U.S. patent application number 12/059635 was filed with the patent office on 2008-10-02 for medical device with retractable needle.
Invention is credited to Thomas J. Shaw.
Application Number | 20080243075 12/059635 |
Document ID | / |
Family ID | 25288947 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080243075 |
Kind Code |
A1 |
Shaw; Thomas J. |
October 2, 2008 |
Medical Device with Retractable Needle
Abstract
A tamperproof retractable non-reusable syringe has a one piece
hollow outer body with a barrel for a slidable plunger, a
transition zone and a smaller diameter nose portion. An elongated
needle holder and spring combination is installable from the rear
of the outer body, guided into the nose portion and held by
cooperating inwardly and outwardly facing surfaces oriented in the
direction of retraction at the most constricted part of the
transition zone where the nose begins. The plunger has an opening
with a dislodgable stopper for receiving parts of the retraction
mechanism. The stopper and the head of the needle holder are of
significantly reduced diameter from the injection fluid chamber to
resist blowing out prematurely. In one embodiment the head of the
needle holder is surrounded by a separable retainer member which is
slidingly removed by contact with the tip of the plunger after the
stopper is mostly or fully removed to avoid cumulation of force
required for retraction after the injection. In a second embodiment
the head of the needle holder is clamped and held by constricting
forces imposed by stress on the outer body induced by interference
fit. Release occurs by slight expansion on the barrel by contact of
the plunger tip with a small internal ramp in the outer barrel.
Both embodiments have a plunger cap configured to enter an opening
in the outer body to provide an additional tamperproof feature. The
retraction cavity is provided with venting structures to assure
that all uninjected fluid is retained within the syringe body.
Inventors: |
Shaw; Thomas J.; (Frisco,
TX) |
Correspondence
Address: |
Locke Lord Bissell & Liddell LLP;Attn: Michael Ritchie, Docketing
2200 Ross Avenue, Suite # 2200
DALLAS
TX
75201-6776
US
|
Family ID: |
25288947 |
Appl. No.: |
12/059635 |
Filed: |
March 31, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09617868 |
Jul 17, 2000 |
7351224 |
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12059635 |
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08843050 |
Apr 25, 1997 |
6090077 |
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09617868 |
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08537242 |
Sep 29, 1995 |
5632733 |
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08843050 |
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08438954 |
May 11, 1995 |
5578011 |
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08537242 |
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Current U.S.
Class: |
604/111 ;
604/110 |
Current CPC
Class: |
A61M 5/508 20130101;
A61M 2005/3236 20130101; A61M 5/502 20130101; A61M 2005/3235
20130101; A61M 2005/3239 20130101; A61M 5/3234 20130101 |
Class at
Publication: |
604/111 ;
604/110 |
International
Class: |
A61M 5/00 20060101
A61M005/00 |
Claims
1-28. (canceled)
29. A medical device comprising a needle retraction mechanism
disposed inside a body, the needle retraction mechanism comprising
a needle holder grounded against forward movement inside the body
and supporting a forwardly extending needle in fixed relation to
the needle holder, the needle holder comprising a head further
comprising an inner head supporting the needle in fixed relation to
the inner head, and a retainer member surrounding the inner head
and disposed in substantially fixed relation to the inner head
prior to retraction, the inner head being biased toward a
retraction position by a retraction spring and held in place prior
to retraction by attachment to the retainer member and by contact
between the retainer member and an inner wall of the body, the
retainer member cooperating with the inner head to provide a fluid
seal between the needle and the body and being detachable from the
inner head by the application of a retraction force to the needle
holder outwardly of the inner head and in a direction coaxial to
the needle, the retraction force being applied as the result of
forward motion of a plunger relative to the body to initiate
retraction, the plunger further comprising a plunger head having a
sealing element slidably engaging the body, the plunger sealing
element being the only structure maintaining the plunger head
inside the body following retraction.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of copending patent
application Ser. No. 08/537,242 filed Sep. 29, 1995 entitled
Tamperproof Retractable Syringe which in turn was a continuation of
Ser. No. 08/438,954 filed May 11, 1995, now U.S. Pat. No. 5,578,011
all by the same inventor for which benefit is claimed under 35
U.S.C. .sctn.120.
FIELD OF THE INVENTION
[0002] This invention relates to a medical device, and more
particularly to a retractable syringe and components suitable for
mass production and assembly having a low triggering force and high
blowout pressure which is nonreusable after one use.
BACKGROUND OF THE ART
[0003] A major cause to the spread of AIDS in the general
population is the presence of IV drug users who share and reuse
hypodermic syringes to inject drugs. Infection can be spread from
AIDS patients in hospitals and medical facilities through
accidental needle sticks from needles used on infected patients.
Used syringes with extended needles present a risk to medical
personnel and sanitation employees and others in the disposal
chain.
[0004] The gravity of the threat posed by AIDS and the fact that
the main vector of the spread of the dreaded disease is through
reuse of syringes by IV drug users has resulted in intense activity
to develop the most practical, most reliable, easily assemblable,
mass-producible syringe.
[0005] There are a number of syringes of different designs which
have needles which will retract at the end of the injection cycle.
Most of these have never reached the market because of various
deficiencies. Prime among the usual deficiencies of the prior art
are problems of complexity, reliability, cost and ease of use. The
most commonly used syringes are 1 cc and 3 cc syringes which must
be mass-produced at the rate of millions per day. Cost is a
significant factor both in manufacture of the parts and assembly of
the device. High speed production requires molds with 64 cavities
or more to reduce unit cycle time. Therefore, molded structures
within the barrel that require collapsing core pins such as are
shown in much of the art are unlikely to be producible at
competitive costs.
[0006] One of the problems of the prior art of retractable syringes
is the sheer number and complexity of parts which must be formed
and assembled. Other problems with the prior art are dependence on
flexing or breaking of internal parts by the plunger in order to
release the retraction mechanism and use of a diaphragm at the end
of the plunger which must be penetrated by a needle holding member
and spring. These structures present serious quality control and
assembly problems. Small broken off pieces can present a risk of
hang-ups. Hooks are often used to releaseably secure retraction
mechanisms. Hooks present difficult holding and control problems,
may cause retention of air bubbles upon filling and may be
undesirably temperature sensitive.
[0007] The prior art frequently has a two-piece barrel in order to
be able to assemble a retraction device in the nose. This requires
at least an additional part and assembly step. It is still
necessary to pass the sharp injection needle through a small
opening often while compressing a spring before the two parts can
be assembled. The tiny needles are produced in the form of coil
tubing and vary significantly from straightness after they are cut
to length. This leads to difficult assembly problems if the needle
must be passed through a small opening. The extremely sharp tip
will catch the edge of a hole and jam the production line.
[0008] The rare prior art that employs a front mounted retraction
mechanism in a one-piece barrel with a plugged hollow plunger, Tsao
U.S. Pat. No. 5,084,018, among other things does not show reduced
barrel area to prevent excessive blowout pressure, employs engaging
flanges to secure all retraction parts, requires concurrent
distortion of internal parts and flanges to effect release,
cumulating in excessive force required to retract and requires
ventilation holes because of a compartmented barrel.
