U.S. patent application number 09/220421 was filed with the patent office on 2001-11-08 for needle-less injector.
This patent application is currently assigned to Duncan A. Greenhalgh. Invention is credited to WESTON, TERENCE EDWARD.
Application Number | 20010039394 09/220421 |
Document ID | / |
Family ID | 26303316 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010039394 |
Kind Code |
A1 |
WESTON, TERENCE EDWARD |
November 8, 2001 |
NEEDLE-LESS INJECTOR
Abstract
A needle-less injector comprises a cartridge (3) prefilled with
liquid ((9), which cartridge contains a free sliding piston (32)
and an injection orifice (10). A ram (22) is urged by a pre-loaded
spring (24) for striking the said piston to cause the injections.
Adjusting means (6) can be provided to vary the volume injected. A
trigger device (26, 30) initiates injection only when the optimum
contact pressure is reached between the discharge orifice (1) and
epidermis of the subject. The initial loading of the power spring
(24) is sufficient to dispense all of the contents of the
medicament cartridge in one dose or multiple sequential doses.
Disposable and reusable embodiments are described.
Inventors: |
WESTON, TERENCE EDWARD;
(EYE, GB) |
Correspondence
Address: |
PATENT ADMINISTRATOR
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Assignee: |
Duncan A. Greenhalgh
|
Family ID: |
26303316 |
Appl. No.: |
09/220421 |
Filed: |
December 24, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09220421 |
Dec 24, 1998 |
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08591585 |
Jan 16, 1996 |
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5891086 |
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Current U.S.
Class: |
604/72 ;
604/68 |
Current CPC
Class: |
A61M 5/288 20130101;
A61M 5/31551 20130101; A61M 5/31513 20130101; A61M 2005/2013
20130101; A61M 5/2033 20130101; A61M 2005/3104 20130101; A61M
5/31561 20130101; A61M 2205/582 20130101; A61M 5/2448 20130101;
A61M 2205/583 20130101; A61M 5/2053 20130101; A61M 5/31593
20130101; A61M 5/3158 20130101; A61M 5/30 20130101 |
Class at
Publication: |
604/72 ;
604/68 |
International
Class: |
A61M 005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 1993 |
GB |
9315915.0 |
Sep 28, 1993 |
GB |
9319981.8 |
Claims
I claim:
1. A needle-less injector comprising an actuator and a cartridge
filled with a liquid to be injected in a subject, the cartridge
having a liquid outlet and a free piston inward of the liquid
outlet in contact with the liquid, the liquid outlet comprising an
opening in the cartridge, a membrane initially covering the
opening, and a perforating member which perforates the membrane to
allow the said liquid to pass therethrough, said actuator
comprising; (a) a housing having a forward portion adapted to be
connected with the cartridges; (b) an impact member mounted within
said housing inward of the forward portion so as to be movable from
a first position toward the forward portion to strike the free
piston when a cartridge is connected and to continue to move the
free piston toward the liquid outlet whereby a dose of the liquid
is expelled through the liquid outlet in the cartridge; and (c) an
energy store which, when released, moves said impact member towards
the liquid outlet.
2. An injector according to claim 1, wherein said energy store
comprises: (i) a spring which exerts a force on said impact member
to normally urge said impact member toward the liquid outlet; and
(ii) a latch within said housing which engages said impact member
to prevent movement of the impact member toward the forward portion
in response to said force exerted by said spring, and being mounted
to be movable out of engagement with said impact member to a firing
position, in which said latch permits such movement.
3. An injector as claimed in claim 2, wherein the said spring is a
compression spring.
4. An injector as claimed in claim 2, wherein the spring is a gas
spring provided by a chamber within said housing refilled with
pressurized gas which constantly exerts a force on said impact
member to normally urge said impact member towards the liquid
outlet.
5. An injector as claimed in claim 4, wherein said pressurized gas
is air.
6. An injector as claimed in claim 2, further comprising trigger
means for operating said latch to thus initiate the injection in
response to a predetermined contact force between the liquid outlet
of the cartridge and the subject.
7. An injector as claimed in claim 6, wherein said actuator has a
user-holdable portion and means for mounting the cartridge so that
the user-holding portion is movable relative to the cartridge by
the liquid outlet of the cartridge being urged into contact with
the subject, and said latch comprises a latch member which is
movable to said firing position by the relative movement between
the user-holdable portion and the cartridge.
8. An injector as claimed in claim 7, wherein said latch member is
resilient.
9. An injector as claimed in claim 1, wherein the energy store is
sufficient to expel a single dose of the liquid.
10. An injector as claimed in claim 1, wherein the energy store is
sufficient to expel a plurality of successive doses of the
liquid.
11. An injector as claimed in claim 1, wherein the cartridge
includes a separately held plurality of components which are to be
mixed with one another prior to injection and a mixing member for
mixing the plurality of components with one another, said impact
member further comprising a mixing means being movable toward the
liquid outlet for striking the mixing member, whereby the plurality
of components are mixed with one another.
12. An actuator in combination with a cartridge to form a
needle-less injector, comprising: (a) said cartridge being refilled
with a liquid to be injected in a subject, said cartridge
comprising: (i) a liquid outlet and a free piston inward of the
liquid outlet in contact with the liquid, the liquid outlet
comprising an opening in the cartridge, a membrane initially
covering the opening, and a perforating member which perforates the
membrane to allow the said liquid to pass therethrough; (ii) a
separately held plurality of components which are to be mixed with
one another prior to the injection; and (iii) a mixing member for
mixing the plurality of components with one another, wherein the
plurality of compartments are separated by at least one partition
and said cartridge further has a penetrating member so mounted
therein as to be movable to a mixing position in which it
penetrates the (or each) partition; and (b) said actuator
comprising: (i) a housing adapted to be connected with the
cartridge; (ii) impact member mounted within said housing inward of
the free piston so as to be movable from a first position toward
the liquid outlet to strike the free piston and to continue to move
the free piston toward the liquid outlet whereby a dose of the
liquid is expelled through the liquid outlet in the cartridge, said
impact member further comprising a mixing means being movable
toward the liquid outlet for striking the mixing member, said
mixing means in striking said mixing member being further operable
to move the penetrating member to the mixing position whereby the
plurality of components are mixed with one another; and (iii) an
energy store which, when released, moves said impact member towards
the liquid outlet.
13. An actuator according to claim 12, wherein the energy store
comprises a spring which exerts a force on said impact member when
said impact member is in said first position to normally urge said
impact member toward the liquid outlet; and a latch within said
housing for engaging said impact member toward the liquid outlet in
response to said force exerted by said spring, and being movable to
a firing position for permitting such movement.
14. An injector as claimed in claim 1, wherein the movement of said
impact member expels a fixed dose.
15. An injector as claimed in claim 1, wherein the distance of
travel of said impact member after striking the free piston is
variable to determine the dose of the liquid expelled through the
liquid outlet in the cartridge.
16. An injector as claimed in claim 1, comprising means for
retaining said cartridge for engagement with said actuator, said
retaining means being constructed to permit removal of said
cartridge.
17. An injector as claimed in claim 1, comprising means for
retaining said cartridge for engagement with said actuator, said
retaining means being constructed to permit the fixed mounting of
said cartridge.
18. An injector as claimed in claim 1, wherein said cartridge has a
body comprising glass.
