CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of pending application Ser. No. 10/769,067, filed Jan. 30, 2004, which claims priority to German Utility Model DE 20 303 231 U1, filed on Feb. 27, 2003, the contents of both of which are expressly incorporated herein by reference. 
     
    
       [0002]     Safety syringes for minimizing accidental contact with users are generally discussed herein with particular discussions extended to safety syringes having manual and automatic retractable carriages.  
       BACKGROUND  
       [0003]     Syringes are used for injecting fluids and for withdrawing fluids from fluid carrying sources. In an effort to reduce the transfer of communicable diseases, safety features were added to commercially available syringes to minimize accidental contact or sticking with used needle tips.  
         [0004]     Principally among these safety features are tip protectors and syringes with retractable carriages. Broadly speaking, in the tip protector technology, a protective element is mounted over a needle and configured to cover the needle tip of the needle subsequent to an injection to block the needle tip. The protective element may be activated manually to cover the needle tip or automatically by way of releasing a spring to then push the protective element over the needle tip.  
         [0005]     In the retractable carriage technology, the syringe is fitted with a movable carriage at a distal end of the syringe barrel. The carriage may incorporate a fixed needle or a Luer tip for mounting a needle hub with a needle. After an injection, the carriage can be retracted into the interior cavity of the syringe barrel along with the needle to prevent needle stick. More particularly, following an injection, the carriage is typically engaged by a plunger and retracted into the interior cavity of the barrel by pulling onto the plunger in the opposite or proximal direction. Alternatively, the carriage is disengaged from the barrel by the plunger and a spring automatically retracts the carriage into the interior cavity of the barrel.  
         [0006]     Although the prior art safety features for syringes are useful, the safety syringes described elsewhere herein are better alternatives. Among other things, the prior art safety devices have shortcomings in that the air cannot be completely expelled from the syringe barrel prior to aspirating fluid without triggering the safety mechanism by the plunger. This premature triggering, when attempting to fill the device, makes the prior art syringe ineffective and frustrates the health care worker trying to use it.  
       SUMMARY  
       [0007]     The present invention may be implemented by providing a syringe comprising a barrel comprising a gripping flange at a proximal end, an opening at a distal end for receiving a needle hub, a wall structure comprising an exterior surface and an interior surface defining an interior cavity, and a pair of female detents on the interior surface positioned closer to the distal end than the proximal end with a plunger disposed in the interior cavity of the barrel, the plunger comprising a push flange at a proximal end, and a tip holder comprising a plunger tip mounted thereon proximate a distal end; wherein said plunger tip comprises a plunger tip distal end surface spaced apart from the push flange by a first distance. A carriage is incorporated comprising a Luer tip, a passage, a pair of legs extending away from the Luer tip with each leg comprising a male detent wherein the carriage is removably secured to the barrel by engaging the male detents on the carriage with the female detents on the barrel. Finally, the plunger may comprise three plunger positions including a first plunger position in which the plunger tip positioned on the plunger is spaced apart from the carriage; a second plunger position in which the plunger tip or tip holder holding the plunger tip contacts the carriage; and a third plunger position in which the push flange on the plunger moves a distal direction relative to the plunger tip distal end surface such that the push flange is now spaced apart from the plunger tip distal end surface by a second distance, which is less than the first distance.  
         [0008]     In another aspect of the present invention, a syringe comprising a barrel comprising a gripping flange at a proximal end, an opening at a distal end for receiving a needle hub, a wall structure comprising an exterior surface and an interior surface defining an interior cavity, and a pair of hinged hooks proximate the opening may be used with a plunger disposed in the interior cavity of the barrel, the plunger comprising a push flange at a proximal end, and a tip holder comprising a plunger tip mounted thereon proximate a distal end; wherein said plunger tip comprises a plunger tip distal end surface spaced apart from the push flange by a first distance. A carriage may be incorporated comprising a Luer tip, a passage, two wells, and two projections located inside the passage with at least one of the projections being positioned subjacent the wells wherein the carriage is removably secured to the barrel by engaging the hinged hooks on the barrel with the wells. Finally, the plunger may comprise three plunger positions including a first plunger position in which the plunger tip positioned on the plunger is spaced apart from the carriage; a second plunger position in which the plunger tip or tip holder holding the plunger tip contacts the carriage; and a third plunger position in which the push flange on the plunger moves a distal direction relative to the plunger tip distal end surface such that the push flange is now spaced apart from the plunger tip distal end surface by a second distance, which is less than the first distance.  
         [0009]     In still yet another aspect of the present invention, there is provided a syringe comprising a barrel comprising a gripping flange at a proximal end, an inward projection at a distal end comprising an opening and defining a first internal shoulder, a wall structure comprising an exterior surface and an interior surface defining an interior cavity, and a second internal shoulder positioned closer to the opening at the distal end than the gripping flange at the proximal end for use with a plunger comprising a tubular body having an interior cavity disposed in the interior cavity of the barrel, a push flange at a proximal end, and a tip holder comprising a push end having a plunger tip mounted thereon abutting a shoulder on the tubular body. A carriage may be incorporated comprising an elongated body having a spring located thereon, a base extending from the elongated body, a shoulder positioned between the elongated body and the base, and a passage comprising a needle attached thereto wherein the spring is compressed by the first internal shoulder of the barrel and the shoulder on the carriage and the carriage is removably secured to the barrel by wedging a resilient holding tire in between the base of the carriage and the interior surface of the barrel. Finally, the plunger may comprise three plunger positions including a first plunger position in which the plunger tip positioned on the plunger is spaced apart from the carriage; a second plunger position in which the plunger tip simultaneously contacts the shoulder on the plunger and the second internal shoulder on the barrel before the holding tire is substantially pushed off of the base of the carriage; and a third plunger position in which the push end on the plunger pushes the holding tire distally off of the base of the carriage.  
         [0010]     In yet another aspect of the present invention, there is provided a syringe comprising a barrel comprising a gripping flange at a proximal end, an inward projection at a distal end comprising an opening and defining a first internal shoulder, a wall structure comprising an exterior surface and an interior surface defining an interior cavity, and a second internal shoulder positioned closer to the opening at the distal end than the gripping flange at the proximal end for use with a plunger comprising a tubular body having an interior cavity disposed in the interior cavity of the barrel, a push flange at a proximal end, a tip holder comprising a push end having a plunger tip mounted thereon abutting a shoulder on the tubular body, and a radially outwardly projection located distal of the shoulder and positioned inside and abutting a surface of an interior bore of the plunger tip. A carriage may be incorporated comprising an elongated body having a spring located thereon, a base extending from the elongated body, a shoulder positioned between the elongated body and the base, and a passage comprising a needle attached thereto wherein the spring is compressed by the first internal shoulder of the barrel and the shoulder on the carriage and the carriage is removably secured to the barrel by wedging a resilient holding tire in between the base of the carriage and the interior surface of the barrel. Finally, the plunger may comprise three plunger positions including a first plunger position in which the plunger tip positioned on the plunger is spaced apart from the carriage; a second plunger position in which the plunger tip contacts the second internal shoulder of the barrel and the radially outwardly projection on the plunger contacts a proximal surface on the plunger tip; and a third plunger position in which the push end on the plunger pushes the holding tire distally off of the base of the carriage.  