[0009] The prior art has not produced a retractable nonreusable
tamperproof syringe for mass production and assembly which is
simple, reliable, cost effective, easy to use and retract, looks
like a conventional syringe, has few parts which are easy to make
and assemble, is not temperature sensitive and not subject to
danger of premature retraction.
[0010] The prior art has not recognized a retraction mechanism with
separable parts that relies entirely on clamping force or friction
at a smooth walled reduced diameter transition zone in the barrel
with mating lands which are slidably or separably released in
response to relatively low thumb pressure while having resistance
to premature retraction and high blowout pressure resulting from
high pressure produced in the fluid chamber during an injection.
The prior art has not recognized that such a structure can be
molded as a one piece outer body over a core that can be pulled out
from behind allowing the retraction mechanism to be easily pushed
into place from behind, steered by the narrow nose portion. Neither
does the prior art in such a combination realize the desirable
non-cumulation of forces resisting retraction in order to minimize
the thumb force required, having a most simple tamperproof feature
and the fewest number of easily made parts.
[0011] The syringe plunger assembly has a combination of features
not found in a prior art syringe. A head end which acts like a
piston when installed in a syringe barrel has a reduced diameter
front end having an opening and a dislodgeable stopper slidingly
mounted in the opening projecting forwardly from the tip.
Cooperating lands within the opening and on the head of the
dislodgeable stopper seal the opening into the hollow interior of
the plunger. The area of the stopper is relatively small when
compared to the area exposed to the piston, which compresses fluid
in a chamber below the piston. The ratio of the total area of the
fluid chamber to the fluid exposed area of the stopper is at least
two to one, more preferably three to one or more so that the
stopper requires less holding force without blowing out back into
the internal cavity. The cooperating lands have sufficient length
so that the stopper can move back to the tip when the plunger moves
forward at the end of an injection stroke without unsealing the
plunger opening. A reduced holding force is sufficient to prevent
blowout of the stopper after the stopper has been moved back to the
tip because the stopper is exposed to a lower pressure generated
force because of its relatively smaller area. The back of the
plunger is vented so that entry of retractable parts which upon
retraction finish dislodging the stopper and carry it back into the
cavity, do not generate internal pressure that can blow out the
nose of the syringe carrying any residual fluid with it. The thumb
cap on the plunger is received and recessed into the opening at the
back of the barrel when retraction occurs. The plunger cannot be
grasped after this occurs to help prevent reuse.
[0012] These features and more are found in the inventive
combination herein further disclosed which is especially suited for
high speed production and assembly at low cost.
SUMMARY OF THE INVENTION
[0013] The invention is a reliable retractable tamperproof syringe
having multiple tamperproof features which operates on a principle
which permits low cost parts which are few in number and well
suited for high speed mass production and assembly. The syringe
structure features a one piece hollow outer body having a
longitudinally extending wall which is stepped. The wall comprises
an elongated barrel and nose with a transition zone connecting the
barrel and nose. The nose has a reduced diameter relative to the
barrel. The outer body has an inwardly facing surface in the wall
at the most constricted part of the transition zone where the nose
begins. A plunger assembly is disposed partially within the
elongated barrel with an end cap for depression of the plunger
extending from an opening in the back of the barrel. The head of
the plunger, which has a retraction cavity for receiving parts of a
retraction mechanism, moves in slidable sealed contact with the
interior of the barrel.
[0014] A retraction mechanism is lodged in the nose of the body.
The retraction mechanism comprises an elongated needle holder and
spring combination wherein the needle holder has an elongated body
with a needle holding portion in front and a head in back. The head
of the needle holder has a cooperating outwardly facing surface
configured to cooperate with said inwardly facing surface along an
interface oriented in the direction of retraction to produce a
holding force on the needle holder when installed in the nose in
the unretracted position. The needle holder and spring are easily
installable from the rear of the barrel toward the nose and
releaseably held by sliding engagement of said cooperating inwardly
and outwardly facing surfaces while compressing the spring and
thereby producing a holding force on the needle holder in
opposition to the retraction force applied to the needle holder by
the spring. The parts are circular in cross section.
[0015] The outwardly facing surface on the circular head of the
needle holder is slightly greater in diameter than the circular
inward facing surface in the wall at the most constricted portion
where the nose begins. The needle holder is thus clamped in
position by hoop stresses induced in the outer body and held in
position by frictional holding force. The needle holder is released
in response to depression of the plunger to a retraction position.
Retraction occurs in response to thumb force on the plunger when a
portion of the plunger passing into the transition zone separates
at least a portion of the inwardly and outwardly facing cooperating
surfaces thereby reducing the holding force on the needle holder to
an amount less than a retraction force on the needle holder
produced by the spring whereby the needle holder is retracted into
the cavity a distance sufficient to withdraw an injection needle,
attached to the needle holder, into the outer body.
[0016] In one embodiment, the head of the needle holder is a two
part head comprising an inner head surrounded by a separable
retainer member wherein the outer surface of the retainer member is
the outwardly facing surface with cooperates with the inwardly
facing surface in the wall to retain the needle holder in an
unretracted position at the most constricted part of the transition
zone where the nose begins. The retainer member is a ring member
coupled to the inner head along a sliding interface oriented in the
direction of retraction with a friction force which exceeds the
retraction force provided by the spring. The front of the needle
holder is grounded in the nose portion against forward movement.
The plunger head is configured to pass through the most constricted
area and push against the retainer member without also pushing
against the head of the needle holder. An alternate construction of
the two part head of the needle holder comprises the separable
retainer member being tack welded to the inner head of the needle
holder, preferably along a very small ridge or bridge between the
mating surfaces which holds the two part head together until the
bridge is ruptured by movement of the plunger after an injection
has occurred.
[0017] The front of the plunger has an opening for a stopper
slidingly fitted therein in an interference fit. The stopper is
fitted in the opening in an interference fit along a sliding
interface oriented in the direction of retraction. The stopper is
mostly or fully dislodged by contact with the retraction mechanism
at the end of an injection cycle by continued depression of the
plunger from a first position at the end of the injection cycle to
a second position with the tip of the plunger in contact with the
retainer ring. This avoids cumulation of the force on the plunger
required to dislodge the stopper from the opening and the force
required to dislodge the retainer member from the head of the
needle holder and outer body wall. Upon further depression of the
plunger from the second position to the retraction position, the
frictional holding force on the needle holder is reduced until the
retraction force provided by the spring exceeds the remaining
holding force and the needle holder and needle connected thereto
are ejected into the cavity carrying the dislodged stopper along
with them. The dislodging of the stopper and the retainer member
alone make the syringe non-reusable. The plunger cannot be removed
after retraction because the graspable end cap enters an opening at
the back of the barrel when the plunger is depressed to the
retraction position to prevent tampering after retraction.
[0018] The retraction cavity of the plunger is preferably vented to
prevent a puff of air coming forward at the instant of retraction
from blowing a tiny amount of retained fluid from the nose. This
condition can occur if the plunger is fully depressed to release
the needle holder and dislodge the stopper while the needle is
physically restrained from retracting by the septum of a vial which
has just been filled with fluid from the syringe. The thumb cap at
the rear of the syringe is preferably provided with channels in
fluid communication with the interior in cooperation with a closure
removably installed in a centrally located opening in the thumb
cap. One or more stepped portions of the opening and closure
provide seating for the closure. Undercut portions at the side of
the closure together with grooves in the interior surface of the
plunger wall create passages for air to vent through channels on
the thumb cap. This structure prevents air from being trapped by
the user's thumb when the thumb cap is pressed to fire the syringe.
