U.S. patent application number 11/218498 was filed with the patent office on 2006-11-16 for single use syringe with improved needle retraction mechanism.
Invention is credited to Bruce Leigh Kiehne.
Application Number | 20060258984 11/218498 |
Document ID | / |
Family ID | 37396070 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060258984 |
Kind Code |
A1 |
Kiehne; Bruce Leigh |
November 16, 2006 |
Single use syringe with improved needle retraction mechanism
Abstract
A single use syringe including shoot back, or retraction,
mechanism for biasing a needle, retained in needle holder, back
into the interior of the syringe body after use. The needle holder
is urged, by a spring in the front of the syringe body, to pass
through a piercable seal formed in the front fact of the piston.
The needle holder comprises an inner part containing the needle, an
outer part engaging the interior wall of the syringe, and a
frangible portion joining the inner and outer parts. A raised
portion, or bump, is formed partially about the outer part of the
needle holder, facing the seal in the piston. The raised portion
provides an initial contact area with the plunger, to reduce the
force required to break the frangible portion and trigger the
shoot-back mechanism. The edge portion of the seal is thickened,
and is relatively compressible, to reduce the dead space prior to
triggering the shoot-back mechanism.
Inventors: |
Kiehne; Bruce Leigh; (Slacks
Creek, AU) |
Correspondence
Address: |
HOFFMAN, WASSON & GITLER, P.C.
Suite 522
2461 South Clark Street
Arlington
VA
22202
US
|
Family ID: |
37396070 |
Appl. No.: |
11/218498 |
Filed: |
September 6, 2005 |
Current U.S.
Class: |
604/110 |
Current CPC
Class: |
A61M 5/508 20130101;
A61M 2005/31516 20130101; A61M 5/3234 20130101 |
Class at
Publication: |
604/110 |
International
Class: |
A61M 5/00 20060101
A61M005/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2005 |
AU |
2005902427 |
Claims
1. A single use syringe which comprises: a syringe body which
contains a front end area containing a longitudinal passageway
which has a front portion and a rear portion, a plunger which
contains a front face which extends into the syringe body, a
pierceable seal extending over the front face of the plunger, a
needle holder that is attached inside and in the front area of the
syringe body, a needle that is attached to the needle holder, a
spring in the front of the syringe body and that is biased to shoot
the needle holder through the pierceable seal in the front face of
the plunger and into the plunger, the needle holder comprising an
inner part and an outer part, the inner part containing the needle,
the outer part engaging with a wall of the longitudinal passageway
and initially in a rear portion of the passageway, a frangible
portion between the inner part and the outer part, the outer part
containing a raised portion directed towards the seal of the
plunger, the raised portion extending only partway about the inner
portion, the raised portion functioning to provide an initial
contact area of the plunger with the outer part of the needle
holder, thereby reducing the force required to break the frangible
portion thereby triggering the shoot back mechanism.
2. The syringe of claim 1, wherein the plunger has a front face
containing an open central portion and an edge portion, the seal
extending over the central portion and the edge portion.
3. The syringe of claim 1, wherein the inner part has a front
portion and a rear portion and an intermediate body portion, the
front portion extending through the front of the syringe body, the
intermediate body portion comprising an elongate substantially
cylindrical portion containing an internal passageway which
communicates with the needle, the rear portion extending towards
the plunger and comprising a projection to assist in the piercing
or breaking of the plunger seal.
4. The syringe of claim 3, wherein the projection has an arrowhead
configuration.
5. The syringe of claim 1, wherein the outer part holds the needle
holder in position in the front part of the syringe body and
against the bias of the spring, the outer part comprising an
annular member having an outer face that engages with the inner
wall of the syringe body
6. The syringe of claim 1, wherein a single raised portion is
provided.
7. The syringe of claim 6, wherein the portion comprises a
button.
8. The syringe of claim 2, wherein the edge portion of the seal on
the plunger is thickened and is relatively compressible whereby
upon pushing of the plunger towards the needle holder, the edge
portion will be the first point of contact with the raised portion
of the outer part, and as this contact occurs, the edge portion is
compressed before the frangible portion is broken the compression
enabling the front of the plunger to be pushed more closely against
the needle holder thereby reducing dead space prior to triggering
the shoot back mechanism.
