PATENT ABSTRACT
A replaceable needle assembly is provided for a retractable syringe comprising a barrel and a plunger, whereby the retractable needle can be replaced by a user without affecting the retraction mechanism. A mounting member is removably mountable to the barrel by way of a screw-thread connection and a needle mount is removably coupled to the mounting member. A needle is mounted to the needle mount. The barrel comprises a needle mount retainer that comprises a plurality of fingers that engage the retractable needle mount to prevent inadvertent retraction. The plunger comprises a collapsible seal which maximizes the efficiency of fluid delivery prior to the plunger engaging the retractable needle mount for retraction. An initially compressed spring decompresses to drive retraction of the plunger and the engaged needle mount. A lock formed between the plunger and barrel prevents further use of the plunger after retraction.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is the U.S. national stage of International Patent Application No. PCT/AU2010/001504, filed Nov. 11, 2010, which claims the benefit of U.S. Provisional Patent Application No. 61/260,253, filed Nov. 11, 2009, the disclosures of which are herein incorporated by reference. 
    
    
     FIELD 
     THIS INVENTION relates to syringes. More particularly, this invention relates to a retractable syringe that includes a replaceable, retractable needle and a plunger capable of engaging the replaceable, retractable needle to facilitate retraction of the needle. 
     BACKGROUND 
     The practice of sharing syringes without adequate sterilization between successive users is a major contributor to the transfer of Human Immunodeficiency Virus (HIV) and Hepatitis C with subsequent severe repercussions for the sufferer and at a high cost to society for supporting and providing medical attention to sufferers. Further problems arise for health professionals administering medicines to infected individuals, where accidental needle stick injury by a used syringe can lead to infection. 
     In response to this problem, syringes have been developed which provide a needle sheathing mechanism and/or a needle retraction mechanism to prevent re-use and/or needle stick injury. 
     However, many such syringes have fixed needles or highly specialized needle assemblies that are not amenable to replacing needles which have been bent or burred or for allowing a user to select alternative needle sizes for filling and injection. 
     SUMMARY 
     The invention is therefore, at least in part, broadly directed to a replaceable needle assembly for a retractable syringe, whereby a retractable needle can be replaced by a user without affecting the retraction mechanism. 
     The invention is also broadly directed to a barrel suitable for mounting the replaceable needle assembly. 
     The invention further provides an improved plunger comprising a plunger seal that improves the efficiency of fluid delivery from a retractable syringe. 
     In a first aspect, the invention provides a replaceable needle assembly for a retractable syringe comprising a plunger and a barrel, said replaceable needle assembly comprising: a mounting member removably mountable to the barrel; a retractable needle mount removably mounted to the mounting member and engageable by said plunger; and a needle mounted to the needle mount. 
     In one embodiment the mounting member comprises a female member which receives a male member of said barrel. 
     Preferably, the mounting member comprises a screw-thread which receives a complementary screw thread of said barrel. 
     In a second aspect, the invention provides a barrel for a retractable syringe to which is removably mountable a replaceable needle assembly. 
     In one embodiment, said barrel comprises a male member receivable by a female member of said replaceable needle assembly. 
     Preferably, said barrel comprises a screw thread receivable by a complementary screw thread of the replaceable needle assembly. 
     In one embodiment, the barrel further comprises a needle mount retainer. 
     Preferably, the releasing member comprises fingers that retain said needle mount until retraction. In one particular embodiment, said fingers are movable radially outwardly to release said needle mount for retraction. 
     In one embodiment, the barrel further comprises a seal. 
     In one embodiment, the barrel further comprises a releasing member. 
     In a third aspect, the invention provides a plunger for a retractable syringe, said plunger comprising: a biasing means; a plunger inner; a plunger outer; and a collapsible seal mounted to the plunger inner; wherein the plunger inner and plunger outer co-operate to maintain said biasing means in an initially energized state prior to retraction. 
     Preferably, said plunger inner comprises a means for engaging a retractable needle mount of said replaceable needle assembly. More preferably, a needle is mounted to the retractable needle mount. 
     In a particular embodiment, said means for engaging the retractable needle mount comprises one or more barbed arms. 
     In a preferred embodiment, the plunger inner further comprises a trigger which initially engages said plunger outer to retain said biasing means in an initially energized state prior to retraction. Preferably, disengagement of said trigger from said plunger outer facilitates release of energy from said biasing means which facilitates retraction of said needle mount when coupled to said plunger inner. 
     Suitably, said biasing member is any device which can store energy in a releasable form, such as a spring, elastic or the like. 
     Preferably, said biasing means is a spring. 
     In one embodiment, the collapsible seal comprises an internal hollow chamber. 