One or more slots at the back of the barrel around the opening
which receives the thumb cap prevent vented air from being trapped
by the user's thumb when the plunger is fully depressed.
[0019] The syringe has a high blowout pressure and a low plunger
thumb force required to cause retraction. Blowout pressure is the
fluid pressure operating on the stopper and retainer ring during an
actual injection. High blowout pressure resistance is obtained
because the retainer ring is mounted in the most constricted
portion of the barrel where the nose begins which significantly
reduces the amount of area exposed to fluid pressure. The smaller
retainer ring allows the use of a small needle holder such that the
opening in the plunger and the stopper can be only a fraction of
the cross sectional area of the fluid chamber below the plunger
head. The ratio of the greatest cross sectional area of the
variable chamber and that of the dislodgeable stopper or the ring
member are selected so that the maximum expected thumb force on the
plunger during an injection will produce a maximum pressure in the
chamber which will generate a blowout force on the stopper and
retainer member slightly less than the amount of dislodging force
necessary to dislodge the stopper and retainer member during
retraction. This ratio should be at least two to one, or more
preferably three to one or more, in order to ensure against
premature blowout of the stopper or retainer ring.
[0020] In an alternate embodiment, the fewest number of easily made
separate parts are used in a retractable syringe. The alternate
embodiment has a similar stopper in the head of the plunger and a
similar needle holder and spring combination with mating
cooperating inwardly facing and outwardly facing interengaged
surfaces at the most constricted part of a transition zone where
the nose begins. In the alternate embodiment, there is no retainer
ring around the head of the needle holder. Instead a tiny ramp is
provided at the transition zone or adjacent the transition zone
whereby the head of the plunger gently spreads the barrel outwardly
while dislodging the stopper thereby reducing the clamping or
friction force on the head of the needle holder provided by the
wall of the outer body. The holding force is thereby reduced below
the retraction force provided by the compressed spring and the
needle holder is ejected into the cavity of the plunger carrying
the dislodged stopper along with it.
[0021] Manufacture and assembly is facilitated by the fact that the
plunger and the outer body can be molded with a non-collapsible
core tool that can be pulled out from behind. The parts are simply
shaped and do not have hooks and parts with reentrant angles that
require collapsible core pin technology. The outer body can be made
in one piece and assembled from the rear. The narrowed nose portion
provides no lateral space with will permit bunching of the spring
and jamming when the retraction assembly is moved forward in the
outer body. In fact, the nose serves as a guide to steer the parts
into the proper position in one smooth stroke.
[0022] The needle does not have to be installed before the
retraction mechanism is put in place because it is readily
installed from the front after the needle holder is slidingly
lodged in the nose. Significant variations in the holding force on
the needle holder and the dislodging force on the stopper due to
slight variances in the tolerance of the mating parts is avoided
because the longitudinal wall of the outer body has some
flexibility. The wall can spread outwardly slightly and the stopper
and head of the needle holder can compress slightly radially and
expand slightly in the longitudinal direction to avoid significant
changes in the holding force caused by small changes in the actual
diameters. Consistency in the amount of retraction force is thereby
provided and economy is assured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross section along the central axis of a first
embodiment of the invention with the plunger positioned in a first
position at the end of an injection cycle;
[0024] FIG. 2 is the syringe of FIG. 1 with the plunger depressed
additionally to dislodge the stopper at a second position of the
plunger wherein the tip of the plunger is ready to operate the
retraction mechanism;
[0025] FIG. 3 is the syringe of FIG. 2 wherein the plunger has been
further depressed to a retraction position, retraction has occurred
and the cap at the back of the plunger is closely received in an
opening at the back of the outer body;
[0026] FIG. 4A is a partial cross section on the central axis of an
alternate tamperproof opening in the back of the outer body prior
to retraction;
[0027] FIG. 4B is the structure of FIG. 4A with the plunger in the
retracted position received in an opening at the back of the outer
body;
[0028] FIG. 5 is a cross section along the central axis of a
simplified alternate syringe structure without a retainer member
around the needle holder, which is released by separation of the
friction surfaces, shown in the plunger position which represents
the end of injection cycle;
[0029] FIG. 6 is the syringe structure of FIG. 5 wherein the
plunger is further depressed to dislodge the stopper and begin to
release the friction surfaces just prior to retraction;
[0030] FIG. 7 is the syringe structure of FIG. 6 with the plunger
further depressed beyond the position of FIG. 6 to the retraction
position where retraction has occurred and the cap is secure within
an opening in the back of the hollow outer body.
[0031] FIG. 8 is a schematic longitudinal cutaway view in elevation
through the center of the two part head showing how a tack weld can
be applied to simultaneously seal and hold the retainer ring in
place on the needle holder.
[0032] FIG. 9 is an exploded perspective view showing the barrel
and retraction mechanism of FIG. 1 with a modified plunger
assembly;
[0033] FIG. 10 is a plan view of the thumb cap of the plunger
assembly shown in FIG. 9 with the preferred closure;
[0034] FIG. 11 is a cut away elevational view of the structure at
the back end of the plunger and end cap of FIGS. 9 and 10 along
line 11-11 showing the preferred closure;
[0035] FIG. 12 is a cut away elevational view of the plunger end
cap and closure of FIG. 11 as the thumb cap is just being received
into the barrel opening;
[0036] FIG. 13 is a plan view of a first alternative thumb cap and
closure combination utilizing a flat sided closure and four
channels in the thumb cap;
[0037] FIG. 14 is a cut away elevational view on the lines 14-14 of
the thumb cap closure combination of FIG. 13;
[0038] FIG. 15 is a plan view of a second alternate thumb cap and
closure combination with four channels in the thumb cap and
undercut portions to provide a vent passage;
[0039] FIG. 16 is a cut away elevational view on the lines 16-16 of
the combination of FIG. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0040] In the description that follows, like parts will be referred
to by the same reference numerals. Parts with a subscript letter
are mean to illustrate a minor variation of a part with the same
number. The drawings are enlarged significantly in order to show
the details of the invention but generally reflect the true scale
which is contemplated. The parts as shown are understood to be
preferably circular and symmetrical as is conventional for
syringes. The drawings reflect a syringe structure typically having
a 1 cc to 3 cc injection fluid capacity.
[0041] FIG. 1 shows the structure of the first embodiment generally
referred to by reference numeral 10. Syringe 10 has a one piece
hollow outer body 12. Body 12 has a longitudinally extending wall
comprising an elongated barrel 14 and a nose 16 with a transition
zone 18 connecting the barrel and nose. A front mounted retraction
mechanism lodged in the nose is generally referred to by the
reference numeral 20. It comprises the combination of an elongated
needle holder 22 and spring 24. The needle holder has an elongated
body with a needle holding portion 26 in front for holding a needle
28 and a head 30 in back. Head 30 may consist of a two part head as
in FIGS. 1-3 or a one part head as in FIGS. 5-7. The needle holder
is released by depression of a plunger that will be described.
