Abstract:
A safety syringe includes a flexible holder-supporting seat that is sleeved around and that clamps a needle holder within a front end portion of a syringe barrel. A flexible sealing member seals an open front end of a plunger so as to define a vacuuming chamber in the plunger. When the plunger moves within the barrel to a front limit position, a holder-retaining front portion of the sealing member engages and retains the needle holder thereon. The plunger pushes the holder-supporting seat to separate from the needle holder such that the sealing member and the needle holder mover rearward within the syringe barrel due to negative pressure produced in the plunger, thereby retracting a needle into the syringe barrel.

Description:
This application is a continuation-in-part application of pending U.S. application Ser. No. 10/347,800, filed Jan. 22, 2003 now U.S. Pat No. 7,074,207, which is a continuation-in-part of Ser. No. 09/931,014, filed Aug. 17, 2001, now abandoned. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a medical syringe, and more particularly to a safety syringe with an automatically retractable needle. 
   2. Description of the Prior Art 
   As shown in  FIG. 1 , a prior syringe includes a syringe barrel  72  with a hole in the front end of the syringe barrel  72  and scales on the surface of the syringe barrel  72 . A needle unit  73  includes needle holder  730  with the thread of a screw for bolting the needle unit  73  in the syringe barrel  72 . The rear end of the needle  731  is fastened across the needle holder  730 , wherein the front end of the needle  731  is projected from the needle holder  730 . The rear end of the syringe barrel  72  includes a rear opening  724  with large cross-sectional area or the diameter. A rubber-sealing ring  743  fastens a rod  74  inside the syringe barrel  72 , wherein the rod  74  is movable across the rear opening  724 . The external diameter of the rubber-sealing ring  743  is slightly larger than the internal diameter of the rear opening  724  and the internal diameter of the syringe barrel  72 . The rubber-sealing ring  743  injects the medicament withdrawn inside the syringe barrel  72  through the needle  731  when the rod  74  is pushed. 
   The needle  731  may accidentally stab an operating staff while the operating staff encloses the needle  731  by a needle sheath. If the syringe  7  is used and the needle  731  comes in contact with the blood of an individual, the stabbed operating staff may become infected with diseases, e.g. AIDS, viral hepatitis b and so on. 
   The medical appliances are improved to protect operating staff from being inflected. Safety syringes protect the operating staff from being stabbed and infected while tidying the needle  731  after injecting the medicament for patients. As shown in  FIGS. 2A and 2B , a safety syringe  8 , which is disclosed by U.S. Pat. No. 5,395,337, includes a syringe barrel  82  and a spring  84 . The syringe barrel  82  includes a tapered wall  824  for fastening a needle holder  830 . A flexible sealing member  85  is wedged in the front end of the spring  84  by a retaining ring  850  having a lead angle. A spring  86  connects with the flexible sealing member  85  to pull the flexible sealing member  85  when the operating staff finishes the injection. As shown in  FIG. 2B , the operating staff can tidy the needle  831  by pushing the spring  84  to wedge the flexible sealing member  85  by the tapered wall  824 . When the tapered wall  824  wedges the flexible-sealing member  85 , the flexible sealing member  85  is released from the retaining ring  850  if the operating staff continuously pushes the spring  84 . The flexible sealing member  85  is pulled by the spring  86  to movably dispose inside the spring  84  after the flexible-sealing member  85  is released from the retaining ring  850 . 
   However, the diameter of the tapered wall  824  of a syringe is very small, e.g. few millimeters, wherein the capacity of the syringe is approximately 1 cubic centimeter or 2 cubic centimeters. It is pretty difficult to push the tapered wall  824  while wedging the flexible-sealing member  85  by the tapered wall  824  without partiality. It is also difficult to set the spring  86  in the spring  84  to connect the flexible sealing member  85  with the rear end of the spring  84  of a tiny syringe  7 . The complex and delicate process for fabricating elements of the tiny syringe  7  increases the cost of the tiny syringe  7 . The syringe  7  may be too expensive for selling. Thus it is necessary to develop more economical safety syringes for protecting the operating staff from being stabbed. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a safety syringe is provided to substantially overcome the drawbacks of the above mentioned problems for automatically retracting the needle unit inside a plunger by pressure. 