         [0011]     In still yet another aspect of the present invention, there is provided a syringe comprising a barrel comprising a gripping flange at a proximal end, a Luer tip at a distal end, and an end surface defining a shoulder having an opening in communication with the Luer tip, and a wall structure comprising an exterior surface and an interior surface defining an interior cavity for use with a plunger disposed in the interior cavity of the barrel, the plunger comprising a push flange at a proximal end, a tip holder comprising a plunger tip mounted thereon proximate a distal end, and a central tubular body comprising a bore; wherein said plunger tip comprises a plunger tip distal end surface spaced apart from the push flange by a first distance and a needle hub comprising a passage defining a lumen mounted to the Luer tip, a well section having a thin-walled surface forming part of the passage, a needle removably attached to the passage via a detent engagement, and a spring compressed inside the passage. Finally, the plunger may comprise three plunger positions including a first plunger position in which the plunger tip positioned on the plunger is spaced apart from the shoulder on the barrel; a second plunger position in which the plunger tip contacts the shoulder; and a third plunger position in which the push flange on the plunger moves a distal direction relative to the plunger tip distal end surface such that the push flange is now spaced apart from the plunger tip distal end surface by a second distance, which is less than the first distance.  
         [0012]     Yet in another aspect of the present invention, there is provided a syringe comprising a barrel comprising a gripping flange at a proximal end, a Luer tip at a distal end, an end surface defining a shoulder, and a wall structure comprising an exterior surface and an interior surface defining an interior cavity capable of receiving a retracted needle; and a plunger disposed in the interior cavity of the barrel, the plunger comprising a push flange at a proximal end and a tip holder comprising a tip flange and a plunger tip mounted thereon proximate a distal end; said plunger tip comprising a plunger tip distal end surface spaced apart from the push flange by a first distance and a bore having an annular ring comprising a distal end surface and a proximal end surface; the tip flange being disposed in an interior cavity of the bore of the plunger tip. The plunger in accordance with this aspect may comprise four plunger positions including a first plunger position in which the plunger retracts proximally to aspirate a fluid and in which the tip flange on the plunger contacts the distal end surface of the annular ring as the plunger is retracted proximally; a second plunger position in which the plunger moves distally and the plunger tip positioned on the plunger is spaced apart from the shoulder on the barrel; a third plunger position in which the plunger tip contacts the shoulder; and a fourth plunger position in which the push flange on the plunger moves a distal direction relative to the plunger tip distal end surface such that the push flange is now spaced apart from the plunger tip distal end surface by a second distance, which is less than the first distance, and in which the tip flange located in the bore of the plunger tip no longer contacts the distal end surface of the annular ring. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     These and other features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims and appended drawings wherein:  
         [0014]      FIG. 1  is a semi-schematic cross-sectional view of a syringe with a manual retractable carriage provided in accordance with aspects of the present invention;  
         [0015]      FIG. 2  is a semi-schematic cross-sectional view of the syringe of  FIG. 1  with the carriage engaged by a plunger for retracting into the barrel of the syringe;  
         [0016]      FIG. 2   a  is a semi-schematic cross-sectional view of an alternative plunger tip provided in accordance with aspects of the present invention;  
         [0017]      FIG. 2   b  is a semi-schematic exemplary plan view of two alignment plates incorporated by the syringe of  FIG. 1 ;  
         [0018]      FIG. 3  is a semi-schematic cross-sectional view of an alternative syringe with a manual retractable carriage provided in accordance with aspects of the present invention;  
         [0019]      FIG. 4  is a semi-schematic cross-sectional view of the syringe of  FIG. 3  with the carriage engaged by a plunger for retracting into the barrel of the syringe;  
         [0020]      FIG. 5  is a semi-schematic cross-sectional view of another alternative syringe with a manual retractable carriage provided in accordance with aspects of the present invention;  
         [0021]      FIG. 6  is a semi-schematic cross-sectional view of the syringe of  FIG. 5  with the carriage engaged by a plunger for retracting into the barrel of the syringe;  
         [0022]      FIG. 7  is a semi-schematic cross-sectional view of yet another alternative syringe with a manual retractable carriage provided in accordance with aspects of the present invention;  
         [0023]      FIG. 8  is a semi-schematic cross-sectional view of the syringe of  FIG. 7  with the carriage engaged by a plunger for retracting into the barrel of the syringe;  
         [0024]      FIG. 9  is a semi-schematic cross-sectional view of yet another alternative syringe with a manual retractable carriage provided in accordance with aspects of the present invention;  
         [0025]      FIG. 10  is a semi-schematic cross-sectional view of the syringe of  FIG. 9  with the carriage engaged by a plunger for retracting into the barrel of the syringe;  
         [0026]      FIG. 11  is a semi-schematic cross-sectional view of a syringe with a spring loaded carriage provided in accordance with aspects of the present invention;  
         [0027]      FIG. 12  is a semi-schematic cross-sectional view of the syringe of  FIG. 11  with the carriage disengaged and ready for retraction;  
         [0028]      FIG. 13  is a semi-schematic cross-sectional view of the syringe of  FIG. 1  with the carriage retracted inside the barrel;  
         [0029]      FIG. 14  is a semi-schematic cross-sectional view of an alternative syringe with a spring loaded carriage provided in accordance with aspects of the present invention;  
         [0030]      FIG. 15  is a semi-schematic cross-section view of the syringe of  FIG. 14  with the carriage disengaged and ready for retraction;  
         [0031]      FIG. 16  is a semi-schematic cross-sectional view of another alternative syringe with a spring loaded carriage provided in accordance with aspects of the present invention;  
         [0032]      FIG. 17  is a semi-schematic cross-sectional view of the syringe of  FIG. 16  with the carriage disengaged and ready for retraction;  
         [0033]      FIG. 18  is a semi-schematic partial cross-sectional view of a syringe with a needle hub having a spring loaded retractable needle provided in accordance with aspects of the present invention;  
         [0034]      FIG. 19  is a semi-schematic partial enlarged view of the needle hub of  FIG. 18 ;  
         [0035]      FIG. 20  is a semi-schematic partial cross-sectional view of the syringe of  FIG. 18  with the needle retracted partially into the barrel;  
         [0036]      FIG. 21  is a semi-schematic partial cross-sectional view of an alternative syringe with a needle hub having a spring loaded retractable needle provided in accordance with aspects of the present invention;  
         [0037]      FIG. 22  is a semi-schematic partial cross-sectional view of another alternative syringe with a needle hub having a spring loaded retractable needle provided in accordance with aspects of the present invention; and  
         [0038]      FIG. 23  is a semi-schematic partial enlarged view of an alternative needle hub having a spring loaded retractable needle provided in accordance with aspects of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0039]     The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of safety syringes provided in accordance with practice of the present invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. The description sets forth the features and the steps for constructing and using the safety syringes of the present invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and structures may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. Also, as denoted elsewhere herein, like element numbers are intended to indicate like or similar elements or features.  
         [0040]     Referring now to  FIG. 1 , an exemplary syringe  10  with a retractable carriage  12  provided in accordance with aspects of the present invention is shown. In one exemplary embodiment, the syringe  10 , which may be of any standard sizes such as 5 ml or 10 ml, comprises a barrel  14 , a proximal end  16  with a grip flange  18 , and a distal end  20  with an opening  22  for receiving a standard needle hub having a needle attached thereto (not shown).  
         [0041]     The barrel  14  defines a wall surface which has an exterior surface  24  and an interior surface  26 , which defines an interior cavity  28 . Positioned in the interior cavity  28  are the plunger  30 , which has a push flange  32  on one end and a plunger tip or seal  34  on another end, and the carriage  12 . In one exemplary embodiment, the carriage  12  comprises a male Luer tip  36 , a sealing ring  38 , and a pair of proximally extending arms  40   a ,  40   b . The sealing ring  38  is configured to seal against the interior surface  26  of the barrel  14  and in combination with a portion of the interior surface  26  of the barrel  14  defines a volume enclosure, which is variable depending on the position of the plunger  30  and plunger tip  34  relative to the barrel. A lumen  42  is defined through the axial center of the carriage  12  for fluid communication between the interior cavity  28  of the syringe and exteriorly of the barrel  14  variable volume enclosure. The plunger tip  34  is dynamically sealed against the interior surface  26  of the barrier by well known methods.  
