Abstract:
A disposable safety syringe in one embodiment includes a syringe barrel; a plunger comprising a push rod; hollow first, second, and third adapters for forming an airtight engagement with an inner surface at one end of the syringe barrel; and a needle threadedly secured to the first adapter to establish a communication with inside of the syringe barrel prior to beginning a liquid dispensing operation with respect to a subject. After injection and pulling the needle out of a subject, a pulling of the plunger can be stopped, a further pulling of the plunger can also be stopped when an annular cutting groove of the plunger is about flush with the other end of the syringe barrel with the needle being retracted into the syringe barrel, and a breaking operation along the cutting groove can break the plunger.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to medical instruments and more particularly to a safety syringe which, after a single use, can be discarded for preventing contamination by retracting the needle into the syringe barrel and breaking the plunger. 
     2. Description of Related Art 
     Safety syringes are medical instruments for dispensing liquid preparations or withdrawing liquid medicines. However, medical employees such as doctors and nurses are liable to accidental puncture of the skin by a needle. The problem can be serious if the needle has been used. Recently, diseases (some fatal), such as hepatitis and Acquired Immune Deficiency Syndrome (AIDS), can be contracted if the needle has been used on an infected person. For preventing contamination, safety syringes are developed and commercially available. 
     A conventional disposable safety syringe comprises a barrel, a plunger inserted into the barrel, a needle hub provided at a front end of the barrel to hold a needle, and a block member having a through hole provided in the needle hub. The barrel has an annular groove on a front wall around the needle hub. After engaging the head of the plunger with the needle hub, the plunger can be pulled backward to break the groove so that the needle hub and the needle are retracted into the barrel. 
     However, in the conventional safety syringe the thin groove on the front wall of the barrel may be broken during injection or transportation of the safety syringe due to thermal expansion and contraction of PP (polypropylene) material of the safety syringe, thereby causing a leakage of the fluid medicine. Further, the desired retraction of the needle hub into the barrel can be jammed due to temperature variations. Thus, the need for improvement still exists. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the invention to provide a safety syringe which, after a single use, can be discarded for preventing contamination by retracting a needle into a syringe barrel and breaking a plunger. 
     To achieve the above and other objects, the invention provides a disposable safety syringe comprising a syringe barrel having both ends open and comprising a plurality of projections equally spaced on an inner surface proximate one end, a plurality of axial raised limit members at one end, and an annular lip distal the limit members; a plunger comprising a push rod projecting out of one end, first locking means at a portion of the push rod joining one end of the plunger, a cylindrical sealing member at one end of the plunger, a stop ring abutted the sealing member, a cross shaped cutting groove adjacent the stop ring, and a thumb pad distal the sealing member; a hollow first adapter comprising a hollow, cylindrical body having locking means, a hollow cylinder extending through the body and being concentric therewith, a shoulder formed between the cylinder and the body, a plurality of risers on an outer surface of the body, a plurality of recesses each defined by the riser and the body, and a first O-ring abutted the shoulder; a tubular second adapter comprising a plurality of latches each having a raised curved member at one end, an annular flange at the other end, and an inward extending rim at the other end; a tubular third adapter having a stepped-diameter outer surface and comprising an enlargement at one end, a stepped-diameter section at one end, second locking means at the other end, and a second O-ring put on the outer surface of the third adapter; and a needle; wherein in an assembled state, wherein in an assembled state, the first adapter is inserted through the syringe barrel until the first adapter is disposed at one end, the first adapter is turned to align the recesses with the limit members, the first adapter is pushed to lockingly dispose the limit members in the recesses, the second adapter is inserted through the syringe barrel to put on the cylinder with the latches being lockingly urged against the projections, the third adapter is inserted through the syringe barrel into a cylindrical space between the cylinder and the second adapter until the first O-ring is clamped by the stepped-diameter section so as to form an airtight engagement of the first, second, and third adapters at one end with the first, second, and third adapters being secured together, and the needle is releasably secured to the locking member; wherein the needle establishes a communication with an internal space of the syringe barrel via the cylinder and the second locking means prior to beginning a liquid dispensing operation with respect to a subject; and wherein at end of the liquid injection operation, the push rod projects out of the cylinder into the needle, the first locking means and the second locking means are locked each other to fasten the plunger and the third adapter together, after a subsequent removing the needle out of the subject, a pulling of the plunger can be stopped when the enlargement is stopped by the rim and the stepped-diameter section is lockingly engaged with the rear end, a further pulling of the plunger can be stopped when the cutting groove is about flush with the other end of the syringe barrel with the needle being retracted into the syringe barrel, and a breaking operation along the cutting groove can break the plunger. 
