Abstract:
A syringe ( 10 ) comprises a barrel ( 12 ) having an open first end ( 16 ) and a second end ( 18 ) having an opening ( 20 ) for passage of fluid therethrough. Furthermore, the syringe comprises a plunger ( 14 ) adapted to be slidably received in the first end and which has a shaft ( 24 ), and a head ( 26 ) for sliding and sealing engagement with an internal wall of the barrel. In addition, at least one locking member ( 30 ) engages the barrel and the shaft, having at least one first tine ( 32 ) for selectively engaging the plunger and at least one second tine ( 34 ) for selectively engaging an internal wall of the barrel. At least one locking member is adapted to restrict outward movement of the plunger relative to the barrel, but has sufficient flexibility to allow limited outward movement of the plunger relative to the barrel, subsequent to inward movement of the plunger following outward movement of the plunger relative to the barrel.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to single use syringes and relates particularly to syringes which are adapted to prevent or at least hinder further use. 
       BACKGROUND OF THE INVENTION 
       [0002]    Disposable syringes are known in which a cylindrical barrel formed of transparent plastic material receives a piston, which is slidable within the barrel. A shaft, which may be of cruciform or other, e.g. circular, cross section extends from the piston to a plunger handle for enabling the piston to be displaced along the barrel in a first direction to cause injectable fluid, e.g. medicament or body fluid like blood, to be drawn into the barrel via an aperture at one end of the barrel, or in a second direction to cause the fluid to be expelled out of the aperture or to be injected into a patient via a needle. 
         [0003]    Syringes of this type are generally sold as disposable items and are intended to be used only once to negate the risk of transmission of diseases between patients. However, such syringes suffer from the drawback that it is difficult to prevent such syringes from being re-used, which increases the risk of transmission of infection. 
         [0004]    Numerous designs have been proposed for syringes, which are intended to negate or reduce the risk of the syringe being re-used. However, there are considerable challenges involved in designing a syringe that meets the following requirements:
       (i) allowing aspiration or flashback of blood to check for correct location of the needle in a patient;   (ii) ability to deliver variable doses;   (iii) smooth operation;   (iv) simplicity of manufacture and use;   (v) ability to inject diluents (e.g. sterile water) into a vial of powdered/lyophilised drug, and/or allow agitation of vial or syringe content to assist powdered drug to go into solution.       
 
         [0010]    EP0925083B1, for example, discloses a single-use syringe comprising a barrel with an internal annular groove at the proximal end and a further annular groove near the distal end but spaced from it. The plunger is formed with an integrally moulded barb-like flange adjacent the head, which flange bears resiliently against the barrel interior wall. The flange is able to move unrestricted in either direction along most of the barrel interior wall. However, the flange is only able to pass the annular grooves in one direction. The syringe is supplied with the plunger not fully depressed, so that the restrictor flange is on one side of one of the two grooves, facing the other groove. Liquid may be drawn up into the syringe until the flange encounters the other groove, which prevents the plunger being withdrawn completely from the barrel. Liquid may be discharged freely from the syringe by depressing the plunger fully into the barrel. In this position, the plunger is now prevented from being withdrawn again because the flange will not pass the grooves in the barrel. 
         [0011]    This design suffers from a number of drawbacks. For example, there is often a slight jolt as the flange passes one of the grooves when an injection is being given, and this jolt is likely to be felt by a patient. Furthermore, because of the unrestricted movement of the plunger between the two grooves, the syringe could potentially be used again and again provided the plunger is never fully depressed. After unpacking a syringe, it is normal to cycle the plunger over a short distance to check that the plunger is free to move and, if it is not, to free it. There can sometimes be a degree of adhesion between the plunger head and the barrel due to the length of time of storage, or due to the effects of gamma sterilisation. This is particularly the case with plunger heads having silicone lubricant. During this movement it would be relatively easy to lock the plunger of the syringe by moving the flange past one of the grooves. 
