Note: Descriptions are shown in the official language in which they were submitted.
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INJECTION DEVICE
This invention relates to the field of injection devices
for the administration of liquid medication, for example,
insulin or growth hormone.
One type of injection device is known as a mini-needle or
micro-needle device. These devices comprise a pressurised
("forced") injection system and have a needle which is
shorter than that of conventional needle systems. The
needle is normally hidden which is advantageous both for
avoiding needle stick injuries and for minimising trauma
to needle-phobic patients. The needle is hidden both
before and after the injection is delivered, appearing
only for the duration of the injection. Mini needle
devices can typically deliver a larger volume of
medication than needle-free devices and can deliver
faster than conventional needle systems.
One such known device is described in W000/09186 (Medi-
Ject Corporation) for "Needle assisted jet injector" and
this document gives a useful summary of prior art
devices.
The device of WO 00/09186 includes a needle which is, in
one embodiment, retractably located within an injector
nozzle assembly. Upon activation of a force generating
source, a portion of the needle extends past the nozzle
assembly and penetrates the outer layer of skin to
deliver medicament via jet injection to a deeper region.
After activation, the needle retracts back into the
nozzle assembly. The retractable needle is housed within
the nozzle and is pushed forward so that it emerges in
order to deliver an injection by the liquid medicament
itself, when the medicament is itself pushed forward by
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the plunger.
Although the present invention may relate to mini-needle
or jet injection devices, the invention is equally
applicable to other types of injection device, for
example those for deep-penetrating muscular injection as
well as those which are for shallower, subcutaneous,
injection.
According to a first aspect of the present invention
there is provided an injection device comprising an outer
housing inside which is located
a barrel for holding a volume of a medicament;
a needle at one end of the barrel, the needle and
barrel being such that at least part of the needle is
axially moveable in and out of said outer housing but is
biased to be normally wholly inside said housing;
a plunger, axially moveable within the barrel;
an inner housing intermediate the outer housing and
the barrel and plunger; and
an energy source in communication with said inner
housing,
wherein the inner housing is moveable by the energy
source between three positions, namely
a first position in which the inner housing is in
communication with both the plunger and the barrel such
that, in use, the plunger and barrel are movable axially
so as to move at least part of said needle out of the
outer housing;
a second position in which the inner housing is in
communication with the plunger but not the barrel such
that, in use, said plunger is movable axially into said
barrel so as to expel medicament through the needle; and
a third position in which the inner housing is in
communication with neither the plunger nor the barrel
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such that, in use, the plunger and barrel are able to
retract in order to retract the needle into the outer
housing.
The injection device according to the present invention
provides a simple and cost-effective means of delivering
medicament through a retractable needle. If desired, the
device is able to deliver medicament to a depth beyond
the length of the needle because of the propulsive force
provided by the energy source. As mentioned above, the
injection device is equally suitable for needle-assisted
jet injection (delivering medicament to a depth beyond
the length of the needle), conventional injection (to the
depth of the needle penetration), or even to a user-
adjustable needle penetration depth.
The device requires that the needle (and hence also the
barrel to which it is normally fixed) is moved axially so
that the needle can appear beyond the end of the nozzle
for the duration of the injection, after which the needle
retracts automatically, out of sight of the user. The
device also requires that the plunger is moved axially
(into the barrel) so that medicament is ejected. The
overall complexity of the injection device is
significantly reduced by both of these requirements being
effected by one component, namely the inner housing.
Preferably, said inner housing includes one or more
radially flexible tags, each preferably located at the
end of a resiliently flexible leg.
Preferably, one or more of said tags are situated at the
rear end of the inner housing and are moveable radially
into and out of communication with the plunger. In one
embodiment, the tags are biased radially inwardly into
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communication with the plunger, pr.eferably by
communication with the outer housing. Alternatively, the
tags are stored in their relaxed condition, before an
injection is initiated.
Each rear tag may be moveable out of communication with
the plunger when aligned with a corresponding recess in
the outer housing. Preferably, each rear tag is
substantially T-shaped. One leg of the T-shape enables
the rear tag to hook over the plunger and, effectively,
pull the plunger forward (in the first and second
positions mentioned above). The other leg of the T-shape
enables the rear tag to move radially outwardly to catch
in a recess in the housing (in the third position
mentioned above).
