Abstract:
A syringe comprising a one-way filter which permits flow of fluid into the syringe unfiltered but which filters the fluid when expelled from the syringe.

Description:
BACKGROUND TO THE INVENTION  
         [0001]    The invention relates to syringes, and in particular, although not exclusively, to such syringes for medical use, incorporating filters, and to filters for incorporation in such syringes.  
           [0002]    When fluids are given to patients from a bag, this generally being known as by means of a drip, an in-line filter is used to ensure that no small particulates left from the manufacturing process enter then body. The filters are generally incorporated in the line used to deliver the fluid during it&#39;s manufacture, and sterilised as part of the manufacture process.  
           [0003]    Patients are also given fluids as injections using a syringe to draw up the appropriate volume of fluid from a supply container and then inject it into the patient. No filtration is used and therefore small particulate by products from the production process may for the syringe, or needle, may be injected into the patient. Clearly this is undesirable, and a suitable form of filtration should be provided.  
           [0004]    It is an object of the present invention to provide a syringe which mitigates the above identified problem.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the present invention there is provided a syringe comprising a one-way filter which permits flow of fluid into the syringe unfiltered but which filters the fluid when expelled from the syringe.  
           [0006]    Preferably the one-way filter comprises a filter membrane through which the fluid passes when expelled from the syringe.  
           [0007]    The filter membrane may be fixed relative to the syringe and the one-way filter comprises valve means which open when the fluid is sucked into the syringe to permit the fluid to by-pass the filter membrane, and closes prior to fluid being expelled from the syringe such that the fluid must pass through the filter membrane.  
           [0008]    The valve means may comprise a valve member providing first and second valve surfaces and a passage there through and being slidable in a fixed member which provides first and second valve seats, the first valve surface closing onto the first valve seat when fluid is drawn into the syringe to by-pass the filter membrane fluid entering the syringe through the passage, the second valve surface closing onto the second valve seat, to close the passage and ensure that the fluid must pass through the filter membrane, prior to the fluid being expelled from the syringe.  
           [0009]    In an alternative form the valve means comprise at least one passage through or around the filter membrane and at least one valve member of resilient material which opens the passage when fluid is drawn into the syringe and closes the passage prior to fluid being expelled from the syringe.  
           [0010]    The filter membrane may be flexible such that at least a portion of it is moved inwardly of the syringe when fluid is sucked into the syringe to open a passage and permit fluid to by-pass the filter membrane, the portion being moved back to close the passage prior to fluid being expelled from the syringe such that the fluid must pass through the filter membrane.  
           [0011]    The filter membrane may have a cut there through to form a flap portion and a hinge line, the flap portion being the portion of the filter membrane which moves.  
           [0012]    The filter membrane may be secured to a spring member which moves in response to the flow of fluid into or our of the syringe and causes the filter membrane to move with it. Conveniently the spring member comprises a cross formation of either side of the filter membrane, the filter membrane being retained between them.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Examples of syringes according to the invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 is a cross section through a first embodiment of a syringe according to the invention, showing the flow of fluid into the syringe;  
         [0015]    [0015]FIG. 2 is a cross section through the embodiment of FIG. 1, showing the flow of fluid out of the syringe;  
         [0016]    [0016]FIG. 3 illustrates in ( a ) side view, ( b ) plan view and ( c ) cross section, a first annular member of the one-way filter assembly of the embodiment of FIGS. 1 and 2;  
         [0017]    [0017]FIG. 4 illustrates in ( a ) plan view and ( b ) cross section a second annular member of the of the one-way filter assembly of the embodiment of FIGS. 1 and 2;  
         [0018]    [0018]FIGS. 5 &amp; 6 illustrate in ( a ) cross section and ( b ) plan view first and second sub-members respectively of a valve member of the one-way filter assembly of the embodiment of FIGS. 1 and 2; and  
         [0019]    FIGS.  7  to  12  illustrate in ( a ) cross section and ( b ) plan view six alternative filters for embodiments of the invention;  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring first to FIGS.  1  to  6 , a first embodiment of a syringe  10  according to the invention will be described. The syringe  10  comprises a main body  11  for receipt of fluid to be injected, a needle engagement formation  12  to which a needle (not shown) is attached in use, an opening  13  through which fluid may pass into or out of the syringe  10  and a plunger (not shown) for control of the flow of fluid into and out of the syringe  10 . The syringe  10  also comprises a one-way filter assembly  14 .  