         [0012]    U.S. Pat. No. 5,000,737 discloses a syringe having a one-piece metal barbed restrictor element located between the plunger shaft and the cylindrical interior syringe barrel wall. The element has barbs facing towards the plunger for preventing movement of the plunger into the barrel, and barbs facing the barrel for preventing movement of the element out of the barrel. The restrictor element is initially located near the end of the barrel remote from the needle, and outward movement of the plunger to draw up liquid is permitted as the plunger can slide past the restrictor in this direction. Subsequent depression of the plunger to deliver liquid is permitted because the restrictor can move inwards relative to the barrel. 
         [0013]    US2003/0060759 also utilises a one-piece metal barbed restrictor element mounted between the plunger shaft and the barrel interior wall, and it employs outwardly facing barbs to restrict the motion of the element relative to the barrel. In this design, however, the plunger shaft has a stepped form with a shoulder part way along it. The restrictor element has a spring tang, which acts against the barrel and forces it against the plunger shaft. The restrictor starts out at the end of the shaft remote from the needle and withdrawal of the plunger past the restrictor is permitted until an enlarged diameter portion of the shaft, near the plunger head, comes into engagement with the restrictor. At the same time, one end of the restrictor snaps behind the shoulder on the plunger. As a result, movement of the plunger in either direction with respect to the restrictor is prohibited. The plunger can be depressed, carrying the restrictor with it to the end of the barrel adjacent the needle, and then the plunger is incapable of further movement. 
         [0014]    However, this syringe suffers from the disadvantage that it may be used repeatedly, provided the user does not draw up the plunger to the point where the restrictor snaps into place on the reduced diameter part of the plunger shaft. Furthermore, once the restrictor has locked into place, aspiration of a flash of blood is not possible. 
         [0015]    U.S. Pat. No. 5,222,942 discloses a design based on a ratchet system. A collar is installed in an initial position between plunger shaft and barrel. The plunger shaft is formed with annular ratchet teeth, and corresponding teeth are formed on the collar. The ratchet does not permit the plunger to be moved outwards past the collar, so when the plunger is initially drawn back in order to draw up liquid, it carries the collar with it to the end of the barrel remote from the needle, where a formation on the barrel prevents the collar and plunger from being withdrawn completely from the barrel. The ratchet is such that the plunger may then be depressed past the collar to dispense liquid, and then the syringe is disabled. This design does not allow for aspiration of a flash of blood. 
         [0016]    WO2005/058397A1 discloses a number of designs that are intended to allow for taking a flash of blood and possibly to allow for reconstitution of powdered drug. The designs described in WO2005/058397A1 are intended to be simple and inexpensive and to have a smooth action, which will not give rise to uncomfortable jolts when a patient is receiving an injection. 
         [0017]    However, the designs described in WO2005/058397A1 work on the principle of providing for a small amount of “lost motion” between a restrictor element and the syringe plunger, which allows for unlimited repeated inward and outward movement over a distance which is just sufficient for the purpose of obtaining a flash of blood (or optionally for reconstitution of powdered drug). The distance may be carefully chosen so that it is sufficiently small to prevent, hinder or discourage repeated use of the syringe to deliver small doses of drug. 
         [0018]    Fulfilment of all of the requirements for a non-reusable syringe in a single design is difficult, and there is normally a trade off between the complexity of the design and the number of these goals which are achieved by the design. One potential drawback with the designs described in WO2005/058397A1 is that they will allow drawing up and delivery of a volume of drug which is smaller than the usable volume of the syringe, and then drawing up and delivery of a further small dose or doses until the total volume of the syringe has been used. For example, a 5 ml syringe may be used to draw up 3 ml of liquid drug and then administer it. At this point the restrictor element has been moved a corresponding distance along the plunger or barrel, but there remains a distance corresponding to 2 ml of syringe volume over which the restrictor may move before the syringe is fully disabled. Further drawing up and delivery of a 2 ml dose of medicament is therefore possible before the syringe is fully disabled. 