9. The syringe of claim 1, wherein the seal on the plunger has a
substantially flat front face.
Description
FIELD OF THE INVENTION
[0001] This invention is directed to the medical field and
particularly directed to a single use syringe that has a needle
shoot back mechanism (retraction mechanism) with improved features.
One particular improvement is that the force required to trigger
the shoot back mechanism is reduced. Another improvement enables
the amount of "dead space" in the syringe to be reduced. Of course,
the invention may have other improvements.
BACKGROUND ART
[0002] In the medical field, needlestick is a continuing problem.
Needlestick is the term used when a contaminated needle pricks or
cuts a person. A contaminated needle can readily become a source of
infection. Another problem with syringes is with sharing of needles
which can also result in infection.
[0003] For this reason, it is known to provide a syringe having a
needle that has a particular design such that the needle can be
used only once. One way that this is achieved is to retract the
needle back into the syringe body after use. This also provides the
other advantage of minimising needlestick injury.
[0004] Many types of single use syringes are known, and most have
some form of retraction mechanism (also called a shoot back
mechanism) to shoot the contaminated needle back into the syringe
body after use.
[0005] It is known to provide single use syringes where the needle
is spring biased and is held in place by a cuttable member. In
order to ensure that the member is properly cut thereby releasing
the needle, a two-part cutting action is usually required. In the
two-part cutting action, the plunger typically has a forward
cutting edge and the front of the needle also has some form of
cutting edge and a double cutting action is required to ensure that
the cuttable member is property cut to release the needle. It is
found that attempting to cut a cuttable member to release a
spring-biased needle is not always reliable and does not always
work.
[0006] Another type of known single use syringe has a base member
that grips an enlargement on the needle. The plunger pushes the
base member forwardly, which further compresses a spring that is
around the needle. The pushing action releases the grip between the
base member and the enlargement on the needle. This allows the
needle containing the enlargement to be shot back into the plunger
while leaving the spring behind. The spring is initially compressed
partially but then becomes compressed fully as the plunger forces
the base member forwardly. This arrangement requires a needle
having a special design (containing an enlargement), which means
that conventional needles cannot be used.
[0007] Another type of syringe has a plunger seal which moves on
the plunger and where the plunger seal slides rearwardly along a
bearing surface in response to a force being applied to the seal
that is in excess of the operational force of the syringe. This
arrangement begins the retraction sequence of the needle. With this
arrangement, a specially designed plunger seal is required which
moves relative to the plunger. Conventional plungers have a plunger
seal that is fixed to the plunger.
[0008] Another type of syringe has a shoot back arrangement
consisting of two parts which slide relative to each other to
release the needle. The two parts consist of an outer part and an
inner part. The inner part holds the needle and is biased by a
helical spring. The two parts are held together by frictional
engagement to each other. A plunger progressively pushes the outer
part forwardly thereby progressively reducing the amount of
frictional engagement between the outer part and the inner part
until such time that the bias of the spring is sufficient to shoot
the inner part away from frictional engagement with the outer part.
This arrangement requires a sliding frictional grip to hold the
two-part together which is considered quite risky and requires
careful manufacture.
[0009] Another arrangement uses a needle holder having an elongate
body portion in front and a head end in back and providing a spring
under the head end that circumscribes the needle holder. The use of
an elongate body in a needle holder makes this arrangement
difficult for use in small and confined spaces.
[0010] It is found that retraction (shoot back) mechanisms that use
a cutting action are not particularly reliable especially for small
syringes, and there would therefore be an advantage if a retraction
mechanism could be used that did not require a cutting action.
While not wishing to be bound by theory, the small syringes have a
very small needle holding attachment, and trying to cut part of the
attachment away using a knife edge on the piston is not
particularly reliable. For instance, variation in the plastic used
in the attachment can cause the plastic to become too rubbery, or
too hard, and this can make the cutting action incomplete or
unreliable.