Preferably, one or more of said tags are situated at the
forward end of the inner housing and are moveable
radially into and out of communication with the barrel.
In one embodiment, the forward tags are biased radially
inwardly into communication with the barrel, preferably
by communication with the outer housing. Alternatively,
the forward tags are stored in their relaxed condition,
before initiating an injection.
Each forward tag may be moveable out of communication
with the barrel when aligned with a corresponding recess
in the =outer housing. Preferably, each rear tag is
substantially L-shaped.
In a preferred embodiment, said energy source is a
compressed gas. Alternatively, said energy source is a
spring.
Preferably, the injection device further includes means
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for allowing the inner housing to move axially only
forward with respect to the outer housing. Ideally, said
means is an arrangement of serrations, barbs, ratchet
teeth or the like intermediate the housings.
5
Preferably, the injection device further comprises guide
means for guiding, in use, the relative axial movement of
the inner and outer housings, the guide means preferably
comprising one or more protrusions on said inner housing
which, in use, cooperate with corresponding recesses on
an interior surface of said outer housing.
Preferably, said needle is biased to be normally wholly
inside said housing by means of a spring intermediate the
barrel and the outer housing.
In one embodiment, the needle is removable from the
device, this being of benefit in applications where the
device is reusable (for example if a multiple-use
cartridge of medicament is utilised).
In a further embodiment, said needle, barrel and plunger
are removable from said device. It is intended that the
device of the present invention could be constructed
around a standard needle, barrel and plunger of known
type.
Preferably, the injection device further includes a
removable needle cover which protects the needle during
storage and before use. Advantageously, said needle cover
includes means for pulling a protective rubber sheath or
the like from said needle when said needle cover is
removed from the device. Said pulling means may include
a floating rivet intermediate the needle cover and the
protective rubber sheath or the like, whereby twisting
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forces applied to said needle cover are substantially
prevented from being transmitted to said rubber sheath or
the like.
Preferably, the presence of said needle cover on said
device serves as a safety lock, substantially preventing
relative forward movement of said outer housing.
In a preferred form, the injection device further
comprises a viewing window in said barrel aligned with a
viewing window in said outer housing such that said
medicament can be viewed by a user prior to an injection
taking place. Preferably, in use during an injection,
said inner housing moves intermediate said viewing window
in the outer housing and said barrel so as to obscure the
window in the barrel from the user's view.
Preferably, the injection device includes means for
emitting an audible and/or physical indication to a user
that the injection is complete.
According to a second aspect of the invention there is
provided an injection device comprising an outer housing
inside which is located
a barrel for holding a volume of a medicament;
a needle at one end of the barrel, the needle
and barrel being such that at least part of the
needle is axially moveable in and out of said outer
housing but is biased to be normally wholly inside
said housing;
a plunger, axially moveable within the barrel;
an inner housing intermediate the outer housing
and the barrel and plunger; and
an energy source in communication with said
inner housing,
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wherein the inner housing is moveable by the energy
source between two positions, namely
a first position in which the inner housing is
in communication with the plunger but not the barrel such
that, in use, said plunger is movable axially into said
barrel so as to expel medicament through the needle; and
a second position in which the inner housing is
in communication with neither the plunger nor the barrel
such that, in use, the plunger and barrel are able to
retract in order to retract the needle into the outer
housing.
According to a third aspect of the invention there is
provided an injection device comprising an outer housing
adapted to receive:
a barrel for holding a volume of a medicament;
a needle at one end of the barrel, the needle
and barrel being such that at least part of the
needle is axially moveable in and out of said outer
housing but is biased to be normally wholly inside
said housing; and
a plunger, axially moveable within the barrel,
characterised in that the injection device further
comprises:
an inner housing intermediate the outer housing
and the barrel and plunger; and
an energy source in communication with said
inner housing,
wherein the inner housing is moveable by the energy
source between three positions, namely
a first position in which the inner housing is
in communication with both the plunger and the barrel
such that, in use, the plunger and barrel are movable
axially so as to move at least part of said needle out of
the outer housing;
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a second position in which the inner housing is
in communication with the plunger but not the barrel such
that, in use, said plunger is movable axially into said
barrel so as to expel medicament through the needle; and
a third position in which the inner housing is
in communication with neither the plunger nor the barrel
such that, in use, the plunger and barrel are able to
retract in order to retract the needle into the outer
housing.
