Abstract:
A syringe assembly includes a needle sheath that has a cavity that receives a needle cannula. The needle sheath can be formed of materials such as thermoplastic elastomers or plastics yet still be utilized with conventional gas sterilizing processes. The needle sheath includes a passage that permits the sterilizing gases to enter the cavity while preventing entry of microorganisms into the cavity. Thus, a syringe assembly is provided that facilitates sterilizing a needle after the needle sheath has been placed over the needle.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention generally relates to a syringe assembly having a needle sheath.  
           [0002]    Increasingly, medicaments are supplied from manufacturers in prefilled syringe assemblies. Such assemblies include a syringe that has a needle cannula and is filled with the medicament. Typically, a needle sheath covers the needle cannula to prevent accidental contact with the needle. Manufacturers supply such syringe assemblies as prepackaged, sterile, single use units. Thus, it is necessary to create a syringe assembly than can be sterilized after the needle sheath is placed over the needle cannula.  
           [0003]    In the past, needle sheaths were primarily composed of rubber. With the advent of modern thermoplastic elastomers, many manufacturers have switched to thermoplastic elastomers as the material of choice for needle sheaths. Thermoplastic elastomers offer the advantages of being: cleaner than natural rubber products; providing better dimensional control of parts; available in a wider variety of synthetic materials to insure compatibility with a particular medicament; lower cost than natural rubber; and reduced leeching of materials from the needle sheath into the medicament.  
           [0004]    Thermoplastic elastomers also permit a wider choice of sterilization methods between gases like ethylene oxide, irradiation, or autoclaving. One problem with some synthetic thermoplastic elastomers is that the particular composition which is most compatible with a particular medicament has a low permeability to a sterilizing gas.  
           [0005]    Thus, it is desirable to provide a needle sheath that can be sterilized using any sterilizing gas while permitting the needle sheath to be composed of any thermoplastic elastomer, including one having a low permeability to the particular sterilizing gas. In addition, it is sometimes desirable to produce a needle sheath formed of plastic. Plastics generally have low gas permeability. Thus, it is desirable to provide a needle sheath that can be formed of materials with low gas permeability and still be sterilized by a sterilizing gas.  
         SUMMARY OF THE INVENTION  
         [0006]    In general terms, this invention provides a syringe assembly having a needle sheath that can be formed of a material having a low gas permeability, but which can be sterilized using a sterilizing gas.  
           [0007]    A syringe assembly designed according to this invention includes a syringe body, a needle cannula, and a needle sheath. The needle sheath has a body portion with a cavity that is open at a first end and closed at a second end opposite the first end. The cavity receives the needle cannula and includes a passage in communication with-the first end of the cavity. The passage has a shape that permits gas from the external atmosphere to flow into the cavity while simultaneously preventing entry of microorganisms from the external atmosphere into the cavity.  
           [0008]    These and other features and advantages of this invention will become more apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross-sectional view of a syringe assembly designed according to the present invention;  
         [0010]    [0010]FIG. 2 is a cross-sectional view of another embodiment of a syringe assembly designed according to the present invention;  
         [0011]    [0011]FIG. 3 is a cross-sectional side view of a needle sheath designed according to the present invention;  
         [0012]    [0012]FIG. 4 is a cross-sectional view along line  4 - 4  of FIG. 3;  
         [0013]    [0013]FIG. 5 is a cross-sectional side view of another embodiment of a needle sheath designed according to the present invention;  
         [0014]    [0014]FIG. 6 is a cross-sectional view along line  6 - 6  of FIG. 5;  
         [0015]    [0015]FIG. 7 is a cross-sectional side view of another embodiment of a needle sheath designed according to the present invention;  
         [0016]    [0016]FIG. 8 is a cross-sectional view along line  8 - 8  of FIG. 7;  
         [0017]    [0017]FIG. 9 is a cross-sectional side view of another embodiment of a needle sheath designed according to the present invention;  
         [0018]    [0018]FIG. 10 is a cross-sectional view along line  10 - 10  of FIG. 9;  
         [0019]    [0019]FIG. 11 is a cross-sectional side view of another example of a needle sheath designed according to the present invention; and  
         [0020]    [0020]FIG. 12 is a cross-sectional view along line  12 - 12  of FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    A syringe assembly is generally indicated at  20  in FIG. 1. The syringe assembly  20  includes a syringe body  22  and a needle sheath  24 . The syringe body  22  has an interior chamber  26  that receives a medicament  32  and is in communication with a passage in a neck portion  28 . An integral needle cannula  30  is supported on the neck portion  28  and in communication with the interior chamber  26  through the passage in the neck portion  28 . A conventional stopper  34  and plunger rod  36  are used to eject the medicament  32  from the needle cannula  30  while administering an injection in a conventional manner.  