[0011] A useful type of retraction mechanism enables the needle
holder to be retracted or shot back into the hollow plunger in a
relatively straightforward manner. There is a disadvantage if the
retraction is impeded. It is always necessary to have some form of
seal or cover over the front of the plunger and this seal or cover
needs to be broken or pierced to allow the needle holder
(containing the contaminated needle) to be shot back into the
hollow plunger and through or past the seal or cover. It is found
advantageous if the front of the plunger contains a relatively thin
seal as this can improve the reliability of the shoot back
mechanism. Conversely, it is found to be a disadvantage if the
front of the plunger contains a stopper, a plug, or some other
relatively bulky member. If a stopper or plug is used, there is no
way that the needle holder can pierce through the stopper or plug,
and therefore, it is necessary for the needle holder to be shot
back with sufficient force to also push back the stopper or plug
into the plunger body. Therefore, there would be an advantage to
provide a single use syringe with a retraction mechanism that has
the front of the plunger containing a relatively thin seal through
which the needle holder can pass as opposed to a relatively bulky
stopper or plug.
[0012] Another important consideration with single use retractable
needle syringes is the force required to activate, or to trigger,
the shoot back mechanism. This force is the pressure that needs to
be applied to the rear of the plunger to push the plunger hard up
against the needle holder to trigger release of the needle holder.
Typically, this force will be applied by the user's thumb. It is
found that this force can be up to 9 kg to enable a conventional
shoot back needle to be triggered, and this is found to be
excessive. However, simply making the shoot back mechanism more
"flimsy" is not a solution, as this can result in accidental or
inadvertent triggering of the shoot back mechanism. Therefore,
there would be an advantage if a single use retractable needle
syringe could be manufactured that would be reliable but that would
also reduce the amount of force required to trigger the shoot back
mechanism.
[0013] Attempts have been made to reduce the triggering force.
However, previous attempts have been directed to providing a
complex design to the front of the plunger. The complex design to
the front of the plunger includes having a part of the plunger
front face projecting forwardly from the remainder of the plunger
front face. Thus, only part of the plunger (the forwardly
projecting part) initially contacts the needle holder to trigger
the shoot back mechanism. This type of arrangement prevents the
front of the plunger from having a "conventional" design which is
usually a substantially flat or planar seal extending over the
otherwise open front of the plunger. As mentioned previously, there
is an advantage in having a substantially "conventional" plunger
head to enable the needle to be shot back through the plunger head
and into the plunger body without needing to push back a stopper
etc. Also, having a relatively ordinary plunger head allows the
needle to shoot back through the plunger head without carrying any
significant debris (from the plunger head) which can impede
efficient retraction of the needle. Another advantage with having a
relatively conventional plunger head design, is that the medical
practitioner can more easily see the operation of the plunger and
especially how close the plunger is to the end of its stroke. With
a complicated plunger head design, it becomes difficult to see
where the "end" of the plunger actually is with respect to the
front of the syringe.
[0014] Another disadvantage with many existing single use syringes
is that the mechanism required to shoot back the needle often has a
portion protruding into the syringe barrel, and can result in
incomplete expulsion of the liquid from the barrel and through the
needle. In other words, many existing single use syringes have a
"dead space" where the syringe fluid can collect and where the
fluid will not be properly expelled from the syringe. This can
result in incomplete or erroneous levels of fluid being injected
into a person. There is therefore a significant advantage if the
volume of "dead space" could be reduced, prior to triggering the
shoot back mechanism. As mentioned previously, it is also
advantageous to reduce the force required to trigger the shoot back
mechanism. The mechanism described above to reduce the force to
trigger the shoot back mechanism (the complex plunger design)
results in part of the plunger front face projecting forwardly with
respect to the remainder of the plunger front face. This particular
design can also increase the "dead space" due to the design of the
plunger.
[0015] Therefore, there would be an advantage to provide a design
that can reduce the force to trigger the shoot back mechanism but
which can also reduce the dead space, and which is reliable in use.