Preferred embodiments of the present invention will now
be more particularly described, by way of example only,
with reference to the accompanying drawings wherein:
Figure 1 is a perspective view, partly in section,
showing the injection device, in the condition in which
it is supplied to a user, apart from the needle cover;
Figure 2, drawn to a larger scale, shows detail of part
of the device shown in Figure 1;
Figure 3 is a perspective view, partly in section,
showing the injection device, during an injection;
Figure 4, drawn to a larger scale, shows detail of part
of the device shown in Figure 3;
Figure 5 is a perspective view, partly in section,
showing the injection device, with the plunger fully
depressed into the barrel;
Figure 6, drawn to a larger scale, shows detail of part
of the device shown in Figure 5;
Figure 7 is a perspective view, partly in section,
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showing the injection device, after use and safe to
dispose of;
Figure 8, drawn to a larger scale, shows detail of part
of the device shown in Figure 7;
Figure 9 is a perspective view of the device, including
the needle cover;
Figure 10 is perspective view, partly in section, showing
detail of the needle cover;
Figure 11 is perspective view, partly in section, showing
detail of the needle cover part way through being removed
from the injection device;
Figure 12 is a schematic view showing the relationship
between tags 7A and ram 4, in one embodiment of the
invention;
Figure 13 is a perspective view of the inner housing
(also referred to as the "plunger housing");
Figure 14 is a side view of the inner housing of Figure
13;
Figure 15 is a perspective view, partly in section,
showing an alternative embodiment of the injection
device, in the condition in which it is supplied to a
user;
Figure 16, drawn to a larger scale, shows detail of the
rear end of the device shown in Figure 15;
Figure 17 shows detail of the interaction between the
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spring housing 41 and the rear of the outer housing 30;
Figure 18 is a perspective view, partly in section,
showing the injection device with the needle cover
5 removed, immediately prior to initiating an injection;
Figure 19 is a perspective view, partly in section and
drawn to a larger scale, showing the front part of the
device immediately before initiating an injection;
Figure 20 is a perspective view, partly in section,
showing the front part of the device at the start of an
injection;
Figure 21 is a perspective view showing the device in the
same condition as Figure 20, i.e. at the start of an
injection with the needle emerging from the end of the
device and the plunger beginning to travel down the
barrel;
Figure 22 is a perspective view, partly in section,
showing the injection device with the plunger fully
depressed into the barrel;
Figure 23 is a perspective view, partly in section,
showing the injection device after use and with the
needle retracted into the device;
Figure 24 is a perspective view of the assembled device,
including the needle cover;
Figure 25 is a schematic view of part of the front end of
the device, showing the helical protrusion on the nozzle.
Figure 26 is perspective view, partly in section, showing
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detail of the needle cover; and
Figure 27 is perspective view, partly in section, showing
detail of the needle cover after removal from the device.
Throughout the following description, reference to a
"forward" direction means the direction which is towards
the patient when the injection device is in use. The
"forward" end of the injection device is the end nearest
the patient's skin when the device is in use. Similarly,
reference to a "rearward" direction means the direction
which is away from the patient and the "rearward" end of
the device is the end furthest from the patient's skin
when the injection device is in use.
Figure 1 is a perspective view, partly in section,
showing the injection device, in the condition in which
it is supplied to a user, apart from the needle cover
(which is described below after describing the main
operation of the device).
The principal components of the device will now be
described with reference to Figures 1 and 2. An energy
source 1 is provided at the rear of the device which, in
this embodiment, is a gas cylinder similar to the type
used in a conventional aerosol can or the like i.e.
having a valve through which gas can be released at will
and in a controlled manner. In an alternative embodiment
of the invention, a spring is used as the energy source
in place of a gas cylinder and this embodiment is
described later with reference to Figures 13 et seq.
