Note: Descriptions are shown in the official language in which they were submitted.
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AUTO-DESTRUCT DISPOSABLE SYRINGE
Field of the Invention
The invention relates to disposable syringes and especially syringes of the auto-destruct
type which are rendered non-reusable during or after a first use.
5 Background of the Invention
Co~ llunicable diseases are transmitted in different ways, for example, by contact with
body fluids of an infected person. Infection with a communicable disease is undesired
and is especially unfortunate when due to inadvertance or ignorance such as whencaused by the sharing or reuse of hypodermic syringes. The practise of sharing and/or
10 reusing hypodermic syringes is especially prevelant among drug users and in third
world counkies where syringes are used in vaccination campaigns. Often several
children are inoculated with the same syringe either by using large capacity syringes
for multiple small injections, or by refilling and reusing the syringes after insufficient
sterilization. As a result potentially disasterous, body fluid transmitted diseases,
15 especially AIDS and Hepatitis have spread at an ~l~rming rate among drug users and in
third world countries, and there particularly among children. Although not all new
cases are attributable to syringe reuse or sharing, it is estimated by the World Health
Org~ni7~tion that the total number of new cases could be significantly reduced if
transmition through cont~min~te~l syringes were prevented. In an effort to frustrate the
20 reuse of hypodermic syringes, disposable syringes have been developed which are
intended to operate only for one single injection.
Various single-use syringe constructions are known in the art, which can be grouped
into three basic categories; the piston or plunger lock type, wherein retraction of the
25 piston is prevented either always or after completion of the injection; the plunger
sepaldlillg type, wherein the plunger separates from the piston or the piston seal when
the plunger is retracted; and the cutting type wherein the barrel wall is cut during
injection. It is a major disadvantage that in the first two types of single-use syringes
the barrel which is the most important part of any functioning syringe remains intact
30 and may be l~lllp~ed with and reused. Thus, single-use syringes wherein the barrel is
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rendered unusable, for example through cutting of the barrel wall, are preferable.
However, the cutting type syringes also have certain disadvantages.
Chiquar-Arias in U.S. Patent No. 3,667,657 disclose prefilled syringes which include a
5 small stationary knife that is laterally fixed to the syringe plunger and engages an
opening in the wall of the syringe barrel. When the plunger is forced down into the
barrel, as during injection, the barrel wall is cut. This destroys the barrel behind the
piston seal and makes reuse of the syringe impossible. However, it is a disadvantage
of prefilled syringes that they can only be used in those cirumstances where injection
10 of the respectively included liquid is desired. In other words, numerous syringes filled
with different inoculants are required which increases m~mlf:~cturing and storage costs.
In U.S. Patent No. 3,951,146 Chiquar-Arias describe syringes wherein the plunger15 includes a housing or recess for a small knife which is forced radially outwardly by a
spring. The knife has a rounded rear edge and a forward cutting edge. The plunger
can be moved backward for fillig of the syringe without cutting or cl~m~gin~; the barrel
wall. For insertion of the plunger, a protection strip is inserted between the knife and
the barrel wall, which strip is then removed. Use of the protection strip is
20 disadvantageous, since it adds an additional m~mlf~cturing step and, thus, increases
production cost. Furthermore, the spring loaded knife stays in contact with the barrel
wall at all times, which, despite the rounded rear edge of the knife, could damage the
barrel wall during aspiration of the inocculant and lead to leakage around the plunger
or through the barrel wall.
An auto-destruct disposable syringe with retractable knives is disclosed in C~n~ n
Patent Application SN. 2,045,499 by Fenet. The syringe includes a barrel, a piston,
and a plunger for moving the piston axially in the plunger. The knives are mounted on
flexible arms which are connected with the plunger and are retracted during the
30 aspiration stroke of the syringe. When the aspirated liquid is expelled from the barrel
during injection, the plunger is pushed against the piston which moves the free end of
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the arms along a ramp on the piston. This forces the knives against the barrel wall.