The applicant considers that reliability can be provided by having
a shoot back mechanism where the needle shoots through a relatively
thin portion of the plunger head (therefore there is no need to
push back any stopper, and there is no "shatter plate" and the like
which can carry debris back into the plunger body), and where the
plunger head is otherwise of a conventional type shape which is
found to be best in reducing dead space and is also relatively easy
to manufacture.
[0016] Another disadvantage with some of the spring biased shoot
back needles, is that in practice, it is possible to reassemble the
mechanism which means that the syringe and needle can be reused.
Clearly, a single use syringe should be manufactured in such a
manner that it would be impossible to reuse the syringe. Therefore,
there would be an advantage in having some form of "destructive
mechanism" which would render the syringe unable to be reused.
[0017] It will be clearly understood that, if a prior art
publication is referred to herein, this reference does not
constitute an admission that the publication forms part of the
common general knowledge in the art.
BRIEF SUMMARY OF THE INVENTION
[0018] It is an object of the invention to provide a single use
syringe having a shoot back mechanism which can be triggered with
reduced force, and optionally which can also reduce the dead space
in the syringe.
[0019] In one form, the invention resides in a single use syringe
which comprises: [0020] a syringe body which contains a front end
area containing a longitudinal passageway which has a front portion
and a rear portion, [0021] a plunger which contains a front face
which extends into the syringe body, [0022] a pierceable seal
extending over the front face of the plunger, [0023] a needle
holder that is attached inside and in the front area of the syringe
body, [0024] a needle that is attached to the needle holder, [0025]
a spring in the front of the syringe body and that is biased to
shoot the needle holder through the pierceable seal in the front
face of the plunger and into the plunger, [0026] the needle holder
comprising an inner part and an outer part, the inner part
containing the needle, [0027] the outer part engaging with a wall
of the longitudinal passageway and initially in a rear portion of
the passageway, a frangible portion between the inner part and the
outer part, [0028] the outer part containing a raised portion
directed towards the seal of the plunger, the raised portion
extending only partway about the inner portion, the raised portion
functioning to provide an initial contact area of the plunger with
the outer part of the needle holder, thereby reducing the force
required to break the frangible portion thereby triggering the
shoot back mechanism.
[0029] An advantage of this particular arrangement is that the
plunger has a conventional flat front face and can be fitted with a
pierceable seal to minimise any interference with the needle holder
shooting back into the plunger body and through or past the seal.
Thus, there is no requirement for a relatively bulky stopper or
plug to be fitted to the front of the plunger. There is also no
need for the front of the plunger to contain a cutting face.
Another advantage is that the triggering mechanism uses a push and
break movement where the outer part is pushed forwardly by the
plunger along the longitudinal passageway while the inner part
remains stationary, and this movement breaks the frangible portion
that holds the inner part to the outer part. This is considered
advantageous over a cutting action or any other type of triggering
action. However, a main advantage is that the force required to
break the frangible portion and therefore trigger the shoot back
mechanism is reduced due to the design of the outer part and
particularly due to the raised portion (bump) that faces the front
of the plunger and which provides the initial point of contact
between the plunger and the outer part. The design also can reduce
dead space, as well as enabling the plunger to be fitted with a
pierceable seal as opposed to the complex design of the plunger
that has a forwardly projecting part and which may be difficult to
contain a pierceable seal.
[0030] It is preferred that the seal that extends over the front
face of the plunger contains a central portion that extends over
the otherwise hollow front of the plunger, and an edge portion that
extends over the edge of the plunger. The central portion can be
designed to be more easily pierced or broken, for instance by
making the wall thickness less.
[0031] It is preferred that the edge portion contains a thicker
area of seal and this area can be compressed or squashed as it
contacts the raised portion of the outer part. The advantage of
this is that the front of the plunger can be pushed quite close to
the needle holder (thereby reducing dead space) before the force is
sufficient to trigger the shoot back mechanism. This will be
described in greater detail below.
[0032] The syringe may be of any suitable shape and size. It is
envisaged that the syringe will vary between a 1 mil syringe up to
a 50 mil syringe or even more. The syringe may be made of any
suitable material such as plastic, glass or even metal. It is
preferred that the syringe is made of plastic.