19. An injector as claimed in claim 18, wherein said glass is
transparent.
20. An injector as claimed in claim 18, wherein said free piston of
said cartridge comprises a plastics material.
21. An injector as claimed in claim 20, wherein said plastic
material is a polymer or copolymer comprising a fluorinated
hydrocarbon.
22. An injector as claimed in claim 20, wherein said plastic
material is a polytetrafluoroethylene.
23. An injector as claimed in claim 20, wherein said plastic
material is selected from the group consisting of
tetrafluoroethylene-hexafluoropropy- lene copolymer,
tetrafluoroethylene-ethylene copolymer,
polychlorotrifluoroethylene, poly (vinylidene fluoride),
tetrafluoroethylene-perfluoro (propel vinyl ether) copolymer, and
hexafluoroisobutylenevinylidene fluoride copolymer.
24. A cartridge for use in conjunction with an actuator to form a
needle-less injector, said cartridge comprising a body comprising
glass and a piston mounted in said body with an interference fit,
said piston comprising a material which is substantially
non-resilient when subjected to a slowly applied force but is
highly resilient when subjected to a rapidly applied force.
25. (Amended) A cartridge as claimed in claim 24, wherein said
glass is transparent
26. (Twice Amended) A cartridge as claimed in claim 24, wherein
said piston comprises a plastic material.
27. (Amended) A cartridge as claimed in claim 26, wherein said
plastic material is a polymer or copolymer comprising a fluorinated
hydrocarbon.
28. (Amended) A cartridge as claimed in claim 26, wherein said
plastic material is polytetrafluoroethylene.
29. (Amended) A cartridge as claimed in claim 26, wherein said
plastic material is selected from the group consisting of
tetrafluoroethylenehexa- fluoropropylene copolymer,
tetrafluoroethylene-ethylene copolymer,
polychlorotrifluoroethylene, poly (vinylidene fluoride),
tetrafluoroethyleneperfluoro (propel vinyl ether) copolymer, and
hexafluoroisobutylene-vinylidene fluoride copolymer.
30. A cartridge as claimed in claim 24, having an outlet orifice
sealed by a perforatable membrane.
31. A cartridge for use in conjunction with an actuator to form a
needle-less injector, comprising a body which is of glass and a
piston which is slidably mounted in the body and which comprises
polytetrafluoroethylene.
32. A cartridge as claimed in claim 31, having an outlet orifice
sealed by a perforatable membrane.
33. A cartridge for use in conjunction with an actuator to form a
needle-less injector, said cartridge comprising a body and piston
mounted in said body with an interference fit, said body having an
outlet orifice sealed by a perforatable membrane.
34. An actuator for use in conjunction with a cartridge to form a
needle-less injector, the cartridge being filled with a liquid to
be injected in a subject, the cartridge having a liquid outlet and
a free piston inward of the liquid outlet in contact with the
liquid, said actuator comprising: (a) a housing having a forward
portion adapted to be connected with the cartridge; (b) an impact
member mounted within said housing inward of the forward portion so
as to be movable from a first position toward the forward portion
to strike the free piston when a cartridge is connected and to
continue to move the free piston toward the liquid outlet whereby a
dose of the liquid is expelled through the liquid outlet in the
cartridge; (c) a spring which exerts a force on said impact member
to normally urge said impact member toward the liquid outlet; (d) a
latch within said housing which engages said impact member to
prevent movement of the impact member toward the forward portion in
response to said force exerted by said spring, and being mounted to
be movable out of engagement with said impact member to a firing
position, in which said latch permits such movement; and (e) means
for varying the said dose of liquid.
35. An actuator as claimed in claim 34 which comprises a distal
portion for carrying the cartridge and a proximal portion of
carrying the impact member, the said means for varying the dose
comprising means for varying the position of the distal portion
with respect to the proximal portion in the said first
direction.
36. An actuator as claimed in claim 35 wherein said position
varying means comprises interengaging screw threads on the distal
and proximal portions.
37. An actuator as claimed in claim 34 wherein the said spring is a
compression spring.
38. An actuator as claimed in claim 34 wherein the spring is a gas
spring provided by a chamber within said housing refilled with
pressurized gas which constantly exerts a force on said impact
member to normally urge said impact member towards the liquid
outlet.
39. An actuator as claimed in claim 38 wherein said pressurized gas
is air.
40. An actuator as claimed in claim 34 further comprising trigger
means for operating said latch to thus initiate the injection in
response to a predetermined contact force between the liquid outlet
of the cartridge and the subject.
41. An actuator as claimed in claim 40 wherein said actuator has a
user-holdable portion and means for mounting the cartridge so that
the user-holdable portion is movable relative to the cartridge by
the liquid outlet of the cartridge being urged into contact with
the subject, and said latch comprises a latch member which is
movable to said firing position by the relative movement between
the user-holdable portion and the cartridge.
42. An actuator as claimed in claim 41 wherein said latch member is
resilient.
43. An actuator as claimed in claim 34 wherein the energy stored by
said spring is sufficient to expel a single dose of the liquid.
44. An actuator as claimed in claim 34 wherein the energy stored by
said spring is sufficient to expel a plurality of successive doses
of the liquid.
45. An actuator as claimed in claim 34 in combination with a
connected cartridge that includes a separately held plurality of
components which are to be mixed with one another prior to
injection and a mixing member for mixing the plurality of
components which one another, said impact member further comprising
a mixing means being movable toward the liquid outlet for striking
the mixing member, whereby the plurality of components are mixed
with one another.
46. An actuator in combination with a cartridge to form a
needle-less injector, comprising: (a) said cartridge being refilled
with a liquid to be injected in a subject, said cartridge
comprising: (i) a liquid outlet and a free piston inward of the
liquid outlet in contact with the liquid; (ii) a separately held
plurality of components which are to be mixed with one another
prior to injection; and (iii) a mixing member for mixing the
plurality of components with one another, wherein the plurality of
compartments are separated by at least one partition and said
cartridge further has a penetrating member so mounted therein as to
be movable to a mixing position in which it penetrates the (or
each) partition; and (b) said actuator comprising: (i) a housing
adapted to be connected with the cartridge; (ii) impact member
mounted within said housing inward of the free piston so as to be
movable from a first position toward the liquid outlet to strike
the free piston and to continue to move the free piston toward the
liquid outlet whereby a dose of the liquid is expelled through the
liquid outlet in the cartridge, said impact member further
comprising a mixing means being movable toward the liquid outlet
for striking the mixing member, said mixing means in striking said
mixing member being further operable to move the penetrating member
to the mixing position whereby the plurality of components are
mixed with one another; (iii) a spring which exerts a force on said
impact member when said impact member is in said first position to
normally urge said impact member toward the liquid outlet; (iv) a
latch within said housing for engaging said impact member to
prevent movement of the impact member toward the liquid outlet in
response to said force exerted by said spring, and being movable to
a firing position for permitting such movement; and (v) means for
varying the said dose of liquid.
47. An actuator as claimed in claim 46, having means for removably
receiving a cartridge.
48. An actuator as claimed in claim 47, in combination with a
cartridge, comprising means for retaining said cartridge for
engagement with said actuator.
49. The combination as claimed in claim 48, wherein said retaining
means are constructed to permit removal of said cartridge.