The plunger and, thus, the knives are oriented to be opposite preselected areas of
reduced thickness in the barrel wall. The reduced wall thickness permits penetration of
the knives and cutting of the barrel wall, thereby destroying the barrel behind the
S piston as it is forced into the barrel during injection. As a result, the syringe cannot be
reused, since the barrel will no longer hold a vacuum and any liquid contained therein
will leak through the cut areas of the barrel wall.
It is a disadvantage of this syringe construction that the auto-destruct mechanism
10 thereof can be rendered useless by rotating the plunger in the barrel until the knives
can no longer engage the weakened areas in the barrel wall during injection.
Furthermore, if the barrel wall in the weakened areas is too thin, barrel integrity may
be coll~lolllised resulting in a bursting of the barrel during injection. On the other
hand, if the wall thickness in the weakened areas is too large, the cumulative force
15 required for moving the piston down the barrel and simultaneously cutting the barrel
wall during injection may become excessively large. This may render the syringe
impractical. It also may result in rejection of the syringe under national and/or
international regulations which, for example, require that a maximum axial forcerequired for pushing the piston down the barrel during injection not be exceeded.
20 Moreover, since auto-destruct syringes must be discarded after a single use, they
should be made available at the lowest possible price to reduce the financial strain on
the patient, the health care system and international health org~ni7~tions. This requires
that the syringe be manufactured from relatively economical materials such as plastics.
However, during tests with knives m~mlf~ctured from plastics material, the inventors
25 of the present application have found that knives made from inexpensive plastics tend
to quickly become blunt. This may lead to failure of the knives part way during the
injection stroke leaving the front portion of the barrel intakt and allowing partial reuse
of the syringe. Thus, an economical auto-destruct syringe is desired which reliably
prevents even partial reuse.
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Summary Of The Invention
These disadvantages are now overcome with an auto-destruct syringe in accordancewith the invention wherein the integrity of the syringe is reliably destroyed not during
the injection stroke but only when refilling of the syringe is attempted, i.e. during a
5 second aspiration stroke. Preferably, this is achieved by cutting of the syringe barrel
starting at the front end or by braking the seal between the barrel wall and the piston,
for example by penTI~nently deforming the barrel wall. Thus, the axial forces required
for permanently deforming the syringe barrel, for example by cutting, are no longer
superimposed onto the basic force required for pushing the piston down the barrel
10 during injection. In other words, the self-destruction operation of the syringe can no
longer interfere with the injection stroke. Furthermore, should the elements used for
deformation of the barrel wall fail after part of the second aspiration stroke, destruction
of the syringe is nevertheless reliably achieved, since deformation of the barrel wall
commences at the front end of the barrel.
In a preferred embodiment, the thickness of the syringe barrel wall is significantly
reduced compared to conventional auto-destruct syringes and along the whole
circumference of the barrel. The wall thickness is selected to permit permanent
deformation of the barrel wall with cutting or burrowing elements mounted to the20 syringe plunger or piston thereby breaking the seal between the barrel wall and the
piston. Since the barrel wall is evenly thin about the whole circumference of the
barrel, deformation or the barrel wall is possible in any rotational orientation of the
plunger or piston.
25 In another preferred embodiment, permanent deformation of the barrel wall is achieved
with blunt burrowing elements mounted to the piston which are forced radially outward
against the barrel wall during the second aspiration stroke and generate a permanent
groove in the inner surface of the barrel wall which cannot be sealed by the piston or a
piston seal mounted thereon so that air can pass around the piston. Thus, the seal
30 between the piston and the barrel wall is broken during the second aspiration stroke
~ 2168201
and ahead of the rearward moving piston, so that the syringe will no longer hold a
vacuum and cannot be refilled.
