Safety syringe abstract
A safety syringe (2) includes a hollow barrel (4) with a barrel
hub (24) threadably mounted to and dismountable from the distal
end (4) of the barrel. A plunger (10) has a piston (14) at its distal
end (20). The plunger and the barrel hub are configured to permit
the distal end of the plunger to engage the barrel hub at the conclusion
of an injection, typically through a splined interface (46 52),
to allow positive rotary engagement of the barrel hub by the plunger.
Thereafter, the plunger is used to withdraw the barrel hub and needle
(43) back into the interior (23) of the barrel. The plunger can
be fractured at a weakened region (57) adjacent the piston thus
leaving the distal end of the plunger, piston, barrel hub and needle
housed within the barrel interior. The hollow stem can then be inserted
through the distal end of the barrel and over the needle for compact
disposal.
Safety syringe claims
What is claimed is:
1. A safety syringe comprising:
a barrel having proximal and distal ends and a hollow interior
defining an axis;
a barrel hub threadably mountable to and dismountable from the
distal end of the barrel;
a plunge, having proximal and distal ends, including a piston at
the distal end of the plunger, the piston movable within the hollow
interior of the barrel; and
means for releasably mechanically coupling the distal end of the
plunger to the barrel hub from within the interior of the barrel,
said mechanically coupling means including:
means for rotating the barrel hub about the axis by the plunger
so to dismount the barrel hub from the distal end of the barrel,
the rotating means including rotary drive surfaces on the distal
end of the plunger and the barrel hub, said rotary drive surfaces
including axially extending splines formed on the distal end of
the plunger and on the barrel hub, the splines mating with each
other to provide a positive rotary drive interface; and
means for pulling the barrel hub from the distal end of the barrel
and to a storage position within the hollow interior of the barrel
by the plunger, the pulling means including an axially segmented
bulbous plug on one of the distal end of the plunger and the barrel
hub and a complementary bulbous pocket on the other of the distal
end of the plunger and the barrel hub.
2. The safety syringe of claim 1 further comprising a needle assembly
mounted to the barrel hub and extending in a distal direction from
the barrel hub, the needle assembly being housed completely within
the barrel when the barrel hub is in the storage position.
3. The safety syringe of claim 2 wherein the needle assembly is
removably mountable to the barrel hub.
4. The safety syringe of claim 1 wherein the barrel hub and the
distal end of the barrel include mating tapered surfaces to provide
a fluid seal therebetween.
5. The safety syringe of claim 1 wherein the plunger includes an
elongate stem having proximal and distal ends, the piston at the
stem distal end.
6. The safety syringe of claim 5 wherein the stem includes a weakened
region between the piston and the stem proximal end.
7. The safety syringe of claim 6 wherein the weakened region is
adjacent the piston.
8. A safety syringe comprising:
a barrel having proximal and distal ends and a hollow interior
defining an axial;
a barrel hub threadably mountable to and dismountable from the
distal end of the barrel;
a plunger, having proximal and distal ends, including a piston
at the distal end of the plunger, the piston movable within the
hollow interior of the barrel, the plunger including an elongate
stem with proximal and distal ends and an exterior surface;
means for releasably mechanically coupling the distal end of the
plunger to the barrel hub from within the interior of the barrel,
said mechanically coupling means including:
means for rotating the barrel hub about the axis by the plunger
so to dismount the barrel hub from the distal end of the barrel,
the rotating means including axially extending rotary drive spline
surfaces on the distal end of the plunger and the barrel hub, said
rotary drive spline surfaces being other than surfaces of revolution
so to provide a positive rotary drive interface; and
means for pulling the barrel hub from the distal end of the barrel
and to a storage position within the hollow interior of the barrel
by the plunger, the pulling means including an axially segmented
bulbous plug on the barrel hub and a complementary bulbous pocket
on the distal end of the plunger;
a needle assembly mounted to the barrel hub and extending in a
distal direction from the barrel hub, the needle assembly being
housed completely within the barrel when the barrel hub is in the
storage position; and
the stem having a step along the exterior surface, the step forming
a large diameter portion at the proximal end of the stem, the large
diameter portion sized to frictionally engage an inside surface
of the distal end of the barrel.