50. The combination as claimed in claim 48, wherein said retaining
means are constructed to permit the fixed mounting of said
cartridge.
51. The combination as claimed in claim 48, wherein said cartridge
has a body comprising glass.
52. The combination as claimed in claim 51, wherein said glass is
transparent.
53. The combination as claimed in claim 51, wherein said free
piston of said cartridge comprises a plastics material.
54. The combination as claimed in claim 53, wherein said plastic
material is a polymer or copolymer comprising a fluorinated
hydrocarbon.
55. The combination as claimed in claim 53, wherein said plastic
material is a polytetrafluoroethylene.
56. The combination as claimed in claim 53, wherein said plastic
material is selected from the group consisting of
tetrafluoroethylene-hexafluoropr- opylene copolymer,
tetrafluoroethylene-ethylene copolymer,
polychlorotrifluoroethylene, poly (vinylidene fluoride),
tetrafluoroethylene-perfluoro (propel vinyl ether) copolymer, and
hexafluoroisobutylenevinylidene fluoride copolymer.
57. An actuator for use in conjunction with a cartridge to form a
needle-less injector, the cartridge being filled with a liquid to
be injected in a subject, the cartridge having a liquid outlet and
a free piston inward of the liquid outlet in contact with the
liquid, said actuator comprising: (a) a housing having a forward
portion adapted to be connected with the cartridge; (b) an impact
member mounted within said housing inward of the forward portion so
as to be movable from a first position toward the forward portion
to strike the free piston when a cartridge is connected and to
continue to move the free piston toward the liquid outlet whereby a
dose of the liquid is expelled through the liquid outlet in the
cartridge; (c) a spring which exerts a force on said impact member
toward the liquid outlet; and (d) a latch within said housing which
engages said impact member toward the forward portion in response
to said force exerted by said spring, and being mounted to be
moveable out of engagement with said impact member to a firing
position, in which said latch permits such movement, the energy
stored by said spring being sufficient to expel a plurality of
successive doses of the liquid.
58. An actuator as claimed in claim 57, wherein the said spring is
a compression spring.
59. An actuator as claimed in claim 58, further comprising trigger
means for operating said latch to thus initiate the injection in
response to a predetermined contact force between the liquid outlet
of the cartridge and the subject.
60. An actuator as claimed in claim 59, wherein said actuator has a
user-holdable portion and means for mounting the cartridge so that
the user-holdable portion is movable relative to the cartridge by
the liquid outlet of the cartridge being urged into contact with
the subject, and said latch comprises a latch member which is
movable to said firing position by the relative movement between
the user-holdable portion and the cartridge.
61. An actuator as claimed in claim 60, wherein said latch member
is resilient.
62. An actuator as claimed in claim 57, in combination with a
connected cartridge that includes a separately held plurality of
components which are to be mixed with one another prior to
injection and a mixing member for mixing the plurality of
components with one another, said impact member further comprising
a mixing means being movable toward the liquid outlet for striking
the mixing member, whereby the plurality of components are mixed
with one another.
63. An actuator in combination with a cartridge to form a
needle-less injector, comprising: (a) said cartridge being refilled
with a liquid to be injected in a subject, said cartridge
comprising: (i) a liquid outlet and a free piston inward of the
liquid outlet in contact with the liquid; (ii) a separately held
plurality of components which are to be mixed with one another
prior to injection; and (iii) a mixing member for mixing the
plurality of components with one another, wherein the plurality of
compartments are separated by at least one partition and said
cartridge further has a penetrating member so mounted therein as to
be movable to a mixing position in which it penetrates the (or
each) partition; and (b) said actuator comprising: (i) a housing
adapted to be connected with the cartridge, (ii) impact member
mounted within said housing inward of the free piston so as to be
movable from a first position toward the liquid outlet to strike
the free piston and to continue to move the free piston toward the
liquid outlet whereby a dose of the liquid is expelled through the
liquid outlet in the cartridge, said impact member further
comprising a mixing means being movable toward the liquid outlet
for striking the mixing member, said mixing means in striking said
mixing member being further operable to move the penetrating member
to the mixing position whereby the plurality of components are
mixed with one another; (iii) a spring which exerts a force on said
impact member when said impact member is in said first position to
normally urge said impact member toward the liquid outlet; and (iv)
a latch within said housing for engaging said impact member to
prevent movement of the impact member toward the liquid outlet in
response to said force exerted by said spring, and being movable to
a firing position for permitting such movement.
64. An actuator as claimed in claim 63, wherein the movement of
said impact member expels a fixed dose.
65. An actuator as claimed in claim 63, wherein the distance of
travel of said impact member after striking the free piston is
variable to determine the dose of the liquid expelled through the
liquid outlet in the cartridge.
66. An actuator as claimed in claim 63, having means for removably
receiving a cartridge.
67. An actuator as claimed in claim 63, in combination with a
cartridge, comprising means for retaining said cartridge for
engagement with said actuator.
68. The combination as claimed in claim 67, wherein said retaining
means are constructed to permit removal of said cartridge.
69. The combination as claimed in claim 67, wherein said retaining
means are constructed to permit the fixed mounting of said
cartridge.
70. The combination as claimed in claim 11, wherein said cartridge
has a body comprising glass.
71. The combination as claimed in claim 14, wherein said glass is
transparent.
72. The combination as claimed in claim 70, wherein said free
piston of said cartridge comprises a plastics material.
73. The combination as claimed in claim 72, wherein said plastic
material is polymer or copolymer comprising a fluorinated
hydrocarbon.
74. The combination as claimed in claim 72, wherein said plastic
material is a polytetrafluoroethylene.
75. The combination as claimed in claim 72, wherein said plastic
material is selected from the group consisting of
tetrafluoroethylene-hexafluoropr- opylene copolymer,
tetrafluoroethylene-ethylene copolymer,
polychlorotrifluoroethylene, poly (vinylidene fluoride),
tetrafluoroethylene-perfluoro (propel vinyl ether) copolymer, and
hexafluoroisobutylenevinylidene fluoride copolymer.
Description
[0001] The present invention relates to a needle-less injector,
wherein a dose of liquid medicament is discharged in a thin jet at
sufficient velocity to penetrate the epidermis of the human, plant
or animal to be treated, thus to introduce the medicament into the
tissues of the subject.
[0002] Needle-less injectors are uses as an alternative to
hypodermic needle type injectors for delivery drugs, vaccines,
local anaesthetics and other fluids into the tissues. The
medicament is discharged in a jet at high velocity to first
puncture the epidermis, and thereafter be deposited in the tissues
of the subject. A variation is to press the discharge nozzle onto
the epidermis and force the medicament at very high pressure
through the epidermis.
[0003] Such injectors offer many potential benefits: because the
hole made by the jet is smaller than that made by a needle, less
pain is experienced by the patient when compared with hypodermic
needle injection; the availability of the medicament to the
capillaries is often enhanced because the spread of the medicament
within the tissues is much greater than achieved with a needle
injection, which deposits the medicament as a bolus at the needle
tip; there is less chance of cross-contamination;
[0004] animals, which are frequently uncooperative, are more easily
injected, because there is no risk of a needle breaking or bending,
and the injection is accomplished much faster than needle
injection; there is no needle disposal problem; the risk of
so-called needle-stick injury is eliminated.