Accordingly, the invention provides an auto-destruct syringe comprising
a syringe barrel for holding a fluid having an open rear end and a
closed front end and a passage extending through the closed front end to permit
expulsion of fluid from the interior of the barrel;
a piston reciprocatable in the barrel and sealingly en~ging the barrel
wall; a plunger having a forward portion normally positioned in the barrel
and a realvv~d portion to be manipulated by a user of the syringe;
coupling means for connecting the piston with the plunger to permit
axial movement of the piston in the barrel by operation of the plunger,
deforming means for permanently deforming the barrel wall to brake
the seal between the piston and the barrel wall, the deforming means being mounted to
lS one of the piston and the plunger and movable from an at rest position wherein the
barrel wall is not deformed by the deforming means, to a barrel wall eng~gin~ position
wherein the barrel wall is permanently deformed by the deforming means; and
eng~gin~ means for forcing the deforming means into the barrel wall
eng~ging position upon re~v~rd movement of the piston after a full or partial injection
stroke, the eng~gin~ means being mounted to the other of the piston and plunger.
The term permanently deforming the barrel wall in the context of this application is
intçn(le~l to include puncturing or cutting of the barrel wall, burrowing into the side
wall to produce a permanent groove, and other actions which will break the seal
between the piston and the barrel wall and allow leakage around the piston, thereby
preventing the generation of pressure or vacuum in the barrel.
Brief Description Of The Drawings
Plefelled embodiments of the invention will now be further described by way of
example only and with reference to the attached drawings, wherein
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Fig. 1 is an axial cross-section of a preferred embodiment of the auto-
destruct syringe in accordance with the invention;
Fig. 2 is an enlarged side view of the plunger of the embodiment shown
in Fig. 1;
S Fig. 2a is a cross-section through the plunger shown in Fig.2 taken
along line 2a-2a;
Fig. 3 is an axial cross-section taken along the plane of Figs. 1 and 2
through the piston/plunger combination of the preferred embodiment shown in
Fig. 1 during the first aspiration stroke;
Fig. 4 is an axial cross-section through the piston/plunger combination
shown in Fig. 3 but taken along a plane orthogonal to the plane of Fig. 3 and
illustrating the combination during the injection stroke;
Fig. 5 illustrates the piston/plunger combination shown in Fig. 4 but
during the second aspiration stroke;
Fig. 6 is an axial cross-section through the piston/stopper combination
of the embodiment shown in Fig. 1;
Fig. 7 is a rear end view of the piston seal of the embodiment shown in
Fig.1;
Fig. 8 is a cross-section through the piston/stopper combination 50
taken along a plane rotated 45 from the one of Fig. 6; and
Fig. 9 illustrates the piston/plunger combination shown in Fig. 5 but
with deforming elements which have blunt edges and burrow into the barrel wall
instead of cutting it.
Detailed Description Of The Preferred Embodiments
The preferred embodiment of an auto-destruct disposable syringe in accordance with
the invention is packaged in the empty condition and allows aspiration of an injectable
liquid prior to injection. The syringe includes a mechanism which breaks the seal
between the piston of the syringe and the syringe barrel when reuse is attempted after
full or partial injection.
~ 2168201
In general, a syringe in accordance with the invention as shown in Fig. 1 of thedrawings consists of a syringe body 10 including a barrel 12, a piston assembly 50
including a piston 60 and an auto-destruct mechanism for permanent deformation of
the barrel wall 13, a plunger 80 and a coupling mechanism connecting the plunger 80
5 with the piston 50 thereby allowing the user of the syringe to reciprocate the piston by
way of the plunger.
The syringe body 10 consists of the cylindrical barrel 12 which has an open rear end
14 and a closed front end 20. A collar 16 is provided at the rear end 14 which
10 includes a pair of diametrically opposite wings 18 that provide finger rests during
aspiration and injection. The front end 20 of the barrel is provided with an integral
needle mount 22 for ~tt~hment of a hypodermic needle 30. The front end 20 further
has a fluid passage 23 for the expulsion of fluid from the barrel interior and into the
needle 30. Although the needle 30 can be removably attached to the mount 22 for
15 separate disposal, it is preferably permanently affixed to the needle mount 22 to
prevent the reuse of possibly cont~min~ted needles with new syringes.