         [0042]     The proximally extending arms  40   a ,  40   b  are cantilevered to the base of the sealing ring  38  by a pair of integrally molded bridges  42   a ,  42   b  ( FIG. 2 ). The cantilevered configuration permit the arms  40   a ,  40   b  to flex radially inwardly in the direction of the longitudinal axis defined by the lengthwise central axis of the barrel for reasons discussed further below. Just proximal of the bridges  42   a ,  42   b  are the raised ridges  44   a ,  44   b  and the male detents  46   a ,  46   b , which matingly engage with the female detents  48   a ,  48   b  formed in the interior surface  26  of the barrel  14  when the carriage  12  is in the ready to use position. Two actuated ramps  50   a ,  50   b  are positioned further proximal of the male detents  46   a ,  46   b . In one exemplary embodiment, the actuated ramps  50   a ,  50   b  incorporate diagonal faces for imparting a pair of component forces to the arms  40   a ,  40   b  when pushed by the plunger  30  to flex the arms  40   a ,  40   b  radially inwardly, as further discussed below. The actuated ramps  50   a ,  50   b  terminate in a hook-like configuration for engaging with the shroud  62  ( FIG. 1 ). The barrel  14 , plunger  30 , carriage  12 , and plunger tip  34  may be made from known materials currently used in the art.  
         [0043]     In one exemplary embodiment, the barrel  14  comprises two tapered sections. A first tapered section  52  is formed in the interior cavity  28  of the barrel and acts as a shoulder to stop the distal or forward advancement of the plunger tip  34 . The second tapered section  54  is formed on the exterior surface  24  of the barrel  14  for aesthetic appeal that may otherwise be eliminated. Alternatively, the tapered sections  52 ,  54  may be squared, or may incorporate a combination of a squared finish and a tapered finish. The barrel is preferably transparent or semi-transparent and may include indicia such as labeling, markings, or other features for references.  
         [0044]     In one exemplary embodiment, the plunger  30  incorporates a pair of elongated plates  55   a ,  55   b  having a plus (“+”)-shaped cross-section. One or more push plates  56  may be formed on plunger  30  for reinforcement. A distally projecting post or tip holder  58  is positioned distal of the one or more push plates  56  for positioning the plunger tip  34  thereon. A plunger disc  60  is formed on the distally projecting post  58  and is preferably spaced from the most distal push plate  56  by a gap, which should be of sufficient width for accommodating a portion of the plunger tip  34 , as further discussed below. A generally cylindrical shroud  62  is positioned distal of the plunger disc  60  having a pusher end  64  ( FIG. 2 ) and a pair of receiving slots  66 . In one exemplary embodiment, the pusher end  64  and the plunger disc  60  each comprises a tapered surface for reasons further discussed below. The receiving slots  66  should have a dimension sufficient to receive the hook-like ends of the actuated ramps  50   a ,  50   b.    
         [0045]     The shroud  62  comprises a distal end surface  67  having a pair of openings  69  for receiving the proximally extending arms  40   a ,  40   b  of the carriage  12 . The plunger tip  34  comprises a bore  68  for receiving the shroud  62 . In one exemplary embodiment, the bore  68  of the plunger tip comprises a first diameter section  70 , a second diameter section  72 , and a third diameter section  74  ( FIG. 2 ). However, the internal bore  68  can have a same diameter by modifying the dimensions of the post  58 , shroud  62 , and/or carriage  12 . An inwardly extending ring  76  is formed on the proximal end of the plunger tip  34  and sized to form a size-on-size friction fit with the distally projecting post  58  of the plunger  30 . A second inwardly extending ring  78  spaced from the first inwardly extending ring  76  is positioned at the transition between the second diameter section  72  and the third diameter section  74  of the plunger tip. The space or gap  80  between the first  76  and second  78  inwardly extending rings functions as an activation gap and is configured to receive the plunger disc  60  when the plunger  30  is advanced distally to activate or retract the carriage  12 , as further discussed below.  
         [0046]     In an alternative plunger tip  34 ′ embodiment ( FIG. 2   b ), the second inwardly extending ring  78  may be omitted and the proximal end  61  of shroud  62 ′ extended or moved further proximal to be adjacent the distal side of extending ring  76 ′. This eliminates the need for a gap  80  and simplifies the form of plunger tip  34 ′. The alternative plunger tip  34 ′ otherwise functions the same as the plunger tip  34  of  FIGS. 1 and 2 .  
         [0047]     To use the syringe  10 , a commercially available needle attached to a needle hub (not shown) is first mounted onto the Luer tip  36 . Because the syringe  10  has a Luer tip  36  and not a permanently attached needle on the carriage  12 , different needle sizes may be mounted onto the Luer tip for aspirating, withdrawing a sample, or performing an injection. Preferably, if the syringe is used to withdraw a sample, the needle with the needle hub should include a tip protector or clip for covering the needle tip.  
         [0048]     With the barrel  14  filled with a medicinal fluid, which can be any number of fluids, to a desired volume and the needle injected into a subject, the plunger  30  is advanced distally with a distally directed force F D  in the direction of the needle to discharge the fluid. The injection is completed when the plunger tip  34  contacts the shoulder or first tapered section  52  of the barrel  14 . At this point, preferably the needle is withdrawn from the subject by pulling on the plunger  30  via the push flange  32  while pushing the barrel  14  distally against the patient&#39;s skin. The needle and carriage  12  retraction into the barrel are simultaneously accomplished as described in detail below. Alternatively, the needle can be withdrawn from the patient prior to retracting the needle into the barrel  14 .  
         [0049]     To retract the carriage  12  with the needle still mounted thereto, the plunger  30  is further advanced distally with an activated force F A  sufficient to bend the proximally extending arms  40   a ,  40   b  inwardly at the bridges  42   a ,  42   b , which act as fulcrum points. In one exemplary embodiment, the activated force F A  is greater than the distally advancing force F D  so that a user in using the syringe  10  can feel a clear delineation between injecting a fluid and withdrawing the carriage  12 .  
         [0050]     The bending of the arms  40   a ,  40   b  occur when the pusher end  64  of the shroud  62 , which preferably comprises a tapered face, contacts the actuated ramps  50   a ,  50   b  of the arms  40   a ,  40   b  and impart a pair of component forces. The arms  40   a ,  40   b  bend radially inwardly and the male detents  46   a ,  46   b  separate from the female detents  48   a ,  48   b  as the plunger  30  advances distally under an actuated force F A . The arms continue to bend as until the hook-like ends of the actuated ramps  50   a ,  50   b  latch with the receiving slots  66   a ,  66   b  located in of the shroud  62 . When the activated force F A  is no longer applied, the arms  40   a ,  40   b , due to their resiliency, snap radially outwardly a small radial distance to securely engage with the slots  66   a ,  66   b  ( FIG. 2 ).  
