Abstract:
A disposable hypodermic syringe, which is provided with the needle fitted and sheathed, provides automatic retraction of the needle after use. The syringe may be supplied pre-charged with an injectant. The completion of the injection stroke attaches the piston to the needle carrier and subsequently dislodges a retaining ring thereby freeing the piston from the plunger and releasing stored energy of a spring or the like to draw the piston and needle carrier into the plunger. The plunger is positively retained inside the housing by the interaction of rings. Alternative methods of locating the needle carrier during use and of attaching the piston to the needle carrier to enable retraction are shown. An alternative method of retaining the piston on the plunger is also shown. A further configuration is shown affording the use of an offset needle. The syringe has optional features to prevent unwanted inward movement of the plunger and to prevent seepage of liquid after use.

Description:
This application is the U.S. national phase of International Patent Application No. PCT/GB99/03170, filed Sep. 22, 1999, which designated the U.S. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to hypodermic syringes. 
     In the often high pressure conditions of medical work, the accidental puncture or scratch with a needle, commonly known as a needlestick injury, and consequent risk of infection with, for example, HIV or hepatitis is becoming increasingly hazardous to the profession and potentially more costly to health authorities. 
     Detailed statistics of needlestick injuries are not generally published in the UK but in the USA such information is more readily available. In 1994 there were some 800,000 cases reported of which 16,000 involved infection with HIV. It is estimated that in the USA, these injuries cost, excluding legal or insurance expenses, $1.8 billion pa. 
     The requirements for a syringe that will prevent needlestick injuries were analysed and listed as follows: 
     1. Reliability and ease of use. 
     2. Automatic and complete retraction of the needle after injection. 
     3. The capability to retract a needle bent intentionally or accidentally. 
     4. Re-exposure of the needle is impossible. 
     5. Suitable for production in larger sizes with an offset needle. 
     6. Supplied with needle fitted and sheathed. 
     7. Suitable for supply charged with an injectant. 
     8. Prevention of accidental needle retraction. 
     9. Low production costs. 
     10. Firm and compact for safe disposal. 
     The urgent need to address this problem has been widely acknowledged and many relevant designs tabled. One such design is known from U.S. Pat. No. 5,211,628 and this document discloses a hypodermic syringe including a housing, a plunger, a needle carrier with a needle mounted thereto positionable during assembly of the syringe within the housing with the needle extending therefrom, a sheath mounted to the needle carrier and surrounding the needle, and stored energy means, the plunger and stored energy means being configured such that when the syringe is used and the plunger reaches the needle carrier, it becomes attached thereto and the stored energy in the stored energy means is released to retract the needle carrier and the needle into the housing. 
     Similar hypodermic syringes having means for retracting the needle into the plunger after use are known from U.S. Pat. No. 5,324,265, EP-A-0505330 and WO91/03269A. 
     It is also known from U.S. Pat. No. 5,211,628 to provide a method of assembling a hypodermic syringe that includes the steps of mounting a needle to the needle carrier and positioning the needle carrier in the housing such that the needle extends therefrom. 
     SUMMARY OF THE INVENTION 
     A hypodermic syringe according to the present invention is provided with a housing configured such that a needle carrier with the needle mounted thereto is positionable during assembly of the syringe within the housing with the needle pre-sheathed. 
     In a preferred embodiment, the plunger comprises a casing and a piston located and movable within the casing. 
     Preferably, the stored energy means is a spring co-operating between the piston and the casing and has a releasable retaining means to release stored energy within the spring. 
     A method of assembling a hypodermic syringe according to the present invention includes the step of mounting a sheath to the needle carrier over the needle before positioning the needle carrier in the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described, by way of example only and with reference to the accompanying drawings, in which: 
     FIG. 1 illustrates a cross-section side elevation of a syringe according to the invention with the plunger about to engage the needle carrier; 
     FIG. 1A is an enlarged view of a portion of FIG. 1; 
     FIG. 2 illustrates the syringe shown in FIG. 1 after retraction of the needle carrier; 
     FIG. 3 illustrates a second embodiment of the syringe according to the invention in which the plunger is about to engage the needle carrier; 
     FIG. 4 illustrates a third embodiment of the syringe in which the plunger is about to engage the needle carrier; 
     FIG. 5 illustrates a fourth embodiment of the syringe in which the plunger is about to engage the needle carrier; 
     FIG. 6 illustrates a fifth embodiment of the syringe in which the plunger is about to engage the needle carrier; 
     FIG. 7 illustrates a sixth embodiment of the syringe having a needle offset from the longitudinal axis of the syringe and in which the plunger is about to engage the needle carrier; 
     FIG. 8 illustrates a plunger stop for attachment to an exposed length of the plunger; and 
     FIG. 9 illustrates an anti-drip cap for attachment to the syringe nose. 
     The principal components referred to in the following description are: 
     