     In a fourth aspect, the invention provides a retractable syringe kit comprising the barrel of the second aspect and the plunger of the third aspect in combination; and a plurality of replaceable needle assemblies according to the first aspect. 
     In one embodiment of the retractable syringe kit, the plurality of replaceable needle assemblies respectively comprise a 0.5 inch needle, a 1.0 inch needle and a 1.5 inch needle. 
     In a fifth aspect, the invention provides a retractable syringe comprising: the replaceable needle assembly of the first aspect removably mounted to the barrel of the second aspect; and/or the plunger of the third aspect. 
     In one embodiment, the retractable syringe further comprises a lock formed between said plunger outer and said barrel which prevents or hinders removal of the plunger outer from the barrel after retraction of the retractable needle mount. 
     In a sixth aspect, the invention provides a method of operating a retractable syringe including the step of removably mounting a replaceable needle assembly to a barrel of a retractable syringe after filling the barrel with fluid contents for subsequent delivery. 
     In one embodiment, the method includes the step of screw-threadedly mounting the replaceable needle assembly to the barrel. 
     Throughout this specification, unless otherwise indicated, “comprise”, “comprises” and “comprising” are used inclusively rather than exclusively, so that a stated integer or group of integers may include one or more other non-stated integers or groups of integers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting embodiments of the invention are described herein with reference to the following drawings wherein: 
         FIG. 1  is a sectional view of an embodiment of a retractable syringe; 
         FIG. 2  is a sectional view of an embodiment of a plunger; 
         FIG. 3  is a sectional view of an embodiment of a replaceable needle assembly mounted on a barrel; 
         FIG. 4  is a sectional view of an embodiment of a retractable syringe during filling with fluid contents; 
         FIG. 5A  is a sectional view of an embodiment of a barrel after filling with fluid contents and after removal of a replaceable needle assembly; and  FIG. 5B  is a sectional view showing the same embodiment where the replaceable needle assembly has been replaced by another replaceable needle assembly mounted to the barrel mounting member; 
         FIG. 6  is a sectional view of a plunger inner engaging a needle mount prior to needle retraction; 
         FIG. 7  is shows an embodiment of a retractable syringe lock formed between plunger outer and barrel and release of plunger inner from plunger outer; 
         FIG. 8A  is a perspective view of a plunger outer comprising hooked teeth and  FIG. 8B  is a sectional view of an embodiment of a retractable syringe during needle retraction; 
         FIG. 9  is a sectional view of another embodiment of a retractable syringe; and 
         FIG. 10  is a sectional view of another embodiment of a plunger. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an embodiment of syringe  10  comprises barrel  11  and plunger  20  having plunger inner  50  and plunger outer  21 . Plunger seal  80  is mounted to plunger inner  50 . Plunger  20  is slidably, axially moveable within barrel  11  with plunger seal  80  forming a fluid-tight seal against inside wall  18  of barrel  11  and against plunger inner  50 . Replaceable needle assembly  30  comprises needle  31  that comprises cannula  32  and needle body  33  mounted to retractable needle mount  34  and mounting member  40 . Barrel  11  comprises plunger end  12  at which is located releasing member  13 , locking pawls  17 A,  17 B and finger grips  14 A,  14 B. Barrel  11  also comprises mounting portion  105  comprising “male” screw thread  1051  at needle end  15  onto which can be mounted complementary “female” screw thread  41  of mounting member  40  of replaceable needle assembly  30 . It will also be appreciated that this male-female orientation may be reversed. Barrel seal  42  is also mounted at needle end  15  of barrel  11  to provide a seal between mounting member  40  and barrel  11 . Barrel  11  further comprises needle mount retainer  60  at needle end  15  and fluid space  19 . Needle cover  95  is also shown, which is removed in use. 
     Referring now to  FIG. 2 , plunger  20  comprises plunger outer  21  comprising body  22 , inner shoulder  23  and flange  24  having inner lip  25 , rim  26  and button recess  27 . Plunger inner  50  further comprises needle mount-engaging portion  51  that comprises needle mount release in the form of head  52  and arms  53 A,  53 B that respectively comprise barbs  54 A,  54 B. Plunger inner  50  further comprises abutment  55 , inner ledge  56 , button  57  operable by a user and trigger  58  comprising notch  59 . Initially, notch  59  of trigger  58  engages inner lip  25  of plunger outer  21  to retain spring  70  in an initially compressed state, compressed between inner shoulder  23  of plunger outer  21  and inner ledge  56  of plunger inner  50 . In this context, “initially compressed” means that spring  70  is compressed (i.e. energized) prior to use of retractable syringe  10 . 