         [0051]     During the activation step, the plunger disc  60  pushes against the inwardly extending ring  76  of the plunger tip  34  until the ring  76 , due to its resiliency, pops over the disc  60  so that the disc can then move into the activated space  80 . As readily apparent, subsequent to the plunger tip  34  abutting the shoulder  52  of the barrel and stop moving, the plunger  30  may still move distally relative to the plunger tip to disengage the carriage  12  from the barrel  14 . Unrestrained, the carriage  12  and needle (not shown) can then be retracted into the interior cavity  28  of the barrel  14  by grasping and pulling on the push flange  32  proximally to retract the needle into the barrel  14 .  
         [0052]     To prevent retracting the carriage  12  too far into the barrel  14  and possibly dislodge the carriage  12  from the barrel  14  and to also prevent the needle from protruding back out the distal end  20  of the barrel, in one exemplary embodiment, a stop ring  82  ( FIG.2 ), which may comprise an annular projection on the interior surface  26  of the barrel near the grip flange  18 , may be incorporated to hold the plunger  30  in the completely retracted position. The plunger  30  may include a notch  84  along each edge of the elongated plates  55   a ,  55   b  to provide a breaking point for breaking off the plunger and avoiding accidentally pushing the needle distally into an unprotected position. Once the carriage  12  is retracted into the barrel and the plunger  30  broken off, the syringe may be safely disposed of per standard protocols.  
         [0053]     For aligning the hooks on the actuated ramps  50   a ,  50   b  of the carriage  12  with the receiving slots  66   a ,  66   b  located on the shroud  62  of the plunger  30 , alignment plates  86   a ,  86   b  may be incorporated at the proximal end  16  of the barrel  14 . The alignment plates  86   a ,  86   b  may be integrally molded with the push flange  18  via living hinges  88  and then glued, welded, or engaged to the push flange  18  by detents. Alternatively, the alignment plates  86   a ,  86   b  may be separately attached to the push flange  18  via adhesive, welding, or detents without the living hinges  88 .  
         [0054]     Referring to  FIG. 2   a , which is an exemplary plan view of the alignment plates  86   a ,  86   b , each alignment plate  86   a  or  86   b  comprises a gripping portion  90  and a semi-circular portion  92  comprising a slot  94  and a part of a slot  96 . The two alignment plates  86   a ,  86   b  come together at a parting line and the two part slots  96  on each alignment plate makes a whole slot. The two whole slots  94  are sized to receive one rectangular plate  55   a  of the plunger  30  while the partial slots  96  together receive the other rectangular plate  55   b  of the plunger  30 . Cooperation between the alignment plates  86   a ,  86   b  and the rectangular plates  55   a ,  55   b  prevents the plunger  30  from angularly rotating and misaligning the hooks on the actuated ramps  50   a ,  50   b  with the receiving slots  66   a ,  66   b  located on the shroud  62 .  
         [0055]     Turning now to  FIG. 3 , an alternative manual retractable syringe  98  provided in accordance with aspects of the present invention is shown. The syringe  98  has features that are similar with features described above for the syringe  10  shown with reference to  FIGS. 1-2A  with the exception of the plunger tip  100  and the manner in which the plunger tip engages and interacts with the plunger  30 . In the present syringe  98  embodiment, the shroud  62  incorporates two openings  102   a ,  102   b  at the distal end surface  67  for receiving the proximally extending arms  40   a ,  40   b . The plunger tip  100  comprises a bore  101  having a substantially uniform inside diameter for receiving the shroud  62 . An inwardly extending ring  104  is incorporated at the proximal end of the plunger tip  100  and sized to form a size-on-size friction fit with the distally projecting post  58  of the plunger  30 . In the ready to use configuration of  FIG. 3 , the inwardly extending ring  104  abuts the plunger disc  106  located on the post  58  of the plunger  30 , which in the present embodiment does not incorporate a tapered face. A shroud  62  comprising a pair of receiving slots  66  and pusher end  64  is disposed inside the bore  101  of the plunger tip  100  for engaging with the hooks on the carriage  12  and retracting the same into the barrel  14 .  
         [0056]     The syringe  98  may be used and the carriage  12  may be retracted into the barrel  14  in the same manner as described above with reference to the syringe  10  of  FIGS. 1 and 2 . More particularly, following an injection, the distal end of the plunger tip  100  abuts the barrel shoulder  52  and the proximally extending arms  40   a ,  40   b  of the carriage  12  project into the openings  69  of the distal end surface  67  of the shroud  62 . To retract the carriage  12 , an activated force F A  is then applied on the plunger  30  to further advance the plunger distally relative to the distal end of the plunger tip  100 . This activated force F A  causes the pusher end  64  of the shroud  62  to exert a pair of component forces to the actuated ramps  50   a ,  50   b , which then bends the proximally extending arms  40   a ,  40   b  radially inwardly. At the same time, the plunger disc  106  pushes against the inwardly extending ring  104  and compresses the plunger tip  100  ( FIG. 4 ).  
         [0057]     The carriage  12  may be withdrawn proximally into the barrel  14  when the male detents  46   a ,  46   b  disengage from the female detents  48   a ,  48   b  and the hooks on the end of the arms  40   a ,  40   b  engage the receiving slots  66  located on the shroud  62 . During the retraction procedure, the plunger tip  100  will expand in the distal direction until it touches or reaches near the proximal edge  108  of the side ridges  44   a ,  44   b  of the carriage  12 .  
         [0058]      FIG. 5  shows another alternative retractable syringe  110  provided in accordance with aspects of the present invention. The syringe  110  is similar to the syringes of  FIGS. 1-4  with the exception the carriage  112  and the manner in which it engages the barrel  114  and is retracted by the plunger  116 . In one exemplary embodiment, the carriage  112  incorporates a pair of actuated pistons  118   a ,  118   b  formed in two wells  120  located on the carriage. The carriage  112  further comprises a female lock  122  around a Luer tip  36 , and a hub  124  proximal of the actuated pistons  118   a ,  118   b . The hub  124  incorporates a flange  126  for abutting against the shoulder  128  located on the barrel  114  to axially align the carriage  112  relative to the barrel  114  during engagement of the carriage  112  to the barrel  114 . The hub  124  includes a proximal surface  127  having a configuration to accommodate the contour of the distal end surface  130  of the plunger tip  132 .  
         [0059]     The carriage  112  comprises a bore  133  which defines a lumen  134  for fluid communication between the variable interior cavity  28  of the barrel  114  and the needle (not shown) which may be mounted to the syringe by the way of mounting a needle hub to the Luer tip  36 . In one exemplary embodiment, the bore  133  incorporates two inward projections for interacting with the plunger  116 . The first projection  136  is located near the opening of the Luer tip  36  and has a tapered or sloped surface on a proximal side. On the edge opposite the sloped surface, the first projection  136  preferably comprises a square finish, for reasons further discussed below. The second projection  138  is formed subjacent the two actuated pistons  118   a ,  118   b . To fixedly secure the carriage  112  to the barrel  114 , the barrel incorporates a pair of hinged hooks  140  at the distal end of the barrel. The hinge hooks  140  engage an edge of the wells  120  located on the carriage  112  to lock the carriage to the barrel. The hinge hooks  140  can be integrally molded on the carriage  112 .  
         [0060]     In one exemplary embodiment, the plunger tip  132  incorporates a bore for receiving the extension pin or distally projected post  142  of the plunger  116 , an internal space or cavity  145 , and a pair of extension legs  144   a ,  144   b  for setting a gap between certain parts of the plunger  116  and of the plunger tip  132 . A gap or a space  146  located in between the extension legs  144   a ,  144   b  are configured to receive a drum  148  located at the base of the extension pin  142 . The gap or space  146  should have sufficient depth to receive the drum  148  and not delimit or restrict the hooks on the plunger  116  from grabbing the first projection  136  located in the Luer tip  36 , as further discussed below. The plunger  116  also comprises a flange  147  set in the internal space  145  of plunger tip  132 , and in one exemplary embodiment, comprises a tapered face on its distal side to facilitate assembly over the tip holder. Flange  147  secures plunger tip  132  to the plunger  116  during aspiration of a fluid. The internal space  145  should be sufficiently long to allow the flange  147  to move from a proximal end within the internal space  145  to a distal end during activation so as not to delimit or hinder the hooks  152  from grabbing first projection  136 .  