9. The safety syringe of claim 1 wherein the plunger includes an
elongate stem with proximal and distal ends and an exterior surface,
the stem having a step along the exterior surface, the step forming
a large diameter portion at the proximal end of the stem, the large
diameter portion sized to frictionally engage an inside surface
of the distal end of the barrel.
Safety syringe description
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to and is an improvement over the syringe
disclosed in U.S. Pat. No. 4710170 the disclosure of which is
incorporated by reference.
BACKGROUND OF THE INVENTION
Hypodermic syringes, once contaminated, can be a source of dangerous
and sometime fatal infectious diseases. Contaminated hypodermic
needles, if not properly handled after use, can result in an unintentional
needle stick of a health care worker. In addition, illicit use of
used syringes can occur if the syringes are not properly disabled
after use.
In response to some of these problems, a disposable, anti-needle-strike,
anti-drug abuse syringe was developed and is disclosed in U.S. Pat.
No. 4170170. The plunger on this syringe has a tapered opening
which is used to engage a similarly tapered extension of the needle
hub at the distal end of the barrel. This provides a frictional
engagement which permits the user to rotate the needle hub, thus
disconnecting it from the distal end of the barrel, by rotating
the stem of the plunger. The frictional interface between the tapered
opening and the tapered extension is designed to be sufficient to
enable the user to pull the coupled needle assembly from the distal
end of the barrel into the interior of the barrel shown in FIG.
14 in the patent. At this point the stem, which has a weakened region
adjacent the piston, is snapped into two pieces leaving the distal
end of the stem, the piston and the needle assembly inside the interior
of the barrel. The hollow stem can then be inserted through the
now open distal end of the barrel to cover the needle assembly and
to permit compact disposal.
While this safety syringe provides significant advantages over
existing safety syringes, the smooth, frustoconically shaped friction
drive surfaces, being surfaces of revolution with respect to the
syringe axis, proved less than ideal. One of the problems was the
manufacturing tolerances for a good frictional fit between the frustoconical
surfaces were quite close. Also, if moisture contaminated the tapered
surfaces, especially if there was not good alignment between the
two parts, the frictional engagement might not be sufficient to
either disengage the barrel hub from the barrel or pull the barrel
hub back into the barrel.
SUMMARY OF THE INVENTION
The present invention is directed to a safety syringe which is
simple in construction and yet provides a positive rotary drive
interface between the plunger and the barrel hub to ensure proper
disengagement of the barrel hub from the barrel while eliminating
sensitive tolerance and alignment aspects of a known safety syringe.
The safety syringe, of the type in which the needle assembly is
shielded after use, includes a hollow barrel with a barrel hub threadably
mounted to and dismountable from the distal end of the barrel. A
plunger has a piston at its distal end. The plunger and the barrel
hub are configured to permit the distal end of the plunger to engage
the barrel hub at the conclusion of an injection; the engagement
is typically through a serrated or splined interface or other interfaces
which do not rely totally on surface friction to allow the positive
rotatable engagement of the barrel hub by the plunger. The rotary
drive, the barrel hub and plunger are also configured to permit
the plunger to withdraw the barrel hub and needle assembly mounted
thereto back into the interior of the barrel after the barrel hub
has been detached from, typically unscrewed from, the distal end
of the barrel. At this point the plunger, which preferably has a
weakened region adjacent the piston, can be fractured at the weakened
region thus leaving the distal end of the plunger, the piston, the
barrel hub and the needle housed within the interior of the barrel.
The stem, which is preferably hollow, can then be inserted through
the distal end of the barrel and over the needle assembly for compact
disposal.