         [0019]    Preferred embodiments of the present invention seek to overcome at least some of the above disadvantages of the prior art. 
       SUMMARY OF THE INVENTION 
       [0020]    According to the present invention, there is provided a syringe comprising:
       a barrel having an open first end and a second end having an opening for passage of fluid therethrough;   a plunger adapted to be slidably received in said first end and having a shaft, and a head for sliding and sealing engagement with an internal wall of said barrel; and   at least one locking member for engaging said barrel and said shaft, having at least one first tine for selectively engaging the plunger and at least one second tine for selectively engaging an internal wall of said barrel;       
 
         [0024]    wherein at least one said locking member is adapted to restrict outward movement of the plunger relative to the barrel, but has sufficient flexibility to allow limited outward movement of the plunger relative to the barrel, subsequent to inward movement of the plunger following outward movement of the plunger relative to the barrel. 
         [0025]    By providing a locking member for selectively engaging the internal wall of the barrel and the plunger to restrict outward movement, wherein the locking member has sufficient flexibility to allow limited repeated movement of the plunger relative to the barrel, this provides the advantage that the locking member only comprises a single part that is able to “lock” the plunger to the barrel after a single use and that allows repeated aspiration or flashback movements at any one point during operation. The invention therefore provides a simplified design requiring fewer parts and therefore significantly reduces the manufacturing costs of a single-use syringe. 
         [0026]    The locking member may be adapted to be supported on said shaft and oriented in a first direction relative thereto, such that at least one said first tine and at least one said second tine face towards said first end. 
         [0027]    At least one said first tine may be adapted to engage said shaft to restrict movement of the corresponding said locking member relative to the plunger when the plunger is moved into the barrel, and at least one said second tine may be adapted to engage said barrel to restrict movement of the locking member relative to the barrel when the plunger is moved out of the barrel. 
         [0028]    At least one said locking member may be adapted to be received on said shaft and oriented in a second direction relative thereto, such that at least one said first tine and at least one said second tine face towards said second end. 
         [0029]    At least one said first tine may be adapted to engage said shaft to restrict movement of the corresponding said locking member relative to the plunger when the plunger is moved out of the barrel, and at least one said second tine may be adapted to engage the internal wall of said barrel to restrict movement of the locking member relative to the barrel when the plunger is moved into the barrel. 
         [0030]    At least part of said shaft may be provided with longitudinal extending ribs. 
         [0031]    This provides the advantage of minimising the material that is necessary to provide a stiff and robust plunger shaft, therefore, minimising not only the weight of the plunger, but also reducing manufacturing costs. 
         [0032]    At least one pair of said ribs may be arranged substantially orthogonally to each other. 
         [0033]    At least one said rib may be arranged in a plane passing through a longitudinal axis of said shaft. 
         [0034]    This provides the advantage of a very simple plunger design that is high in mechanical stability, low in weight and that provides support for a locking member. 
         [0035]    At least one said locking member may be adapted to be received on at least one said rib. 
         [0036]    At least one said locking member may have a said first tine and a said second tine arranged on opposite sides of said rib. 
         [0037]    Said first tine and said second tine may be arranged on the same side of said rib. 
         [0038]    This provides the advantage that the first and second tine can engage the barrel wall and plunger shaft on opposite sides of the rib providing a substantially symmetrical arrangement between the plunger shaft and the locking member. This therefore improves the robustness of the syringe. 
         [0039]    At least one said locking member may further comprise a folded section adapted to engage said rib and to limit rotation of said locking member relative to said plunger. 
         [0040]    This provides the advantage that the locking member is stable within the confines of the syringe barrel during operation. 
         [0041]    At least one said first tine may be adapted to penetrate a wall of said shaft. 
         [0042]    This provides the advantage that the locking member is able to sufficiently “friction-lock” to the plunger shaft when the plunger shaft is moved in the relevant direction, allowing the locking member to be moved with the plunger. 
         [0043]    At least one said second tine may be adapted to penetrate a wall of said barrel. 