         [0061]     A hooking rod  150  comprising a pair of hooks  152  ( FIG. 6 ) extends from the distal end of the extension pin  142  for hooking engagement with the first projection  136  located in the bore of the Luer tip  36 . The hooks  152  are configured to deflect when moved distally past a reduced diameter created in the bore of the Luer tip by the first projection  136  to grab the square face of the first projection  136  in a detent configuration.  
         [0062]     To retract the carriage  112  into the interior cavity  28  of the barrel  114 , the plunger  116  is first advanced distally with a distally directed force F D  until the distal end surface  130  of the plunger tip  132  contacts the proximate surface  127  of the hub  124  of the carriage  112 . In this position, the distal end of the extension pin  142  should reside just proximal of the second projection  138  located subjacent the actuated pistons  118   a ,  118   b  ( FIG. 5 ). As a distally actuated force F A  force is then applied to the plunger  116 , the force causes the extension legs  144   a ,  144   b  to bend outwardly, which then moves the extension pin  142  past the second projection  138  to push the actuated pistons  118   a ,  118   b  radially outwardly. Concurrently therewith, the actuated pistons  118   a ,  118   b  push the hinged hooks  140  on the barrel to unlock the hinged hooks  140  from the wells  120 . Also at the same time, the hooks  152  on the hooking rod  150  moves distal of the first projection  136  to then grab the projection. When the plunger is moved in the opposite proximal direction, the interaction between the hooks  152  and the first projection retracts the carriage  112  into the barrel  114 .  
         [0063]     Although alignment plates  86   a ,  86   b  are not required to align parts of the plunger  116  to parts of the carriage  112 , the plates  86   a ,  86   b  may be included to prevent retracting the plunger  116  completely outside of the barrel  114 . Alternatively or in addition thereto, a stop ring  82  may be incorporated near the proximal end of the barrel to engage with the proximal most push plate  56  on the plunger  116  to prevent proximal movement of the plunger. The plunger can then be broken off at the notches  84 , as previously described.  
         [0064]     In another alternative embodiment (not shown), the hooking rod  150  and hooks  152  are eliminated from the end of the extension pin  142  of the syringe of  FIG. 5 . A second set of actuated pins proximal of the existing actuated pins  118   a ,  118   b  on the carriage  112  are added, which are to be actuated and engaged by a pair of projections or ramps located on the extension pin  142 . In this alternative embodiment, the extension pin  142  would actuate the first set of actuated pins  118   a ,  118   b  to disengage the carriage  112  from the barrel  114  and the two projections or ramps on the extension pin  142  would latch or engage with the second set of actuated pins to grab the carriage  112 . Once the plunger is retracted, the cooperation between the ramps and the second set of activated pins retract the carriage proximally into the barrel. In this embodiment, the diameter of the extension pin proximal of the two projections or ramps (i.e., the base of the extension pin) should have the same diameter as the largest cross-sectional dimension of the projections or ramps measured at their widest peaks.  
         [0065]      FIG. 7  is another alternative retractable syringe  154  provided in accordance with aspects of the present invention. The syringe  154  is substantially similar to the syringe  110  described above with reference to  FIGS. 5 and 6  with the exception of the plunger tip  156  and extension pin  158  of the plunger  160 , which are different. In the present embodiment, the extension legs  144   a ,  144   b  of the plunger tip are eliminated and a bore  162  incorporated with an annular ring  164 . A proximal end annular ring  166  spaced apart from the interior annular ring  164  is also incorporated. The two rings define an activation space or gap  168  for accommodating a part of the extension pin  158 , as further discussed below.  
         [0066]     A pair of plunger discs  172 ,  174  are incorporated with the base  170  of the extension pin  158  for cooperating with the plunger tip  156 . The distal most plunger disc  174  preferably comprises a tapered surface for facilitating advancing the disc past the interior annular ring  164 . In one exemplary embodiment, the proximal most plunger disc  172  incorporates a square finish for pushing the proximal annular ring  166  of the plunger tip  156  distally when a distally directed force F D  is applied. However, a slight taper, of less angular offset than the distal most disc  174 , may be incorporated by the proximal most disc  172  to facilitate moving the disc  172  past the end annular ring  166  when an activated force F A  is applied ( FIG. 8 ).  
         [0067]     To retract the carriage  112  into the interior cavity  28  of the barrel  114 , the plunger  160  is first advanced distally with a distally directed force F D  until the distal end surface  130  of the plunger tip  156  contacts the proximal surface  127  of the carriage  112 . In this position, the distal end of the extension pin  158  should reside just proximal of the second projection  138  located subjacent the actuated pistons  118   a ,  118   b . As a distally actuated force F A  force is then applied on the plunger  160 , the force causes the two plunger discs  172 ,  174  to move past the two annular rings  166 ,  164  positioned inside the bore  162  of the plunger tip  156 , which concurrently moves the extension pin  158  past the second projection  138  to push the actuated pistons  118   a ,  118   b  radially outwardly. Also concurrently therewith, the actuated pistons  118   a ,  118   b  push the hinged hooks  140  on the barrel  114  to unlock the hinged hooks  140  from the wells  120 . Also at the same time, the hooks  152  on the hooking rod  150  moves distal of the first projection  136  to then grab the projection. The carriage  112  can now be retracted by pulling on the plunger  160  in the proximal direction. The plunger  160  can then be broken off as previously described.  
         [0068]      FIG. 9  shows yet another alternative manual retract syringe  176  provided in accordance with aspects of the present invention. The syringe  176  is substantially similar to the syringes  110 ,  154  described above with reference to  FIGS. 5-8  with the exception of the plunger tip  178  and extension pin  183  of the plunger  180 , which are different. More particularly, the extension pin  183  in the present embodiment extends directly from the distal most push plate  56  on the plunger  180  without a base or a drum. In addition, the plunger tip  178  has a single annular end ring  182  without internal annular rings. The extension pin  183  comprises a flange  185  located just distal of the annular end ring  182 . The flange  185  is preferably tapered on its distal side to facilitate assembly through the annular end ring  182 , but flat on its proximal side to secure the plunger tip  178  on plunger  180  during aspiration of a fluid. The bore or cavity  184  inside the plunger tip  178  should be sufficiently dimension to permit flexing of the plunger tip when compressed by the plunger  180  ( FIG. 10 ).  
         [0069]     To retract the carriage  112  into the interior cavity  28  of the barrel  114 , the plunger  180  is first advanced distally with a distally directed force F D  until the distal end surface  130  of the plunger tip  178  contacts the proximal surface  127  of the carriage  112 . In this position, the distal end of the extension pin  183  should reside just proximal of the second projection  138  located subjacent the actuated pistons  118   a ,  118   b . As a distally actuated force F A  force is then applied on the plunger  180 , the force causes the push plate  56  to push against the annular ring  182  of the plunger tip  178  and compresses the plunger tip ( FIG. 10 ). At the same time, the extension pin  183  travels past the second projection  138  to push the actuated pistons  118   a ,  118   b  radially outwardly. Also, concurrently therewith, the actuated pistons  118   a ,  118   b  push the hinged hooks  140  on the barrel  114  to unlock the hinged hooks  140  from the wells  120  on the carriage  112 . Also at the same time, the hooks  152  on the hooking rod  150  moves distal of the first projection  136  to then grab the projection. The carriage  112  can now be retracted by pulling on the plunger in the proximal direction. The plunger can then be broken off at the notches  84 , as previously described.  