[0042] A plunger generally designated by the reference numeral 32
is disposed for use partially within barrel 14. The plunger has a
head and seal generally referred to by reference numeral 34, in
slidable sealed contact with the interior of barrel 14 of outer
body 12. The plunger has a seal element 36 that is conventional and
a retraction cavity 38 therein.
[0043] Head 34 has a tip portion 40 forming an opening 41 into
retraction cavity 38. A resilient dislodgable stopper 42 is
sealingly positioned in opening 41 with a front portion thereof
extending beyond tip 40. Head portion 34 and the back part of
stopper 42 have cooperating lands 44, 46, respectively, which seal
opening 41. Plunger 32 has an end cap 48 for depression of the
plunger by the thumb. End cap 48 has a central opening for
permanently receiving force fit plug 50 to close retraction cavity
38 at the back end.
[0044] A plurality of longitudinally extending flutes 52 slidingly
support plunger 32 in barrel 14. In the embodiment of FIG. 1, outer
body 12 has a collar 54 extending behind finger grips 56 having
opening 58 which closely receives the outer periphery 60 of cap 48
when the plunger is depressed to the retracted position. An
alternate arrangement is shown in FIGS. 4A and 4B in which barrel
14 is extended longitudinally, if necessary, so that end cap 48
fits closely within an opening at the back of the barrel where the
finger grips are. FIG. 4B shows the tamperproof position with the
plunger in the retracted position. It should be noted that
depending on the relationship of the inside diameter of the barrel
and the diameter of the end cap, the end cap could instead be
received right inside the opening at the back of the barrel.
Regardless of how the end cap in back of the outer body and barrel
are configured, the plunger can no longer be grasped after
retraction has occurred because end cap 48 is depressed into an
opening.
[0045] The wall of outer body 12 and head 30 of the needle holder
have mating cooperating smooth surfaces which hold needle holder 22
in the position shown in FIG. 1 with spring 24 compressed. Nose 16
has a reduced diameter relative to the barrel. The outer body has a
most constricted part where head 30 of needle holder 22 is engaged
and held. The outer body has an inwardly facing surface 62 at the
most constricted part of the transition zone where nose 16 begins.
Similarly, head 30 has an outwardly facing surface 64 configured to
cooperate with inwardly facing surface 62 to produce a holding
force on needle holder 22 when the retraction mechanism is
installed in the nose from the rear. Mating surfaces 62, 64
constitute a sliding interface oriented in the direction of
retraction, which seals nose 16. Mating surfaces 62, 64 are
preferably friction surfaces which have an interference sliding fit
to apply a frictional holding force which holds needle holder 22 in
position by friction between the mating parts. It is within
contemplation of the invention that one or more of the cooperating
interface surfaces could employ a coating or adhesive bond which is
ruptured or released when the mating surfaces or lands are
separated or moved relative to each other.
[0046] Head 30 provides a lower boundary for a variable fluid
chamber 68 below head 34. Needle holder 22 has a fluid path 70 in
fluid communication with fluid chamber 68 and needle 28. Needle
holder 22 has a smaller diameter inner head 72 which is part of
head 30. Retainer member 66 is coupled to inner head 72 along
sliding interface 74 oriented in the direction of retraction.
Retainer member 66 is coupled to inner head 72 with a holding force
which exceeds a retraction force applied to the underside of inner
head 72 by means of the end of compressed spring 24. A reduced
diameter portion 27 of needle holder 22 protrudes through an
opening in front 76 of nose 16.
[0047] Importantly, retainer member 66 can be visualized as an
annular ring surrounding circular inner head 72. The location of
retainer member 66 at the most constricted part of the transition
zone where the nose begins and the relatively small area exposed to
pressurized fluid in chamber 68 results in a high blowout pressure.
Since the front portion 26 of the needle holder is grounded or
bottomed inside front 76 of nose 16, no amount of pressure will
allow needle holder 22 or needle 28 to move forward. Blowout
pressure may be defined as the pressure in chamber 68 acting on the
exposed area of retainer member 66 to produce a force sufficient to
overcome the holding force such that retainer 66 could "blowout" by
moving forward and prematurely release needle holder 22.
[0048] Some users have strong hands and might, at the outer limit
in an emergency, be able to generate a force of as much as fifteen
to eighteen pounds on the plunger during an injection. It is
considered almost impossible for anyone to exert a force of more
than eighteen pounds. This may be regarded as the maximum expected
force which must be taken into account so that ring member 66 will
not blowout while an injection is being made. The greatest cross
sectional area of variable chamber 68 and the area of retainer
member 66 exposed to fluid pressure are selected so that the
blowout pressure is higher than the maximum pressure in chamber 68
expected to result from the maximum expected thumb force applied to
cap 48 during an injection. This ratio is preferably about two to
one and more preferably about three to one or more so that the
holding force holding the retraction mechanism in place can be kept
at a comfortably low level while the blowout pressure remains
high.
[0049] Dislodgeable stopper 42 has a similar blowout problem to
recognize. The front and middle portion of stopper 42 are relieved
slightly from opening 41 such that the fluid pressure in chamber 68
is directed against the cross sectional area at cooperating lands
44, 46 and could cause stopper 42 to blowout. A frictional holding
force is generated at the lands 44, 46 which may be called a
dislodging force which must be overcome to slide stopper 42
rearwardly before retraction. The ratio of the maximum cross
sectional area across the interior of variable chamber 68 to the
maximum cross sectional area of stopper 42 exposed to pressure in
chamber 68 are selected so that the maximum expected thumb force on
plunger 32 during an injection will produce a maximum force
slightly less than the amount of dislodging force necessary to
dislodge the stopper so that stopper 42 will not blowout during an
injection. This ratio is preferably not less than about two to one,
more preferably three to one or more, whereby a force of about
eighteen pounds on the plunger, for example, would produce a
pressure generated force of only about nine or six pounds,
respectively, on the stopper, so that the stopper can be easily
dislodged in advance of retraction at the end of the injection
cycle but will not blowout during an injection. The stopper is
dislodged after the injection by thumb force applied to the stopper
by movement of the plunger.
[0050] The components used for retraction are arranged to avoid
cumulation of force during the retraction sequence. In FIG. 1,
stopper 42 has a forward extension beyond tip 40 which allows full
thumb pressure to be applied to the stopper before any other
portion of the retraction mechanism is engaged. The amount of
forward extension beyond tip 40 is related to the length of lands
44, 46 such that the forward extension of stopper 42 preferably
represents about 80 percent of the engaged land length. When
stopper 42 is moved back until the front is even with tip 40, as
seen in FIG. 2, only about 20 percent of engaged land remains. In
FIG. 2 it can be seen that thumb force on plunger cap 48 has been
applied to partially dislodge stopper 42 such that a gap 78 is
created and the remaining engaged land area is represented as area
80.
[0051] Since I believe the amount of frictional holding force or
dislodging force is roughly proportional to the amount of the
length of the sliding interface between cooperating lands 44, 46,
it follows, ignoring dynamic effects, that the amount of force
remaining decreases as the engaged sliding interface area is
reduced. This is what happens as stopper 42 moves back into cavity
38 from the position of FIG. 1 to the position of FIG. 2. It is
believed appropriate to set the initial dislodging force to allow
about five pounds at the position of FIG. 1 which is reduced to
about one pound remaining when the stopper or plug member 42
reaches the position of FIG. 2. It might be noted at this point in
the description that the front portion of tip 40 preferably has
some longitudinally extending slits or openings so that fluid is
not trapped in the trapezoidal shaped area of chamber 68, seen in
FIG. 2, because of contact between tip 40 and the upper surface of
retainer ring 66.