         [0021]    The one-way filter assembly  14  comprises an annular filter membrane  15  fixed relative to the main body  11  of the syringe  10  by means of a first annular member  16  which is a push fit within the main body  11 . The first annular member  16  has a recess  17  into which the filter  15  is located and retained by a second annular member  18 . Both annular members  16 ,  18  comprise a plurality of holes  16   a ,  18   a  there through, in this case four, which leave the majority of the area of the filter membrane  15  exposed. Preferably, as illustrated the two sets of holes  16   a  and  18   a  are of substantially the same size and shape, and when the assembly  14  is assembled they are arranged to overlay each other. This ensures that the maximum area of the filter membrane  15  is left exposed and that it is supported as well as possible.  
         [0022]    The first annular member  16  also comprises three legs  16   b  spaced around it&#39;s periphery which space the member  16  from the needle attachment formation  12  of the syringe  10 .  
         [0023]    The first and second annular members  16 ,  18  combine to form a first valve seat  19  facing towards the needle attachment formation  12 , whilst the first annular member  16  forms a second valve seat  20  facing the main body  11  of the syringe  10 .  
         [0024]    A valve member  21  comprises, for manufacturing convenience only, first and second sub-members  22 ,  23 , the second sub-member  23  being a push fit onto first sub-member  22  to form the valve member  21 . The valve member  21  is located in the centre of the first and second annular members  16 ,  18  such that it can move relative to those members  16 ,  18 . The valve member  21  provides a first valve surface  24  which is adapted to abut and seal against the first valve seat  19 , and a second valve surface  25  which is adapted to abut and seal against the second valve seat  20 . The valve member  21  also comprises a passage  26  there through.  
         [0025]    The valve member  21  operates as follows when the syringe  10  is in use. When the plunger is withdrawn to draw fluid into the syringe  10  the fluid pushes the valve member  21  upward such that the first valve surface  24  abuts and seals against the first valve seat  19 , fluid then passes through the passage  26  in the valve member  21  into the main body  11  of the syringe  10 , as shown by the arrows in FIG. 1. When the plunger is depressed to expel the fluid from the syringe  10  the fluid passes through the filter membrane  15  and pushes the valve member  21  such that it moves towards the opening  13 . This movement opens the first valve surface  24  from the first valve seat  19  and closes the second valve surface  25  onto the second valve seat  20 , the flow of fluid being illustrated by the arrow in FIG. 2. Thus fluid passing into the syringe  10  is not filtered whilst fluid passing out is filtered, the filter assembly  14  acting a s a one-way filter.  
         [0026]    Referring now to FIG. 7 a first alternative filter embodiment will be described. The one-way filter  30  comprises a single piece of thermally moulded filter material of known kind. The filter  30  has an outer ring  31  adapted to be a snap fit into a recess formed within the main body of a syringe (not shown). The filter  30  is of a conical form as best seen in cross section, and is intended to be fitted into the syringe with the apex of the cone towards the opening and needle. A cut  32 , being an arc of a circle, is provided in the central region of the filter  30 . This cut  32  forms a flap portion  33  and a hinge line  34  (shown in chain line in FIG. 7( b )).The cut  32  is formed at an angle to the surfaces of the filter  30  such that the flap portion  33  can only move into the syringe body and not towards the opening and needle, and such that when it provides a good seal to fluid moving in the opposite direction.  
         [0027]    The filter  30  operates as follows. When the plunger is withdrawn to draw fluid up into the syringe the pressure drop causes the flap portion  33  to move on it&#39;s hinge line  34  and fluid flows through the passage which is thus provided. When the plunger is depressed to expel fluid from the syringe the flap portion  33  moves back into the position shown in FIG. 7( a ) and seals. The fluid can then only pass out of the syringe by passing through the filter material itself.  
         [0028]    For the following alternative filter embodiments features common to the foregoing filter will not be described again. All are substantially conical and comprise a ring such that they are designed to snap fit into a recess in a main body of a syringe with the apex of the cone towards the opening or needle.  
         [0029]    Referring now to FIG. 8 a second alternative form of filter  40  is illustrated. It comprises a ring  41 , a filter membrane  42  and a spring member  43  of resilient material. The spring member  43  comprises an annular portion for a snap fit onto the ring  41 , and comprises a cross formation within the annular portion which define a four holes through the spring member  43 . The filter membrane  42  is secured to the cross formation of the spring member  43  by adhesive or any other appropriate method. The edges of the ring  41  and filter membrane  42  are formed such that when adjacent to each other they form a seal as for the cut of the previous embodiment. This is conveniently manufactured by forming the single piece moulding as for the last embodiment and then cutting out the whole of the centre rather than making a partial cut.  
