Syringe with retractable needle assembly

A hypodermic syringe employing a plunger slidably disposed within a barrel. The plunger has a mounting hole extending through the seal end thereof to receive a mandrel. The mandrel has a flexible flange to be releasably engaged with the plunger. A spring element withdraws the mandrel into a cavity within the plunger upon full extension of the plunger within the barrel. The barrel includes a hub retainer at the forward end thereof and a needle hub retained therein the mandrel includes barbed tines with surfaces having axes of the conical surfaces that are displaced from one another such that movement of the tines toward one another also brings the axes closer. A catch associated with the back end of the spring element coupled with the mandrel at the other end cooperates with shoulders on smooth surfaces within the cavities to retain tension within the bungee. The hub retainer and the needle hub cooperate to insure that the needle hub is constrained to limited motion such that the mandrel will fully engage the needle hub.

BACKGROUND OF THE INVENTION

The field of the present invention is syringes and, more particularly, syringes offering protection against accidental sharps injury.

Accidental sharps injuries, in this context needle sticks, have long been recognized as potentially dangerous to health care workers. More recently, the transmission of serious and potentially fatal infections from such sharps injuries have created greater concern. Legislation has been contemplated in a number of States and before the Occupation Safety and Health Administration which would require safe needle technology.

A number of approaches have been undertaken to provide protection against such sharps injuries. International Publication WO 01/41843A1 discloses a syringe with a retractable needle which includes a plunger having a cavity extending longitudinally therein. A spring element is located in the cavity and is fixed to a mandrel extending into the syringe barrel from the mandrel which attaches to and retracts a needle into the barrel. The other end of the spring element is associated with a catch which causes the spring element to be placed in tension as the plunger is advanced within the barrel. A retention assembly associated with the end of the plunger receives and secures the catch to retain the spring element in tension. Advancement of the plunger to the end of its stroke results in the capture of the needle assembly by the mandrel and the release of the mandrel from the seal end of the plunger, resulting in retraction.

A further refinement of the foregoing design is disclosed in International Publication WO 01/41830A2. Improvements incorporated into this latter device include resilient dogs retaining the needle assembly in the forward end of the barrel. A driver surface is provided on the plunger to move the dogs from engagement for retraction of the needle assembly. Further, teeth are provided along either side of the cavity through the plunger to provide a range of engagements for the catch on the back end of the spring element. The disclosures of the foregoing patent publications are incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention is directed to a hypodermic syringe including a barrel with a plunger slidably disposed therein. The plunger has a cavity extending longitudinally. A hole extends through the seal end of the plunger and receives a mandrel. A spring element within the cavity is fixed to the mandrel at one end and fixable relative to the plunger in a tensioned state at the other end. A needle hub is releasably mounted in a hub retainer at one end of the barrel. A number of specific features are provided to enhance syringe operation.

In a first separate aspect of the present invention, the mandrel positioned within the hole includes an annular flange which is flexible longitudinally of the plunger and engages one or more detents extending into the hole. This flexible flange provides a more uniform release without the need for very close tolerances and flexure of less resilient materials. The detent or detents may each provide an engagement surface which is at an acute angle to the longitudinal direction of the plunger to further enhance the uniformity of mandrel release.

In a second separate aspect of the present invention, the mandrel is provided with tines extending longitudinally of the plunger. These tines have a spaced therebetween and each has a barb with a conical surface facing outwardly. The axes of the conical barb surfaces are offset from one another such that they approach one another as the resilient tines are bent toward one another. The arrangement of the barbs is such that, as the barbs move, corresponding elements on the barb surfaces move toward defining a circle. This motion takes place as the tines are forced into an engagement hole on the needle hub. In this way, the center of the barb surfaces define the resistance to insertion within the engagement hole, insuring a more predictable and uniform resistance.

In a third separate aspect of the present invention, the barrel includes dogs which retain the needle hub at one end thereof. The barrel also includes a shoulder normal to the longitudinal direction of the barrel facing into the barrel. The needle hub includes a shoulder also normal to the longitudinal direction of the barrel which faces the barrel shoulder. The dogs and the shoulders define two positions, one with the needle hub against the dogs and one with the shoulders engaged. These positions are displaced from one another. The normal aspect of the shoulders provides a fixed position upon engagement of the shoulders advantageous for engagement and retraction of the needle hub by the mandrel. The displacement between positions aids in the assurance of the release of the needle hub by the dogs. It is also possible that an O-ring seal between the needle hub and the barrel is able to bias the hub toward the first position to give stable placement for injection. The location of the shoulders may be advantageously selected along the length of the needle hub.

In a fourth separate aspect of the present invention, the spring element includes a catch which is slidably mounted within the cavity of the plunger. The catch includes elements which are engageable with the barrel as the plunger moves further into the barrel. Additional elements engage shoulders defined within the plunger cavity. There are two opposed smooth walls in the cavity with one shoulder only in each wall. This enables placement of the shoulders to retain the catch such that resistance is not encountered from multiple engaging elements and yet the plunger need not be fully extended within the barrel for engagement.