     The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded of a disposable safety syringe according to a first preferred embodiment of the invention; 
         FIG. 2  is a longitudinal sectional view of the safety syringe in  FIG. 1 ; 
         FIG. 3  is a longitudinal sectional view of the assembled safety syringe in  FIG. 1  in which the syringe barrel is filled with liquid preparations to be dispensed; 
         FIG. 4  is a fragmentary view of the needle and adjacent parts in  FIG. 3 ; 
         FIG. 5  is a view similar to  FIG. 3  in which the liquid preparations have been dispensed; 
         FIG. 6  is a fragmentary view of the needle and adjacent parts in  FIG. 5 ; 
         FIG. 7  is a view similar to  FIG. 5  showing a first step of retracting the needle and adjacent parts into the syringe barrel after dispensing; 
         FIG. 8  is a fragmentary view of the needle and adjacent parts in  FIG. 7 ; 
         FIG. 9  is a view similar to  FIG. 7  showing a second step of retracting the needle and adjacent parts into the syringe barrel after dispensing; 
         FIG. 10  is a fragmentary view of the needle and adjacent parts in  FIG. 9 ; 
         FIG. 11  is a view similar to  FIG. 9  showing the needle and adjacent parts have been retracted into the syringe barrel and the plunger has been broken in the final step of retracting the needle and adjacent parts into the syringe barrel after use; 
         FIG. 12  is a fragmentary view of a needle and adjacent parts according to a second preferred embodiment of disposable safety syringe of the invention; 
         FIG. 13  is a fragmentary view of a needle and adjacent parts according to a third preferred embodiment of disposable safety syringe of the invention; and 
         FIG. 14  is a fragmentary view of a needle and adjacent parts according to a fourth preferred embodiment of disposable safety syringe of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 to 11 , a disposable safety syringe in accordance with a first preferred embodiment of the invention comprises the following components as discussed in detail below. 
     A syringe barrel  10  comprises an internal space  11  for containing a quantity of liquid preparations, three spaced projections (only one is shown in  FIG. 1 )  14  equally spaced on an inner surface proximate one end  12 , a plurality of axial raised limit members  13  at one end  12 , and an annular lip  15  at the other end. 
     A plunger  50  comprises a push rod  57  projecting out of one end, a frusto-conical locking member  56  proximate the other end of the push rod  57 , an annular groove  55  at the other end of the push rod  57  adjacent to the locking member  56 , a cylindrical rubber sealing member  54  at one end of the plunger  50 , an annular stop ring  53  proximate the sealing member  54 , a cross shaped cutting groove  52  adjacent the stop ring  53 , and a disc shaped thumb pad  51  at the other end. The portion of the plunger  50  between the stop ring  53  and the thumb pad  51  has a cross-section of cross. A needle  60  has a toothed rear hub  61 . 
     An airtight adapter assembly is provided at one end  12  of the syringe barrel  10  and comprises first, second and third adapters  20 ,  30  and  40 . The hollow first adapter  20  comprises a hollow forward cylindrical body  28 , threads  23  on an inner surface of the body  28  to be threadedly (i.e., releasably) secure to the toothed hub  61 , a hollow rear cylinder  26  having a diameter less than that of the body  28  and having a tunnel  24  projecting through the body  28  (i.e., concentric) and further out of the mouth of the body  28  a small distance, the cylinder  26  having a flared rear end  27 , a shoulder  29  between the large body  28  and the small cylinder  26 , three spaced risers  22  on an outer surface of the body  28 , a plurality of recesses  21  each defined by either half of the riser  22 , and an O-ring  25 . 
     The tubular third adapter  40  comprises an axial channel  44 , a locking element  41  at the other end, an annular bottom wall  42  proximate the locking element  41 , an enlargement  47  at one end, an annular wall  43  open to one end, an annular shoulder  46  adjacent the wall  43 , a smooth intermediate portion  48 , and an O-ring  45 . 
     The tubular second adapter  30  comprises a raised other end  31 , four latches  32  equally spaced around the other end  31 , each latch  32  having a raised curved end  33 , an inward extending rim  35  on an inner surface of the other end  31 , and a space  34  defined by any two adjacent latches  32 . 
     A partial assembly of the safety syringe will be described in detail below. The O-ring  45  is put on a shoulder behind the intermediate portion  48 . The O-ring  25  is put on the joining portion of the shoulder  29  and the cylinder  26 . Next, the first adapter  20  is inserted through the other end of the syringe barrel  10  through the projections  14  (i.e., each projection  14  passing the gap between any two adjacent risers  22 ) until the first adapter  20  reaches one end  12  with the recesses  21  aligned with the limit members  13 . Next, further push the first adapter  20  to complementarily dispose the limit members  13  in the recesses  21  for locking (i.e., a turning of the first adapter  20  with respect to the syringe barrel  10  and a forward pushing of the first adapter  20  are prohibited). Next, the second adapter  30  is put on the cylinder  26  by inserting through the other end of the syringe barrel  10  with the projections  14  passing the raised curved ends  33  to fasten in the spaces  34 . That is, each projection  14  is secured to the latch  32 . Next, the third adapter  40  is inserted through the other end of the syringe barrel  10  into a cylindrical gap between the cylinder  26  and the second adapter  30  until the O-ring  25  is fitted in the annular wall  43  and the O-ring  45  is biased between the shoulder behind the intermediate portion  48  and the raised other end  31 . The shoulder  29  acts as a stop member by tightly engaging with the front ends of both the second and third adapters  30 ,  40 . The latches  32  thus press the enlargement  47  and the shoulder  46  to clamp the cylinder  26 . Hence, a rearward removal of the adapter assembly from the syringe barrel  10  is prohibited. Next, insert the plunger  50  into the syringe barrel  10  until the push rod  57  is disposed in the tunnel  24  but the locking member  56  is not engaged with the locking element  41 . Next, a protective cap  70  is put on a cylindrical portion of the hub  61  to hide the elongated needle  60  and frictionally fastened together. Next, the needle  60  is attached to and secured to the first adapter  20  by rotating the hub  61  along the spiral groove of the threads  23  in a storage position of the syringe. 
