunger of the syringe is pushed to the bottom of the barrel, the needle is released from the clamp and is pushed by the spring to drop and further follow a rubber plug to be squeezed into a chamber in the plunger. Again, no successful commercial product has resulted from this disclosure, which would be complex to manufacture and appears to have a considerable undeliverable dead volume.

[0009] Another example of a syringe with a retractable needle is disclosed in U.S. Pat. No. 5,053,010. The disclosed syringe retracts the needle into a hollow plunger additional pressure on the plunger after the contents of the syringe are expelled. The disclosed design incorporates a sliding elastomeric seal which displaces from its forward position to a retracted position, thereby allowing additional forward travel of the plunger to actuate the retraction mechanism. A problem reported with this design is that, because of the soft nature of the seal, the seal may be prematurely displaced during its use in an injection. Attempts to overcome this difficulty by increasing the stiffness of the sealing member could impair the seal integrity.

[0010] U.S. Pat. No. 5,180,369 discloses a self destructive syringe assembly having a needle cannula fixed to a slidable piston. The slidable piston and slidable piston flange are held within the barrel of the syringe assembly by a compressed spring, a guide tube and a shatter ring. The plunger of the syringe assembly is a hollow elongated tube with a thumb flat at one end, a sliding gasket, a plunger shatter plate and a hook rim at the other end. The patent reports that when medicament is injected, the elongated hollow plunger is further thrust into the shatter ring, the shatter ring shatters, further allowing the slidable piston and slidable piston flange to thrust into the plunger shatter plate to shatter. The shattering of the plunger shatter plate causes the slidable piston and needle cannula to be thrust into the hollow plunger by the spring and is thus prevented from re-entering the guide tube. Again, no successful commercial product has resulted from this disclosure.

[0011] U.S. Pat. No. 5,180,370 discloses a syringe which has an internal mechanism for retracting the needle into the syringe after the injection has been given. In one disclosed embodiment, the needle is manually retracted by pulling back on the plunger, and in another, the needle is propelled by a compressed spring into a hollow chamber within the plunger. A syringe produced with this disclosure would be complex to manufacture, and no successful commercial product has resulted from this disclosure.

[0012] U.S. Pat. No. 5,188,599 discloses a hypodermic injection system with a needle that retracts within an interior cavity of the syringe plunger. The needle when retracted is held within the plunger. The disclosed device includes a cylindrical spring housing that has resilient fingers which capture a spring under bias holding a needle holder against the retaining force of resilient fingers. The plunger has a frangible end which dissociates when the outwardly tapered shoulders spread the resilient fingers, allowing the coiled spring to eject the needle and its holder into the interior cavity of the syringe plunger. The patent also discloses a body fluid sampling device that includes a double-ended needle for communication with an evacuated blood collection tube. This patent also includes a review of several earlier disclosures related to retractable needles. Attempts have been made to produce commercial products based on the disclosures of this patent, but as yet there is no successful commercial product.

[0013] U.S. Pat. No. 5,201,710 discloses a syringe fitted with a clamping device for the needle and with a mechanism to enable the needle to be automatically retractable into the syringe body at the end of an injection. The disclosed device includes inner and outer cylinders, openings at the ends of the outer cylinder, a third opening at an end of the inner cylinder and a closure for the third opening. The disclosed device further includes a needle with a head, a seal, a first spring to push the needle against the closure and a clamping device loaded by a second spring to maintain outward to the syringe and to release the needle. There is a diaphragm in the closure that bends before breaking and a sharp element to break the diaphragm. There also is a closure to prevent the needle from being accessible and a stop to prevent the second cylinder from being moved outwardly after the syringe is used. As is apparent from the description, the device disclosed by this patent is complex and would be difficult to assemble. No successful commercial product has resulted from the disclosure in this patent.

[0014] U.S. Pat. No. 5,385,551 discloses a non-reusable medical device that has a needle which is retractable by depression a plunger slidably mounted in the device. The disclosed device includes a front-mounted retraction mechanism that has a needle holder connected to the needle. The needle holder is supported along the axis of the device by a frictionally engaged retainer ring member coupled to the needle holder along an axially aligned sliding interface. The needle holder and retainer are positioned in the front portion of a hollow body. The front of a movable member or plunger presses against the retainer member passing around the needle holder which cannot move forward, thereby separating the retainer from the needle holder. The separation occurs by gradually reducing the extent of the sliding interface area until the retainer member pops loose from the needle holder whereupon the needle holder and needle are retracted into a cavity in the plunger in response to a retraction force applied to the needle holder by a previously compressed spring. Again, the device disclosed in this patent is complex, difficult to manufacture and appears to have significant undeliverable dead volume. Attempts have been made to commercialize products from this disclosure with only limited success.