   Accordingly, it is another objective of the present invention to provide a safety syringe, which can be conveniently operated, with convenient fabricated elements for protecting the operating staff from being stabbed and infectious diseases. 
   In accordance with the present invention, a safety syringe is disclosed. The present safety syringe includes a syringe barrel, a flexible holder-supporting seat, a needle unit, a plunger and a flexible sealing member. The syringe barrel includes a barrel body with a front opening and a rear opening, wherein the cross-sectional area or the diameter of the rear opening is larger than the front opening. A spacer portion is disposed in the front end of the barrel body, wherein the front opening penetrates the spacer portion. The flexible holder-supporting seat is sleeved around and clamps a needle holder of the needle unit within the front-end portion of a syringe barrel, wherein the flexible holder-supporting seat includes a through hole. The needle unit includes the needle holder and a needle fastened on the needle holder, wherein the needle includes a rear opening. The needle unit is inserted into the front end of the syringe barrel. The needle holder is propped by a spacer portion. The needle inserts through the spacer portion and is projected from the front opening. The plunger includes a front-end wall, a rear end wall and a plunger body formed between the front-end wall and the rear end wall. The cross-sectional area or the diameter of a front opening of the plunger is larger than the external diameter of the spacer portion. An inward flange is formed in the front portion of the plunger. The plunger is disposed inside the syringe barrel and is movable between the flexible holder-supporting seat and the rear opening. The sealing member is disposed continuously within the inward flange to seal the front opening formed in the front of the plunger for defining a sealed space with lower pressure. The sealing member combines with the needle unit when the front end of the plunger is pushed to be close to the holder-supporting seat. The plunger pushes the holder-supporting seat to release the needle holder combined with the sealing member. The needle holder is propped by the spacer portion to stop the movement of the sealing member, so the sealing member is released from the inward flange while the sealing member being not contacted by the inward flange. Thus the sealing member and the needle unit is automatically retracted into the plunger body due to negative pressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  illustrates a schematic diagram of a safety syringe in the prior art 
       FIG. 2A  illustrates a longitudinal cross-sectional view of a safety syringe incorporating the plunger in the prior; 
       FIG. 2B  illustrates a view similar to  FIG. 2A , showing final movement of the safety syringe in the prior art 
       FIGS. 3A-3G  illustrate sectional views of a safety syringe of the first embodiment of the present invention; 
       FIGS. 4A-4E  illustrate sectional views of a safety syringe of the second embodiment of the present invention 
       FIGS. 5A-5D  illustrate sectional views of a safety syringe of the third embodiment of the present invention; 
       FIG. 6  illustrates a sectional view of a safety syringe of the fourth embodiment of the present invention; 
       FIGS. 7A-7D  illustrate sectional views of a safety syringe of the fifth embodiment of the present invention 
       FIG. 8  illustrates a sectional view of a safety syringe of the sixth embodiment of the present invention; 
       FIGS. 9A-9B  illustrate sectional views of a safety syringe of the seventh embodiment of the present invention; 
       FIG. 10  illustrates a sectional view of a safety syringe of the eighth embodiment of the present invention; 
       FIGS. 11A-11C  illustrate sectional views of a safety syringe of the ninth embodiment of the present invention; and 
       FIG. 12  illustrates a sectional view of a safety syringe of the tenth embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   These preferred embodiments of the present invention are now described in greater detail. Nevertheless, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited except as specified in the accompanying claims. 
   As shown in  FIGS. 3A-3D , the first embodiment of the present invention provides a safety syringe including a syringe barrel  2 , a needle unit  3  set in the front end of the syringe barrel  2 , a plunger  4  movably disposed within the syringe barrel  2  and a flexible sealing member  5  disposed movably within the front end of the plunger  4 . 