The valve 2 of the gas cylinder opens into a chamber 3,
which in Figure 1 is of relatively small volume. The
front wall of the chamber 3 is defined by a ram 4 which
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has an annular seal 5 at the rear thereof in order to
make the chamber 3 gas-tight. The rear wall of the
chamber 3 is defined by the back face of a generally
cylindrical chamber housing 6.
The forward part of the ram 4 abuts or alternatively is
integrally-formed with an inner housing 7 which closely
surrounds a plunger 8 (and can therefore be referred to
as the "plunger housing"). The rear of the plunger
housing includes four orthogonally placed tags 7A, which
each have a "hammer head" or T-shape and whose tendency
to spring radially outwardly is restricted by the
diameter of the chamber housing 6. If the ram 4 is
integrally formed with the plunger housing 7 as
illustrated in Figures 13 and 14, the tags 7A are
positioned at the end of flexible legs cut into the
housing, so that the tags 7A can move radially, with
respect to the ram 4 and remainder of housing 7.
The hammer head of each tag 7A hooks over the enlarged
head 8A of the plunger 8, so that the tags 7A are in
contact with the plunger head 8A, as shown best in Figure
2.
The plunger 8 is the plunger of a syringe arrangement
comprising a barrel 9 in which a predefined volume of
liquid medicament is supplied and a needle 10 through
which the medicament can be delivered to the patient. A
nozzle 11 at the front end of the injection device
normally conceals the needle 10 from the user's view. A
spring 12, positioned between the outer housing and the
barrel 9 biases the needle to be normally wholly within
the nozzle 11.
At the front end -of the plunger housing 7, there are
further orthogonally placed tags 7B, which each have a
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generally L shape and whose tendency to spring radially
outwardly is restricted by the diameter of the chamber
housing 6. The tags 7B each abut the flange at the rear
of barrel 9.
Other means of interaction between the inner housing and
the plunger may be envisaged, instead of tags 7A, for
example tags that are not T-shaped, or means that push
the plunger rather than pulling as in the described
embodiment.
There are four main stages in the operation of the
device. Stage 1 is the condition shown in Figures 1 and
2, i.e. the device as supplied to a user, and as
described above. The medicament is already present in the
barrel 9 and the needle 10 is concealed from view within
the nozzle 11. The plunger 8 is fully withdrawn from the
barrel 9 (because of the liquid medicament contained
within the barrel) and the head of the plunger 8A abuts
the tags 7A. The rear of the remainder of housing 7
abuts the ram 4. The chamber 3 is of minimal volume.
Stage 2 of operation is the injection stage illustrated
in Figures 3 and 4. With the injection device held
against the patient's skin at the injection site,
downward force is applied to the device in the direction
indicated by the arrow F in Figure 2. This force causes
the valve of the gas cylinder 1 to open, releasing gas
into the chamber 3. As the chamber 3 fills with gas, the
ram 4 is urged forward, consequently urging tags 7A
against the plunger 8. As the tags 7A, and hence the
plunger housing 7, are urged forward, the cooperation of
the tags 7B against the barrel 9 means that the barrel is
also urged forward, against the bias of a spring 12
(shown in Figure 3) As the barrel 9 moves forward, so
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does the needle 10 which is attached thereto and so the
needle protrudes out of the nozzle 11 sufficiently to
enable an injection to be delivered. Therefore,
initially, the ram 4 causes the plunger housing 7, the
plunger 8, the barrel 9 and the needle 10 to move
forwards.
Shortly after the plunger housing 7 starts to move
forward, the tags 7B reach a lip in the chamber housing
6. The tags 7B spring radially outwardly over this lip,
as shown in Figures 3 and 4. Once the tags 7B have
sprung outwardly in this way, they are no longer in
abutment with the barrel 9. This means that the barrel 9
(and hence needle 10) is no longer urged forwards because
the forwardly-moving plunger housing 7, including tags
7B, are free to continue moving forward without
contacting the barrel 9.