[0015] U.S. Pat. No. 5,407,436 discloses a hypodermic syringe that has a hollow needle that is automatically retractable after use. The disclosed syringe includes a one-piece body molding has a main chamber for a plunger, sample container or drug cartridge, a forward chamber to house a spring to bias a needle holder, and internal latching formations to retain the needle holder with the spring compressed in the forward chamber until automatic retraction when the latching formations are released by end of plunger movement. The patent discloses that the sealing between the plunger and the body is accomplished by an over-sized plunger head that forces head and wall deformation. The disclosed spring has seals at both ends for the forward chamber. The patent teaches that the needle, its holder, spring and seals can be installed using a sliding guide. In using a syringe produced using this disclosure, the practitioner would need to exercise care when drawing and expelling a fluid during filling, because the retraction of the needle is activated by depressing the plunger sufficiently to engage cooperating latches. The engagement occurs at the bottom of the stroke to expel fluid from the syringe.

[0016] U.S. Pat. No. 5,769,822 discloses a non-reusable syringe with a hollow plunger that has a seal member thereon. The position of the plunger and the seal relative to the barrel permits the plunger, with sufficient strength, to carry applied pressure through the device during injection of a fluid and yet permit the seal disposed at one end of the plunger to have maximum sealing integrity between the plunger and a cylindrical barrel disposed around the exterior of the plunger to abate leakage of the liquid in a chamber within the barrel, as the plunger is manipulated from an expanded position to and expended position and thereafter to a third or collapsed position.

[0017] U.S. Pat. No. 6,010,486 discloses a retracting needle syringe that substantially prevents reuse of the syringe by destroying the plunger rod and the needle hub and additionally, retracts the needle into the plunger rod. The disclosed syringe includes provisions that upon fully depressing the plunger rod and applying distally directed axial force, a frangible portion of the inner hub is broken and the plunger tip dislodges to allow a spring to urge a cutter to open the chamber inside the plunger.

[0018] Most of the devices discussed in the above referenced disclosures are somewhat complex, and many require manufacture and assembly of parts with potentially difficult assembly or tight tolerance requirements. Many of the designs depend upon a careful application of forces by the practitioner to draw and expel fluids from the syringe. Also, if the tolerances between the multiple components of the device are not carefully adhered to during manufacture and assembly, normal usage may result in premature activation of the retraction function of the syringe. Current conventional syringes are considered by users to be virtually fault-free and reliable. They are used for a variety of different procedures involving both “one-shot” fill and inject procedures, as well as more complex mixing, measuring and delivery functions. In order for a retractable syringe to displace these functional, utilitarian and reliable conventional syringes, the retractable syringe should not significantly interfere with the users current practices, it needs to be substantially reliable and its cost should not be prohibitive. Current conventional syringes are often manufactured at rates of several hundred per minute and their cost is generally not a significant factor in their usage. Additionally every year, hundreds of millions of small capacity (one milliliter) syringes are used outside of the normal controlled health care environment by diabetics and other self-injectors who must daily accurately inject small amounts, often only a few tenths of a milliliter. These small capacity syringes are physically quite small, with an overall length of less than five inches and an inside bore diameter of less than one-quarter inch. Reviewing the disclosures above, one skilled in the art of high volume manufacturing recognizes that assembling hundreds of millions of most of these relatively complex devices with their retraction elements contained in such a small space as a one-quarter inch diameter bore is a daunting task. Additionally, many of the disclosed devices have substantial undeliverable “dead volumes” that substantially confound many diabetics' need for accurate measuring, mixing of more than one type of insulin in the syringe and delivering small doses of insulin. The need thus exists for a selectively retractable syringe that is compatible with a small capacity syringe, that is capable of being manufactured at high volumes and is sufficiently non-complex to be reliable in use when produced at volumes of hundreds of millions per year. Such a device is disclosed herein below.