         [0044]    This provides the advantage that the syringe is rendered unusable when a user tries to re-use the syringe after it has been “locked”. 
         [0045]    The syringe may further comprise at least one flange adjacent a said first and/or second tine for limiting penetration of said tine through the corresponding wall of said barrel or plunger. 
         [0046]    This provides the advantage of preventing injury to the operator when trying to re-use the syringe. 
         [0047]    The barrel may further comprise at least one protrusion adjacent said first end to restrict removal of said locking member from said barrel. 
         [0048]    This provides the advantage that the locking member can generally not be removed from the syringe, therefore, maintaining its functionality and improving durability and reliability of the syringe. 
         [0049]    At least one said protrusion may be annular. 
         [0050]    This provides the advantage that the locking member can engage the protrusion at any angular position of the plunger relative to the barrel. 
         [0051]    At least one said locking member may be formed by bending an elongated member. 
         [0052]    This provides the advantage that the locking member is easy to manufacture and therefore reduces manufacturing costs. 
         [0053]    At least one said locking member may have at least one bend to provide sufficient flexibility to allow limited outward movement of the plunger relative to the barrel. 
         [0054]    This provides the advantage that the limitation of movement of the plunger is adjustable through the number of bends provided at the locking member. This therefore allows syringes to be manufactured allowing different aspiration or flashback volume. 
         [0055]    The feature which allows aspiration of blood may be operative at any position of the plunger so that the feature can be used whatever volume of injectable material is contained in the syringe and also may be used to check the needle position in a patient prior to drawing a blood sample, i.e. when the syringe is substantially empty and the plunger is fully inserted into the barrel. Therefore, preferably the said limited repeated cycles of distal and proximal movement referred to above are permitted at substantially every relative position of the plunger and barrel over the usable range. 
         [0056]    The distance over which repeated movement is possible is, desirably, sufficient to aspirate a small volume of blood from a patient so as to check the position of the needle. 
     
    
     
         [0057]    Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: 
           [0058]      FIG. 1  shows a sectional view of a syringe according to a first embodiment of the invention; 
           [0059]      FIG. 2   a  is a perspective view of a locking member of the syringe of  FIG. 1 ; 
           [0060]      FIG. 2   b  is a perspective view of a syringe plunger shaft with the locking member of  FIG. 2   a;    
           [0061]      FIG. 3  shows a sectional view of the syringe of  FIG. 1  at three stages during operation, (a) in the starting position, (b) with the plunger fully withdrawn and (c) with the plunger partly depressed during operation; 
           [0062]      FIG. 4  shows a sectional view of the syringe of  FIG. 1  at two stages during operation, (a) with the plunger partly depressed subsequent to withdrawal of the plunger and (b), with the plunger pulled back due to sufficient flexibility of the locking member; 
           [0063]      FIG. 5  shows a close-up of a partial sectional view of the syringe of  FIG. 1  with the assembled locking member (a) under compression by the plunger and (b) in a relaxed position; 
           [0064]      FIG. 6  shows a partial view of a tine having a flange from the side (a) and from the top (b); 
           [0065]      FIG. 7  shows a sectional view of a syringe according to a second embodiment of the invention at three stages during operation, (a) in the starting position, (b) with the plunger fully withdrawn and (c) with the plunger partly depressed subsequent to the withdrawal of the plunger; 
           [0066]      FIG. 8   a  is a perspective view of a locking member according to a third embodiment of the invention; 
           [0067]      FIG. 8   b  is a perspective view of a syringe plunger shaft with the locking member of  FIG. 8   a;    
           [0068]      FIG. 9  shows a sectional view of a syringe according to the third embodiment of the invention with the locking member located in a first direction; and 
           [0069]      FIG. 10  shows a sectional view of a syringe according to the third embodiment of the invention with the locking member located in a second direction. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First embodiment 
       [0070]    Referring to  FIG. 1 , a first embodiment is based on a standard syringe  10 , normally constructed from plastic material, comprising a barrel  12  and a plunger  14 . The barrel  12  has an open first end  16  and a generally closed second end  18  having an opening  20  that allows gases or liquids to pass and a nipple-like protuberance  22  or, for example, a Luer connector, allowing needles or tubing to be connected. Preferably, the barrel  12  has a tubular cross-section, but could also be of any other suitable cross-section. The barrel  12  further comprises, for example, an annular protrusion  23  that is located adjacent to the open end  16  preventing the removal of the plunger  14 . 