Therefore, once the device has reached the condition
illustrated in Figures 3 and 4, continued forward
movement of the ram 4 and plunger housing 7 causes the
plunger 8 to be urged forward into the barrel 9. This
expels the liquid medicament from the barrel 9, through
the needle 10 to deliver an injection. It is the
cooperation of the tags 7A with the enlarged head 8A of
the plunger which transmits the forward force from the
ram 4/housing 7 to the plunger 8.
The third stage in the operation of the device is
illustrated in Figures 5 and 6. When the plunger 8 is
depressed into the barrel 9, the desired dose of
medicament is delivered into the patient. At this point,
the tags 7A reach recesses 13 cut into the plunger
housing 6 whereupon they are able to spring radially
outwardly into those recesses (as illustrated in Figures
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5 and 6). An audible click may be emitted which
indicates to the user that the injection is complete. In
addition, the user may "feel" that the injection is
complete as a result of the tags 7A locating in recesses
5 13.
The outward movement of the tags 7A means that the
"hammer head" shape is no longer in contact with the
enlarged head 8A of the plunger 8 and therefore the
'10 plunger 8 is no longer driven forward by the ram 4 and
tags 7A. The plunger housing 7 may continue further
forward until an end stop is reached.
The final stage in the operation of the device is
15 illustrated in Figures 7 and 8. With the tags 7A located
within recesses 13, neither the plunger 8 nor the barrel
9 is impeded by any part of the plunger housing 7.
Therefore the spring 12, which had been compressed by the
forward motion of the barrel 9, urges the barrel 9 and
hence the plunger 8 backwards until the ram 4 prevents
further backward movement thereof. The backward movement
is sufficient to cause the needle 10 to retract into the
nozzle 11 so that it is no longer visible to the user and
safe from the risk of causing a needle-stick injury. The
used injection device can then be safely disposed of.
Blow-back is prevented by the provision of serrations 14
which guide the relative movement of the chamber housing
6 and the outermost housing. These serrations only
permit relative movement in one direction, i.e. the
chamber housing 6 moving forward with respect to the
outermost housing.
Figure 9 is a perspective view of the injection device
which, in this Figure, includes a needle cover 15. The
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needle cover is shown in further detail in Figures 10 and
11 and is used to protect the needle end of the injection
device during transit, storage and before use to deliver
an injection. The needle cover 15 has the further
advantage of preventing accidental or unintended
activation of the device, as it is not possible to fire
the device with the needle cover 15 in place.
Regulations require that the needle (which is in direct
communication with the medicament in the barrel) is
sealed from the outside environment before use. This is
achieved by providing protection in the form of a rubber
moulding 16 which covers the end of the needle, the
rubber moulding 16 being surrounded by a nylon sheath 17.
The rubber moulding and nylon sheath (the "needle
protection") are fixed with respect to one another by a
friction fit between one or more protrusions 16A on the
rubber moulding and a corresponding one or more recesses
17A in the nylon sheath.
The configuration of the needle protection depends upon
the type of needle/barrel/plunger ("syringe assembly")
employed in the injection device. It is envisaged that
the injection device of the present invention could be
assembled around a standard syringe assembly of known
type (the selection thereof depending upon the required
dose range, the type of medicament to be administered
etc, for example). Different syringe assemblies may be
supplied with slightly differing needle protection.
The nylon sheath and rubber moulding are firmly fixed on
the needle 10 and it is difficult, if not impossible, for
a patient to pull them from the needle using his/her
fingers alone because of their position inside the nozzle
11. Therefore an outer needle cover 15 is provided which
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not only improves the aesthetic appearance of the
injection device, before use, but also serves the
function of facilitating the removal of the nylon sheath
and rubber moulding.
The needle cover 15 is releasably retained on the front
end of the injection device by the fit of annular
protrusions 18 on part of the device housing with grooves
19 on the interior of the needle cover. The protrusions
18 and corresponding grooves 19 preferably extend around
two equally opposed 60 portions of the circumference of
the nozzle 11.
The grooves 19 are located on one or more (preferably
equally spaced) flexible legs 20 which are flexible
compared to the rest of the needle cover 15, about point
P shown in Figure 9. Forward of each groove 19 is
provided an inwardly projecting tab 21 on each flexible
leg 20. Each tab 21 abuts the rear of the nylon sheath
17.