[0019] A hypodermic syringe with a selectively retractable needle of the present invention includes an elongate barrel having an open proximal end and a distal end that defines a receiver with an inwardly projecting shoulder. The barrel has a hollow bore therethrough with an inside surface extending from the proximal end to the distal end. The syringe of the invention has a hollow elongate plunger with an open proximal end and a closed distal end. There is an elongate plug extending distally into the hollow plunger from the open proximal end forming an enclosed cavity within the plunger. The distal end of the plunger forms a slidable seal with the inside surface of the barrel to define a chamber for drawing and expelling fluid. The syringe also has an elongate hub having a passageway therethrough, a distally extending stem, and a proximal flange with an engagement for engaging the barrel. The stem is disposed within and sized for slidable movement within the receiver at the distal end of the barrel. The flange has a distal surface with a groove therein and a proximal surface defining the chamber in the barrel. The syringe of the invention has an elongate needle having a fluid path therethrough, a sharpened distal end and a proximal end. The needle is mounted in the passageway in the hub so that the sharpened distal end projects distally outwardly and the fluid path is fluidly communicative with the chamber in the barrel. The syringe also has an elongate spring disposed about the stem of the hub that is compressed between the flange and the inwardly projecting shoulder of the receiver to provide a bias. There is a hollow sleeve sized to fit within the receiver over the elongate spring. The sleeve has a distal end disposed at shoulder and a proximal end with a sharpened edge that is disposed in the groove in the distal surface of the flange. When a user applies a sufficient force, a force greater than necessary to expel fluid from the chamber, to the plunger, the hub is sufficiently moved distally in the receiver for the cutting edge of the sleeve to cut through the flange and the closed distal end of the plunger to expose the cavity in the plunger. When the cavity in the plunger is exposed, the bias of the spring urges a sufficient movement of a cut portion of the hub having the needle mounted therein, a cut portion of the distal end of the plunger and the sleeve into the cavity in the plunger to a position wherein an inadvertent exposure of the sharpened distal point is substantially prevented.

[0020] The syringe of the invention has an undeliverable “dead-space” volume substantially similar to conventional syringes, i.e., substantially no undeliverable volume. The syringe of the invention is as suitable for use in drawing, measuring, mixing and delivering small volumes of medicaments as conventional syringes. Unlike many of the devices disclosed above, the syringe of the invention is substantially unlikely to be inadvertently retracted by a user following currently used practices and procedures. The syringe of the invention does not depend on a user having to exercise substantially more care than with a conventional syringe when drawing and mixing fluids in the syringe to avoid inadvertent activation, and importantly, the syringe of the invention is compatible with the efficiency of high volume automated manufacture that utilizes much existing manufacturing equipment. Once needle is retracted in the syringe of the invention, the syringe cannot be restored to functionality, as the hub flange is cut through and the plunger is cut through rendering the syringe substantially unusable and protecting the needle point from inadvertent contact by anyone.

[0021] FIG. 1 is a partially exploded perspective view of the hypodermic syringe of the invention;

[0022] FIG. 2 is a perspective view of the hypodermic syringe of FIG. 1 assembled and sealed in a package;

[0023] FIG. 3 is an exploded perspective view of the hypodermic syringe of FIG. 1;

[0024] FIG. 4 is a schematic cross-sectional view of the hypodermic syringe of FIG. 1 with the plunger partially distally retracted taken on the line 4—4;

[0025] FIG. 4ais an enlargement of a distal portion of the cross-sectional view of FIG. 4;

[0026] FIG. 5 is a schematic cross-sectional view of the hypodermic syringe of FIG. 1 with the plunger at the distal end of the barrel taken on the line 5—5;

[0027] FIG. 5ais an enlargement of the distal portion of the cross-sectional view of FIG. 5;

[0028] FIG. 6 is a schematic cross-sectional view of the hypodermic syringe of FIG. 1 with the plunger moved distally to activate the needle retraction sequence;

[0029] FIG. 6ais an enlargement of the distal portion of the cross-sectional view of FIG. 6;

[0030] FIG. 7 is a cross-sectional view of the hypodermic syringe of FIG. 1 after the needle retraction sequence is completed;

[0031] FIG. 7ais an enlargement of a portion of the cross-sectional view of FIG. 7;

[0032] FIG. 8 is a schematic cross-sectional view of a method of assembly of the hypodermic syringe of FIG. 1;

[0033] FIG. 8ais an enlargement of the distal portion of the cross-sectional view of FIG. 8;

[0034] FIG. 9 is an illustration of an alternate embodiment of a portion of the hypodermic syringe of FIG. 1;

[0035] FIG. 10 is an illustration of an alternate embodiment of another portion of the hypodermic syringe of FIG. 1; and

[0036] FIG. 11 is an illustration of the embodiment of FIG. 10 in a portion of a cross-sectional view, analogous to FIG. 6, of the hypodermic syringe of FIG. 1.