       
         
               
               
             
               
               
             
           
               
                   
               
               
                 Reference No. 
                 Component Title 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Housing 
               
               
                 2. 
                 Plunger 
               
               
                 3. 
                 Piston 
               
               
                 4. 
                 Spring 
               
               
                 5. 
                 ‘O’ seal (piston) 
               
               
                 6. 
                 Retaining ring 
               
               
                 7. 
                 Plunger closure piece 
               
               
                 8. 
                 Needle carrier 
               
               
                 9. 
                 ‘O’ seal (needle) 
               
               
                 10. 
                 Plunger stop 
               
               
                 11. 
                 Drip stop 
               
               
                   
               
             
          
         
       
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 and 1A show a typical construction of the syringe. The cylindrical housing ( 1 ), graduated as required, carries a flange ( 1 . 1 ) and the open end of the bore has a tapered entry with a locally reduced diameter forming a wedge section ring ( 1 . 2 ). 
     At the distal end of the housing the diameter is reduced to form a nose ( 1 . 3 ). An internal lip ( 1 . 4 ) is formed at the point where the nose ( 1 . 3 ) meets the main body of the housing ( 1 ). The distal end of the nose ( 1 . 3 ) is partly closed leaving an aperture ( 1 . 5 ). 
     The plunger ( 2 ) has on its outer surface a flange ( 2 . 1 ) and two wedge section rings ( 2 . 2 ) and ( 2 . 3 ). 
     On the inner surface of the plunger ( 2 ) at the flanged end is a tapered entry and a locally reduced diameter forming a wedge section ring ( 2 . 4 ). 
     At the distal end of the plunger ( 2 ) is an inward facing flange ( 2 . 5 ). 
     The piston ( 3 ) has an outward facing flange ( 3 . 1 ). The principal diameter of the piston is reduced locally forming a triangular section ring ( 3 . 2 ). The close end of the piston terminates in a head ( 3 . 3 ). The shoulder ( 3 . 4 ) of the piston is grooved to form a fluid bypass ( 3 . 5 ). 
     The spring ( 4 ) is held in compression between flanges ( 2 . 5 ) and ( 3 . 1 ). 
     The ‘O’ seal ( 5 ) is held between the retaining ring ( 6 ) and the flange ( 2 . 5 ). The retaining ring ( 6 ) is dislodgeably held in place by the triangular section ring ( 3 . 2 ). 
     The plunger closure piece ( 7 ) has a locally reduced diameter ( 7 . 1 ) and is irreversibly retained by the wedge section ring ( 2 . 4 ) of the plunger ( 2 ). An orifice ( 7 . 2 ) is provided in the plunger closure piece. 
     The needle carrier ( 8 ) incorporates a needle ( 8 . 1 ) and a flange ( 8 . 2 ) on which are claw ended arms ( 8 . 3 ). The inwardly sprung arms ( 8 . 3 ) are held in engagement with the lip ( 1 . 4 ) by a spring ring ( 8 . 4 ). 
     The ‘O’ seal ( 9 ) is located and held in place by the flange. 