The piston assembly 50 includes a subst~nti~lly cup-shaped piston seal or stopper 52
which is made of elastomeric seal material such as butyl rubber used in conventional
20 syringe piston seals. Although use of a piston seal in the form of a separate stopper is
preferred, it is known in the art that a s~ti~f~ctory seal between the piston and the
barrel wall can be achieved without separate stoppers, i.e. by seals integrated into the
piston or by tight engagement between the piston and the barrel wall. The stopper 52
is connected with piston 60 by way of an interference fit (see Figs. 6-8). The
25 cylindrical sidewall 51 of the stopper 52 has an outer diameter which is slightly larger
than the inner diameter D of the barrel 12 to ensure a liquid tight sliding engagement
therebetween. A circumferential groove 53 is provided in the outer surface of the
stopper sidewall 51 to improve the sealing characteristics of the stopper. In the
alternative, the stopper can have a diameter which is marginally smaller than the barrel
30 diameter D and include one or more circumferential sealing ribs giving the stopper an
overall diameter larger than D thereby ensuring a reliable seal. At the piston en~~ging
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end, the stopper sidewall 51 is provided with four circumferentially equally spaced,
radially inwardly projecting flaps 55 which are integral with the sidewall 51 and
extend between the drag/carrier arms of the piston that will be described in more detail
in the following.
The piston 60 (see Figs. 3-5) has a cylindrical base 61 which snugly fits into the
stopper 52 and two pairs of arms extending from the base in rearward direction. A
pair of diametrically opposed axially extending drag arms 62 form a coupling
mech~ni~m for connecting the piston 60 with the plunger 80. To this end, each drag
10 arm has a hook-shaped rear end 63 for engagement with an enlarged, mushroom
shaped head 81 on the forward end 83 of the plunger 80. This provides a couplingmech~ni.cm which allows the piston 60 to be moved rearward in the barrel 12 by
pulling back the plunger 80 during the initial aspiration stroke.
The plunger 80 (see Figs. 2 and 2a) has a shaft 82 of subst~nti~lly square cross-section
and guide plates 83 integral with the shaft 82 to center the shaft in the barrel. A
thumb plate 84 is integrally molded onto a rear end 85 of the shaft, while the forward
end 86 of the plunger, which end normally extends into the barrel 12, includes the
mushroom-shaped head 81 for engagement by the hook-shaped ends 63 of the drag
20 arms 62. The shaft front end is further provided with a frustoconical forwardly
inclined ramp portion 87 which is located behind head 81 and forms part of a barrel
wall deforming mechanism 90 of the syringe.
The barrel wall deforming mech~ni~m 90 provides for permanent deformation of the25 barrel wall 12 when an attempt is made to refill the syringe. This breaks the seal
between the stopper 52 and the barrel wall, which renders the syringe useless. The
deforming mech~ni~m consists of a pair of diametrically opposed axially extending
flexible carrier arms 64 connected to and extending rearward from the piston base 61.
The carrier arms 64 and the drag arms 62 are alternately positioned and
30 circumferentially evenly spaced about the center of the piston base 61. The carrier
arms 64 respectively include at their free end a radially outwardly protruding integral
2168201
deforming element 66 such as the sharp- edged cutters 67 of substantially triangular
cross-section illustrated in Figs. 3-5, or a blunt edged burrowing element 67a (see Fig.