         [0070]     Referring now to  FIG. 11 , an automatic needle retract syringe  186  provided in accordance with aspects of the present invention is shown. The syringe  186  comprises a syringe barrel  188 , a plunger  190  with a plunger tip  192 , and a carriage  194  that is spring loaded with a spring  196 . The barrel  188  in the present embodiment comprises a gripping section  198  having a grip flange  18  and an enlarged barrel section  200  sized to receive a part of the push flange  202  on the plunger  190 . In one exemplary embodiment, the proximal end  204  of the enlarged barrel section  200  comprises a projection or ring for engaging with the perimeter of the push flange  202  when the push flange is pushed up against the barrel  188  to retract the needle ( FIGS. 12 and 13 ), as further discussed below. Alternatively, the diameter of the enlarged barrel section  200  could be sized to form an interference fit with the push flange  202  when the same is moved into the barrel to retract the needle.  
         [0071]     Distally of the gripping section  198  is the variable chamber section  206 , which stores fluid to be infused or injected and varies in volume depending on the position of the plunger tip  192  relative to the barrel  188 . Distal of the variable chamber section  206  is the engagement chamber  208 . The engagement chamber  208  comprises a first engagement section  210  comprising an annular interior surface  212  that cooperates with the carriage  194  to compress a holding tire  214 , which may be made from any number of elastomeric rubber or of the same elastomer as the plunger tip  192 . Distal thereof is the second engagement section  211 . The compressed holding tire  214  acts as an anchor to hold the carriage  194  in place or position, which then allows the spring  196  to be compressed between the end wall  216  at the distal end  218  of the barrel  188  and the shoulder  220  located near the base  222  of the carriage  194 . As readily apparent, the holding tire  214  should have a compression force exerted on it by the carriage  194  and the barrel  188  sufficient to resists the spring force generated by the compressed spring  196 . Additional hold on the holding tire  214  can come from the projection  244  located at the shoulder  241  of the barrel  188 .  
         [0072]     A passage or lumen  224  is formed at the axial center of the carriage  194  to permit fluid communication between the interior cavity of the barrel  188  and outside the barrel. In one exemplary embodiment, a needle  226  comprising a needle tip is permanently secured to the carriage  194  via gluing the same to the carriage at the glue well  228 .  
         [0073]     In one exemplary embodiment, the plunger  190  comprises a first tubular section  230  and a second tubular section  232 , which defines an exterior shoulder  234  therebetween. The plunger tip  192  is positioned on the exterior surface of the first tubular section  230  and abuts the exterior shoulder  234 . Interiorly, a plug  236 , which can be made from an elastomer material, is compressed against the interior surface of the second tubular section  232  by its base section  238 , which is relatively larger than its frontal projection  240 . Prior to activating the spring ( FIG. 11 ), the distal end of the plug  236 , the cylindrical end of the first tubular section  230 , and the plunger tip  192  are substantially aligned so that they occupy substantially all of the head space of the variable chamber section  206  to substantially discharge all of the fluid within the barrel. To facilitate this goal, the shoulder  241  between the variable chamber section  206  and the engagement chamber  208  can be square to minimize head space. Alternatively, the plunger  192  can be shaped to occupy substantially all of the head space.  
         [0074]     To retract the carriage  194 , the plunger  190  is first moved distally with a distally directed force F D  until the distal end surface of the plunger tip  192  contacts the shoulder  241  located at the interface between the first engaging section  210  and the variable chamber  206 . At this point, the end tip or distal tip  229  of the first tubular section  230  of the plunger  190  contacts the holding tire  214  and the proximal end  231  of the carriage  194  contacts the tip of the plug  236 . When an actuated force F A  is then applied on the plunger  190 , the first tubular section  230  of the plunger  190  moves over the proximal end of the carriage  194  in a telescoping fashion. At the same time, the plunger tip  212  is compressed by the exterior shoulder  234  on the plunger  190  and the shoulder  241  on the barrel  188 .  
         [0075]     Further plunger  190  distal movement causes the tip  229  of the tubular portion  230  to move the holding tire  214  distally off the base section  222  of the carriage  194  and the base  238  of the plug  236  away from the interior surface of the first tubular section  230 . In one exemplary embodiment, the holding tire  214  and the base  238  of the plug are released simultaneously from their respective seats when the plunger  190  moves distally to retract the carriage  194 . In an alternative embodiment, the holding tire  214  moves off of its seat prior to the base  238  of the plug  236  moves off of its seat. Still alternatively, the base  238  of the plug  236  moves off of its seat prior to the holding tire  214  moves off of its seat.  
         [0076]     Once both the holding tire  214  and the plug  236  move off of their respective seats, the spring  196  is released and launches proximally in the direction of the push flange  202 . Because they are either directly or indirectly in contact with the spring  196 , the carriage  194 , the needle  226 , and the plug  236  are also simultaneously launched distally by the spring. The spring action thus retracts the needle  226  into the interior cavity of the plunger  190  to thereby prevent accidental contact with the needle tip ( FIG. 13 ).  
         [0077]     To further assist in securing the holding tire  214  against its seat, which is the mating surface area provided by the interior surface of the barrel and the base  222  of the carriage  194 , in one exemplary embodiment, a projection  244  is incorporated at the shoulder  241  inside surface of the barrel  188 . The raised area  244  aids in snapping the holding tire  214  in place against the spring force when the plunger is in a withdrawn position.  
         [0078]     In one exemplary embodiment, the plunger push flange  202  is seated inside a recessed section  242  ( FIGS. 12 and 13 ) of the enlarged barrel section  200  of the barrel  188  following the retraction of the carriage. Because the push flange  202  incorporates a smooth contour, the plunger  190  is made difficult to be grasped and moved proximally. In an alternative embodiment, a detent engagement between the barrel and the push flange may be incorporated to further deter access to the used needle.  
         [0079]     An alternative automatic needle retract syringe  246  provided in accordance with aspects of the invention is shown in  FIGS. 14-15 . The syringe  246  is substantially similar to the syringe  186  described above with reference to  FIGS. 11-13  with the exception of the plunger tip  248  and plunger first tubular section  230 , which are different. In the present embodiment, the plunger tip  248  incorporates a pair of extension legs  250   a ,  250   b  and the first tubular section  230  of the plunger  190  incorporates a flange  227 . The extension legs  250   a ,  250   b  establish a gap or space between the exterior shoulder  234  on the plunger  190  and the plunger tip  248  when the syringe is in a ready to use position and during an injection when a distally directed force F D  is applied. The flange  227  of plunger  190  first tubular section  230  is positioned at the proximal end of space  251  inside the plunger tip  248 . The flange  227  secures the plunger tip  248  onto plunger  190  during aspiration of a fluid, and in one exemplary embodiment comprises a tapered face on its distal side. However, when an actuated force F A  is applied on the plunger  190 , the shoulder  234  bends the extension legs  250   a ,  250   b  outwardly to permit further distal movement of the plunger  190  relative to the plunger tip to retract the carriage  194  ( FIG. 15 ). During activation, the flange  227  moves from a proximal position to a distal position within the space  251  ( FIG. 15 ).  