     The needle protective sheath ( 8 . 5 ) is mounted on the needle carrier ( 8 ) and is of a lesser diameter than the aperture ( 1 . 5 ). The end cap ( 8 . 6 ) fits over the needle protective sheath ( 8 . 5 ) to form an air-tight seal and is of a larger diameter than the aperture ( 1 . 5 ). 
     FIGS. 3,  4  and  5  show alternative constructions of the needle retention and pick up means. 
     FIG. 3 shows a needle carrier ( 8 ) which has a cup ( 8 . 7 ) displaced from the centre line and lodged behind the lip ( 1 . 4 ). The open end of the cup has a retaining lip ( 8 . 8 ). An ‘O’ seal ( 9 . 1 ) is located in the needle carrier ( 8 ). The piston ( 3 ) has a fluid bypass ( 3 . 5 ). The piston head ( 3 . 3 ) has a fluid passage ( 3 . 6 ). 
     FIG. 4 shows a needle carrier ( 8 ) in which the cup ( 8 . 7 ) is in firm ring contact with the cylindrical portion of the nose ( 1 . 3 ). No separate seal is used. The closed end of the cup is dished ( 8 . 9 ). The open end of the cup has a retaining lip ( 8 . 8 ). The piston ( 3 ) has a fluid bypass ( 3 . 5 ). The piston head ( 3 . 3 ) has a fluid passage ( 3 . 6 ). 
     FIG. 5 shows a needle carrier ( 8 ) with outwardly sprung arms ( 8 . 10 ). The arms have claw ends ( 8 . 11 ) and catches ( 8 . 12 ) that engage with an internal lip ( 1 . 6 ). A flange ( 8 . 13 ) abuts an internal shoulder ( 1 . 7 ) of the nose ( 1 . 3 ). An ‘O’ seal ( 9 . 1 ) is located in the needle carrier. The piston ( 3 ) has a cup end ( 3 . 7 ) with an inwardly facing lip ( 3 . 8 ) and a fluid passage ( 3 . 9 ). 
     FIG. 6 shows a construction with an alternative co-action between the plunger ( 2 ) and the piston ( 3 ). The plunger  2  provides a sealing surface ( 2 . 6 ) and a face ( 2 . 7 ) that locates the spring ( 4 ). The plunger head ( 2 . 8 ) has an inward facing lip ( 2 . 9 ) which lodges against the triangular section ring ( 3 . 2 ). 
     FIG. 7 shows a typical construction in which the needle ( 8 . 1 ) is offset from the centre line. The housing ( 1 ) has a nose ( 1 . 3 ) of reduced diameter with an aperture ( 1 . 5 ) through the end wall. 
     The needle carrier ( 8 ) has the needle ( 8 . 1 ) eccentrically positioned and aligned with the aperture ( 1 . 5 ). The flange ( 8 . 14 ) has a reduced diameter which carries the ‘O’ seal ring ( 9 . 2 ) and the claw ended arms ( 8 . 3 ) which are held in engagement with the lip ( 1 . 4 ) by a spring ring ( 8 . 15 ) which has a recess ( 8 . 16 ) and one or more cut-outs ( 8 . 17 ). 
     The piston ( 3 ) has a triangular section annular ridge ( 3 . 2 ) on the outer cylindrical surface. The piston ( 3 ) terminates in a head ( 3 . 3 ). 
     A sprung anchor ( 3 . 10 ) is fitted inside the piston ( 3 ). A separate anchor ( 7 . 3 ) is attached to the plunger closure piece ( 7 ). The spring ( 4 . 1 ) is attached at both ends to the anchors ( 3 . 10 ) and ( 7 . 3 ). 
     The plunger has a sealing surface ( 2 . 6 ) and the plunger head ( 2 . 8 ) has an inward facing lip ( 2 . 9 ). The inward lip ( 2 . 9 ) lodges against the triangular section annular ridge ( 3 . 2 ) thereby holding the spring ( 4 . 1 ) in tension. 
     FIG. 8 shows a plunger stop ( 10 ) with suitably radiused members ( 10 . 1 ) to fit over the exposed length of the plunger ( 2 ) between the flanges ( 1 . 1 ) and ( 2 . 1 ) as shown in FIG.  1 . The length of the stop will be dependent upon whether it is being used to prevent accidental needle retraction before use or to prevent accidental discharge of pre-loaded injectant. The members are capable of having a label ( 10 . 2 ) attached. 