Accordingly, it is an object of the present invention to provide an improved safety syringe with a retractable needle. Other and further objects and advantages will appear hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning in detail to the drawings,FIG. 1illustrates a syringe with a retractable needle. This view illustrates the device as shipped.FIG. 2illustrates the same device in an exploded assembly view as including a barrel80, a plunger assembly30, a protective needle cap160and a needle hub100with an associated needle106.

The plunger assembly is illustrated in various positions within the barrel80inFIGS. 4,5,6and7. Further, the plunger assembly is shown by itself inFIG. 11. The plunger assembly30includes a molded body32having a seal end34and an outer end36. The outer end36defines a thumb button for actuation of the syringe while the seal end34acts as a piston with a ring seal38extending about a waist40. A substantially conical forward surface defines a driver surface42which will be described later as interacting with the forward end of the barrel.

A cavity44lies between the seal end34and the outer end36. This cavity is shown to be open on two sides and defined by two smooth surfaces46which are opposed and extend substantially the length of the cavity44. Each of the smooth surfaces46has one shoulder48. The shoulders48in the two surfaces face the outer end36. These two shoulders48are aligned with one another to receive a catch as will be described below. The smooth surfaces46are curved near the middle of the body32to constrict the width of the cavity. This may be employed to arrest the motion of the needle as it is being retracted into the syringe as will be discussed below.

A mounting hole50extends longitudinally of the plunger assembly30through the seal end to the cavity44. This hole50is best illustrated inFIG. 12. It is substantially circular in all transverse cross sections but for two detents52located diametrically opposed near the seal end34of the plunger assembly30. The plunger body32is relieved around the detents52in order that they may have some resilience. As the relief is extended downwardly about the detents52, greater resilience is realized. The detents52include an engagement surface54at an acute angle to the longitudinal direction of the plunger assembly30. These engagement surfaces54extend inwardly into the otherwise generally cylindrical mounting hole50.

A mandrel56is associated with the plunger assembly30in the mounting hole50. This mandrel56includes an annular seal cavity58receiving an O-ring seal60. The mounting hole50is relieved as best seen inFIG. 12near the location of the O-ring seal60such that retraction of the mandrel56from the mounting hole50is facilitated. The inner end of the mandrel56includes an anchor pin62having a varied profile for bonding to a bungee molded in situ on the pin62.

The mandrel56is relieved by annular grooves to define an annular flange64. Further the mandrel56is preferably of a more resilient material than the body32of the plunger30. This flexibility of the material along with the geometry of the annular flange64makes the flange64flexible longitudinally of the plunger. It extends radially outwardly and circumscribes the mandrel56at that location. The flange64is rounded at its periphery to a substantially semi-circular surface in cross section. This annular flange64is held against retraction of the mandrel56by the engagement surfaces54of the detents52. This configuration offers more consistent extraction forces of the mandrel56from the mounting hole50.

Resilient tines66are located at the outer end of the mandrel56. These tines66are spaced apart and each includes a barb68. The barbs68face outwardly away from one another and are defined by a segment of a truncated conical surface70. The surfaces70each define a conical axis which extends longitudinally of the mandrel56. These conical axes of the two surfaces70are offset from one another such that they approach one another as the resilient tines66are bent toward one another. In this way, the centers of the conical surfaces rather than their edges define the resistive force to insertion into the needle hub as discussed below.

The barrel80includes an open end82and a hub end84. The hub end is illustrated in detail in various embodiments inFIGS. 14 through 20. The barrel includes a hub retainer86at the hub end84. The body of the barrel80has an engagement flange88about the hub end84thereof. This engagement flange88receives shoulders90on the hub retainer86which has periodic longitudinal slits92to accommodate assembly. The retainer86includes a bore94therethrough coaxial with the barrel80. Three dogs96extend into that bore94to retain a needle hub from moving inwardly into the barrel80. The dogs96are resiliently mounted and have an inclined surface98to interact with the plunger assembly30.

The needle hub100is located in the bore94of the barrel80at the hub end84. The needle hub100includes a mounting body102and a lower engagement body104. The mounting body102is generally cylindrical with a cavity to receive a needle106. The needle106may be cemented in place.

The engagement body104includes an engagement hole108concentrically arranged at the inner end of the needle hub100. This hole108is sized to receive the tines66of the mandrel56, forcing the barbs inwardly. An engagement shoulder110receives the barbs once having passed through the hole108. This secures the needle hub100to the mandrel56. At the inner end of the engagement body104, an inner surface112is provided for releasable retention by the dogs96. An annular space is provided about the intersection between the mounting body102and the engagement body104and by the main body of the barrel80and the hub retainer86for an O-ring114. The needle hub100is able to axially move a small amount within the hub retainer86. This movement is resisted by the O-ring114.