[0037] While this invention is satisfied by embodiments in many different forms, there are shown in the drawings and herein described in detail, embodiments of the invention with the understanding that the present disclosure to be considered as exemplary of the principles of the present invention and is not intended to limit the scope of the invention to the embodiments illustrated. The scope of the invention is measured by the appended claims and the equivalents. In this disclosure, a convention is followed wherein the distal end of the device is the end closest to a patient and the proximal end of the device is the end away from the patient and closest to a practitioner.

[0038] Referring to the FIGS. 1-8a,a hypodermic syringe 10 with a selectively retractable needle 12 of the present invention includes an elongate barrel 14 having an open proximal end 16 and a distal end 18 that defines a receiver 20 with an inwardly projecting shoulder 22. Barrel 14 has a hollow bore 24 therethrough with an inside surface 26 extending from proximal end 16 to distal end 18. Syringe 10 has a hollow elongate plunger 28 with an open proximal end 30 and a closed distal end 32. There is an elongate plug 34 extending distally into hollow plunger 28 from open proximal end 30 forming an enclosed cavity 36 within the plunger. Distal end 32 of plunger 28 forms a slidable seal 38 with inside surface 26 of the barrel to define a chamber 40 for drawing and expelling fluid. Syringe 10 also has an elongate hub 42 having a passageway 44 therethrough, a distally extending stem 46, a proximal flange 48 with an engagement 50 for engaging the barrel, stem 46 being disposed within and sized for slidable movement within receiver 20 at distal end 18 of the barrel, flange 48 having a distal surface 52 having a groove 54 therein and a proximal surface 56 defining chamber 40 in the barrel. Syringe 10 of the invention has elongate needle 12 having a fluid path 60 therethrough, a sharpened distal end 62 and a proximal end 64. Needle 12 is mounted in passageway 44 in hub 42 so that sharpened distal end 62 projects distally outwardly and fluid path 60 is fluidly communicative with chamber 40 in the barrel. Syringe 10 also has an elongate spring 66 disposed about stem 46 of hub 42 that is compressed between flange 48 and inwardly projecting shoulder 22 of receiver 20 to provide a bias. There is a hollow sleeve 68 sized to fit within receiver 20 over elongate spring 66. Sleeve 68 has a distal end 70 disposed at shoulder 22 and a proximal end 72 with a sharpened cutting edge 74 that is disposed in groove 54 in distal surface 52 of the flange. When a user applies a sufficient force, as illustrated in FIGS. 6 and 6a,a force greater than necessary to expel fluid from chamber 40, to plunger 28, hub 42 is sufficiently moved distally in receiver 20 for cutting edge 74 of sleeve 68 to cut through flange 48 and closed distal end 32 of the plunger to expose cavity 36 in the plunger as seen in the Figs. When cavity 36 in the plunger is exposed, the bias of spring 66 urges a sufficient movement of a cut portion 47 of the hub having needle 12 mounted therein, a cut portion 33 of distal end 32 of the plunger and sleeve 68 into cavity 36 in the plunger to a position, best seen in FIGS. 7 and 7a,wherein an inadvertent exposure of sharpened distal point 62 is substantially prevented. Preferably, closed distal end 32 of the plunger includes a projection 35 that is sized and shaped to engage a conjugate taper in flange 48 to hold the flange in position when sharpened end 74 cuts into the flange and the closed distal end of the plunger.