   The syringe barrel  2  includes a barrel body  20 , a front-end wall  21  and a rear end wall  22 . A front opening  210  and the front-end wall  21  are integrally formed. A rear opening  220  is formed integrally with the rear end wall  22 . The cross-sectional area of the rear opening  220  is slightly larger than the cross-sectional area of the plunger  4 ; thus the plunger  4  can be inserted into the syringe barrel  2 . A spacer portion  212  is disposed on the front end wall  21 , wherein the front opening  210  penetrates the spacer portion  212 . The spacer portion  212  and the barrel body  20  can be formed integrally. However, the spacer portion  212  may be an independent element set on the front end of the barrel body  20 . The cross-sectional area or the diameter of the front opening  2   10  is slightly smaller than that of the rear opening  220  and the plunger  4 . The internal diameter of the syringe barrel  2  and the internal diameter of the rear opening  220  are approximately the same. A flexible holder-supporting seat  24  including a central hole  240  can be pushed into the syringe barrel  2  through the rear opening  220  to be set inside the syringe barrel  2 . There is a distance between the flexible holder-supporting seat  24  and the front-end wall  21  of the barrel body  20 . 
   A needle unit  3  includes a needle body  30  and a needle  31  set across the needle body  30 . The needle body  30  is movably set inside the flexible holder-supporting seat  24 . The front end of the needle  31  is set across the spacer portion  212  to pierce through the spacer portion  212 . 
   The plunger  4  includes a plunger body  40  including an open front end  41  formed on an end of plunger body  40 . The open front end  41  includes a front opening  410 , wherein the internal diameter of the front opening  410  is slightly larger than the cross-sectional area or the diameter of the needle body  30 . A flexible sealing member  5  is fastened inside the front opening  410  to form a sealed space inside the plunger body  40 . A rear end wall  45  is fastened on another end of plunger body  40  to form the sealed space inside the plunger body  40 . The plunger  4  fastened inside the barrel body  20  can be moved away from the syringe barrel  2  by pulling the rear end wall  45  to withdraw the medicament. The plunger  4  can be pushed to inject the medicament by pushing the rear end wall  45 . The plunger body  40  may include a rubber seal ring  43  to fasten the syringe barrel  2  and the plunger  4  better for preventing the medicament inside syringe barrel  2  from overflowing. 
   As shown in  FIG. 3B , the flexible holder-supporting seat  24  is set inside the syringe barrel  2  to fasten the needle body  30  on. The needle body  30  includes a needle holder  302 , a rear opening  300  and an outward flange  303 , wherein the cross-sectional area or the diameter of the outward flange  303  is slightly larger than that of the needle holder  302 . The cross-sectional area or the diameter of the needle holder  302  may be equal to or slightly larger than that of the spacer portion  212 . The flexible holder-supporting seat  24  includes a rear end surface  241 . The side of the central hole  240  of the flexible holder-supporting seat  24  fastens the needle holder  302  when the needle body  30  is stuffed into the flexible holder-supporting seat  24 . The side of the central hole  240  also fastens the outward flange  303 . After the needle body  30  is fastened by the flexible holder-supporting seat  24 , the needle body  30  and the flexible holder-supporting seat  24  can be pushed into the syringe barrel  2  through the rear opening  220  until the needle holder  302  contacting with the spacer portion  212 . The needle unit  3  set on the front end of the syringe barrel  2  is fastened well and stable because the area of the needle holder  302  contacting with the spacer portion  212  is large enough to provide enough force of stability. When the volume of the medicament withdrawn inside the syringe barrel  2  is approximately 1 cubic centimeter or 2 cubic centimeters, the layout of the prevent invention provides effective stability of the safety syringe for fastening the needle unit  3  and the syringe barrel  2 . 