         [0022]    The needle sheath  24  includes a body portion  38  with a cavity  40 . The needle sheath  24  has a first end  42  and a second end  44 . The first end  42  defines the cavity opening and is received over the neck portion  28 . In FIG. 1, the syringe assembly  20  is shown as prefilled syringe containing the medicament  32  loaded in the interior chamber  26 . Of course, the syringe assembly  20  could be packaged without any medicament  32  in the interior chamber  26 .  
         [0023]    [0023]FIG. 2 illustrates another syringe assembly  20  designed according to the present invention. The syringe assembly in FIG. 2 does not include an integral needle cannula  30 , but includes a needle cannula  46  extending from a hub  48 . The hub  48  and needle cannula  46  are supported on the neck portion  28  of the syringe body  22 .  
         [0024]    A cross-sectional side view of a needle sheath  24  designed according to one embodiment of the present invention is shown in FIGS. 3 and 4. The cavity  40  has an inner surface  52 . Ridges  54  are located on the inner surface  52  of the cavity  40 . Each ridge  54  includes a gap  56 . Preferably, the gap  56  has a cross-sectional size that is between about 0.00001 and 0.00008 square inches. The gap  56  of adjacent ridges  54  are circumferentially offset from each other. The amount of offset between gaps  56  may be varied as needed in a particular situation. In one example, only a single ridge  54  is used.  
         [0025]    When the needle sheath  24  is fit over the neck portion  28 , the ridges  54  sealingly engage the outer surface of the neck portion  28 , for example. The gap  56  provides a passage between the first end  42  and the cavity  40 . The size of the gap  56  permits sterilizing gas from outside of the cavity  40  to flow into the cavity  40  while simultaneously preventing undesirable microorganisms from entering the cavity  40 .  
         [0026]    The design of this invention permits a syringe assembly  20  to be assembled under non-sterile conditions and to subsequently be sterilized by a sterilizing gas such as ethylene oxide while using thermoplastic elastomers to form the needle sheath  24 . The gaps  56  permit the sterilizing gas to flow into the cavity  40  and to sterilize the interior of the cavity  40  and either the integral needle cannula  30  or the needle cannula  46 .  
         [0027]    [0027]FIGS. 5 and 6 illustrate an alternative embodiment of a needle sheath  24  designed according to the present invention. The needle sheath  24  includes a groove  58  formed on the inner surface  52  of the cavity  40 . The groove  58  has a shape that provides a non-linear pathway from the first end  42  into the cavity  40 . The nonlinear pathway provided by the groove  58  permits a sterilizing gas to enter the cavity  40  while simultaneously preventing undesirable microorganisms from entering the cavity  40 . The groove  58  must extend into the cavity  40  sufficient to allow the sterilizing gas to contact the needle.  
         [0028]    As shown in FIGS. 7 and 8, a groove  58 ′ could provide a pathway that spirals around the inner surface  52  of the cavity  40 . In the embodiments shown in FIGS.  5 - 8  the inner surface  52  of the needle sheath  24  will be in sealing engagement with either the neck portion  28  or the hub  48  when the syringe assembly  20  is complete. The groove  58  and  58 ′, however, allows for the sterilizing gas to enter the cavity  40  during a sterilizing process.  
         [0029]    An alternative embodiment of the needle sheath  24  is shown in FIGS. 9 through 12. In FIG. 9, a plurality of ridges  60  are formed on the inner surface  52  of the cavity  40 . A gap  62  is located between the plurality of ridges  60 . The gap  62  provides a passage from the first end  42  into the cavity  40 . The gap  62  permits sterilizing gases to enter the cavity  40  while preventing undesirable microorganisms in the external atmosphere from entering the cavity  40 . In the embodiment shown in FIGS. 9 and 10, the ridges  60  and the majority of the inner surface  52  will be in sealing engagement with either the neck portion  28  or the hub  48  when the syringe assembly  20  is fully assembled. As shown in FIGS. 11 and 12, the ridges  60  have a shape that provides a spiralling gap  62  around the inner surface  52  of the cavity  40 .  
         [0030]    The shape of the passage permitting sterilizing gas to enter the cavity  40  may take a variety of forms. It is imperative that the passage have some contour or non-linearity so that microorganisms cannot find their way into the cavity  40 . Otherwise, sterility would not be preserved. The example passages disclosed in this description provide the necessary two-fold function of allowing gas flow while simultaneously preventing microorganism entry.  
         [0031]    The needle sheath  24  can be formed from rubber, thermoplastic elastomers, or plastics. The particular material used to form the needle sheath  24  is selected based on compatibility with the medicament  32  that is eventually loaded into the syringe assembly  20  and other design considerations.  
         [0032]    The foregoing description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of this invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.