[0033] The syringe has a syringe body. The body will typically be
cylindrical in design as is conventional, although if necessary,
the body may have other shapes such as rectangular in
cross-section, oval in cross-section and the like. The length of
the syringe body will vary depending on the size of the syringe and
will typically be between 30-200 millimetres although this can
vary. The diameter of the syringe body may also vary and will
typically be between 5-20 millimetres although this can vary. The
syringe body will typically have a wall thickness of between 0.3-4
mm although this can vary. The syringe body may be provided with
grip enhancing features or positioning enhancing features such as
outwardly extending tabs or flanges, exterior ribs and the
like.
[0034] The syringe body may have a front end area from which the
puncture needle will project. The front end area will typically
have a front opening through which the needle can extend. The front
end area will contain a longitudinal passageway which will
typically be designed such that the plunger can pass along or at
least partially along this passageway, and the passageway forms
part of the shoot back mechanism which will be described in greater
detail below. The passageway will typically have a front portion
which is more towards the front opening through which the needle
extends, and a rear portion. The size and shape of this passageway
can vary, but it is envisaged that this passageway may comprise a
continuation of the internal bore of the syringe body. The front
passageway may have a length of between 5-30 mm depending on the
size of the syringe.
[0035] The syringe will have a plunger. The length of the plunger
will vary depending on the size of the syringe and the plunger will
typically have a length of between 30-200 mm although this can
vary. The plunger is designed to slide in the syringe body and
therefore the plunger will have a diameter or cross-section which
enables it to do so. The plunger will typically be substantially or
entirely hollow such that the contaminated needle can be shot back
into the hollow interior of the plunger. However, it may also be
possible to have the forward part of the plunger hollow
(sufficiently to at least partially hold the needle) and the rear
part solid or of different design. It is also envisaged that the
plunger need not be hollow and may comprise an X type
cross-section, or other cross-section such that the contaminated
needle can pass into the passageway which is defined between the
cross-section and the internal wall of the syringe. Other
configurations of the plunger are envisaged providing that space is
provided by the inside the plunger or between the plunger and the
syringe body to accommodate the contaminated needle after the shoot
back mechanism is triggered. However, it is considered useful that
the plunger comprises a hollow cylindrical member.
[0036] The plunger has a front face which is the part of the
plunger that extends into the syringe body and is pushed towards
the front of the syringe. If the plunger is cylindrical, the front
face will also be substantially cylindrical. A seal is provided
over the front face of the plunger. The seal is of the type that
can be pierced or broken such that the contaminated needle can
pierce through or pass by the seal when the shoot back mechanism is
triggered. Various types of seals are envisaged including rubber
seals, plastic seals, metallic seals, elastic seals, laminated
seals and the like. The seal will typically extend entirely over
the front face of the plunger although depending on the size of the
needle and the needle body, the seal may pass only over a central
portion or other portion of the plunger. It is however preferred
that the seal extends entirely over the front face of the plunger.
If desired, the seal may have a central portion that extends over
the central portion of the plunger and which can be of a different
design (typically thinner) to enable it to be pierced or broken
more easily, and an edge portion that extends over the edge of the
plunger and which may be thicker and more easily compressed or
squashed, the reason for which will be described in greater detail
below. The seal may also extend over the sides of the plunger to
provide a good sealing effect and to also assist in sealing the
plunger against the inside wall of the syringe body.
[0037] The syringe contains a needle holder that holds the needle.
The needle holder will typically be attached inside and in the
front area of the syringe body. The needle holder may comprise an
inner part and an outer part which are attached to each other by a
frangible portion. Thus, it is not preferred that the inner part
and the outer part are engaged frictionally; instead, the inner
part and the outer part are bonded or joined together via the
frangible portion. This provides a more reliable action and
minimises accidental release of the needle holder. The inner part
may comprise a front portion and a rear portion and an intermediate
body portion. The front portion may extend through the opening in
the front of the syringe body. The intermediate body portion may
comprise an elongate substantially cylindrical portion containing
an internal passageway which communicates with the puncture needle.