9) which is preferably of the same size and shape as the cutters 67, but has rounded
edges and therefore burrows into the barrel wall instead of cutting it. A radially
inwardly directed hook portion 68 is provided at the free end of each carrier arm 64
which hook portion provides for a reliable connection between the piston and theplunger during the second aspiration stroke (auto-destruction stroke) and, thus, prevents
disconnection of the plunger from the piston subsequent to injection. In the normal, at
rest position of the carrier arms, the deforming elements 66 are not forced against the
barrel wall and are preferably closely spaced therefrom (see Fig. 3). However, the
hook portions 68 protrude radially inwardly to such an extend that they engage the
ramp portion 87 on the forward end 83 of the plunger 80 when the latter is completely
inserted into the piston 60 (see Fig. 4). Furthermore, the hook portions 68 ride up on
the ramp portion 87 when the plunger is pulled back in the piston 60 until the rear face
of the plunger head 81 engages the hook portions, thereby forcing the attached
deforming elements 66 into the barrel wall. The angle of the ramp portion 87 is
selected such that the deforming elements are pushed radially outwardly with sufficient
force to result in permanent deformation of the barrel wall and, thus, breaking of the
seal between the stopper and the barrel wall. In the preferred embodiment the ramp
portion 87 encloses an angle with the longitudinal axis of the plunger 80 of 15-
45depending on the material, shape and type of the deforming element 66 respectively
used and on the material and thickness of the barrel wall adjacent the deformingelement. The cutting elements are preferably extrusion molded of the same material as
the remainder of the piston 60, for example poly~ro~ylene. However, they can also be
made of a tougher or harder material such as polycarbonate, especially when the
deforming elements are intçn-le~l to cut the barrel wall.
Although the above described coupling mechanism is preferred for use in a syringe in
accordance with the invention, other coupling elements which provide a reliable
connection between the plunger and the piston during the first and second aspiration
strokes and permit sufficient movement therebetween for engagement of the deforming
2168201
mech~ni.cm. Furthermore, the coupling mechanism and the deforming mechanism can
be combined into a single structure, for example, by mounting the hook portions 68
and the deforming elements 66 on the drag arms.
5 The drag arms 62 in the preferred embodiment are longer than the carrier arms 64.
The hook-shaped ends 63 of the drag arms 62, the head 81Of the shaft, the ramp
portion 87 and the hook portions 68 of the carrier arms 64 respectively are
dimensioned such that when the plunger is inserted into the piston until the hook-
shaped ends 63 engage behind the head 81, the hook portions 68 and ramp portion 87
10 are axially spaced apart. Furthermore, the drag arms 64 are shaped such that the hook-
shaped ends 63 thereof are normally radially spaced apart from the barrel wall. The
spacing is selected such that the drag arms 62 do not engage the barrel wall when the
mushroom-shaped head 81 of the plunger 80 is positioned therebetween during
assembly of the syringe. It will be apparent from the above description and the
15 attached drawings that the stopper 52 extends rearward around the piston 60, or in
other words the piston is recessed into the stopper in the preferred embodiment. As a
result, the deforming elements 66 are located closely adjacent the seal line between the
stopper 52 and the barrel wall 12 so that subst~rlti~lly no portion of the barrel wall will
remain intact when refilling of the syringe is attempted after injection.
The piston 60 with the drag and carrier arms 62, 64 and the plunger 80 are each
preferably integrally extrusion molded from an extrudable, thermoplastic material,
preferably polypropylene.
25 Although in the above described arrangement of the coupling and deforming
mech~ni~m~ is preferred, it will be readily al,palent that the location of the drag arms
62 and the mushroom shaped head 81 on the piston 60 and plunger 80 respectively can
be exchanged without having an effect on the function of the syringe of the invention.
Equally, the positions of the carrier arms 64 with the deforming elements 66 and of the
30 ramp portion 87 may be exchanged so that the carrier arms are affixed to the plunger
80 and the ramp portion is provided on the piston 60.
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2168201
To facilitate permanent deformation of the barrel wall, the thickness of the barrel wall
can be reduced along diametrically opposite grooves 106 as known in the art from the
self-destruct syringe disclosed by Fenet in C~n~ n Patent Application SN 2,045,499.