The barrel hub is preferably threadably mounted to the distal end
of the barrel. This, coupled with a tapered interface between the
barrel hub and the interior surface of the barrel, permits a secure
fluid-tight seal between the two components without requiring tolerances
as tight as would be required if, for example, a bayonet or twist-lock
type of securement were used. Due to the positive rotary drive interface
between the plunger and the barrel hub, there is no problem with
exerting sufficient torque to unscrew the barrel hub from the barrel.
Other features and advantages of the invention will appear from
the following description in which the preferred embodiment has
been set forth in detail in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a safety syringe made according
to the invention in its pre-use condition;
FIG. 1A is cross-sectional view of the distal portion of the syringe
of FIG. 1;
FIG. 2 is an exploded isometric view of the syringe of FIG. 1;
FIG. 3 is a cross-sectional view of the safety syringe of FIG.
1 in the post-injection position;
FIG. 3A is an enlarged view taken along line 3A--3A of FIG. 3;
and
FIG. 4 is an enlarged cross-sectional view of the syringe of FIG.
1 shown after use in a safe/disposal condition.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 illustrate a safety syringe 2 including a barrel
4 having a distal end 6 and a proximal end 8. Syringe 2 also includes
a plunger 10 made of an elongate stem 12 and a seal ring 14. Seal
ring 14 is mounted between a pair of flanges 16 18 at the distal
end 20 of stem 12. Seal ring 14 is sized to engage the inner surface
22 defining the interior 23 of barrel 4 so that the distal end 20
of stem 12 acts as a piston.
Syringe 2 also includes a barrel hub 24 having external barrel
threads 26 formed at a distal end thereof and sized to engage internal
barrel threads 28 formed at distal end 6 of barrel 4. Barrel hub
24 also has a tapered flange 30 at its proximal end with an externally
facing tapered surface 32. Tapered surface 32 is sized and positioned
to engage a complementary tapered surface 34 formed within barrel
4 adjacent internal threads 28. In this way, barrel hub 24 can be
screwed tightly onto distal end 6 of barrel 4 using threads 26
28 to provide a good fluid seal between hub 24 and barrel 4 through
the engagement of mating surfaces 32 34.
Barrel hub 24 has a conventional Luer lock fitting 36 surrounding
a central fluid bore 38. Luer lock fitting 36 is sized to engage
a conventional needle assembly 40 of the type having a needle hub
42 and hollow needle canula 43.
Barrel hub 24 has an annular opening 44 defined by internal splines
46 around its circumference and a bulbous, segmented plug 48 at
its center. Segmented plug 48 is sized to snap fit within a pocket
50 formed at distal end 20 of stem 12. The part of distal end 20
surrounding pocket 50 has external splines 52 formed thereon. Splines
46 52 are sized for complementary mating engagement when segment
plug 48 snapped into pocket 50 as discussed below.
FIGS. 1 and 1A illustrate syringe 2 in its pre-use condition. As
can be seen in FIG. 1A, plunger 10 and barrel hub 24 are not engaged.
The user then fills syringe 2 in a conventional manner and gives
the injection. FIGS. 3 and 3A illustrate syringe 2 in its post-injection
condition with plunger 10 having been driven against barrel hub
24 so that segmented plug 48 enters pocket 50 and splines 46 52
engage. This permits the user to uncouple barrel hub 24 from barrel
14 by grasping the oblong stem flange 54 at the proximal end 55
of stem 12 and rotating stem 12 relative to barrel 4. The positive
engagement created by splines 46 52 permit a great deal of torque
to be applied to barrel hub 24 allowing the user to easily overcome
the frictional engagement between threads 26 28. After unscrewing
barrel hub 24 from distal end 6 of barrel 4 barrel hub 24 and needle
assembly 40 therewith are pulled into interior 23 of barrel 4 to
the position shown in FIG. 4 by pulling plunger 10 proximally relative
to barrel 4. This proximal motion is possible due to the engagement
of plug 48 within pocket 50. The proximal motion is halted by the
engagement of tapered flange 30 of barrel hub 24 with an internal
flange 56 at proximal end 8 of barrel 4. At this point, the user
can break apart stem 12 adjacent proximal flange 16 by pushing stem
12 laterally, causing stem 12 to break at a weakened region 57 adjacent
flange 16. While someone could push the assembly of distal end 20
of stem 12 sealing ring 14 barrel hub 24 and needle assembly
40 back down barrel 4 the syringe is no longer functional because
distal end 20 of stem 12 cannot be separated from barrel hub 24
and the severed portion 58 of the stem cannot be reattached to hub
24.