         [0071]    The plunger  14  comprises a plunger shaft  24 , which sealingly engages the interior wall of the barrel  12  and is usually of cruciform construction, and a flexible bung  26 , which is affixed to the distal end of the plunger shaft  24  forming a slidable seal. A handle  28  is incorporated on the proximal end of the plunger shaft  24  to facilitate forward and backward movement of the plunger  14 . 
         [0072]    A locking member  30  in the form of a small jockey is constructed from a spring-like material, e.g. steel or plastic, and fixed to one of the ribs of the cruciform plunger shaft  24 . The locking member  30  may be made from an elongated wire, having a sharpened first tine  32  and a sharpened second tine  34  on respective ends of the wire, and which is bent in such a way that the first tine  32  is able to engage the plunger shaft  24  and the second tine  34  is able to engage the interior wall of the barrel  12 . In this first embodiment of the invention, the locking member  30  is oriented in a first direction relative to the plunger shaft  24 , as shown in  FIGS. 1 to 5 , where both tines face away from the needle of the syringe towards the first end  16  of the barrel  12 . 
         [0073]    Referring to  FIGS. 2   a  and  2   b , the locking member  30  may comprise a folded section  36 , which sits on top of a rib of the plunger shaft  24  in order to provide stability to the locking member  30  during operation of the syringe  10 . In particular, the folded section  36  prevents the locking member  30  from rotating about an axis perpendicular to the longitudinal wall of the rib. Also, the locking member  30  may have at least one additional bend  38  to provide a predetermined flexibility to the locking member, in order to allow repeated aspiration or flashback at any one point during operation. 
         [0074]    The operation of the syringe  10  according to the first embodiment is now described with reference to  FIGS. 3  ( a ), ( b ) and ( c ). The syringe  10  may be delivered in assembled form with the plunger  14  and the locking member  30  already in starting position  3 ( a ). Here, the plunger  14  is fully depressed inside the barrel  12  and the locking member  30  is located on the plunger shaft  24  at the first end  16  and inside the barrel  12 . The first and second tine  32 ,  34  face towards the first end  16  and the second tine  34  abuts the annular protrusion  23 . On the other hand, the syringe  10  may be delivered in disassembled form, wherein the operator simply attaches the locking member  30  to the proximal end of one of the ribs of the plunger shaft  24  and pushes the plunger  14  inside the barrel by carefully negotiating the locking member  30  past the annular protrusion  23 . 
         [0075]    Once in starting position, as shown in  FIG. 3  ( a ), the operator may attach a needle or tubing to the nipple-like protuberance  22  and the syringe is ready for use. The needle may now be placed inside a vein of a patient to withdraw blood or may be used to fill the barrel  12  with a medicament, which might be administered to the patient. During operation, the operator withdraws the plunger  14  moving the flexible bung  26  towards the first end  16  of the barrel  12 , thus filling the syringe  10  with blood or medicament. The resilience of the locking member  30  in combination with its first and second tine  32 ,  34  is such that during withdrawal of the plunger  14 , the locking member  30  remains in place as shown in  FIG. 3(   b ). When the plunger  14  is then depressed to expel the contents of the syringe  10 , the first tine  32  engages and digs into the rib of the plunger shaft  24 , the second tine  34  is positioned such that it slides against the interior wall of the barrel  12 . This allows the locking member  30  to travel with the plunger  14  towards the second end  18  of the barrel  12  as shown in  FIG. 3  ( c ). 