If the barrel wall is provided with such grooves, the rotational position of the carrier
5 arms 64 in the barrel must be controlled to ensure reliable engagement of the
deforming elements 66 with the grooves. Furthermore, it may be possible to render
the syringe reusable by rotating the piston 60 in the barrel until the deforming elements
66 are no longer opposite one of the grooves. In order to prevent this, the barrel wall
in the preferred embodiment is made evenly thin along its whole circumference so that
10 rotation of the piston 66 in the barrel no longer has any effect on the function of the
deforming elements. Furthermore, in the most preferred embodiment, the deformingelements 66 are burrowing elements 67 which have a blunt radially outer edge that
does not cut the barrel wall but simply burrows into the barrel wall to create apermanent groove which permits air to pass around the plunger. Consequently, reuse
15 of the syringe is made impossible, since the barrel will no longer hold the vacuum
required for refilling of the syringe. Moreover, when the barrel wall is made evenly
thin, permanent deformation of the barrel wall by the deforming elements may be
carried out either during the injection or the second aspiration stroke. The barrel wall
is preferably of a thickness of 0.01 to 0.2 mm and extrusion molded of a substantially
20 rigid thermoplastic material to withstand the pressures created during aspiration and
injection. The barrel wall is preferably extrusion molded from polypropylene, but
other thermoplastic materials may be used as well.
The syringe is preferably assembled by pushing the piston completely into the barrel
25 and inserting the plunger into the barrel. The plunger 80 is then forced against the
piston 60 until the mushroom-shaped head 81 of the plunger snaps into the pistonimmediately behind the hook-shaped ends of the drag arms 62. A circumferential
crimp 100 is then provided in the barrel wall 12. The location of the crimp is selected
such that it limits the maximum volume of liquid which can be aspirated. Ch~n~ing
30 the location of the crimp 100 allows syringes of the same construction and dimensions
being used for a range of standard injection volumes (0.1 ml - 0.5 ml). The crimp also
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2168201
prevents disassembly of the syringe and tampering with the barrel wall deformingmech~ni~m 90. Once fully assembled, the syringe is sterilized, packaged and shipped
in the completely assembled but empty condition.
5 During use, the syringe is first filled or aspirated by pulling back the plunger 80 which
creates a vacuum in the syringe and leads to filling of the barrel with aspirated fluid in
a manner well known in the art. For injection, the plunger is forced into the barrel to
advance the piston 60 and expell the fluid contained in the barrel. The forward force
imparted on the thumb plate 84 during the injection stroke forces the head 81 of the
10 plunger deeper into the piston until the front surface 85 of the head engages the base
61 of the piston. At this point, the hook portions 68 have moved sufficiently past the
peaks of the ramp portion 87 to prevent engagement of the deformation elements 66
with the barrel wall during injection. The deforming elements 66 are only temporarily
forced into engagement with the barrel wall at the beginning of the injection stroke
15 when the hook portions 68 move past the ramp potion 87. Thus, at the end of the
injection stroke, the integrity of the barrel is still in place. However, if the plunger is
pulled back to attempt a second aspiration, the ramp 87 and the hook portions 68 are
forced into mutual engagement and the deforming elements are forced into or through
the sidewall and held in a sidewall deforming position as long as the plunger is pulled
20 back during this third stroke of the piston/plunger combination. This results in the
barrel wall being permanently deformed and the syringe rendered completely unusable
as soon as a second aspiration is attempted. The connection between the front end 83
of the plunger 80 and the cutter arms is sufficient to prevent disconnection of the
plunger from the piston during the third stroke. Furthermore, the front end of the
25 plunger is preferrably of sufficient strength to withstand the tension forces created
during the third stroke so that the plunger front end does not break off during the
cutting operation. However, in an alternate embodiment, the plunger shaft 82 may be
provided with an area of reduced cross-section (not illustrated) behind the mushroom
shaped head 81so that the head will break off when excessive rearward force is applied
30 to the plunger 80. For situations where it is desired that the user of the syringe be able
to remove a portion of the plunger before disposal of the syringe for exchange of that
2168201
portion for a new syringe, as in a needle exchange program, the plunger shaft 82 is
provided with a region of reduced cross-section 109 behind the rearmost guide plate 83
of the plunger 80.
S Changes and modifications in the specifically described emvodiments can be carried
out without departing from the scope of the invention which is intended to be limited
only by the scope of the appended claims.
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