         [0080]     In the ready to retract position ( FIG. 14 ), the plunger tip  248 , plug  236 , and first tubular section  230  of the plunger  190  should occupy substantially all of the head space of the variable volume chamber to minimize fluid waste. In this configuration, the plunger tip  248  should be in contact with the shoulder  252  on the barrel  188 , the end tip  229  of the plunger  190  should be in contact with the holding tire  214 , and the proximal end  231  of the carriage  194  should be in contact with the plug  236 . Thus, as the plunger  190  is then moved distally to retract the carriage  194 , the extension legs  250   a ,  250   b  are bent outwardly by the shoulder  234 , the holding tire  214  and the plug  236  are moved off of their respective seats, and the spring  196  is released to expand and retract the carriage  194  ( FIG. 15 ) into the interior cavity of the barrel  188 .  
         [0081]      FIGS. 16 and 17  show yet another alternative automatic needle retract syringe  254  provided in accordance with aspects of the present invention. The syringe  254  is substantially similar to the syringes  186 ,  246  described above with reference to  FIGS. 11-15  with the exception of the plunger tip  256 , which is different. In addition, the first tubular section  230  of the plunger  190  has been slightly modified to cooperate with the plunger tip  256 , as further discussed below.  
         [0082]     The plunger tip  256  in the present embodiment comprises a distal annular ring  258  and a proximal annular ring  260 , which define a space  262  therein between. The distal and proximal annular rings  258 ,  260  form a size-on-size friction fit with the exterior surface of the first tubular section  230  of the plunger. Internally, a projection  264  on the first tubular portion  230  contacts the interior surface of the space  262  of the plunger tip  256 . The contact between the interior surface of the space  262  and the projection  264  provide added resistance against movement of the plunger tip  256  relative to the plunger  190  during proximal movement of the plunger, i.e., during aspiration of a fluid. In addition, the projection  264  establishes a gap between the proximal annular ring  260  and the exterior shoulder  234  formed at the intersection of the first tubular portion  230  and the second tubular portion  232 . Still further, the projection  264  facilitates aspirating fluid into the syringe by securing the plunger tip  256  from falling off of the first tubular portion  230  when the plunger moves proximal. Alternatively, a second projection or flange  172  (as shown in  FIGS. 7 and 8 ) can be incorporated just proximal of the plunger tip  256 , just proximal of the annular ring  260 , to further secure the plunger tip  256  on the plunger  190 . If incorporated, the proximal annular ring  260  of the plunger tip  256  would be secured in the gap between both projections  264  and  172 .  
         [0083]     When the plunger  190  is in position to retract the carriage  194  ( FIG. 16 ), the plunger tip  256 , plug  236 , and first tubular section  230  of the plunger  190  should occupy substantially all of the head space of the variable volume chamber to minimize fluid waste. In this configuration, the plunger tip  256  should be in contact with the shoulder  252  on the barrel  188 , the end tip  229  of the plunger  190  should be in contact with the holding tire  214 , and the proximal end  231  of the carriage  194  should be in contact with the plug  236 . Thus, as the plunger  190  is then moved distally to retract the carriage  194 , the actuated force F A  overcomes the friction between the plunger tip  256  and the first tubular portion  230  and allows the plunger  190  to move relative to the plunger tip  256 . Concurrently therewith, the holding tire  214  and the plug  236  are moved off of their respective seats and the spring  196  is released to expand and retract the carriage  194  ( FIG. 17 ) into the interior cavity of the barrel. In the alternative embodiment (not shown), the most proximal projection  172  (as shown in  FIGS. 7 and 8 ) would be forced under the proximal annular ring  260  when an actuated force F A  is applied.  
         [0084]     Turning now to  FIG. 18 , a syringe  266  for use with a needle hub  268  having a spring loaded retractable needle  270  provided in accordance with aspects of the present invention is shown. The barrel  272  in the present embodiment comprises an integrally molded Luer tip  274  and a female lock  276  at the distal end  278  and a grip flange  280  at the proximal end  282 . A plunger  284  is positioned internally of the barrel. The plunger  284  comprises an elongated tube  286  defining a bore  288 , and four rectangular plates or fins  290  attached to the tube  286  with both the fins and tube attached to the push flange  292 , which has an opening  294  for molding the tube  286  and a frangible seal  296  for holding an end cap  297  at the distal end of the tube ( FIGS. 18 and 19 ). Preferably, the bore  288  has a greater inside diameter than the end cap  297 , for reasons explained below. The opening  294  is then sealed with a plug  298 . The plunger  284  also includes a push plate  300  and a distally projecting tip holder  302 , which is located proximal of an extension pin  304 , and which makes up part of the tube  286 . The extension pin  304  is sized to fit within the Luer tip  274 , which is sized to receive the needle hub  268 , as further discussed below. In one exemplary embodiment, the elongated tube  286  is cylindrical in shape. However, other elongated shaped bodies may be incorporated without deviating from the scope of the present invention.  
         [0085]     The plunger tip  308  comprises an opening  310  for accommodating the extension pin  304 , a proximal annular ring  312  forming a size-on-size friction fit with the tip holder  302 , and a pair of proximally extending extension legs  314   a ,  314   b . In one exemplary embodiment, the extension legs  314   a ,  314   b  and the annular ring  312  contact both the push plate  300  and the tip holder plate  316 . However, a small gap between the annular ring  312  and the tip holder plate  316  is acceptable.  
         [0086]     In one exemplary embodiment, the needle hub  268  useable with the syringe  266  of the present embodiment comprises a housing  318 , which comprises a distal housing structure  320  having a needle  270  protruding therefrom, a proximal housing structure  322  having male threads  320  thereon for threaded engagement with the female lock  276 , a central activation compartment  324  disposed therebetween, and a bore  326  defined therethrough. A generally cylindrical tube  323  with optional support fins  325  are located at the distal end of the needle hub  268 . The bore  326  extends through the cylindrical tube  323  and has a size sufficient to accommodate the needle  270  and a spring  327 , as further discussed below. At the distal end of the cylindrical tube  323  is an annular cap  329  having a close tolerance fit with the outside diameter of the needle  270 . The annular cap  329  provides an anchor and supports one end of the spring  327 , as further discussed below.  
         [0087]     Exteriorly, the housing  318  is tapered inwardly in the direction from the proximal housing structure  322  towards the distal housing structure  320 , although a straight cylinder or wall may be acceptable. At the central activation compartment  324 , the housing incorporates two wells  328   a ,  328   b  ( FIG. 19 ), which form two thin-walled sections  330  with the bore  326  of the hub  268 . The thin-walled sections  330  each include a bulge section  332  that forms a receiving space inside the bore  326  for mating engagement with the needle sleeve  334 , as further discussed below. Referring to  FIG. 19  in addition to  FIG. 18 , the thin-walled sections  330  of the wells  328   a ,  328   b  each includes a base section  336 , a transition section  338 , which is tapered or angled from the base section, and a gripping section  340 , where the bulge  332  is located. Alternatively, a single well with a single thin-walled section may be incorporated in the needle hub.  
         [0088]     The needle sleeve  334  ( FIG. 19 ) comprises a generally elongated tube that includes a bulge section  342  and a bore. In one exemplary embodiment, the exterior surface  344  of the sleeve  334  comprises an undulating surface for increased gripping engagement with the gripping sections  340  of the wells  328   a ,  328   b.  To secure the needle  270  to the sleeve  334 , the sleeve bore comprises a glue well  346  for gluing the needle to the sleeve ( FIG. 19 ).  