The rear portion may extend towards the plunger and may comprise a
profile or have a projection or have any other configuration to
assist in the piercing or breaking of the plunger seal. Typically,
the rear portion will have an "arrowhead" type configuration.
[0038] A spring is provided to bias the needle holder towards the
retraction or shoot back position. The spring may comprise a
helical spring and the helical spring may extend about the
intermediate body portion of the needle holder.
[0039] The outer part of the needle holder may comprise the part
that holds the needle holder in position in the front part of the
syringe body and against the bias of the spring. The outer part may
comprise an annular member. The annular member may have an outer
face that engages with the inner wall of the syringe body. The
engagement may comprise frictional engagement, but may also
comprise abutment of part of the outer face with a shoulder,
recess, or other configuration of the syringe body.
[0040] The outer part of the needle holder will typically be
positioned in a rear portion of the passageway that is in the front
of the syringe body. Thus, the outer part will typically be able to
be pushed along the passageway from the rear portion of the
passageway towards the front portion of the passageway. This
distance may be between 1 mm up to 20 mm depending on the size of
the syringe. Movement of the outer part in this manner relative to
the inner part will cause the frangible portion to break thereby
releasing the inner part from the outer part and triggering the
shoot back mechanism.
[0041] Pushing of the plunger to the front of the syringe will
cause the plunger to engage with the outer part and to push the
outer part along the passageway thereby breaking the frangible
portion and triggering the shoot back mechanism.
[0042] The outer part will typically contain at least one raised
portion/zone/area which is directed towards the front of the
plunger, that is which is pointing inwardly into the syringe body.
The raised portion etc may be formed integrally with the outer part
or may be formed separately and attached thereto, or relative
thereto. The raised portion may comprise a bump, a rib, a tooth, a
"button", or any other type of configuration which will serve the
purpose which will be described in greater detail below. It is
preferred that the raised portion extends only partially about the
outer part, or only partially about the inside of the syringe. The
arrangement will typically be such that as the plunger is pushed
forwardly, the plunger will contact the raised portion first before
the rest of the outer part is contacted by the plunger. This
provides several benefits including a reduction in the force
required to trigger the shoot back mechanism. For instance, the
arrangement can concentrate the initial force of the plunger into a
smaller area (typically on the outer part of the needle holder) to
cause this part to move forwardly to break the frangible portion in
this area. It is found the once the frangible portion is at least
partially broken, less force is required to entirely rake the outer
part from the inner part.
[0043] It is preferred that the edge portion of the seal on the
plunger is thickened and is also preferred that this portion is
relatively compressible. The reason for this is that the edge
portion will be the first point of contact with the raised portion
of the outer part, and as this contact occurs, the edge portion is
compressed before the frangible portion is broken. This compression
enables the front of the plunger to be pushed more closely against
the needle holder thereby reducing dead space prior to triggering
the shoot back mechanism.
[0044] The shoot back mechanism has similarities to that described
in our earlier PCT application PCT/AU01/00183 which is incorporated
here in by cross-reference; U.S. patent application Ser. No.
10/181,950, filed Aug. 2, 2002 corresponds to PCT/AU01/00183.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] An embodiment of the invention will be described with
reference to the following drawings in which:
[0046] FIG. 1. Illustrates in cross-section a front portion of the
syringe with the plunger moving towards the forward part of the
syringe but not yet contacting any part of the shoot back
mechanism.
[0047] FIG. 2. Illustrates in cross-section the plunger just
beginning to make contact with the raised portion of the outer part
of the needle holder, and also just beginning to make contact with
the "arrowhead" configuration on the inner part of the needle
holder. At this stage, there is still an appreciable "dead space",
and the shoot back mechanism has not yet been triggered.
[0048] FIG. 3. Illustrates in cross-section the plunger having been
pushed forwardly a little further than the position of FIG. 2, and
illustrating the "arrowhead" configuration beginning to stretch the
central part of the plunger seal, and also illustrating the plunger
making greater contact with the outer part of the needle holder and
having part of the plunger seal compressed to reduce the dead
space. This position is just prior to triggering the shoot back
mechanism.