[0005] Prior art devices typically use a spring-loaded piston pump
to generate the injection pressure, in which the piston is
retracted against a spring to withdraw fluid from a reservoir. At
the end of the piston stroke (which may be adjustable) the piston
is disengaged from the retracting mechanism and is urged suddenly
by the spring to pressurise and discharge the fluid from the
delivery nozzle. The retracting mechanism may be manual or
motorised. In some devices, the piston is driven on the discharge
stroke by gas or an electric motor instead of a spring.
[0006] Manually operated injectors generate a pressure in the
medicament of about 100 bars. In operation, the discharge orifice
is placed a small distance (about 10 mm) from the epidermis, and
the high velocity jet strikes then penetrates the epidermis (free
jet mode). The principle appears to be that the jet sacrifices some
of its kinetic energy to puncture the epidermis, because if the
nozzle is pressed firmly on the skin (contact mode), and the
injector operated, the liquid is pressurised but has no kinetic
energy, and is unable to pierce the skin. In the jet free mode,
medicament is wasted, since some of the liquid is deflected
sideways before puncture is completed, whilst in the contact mode,
the epidermis deforms under the pressure of the liquid, which
allows all of the medicament to escape without achieving
penetration.
[0007] Powered injectors generate higher pressure--typically 600
bars or more, which is sufficient to penetrate the epidermis even
when the discharge orifice is placed firmly on the skin (the
contact mode). However, even in the contact mode a variable
quantity of liquid is lost on each injection because the epidermis
initially deforms before puncturing, and allows some liquid to
escape. A further reason that the contact mode injectors leak is
that often the orifice fitted to the injector is an artificial
jewel of the type used for bearings in chronometers (because they
are inexpensive, accurate, and efficient), but the method of
mounting the jewel is such that the face of the orifice is always a
small distance from the skin, and the consequent broadening of the
jet results in lower force per unit area, and poor penetration.
[0008] The basic aim of all these devices is to apply the
medicament with sufficient force to pierce the epidermis, but it is
the rate of increase in force which is important rather than the
nominal pressure used, and few prior art injectors can achieve a
sufficiently high rate of pressure rise to ensure reliable and
repeatable injections.
[0009] Laboratory tests on both manual and powered injectors often
give encouraging results, but in practical situations, such as the
vaccination of animals, very variable amounts are
injected--frequently over 50% of the vaccine may be wasted, because
of hairs and dirt on the skin, and movement of the animal. The
difficulty in achieving successful: injections is exacerbated if
the subject does not co-operate, as in the case of animals, young
children or elderly patients. Premature operation of the injector
is common, as is relative movement between the injector orifice and
epidermis which can cause tearing of the epidermis during
injection. The amount of contact pressure applied varies between
operators, and the action of releasing the trigger mechanism
frequently results in a jerk of the injector just as it operates,
again causing poor injections and poor reproducibility.
[0010] Various methods have been proposed to overcome these
problems, although in the case of the free jet types, little can be
achieved. Powered injectors frequently employ a vacuum device to
suck the epidermis firmly onto the discharge orifice (see WO
82/02835--Cohen, and EP-A-347190--Finger) and thereby improve the
seal between the orifice and the epidermis, and prevent relative
movement. Alternatively, a pressure sensitive sleeve on the
injector (see U.S. Pat. No. 3,859,996--Mizzy) is placed on the
subject, whereby operation of the injector is prevented until the
correct contact pressure between the orifice and skin is
achieved.
[0011] Powered injectors have available a variety of sensing and
control devices to enhance their performance, which are denied to
manually powered injectors. However, they are frequently more
complex and not easily adapted for portable use. The fact that they
develop higher pressures than manual injectors means that their
power consumption is high; gas powered injectors require a heavy
cylinder of compressed gas, and electrically powered injectors are
often mains powered; battery powered injectors require a heavy
battery pack, and the limited availability or inconvenience of the
power sources has meant that the use of powered injectors has been
mainly confined to mass vaccination programs. In the case of
batteries and gas cylinders, it is usually difficult to judge the
number of operations available from power stored. Furthermore, the
sensing methods used to enable optimum operation are invariably
secondary or indirect. For example, U.S. Pat. No.
3,859,996--(Mizzy) discloses a controlled leak method to ensure the
injector orifice is correctly placed at the required pressure on
the subject's skin. When the placement conditions are met, the
controlled leak is sealed off by contact with the subject's skin,
and the pressure within the injector control circuitry rises until
a pressure sensitive pilot valve opens high pressure gas to the
drive piston. However, the actual pressure of the orifice on the
skin is not being measured; a hair of dirt of other irregularity on
the skin or sealing face of the orifice will prevent or retard the
pressure rise in the control circuit, and the operator will
unconsciously press the injector harder onto the skin. Also the
timing characteristics may vary because of the said ineffective
sealing, hysteresis of the pressure switch, and variations in the
supply pressure. In other words, the parameters being measured are
the effectiveness of the seal of the controlled leak sensor on the
skin and the pilot valve response, not the actual pressure of the
orifice on the epidermis. Still other devices us a sliding sleeve
in contact with the subject's skin, whereby displacement of the
sleeve is used to initiate the injection, but this method measures
the load on the sleeve, not on the orifice as required.
[0012] It may be seen therefore that whilst needle-less injection
potentially is more efficient than hypodermic needle injections for
certain applications, the technique is very dependent on the
ability of the operator and the compliance of the subject. Those
injectors that have features designed to reduce these problems tend
to be more complex and costly, and less portable. Furthermore, the
simpler injectors designed for use by the patient are invariably
complicated to load, clean, adjust and operate, and have not been
particularly well designed to be "user friendly". For example, self
injection of insulin by the diabetic patient has been an area of
intense development, because such patients often have to inject
themselves four time daily, and needle-less injectors offer the
possibility of less pain and tissue damage. Nevertheless, the
aforesaid variability in performance has prevented the widespread
adoption of the technique, and the recommended cleaning and
sterilization procedures are extremely inconvenient.
[0013] WO 93/03779 describes a needle-less injector of the present
inventor, which aims to overcome, or at least mitigate, the
problems described above. In summary, it provides a needle-less
injector which comprises-a chamber for containing liquid to be
injected, the chamber being provided with a liquid outlet; a
dispensing member movable in a first direction to reduce the volume
of the chamber to cause liquid contained therein to be expelled
through the said liquid outlet; and an impacting member arranged to
strike the said dispensing member to cause movement thereof in the
said first direction; the injector comprising a front portion which
carries means defining said liquid outlet, a rear portion having
means defining a handle for the injector, means for urging the rear
portion away from the front portion, and means for actuating the
injector, or permitting actuation thereof, in response to the
movement of the rear portion towards the front portion against the
force of the means urging them away from one another.
[0014] The injector described in WO 93/03779 has been found to give
excellent results. The design described in detail therein is,
however, essentially one intended for dispensing a large number of
doses, say 1500, and uses a built-in electric motor and battery to
provide power. There remains a need, which has not been adequately
met by the prior art, for a needle-less injector which is suitable
for dispensing a single dose, or a small number of doses, and which
is sufficiently inexpensive that it can be disposed of
thereafter.