   As shown in  FIG. 3C , an inward flange  44  of the plunger  4  fastens the flexible sealing member  5 . A rear opening  420  and the open rear end  42  are formed integrally. The plunger  4  further comprises a rear end wall  45  sealing the rear opening  420 . The rear end wall  45  includes a plate  452  and a circular projection  451  extended from the plate  452 . The circular projection  451  is fastened inside the plunger body  40  of the plunger  4 , wherein the external diameter of the circular projection  451  is a slightly larger than the internal diameter of the rear opening  420  of the plunger  4 . The flexible sealing member  5  includes a sealing rear portion  52  and a holder-retaining front portion  51  extended from the front end of the sealing rear portion  52 . The flexible sealing member  5  further includes a rear end skirt portion  53  in the rear end of the flexible sealing member  5 . The external diameter of the sealing rear portion  52  is slightly smaller than the internal diameter of the rear opening  420 , the sealing rear portion  52  can be pushed into the rear opening  420  of the plunger body  40  thus. The external diameter of the sealing rear portion  52  is slightly larger than the internal diameter of the inward flange  44  of the plunger  4 . The flexible sealing member  5  can be fastened on the open front end  41  by fastening to the inward flange  44  to seal the space inside the plunger  4 . Thus, the air inside the plunger body  40  is pumped out to form a sealed space with lower pressure inside the plunger body  40 , and then the rear end wall  45  is fastened on the rear opening  420  to seal the sealed space. A rubber seal ring  43  is covered on the front end of the plunger  4 , wherein the external diameter of the rubber seal ring  43  is slightly larger than the internal diameter of the barrel body  20 . 
   The cannular holder-retaining front portion  51  of the flexible sealing member  5  is extended forward from the sealing rear portion  52 , and the external diameter of the holder-retaining front portion  51  is as small as the forward extension. A blind hole  510  is formed inside the holder-retaining front portion  51 , wherein the bottom of the blind hole  510  is a sealing rear portion  520 , and the top of the blind hole  510  is surrounded by the front end of the holder-retaining front portion  51 . The internal diameter of the front end of the holder-retaining front portion  51  is slightly smaller than the external diameter of the outward flange  303 . As shown in  FIG. 3D , the plunger  4  is set inside the syringe barrel  2 . As shown in  FIG. 3E , the blind hole  510  sleeves around the outward flange  303 . The sealing rear portion  520  seals the rear opening  300  of the needle body  30  to stop the medicament from being injected, when the open front end  41  is pushed to contact with the flexible holder-supporting seat  24 . When the open front end  41  is pushed continuously, the needle holder  302  is fastened on the spacer portion  212  but the open front end  41  continuously pushes the flexible holder-supporting seat  24 . The flexible holder-supporting seat  24  does not fasten the needle body  30 , if the flexible holder-supporting seat  24  is pushed continuously by the open front end  41 . 
   As shown in  FIG. 3F , the flexible sealing member  5  stops moving because the needle body  30  props the flexible sealing member  5  up, even if the open front end  41  continuously pushes the flexible holder-supporting seat  24 . The flexible sealing member  5  is released from the inward flange  44  when the inward flange  44  does not contact with the flexible sealing member  5 . The pressure inside the space sealed by the sealing rear portion  52  and the plunger body  40  is lower than the pressure pulling the sealing rear portion  52 . As shown in  FIG. 3G , the needle unit  3  that is combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the different pressures. The operating staffs using the safety syringe of the present invention are protected from being stabbed. Furthermore, the sealing rear portion  52  stops air being transported into the sealed space to maintain the lower pressure of the sealed space inside the plunger body  40 . 
   The safety syringe of the second embodiment of the present invention is illustrated as  FIGS. 4A-4E . The difference between the first embodiment and the second embodiment of the present invention is the length of the holder-retaining front portion  51  of the flexible-sealing member  5 . The holder-retaining front portion  51  can shrink to sleeve the needle unit  3  when the plunger  4  is pushed to contact with the flexible holder-supporting seat  24 . As shown in  FIG. 4A , the flexible sealing member  5  includes a sealing rear portion  52  and a holder-retaining front portion  51 , wherein the external diameter of the sealing rear portion  52  is slightly larger than the internal diameter of the inward flange  44 . The inward flange  44  can clench the sealing rear portion  52 . Thus, the side in the front end of the inward flange  44  expands slightly and does not contact with the holder-retaining front portion  51 . As shown in  FIG. 4B , the holder-retaining front portion  51  curves because the holder-retaining front portion  51  contacts with the flexible holder-supporting seat  24  and the needle body  30  when the plunger  4  is pushed forward to contact with the flexible holder-supporting seat  24 . As shown in  FIG. 4C , the curved holder-retaining front portion  51  curves