[0052] Needle holder 22 and spring 24 are combinably installable
from the rear of the barrel before the plunger is assembled and
releasably held at the most constricted part of the transition zone
where the nose begins by sliding engagement of the cooperating
inwardly and outwardly facing friction surfaces 62, 64 while
compressing spring 24. The length of the engaging land 64 and the
amount of interference fit is preferably designed to provide a
frictional holding force in opposition to the retraction force
provided by the compressed spring 24 of somewhere around five
pounds even though the spring may apply a retraction force in the
retraction direction of somewhere around a half pound. In use the
needle is pushed against a rubber seal in a vial so the needle
holder must resist a resulting backward force without being
dislodged during the filling operation. This requirement and
blowout pressure limits the low end of the holding force on the
needle holder.
[0053] Referring again to FIG. 2, it can be seen that further
depression of the plunger beyond the second position of FIG. 2
dislodges retainer ring member 66 along the sliding interface 74
provided by the outer surface of inner head 72 and along the
inwardly facing friction surface 62. As the amount of remaining
engaged interface is reduced, the amount of force required to
continue moving retainer member 66 off needle holder 22 is reduced
and the small remaining engagement area 80 between lands 44, 46 of
the plunger and stopper preferably cause stopper 42 to be dislodged
before needle holder 22 is released. When the remaining residual
friction force during continued depression of the plunger becomes
less than the retraction force provided by compressed spring 24,
the retraction position of FIG. 3 is reached whereby retraction
occurs.
[0054] When retraction occurs needle holder 22 moves through
opening 41 into cavity 38. The uncompressed length of spring 24 is
selected to provide backward movement sufficient to withdraw an
injection needle 28 fixed in front portion 26 entirely within outer
body 12, carrying dislodged stopper 42 with it. At the same time,
cap 48 enters opening 58 of the barrel with peripheral edge 60
closely confined, in order to prevent tampering after retraction.
It is immaterial whether cap 48 moves into the opening at the
instant of retraction or after retraction has already occurred
because the movement is automatic due to the continued thumb force
applied to trigger the retraction. Sufficient unengaged length of
inwardly facing friction surface 62 is provided so that retainer
member 66 can move downwardly a sufficient distance to reach the
retraction position of FIG. 3. After retraction, retainer member 66
preferably remains stuck and prevents any possibility of any one
being able to reengage it with the head of needle holder 22. The
diameter of land 62 in the area designated 63 can be increased
slightly to provide relief for retainer ring 66 as it is pushed
down by tip 40.
[0055] It is also within the contemplation of the invention that
separable retainer member 66 may be removably coupled to inner head
72 of needle holder 22 by means of a relatively small in area
"tack" weld which is sufficient to resist the retraction force
applied to needle holder by spring 24 but which can be ruptured or
separated by depression of the plunger beyond the position shown in
FIG. 2, to release the needle holder and allow retraction. This is
schematically illustrated in FIG. 8 with respect to alternate head
30a with the parts of syringe body 12 and needle holder 22 cutaway
to focus on the modification. The remainder of the syringe
structure would be like FIGS. 1-3.
[0056] In FIG. 8, inner head 72a has an outwardly facing surface
74a and a very small raised portion or series of horizontally
spaced apart raised portions 73 around the periphery in a
continuous band or annular ring which extend relatively uniformly
outwardly beyond peripheral surface 74a of head 72a. The raised
portion could be on the inner surface 75 of retainer 66a instead of
being on surface 74a of the needle holder. The head of the needle
holder is preferably circular but could be conceivably another
shape with the retainer member 66a correspondingly configured to
conform to it.
[0057] The inwardly facing surface 75 of inner head 72a is in
contact with raised portion 73 on the outer surface of inner head
72a and there may be a small gap 77 between them all around. The
raised portion 73 couples retainer 66a to inner head 72a and may be
referred to as a bridging portion which resists the blowout
pressure referred to above and holds the needle holder in place
against the retraction force imposed on the needle holder by spring
24 together with any small additional forces that may be applied
when the needle is pushed against the rubber seal of a vial in
preparation for use. The bridging portion may be formed by "tack"
welding the raised portion 73 to the inner surface of the ring 66a
or by providing any other form of frangible bridging portion that
holds the separable ring member 66 and needle holder head 72a
together. It is required that however done, the bridging portion
must also serve as a seal between the facing surfaces of the ring
member and inner head so that fluid under pressure cannot pass from
chamber 68 through gap 77 to reach the nose portion of the device.
All fluid must pass through fluid passage 70.
[0058] It can be seen that when the position of FIG. 2 is reached
the front tip 40 of the plunger presses against retainer ring 66a
after stopper 42 is almost dislodged and uncouples the retainer
ring 66a from the inner head 72a of needle holder 22a. Any tack
weld connecting the separable parts at the bridging portion is
ruptured, fractured or otherwise separated so as to separate
retainer ring 66 a from inner head 72a thus releasing needle holder
22a from further restraint. They and the force applied by spring 24
causes retraction to occur much as before described and shown in
FIG. 3.
[0059] It is believed that the increased diameter of the raised
portion 73 should be within the range of about 1 to 8 thousandths
of an inch which may be dictated by the ability of the molding
equipment available to produce a consistent bridging portion
without defects. It is believed that it may be desirable to employ
different polymeric materials for the retainer ring and needle
holder to facilitate tack welding, such as a suitable polyvinyl
chloride (PVC) for the retainer ring and a suitable polycarbonate
plastic material for the needle holder. One way to couple these two
parts may be to assemble them and expose them to a temperature of
about 120.degree. C. for twenty minutes or so to allow some
diffusion or incipient melting to occur where they touch. The
raised portion creates a high unit pressure where it comes into
contact with the inwardly facing surface of retainer 66a. Sonic
welding could also be employed. A coating or adhesive which couples
the retainer ring to the needle holder and can be uncoupled by
means of force applied to the retainer ring by the plunger is also
within the contemplation of the invention.
[0060] An alternate syringe 82 is disclosed in FIGS. 5-7. In FIG.
5, Syringe 82 has a one piece hollow outer syringe body 84. Body 84
has a longitudinally extending wall comprising an elongated barrel
86 and a nose 88 with a transition zone 90 connecting the barrel
and nose. A front mounted retraction mechanism lodged in nose 88 is
generally referred to by the reference numeral 92. It comprises the
combination of an elongated needle holder 94 and spring 96. The
needle holder has an elongated stem body with a needle holding
portion 100 in front for holding needle 28 and a head 102 in back.
In this case, head 102 is a one part head integral with the rest of
needle holder 94. Spring 96 delivers a retraction force in a
retraction direction to the underside of head 102.