     Plunger seal  80  is mounted to plunger inner  50  and located between head  52  and abutment  55 . Plunger seal  80  is collapsible or otherwise compressible or axially deformable by way of internally-located hollow chamber  81  and further comprises sealing ribs  82 A,  82 B which seals against inside wall  18  of barrel to prevent fluid leaking from fluid space  19 . 
     As shown in  FIG. 3 , replaceable needle assembly  30  comprises needle  31  that comprises cannula  32  and needle body  33  mounted to retractable needle mount  34  comprising annular base  35 . Cannula  32  is glued to, or co-moulded with, needle body  33 . Needle body  33  is glued to, interference fitted into, or co-moulded with, retractable needle mount  34 . Needle mount retainer  60  comprises bore  61  and fingers  62 A,  62 B that bear against annular base  35  of needle mount  34  to prevent inadvertent axial movement of needle  31  and retractable needle mount  34  toward plunger end  12  of barrel  11 . This could occur, for example, when a user applies a force to cannula  32  such as when piercing skin during injection. 
     Referring now to  FIG. 4 , fluid space  19  of barrel  11  is filled with fluid contents by a user by moving plunger  20  axially away from needle end  15  of barrel  11 . Optionally, particularly in the case of viscous fluid, the user may choose to fill barrel  11  using needle  31  having a larger cannula  32  and then replace needle  31  with a needle  31  having a smaller cannula  32  for injection. As is evident in  FIGS. 5A and 5B , replaceable needle assembly  30  may be unscrewed from barrel  11  and another needle assembly  30  (e.g. with a needle  31  having a smaller cannula  32  or to replace a bent or burred cannula  32 ) screwed onto barrel  11 , as indicated by the curved arrow in  FIG. 5A . 
     Referring to  FIG. 6 , to deliver fluid contents of syringe  10 , plunger  20  is moved axially by the user in the direction of the hatched arrow toward needle end  15  of barrel  11 . Towards the end of plunger  20  depression, collapsible seal  80  “bottoms out”, but continued movement of plunger  20  in the direction of the hatched arrow in  FIG. 6  is allowed by compression of seal  80 . This continued axial movement of plunger  20  and collapsible seal  80  facilitates “squeezing out” remaining fluid to thereby assist delivery of the last remaining fluid contents of syringe  10 . As evident in  FIG. 6 , this continued axial movement of plunger  20  allows arms  53 A,  53 B of needle mount engaging portion  51  to enter bore  61  in needle retainer  60 , followed by head  52 , until barbs  54 A,  54 B engage base rim  35  of needle mount  34 . Head  52  acts to move fingers  62 A,  62 B of needle mount retainer  60  radially outwardly in the direction of the solid arrows in  FIG. 6  out of contact with annular base  35  of retractable needle mount  34 , thereby forming an unobstructed passageway in bore  61  of retainer  60 , through which retractable needle mount  34  can be retracted. 
     Reference is now made to  FIG. 7 ,  FIG. 8A  and  FIG. 8B . At the end of plunger  20  depression to deliver fluid contents of syringe  10  when needle mount engaging portion  51  of plunger inner  50  and needle mount  34  are coupled, a releasing member in the form of release ring  13  bears against trigger  58  of plunger inner  50 , thereby moving trigger  58  radially inwardly in the direction of the solid arrow in  FIG. 7 . This disengages notch  59  from inner lip  25  of plunger outer  21 , which thereby triggers release of plunger inner  50  from plunger outer  21  and allowing compressed spring  70  to decompress and forcibly bear against inner ledge  56  of plunger inner  50  to thereby retract plunger inner  50  and needle mount  34  coupled to needle mount engaging portion  51  of plunger inner  50 . As best seen in  FIG. 8A , plunger outer  21  comprises one or more locking elements in the form of hooked teeth  28 A,  28 B in underside of flange  24 . As best seen in  FIG. 8B , at the end of plunger  20  depression and before plunger inner  50  retraction, hooked teeth  28 A,  28 B of plunger outer  21  form lock  90  with one or more locking elements  17  of barrel  11 , in the form of locking pawls  17 A,  17 B located at plunger end  12  of barrel  11 , to thereby prevent withdrawal of plunger outer  21  from barrel  11 . This also effectively prevents removal of plunger inner  50 . In this regard, axial travel of retracting plunger inner  50  is limited by seal  80  bearing against locked plunger outer  21 , so that plunger inner  50  and decompressed spring  70  cannot be removed from barrel  11 . 