         [0076]    Any attempt to withdraw the plunger  14  and its associated bung  26 , after the plunger  14  has been withdrawn and moved back inside the barrel  12 , will push the plunger  14  against the locking member  30  and engage the second tine  34  with the interior wall of the barrel  12 , preventing the locking member  30  from moving towards the first end  16  of the barrel  12 . Further application of a withdrawing force results in compressing of the additional bends  38  of the locking member. In case a predetermined withdrawing force is exceeded, the second tine  34  may destroy the barrel  12  of the syringe  10  by cutting through the barrel wall. 
         [0077]      FIG. 4(   a ) shows the plunger  14  in a partly depressed position after the plunger  14  has been withdrawn from the starting position shown in  FIG. 3(   a ) and pushed back into the barrel  12  and without any withdrawing force acting on the plunger  14 .  FIG. 4  ( b ) shows the locking member  30  in a compressed form during further application of a withdrawing force. This allows repeated aspiration or flashback denoted by the plunger movement  42 . Aspiration or flashback is primarily determined by the flexibility of the locking member  30 . An increased number of additional bends  38 , different designs of bends, and/or a ‘softer’ material of the locking member  30  may therefore increase the aspiration or flashback movement  42  of the syringe  10 . On the other hand, a decreased number of bends  38  and/or a ‘harder’ material of the locking member  30  may decrease the aspiration or flashback movement  42  of the syringe  10 . 
         [0078]      FIGS. 5  ( a ) and ( b ), show respectively a close-up of a sectional view of the locking member  30  during operation when (a) compressed by a withdrawing force of the plunger  14  and (b) in a relaxed state without any additional withdrawing force from the plunger  14 . Both first tine  32  and second tine  34  are engaged with the plunger shaft  24  and the interior wall of the barrel  12 , respectively, therefore restricting the movement of the plunger  14  towards the first end  16  of the barrel  12 . 
         [0079]    Referring to  FIGS. 6  ( a ) and  6  ( b ), a flange  44  may be located adjacent to the first tine  32  and/or adjacent to the second tine  34  to prevent the first and/or second tine  32 ,  34  from completely penetrating the wall of the barrel  12 . This prevents the operator from being injured on a tine that protrudes from the wall of the barrel  12 . In particular, the flange  44  may be located at a predetermined distance from the first and/or second tine  32 ,  34  that is equal or less than the thickness of the interior wall of the barrel  12 . Hence, the first and/or second tine  32 ,  34  will not be able to travel through and onto the outside of the barrel wall, therefore, minimizing the risk of injuries to the operator. The application of extreme withdrawal forces will cause tine  34  to plough a groove into the wall of the barrel to destroy the integrity of the syringe. 
       Second Embodiment 
       [0080]    A second embodiment of the invention will now be described with reference to  FIGS. 7  ( a ),  7  ( b ) and  7  ( c ). Here, the locking member  130  is attached to the plunger shaft  124  oriented in a second direction. The syringe  100  may be delivered in assembled form with the plunger  114  and the locking member  130  already in starting position as shown in  FIG. 7  ( a ). Here, the plunger  114  is fully depressed inside the barrel  112  and the locking member  130  is located on the plunger shaft  124  at the second end  118  inside the barrel  112 , with the first tine  132  and the second tine  134  facing towards the second end  118 . On the other hand, the syringe  100  may be delivered in disassembled form, wherein the operator simply attaches the locking member  130  to the distal end of one of the ribs of the plunger shaft  124  and with the aid of a suitable tool, which will be familiar to persons skilled in the art, pushes the plunger  114  inside the barrel  112  by carefully negotiating the locking member  130  past the annular protrusion  123  to the second end  118  of the barrel  112 . 