[0061] A plunger generally designated by reference numeral 104 is
disposed for use partially within barrel 86. Plunger 104 has a head
portion 106 which moves in slidable sealed contact with the
interior of barrel 86 of outer body 84. Although a separate seal
might be used on head 106, this embodiment is suitable for a
smaller diameter, such as a 1 cc syringe, and can be used with head
106 also serving as the seal. A retraction cavity 108 is provided
in the interior of hollow plunger 104. Head 106 has a tip portion
110 forming an opening 112 for a dislodgable stopper 114 having a
front portion extending beyond tip 110. Head portion 106 has an
inwardly facing land 116 and the back of stopper 114 has an
outwardly facing land 118 comprising cooperating friction surfaces
which seal opening 112. The back portion of outer body 84 may have
finger grips 120 and the same collar 54 and end cap 48 previously
disclosed. The alternate arrangement of FIGS. 4A and 4B may also be
employed.
[0062] The outer portion of tip 110 may be equipped with an angled
surface 122 designed to cooperate with a small ramp surface 124
located in the vicinity of transition zone 90. The wall of outer
body 84 and head 102 of the needle holder have mating cooperating
friction surfaces which frictionally hold needle holder 102 in the
position shown in FIG. 5 with spring 96 compressed. Nose 88 has a
reduced diameter relative to barrel 86. The outer body has a most
constricted part where the head 102 of needle holder 94 is
frictionally engaged. The outer body has an inwardly facing surface
or land 126 at the most constricted part of the transition zone
where nose 88 begins. Similarly, head 102 has an outwardly facing
friction surface 128 configured to cooperate with inwardly facing
surface 126 to produce a frictional holding force on needle holder
94 when the retraction mechanism is installed in the nose from the
rear.
[0063] Mating surfaces 126, 128 constitute a sliding interface
oriented in the direction of retraction, which seal nose 88. Mating
surfaces 126, 128 are preferably smooth friction surfaces which
have an interference sliding fit when needle holder 94 is installed
from the rear whereby a frictional holding force holds needle
holder 94 in position by friction between land 126 and head 102 of
needle holder 94. It is within contemplation of the invention that
one or both of these surfaces could have a coating or adhesive bond
which is ruptured when the mating surfaces are separated to release
the needle holder.
[0064] Head 106 provides the upper boundary for a variable fluid
chamber 130 below head 106. Needle holder 94 has a fluid path 132
in fluid communication with chamber 130 and needle 28. Needle
holder 94 is releasably coupled at surfaces or lands 126, 128 with
a holding force that exceed the retraction force applied to the
underside of head 102 by the end of compressed spring 96. A reduced
diameter portion 134 of needle holder 94 protrudes through an
opening in front 136 of nose 88. Blowout pressure is not a factor
with respect to the needle holder on the alternate embodiment. No
amount of pressure will allow needle holder 94 or needle 28 to move
forward since the front portion 100 of the needle holder is
grounded or bottomed inside front 136 of nose 88.
[0065] Blowout pressure is still a factor to be considered in
connection with stopper 114. Blowout pressure would be the pressure
in chamber 130 produced by thumb force on cap 48 acting on the
cross sectional area of stopper 114 which could overcome the
holding force, causing stopper 114 to dislodge from opening 112
prematurely. The ratio of the maximum cross sectional area across
the interior of variable chamber 130 to the maximum cross sectional
area of stopper 142 exposed to pressure in chamber 130, and the
dislodging force necessary to dislodge stopper 144, are selected so
that the maximum expected thumb force on plunger 104 during an
injection will not cause the stopper to blowout. Yet the stopper
will still be dislodged by the dislodging force on the plunger once
the front of stopper 114 contacts the retraction mechanism after
the injection has ended. The ratio referred to is preferably not
less than about two to one, or more preferably about three to one
or more, whereby a force of about eighteen pounds on the plunger,
for example, would produce a pressure generated force of only about
nine or six pounds respectively, on the stopper, so that the
stopper can be easily dislodged in advance of retraction at the end
of the injection cycle but will not blowout during an injection.
The smaller diameter stopper allows two or three times the thumb
force to be used during the injection cycle than required to
actually dislodge the stopper by direct application of force.
[0066] By reference to FIGS. 5-7, the operation and further
features of the alternate embodiment are discussed. The syringe is
used in the normal manner until the plunger is depressed to the
first position of FIG. 5 which is the end of the injection cycle.
Stopper 114 has a forwardly extending end which has come into
contact with head 102 of needle holder 94 to block fluid path 132.
Further depression of plunger 104 toward the position of FIG. 6
mostly or fully dislodges stopper 114 and begins spreading barrel
84 at the transition zone by sliding contact between head portion
106 and ramp 124. Ramp 124 is a very small inwardly extending
annular thickening of the wall of barrel 86 which can take many
shapes or forms. For example, ramp 124 may be a small step 125 in
the wall which continues vertically downward as indicated by the
dotted line, which is somewhat exaggerated in FIG. 5.
[0067] The barrel is flexible and is spread outwardly a slight
amount to the position of FIG. 6 just prior to retraction. Here the
mating surfaces 126, 128 are separated an amount which reduces the
clamping force on the needle holder 94. The spreading shown in FIG.
6 is greatly exaggerated for illustration. It is estimated that an
expansion of only about four thousandths of an inch is sufficient
to release needle holder 94 from nose 88. By slight further
depression of the plunger from the position of FIG. 6 to the
retracted position of FIG. 7, retraction occurs when the retraction
force applied by spring 96 exceeds the remaining holding force on
needle holder 94. Needle holder 94 then moves through opening 112
into cavity 108 along with a portion of spring 96. The uncompressed
length of spring 96 is designed to provide sufficient backward
movement to withdraw an injection needle 28 fixed in front portion
94 and carry dislodged stopper 114 with it. At the same time, cap
42 enters opening 138 at the rear of a barrel extension 54 where
the peripheral edge is closely confined in order to prevent
tampering after retraction.
[0068] The location and configuration of ramp 124 is arranged to
avoid cumulation of force required during the retraction sequence.
Most of stopper 114 should be dislodged by thumb pressure on
plunger 104 before significant resistance develops as angled
surfaces 122 begin pushing outwardly on ramp 124. The selection of
the location of ramp 24 and the angle of the engaging surfaces make
it possible to have a fairly smooth continuous force since the
dislodging force continuously decreases as the sliding interface
area 116, 118 between the plunger and the stopper is linearly
decreased. Because ramp 124 is relatively very small, it is still
possible to remove a stepped molding core from the rear of the
outer body 84. Alternately, ramp 124 can be the smaller diameter
step 125 which avoids reentrant angles whereby resistance to
removal of the molding core could occur. After retraction, the back
of the plunger is unaccessible and there is no way to reach to
stopper or the needle holder in order to reinstall them for
re-use.
[0069] When used normally, syringe 10 may have a small amount of
fluid remaining in the variable chamber in the second position
shown in FIG. 2 which is, of course, greatly exaggerated in scale.
This may amount to no more than a drop or a few drops of fluid in
the remaining space above the retraction mechanism. When syringe 10
is fired by pushing down on end cap 48, to the position of FIG. 3,
the expanding spring and rearwardly moving needle holder carry any
remaining fluid up into retraction cavity 38. Surface tension
effects hold the tiny droplets in place along the walls of the
plunger and no fluid escapes from nose 16. The syringe is normally
used to withdraw fluid from a vial. The fluid is injected into a
patient followed by immediate retraction of the needle holder and
needle in one step. No leakage of fluid from the nose is observed
when the syringe is used to inject fluid into a patient.