         [0089]     To assemble the needle hub  268 , the spring  327  is first mounted over the combination needle  270  and needle sleeve  334 . The needle  270  and spring  327  are then inserted into the bore  326  of the needle hub  268  from the proximal end opening of the hub. The needle  270  is pushed distally through the bore  326  until the needle sleeve  334  engages the gripping section  340  of the needle hub, at the two wells  328   a ,  328   b . In one exemplary embodiment, the engagement is achieved when the bulge  342  on the sleeve  334  fits into the space provided by the bulge  332  of the gripping section  240 .  
         [0090]     To retract the needle  270 , the plunger  284  is first moved distally with a distally directed force F D  until the distal end surface of the plunger tip  308  contacts the shoulder or end  348  of the barrel  272 . At this point, the extension pin  304  is positioned inside the Luer tip  274  with the end cap  297  on the extension pin  304  slightly spaced apart from the proximal end  350  of the needle  270  ( FIG. 19 ). As an actuated force F A  is then applied to the plunger  284 , the push plate  300  moves distally to bend the extension legs  314   a ,  314   b  inwardly (or outwardly if the extensions legs  314   a ,  314   b  were positioned closer to the tip holder  302 ). Concurrently therewith, the extension pin  304  moves forward and causes the transition section  338  of the wells  328   a ,  328   b  to deform outwardly to separate from the bulge  342  on the needle sleeve  334 . The forward motion also pushes the end cap  297  of the extension pin  304  against the proximal end  350  of the needle  270 . Because the needle  270  is anchored by the needle sleeve  334  abutting against the hub  268 , the needle  270  pushes back against the end cap  297  with an equal but opposite force and causes the frangible seal  296  to tear or separate. The proximal end  350  of the needle  270  eventually completely tears the end cap  297  from the extension pin  304 , which then provides a passage for the spring  327  to expand. The expanding spring  327  then pushes the needle sleeve  336  proximally, which is attached to the needle  270  and pushes the needle proximally into the bore  288  located in the plunger  284  to thereby prevent accidental contact with the needle tip. Once the needle is retracted, the syringe may be safely disposed of per normal protocols.  
         [0091]     As best shown in  FIGS. 18 and 20 , when the actuated force F D  is applied to the plunger  284  to retract the needle  270 , the plunger moves distally relative to the plunger tip  308 . As discussed above, this relative movement is provided by a gap between the tip holder plate  316  of the syringe tip holder  302  and the end surface  313  of the plunger tip  308 . Said gap should be of sufficient dimension so as to not delimit the proximal end  350  of the needle  270  from puncturing the frangible seal  296 .  
         [0092]     Referring now to  FIG. 21 , an alternative syringe  352  for use with a needle hub  268  having a spring loaded retractable needle  270  provided in accordance with aspects of the present invention is shown. The syringe  352  is substantially similar to the syringe  266  described above with reference to  FIGS. 18-20  with the exception of the plunger tip  354 , which is different. In addition, the tip holder  356  of the plunger  284  has been slightly modified to cooperate with the plunger tip  354 , as further discussed below.  
         [0093]     The plunger tip  354  in the present embodiment comprises an internal bore  358  comprising an internal diameter sized to frictionally engage the exterior surface of the tip holder  356 . As before, a gap for relative movement between the plunger tip  354  and the plunger  284  are provided inside the plunger tip bore, between the distal end of the tip holder  356  and the end surface  360  of the plunger tip  354 . The proximal end of the plunger tip  354  abuts the push plate  300  on the plunger  284 . This contact enables the push plate  300  to move the plunger tip  354  distally when a distally directed force F D  is applied, and to compress the plunger tip to retract the needle  270  when an actuated force F A  is applied. The mechanism for retracting the needle  270  for the needle hub  268  is the same as that discussed above with reference to the needle hub of  FIGS. 18-20 .  
         [0094]     Turning now to  FIG. 22 , an alternative syringe  362  for use with a needle hub  268  having a spring loaded retractable needle  270  provided in accordance with aspects of the present invention is shown. The syringe  362  is substantially similar to the syringes  266 ,  352  described above with reference to  FIGS. 18-21  with the exception of the plunger tip  364 , which is different. In addition, the tip holder  366  of the plunger  284  has been slightly modified to cooperate with the plunger tip  364 , as further discussed below.  
         [0095]     In the present embodiment, the plunger tip  364  incorporates a groove  368  in the interior bore  358  of the plunger tip. The groove  368  is sized to receive a plunger disc  370  on the plunger  284  and allows it to move distally upon application of an actuated force F A  as described below. In one exemplary embodiment, the pusher plate  300  is located apart from the proximal annular ring  372  of the plunger tip  364  when in the ready to use position.  
         [0096]     To retract the needle  270 , the plunger is first advanced from a proximal to a distal position shown in  FIG. 22 . At this position, the end surface  360  of the plunger tip  364  contacts the end shoulder  348  of the barrel  272 . When an actuated force F A  is then applied to the plunger  284 , the plunger disc  370  moves distally within groove  368  of the plunger tip  364  and the plunger  284  moves distally relative to the end surface  360  of the plunger tip. The pusher plate  300  moves to meet the proximal annular ring  372  of the plunger tip  364 . Concurrently therewith, the extension pin  304  contacts the needle  270  to retract the needle as discussed above with reference to  FIGS. 18-20 .  
         [0097]     Turning now to  FIG. 23 , a partial cross-sectional view of an alternative needle hub  374  provided in accordance with aspects of the present invention is shown. The needle hub  374  is substantially similar to the needle hub  268  described above with reference to  FIGS. 18-20  with the exception of the way in which the gripping section  340  of the wells  328   a ,  328   b  of the needle hub grips the needle  376 . The needle hub  374  may be used with any of the syringes  266 ,  352 ,  362  described above with reference to  FIGS. 18, 21 , and  22  and may be actuated to retract the needle  376  the same way as described with those syringes  266 ,  352 ,  362 . However, instead of utilizing a needle sleeve  334  ( FIG. 19 ), in the present embodiment, the proximal end of the needle  376  incorporates a crimp or a bulge  378 . The bulge or crimp  378  may be made by pinching the needle to create a crimp or by a controlled compression process to create a bulge.  
         [0098]     The needle hub  374  may be assembled by first positioning a spring  327  over the needle  376 , which then rests on an end against the bulge or crimp  378 . The combination needle  376  and spring  327  is then inserted into the bore  326  of the needle hub and pushed distally until the bulge or crimp  378  engages with the space provided by the bulge  332  formed in the thin-walled sections  330  of the wells  328   a ,  328   b . Once engaged, the crimp or bulge  378  and the annular ring or cap  329  on the tube section  323  of the needle hub (See, e.g.,  FIG. 18 ) compresses the spring and loads the needle  376  for retraction.  
         [0099]     Although limited embodiments of the syringe assemblies and their components have been specifically described and illustrated herein, many modifications and variations will be apparent to those skilled in the art. Accordingly, it is to be understood that the syringe assemblies and their components constructed according to principles of this invention may be embodied other than as specifically described herein. The invention is defined in the following claims.
Syringes are disclosed herein incorporating a variety of safety mechanisms for protecting the users from accidental needle stick. In certain embodiments, the syringes incorporate retractable carriages that can be retracted into the syringe barrels by engaging with the plungers. The carriages are configured to receive different needle hubs having any number of needle sizes. In certain other embodiments, the carriages are spring loaded so that as the plungers disengage the carriages from the syringe barrels, the springs automatically retract the needles into the barrels. Still in certain other embodiments, needle hubs with spring loaded needles are used with the syringes. The needles are retracted into the barrels when the plungers activate certain mechanisms incorporated into the hubs to thereby release the needles.