Syringe Assembly Having Disabling Mechanism

Abstract

A syringe assembly having passive disabling structure includes a barrel and a plunger rod assembly. The plunger rod assembly includes a plunger rod and a stopper connected by an indexing locking element. The number of strokes of the syringe plunger before the stopper is locked into the barrel rendering the syringe assembly unusable is determined by the number of detents on the plunger rod and stopper which engage the locking mechanism. Upon completion of the final delivery stroke, any attempt to withdraw the plunger rod from the barrel will cause the locking element to engage the barrel and trap the stopper in the barrel preventing further use of the syringe.

1 . An operable syringe assembly having passive disabling structure comprising:
 a barrel including a cylindrical side wall having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall having a passageway therethrough in fluid communication with said chamber;   an elongate hollow plunger rod having a proximal end, an open distal end and an interior surface, at least one detent on said interior surface at said distal end of said plunger rod;   a stopper moveably engaged with the plunger rod, the stopper including a circular shaped sealing element having a peripheral surface forming a seal with said inside surface of said barrel, a boss member projecting proximally from said sealing element, at least one boss detent on said boss;   a locking element including a central body portion having an aperture therethrough, at least one cantilevered leg extending distally outwardly from said body portion, and at least one finger element extending proximally inwardly from said aperture, said at least one leg having a sharp free end directed outwardly for engaging said inside surface of said barrel;   said locking element being positioned with said sharp free end contacting said interior surface of said plunger rod proximally of said at least one detent, said boss member being positioned in said aperture of said locking element wherein said at least one finger element is contacting said boss proximally of said at least one boss detent, so that applying a proximally directed force to said plunger rod while holding said barrel causes said plunger rod to move proximally with respect to said stopper until said free end of said cantilevered leg moves distally along said inner surface of said plunger rod to said at least one detent, and subsequently applying a distally directed force to said plunger rod to discharge fluid from said chamber through said passageway causing said plunger rod to move in a distal direction along with said locking element due to its engagement with said at least one detent until said finger element of said locking element rides over said at least one boss detent and into contact with said at least one boss detent and said plunger rod contacts said stopper to move said stopper distally to discharge fluid from said chamber, after which applying a proximally directed force to said plunger rod will cause said plunger rod to move proximally until said free end of said cantilevered leg moves distally along said inner surface past said distal end of said plunger rod so that said sharp end of said at least one cantilever leg engages said inside of said barrel to help prevent proximal movement of said stopper to render said syringe assembly unusable.   
   
   
       2 . The syringe assembly of  claim 1 , wherein said at least one detent in said plunger rod includes two axially spaced detents and said at least one detent on said boss includes two axially spaced boss detents so that said plunger rod can be moved distally two times before proximal motion of said plunger rod causes said locking element to engage said inside surface of said barrel. 
   
   
       3 . The syringe assembly of  claim 2 , wherein said two axially spaced detents in said plunger rod include two axially spaced steps each having a blunt surface at its distal end extending inwardly from said interior surface. 
   
   
       4 . The syringe assembly of  claim 2 , wherein said two axially spaced boss detents each include an inclined surface extending proximally inwardly and a blunt surface at a distal end of each of said inclined surfaces extending radially inwardly. 
   
   
       5 . The syringe assembly of  claim 2 , wherein said at least one cantilevered leg of said locking element includes two cantilevered legs positioned on opposite sides of said central body portion and two additional axially spaced detents are provided in said plunger rod opposite said two axially-spaced detents. 
   
   
       6 . The syringe assembly of  claim 5 , wherein said stopper further comprises two radial projections positioned to engage and force said two cantilevered legs outwardly when excessive proximally directed force is applied to said plunger rod in an attempt to overcome said locking element's engagement of said inside surface of said barrel. 
   
   
       7 . The syringe assembly of  claim 1 , further comprising a discontinuity on said inside surface of said barrel sidewall positioned to engage said sharp free end of said locking element when said sharp free end is contacting said inside surface of said barrel. 
   
   
       8 . The syringe assembly of  claim 1 , wherein said distal wall of said barrel further includes an elongate tip extending distally therefrom having a passageway in fluid communication with said passageway in said distal wall. 
   