Turning now to Figure 11, when it is desired to remove
the needle cover 15 from the device, the user grips the
needle cover, preferably in a region having texture or
other grip-improving means 22, and pulls in the direction
indicated by the arrow in Figure 11. The flexibility of
the legs 20 permits the needle cover to ride over the
protrusions 18, disengaging them from the grooves 19.
The flexibility of the legs 20 is minimal enough not to
cause the tabs 21 to become disengaged from the rear of
the nylon sheath 17.
Therefore, as the needle cover 15 is pulled in the
direction indicated by the arrow, the tabs 21 are urged
against the rear of the nylon sheath 17 and sufficient
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force can be applied thereby to disengage the needle 10
from the rubber moulding 16. In this. way, the entire
moulding 16, nylon sheath 17 and needle cover 15 can be
removed from the injection device and discarded, so that
the injection device is then ready to use.
Other types of needle cover 15 may be envisaged, suited
to the particular type of syringe assembly used in the
device, for example that described below with reference
to Figure 25 et seq.
Figures 13 and 14 show more detail of an embodiment of
the inner housing 7 in which the ram 4 is integral with
the housing 7.
The inner housing is injection moulded as a single piece
having four orthogonally placed tags at each end thereof.
Each tag 7A, 7B is at the end of a resiliently flexible
leg, cut out of the material of the housing 7, so that
each leg (and its respective tag) is able to flex
radially with respect to the remainder of the housing 7.
The rear part of the inner housing 7 constitutes the
equivalent of the ram 4 described above. The ram is
provided with an annular groove or recess 4A, into which
the ball bearings 42 locate.
The inner housing 7 may also be provided with one or more
guide means which, in the illustrated embodiment, take
the form of elongate protrusions 7C. These protrusions
7C cooperate with corresponding recesses on the interior
surface of the outer housing 30 so that, in use, relative
axial movement of the inner and outer housings is guided.
A spring-powered embodiment of the injection device is
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described below with reference to Figure 15 et seq.
In this embodiment, there is a generally cylindrical
outer housing 30 extending all the way from the rear of
the device to the needle cover 15. The gas cylinder 1
and valve 2 are replaced by a spring-powered energy
source. Referring particularly to Figure 16, a spring 40
is provided under compression at the rear of the device,
intermediate the rear of a spring housing 41 and the ram
4. The spring 40 is retained in its compressed condition
by means of one or more ball bearings 42 sitting in
annular recess 4A on the ram 4, the ball bearings 42
being wedged against the outer housing 30 and located in
apertures 41C at the front of the spring housing 41. The
spring housing 41 interacts with the back of the outer
housing 30 by means of an arrangement illustrated in
Figure 17.
The spring housing 41 is provided with elongate slots 41B
and generally circular apertures 41C. The corresponding
part of the outer housing is provided with elongate
protrusions 30B on the interior surface thereof, which
fit into the slots 41B as illustrated in Figure 17. The
ball bearings 42 (not shown in Figure 17) fit through the
circular apertures 41C.
In Figure 15 it can be seen that the front end of the
outer housing 30 is in close relation, or abutting, the
needle cover 15. This substantially prevents any forward
movement of the outer housing 30 in relation to the
spring housing 41 and other components.
In Figure 18, the needle cover has been removed and it is
now possible to place the device against the user's leg
(or other injection site) ready to initiate an injection.
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Figure 19 shows the front part of the device at this
stage, in more detail.
Referring now to Figures 19 and 20, the front part of the
5 device is shown in more detail. At the front of the
outer housing 30, there are provided two annular grooves
30A and 30A' on the interior surface thereof. A spacer
part 50 is fixed with respect to the nozzle 11 and other
components internal of the outer housing 30. The spacer
10 part 50 is provided with an exterior annular protrusion
51 which initially locates in the forwardmost groove 30A.
The leading edge of forwardmost groove 30A is generally
blunt so that location of protrusion 51 therein (as
15 illustrated in Figure 19) inhibits the user from pulling
the outer housing 30 rearwardly off the spring housing 41
et al, which might dangerously expose the internal
components of the device. It is difficult for a user to
apply sufficient rearward force to cause the protrusion
20 51 to ride over the blunt leading edge.