     FIG. 9 shows an anti-drip cap ( 11 ) designed to fit over the syringe nose ( 1 . 3 ) (shown in FIG.  1 ). The substantially flat end is split to form segments ( 11 . 1 ) which are flexible to allow the passage of the needle sheath ( 8 . 5 ) (shown in FIG. 1) during assembly and also to re-close after needle retraction. A similar cap may be provided un-segmented when capping after needle retraction is required. 
     Operation of the syringe follows the established practice for disposable syringes. When the operator is charging the syringe, over extension of the plunger ( 2 ) is prevented by the interaction of the rings ( 1 . 2 ) and ( 2 . 3 ). On completion of the injection stroke, automatic needle retraction is triggered by continued pressure on the plunger. Description of this operation follows and is with reference to FIGS. 1 and 2. 
     When the piston shoulder ( 3 . 4 ) meets the end wall of the housing ( 1 ), the piston head ( 3 . 3 ) has entered between the clawed arms ( 8 . 3 ) of the needle carrier ( 8 ) and displaced the spring ring ( 8 . 4 ), allowing the clawed arms ( 8 . 3 ) to snap onto the piston head ( 3 . 3 ) providing positive attachment with some angular freedom to ensure positive needle retraction. The fluid bypass ( 3 . 5 ) ensures freedom from fluid lock. 
     Further pressure on the plunger ( 2 ) against the now stationary piston ( 3 ), dislodges the retaining ring ( 6 ), freeing the spring ( 4 ) to snap the needle carrier ( 8 ) into the plunger ( 2 ) and to retain it therein. 
     FIG. 2 shows the syringe after needle retraction. As shown, the ‘O’ seals ( 9 ) and ( 5 ) and the retaining ring ( 6 ) remain at the nose end ( 1 . 3 ) of the housing ( 1 ), ensuring minimum friction during needle retraction. Release path for air is afforded by the plunger closure piece orifice ( 7 . 2 ). During the injection stroke the wedge section ring ( 2 . 2 ) snaps past the co-acting wedge ring ( 1 . 2 ) thereby preventing re-extension of the plunger. 
     The optional un-segmented end cap is, if required, now fitted over the nose ( 1 . 3 ). 
     Operation of a syringe containing an alternative construction of the needle carrier as described with reference to FIGS. 3,  4  and  5 , is essentially as outlined with reference to FIGS. 1 and 2. 
     FIG. 3 shows a revised needle carrier ( 8 ) of resilient material with a cup ( 8 . 7 ) displaced from the centre line of the syringe so as to latch behind the lip ( 1 . 4 ) during assembly. Near the end of the injection stroke the piston head ( 3 . 3 ) centralises the cup ( 8 . 7 ) which snaps behind the retaining lip ( 8 . 8 ) disengaging the cup ( 8 . 7 ) from the lip ( 1 . 4 ). The fluid bypass ( 3 . 5 ) and the fluid passage ( 3 . 6 ) ensure freedom from fluid lock. Needle retraction follows the sequence described with reference to FIGS. 1 and 2 except that the needle seal ( 9 . 1 ) remains in the needle carrier ( 8 ). 