continuously to be extruded in the space surrounded by the expanded inward flange  44  and the flexible holder-supporting seat  24  when the plunger  4  is continuously pushed. When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the sealing rear portion  520  of the holder-retaining front portion  51  contacts with the rear opening  300  to stuff the rear opening  300 , and the holder-retaining front portion  51  expands due to the outward flange  303 . As shown in  FIG. 4D , the holder-retaining front portion  51  sleeves the outward flange  303  to combine with the needle unit  3  after the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 , wherein the needle body  30  is fastened by the spacer portion  212 . The needle unit  3  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . As shown in  FIG. 4E , the flexible sealing member  5  stops moving due to the immovable needle body  30  and then is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24  and release the flexible sealing member  5 . Thus the needle unit  3  combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   It is to be understood that many modifications and variations of the structures of the annular flexible holder-supporting seat, the sealing member and the needle unit, and the method for disposing the sealing member are possible in light of the above teachings.  FIGS. 5A-5D  illustrate the third embodiment of the present invention. The side of the central hole  240  of the flexible holder-supporting seat  24  fastens a U-shaped flexible element  6  including a hole  60 . The U-shaped flexible element  6  is clenched by the flexible holder-supporting seat  24  and the needle holder  302 ′. The needle  31  projected from the U-shaped flexible element  6  is clenched by the hole  60 . The external diameter of the U-shaped flexible element  6  is slightly larger than the internal diameter of the plunger  4 . The needle  31  is fastened by the needle holder  302 ′ and projected from the needle holder  302 ′. The shape of the flexible sealing member  5  of this embodiment is also different from the shape of the flexible sealing member  5  of the above embodiments of the present invention. The curved projection  520 ′ of the sealing rear portion  52  may be a cambered surface as shown in  FIG. 5A . As shown in  FIG. 5B , the needle  31  stabs into the curved projection  520 ′ to seal the needle  31  and combine with the U-shaped flexible element  6  and the flexible sealing member  5  when the plunger  4  is pushed to contact with the flexible holder-supporting seat  24 . As shown in  FIG. 5C , when the plunger  4  is continuously pushed, the flexible holder-supporting seat  24  is pushed by the plunger  4  to slip and release the U-shaped flexible element  6 . Because the needle holder  302 ′ is propped up by the spacer portion  212 , the U-shaped flexible element  6  is also pushed by the plunger  4  until the bottom of the U-shaped flexible element  6  contacting with the needle holder  302 ′. The needle  31  stabs into the flexible sealing member  5  deeper when the U-shaped flexible element  6  is pushed forward to contact with the needle holder  302 ′. The flexible sealing member  5  is pushed by the U-shaped flexible element  6  during the plunger  4 , which then pushes the flexible holder-supporting seat  24 . After the flexible holder-supporting seat  24  being pushed by the plunger  4  continuously and the inward flange  44  releasing the flexible sealing member  5 , the flexible sealing member  5  combining with the needle unit  3  and U-shaped flexible element  6  is withdrawn by the lower pressure inside the plunger  4 . As shown in  FIG. 5D , the needle unit  3 , the U-shaped flexible element  6  and the flexible sealing member  5  is withdrawn into the plunger body  40  due to the pressure. 
   As shown in  FIG. 6 , the fourth embodiment of the present invention provides a safety syringe including a syringe barrel  2  with a different front-end wall  21 . The front-end wall  21  includes a front opening  210 ′ for fastening a needle  31 , wherein the needle  31  projects from the front end wall  21 . The needle  31  stabs into the sealing rear portion  520  to seal the needle  31  and combine the needle unit  3  with the U-shaped flexible element  6  and the flexible sealing member  5  when the plunger  4  is pushed to contact with the flexible holder-supporting seat  24 . When the plunger  4  is continuously pushed, the flexible holder-supporting seat  24  is pushed by the plunger  4  to slip and release the U-shaped flexible element  6 . Because the  210  prop up the needle holder  302 , the U-shaped flexible element  6  is also pushed by the plunger  4  until the bottom of the U-shaped flexible element  6  contacting with the needle holder  302 . The needle  31  stabs into the flexible-sealing member  5  deeper when the U-shaped flexible element  6  is pushed to contact with the needle holder  302 . The flexible sealing member  5  is pushed by the U-shaped flexible element  6  during the plunger  4  pushes the flexible holder-supporting seat  24 . After the flexible holder-supporting seat  24  being continuously pushed by the plunger  4  and the inward flange  44  releasing the flexible sealing member  5 , the flexible sealing member  5  combining with the needle unit  3  and U-shaped flexible element  6  is withdrawn by the lower pressure inside the plunger  4 . The needle unit  3 , the U-shaped flexible element  6  and the flexible-sealing member  5  is withdrawn into the plunger body  40  due to the pressure. 