For additional safety and reduced debris bulk, the separated stem
portion 58 can be inserted through distal end 6 of barrel 4 until
the severed portion covers needle assembly 40. To help retain stem
portion 58 within barrel 4 stem 12 has a step 60 along its length
so that the outside diameter of stem 12 is larger at proximal end
55 of stem 12 than on the other side of step 60. This enlarged diameter
frictionally engages internal threads 28 to help keep severed portion
58 in place.
In use, syringe 2 in its pre-use condition of FIGS. 1 and 1A,
is filled with a pharmaceutical in a conventional fashion by inserting
hollow needle cannula 43 into a vial or other pharmaceutical container.
The user then grasps stem flange 54 and pulls plunger 10 in a proximal
direction, thus aspirating the liquid pharmaceutical into interior
23 of barrel 4. The injection is given in a conventional manner
by pushing plunger 10 back into barrel 4. After the injection has
been given, plunger 10 is driven distally until it assumes the position
of FIGS. 3 and 3A. At this point, the user can unscrew barrel hub
24 from distal end 6 of barrel 4 by rotating plunger 10 relative
to barrel 4 through the positive engagement of splines 46 52. After
being unthreaded, plunger 10 is pulled proximally, thus pulling
barrel hub 24 and needle assembly 40 into interior 23 of barrel
4. Once in the position of FIG. 4 severed portion of stem 12 is
snapped off from the remaining portion of the stem at weakened region
57 adjacent flange 16 to permanently disable the syringe. Portion
58 is then inserted through distal end 6 of barrel 4 and over needle
assembly 40 for disposal.
Other types of rotatable locking structures can be used to mount
barrel hub 24 to distal end 6 of barrel 4. The threaded mounting
arrangement is, however, preferred because of the high force it
can create between tapered surfaces 32 34 without the need for
tight tolerances, as are often required when a bayonet-type of rotary
lock mechanism is used.
The components used in syringe 2 are of pharmaceutically compatible
materials. For example, seal ring 14 is preferably a medical grade
silicone rubber while hollow needle 43 is stainless steel. The remaining
components are made of medical grade plastic, such as polycarbonate,
or other suitable materials. The choice of these materials for the
preferred embodiment does not, of course, limit the use of other
suitable materials as well.
Further modifications and variation can be made to the disclosed
embodiment without departing from the subject of the invention as
defined in the following claims. For example, instead of the use
of splines 46 52 and segmented plug 48/pocket 50 plunger 10 and
barrel hub 24 could be secured to one another using other connecting
structures in which abutting, interfering rotary drive surfaces
provide positive rotational engagement as opposed to the purely
sliding frictional engaging provided by the syringe disclosed in
the above-mentioned patent. For example, a bayonet or twist lock
type of connecting structure could be used to provide both the rotational
and axial movement interfaces needed. Also, severed portion 58 of
stem 12 could be more positively locked within barrel 4 than through
the use of frictional engagement. For example, severed portion 58
could include threads to engage internal threads 28. Also, some
type of locking ledges or fingers could be incorporated into the
outer surface of stem 12 near proximal end 55 to prevent removal
of severed portion 58 of stem 12 from barrel 4 when in the safe/disposal
condition of FIG. 4. Similarly, locking ledges or fingers could
also be used to positively engage hub 24 when in the position of
FIG. 4. |