[0070] It has been discovered, however, that if the needle is
forcibly prevented from retracting after syringe 10 is "fired" by
pushing down until plunger 48 enters opening 58, the small amount
of retained fluid from variable chamber 68 can flow into the nose
in the space between the needle holder and nose. If the seal around
the head of the needle holder is removed while the needle holder is
being restrained from retracting, remaining fluid has time to move
down into the nose, but it does not leak out from the opening in
the front of the nose. Then if the needle holder is suddenly
released and allowed to retract normally, it has been found that
leakage of fluid from the opening in the front of the nose could be
observed. This undesirable scenario was found to occur under the
following circumstances. If the syringe is used to draw blood from
the patient, the blood filled syringe is removed from the patient
and the needle passed through a rubber septum in a sterile vial.
The plunger is then depressed to discharge the patient's blood into
the vial. Users expect to depress the plunger fully after the fluid
is discharged to retract the needle. When the plunger is depressed
fully to cause retraction, the needle cannot retract normally due
to the fact it is frictionally held by the rubber septum of the
vial. When the empty syringe is then withdrawn from the vial by
pulling the needle out of the septum, it immediately retracts.
Droplets of fluid were observed on the vial as soon as retraction
took place.
[0071] Surprisingly, it was found that a small "puff" of air is the
source of this problem. If the needle or needle holder is
temporarily restrained and prevented from retracting in the normal
manner, a brief puff of forwardly directed air is generated when
the needle holder is finally allowed to retract. This puff of air
was found to emerge from the front of the syringe causing retained
fluid trapped around the needle holder to be blown out of the
opening left in the nose when the needle holder retracts. It was
discovered that if the hollow interior of the plunger is vented,
preferably in the area of thumb cap, this condition does not occur
and the fluid is entirely retained within the syringe body.
[0072] FIGS. 9 through 16 illustrate the syringe generally
designated as syringe 10 with a modification on the end cap or
thumb cap on the plunger to provide for venting of the hollow
interior of the plunger which is the retraction cavity. Insofar as
possible the original numbering of FIGS. 1-4 is retained with
primes used to indicate differences.
[0073] Head 34' of plunger 32' is preferably slightly modified from
plunger head 34 of FIG. 2 in the following respects. The elongated
plunger has a longitudinally extending generally tubular wall 140
defining a hollow interior along the length of the plunger. The
plunger has a head end 34' in front and a rear end portion 142 with
a thumb cap 48' behind. The outer side of wall 140 at head end 34'
is sealingly surrounded with a resilient plunger seal member 36'
which is like a band with a pair of separated raised rings 144.
Plunger seal 36' fits in a depression in the outer surface of wall
140 where it is securely held in position and prevented from
longitudinal movement. Seal member 36' is adapted to slide in
sealed contact with a tubular wall when the plunger is moved within
syringe barrel 14. It is within contemplation of the invention to
have a raised piston molded as part of the plastic plunger to serve
as a plunger seal in place of a separate rubber plunger seal 36',
although the rubber seal member is preferred.
[0074] Wall 140 at head end 34' of the plunger 32' has a reduced
diameter front portion extending forward from seal member 36'
terminating at tip 40 at the front of plunger 32'. Tip 40 defines
the opening 41 which leads into the hollow interior 38. The
internal structure is as shown in FIG. 1. The wall 140 behind tip
40 has a stepped inner side surface comprising a land having an
inwardly facing surface and a larger diameter portion extending
behind the land into the hollow interior. A separate dislodgeable
stopper 42 is slidingly held within the reduced diameter front
portion of plunger head 34' by a holding force in excess of the
fluid injection pressure force to be expected during use of the
plunger in syringe barrel 14. Stopper 42 has a back end portion
comprising a land 46 and a reduced diameter front end portion
extending forwardly beyond tip 40 a fixed distance to its front
146. The fixed distance is the distance between front 146 and tip
40.
[0075] As is seen in FIG. 1, the outwardly facing surface 46 of
dislodgeable stopper 42 is in sliding sealed engagement with the
inwardly facing surface of land 44 in the plunger wall. These lands
cooperate to apply a holding force to the stopper and seal hollow
interior 38 of plunger 32' from the expected amount of fluid
injection pressure force generated in the variable chamber 68
during an injection. The ratio of the effective area of variable
chamber 68 to the area of stopper 42 exposed to fluid pressure is
at least two to one and preferably three to one or more as
previously indicated. This makes it possible to utilize lower
holding forces without blowing out the stopper during an injection.
The cooperating lands on the inside of the plunger head and the
stopper have sufficient longitudinal length to allow dislodgeable
stopper 42 to move the fixed distance between its initial extension
at 146 and tip 40 in sliding response to forward movement of the
plunger after front 146 of stopper 42 contacts a stop.
[0076] As indicated in FIGS. 1-3, front 146 of the stopper 42
encounters head 72 of needle holder 22 which serves as a stop. The
fluid opening in head 72 of needle holder 22 is preferably provided
with some fine slots or grooves so that fluid can continually enter
fluid path 70 as the plunger moves from the position of FIG. 1 to
that of FIG. 2. As the position of FIG. 2 is reached, the holding
force on stopper 42 is reduced by substantial disengagement of the
cooperating lands 44, 46 in preparation for dislodgement of the
stopper, without unsealing the hollow interior/retraction chamber
38 within plunger 32'. A notch 148 is preferably provided in the
tip to prevent trapping fluid at the tip.
[0077] Thumb cap 48' at the rear end portion 142 of plunger 32'
includes one or more channels 150 which receive vented air from
hollow interior 38. Thumb cap 48' has an opening 152 for a closure
154 best seen in FIGS. 10 and 11. Channels 150 are open at the top
for ease of molding although closed channels could also be
used.
[0078] FIG. 10 shows an enlarged top plan view illustrating the use
of three channels 150 in combination with a preferred closure 154
installed in circular opening 152. FIG. 11 best shows how the
channels 150 receive vented air from hollow interior 38. Closure
154 preferably has a stepped outer surface comprising a rear step
156 which rests in opening 152, an intermediate step 158 which
rests in an enlarged portion 160 of the inner side of wall 140 and
a front step 162 which rests against inner surface 164 of wall 140.
In effect, these structures provide convenient seating for closure
154. Steps 158 and 162 are conveniently provided in a downwardly
depending skirt 166.
[0079] Importantly, inner surface 164 everywhere there is a channel
150, is provided with a longitudinally extending groove 168 in
fluid communication with the hollow interior 38 and the channels
150. Any convenient number may be chosen as the channels are easily
molded into the end cap when it is formed. The longitudinally
extending grooves 168 do not extend through the entirety of the
wall 140 although they could. They are designed for ease of molding
since they can formed in the mold that makes the plunger without
using separate pins to form an opening. This is an important cost
consideration in a multiple out high speed molding process. This
structure is designed for preventing the user's thumb from
obstructing the vent opening leading from the interior of the
plunger thereby assuring that venting will take place.