     FIG. 4 shows a needle carrier ( 8 ) of resilient material with a cup ( 8 . 7 ) in firm ring contact with a cylindrical section of the nose ( 1 . 3 ) obviating the need for a seal. During operation any end load on the needle tends to flatten the dished area ( 8 . 9 ) increasing the radial load against the cylindrical portion of the nose ( 1 . 3 ), preventing axial movement and making additional locking unnecessary. At the end of the injection stroke, when the piston head ( 3 . 3 ) enters the cup ( 8 . 7 ) it is retained by the lip ( 8 . 8 ). Subsequent pull on the cup during needle retraction tends to elongate the cup, reducing its radial pressure against the nose ( 1 . 3 ) allowing free movement. The fluid bypass ( 3 . 5 ) and the fluid passage ( 3 . 6 ) ensure freedom from fluid lock. Needle retraction follows the sequence as described with reference to FIGS. 1 and 2 except for the absence of the ‘O’ seal ( 9 ). 
     FIG. 5 shows a needle carrier ( 8 ) with outwardly sprung arms ( 8 . 10 ) with catches ( 8 . 12 ) such that on insertion into the housing ( 1 ), the catches ( 8 . 12 ) snap behind the lip ( 1 . 6 ) to lock the needle carrier ( 8 ) in position. 
     Towards the end of the injection stroke the piston cup end ( 3 . 7 ) passes over claw ends ( 8 . 11 ) closing the arms ( 8 . 10 ) and disengaging the catches ( 8 . 12 ) from the lip ( 1 . 6 ) and connecting the claw ends ( 8 . 11 ) to the lip ( 3 . 8 ) of the piston cup end ( 3 . 7 ). The fluid passage ( 3 . 9 ) ensures freedom from fluid lock. Needle retraction follows the sequence described with reference to FIGS. 1 and 2 except that the seal ( 9 . 1 ) is retained in the needle carrier ( 8 ). 
     FIG. 6 depicts an alternative construction of the plunger seal and the dislodgeable retaining means for the piston. 
     In this construction the plunger ( 2 ) has a head ( 2 . 8 ) of sufficient resilience to effect a dynamic seal ( 2 . 6 ) against the inner surface of the housing ( 1 ). The head ( 2 . 8 ) has an inward facing lip ( 2 . 9 ) which co-acts with triangular section ring ( 3 . 2 ) of the piston ( 3 ) to effect a seal between the plunger ( 2 ) and the piston ( 3 ). 
     The spring ( 4 ) is compressed and retained between faces ( 2 . 7 ) and ( 3 . 1 ) by the reversible snap co-action of the triangular section ring ( 3 . 2 ) and the inward facing lip ( 2 . 9 ) of the plunger ( 2 ). At the completion of the injection stroke the inward facing lip ( 2 . 9 ) snaps past the triangular section ring ( 3 . 2 ) releasing the spring to effect needle retraction. 
     Needle retraction follows the sequence described with reference to FIGS. 1 and 2 except for the absence of the ‘O’ seal ( 5 ). 
     FIG. 7 shows an adaptation of the invention in which the needle is offset from the centre line of the syringe in order to meet the operational requirements of larger capacity syringes. 
     To allow the maximum eccentricity of the needle ( 8 . 1 ), extra space has been obtained by replacing the compression spring of the standard models with a tension spring ( 4 . 1 ). 
     Operation follows the usual procedure. Towards the end of the injection stroke the piston head ( 3 . 3 ) displaces the spring ring ( 8 . 15 ), allowing the claw ended arms ( 8 . 3 ) to snap onto the piston head ( 3 . 3 ). 
     To ensure continuous free fluid flow the spring ring ( 8 . 15 ) is recessed at ( 8 . 16 ) and cut away at one or more points ( 8 . 17 ). 
     When the piston ( 3 ) bottoms at the end of the stroke, continued pressure on the plunger ( 2 ) causes the inward facing lip ( 2 . 9 ) to override the triangular section ring ( 3 . 2 ), allowing the spring ( 4 . 1 ) to effect needle retraction. 
     Needle retraction generally follows the sequence as described with reference to FIGS. 1 and 2.