Having generally described the mounting of the needle hub100within the hub end84of the barrel80, specific reference to the differences between embodiments are here addressed.FIGS. 14 and 15constitute a first embodiment. In this embodiment, six longitudinally extending ribs116are located about the periphery of the mounting body102. These ribs define a series of stops as a composite first shoulder118. The hub retainer86includes an inwardly extending flange120having a second shoulder122which opposes the shoulder118. These shoulders118and122are normal to the longitudinal direction of the barrel80. Through a comparison ofFIGS. 14 and 15, it can be seen that the needle hub100has a first position positioned against the dogs96. A second position illustrated inFIG. 15has the shoulders118and122engaged. These two positions are displaced from one another to a small extent. This spacing gives some additional advancement past the engagement of the mandrel56with the needle hub100. The resistance of the O-ring114against movement of the needle hub100provides for engagement of the mandrel56. However, further advance of the plunger assembly30may be needed to release the dogs96. The operator will know to push harder until the needle hub100is released and the needle106retracts. Having the shoulders be normal to the longitudinal direcion of the barrel80defines a fixed second position. Without such a fixed limit to movement, the O-ring114can get hung up with the hub100or the components wedge together and inhibit needle retraction.

InFIGS. 16 and 17, another embodiment is employed where a first shoulder124is found at the outer end of the needle hub100and the flange120includes a second shoulder126receiving that shoulder124.FIGS. 18 and 19represent yet another embodiment where the first shoulder128is defined at the intersection between the mounting body102and the engagement body104while the resisting second shoulder130forms the lower end of the upper portion of the bore94. A further embodiment is contemplated where an entire circular shelf is created at a location similar to that defined by the ribs116about the full periphery of the mounting body102.

A spring element in the form of a bungee140is located within the cavity44of the plunger assembly. The bungee140is molded about the anchor pin62of the mandrel56at one end. At the other end, the bungee140is molded onto another anchor pin142of a catch144. The catch144includes elements146which extend outwardly from the anchor pin142. The barrel80includes an inwardly extending shoulder148which engages the elements146to prevent the catch from moving into the inner portion of the barrel80.

The catch144also includes side elements150extending to a lesser extent outwardly from the anchor pin142. These side elements150slide along the smooth surfaces146defining the cavity44. There is some spring resilience to the plunger at the surfaces such that, in a relaxed position, the side elements150will be engaged by the two shoulders48and yet the catch144can move fairly easily within the cavity44toward the shoulders48. This single set of shoulders48helps define a point at which the plunger assembly30is cocked the shoulders48can be positioned such that the thumb button can be grasped and the plunger easily retracted to charge the barrel80. Likewise, the force profile in advancing the plunger assembly30provides clearer transition such that premature needle retraction can more easily be avoided.

In operation, the syringe comes as illustrated inFIG. 1with the plunger assembly30partially inserted into the barrel80. A protective needle cap160isolates the needle106. The configuration ofFIG. 1is also illustrated inFIG. 4. As can be seen, the bungee140can be in a relaxed or substantially relaxed condition to avoid any long term creep, thereby extending the shelf life of the syringe.

FIG. 5illustrates an advance of the plunger30substantially fully into the barrel80. As the catch144is prevented from entering the barrel because of the elements146engaging the shoulder148, the bungee140is stretched and tensioned by this insertion. Further, the catch144comes into engagement with the shoulder148on the smooth surfaces46of the cavity44.

With the shoulders148engaging the catch144, the bungee will remain in tension until such time as the mandrel56is extracted from the mounting hole50. The bungee will not lose tension as the plunger assembly30is drawn back to intake the substance to be injected.

Once the appropriate amount of fluid is drawn into the syringe, the injection may be given until the plunger assembly30again is fully within the barrel80. The syringe may then be withdrawn from the injection site and further pressure exerted against the thumb button of the outer end36of the plunger assembly30. This action drives the resilient tines66into the engagement hole108of the needle hub100to the point that the barbs68engage the engagement shoulder110within the engagement body104. Concurrently, the driver surface42on the seal end34of the plunger assembly30engages the inclined surfaces98of the dogs96and forces them outwardly to release the needle hub100. The engagement of the needle hub100with the mandrel56requires less force than and precedes the release of the mandrel56from the mounting hub50.

With the dogs96retracted and the mandrel56engaged with the needle hub100, the mandrel56is released from the seal end34of the plunger assembly30and tensioned bungee retracts the needle hub100and the needle106into the cavity44of the plunger assembly30. This last condition can best be seen inFIG. 7. In the retraction, the annular flange64is flexed longitudinally by being dished toward the outer end of the mandrel56. This releases the mandrel56from the detents52to permit retraction of the bungee140and withdrawal of the mandrel56. Once the mandrel has been separated from the mounting hole50, the assembly cannot be reused as a syringe without full disassembly of the device.

Accordingly, an improved syringe having a retractable needle is disclosed. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore is not to be restricted except in the spirit of the appended claims.