[0015] According to the present invention there is provided an
actuator adapted, in conjunction with a cartridge, to form a
needle-less injector, the cartridge being pre-filled with a liquid
to be injected in a subject, and having a liquid outlet and a free
piston in contact with the liquid, the actuator comprising an
impact member urged by a spring and temporarily restrained by a
latch means, the impact member being movable in a first direction
under the force of the spring to first strike the free piston and
then to continue to move the piston in the first direction to expel
a dose of liquid through the liquid outlet, the spring providing a
built-in energy store and being adapted to move from a higher
energy state to a lower energy state, but not vice versa. The
actuator may comprise trigger means to operate the said latch, and
thus initiate the injection, only when a predetermined contact
force is achieved between the liquid outlet of the said cartridge
and the subject.
[0016] The term "liquid" as used herein includes, inter alia,
solutions, suspensions, emulsions and colloids.
[0017] The cartridge is preferably a hollow cylindrical cartridge
containing the medicament, having an outlet orifice which may be
formed as part of the cartridge, or comprising a separate nozzle
sealingly fitted to the outlet end of the cartridge. Preferably the
cartridge is made of glass. The glass, or any alternative material
of which the cartridge may be made, is preferably transparent, and
may have markings to indicate the amount of medicament contained
therein. The outlet orifice is that which is placed directly on the
epidermis to cause the injection. The pre-filled cartridge may be
supplied for insertion in the apparatus by the user, or supplied
ready fixed onto the injector by the manufacturer.
[0018] In one aspect thereof, the invention provides a cartridge
for use in conjunction with an actuator to form a needle-less
injector, comprising a body which is of glass and a piston slidably
mounted in the body and comprising a material which is
substantially non-resilient when subjected to a slowly applied
force but is highly resilient when subjected to a rapidly applied
force. The preferred material for the cartridge body is
polytetrafluoroethylene.
[0019] The cartridge may be a pre-filled cartridge as described
heretofore, having an outlet end sealed by a frangible membrane.
The cartridge can then be inserted into the apparatus and retained
by a screw cap or similar device, interposed by a discharge nozzle
with a piercing tube that punctures the frangible diaphragm so as
to create an hydraulic connection with the medicament contained in
the cartridge. Alternatively, the retaining cap may serve also as
the nozzle, and have an integral piercing tube.
[0020] In an embodiment of the invention the spring may be a
compression spring which acts against the impact member
(hereinafter referred to as the "ram") which is restrained from
movement by a manually adjustable nut and a latch. The nut may be
adjusted away from its abutment, by an amount which represents the
required stroke of the piston plus an acceleration distance between
the ram face and the piston in the medicament cartridge, the ram
being temporarily held by the latch on disengaging the latch, the
spring accelerates the ram in a forward direction so that it
strikes the piston to give a high skin-piercing force within the
medicament at the discharge orifice of the cartridge, and
thereafter continues to move the piston to discharge the medicament
until the nut comes to rest again on its abutment.
[0021] Thus it may be seen that if the aspects of the present
invention as described above are combined, the device of the
invention employs impact to create a high piercing pressure in the
medicament, may dispense multiple doses from a pre-filled
cartridge, has only one adjustment knob which sets the dose and the
impact gap, and uses direct contact pressure sensing to initiate
the injection and ensure repeatable performance. The injector may
be configured as a single or multiple dose disposable item,
supplied with the spring pre-loaded and the cartridge prefilled, or
with a facility for loading a fresh cartridge. The medicament may
be a one-part or multi-part liquid or. liquid and solid which may
be mixed immediately prior to injection.
[0022] Injectors in which the power source is reloadable, for
example the prior art devices which have a reloadable spring, must
employ a certain factor of safety to ensure a reasonable working
life. This is because as the spring is repeatedly stressed and
unstressed it gradually loses its resilience. This loss is most
pronounced if the spring is fully stressed at the start of each
working cycle. It is therefore necessary to operate with the spring
stressed to less than the maximum possible extent, say 60% of the
maximum. By contrast, when using a spring which is nonreloadable
during use of the device, as in the present invention, one can
employ a spring which is loaded to the maximum possible extent. One
can therefore have a spring which is smaller for a given amount of
stored energy, or more powerful for a given size of a spring.
Either way, one achieves a significant increase in the energy
density of the device, i.e. the amount of energy stored per unit
volume. Also by avoiding any need for a mechanism for reloading the
spring, the size, weight and complexity of the device are reduced,
and the problem of designing a reloading mechanism which is
ergonomically correct is avoided.
[0023] One embodiment of the invention comprises a tubular body,
one end of which terminates as a support plate with a co-axial hole
therein, and the other end of which is configured to receive a
cylindrical cartridge of liquid medicament. Passing through the
hole in the support plate is a threaded rod, which is itself fully
screwed into an internally threaded tube located within the tubular
body. The threaded tube terminates in a curved face and further has
an external shoulder on which a co-axially located compression
spring abuts; this assembly constitutes a ram. The other end of the
spring abuts at the outer face of the support plate and resiliently
engages with one or more threads on the threaded rod. Before a
cartridge is placed in the injector body, the spring is compressed
by pressing on the curved face of the ram, and is held in the
compressed condition by the latch.
[0024] The cartridge has a discharge nozzle at one end, and is
sealed at the other end by a free sliding piston which is in
contact with the medicament. The cartridge is located
longitudinally within the tubular body against a shoulder in the
tubular body, so that the piston contacts the curved face of the
ram. The cartridge is retained in the tubular body by crimping or
otherwise deforming the body around the orifice end of the
cartridge, leaving a hole for the orifice.
[0025] A nut is screwed onto the threaded rod and reacts against
the outside face of the support plate via a bridge over the latch.
Initial rotation of the nut on the threaded rod in a first
direction to a stop position further retracts the ram and creates a
gap between the ram face and the piston. During the translation of
the threaded rod, which is prevented from turning, the latch acts
as a ratchet on the threads. The nut is then rotated in a second
direction to a stop position where it locks onto the threaded rod,
so that continued rotation now rotates the threaded rod also. The
threaded rod unscrews from the internally threaded tubular member,
so that there is now a gap between the abutment faces of the nut
and support plate, which gap represents the impact distance plus
the required stroke of the piston; the ram is prevented from
forward movement of the latch. On disengagement of the latch, the
spring accelerates the ram in a forward direction a distance set by
the first rotation of the nut, so that it strikes the piston with
considerable force, and then continues to push the piston for a
distance determined by the gap set by the second rotation of the
nut between the abutment faces of the nut and support plate, which
distance is the sum of the impact gap and piston stroke. This cycle
may be repeated until the spring is fully extended and all of the
medicament is dispensed.
[0026] Operation of the latch is provided by a sliding sleeve
assembled co-axially on the tubular body, and urged in a rearwards
direction by a compression spring. In use, the injector orifice is
placed on the subject's skin, and the injector is pushed firmly in
the forward direction onto the skin by acting on the sliding
sleeve. The sleeve moves forward against the force of the spring,
and at a position representing the required contact force, a cam
surface on the sleeve disengages the latch from the threaded rod,
which accelerates under the action of the main spring to cause the
injection, as described.
[0027] In another embodiment, the injector is configured as
described, except that it allows a selected medicament cartridge to
be installed by the user, and retained within the tubular body by a
screwed or bayonet fitting cap. A variation of this embodiment is
that the medicament cartridge is fitted with a frangible membrane
seal instead of a discharge orifice, and the orifice is contained
within the retaining cap, which has a piercing tube to puncture the
membrane and make hydraulic connection with the medicament.