         [0030]    The filter  40  operates as follows. When the plunger is withdrawn and fluid is drawn up into the syringe the vacuum formed pulls the spring member  43  away from the opening such that the cone is reversed, and the filter membrane  42  is pulled with it. The fluid thus flows into the syringe around the edge of the filter membrane  42  and through the holes in the spring member  43 . When the plunger is depressed the pressure pushes the spring member  43  and filter membrane  42  back to the positions shown in FIG. 8( a ). The filter membrane  42  seals onto the ring  41  and the fluid must pass through the filter membrane  42  if it is to be expelled from the syringe.  
         [0031]    Referring now to FIG. 9, a third alternative form of filter  50  will be described. The filter  50  comprises a ring  51  formed in one piece with a first cross formation  52 , and a second cross formation  53  which snap fits to the ring with the cross formations  52 ,  53  aligned. In between the two cross formations  52 ,  53  a filter membrane  54  is retained, with cuts  55  (shown as chain lines) in the form of arcs of circles between the cross formations  52 ,  53  forming four flap portions  56  with seal lines of the kind previously described. The cross formations  52 ,  53  are of rigid material whilst the filter membrane  54  is flexible.  
         [0032]    The filter  50  operates as follows. When the plunger is withdrawn the drop in pressure pulls the filter membrane  54  flap portions  56  inwardly allowing the fluid to pass around the filter membrane  54 . When the plunger is depressed the flap portions  56  are forced back into their positions shown in FIG. 9( a ) and seal such that the fluid can only be expelled from the syringe by passing through the filter membrane  54 .  
         [0033]    Referring now to FIG. 10 a fourth alternative filter  60  embodiment will be described. The filter  60  comprises a ring  61  and integral filter membrane  62 . A spider formation  63  is formed of resilient material and comprises four legs  64  which snap fit to the ring  61 , and four legs  65  with broader formations  66  at their free ends. The broader formations  66  overlie, as shown in FIG. 10( b ) small holes  67  through the filter membrane  62 .  
         [0034]    The filter  60  operates as follows. When the plunger is withdrawn the pressure drop in the main body of the syringe pulls the legs  65  inwardly such that the broader formations  66  lift off the holes  67  and the fluid can pass through them. When the plunger is depressed the legs  65  are pushed back to their original position and seal the holes such that the fluid can only be expelled from the syringe by passing through the filter membrane  62 .  
         [0035]    Referring now to FIG. 11 a fifth alternative filter  70  will be described. The filter  70  comprises a ring  71  formed integrally with an annular filter membrane  72 . It further comprises a cross formation  73  having four legs  74  adapted to snap fit to the ring  71  and joined to a central circle  75  over which a spring member  76  is located. The spring member  76  has connected thereto a central circular valve member  77  which fits into and can seal the hole in the centre of the annular filter membrane  72 .  
         [0036]    The filter  70  operates as follows. When the plunger is withdrawn the drop in pressure pulls the spring member  76  inwardly and thus lifts the valve member  77  out of the hole in the filter membrane  72  allowing the fluid to enter. When the plunger is depressed the spring member  76  and valve member  77  are forced back to their positions shown in FIG. 11( a ) such that the only way the fluid can leave the syringe is by passing through the filter membrane  72 .  
         [0037]    Finally, referring to FIG. 12 a sixth alternative filter  80  is will be described. The filter  80  comprises a ring  81  moulded integrally with a filter membrane  82 , which provides two passages  83  there through. A second moulded component of resilient material comprises a ring  84  which snap fits to the ring  81  and carries on it two valve members  85  which overlie the passages  83  and when in the position shown in FIG. 12( b ) seal them closed.  
         [0038]    The filter  80  operates as follows. When the plunger is withdrawn the pressure reduction within the syringe pulls the valve members  85  inwards opening the passages  83  and the fluid flows in. When the plunger is depressed the valve members  85  are pushed back to the position where they seal the passages and the fluid can only leave the syringe by passing through the filter membrane  82 .  
         [0039]    The filter membranes in all the foregoing embodiments may be formed of any appropriate material, such as Polymide  6 . The other component parts of the filters may also be formed of any appropriate materials such as those known in the prior art.  
         [0040]    The filters described above are preferably inserted into the syringes during manufacture thereof and can thus be sterilised in-situ by known methods. However, it may be appropriate in some situations for the filters to be supplied separately for subsequent fitting.  
         [0041]    The embodiments described above are merely examples of ways in which the invention may be implemented, many other embodiments being possible within the scope of the present invention.  
         [0042]    The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.