[0039] Referring to FIGS. 3 and 4, slidable seal 38 on plunger 28 is preferably formed by a resilient sealing member 39 that substantially surrounds a portion of plunger 28 adjacent distal end 32 leaving the distal end exposed. Sealing member 39 may be formed from resilient materials such as natural rubber, synthetic rubber, thermoplastic elastomer and combinations. Suitable materials include a separate gasket, one or more “O” rings and the like. Preferably, sealing member 39 is formed from a resilient thermoplastic elastomer that is integrally formed with plunger 28 as a single article of manufacture. Plunger 28 is preferably formed by an injection molding process from thermoplastic materials such as polypropylene, polyethylene, polystyrene, polycarbonate, copolymers of theses materials and the like, with the thermoplastic elastomeric material selected for sealing member 39 being selected as a material that may be successfully co-injected with the material selected for the used to form plunger 28 as a single article of manufacture including sealing member 39.

[0040] Referring now to FIGS. 3-7a,sleeve 68 preferably includes an outward step 67 adjacent proximal end 72. When the needle retraction process is initiated by the user's application of sufficient distal force to plunger 28, best seen in FIGS. 5-6a,outward step 67 serves as a receptacle for cut portion 47 of flange 48, when sharpened edge 74 cuts through flange 48. As further distal force is applied to plunger 28 by the user, cutting edge 74 cuts through distal end 32 of plunger 28 to expose cavity 36 by cutting portion 33 from distal end 32. Once cavity 36 is exposed, spring 66 urges sleeve 68, with cut portions 33 and 47 into cavity 36 thereby withdrawing needle 12 to a position, best seen in FIGS. 7 and 7a,where sharpened distal end 62 is within syringe 10 and substantially protected from inadvertent contact. By containing cut portions 33 and 47 within the receptacle formed by step 67, the reliability of the retraction is facilitated because the contained cut portions are substantially unable to interfere with the movement of sleeve 68 and needle 12.

[0041] Sleeve 68 is preferably formed from a metallic material such as carbon steel, stainless steel and the like. Preferably, sleeve 68 is formed by deep drawing of stainless steel and then subjected to a secondary process such as grinding, honing, polishing, electrochemical processing or combinations of these processes to produce sharpened cutting edge 74 at proximal end 72 of the sleeve. Electrochemical processing after forming is most preferred.

[0042] Referring to FIGS. 4-7a,hollow bore inside surface 26 preferably includes a protuberance 76 thereon for interacting with a conjugate depression 78 on flange 48 to form engagement 50 with protuberance 76. Engagement 50 serves to hold hub 42 in position in the barrel so that needle 12 projects outwardly with spring 66 in compression between flange 48 and shoulder 22 of the receiver.

[0043] Referring now to FIG. 9, an alternate preferred embodiment to the engagement 50 is illustrated. In this embodiment, hollow bore inside surface includes a depression 77 to engage a conjugate protuberance 79 on flange 48. In this alternate embodiment, the conjugates 77 and 79 again engage to retain hub 42 in position within the barrel.

[0044] Returning to FIGS. 3 and 4a,proximal end 16 of barrel 14 further includes a finger grip 80 to facilitate a users grip of the syringe. Additionally, elongate plug 34 is preferably retained in open plunger 28 by an interference fit and includes a finger press 82 with an outside diameter “y”. Finger press 82 is disposed at proximal end 30 of plunger 28 to facilitate the user's movement of plunger 28 to draw and expel fluid from chamber 40 and to apply additional force to the plunger to initiate the retraction of needle 12. Finger grip 80 also includes a collar 84 that preferably has an inner projection 85 with an inside diameter “x” that is less than outside diameter “y” of the finger press. When the force greater than the force required to expel fluid from chamber 40 is applied so that needle 12 is retracted into the syringe barrel, finger press 82 is moved distally past the interference between diameters “x” and “y”, substantially contained within collar 84 and thereby substantially retained in the collar by projection 85. At this point, flange 48 is cut through, plunger distal end 32 is cut through, spring 66 has urged the movement of needle 12 into the syringe and finger press 82 is substantially retained in collar 84 thus rendering syringe 10 substantially non-reusable.