   The fifth embodiment of the present invention is illustrated as  FIGS. 7A-7D . The difference between the first embodiment and the fifth embodiment of the present invention is the structure of the flexible sealing member  5 . As shown in  FIG. 7A , the flexible sealing member  5  includes a holder-retaining front portion  51 , a blind hole  510 ′ and a piston body  521 , wherein the blind hole  510 ′ is formed within the holder-retaining front portion  51 . As shown in  FIG. 7B , the holder-retaining front portion  51  becomes slightly flat, because the holder-retaining front portion  51  contacts with the needle body  30  when the plunger  4  is pushed forward to be close to the flexible holder-supporting seat  24 . As shown in  FIG. 7C , the slightly flat holder-retaining front portion  51  is continuously pushed to combine with the outward flange  303  when the plunger  4  is continuously pushed. When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the piston body  521  contacts with the rear opening  300  to stuff the rear opening  300  to lock the needle  31  from injecting the medicament. The holder-retaining front portion  51  sleeves the outward flange  303  to combine with the needle unit  3  after the plunger  4  is pushed continuously to push the flexible holder-supporting seat  24 , wherein the needle body  30  is propped by the spacer portion  212 . As shown in  FIG. 7D , the needle unit  3  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . The flexible sealing member  5  stops moving due to the immovable needle body  30  and then is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24  and release the flexible sealing member  5 . Thus the needle unit  3  combined with the flexible sealing member  5  and the piston body  521  is automatically retracted into the plunger body  40  due to the different pressures. 
   As shown in  FIG. 8 , the sixth embodiment of the present invention provides a safety syringe including a syringe barrel  2  with a different front-end wall  21 . The front-end wall  21  includes a front opening  210 ′ for fastening a needle  31 , wherein the needle  31  projects from the front end wall  21 . The holder-retaining front portion  51  is pushed to combine with the outward flange  303  when the plunger  4  is pushed to be close to the flexible holder-supporting seat  24 . When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the piston body  521  contacts with the rear opening  300  to stuff the rear opening  300  to lock the needle  31  from injecting the medicament. The holder-retaining front portion  51  sleeves the outward flange  303  to combine with the needle unit  3  after the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 , wherein the needle body  30  is propped by the spacer portion  212 . The needle unit  3  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . The flexible sealing member  5  stops moving due to the immovable needle body  30  and the piston body  521 , and then the flexible sealing member  5  is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 . Thus the needle unit  3  combined with the flexible sealing member  5  and the piston body  521  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   The seventh embodiment of the present invention is illustrated as  FIG. 9A  and  FIG. 9B . The difference between the fifth embodiment and the seventh embodiment of the present invention is the structure of the flexible sealing member  5 . As shown in  FIG. 9A , the flexible sealing member  5  includes a holder-retaining front portion  51 , a sealing rear portion  52 ′ and a curved projection  520 ′, wherein the holder-retaining front portion  51  is a hollow awl extended forward from the hollow sealing rear portion  52 ′. The sealing rear portion  52 ′ includes a hollow space therein. The external diameter of the holder-retaining front portion  51  is as small as that extending forward. The surface of the curved projection  520 ′ is a cambered surface formed on the hollow sealing rear portion  52 ′. As shown in  FIG. 9B , the holder-retaining front portion  51  is pushed to combine with the outward flange  303  when the plunger  4  is pushed forward to be close to the flexible holder-supporting seat  24  when the plunger  4  is pushed continuously. When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the curved projection  520 ′ contacts with the rear opening  300  to stuff the rear opening  300  to prevent the needle  31  from injecting the medicament. The holder-retaining front portion  51  sleeves the outward flange  303  to combine with the needle unit  3  after the plunger  4  is pushed continuously to push the flexible holder-supporting seat  24 , wherein the needle body  30  is propped by the spacer portion  212 . The needle body  30  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . The flexible sealing member  5  stops moving due to the immovable needle body  30  and is then released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24  and release the flexible sealing member  5 . Thus the needle unit  3  combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   As