   
       9 . The syringe assembly of  claim 1 , further comprising a needle cannula having a distal end, a proximal end and a lumen therethrough, said proximal end of said needle cannula being connected to said distal end of said barrel so that said lumen is in fluid communication with said passageway. 
   
   
       10 . The syringe assembly of  claim 1 , wherein said locking element is made of sheet metal. 
   
   
       11 . The syringe assembly of  claim 1 , wherein said stopper is integrally formed of thermoplastic material. 
   
   
       12 . An operable syringe assembly having passive disabling structure comprising:
 a barrel including a cylindrical side wall having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall having an elongate tip extending distally therefrom and a passageway therethrough in fluid communication with said chamber;   an elongate hollow plunger rod having a proximal end, an open distal end and an interior surface, said interior surface at said distal end of said plunger rod including two pairs of axially spaced opposed steps, each step extending inwardly from said sidewall and having a blunt surface at its distal end and each recess having a distal face;   a stopper moveably engaged with the plunger rod, the stopper including a circularly shaped sealing element having a peripheral surface forming a seal within said inside surface of said barrel, a boss member projecting proximally from said sealing element, two axially spaced detents on said boss each having an inclined surface extending proximally inwardly and a blunt surface extending radially away from said boss;   a locking element including a central body portion having an aperture therethrough and two opposed cantilevered legs extending distally outwardly from said body portion, two finger elements extending proximally inwardly from said aperture, said legs having free ends including a hook-shaped portion, said hook-shaped portion having a sharp end directed proximally outwardly from engaging said inside surface of said barrel and said blunt surface in said plunger rod;   said locking element being positioned with said sharp ends of said hook-shaped portions contacting said interior surface of said plunger rod proximally of said blunt surface of said steps, said boss member being positioned in said aperture of said locking element wherein said finger elements contact said boss proximally of said blunt surface of said detents, so that applying a proximally directed force to said plunger rod while holding said barrel causes said plunger rod to move proximally with respect to said stopper until said hook-shaped portions of said cantilevered legs move distally along said inner surface of said plunger rod and moves outwardly at said blunt surface of proximal-most of said two steps to move said stopper in a proximal direction for a selected distance, and subsequently applying a distally directed force to discharge fluid from said chamber through said passageway causes said plunger to move in a distal direction with said locking element due to said locking element's engagement with the proximal-most of said blunt surfaces until said finger elements of said locking element ride over said inclined surface of the proximal-most said two detents and into contact with said blunt surface and said plunger rod contacts said stopper to move said stopper distally to discharge fluid from said chamber, an additional proximal and distal movement of said plunger rod to draw fluid into said chamber and to deliver fluid from said chamber will cause said locking element to be repositioned so that said hook-shaped portions of said legs engage the distal-most of said two steps and said finger elements engage the distal-most of said blunt surfaces, after which applying a proximally directed force to said plunger will cause said plunger rod to move proximally until said hook-shaped portions of said cantilevered legs move distally along said inner surface of said plunger rod past said distal end of said plunger rod so that said sharp ends of said hook-shaped projections engage said inside surface of said barrel to help prevent proximal motion of said stopper to render said syringe assembly unusable.   
   
   
       13 . The syringe assembly of  claim 12 , wherein said stopper further comprises two radial projections positioned to engage and force said two cantilevered legs outwardly when excessive proximally directed force is applied to said plunger rod in an attempt to overcome said locking element's engagement of said inside surface of said barrel. 
   
   
       14 . The syringe assembly of  claim 12 , further comprising a discontinuity on said inside surface of said barrel sidewall positioned to engage said sharp free end of said locking element when said sharp free end is contacting said inside surface of said barrel. 
   
   
       15 . The syringe assembly of  claim 12 , further comprising a needle cannula having a distal end, a proximal end and a lumen therethrough, said proximal end of said needle cannula being connected to said distal end of said barrel so that said lumen is in fluid communication with said passageway. 
   
   
       16 . The syringe assembly of  claim 12 , wherein said locking element is made of sheet metal. 
   
   
       17 . The syringe assembly of  claim 12 , wherein said stopper is integrally formed of thermoplastic material.