The trailing edge of the forwardmost groove 30A and both
edges of the groove 30A' are curved or tapered.
To initiate an injection, the user grasps the outer
housing 30 and effects forward movement of the outer
housing 30 in relation to the spring housing 41. As
shown in Figure 20, the forward movement causes the
protrusion 51 to disengage from the forwardmost groove
30A and, as the outer housing 30 moves forward with
respect to the spacer 50, the protrusion 51 engages in
the rearmost groove 30A'.
Referring now to Figures 18 and 21, the relationship
=35 between the ram 4, ball bearings 42 and spring housing 41
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21
is described in more detail. In the first position,
shown in Figure 18, the ball bearings 42 sit in the
annular groove 4A in the ram 4 and are wedged in place in
the apertures 41C at the front of the spring housing 41.
Figure 21 shows the device in the same condition as in
Figure 20 i.e. wherein forward movement of the outer
housing in relation to the spring housing has caused the
protrusion 51 to be engaged in the rearmost groove 30A'.
In this position, the spring housing 41 has moved closer
to the rear of the outer housing 30. This relative axial
movement is sufficient to cause the apertures 41C to
retreat back past an undercut area 30A" inside the outer
housing 30. The ball bearings 42 are now free to move
radially out of the apertures 41C and into said undercut
area 30A". out of engagement with the ram 4. The ram 4
is now free to travel forwards in the direction indicated
by the arrow in Figure 21, under the power of the spring
40.
The forward-moving ram 4 causes the inner housing 7 to
deliver the injection as previously described. This is
illustrated in Figure 21 (Stage 2 as previously
described) and Figure 22 (Stage 3 as previously
described).
Figure 23 shows the position in which the injection has
been fully delivered and the needle caused to retract
back inside the nozzle (final stage as previously
described).
In an alternative embodiment (not illustrated), the ball
bearings 42 are replaced by a living joint, moveable into
undercut area 30A" and out of engagement with the ram 4.
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22
In another embodiment (not illustrated), the protrusion
51 and grooves 30A, 30A' are replaced or supplemented by
a ratchet arrangement described hereafter. A spring
housing is provided which has a substantially square
cross-section. A portion of the inside of the outer
housing 30 is correspondingly shaped with a square cross-
section so that the spring housing and outer housing
closely fit together but relative axial movement between
them is possible. Relative rotational movement between
them is substantially prevented by the square cross-
section. At least one surface of the square cross-
section spring housing is provided with a plurality of
barbs, protrusions, ratchet teeth or the like which
cooperate with an inwardly-depending protrusion or tag on
the inside of the outer housing.
The ratchet arrangement performs the same function as
protrusion 51 and grooves 30A, 30A' i.e. to control
forward movement of the outer housing 30 in relation to
the spring housing 41. The ratchet arrangement may
provide further advantages, for example:
= Improved strength;
= Rotational alignment between spring housing and
outer housing;
= Improved resistance to rearward force generated by
the user pushing the device hard into the injection
site;
= Improved resistance to the user pulling the outer
housing rearwardly off the device, the ratchet teeth
permitting forward movement of the outer housing
only;
= Improved defining of the relative axial position of
the outer housing and internal components of the
device.
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23
Alternative embodiments are envisaged in which, instead
of a square cross-section, the spring housing has at
least one flat surface on which the barbs, protrusions,
ratchet teeth or the like are disposed; the remainder of
the spring housing may be of any cross-sectional shape so
long as the inside of the outer housing is
correspondingly shaped.
Other modifications to the injection device are
illustrated in Figure 13 et seq which are equally
applicable to the gas-powered embodiment described
earlier.
The barrel 9 may be provided with a transparent window 9a
which, in use, is aligned with a window 32 in the outer
housing (see Figure 24) so that the liquid medicament is
visible. During the injection (i.e. during firing of the
injection device), the plunger housing 7 becomes visible
as it moves forwardly intermediate the barrel 9 and outer
housing. As the plunger housing 7 moves forwardly, it
progressively obscures the window 9a thus giving a visual
indication to the user of the progress of the injection.