[0028] It is frequently desirable to inject a single dose of
medicament and discard the injector after use, and another
embodiment comprises a pre-filled cartridge of medicament having a
free piston in contact with the medicament and an outlet orifice,
retained in the injector casing, which casing supports a ram member
urged by a spring but restrained by a latch. The latch may be a
spring material and additionally bias a sliding trigger member, so
that relative displacement of the trigger member to the injector
casing against the bias disengages the latch and permits the ram to
accelerate and strike the free piston, as described.
[0029] To enable the injection of two-part-drugs--for example a
lyophilized (freeze dried) drug and a solvent--a further embodiment
describes a method of storing and subsequently mixing the
components prior to making an injection.
[0030] Embodiments are also described herein in which the gas
spring rather than a compression spring, provided, for example, by
compressed air with which a chamber in the injector is filled
during manufacture.
[0031] In the accompanying drawings:
[0032] FIG. 1 is a general external view of the first embodiment of
the injector, showing a plan elevation thereof;
[0033] FIGS. 1a and 1b are side and end elevations respectively of
the injector of FIG. 1;
[0034] FIG. 2 is a longitudinal sectional view of the injector,
fully loaded with medicament, as would be supplied in disposable
form;
[0035] FIG. 2a shows the righthand portion of the actuator of FIG.
2, on a larger scale;
[0036] FIG. 3 is a view corresponding to FIG. 2, but showing the
nut rotated in a first direction to create an impact gap between
the ram face and medicament piston;
[0037] FIG. 4 shows the injector with the nut screwed out to set
the stroke of the ram;
[0038] FIG. 5 corresponds to the previous views, but showing the
components in a position immediately after injection, with the
sliding sleeve disengaging the latch;
[0039] FIG. 6 is an enlarged longitudinal sectional view of the
latch;
[0040] FIG. 6a is an enlarged end view of the latch;
[0041] 12
[0042] FIG. 7 shows part of the injector modified to allow a
selected cartridge of medicament to be loaded;
[0043] FIGS. 8a and 8b show respectively a cartridge having a
frangible diaphragm seal and a nozzle cap fitted to same;
[0044] FIGS. 9a and 9b depict a single dose disposable injector,
ready to use and injecting medicament into the tissues of a
subject;
[0045] FIGS. 10a and 10b show a single dose disposable injector in
which the free piston is adapted to store a component of a two-part
medicament, and having means to connect the components and mix them
before injection; and
[0046] FIGS. 11, 11a and 11b show a further embodiment of the
invention in, respectively, longitudinally section view before use,
cross section view, and longitudinal sectional view after
firing.
[0047] For convenience and to avoid confusion, like parts are given
the same reference numerals throughout.
[0048] The injector shown in FIG. 1 comprises a tubular body 1,
which retains a cartridge 3 pre-filled with medicament, and visible
through one or more windows 4 in the body 1. The body 1 has an
aperture in the end to permit a nozzle 5 to protrude. A finger nut
6 is used by the operator to control the dose volume, and has
markings 7 thereon to indicate its position relative to a scale 8
on sliding sleeve 2, which is arranged co-axially on the body
1.
[0049] In FIG. 2, the cartridge 3 is shown filled with medicament,
and fitted with a nozzle 5 having an orifice 10, and a free piston
32. The nozzle 5 may be a separate component as shown, sealingly
fixed into the cartridge 3, or may be formed integrally with the
cartridge 3. Preferably the cartridge 3 is made of a transparent
material compatible with the medicament 9, to enable the contents
to be viewed through the windows 4 in body 1. The cartridge 3 abuts
a shoulder 11 formed on body 1, and is retained in this position by
the crimped end 13 of body 1. The cartridge 3 is biassed toward the
crimped end 13 by a resilient gasket or wave washer 12 interposed
between shoulder 11 and an end face of the cartridge 3.
[0050] The sliding sleeve 2 is assembled co-axially on body 1 and
is urged away from nozzle 5 by a spring 14 supported by a shoulder
16 on body 1 and acting on a shoulder 15. The extent of the
rearward movement is limited by shoulder 15 resting on one or more
stops 17. A cam 30 is formed inside the sleeve, so that when the
sleeve is moved towards the nozzle 5, the cam strikes a latch 26 to
initiate the injection.
[0051] Support flange 18 is formed on the end of the body 1 and has
a hole co-axially therein through which passes a threaded rod 19,
which may be hollow to save weight. A tubular member 20 is located
coaxially within the rear portion of the body 1 and has an internal
thread 21 at one end into which the rod 19 is screwed. The other
end of the tubular member 20 has a button having a convex face 22
pressed therein. Alternatively, the tubular member 20 may be formed
to provide a convex face 22. A flange 23 is formed on the tubular
member, and serves to support a spring 24, the other end of which
abuts the inside face of support flange 18. In the position shown,
the spring 24 is in full compression, and held thus by the nut 6
which is screwed onto threaded rod 19, and rests against the face
of the bridge 25. In the illustrated embodiment the nut 6 consists
of three components, held fast with one another, namely a body 6a,
an end cap 6b and a threaded insert 6c. The insert 6c is the
component which is screwed on to the rod 19, and is preferably made
of metal, for example brass. The other components of the nut can be
of plastics materials.
[0052] Beneath the-bridge and guided by same is a latch 26 which is
attached to the body 1 and resiliently engaged with one or more
threads on the screwed rod 19. The latch 26 is shown in more detail
in FIG. 6, and is made from a spring material and has a projection
27 which has a partial thread form thereon, so that it engages
fully with the thread formed on rod 19. The latch 26 is attached to
body 1 and has a resilient bias in the direction of arrow X, thus
maintaining its engagement with the thread on rod 19. Movement
against the direction of arrow X disengages the latch from the
thread. As will be described, the rod 19 will be translated without
rotation in the direction of arrow Y when setting the impact gap,
and the latch 26 will act as a ratchet pawl. The thread on rod 19
is preferably of a buttress form (each thread has one face which is
perpendicular or substantially perpendicular, say at 50, to the
axis of the rod, and the other face is at a much shallower angle,
say 45.degree.), giving maximum strength as a latch member, and a
light action as a ratchet member.
[0053] Referring again to FIG. 2, nut 6 is screwed part way onto
threaded rod 19, so that there is a portion of free thread 28
remaining in the nut 6, defined by the end of rod 19 and stop face
29 in nut 6. A stop pin 31 has a head which bears against the stop
face 29, and a shaft which is fixedly secured to the inside of rod
19, for example by adhesive. The stop pin 31 prevents the nut 6
being completely unscrewed from rod 19, since when the nut 6 is
rotated anticlockwise, it will unscrew from the rod 19 only until
the head of pin 31 contacts the face of the recess in the nut 6 in
which it is located. The pin 31 also defines the maximum length of
free thread in nut 6 when fully unscrewed.
[0054] Referring to FIG. 3, the first stage in the operating cycle
is to rotate the nut 6 on threaded rod 19 in a clockwise direction
(assuming right-hand threads, and viewing in direction arrow Z).