[0080] Referring now to FIGS. 9 and 12, it will be noted that
opening 58 in the back end of barrel 14 includes slots 172 in fluid
communication with the hollow interior of the plunger through one
or more channels 150 so that when thumb cap 48' is received in
opening 58, no seal is created by the thumb being in contact with
opening 58 which might otherwise prevent air from venting. The
outer periphery of thumb cap 48' is closely received in opening 58
as the syringe is fired, to prevent reuse. Thumb cap 48' is
preferably sized in relation to barrel 14 such that opening 58 is
simply an extension in a linear direction of the wall of barrel 14
rather than enlarged as shown. Finally, the interior surface 164
preferably has several annular constrictions 170 designed to catch
the head of stopper 42 during its rearward travel. Since stopper 42
is preferably installed from the rear of the plunger before closure
154 is put in place, the constrictions 170 must allow stopper 42 to
be forced through to the front.
[0081] A first alternative thumb cap and closure arrangement is
illustrated in FIGS. 13 and 14. In this embodiment, four channels
150 are provided in thumb cap 48''. Closure 174 has four flat side
portions 176 spaced around the periphery at 90.degree. intervals,
each in fluid communication with a channel 150. A gap is created at
each flat side between the flat sides 176 and the opening 152'
which are in fluid communication with interior 38 to create a flow
passage for air from interior 38 through the gap along the flat
side then into channel 150. Annular groove 178 in closure 174 may
be used to fluidly connect each of the flat areas 176 at the level
of channels 150. In addition to equalizing air flow, the annular
groove allows venting of air regardless of the angular orientation
of closure 174 with respect to thumb cap 48''.
[0082] A second alternate embodiment has the same thumb cap 48''
with a modified closure 180. Closure 180 has a head 182 which
snugly fits within opening 152' which is at the back of the
plunger. Opening 152' is only slightly larger than the interior of
the plunger to provide a seat for the closure. Four undercut
portions 186 are each in joint fluid communication with the
interior 38 and one of the channels 150 to create a flow passage
from the interior 38. Closure 180 effectively seals the opening
152' so that no fluid particles can escape from the opening. As in
the previous embodiment, an annular groove 178 bridges each
undercut portion opening into a corresponding channel 150 thereby
tying the undercut portions together in fluid communication
regardless of the angular orientation of the parts.
[0083] In operation, there are many advantages to the improved
combination disclosed herein. The diameter of the stopper in both
embodiments and the slidable retaining ring member in the first
embodiment, in relation to the diameter across the fluid chamber,
makes it possible to produce a syringe which withstands high
blowout pressure. By minimizing the effective surface area exposed
to the pressurized fluid during an injection, the syringe will
withstand injection thumb force of around fifteen to eighteen
pounds during injection and at the same time retract in response to
as little as five to six pounds of force on the plunger once the
injection fluid has been injected. Once the fluid has been
injected, cumulation of force required to concurrently operate the
retraction mechanism is avoided. First the stopper is moved back
and then the needle holder is released. By constricting the
diameter of the syringe near a transition zone where the nose
begins, a constriction enables the needle holder to be smaller
which in turn allows it to fit in a smaller opening with a smaller
stopper in the retraction cavity of the hollow plunger.
[0084] A vacuum must be pulled in order to fill the syringe. The
ring member or the needle holder, as the case may be, must seal the
front nose of the syringe body because otherwise vacuum could be
lost and fluid could enter the spring area and leak out the front.
The hollow outer body and syringe plunger are preferably made from
conventional plastic material used for syringes, which has some
flexibility. The tolerances on the diameter of mating facing
surfaces between the head of the needle holder and the barrel and
between the stopper and head of the plunger are not critical in
order to maintain a consistent holding and dislodging force. This
is believed to be because increasing interference fit increases the
frictional holding force only up to a point and then the
surrounding wall simply expands a small amount or the internal
parts are compressed a small amount without a corresponding
increase in the longitudinal force required to move the retainer
member or plug member in the retraction direction. It is a
desirable self correcting mechanism which is a cost and quality
benefit in making the parts. It is believed that a plastic retainer
member could be used and the same self limiting frictional holding
force would be obtained.
[0085] In the best mode the stopper and the ring member are
preferably made from a thermoplastic rubber material designated
number 181-55 available from Advanced Elastomer Systems, 540
Maryville Centra Drive, St. Louis, Mo. and sold under the trade
name Santopreneg. It is said to have a characteristic hardness
around 55 on the Shore A durometer scale which allows for the right
amount of resistance to compression, fluid resistance such that the
material does not swell when in contact with most fluids,
environmental stability allowing the friction and sealing
properties to remain non-temperature sensitive, good property
retention after aging and excellent property retention after
sterilization by all accepted methods. The plunger seal around the
head of the plunger is conventional.
[0086] The parts are few in number and easily mass produced. The
alternate embodiment has the fewest number of separate parts of any
tamperproof retractable syringe. The plunger has a one piece hollow
outer body with a transition zone and a narrow nose portion. The
internal diameter is stepped to greater diameters from front to
back for molding around a non-collapsible core which can be
extracted from the rear. The same is true for the plunger.
[0087] Assembly is greatly simplified and can be accomplished with
high speed mechanized equipment. The needle holder and spring are
installable from the rear of the barrel without the needle. In the
first embodiment the retainer member is forced fit over the inner
head of the needle holder and the assembly together with the
uncompressed spring are pushed forward and held by sliding
engagement of the cooperating inwardly and outwardly facing
surfaces while compressing the spring. The front of the needle
holder passes through an opening in the nose which makes it easy to
install the needle from the front by conventional means. The
alternate embodiment is installed the same way except that there is
no separable retainer member around the head of the needle
holder.
[0088] The narrow nose provides a particular advantage for
mechanized assembly. The nose has a wall defining an elongated
internal cavity which closely confines the spring and needle holder
combination. During installation this cavity serves as a guide to
steer the needle holder and uncompressed spring into a compressed
state of the spring. This solves an important assembly problem. If
there is much lateral space in the nose around the spring, when the
uncompressed spring is being compressed, it is a laterally unstable
column which flexes sideways and bunches up causing a jam up. It
might be added that rounded edges on the bottom of the slot
directly below retainer 66 would further facilitate entry of the
end of the spring.
[0089] The stopper is also installable from the rear of the plunger
by pushing it forward until the cooperating lands are slidingly
engaged. Then plug member 50 is force fit or otherwise fixed in the
opening at the back of the plunger and the plunger is installed in
the outer body. It is not necessary to try to pass the sharp needle
through an elongated body with constricted openings where slight
misalignment could cause hangups. The head of the needle holder
simultaneously acts as a seal as well as a holding device such that
no seal is required at the tip of the nose and no ultrasonic
welding of separate parts is required.
[0090] There is no necessity for using internal locking teeth of
any kind. No locking teeth are needed to hold the retraction
mechanism or to lock the plunger after retraction. Locking teeth
present difficult molding and quality control problems, tend to be
temperature sensitive and tend to require a larger diameter barrel
which increases premature blowout problems. In addition to the
non-reusability provided by separation of the retainer ring from
the head of the needle holder and dislodgement of the stopper, the
plunger is not accessible after retraction because it is depressed
within an opening at the back of the outer body. This additional
tamperproof feature is provided in a one piece body without the
necessity for hooking anything or twisting anything. The easily
made and installed force fit plug at the back of the retraction
cavity prevents access to the retracted components. The Federal
government has rights in the invention under 35 U.S.C. .sctn.203.
The Federal government has a nonexclusive, nontransferable
irrevocable, paid up license to the invention as set forth in the
priority documents.
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