     A liquid dispensing operation of the syringe will be discussed in detailed below. First, remove the cap  70  from the needle  60 . Next, pull the plunger  50  to create vacuum in the syringe barrel  10 . Next, push the plunger  50  until the push rod  57  projects out of the tunnel  24  into a rear chamber of the needle  60  but the locking member  56  is still not engaged with the locking element  41  (i.e., spaced from the locking element  41  by a small distance). Next, insert the needle  60  into an injection liquid container (not shown). Next, pull the plunger  50  backward to withdraw a desired amount of liquid preparations from the container into the airtight, leak free space  11  via the needle orifice, the tunnel  24 , the bottom wall  42 , and the locking element  41  due to the substantially vacuum state of the syringe barrel  10 . Next, remove the needle  60  from the container. Next, replace the needle  60  with another needle  60  having a smaller orifice (optional). Next, slowly push the plunger  50  to expel remaining air in the front portion of the space  11  and a minimum amount of liquid preparations out of the orifice of the needle  60 . Next, insert the needle  60  into the skin of a patient and slowly push the plunger  50  to completely inject the liquid preparations into the patient. At end of the injection, the locking member  56  and the groove  55  together are matingly lockingly engaged with the locking element  41  and the bottom wall  42  (see  FIG. 6 ). That is, the plunger  50  and the third adapter  40  can move as a whole. 
     Next, remove the needle  60  from the patient. Next, pull both the plunger  50  and thus the third adapter  40  backward until the enlargement  47  is stopped by the rim  35  (see  FIG. 8 ). Next, further pull the plunger  50  to disengage the projections  14  from the latches  32 . Next, further pull the plunger  50  until the shoulder  46  is stopped by the rear end  27  and secured together. Hence, the plunger  50 , the third adapter  40 , the second adapter  30 , and the first adapter  20  can move as a whole. Next, further pull the plunger  50 , the third adapter  40 , the second adapter  30 , and the first adapter  20  backward until they completely disengage from one end  12  and the stop ring  53  is engaged with and stopped by the lip  15 . At this position, the cutting groove  52  is about flush with the other end of the syringe barrel  10  and the adapter assembly and the needle  60  are completely retracted into the syringe barrel  10  (see  FIG. 11 ). Thereafter, a medical employee doing the dispensing operation can break the plunger  50  along the cutting groove  52 . Finally, two broken parts of the syringe can be discarded to finish a safe disposal. This can prevent a next use of the syringe from occurring since it may be contaminated in the above dispensing operation. 
     Referring to  FIG. 12 , a disposable safety syringe in accordance with a second preferred embodiment of the invention is characterized below. An annular trough  261  is formed around the cylinder  26  at a joining portion of the shoulder  29  and the cylinder  26 . The O-ring  25  can be fitted in the trough  261 . Also, an inner surface of the front end portion of the third adapter  40  is a smooth even surface and is tightly clamped around the O-ring  25 . Further, the number of the projections  14  is a multiple of two and the projections  14  are symmetrical. 
     Referring to  FIG. 13 , a disposable safety syringe in accordance with a third preferred embodiment of the invention is characterized below. The body  28  of the first adapter  20  is formed integrally with the needle  60 . A substantially conic chamber  281  is formed on a rear end of the body  28 . The push member  57 A is shaped as a bullet head and is complementarily disposed in the chamber  281 . The locking member  56 A and the groove  55 A together are matingly lockingly engaged with the locking element  41  and the bottom wall  42 . Further, the number of the projections  14  is a multiple of two and the projections  14  are symmetrical. 
     Referring to  FIG. 14 , a disposable safety syringe in accordance with a fourth preferred embodiment of the invention is characterized below. The fourth preferred embodiment is a combination of the second and third preferred embodiments. In detail, an annular trough  261  is formed around a reduced diameter cylinder  26  abutted the shoulder  29 . The O-ring  25  can be fitted in the trough  261 . Also, an inner surface of the front end portion of the third adapter  40  is a smooth even surface and is tightly clamped around the O-ring  25 . The cylindrical body  28  of the first adapter  20  is formed integrally with the needle  60 . A substantially conic chamber  281  is formed on a rear end of the body  28 . The push member  57 A is shaped as a bullet head and is complementarily disposed in the chamber  281 . The locking member  56 A and the groove  55 A together are matingly lockingly engaged with the locking element  41  and the bottom wall  42 . Furthermore, the projections  14  are equally spaced apart. 
     While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.