         [0081]    During operation, the operator withdraws the plunger  114  moving the flexible bung  126  and the locking member  130  to the first end  116  of the barrel  112 , thus filling the barrel  112  with blood or a medicament. During movement of the plunger  114 , second tine  134  slidably moves past the interior wall of the barrel  112 , wherein first tine  132  engages with the flexible bung  126 , preventing movement of the locking member  130  relative to the plunger  114 . As shown in  FIG. 7  ( b ), the locking member  130  is now located at the first end  116  of the barrel  112  abutting the annular protrusion  123 . When the plunger  114  is depressed to expel the content of the syringe  100 , the second tine  134  engages and digs into the interior wall of the barrel  112 , therefore, preventing any movement of the locking member  130  relative to the barrel  112 , as shown in  FIG. 7  ( b ), As shown in  FIG. 7  ( c ), the first tine  132  is positioned such that it slides against the rib of the plunger shaft  124  allowing the plunger  114  to travel towards the second end  118  of the barrel  112 . 
         [0082]    Any attempt to withdraw the plunger  114  and its associated bung  126 , after the plunger  114  has been withdrawn and moved back inside the barrel  112 , will engage the locking member  130  with the annular protrusion  123  of the barrel  112 , the first tine  132  with the plunger shaft  124  and the second tine  134  with the interior wall of the barrel  112  preventing any movement of the plunger  114  relative to the barrel. Further application of a withdrawing force may result in the bends  138  of the locking member being compressed, allowing repeated aspiration or flashback. In the event that a predetermined withdrawing force is exceeded, the second tine  134  may destroy the barrel  112  by puncturing the wall. With the locking member at the end  116 , the plunger can again be moved towards end  118 . Tine  134  engages the internal wall of the syringe barrel  112  locking the member  130  in place at the position  116 . Tine  132  is so positioned that the plunger shaft  114  is free to move towards the end  118 . Any additional movement towards the end  116  causes tine  116  to engage the plunger shaft stopping any further withdrawal. Compression of member  130  allows flashback. 
         [0083]    It will be appreciated by persons skilled in the art that an increased number of additional bends  138  and/or a ‘softer’ material of the locking member  130  may increase the aspiration or flashback movement of the syringe  100 , and that a decreased number of bends  138  and/or a ‘harder’ material of the locking member  130  may decrease the aspiration or flashback movement of the syringe  100 . 
         [0084]    The locking member  130  may also comprise a flange adjacent to the first and/or second tine  132 ,  134  as described in the first embodiment to prevent the operator from being injured by exposed tines. 
       Third Embodiment 
       [0085]    A third embodiment of the invention will now be described with reference to  FIGS. 8  ( a ),  8  ( b ),  9  and  10 . The third embodiment comprises a syringe  200  similar to the first embodiment, having a locking member  230 , for example in the form of a small jockey, that is constructed from a spring-like material, e.g. steel or plastic, and fixed to one of the ribs of the cruciform plunger shaft  224 . The locking member  230  may be made from an elongated wire, having a sharpened first tine  232  and a sharpened second tine  234  on respective ends of the wire, which is bend in such a way that the first tine  232  is able to engage the plunger shaft  224  and the second tine  234  is able to engage the interior wall of the barrel  212  of the syringe  200 . As shown in  FIG. 9 , the locking member  230  may be oriented in a first direction relative to the plunger shaft  224 , where both tines face away from the needle of the syringe towards the first end  216  of the barrel  212 . On the other hand, as shown in  FIG. 10 , the locking member  230  may be oriented in a second direction relative to the plunger shaft  224 , where both tines  232 ,  234  face towards the second end  218  of the barrel  212 . 
         [0086]    Referring to  FIGS. 8   a  and  8   b , the locking member  230  may only comprise a single additional bend  238  on one side of the rib of the plunger shaft  214  to provide a predetermined flexibility to the locking member, therefore allowing repeated aspiration or flashback at any one point during operation. 
         [0087]    The operation of the syringe according to the third embodiment, with the locking member  230  in the first direction, resembles with the operation described for the syringe according to the first embodiment and, with the locking member  230  in the second direction, resembles with the operation described for the syringe according to the second embodiment. 
         [0088]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by appended claims.