shown in  FIG. 10 , the eighth embodiment of the present invention provides a safety syringe including a syringe barrel  2  with a different front-end wall  21 . The front-end wall  21  includes a front opening  210 ′ for fastening a needle  31 , wherein the needle  31  projects from the front end wall  21 . The holder-retaining front portion  51  is pushed to sleeve and combine with the outward flange  303  when the plunger  4  is pushed to be close to the flexible holder-supporting seat  24 . When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the curved projection  520 ′ contacts with the rear opening  300  to stuff the rear opening  300  to prevent the needle  31  from injecting the medicament. The holder-retaining front portion  51  sleeves the outward flange  303  to combine with the needle unit  3  after the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 , wherein the needle holder  302  is propped by the spacer portion  212 . The needle unit  3  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . The flexible sealing member  5  stops moving due to the immovable needle body  30 , and then the flexible sealing member  5  is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 . Thus the needle unit  3  combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   The ninth embodiment of the present invention is illustrated as  FIG. 11A  to  FIG. 11C . The difference between the ninth embodiment and the first embodiment of the present invention is the structure of the needle unit  3  and the flexible-sealing member  5 . As shown in  FIG. 11A , that the needle unit  3  includes a needle holder  302  and a crook  304 , wherein the crook  304  is fastened on the needle holder  302 . As shown in  FIG. 1B , the flexible sealing member  5  includes a sealing rear portion  52  and a curved projection  520 , wherein the curved projection  520  is a cambered surface. An opening  523  is formed inside the sealing rear portion  52  for wedging the crook  304  of the needle body  30 . As shown in  FIG. 11C , the opening  523  of the sealing rear portion  52  is pushed to wedge the crook  304  for combining with the needle body  30  when the plunger  4  is pushed forward to be close to the flexible holder-supporting seat  24 . When the open front end  41  of the plunger  4  is pushed to be close to the flexible holder-supporting seat  24 , the curved projection  520  contacts with the rear opening  300  to stuff the rear opening  300  to lock the needle  31  from injecting the medicament. The flexible sealing member  5  stops moving due to the immovable needle body  30  propped by the spacer portion  212 , after the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 . The needle body  30  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not contact with the needle unit  3 . The flexible sealing member  5  stops moving due to the immovable needle body  30  and then is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24  and release the flexible sealing member  5 . Thus the needle unit  3  combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   As shown in  FIG. 12 , the tenth embodiment of the present invention provides a safety syringe including a syringe barrel  2  with a different front-end wall  21 . The front-end wall  21  includes a front opening  210  for fastening a needle  31 , wherein the needle  31  projects from the front-end wall  21 . The curved projection  520  is pushed to wedge the crook  304  and combine with the needle body  30  when the plunger  4  is pushed to be close to the flexible holder-supporting seat  24 . When the inward flange  44  is still pushed forward to push the flexible holder-supporting seat  24 , the curved projection  520  contacts with the rear opening  300  to stuff the rear opening  300  to prevent the needle  31  from injecting the medicament. The flexible sealing member  5  stops moving due to the immovable needle body  30  propped by the spacer portion  212 , after the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 . The needle body  30  is released from the flexible holder-supporting seat  24  when the flexible holder-supporting seat  24  does not make contact with the needle body  30 . The flexible sealing member  5  stops moving due to the immovable needle body  30 , and then the flexible sealing member  5  is released from the inward flange  44  because the plunger  4  is continuously pushed to push the flexible holder-supporting seat  24 . Thus the needle unit  3  combined with the flexible sealing member  5  is automatically retracted into the plunger body  40  due to the difference between two different pressures. 
   The present invention provides a safety syringe including simple elements. The present invention also economizes the cost for manufacturing the safety syringes and effectively protects the operating staff from becoming stabbed. 
   Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that within the scope of the appended claims, the present invention may be practiced other than as specifically described herein. 
   Although the specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.