[0049] FIG. 4. Illustrates the syringe after the shoot back
mechanism has been triggered with the contaminated needle (and the
inner part of the needle holder) being safely within the confines
of the plunger.
DETAILED DESCRIPTION
[0050] Referring to the drawings and initially to FIG. 1, there is
illustrated in cross-section the front part of a single use
syringe. Briefly, the syringe comprises the following components:
they syringe body 10 which has a front end area 11 which contains a
longitudinal passageway 12, the passageway having a front portion
13 and a rear portion 14, a plunger 15 which is hollow and which
contains a front face 16, a pierceable seal 17 which extends over
the front face 16 of plunger 15, and which has a thickened edge
portion 18, a needle holder 19 which comprises an inner part 20 and
an outer part 21, the inner part further having a front portion 22
that extends through an opening 23 in the front of syringe body 11,
a rear portion 24 which has an arrowhead type configuration, and an
intermediate body portion 25, a needle (puncture needle) 26 that is
fixed to the inner part 20, a spring 27 which extends about the
intermediate body portion 25. Further more particular details will
be described below.
[0051] The syringe body 10 has a front end area 11 which has a
particular profile (see FIG. 1). The particular profile contains a
forwardmost opening 23, a narrower diameter passageway behind
opening 23 to contain part of the intermediate body portion 25, and
a large diameter passageway 12, which essentially forms an
extension of the internal bore of the syringe body through which
the plunger 15 can pass.
[0052] The inner part 20 of the needle holder 19 cannot move
through opening 23 (by virtue of intermediate body portion 25
having a larger diameter than the front portion 22 and this
diameter being larger than opening 23). Thus, if the plunger 15
pushes against the inner part 20, inner part 20 cannot move.
[0053] One end of spring 27 abuts against the end of the narrower
diameter passageway behind opening 23, and the other end of spring
27 abuts against a small shoulder just behind the arrowhead
configuration of the rear portion 24 of inner part 20. With this
configuration, the spring is compressed and biases the inner part
20 into the shoot back position which is inside the hollow interior
of plunger 15. However, this is prevented by the inner part 20
being attached to the outer part 21.
[0054] Outer part 21 in the particular embodiment is annular in
configuration and extends entirely about inner part 20 and in the
area of the arrowhead configuration of the inner part, this being
illustrated in FIG. 1. Outer part 21 has an outer face 28 which
presses against the inside wall of passageway 12. A small abutment
in the inside wall may be provided to positively position the outer
part 21 in place, and to prevent the outer part from moving towards
the plunger. The outer part is attached to the inner part by a
frangible portion 29 which is referenced in FIG. 2. The frangible
portion 29 in the particular embodiment extends entirely between
the inner part and the outer part. This prevents fluid from leaking
part the needle holder and into a forward part of passageway
12.
[0055] The outer part 21 contains a raised portion 30 (best
illustrated in FIG. 2) but also illustrated in the other figures)
which extends only partway (typically about quarter) about the
outer part. The raised portion projects in the direction of plunger
15 and fimctions to reduce the pressure required to trigger the
shoot back mechanism as will be described in greater detail
below.
[0056] The triggering of the shoot back mechanism is somewhat
similar to that described in our earlier international patent
application given above, and basically occurs when plunger 15 is
pressed hard up against the needle holder which is progressively
illustrated in FIGS. 2-3. As this happens, the plunger contacts the
outer part 21 and further forward pushing of the plunger enables
the outer part to be pushed forwardly along passageway 12. As the
inner part 20 of the needle holder cannot move in the same way,
continued pressing on the plunger will cause the frangible portion
29 to be broken thereby releasing the inner part 20 from the outer
part 21. As soon as this happens, spring 27 shoots the inner part
20 (containing the puncture needle 26) through the front of plunger
15 and into the hollow interior of the plunger. The final position
is illustrated in FIG. 4.
[0057] However, in the present invention, a modification has been
made to provide certain advantages. The modification includes
providing the raised portion 30 on only a portion of the outer part
21. Thus, as plunger 15 moves forwardly from the position
illustrated in FIG. 1 to the position illustrated in FIG. 2, an
edge 31 of the plunger contacts the raised portion 30 (see FIG. 2).