The rod 19 is prevented from turning, since the friction between
the screw thread and the latch 26 is much higher than that between
the nut 6 and the rod 19. This is mainly because the nut is
unloaded, whereas the rod 19 has the full spring load engaging it
with the latch 26. The rod 19 therefore moves into the nut 6 as far
as the stop face 29. Alternative ways could be used to prevent the
rod 19 from turning, for example using a ratchet or the like, or a
manually operated detent pin. Since the threaded rod is attached to
the tubular member 20, by the interengagement of the thread on rod
19 with the thread 21 on member 20, the latter is also moved
rearwards (i.e. to the right as viewed in FIG. 2), increasing the
compression on spring 24, and thus creates a gap A.sub.1 between
the convex face 22 of the tubular member 20 and the inner face 33
of piston 32. When the rod 19 is fully screwed into nut 6 the stop
pin 31 projects a distance A.sub.2 from face 34 which is equal to
the gap A.sub.1.
[0055] Referring to FIG. 4, nut 6 is now rotated anticlockwise
until it contacts stop pin 31, which locks the nut 6 to the
threaded rod 19. There is now a gap between face 35 on nut 6 and
the abutment face 36, which gap is equal to gap A.sub.1. Continued
rotation of the nut now rotates the threaded rod also, because of
the attachment of the shaft of the pin 31 to the side of the rod
19, and unscrews it in a rearward direction. The face 35 on nut 6
thus moves further away from its abutment face 36 on bridge 25. The
increase in the gap is equivalent to the required stroke of the
piston, and thus the total gap is the sum of the impact gap A.sub.1
and the required stroke. The nut 6 has markings on the perimeter
which are set to a scale on the sliding sleeve 2, in the manner of
a micrometer. The zero stroke indication refers to the position of
nut 6 when it first locks to the threaded rod 19, and immediately
before the threaded rod is rotated to set the stroke.
[0056] The injector is now ready to inject, and referring to FIG.
5, the injector is held in the hand by sliding sleeve 2, and the
orifice 10 is placed on the epidermis 38 of the subject. Force is
applied on the finger stops 37 in the direction of arrow W. The
sliding sleeve 2 compresses spring 15 and moves towards the subject
so that the force is transmitted through spring 14 to the body 1
and thus to the orifice 10, so as to effect a seal between the
orifice 10 and epidermis 38. When the contact force has reached the
predetermined level, the cam 30 on sliding sleeve 2 contacts latch
26 and disengages it from threaded rod 19. The spring 25
accelerates the tubular member 20 towards the piston through the
distance A.sub.1, and the convex face 22 strikes the face 33 of
piston 32 with a considerable impact. The tubular member 20 thus
acts as an impact member or ram. Thereafter the spring 24 continues
to move the piston 32 forward until the face 35 on nut 6 meets the
face 36 on bridge 25. The impact on the piston causes within the
medicament a very rapid pressure rise effectively a shock
wave--which appears almost simultaneously at the injection orifice,
and easily punctures the epidermis. The follow-through discharge of
the medicament is at a pressure which is relatively low but
sufficient to keep open the hole in the epidermis.
[0057] Spring 24 should be given sufficient pre-compression to
ensure reliable injections throughout the full stroke of the ram. A
30% fall in force as the spring expands has been found to give
reliable results. Alternatively, a series stack of Belleville
spring washers in place of a conventional helical coil spring can
give substantially constant force, although the mass and cost will
be slightly higher.
[0058] The embodiment thus described provides an inexpensive,
compact, convenient and easy-to-use disposable needle-less
injector, capable of making sequential injections from a single
cartridge of medicament. The power source is a spring which is
pre-loaded by the manufacturer, and the medicament cartridge is
also pre-filled and assembled into the injector. Thus the user
merely rotates the single adjustment nut and presses the injector
onto the epidermis, and the injection is triggered automatically.
The size and mass of the injector will depend on the quantity of
medicament contained therein, but typically, using a lightweight
aluminium body and thin-walled construction where possible, a 5 ml
injector would be about 135 mm long, 24 mm diameter (nut), with a
mass of about 85 g including fluid.
[0059] It may be desirable to allow the user to select a particular
medicament and actuator combination. For example, a veterinarian
may have a large selection of doses and types of medicament, and
may wish to combine one of these with an actuator that has
characteristics suitable for the animal to be treated. FIG. 7 shows
a modification to the injector to enable the user to install a
fresh cartridge of medicament in the injector body 1. In this
modification there is provided a thread 40 on body 1, and a screwed
retaining cap 39 which clamps the cartridge 3 firmly against the
resilient washer 12. Alternatively the cap 39 may have a bayonet
connection with body 1.
[0060] In the example of the second embodiment thus described the
discharge orifice is shown as being part of the medicament
cartridge. However, there may be occasions when a different nozzle
may be required. For example the epidermis of piglets is vastly
different to that of mature sows, and specially configured nozzles
may be required or in the case of diabetic patients, the patient
may find that a particular nozzle shape gives more comfortable
injections. In a further modification, shown in FIG. 8a and 8b,
there is provided a cartridge 41 containing medicament 9, sealed
with free piston 32 at one end, and having a frangible diaphragm
seal 42 the other. Preferably the diaphragm material should be
tearable and not break into small pieces when ruptured. Body 1 has
a thread 40 on which may be screwed a nozzle 43, which also retains
cartridge 41 within body 1. Nozzle 43 has a piercing tube 44
thereon, so that when the nozzle is first assembled onto the body
1, the piercing tube 44 ruptures the frangible diaphragm 42, making
hydraulic connection with the medicament 9. Sealing of the nozzle
43 to the cartridge 41 is effected by a seal 45. Alternatively
there may be provided a separate nozzle and retaining cap (not
shown) which will serve an equivalent function. The cartridge with
a frangible seal will be less expensive that the cartridge having
an integral nozzle, and this may be important when large numbers of
cartridges are used, as would be the case with insulin for
example.
[0061] The embodiment shown in FIGS. 9a and 9b is a single use
disposable injector. Referring to FIG. 9a, cartridge 3 containing
medicament 9 and free piston 32 is firmly located in the injector
casing 44 and retained by one or more resilient lugs 45, so that
there is no longitudinal free play. A ram 46 is located
concentrically with the cartridge and such that there is an impact
gap A.sub.1 between the adjacent faces of the piston 32 and ram 46.
Ram 46 is urged towards piston 32 by spring 24, but is prevented
from moving by latch 26 supported on flange 18 and engaged with
notch 47 in the stem of the ram 46. Latch 26 is made from a
resilient material, and is configured to apply a bias in the
direction of arrow X. A sliding sleeve 2 is located over the casing
44, with cam surface 30 just touching the bend 53 on latch 26, and
retained on casing 44 by lug 54. Thus the latch 26 acts also as a
spring to bias the sleeve 2 in direction of arrow X relative to the
casing 44. The medicament 9 and orifice 10 are protected by a cap
51 snap fitted to the sliding sleeve 2 as shown, or attached to the
cartridge 3. Distal end 48 of ram 46 is located within aperture 49
in sliding sleeve 2, giving visual and tactile indication that the
injector is loaded and ready for use.
[0062] Referring now to FIG. 9b, to make an injection, cap 51 is
removed and the orifice 10 is placed on the subject's skin 38, with
the axis of the injector approximately normal to the skin.