     As also shown in  FIG. 8B , following retraction of plunger inner  50 , needle mount  34 , needle body  33  and cannula  32  are retracted into barrel  11  while retainer  60 , mounting member  40  and barrel seal  42  remain at needle end  15  of barrel  11 . 
     It will be appreciated from the foregoing that syringe  10  is arranged so that disengagement of plunger inner  50  from plunger outer  21  to allow decompression of spring  70  occurs only when fluid contents have been delivered and after needle mount engaging means  51  and needle mount  34  are coupled. This prevents inadvertent triggering of the retraction mechanism and ensures that needle mount  34  and needle  31  mounted thereto are retracted when the retraction mechanism is triggered. 
     The embodiment described in  FIGS. 1-8  is particularly suited to a 3 mL or 5 mL capacity syringe  10 . 
     Reference is now made to  FIGS. 9 and 10  which describe a related embodiment particularly suited to a 1 mL capacity syringe  110  comprising barrel  111  and plunger  120  having plunger inner  150  and plunger outer  121 . Plunger seal  180  is mounted to plunger inner  150 . Replaceable needle assembly  130  comprises needle  131  that comprises cannula  132  and needle body  133  mounted to retractable needle mount  134  and mounting member  140 . Barrel  111  comprises plunger end  112  which comprises flared portion  900  which accommodates body  122  of plunger outer  121  and comprises inner waist  901  that limits axial travel of plunger  120  when delivering fluid contents of syringe  110 . Plunger end  112  of barrel further comprises releasing member  113 , locking pawls  117 A,  117 B and finger grips  114 A,  114 B. 
     Barrel  111  also comprises mounting portion  1105  comprising “male” screw thread  11051  at needle end  115  onto which can be mounted complementary “female” screw thread  141  of mounting member  140 . Seal  142  is also mounted at needle end  115  of barrel  111  to provide a fluid-tight seal between mounting member  140  and barrel  111 . Barrel further comprises needle mount retainer  160  at needle end  115 . Needle cover  195  is also shown, which is removed in use. 
     Referring particularly to  FIG. 10 , plunger  120  comprises plunger outer  121  comprising body  122 , inner shoulder  123  and flange  124  having inner lip  125 , rim  126  and button recess  127 . Plunger inner  150  further comprises needle mount engaging portion  151  that comprises head  152  and arms  153 A,  153 B that respectively comprise barbs  154 A,  154 B. Plunger inner  150  further comprises abutment  155 , inner ledge  156 , button  157  operable by a user and trigger  158  comprising notch  159 . Initially, notch  159  of trigger  158  engages inner lip  125  of plunger outer  121  to retain spring  170  in an initially compressed state, compressed between inner shoulder  123  of plunger outer  121  and inner ledge  156  of plunger inner  150 . 
     Plunger seal  180  is mounted to plunger inner  150  and is located between head  152  and abutment  155 . Plunger seal  180  is collapsible or otherwise compressible or axially deformable by way of internally-located hollow chamber  181  and further comprises sealing ribs  182 A,  182 B which seal against inside wall  118  of barrel to prevent fluid leaking from fluid space  119  of barrel  111 . Seal  180  shown in  FIGS. 9  and  10  is relatively elongate in structure compared to seal  80  shown in  FIGS. 1-8  given the relatively narrower internal diameter of barrel  111  of 1 mL syringe. 
     Needle mount  134  engagement and retraction by plunger inner  150  is essentially as described for the syringe  10  embodiment described in  FIGS. 1-8 . Similarly, lockdown of plunger outer  121  onto barrel  111  is also as described in  FIGS. 1-8 . Although not shown in  FIG. 9  or  10 , hooked teeth  128 A,  128 B of plunger outer  121  form lock  190  with locking pawls  117 A,  117 B located at plunger end  112  of barrel  111 , to thereby prevent withdrawal of plunger outer  121  from barrel  111 . 
     In light of the foregoing it will be appreciated that the present invention provides a relatively simple, robust and inexpensive syringe that is automatically disabled with little or no assistance from the user to thereby prevent, or at least minimize the likelihood of, re-use of the syringe or needle-stick injury to the user. 
     Furthermore, the replaceable needle assembly allows a user to select a needle of appropriate size of gauge or needle length and/or to replace a needle that becomes bent or burred. Another advantage of the retractable syringe described herein is that it can accommodate and fully encapsulate on retraction, needles of varying length up to 1.5 inches (˜3.8 cm) in length, thereby providing great flexibility to the user. 
     It will also be appreciated that the collapsible plunger seal improves the efficiency of fluid delivery from the retractable syringe. 
     Throughout the specification, the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention. 
     The disclosure of each patent and scientific document, computer program and algorithm referred to in this specification is incorporated by reference in its entirety.