At this stage, the remainder of the plunger does not yet contact
the remainder of the outer part 21; instead, only part (edge 31) of
the plunger contacts only part (the raised portion 30) of the outer
part. This concentrates the force of the plunger on to only part of
the outer part 21 and enables the frangible portion in this area to
be broken. It is found that once part of the frangible portion is
broken, the remainder of the frangible portion can be broken with
much less force.
[0058] However, there is a further modification which also reduces
the dead space. The dead space is defined as the volume that cannot
be expelled from the syringe due to the design of the internal
components. Clearly, the amount of dead space should be reduced as
much as possible.
[0059] In the present embodiment, once the plunger is in the
position illustrated in FIG. 2, there is only slight contact
between the edge 31 of the plunger and the raised portion 30 of the
outer part. The arrowhead portion of the inner part has also
contacted the seal 17 and is beginning to stretch the seal and
weaken the seal. However, at this stage, the shoot back mechanism
has not been triggered in that the frangible portion has not yet
been stretched and broken.
[0060] Instead, the plunger is moved slightly more forwardly as
indicated in FIG. 3. The forward movement need not be much (perhaps
1 mm), but is sufficient to bring the seal 17 into relatively close
contact with the internal edges of the needle holder to reduce the
amount of dead space. To accommodate the raised portion 30, the
edge 31 of seal 17 is relatively thick (compared to the remainder
of the front portion of the seal) and can be compressed or
squashed. Therefore, in the position illustrated in FIG. 3, the
plunger has been moved more forwardly and the raised portion 30 has
been compressed into the rubbery edge 31 still without triggering
the shoot back mechanism. It can be seen that in this particular
position, the remainder of the front of the plunger is now in
contact with the rest of the outer part 21. In this position, the
amount of dead space has been reduced with respect to the amount of
dead space when the plunger was in the position illustrated in FIG.
2.
[0061] Further forward movement of the plunger will now push the
outer part 21 along passageway 12 and because of raised portion 30,
the greatest force (and therefore greatest pushing action) will be
on the raised portion 30 which will cause a preferential breaking
or rupture of the frangible portion in this area only. This results
in a reduced force being required to break the frangible portion.
Once the frangible portion has been preferentially ruptured, it is
found that less force is required to completely rupture the
remainder of the frangible portion. As the plunger is pushed
forwardly, the seal 17 is also stretched even further by the
arrowhead configuration of the inner part 20 and the seal can be
ruptured via the arrowhead configuration, or release of the spring
is sufficient to now shoot the inner part and the contaminated
needle through the seal and into the hollow plunger is illustrated
in FIG. 4. The outer part 21 is slightly tilted as it is pushed
forwardly.
[0062] The arrangement is found to reduce the force required to
trigger the shoot back mechanism from approximately 9 kg to between
2-3 kg. The shoot back mechanism is still robust and has not been
made "flimsy" in order to reduce the force required. This is
achieved by having a raised portion on the outer part 21 and having
the seal on the plunger being relatively conventional and not
requiring any complicated design on the front of the plunger. By
enabling the plunger to be relatively conventional, the raised
portion 30 can be partially pushed into (compressed) into the edge
of the seal to reduce the dead space prior to triggering the shoot
back mechanism. It is not considered that such a relatively simple
and reliable mechanism is possible with a complicated plunger
shape.
[0063] Throughout the specification and the claims (if present),
unless the context requires otherwise, the term "comprise", or
variations such as "comprises" or "comprising", will be understood
to apply the inclusion of the stated integer or group of integers
but not the exclusion of any other integer or group of
integers.
[0064] Throughout the specification and claims (if present), unless
the context requires otherwise, the term "substantially" or "about"
will be understood to not be limited to the value for the range
qualified by the terms.
[0065] It should be appreciated that various other changes and
modifications can be made to any embodiment described without
departing from the spirit and scope of the invention. Thus, the
appended claims should be broadly construed in a manner consistent
with the spirit of applicant's unique invention, and should not be
restricted to their literal terms.
* * * * *