[0045] Referring to FIGS. 10 and 11, an alternate embodiment of plunger 28 and proximal end 16 is illustrated. In this embodiment which may be preferred for particular applications, components having similar function to those in FIGS. 1-8aare shown with the addition of a suffix a. The Figs. show the proximal portion of plunger 28a,analogous to the proximal portion of plunger 28 in FIG. 3 and a proximal portion of barrel 14a,analogous to that shown in FIG. 6. In this embodiment, plunger 28ahas an outside surface 100 that includes a portion 102 having an enlarged diameter disposed proximally. Hollow bore 24aof the barrel has an inside diameter larger than enlarged portion 102 at proximal end 16athan at a distance distally. This enlarged diameter allows plunger 28afreedom to slidably move proximally and distally in the barrel for drawing and expelling fluid from chamber 40. When a sufficient force, greater than the force necessary to expel fluid from chamber 40 is applied to plunger 28aso that the retraction sequence is initiated, as shown in FIGS. 4-6a,enlarged portion 102 engages the inside diameter of hollow bore 24aand substantially prevents further movement of plunger 28athereby retaining plunger 28ain barrel 14a.In this embodiment, plug 34aincludes a thumb press area 82athat fits through an opening in thumb press 83 that is part of plunger 28ato form the thumb press for the plunger. In this embodiment, collar 84aserves only to accept a cap, thumb press area 82aand 83 projects beyond collar 84ato facilitate the user's drawing and expelling fluid from chamber 40 of the barrel.

[0046] Referring back to FIGS. 1 and 2, syringe 10 preferably further includes a removable cap 86 sized to engage an exterior surface of collar 84 and cover finger press 82 of the plunger as well as a removable shield 88 sized to engage receiver 22 and cover distally extending needle 12. Syringe 10 also may be sealed in a package 90 formed from materials substantially resistant to the passage of microorganisms and exposed to conditions that render any microorganisms within substantially non viable. Cap 86 and shield 88 preferably are frangibly attached to collar 84 and receiver 20 respectively. When the cap and shield are frangibly attached, and syringe 10 is exposed to conditions that render microorganisms substantially non-viable, a user can be substantially assured that the syringe is unused and that the fluid path of the syringe is substantially free of microorganisms until the frangible attachments are breached and the cap and shield is removed. Suitable frangible attachments include, but are not limited to heat staking, laser welding, paper or film labels, and the like. Sealed package 90 also serves as a tamper-evidence feature. Suitable materials for forming package 90 include, but are not limited to paper, polymeric film, foil, non-wovens and combinations thereof. Suitable conditions for rendering microorganisms non-viable include, but are not limited to ionizing radiation such as gamma, electron beam and ultra-violet, exposure to chemical agents such as ethylene oxide, gaseous peroxide and the like. When selecting materials for forming syringe 10 and package 90, consideration should be given to the sterilization conditions to ensure that the materials selected are compatible with the sterilization method selected.

[0047] Referring now to FIGS. 8 and 8a,a method for assembling hypodermic syringe 10 includes inserting an assembly pin 92 into distal end 18 of barrel 14 through hollow bore 24 to a position where pin 92 projects beyond proximal end 16 of the barrel. Hub 42 is then acquired by an assembly mandrel 94, preferably with flange 48 being held by a vacuum against mandrel 94 with stem 46 extending distally and axially aligned with assembly pin 92. Pin 92 is preferably shaped to engage stem 46. Sleeve 68 is placed on assembly pin 92 followed by spring 66 and assembly mandrel 94 is advanced so that stem 46 engages assembly pin 92. Assembly mandrel 94 and assembly pin 92 are then distally advanced through hollow bore 24 until spring 66 is compressed between receiver shoulder 22 and flange 48 with engagement 50 being formed between the conjugate protuberance 76 and depression 78 on flange 48. Once engagement 50 is formed, the assembly pin and the assembly mandrel are withdrawn and barrel 14 is ready for further assembly. Needle 12 is mounted in passageway 44 so that distal point 62 projects outwardly. Plunger 28 is then introduced into proximal end 16 of the barrel and advanced distally to complete the assembly of syringe 10 with selectively retractable needle 12.

[0048] Syringe 10 of the invention provides users with a selectively retractable needle syringe that is substantially usable in most normal use techniques. Unlike many of the devices disclosed in the patents referenced above, syringe 10 of the invention is compatible with many current assembly practices and machines, thus is well suited for the high speed, high volume manufacture necessary for commercial success. Additionally, since the retraction mechanism is both simple and positive, syringe 10 may readily be manufactured in small sizes such as a one milliliter capacity with an inside bore diameter of about one quarter inch. The syringe of the invention provides users of conventional small capacity syringes with a selectively retractable alternate that does not appear or function significantly differently from the current devices, thus addressing a need in the medication delivery industry.