The window 9a may be completely obscured by the plunger
housing 7 when the injection is complete. The plunger
housing 7 may be brightly coloured e.g. red to increase
its visibility through the window 32.
It is observed that plastics of the type which may be
used to form the plunger housing 7 will, over time, tend
to gain a memory of the position in which they are
stored. It is essential for operation of the device that
the tags 7A spring properly into and out of engagement
with the enlarged head 8A of the plunger. Therefore, as
visible in Figure 18, a tapered surface 31 is provided on
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24
the interior of the outer housing 30. This enables the
tags 7A to be stored in their "relaxed" position, i.e.
sprung radially-outwardly to abut the outer housing 30,
as illustrated in Figure 18.
When an injection is initiated as shown in Figure 21, the
forward movement of the outer housing 30 in relation to
the plunger housing 7 causes the tags 7A to ride up the
tapered surface 31 and into engagement with the enlarged
head 8A of the plunger.
When the plunger housing 7 has moved forward sufficiently
for tags 7A to reach recesses 13, the tags 7A will have
an increased tendency to spring outwardly into the
position in which they had been previously stored,
ensuring efficient operation of the device.
Figures 26 and 27 show an alternative embodiment of the
needle cover 15. Like parts are given the same reference
numerals as in Figure 11. In the Figure 26 embodiment,
the needle cover 15 is releasably retained on the front
end of the injection device by the fit of protrusions 11A
on the exterior of the nozzle 11 with corresponding
recesses on the interior of the needle cover 15.
The protrusions 11A may take the form of a single helical
protrusion as illustrated in Figure 25, or alternatively
several discrete protrusions may be used.
At the front end of the needle cover 15 is a floating
rivet 35 which has rearwardly directed barbed fingers 36
which pass through an aperture in the front end of the
sheath 17.
The protrusions 11A the barbed fingers 36 and the
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interaction of the nozzle with the needle cover 15 at
surface 15A mean that the nozzle 11 and associated
components are prevented from moving axially with respect
to the housing 30 in the situation illustrated in Figure
5 26. This means that the device cannot be inadvertently
fired whilst the needle cover 15 is still in place.
When it is desired to remove the needle cover 15 from the
device, the user grips the needle cover and pulls in the
10 direction indicated by the arrow in Figure 26, using a
twisting motion to cause the needle cover to ride along
the nozzle guided by the helical protrusion 11A.
The floating rivet 35 allows the needle cover 15 to be
15 twisted in order for it to move along helical protrusion
11A, but the sheath 17 does not twist and is simply
pulling axially off the needle. This means there is no
risk of damage to the needle 10 caused by twisting
forces.
As the needle cover 15 is pulled in the direction
indicated by the arrow, the barbed fingers 36 pull the
sheath 17 with sufficient force to disengage the needle
10 from the rubber moulding 16. In this way, the entire
moulding 16, nylon sheath 17 and needle cover 15 can be
removed from the injection device and discarded, so that
the injection device is then ready to use. Removal of
the needle cover 15 has the second function of allowing
the nozzle etc to be free to move axially with respect to
the housing 30, which enables the device to be fired as
described above.
When the end of the protrusion 11A is reached, the needle
cover 15 is disengaged from the nozzle 11 as illustrated
in Figure 27.
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A further embodiment of the present invention is
envisaged wherein the needle is exposed upon removal of
the needle cover 15. Such an embodiment may be suitable
for users where needle-phobia is not a concern and where
the complexity (and hence cost) of the device can be
reduced by eliminating the need for the first stage (i.e.
the forward movement of the needle out of the nozzle 11).
The optional needle cover 15 may be omitted from such an
embodiment. As mentioned above, it is possible that the
injection device of the present invention may be supplied
separately from and then assembled around a standard
syringe assembly (needle/barrel/plunger) of known type.
In a further development, it is envisaged that it would
be readily possible to adapt the device of the present
invention to be operable with a standard cartridge or
vial of medicament (containing a volume of medicament
from which several doses of user-defined volume can be
provided) instead of a syringe assembly. In such case
the needle could be removable and replaceable so that the
device could be reused until the medicament cartridge is
empty.