Sufficient force is applied on sliding sleeve 2 in the direction of
arrow W to overcome the biassing force of the latch 26 on cam
surface 30. The sleeve 2 moves in the direction of arrow W and the
cam surface 30 thus disengages the latch 26 from the notch 47 in
ram 46 which is then rapidly accelerated by spring 24 to strike
piston 32, and the injection is accomplished as previously
described. The point at which the latch 26 disengages from the ram
46 is directly related to the reaction force on the subject's skin,
and by suitable selection of components, accurate and repeatable
placement conditions may be met, ensuring predictable triggering of
the injection. A safety bar 50 on sliding sleeve 2 prevents
accidental disengagement of the latch 26 (by dropping, for
example), and this safety feature may be augmented by a manually
operated detent (not shown) that prevents movement of the sliding
sleeve 2 until operated. In an alternative arrangement (not shown)
the latch 26 may be biassed in the opposite direction to that
described, so that it tries to disengage itself from the notch 47
but is prevented from doing so by a bar on sliding sleeve 2.
Movement of the sliding sleeve 2 and bar permits the latch 26 to
disengage itself from the notch 47, thus initiating the injection:
in this example a separate spring means may be required to bias the
sliding sleeve 2 against the direction of arrow W.
[0063] The embodiment shown in FIGS. 10a and 10b is similar to that
shown in FIGS. 9a and 9b and described above, but modified to
permit the storage of a lyophilized drug and solvent, or other
two-part formulations. FIG. 10a shows a single dose injector,
loaded and ready for use. Free piston 56 is hollow and stores one
component 60 of the medicament--for example a lyophilized
drug--which is retained in piston 56 by frangible membrane 57 which
also separates the drug 60 from its solvent 61 stored in cartridge
3. A membrane cutter 58, which has one or more cutting edge, is
sealingly and slidingly located in piston 56, so that its cutting
edge is a small distance from the frangible membrane 57. Ram 55 is
hollow, and located within its bore is a cutter operating rod 59.
Referring also to FIG. 10b, the rod 59 is pushed in the direction
of arrow W so that it acts on membrane cutter 58. The membrane
cutter 58 cuts membrane 57, thus allowing the solvent 61 to mix
with and dissolve the drug 60. The injector may be agitated to
accelerate the mixing process. Throughout the membrane cutting and
mixing period, protective cap 51 seals orifice 10 to prevent loss
of fluid. After sufficient time has elapsed to ensure thorough
dissolution of the drug, cap 51 is removed, orifice 10 is placed on
the subject's skin, and the injection is accomplished as previously
described.
[0064] Except during the injection, the main reaction forces of the
spring 24 and the latch 26 are taken on the support flange 18.
During the injection, although the shock forces are high, they are
of very short duration, and therefore the body components may be of
very lightweight construction. Thus, although the use of thin metal
tube is described in the embodiments, plastics may be used for most
structural parts because they would not be subject to sustained
forces which could lead to creep and distortion.
[0065] Whilst the shape of the nozzle may be such to achieve
optimum sealing efficiency and comfort, the geometry of the orifice
within the nozzle should have a length to diameter ratio of
preferably not more than 2:1, preferably in the order of 1:2, and
the exit of the orifice should be placed directly onto the
epidermis. It is sometimes necessary to use multiple orifice
nozzles, particularly when dispensing large volumes, and each
orifice in the nozzle should ideally have a maximum L:D ratio of
2:1, preferably 1:2.
[0066] In the embodiments described, the force to move the ram is
provided by a spring, as described, a compression spring) which is
initially in its high energy state (i.e. compressed in the case of
a compression spring). The ram member is moved by permitting the
spring to move to a lower energy state (i.e. uncompressed, or less
compressed, in the case of a compression spring). In contrast, the
embodiment described below with reference to FIGS. 11, 11a and 11b
uses gas under pressure to provide the driving force for the
ram.
[0067] The illustrated embodiment comprises a gas cylinder 101
containing a ram 102 having piston end 104 sealingly and slidingly
fitted into cylinder 101. The ram 102 is guided in a bush 103, and
temporarily retained from longitudinal movement by a spring latch
105 engaged in a detent groove 106. The bush 103 is crimped or
otherwise retained in cylinder 101 so as to withstand forces
created during storage and operation of the injection Which would
otherwise cause the cylinder and bush to separate.
[0068] Gas, such as air, at high pressure, is introduced through a
filling hole 118 into a chamber 117 and sealed by an elastomeric
bung 107. Thus, piston 104 and ram 102 are urged in a first
direction, but retained from movement by the latch 105 engaged in
the detent 106. It is to be noted that the gas in chamber 117
applies pressure directly to the piston and thus exerts a force on
the piston at all times. A cartridge 109 containing drug 110 and a
device piston 108 is firmly fitted into bush 103. An outer case 111
is slidingly fitted over the assembly of cylinder 101 and bush 103,
and restrained from coming off the assembly by one or more
retaining lugs 112. The injector is now ready for use.
[0069] To operate the injector, the drug cartridge is placed on the
subject's skin, and the outer case is pressed in the direction of
the skin. A cam 113 integral with case 111 pushes on latch 105 to
disengage the latch from the detent groove 106 on the ram 102. The
ram 102 is thus able to accelerate rapidly under the action of
pressurised gas in chamber 117 on drive piston 104, and strikes
drivably piston 108 to cause the injection.
[0070] To prevent inadvertent operation, the latch 105 cannot
disengage from the detent 106 until a slot 116 in the wall of the
case 111 is moved in the said first direction when initiating the
injection. A further safety feature (not shown) is a removable plug
which fits into hole 116 and prevents operation of latch 105 until
removed.
[0071] When piston 104 moves in the first direction the air trapped
in the low pressure part of the cylinder 101 is allowed to escape
through a vent 114. When the piston 104 comes to rest, residual
pressurised gas in chamber 117 is allowed to bleed away through a
safety bleed hole 115, which is of small area so as not to
adversely affect the final part of the stroke of the piston 104 as
it uncovers the hole 115.
[0072] As mentioned earlier, the cartridges used in the present
invention are preferably made of glass. In a preferred embodiment
thereof, the forward end of each cartridge has a circular hole of
preferably from 0.15 to 0.3 mm diameter formed therein as the
outlet orifice. The free piston in the cartridge is of a suitably
inert material, and polytetrafluoroethylene (PTFE) is preferred as
the material for the whole or part thereof. PTFE has the advantage
that its coefficients of static and dynamic friction are similar to
one another and extremely low (about 0.01). It also has the
property that it is substantially non-resilient when subjected to a
slowly applied force but is highly resilient when subjected to a
rapidly applied force. This makes it particularly suitable for use
in the context of the present invention, where a rapidly applied
force is exerted on the piston at the time of impact. Other
materials which can be used instead of PTFE, or in combination
therewith, include tetrafluoroethylene-hexafluoropropylene
copolymer, tetrafluoroethylene-ethylene copolymer,
polychlorotrifluoroethylene, poly (vinylidene fluoride),
tetrafluoroethyleneperfluoro(propyl vinyl ether) copolymer, and
hexafluoroisobutylene-vinylidene fluoride copolymer. Yet another
material which can be used is acetal, though this is believed not
to have the resilient/non-resilient property which characterises
PTFE. The initial diameter of the free piston, at least when made
of PTFE, can be greater than the internal diameter of the cartridge
by up to about 0.25 mm. When forced into the cartridge, the creep
of the PTFE is sufficient to allow this, and the resulting seal
between the piston and wall of the cartridge is excellent.
* * * * *