U.S. patent application number 09/778268 was filed with the patent office on 2001-08-09 for needle for subcutaneous delivery of fluids.
This patent application is currently assigned to Elan Medical Technologies. Invention is credited to Danon, Haim, Gross, Joseph.
Application Number | 20010012926 09/778268 |
Document ID | / |
Family ID | 11041187 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012926 |
Kind Code |
A1 |
Gross, Joseph ; et
al. |
August 9, 2001 |
Needle for subcutaneous delivery of fluids
Abstract
A needle (10) for delivering a liquid to a subject comprises a
shaft (11) having an internal surface defining a longitudinally
extending internal bore having an open end (15) to receive a liquid
supply, the other end (16) being sharpened for penetration of the
subject's skin. A plurality of apertures (18) are provided, each
being a cut extending across the external surface of the shaft side
(11) at a sufficient depth to establish communication with the
bore. The external aperture area is approximately three times
greater than the internal aperture area, thereby ensuring that the
liquid is delivered to a large surface area of tissue to improve
absorption and eliminate fluctuations in delivery rate. The needle
(10) can be mass-produced by aligning a batch of shafts alongside
one another and running a grinder across the shafts' surfaces to
create apertures (18) in the entire batch of needles
simultaneously.
Inventors: |
Gross, Joseph; (Moshav
Mazor, IL) ; Danon, Haim; (Kiryat Ona, IL) |
Correspondence
Address: |
CAESAR, RIVISE, BERNSTEIN,
COHEN & POKOTILOW, LTD.
12TH FLOOR, SEVEN PENN CENTER
1635 MARKET STREET
PHILADELPHIA
PA
19103-2212
US
|
Assignee: |
Elan Medical Technologies
|
Family ID: |
11041187 |
Appl. No.: |
09/778268 |
Filed: |
February 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09778268 |
Feb 6, 2001 |
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09202176 |
Jun 1, 1999 |
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09202176 |
Jun 1, 1999 |
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PCT/IE97/00041 |
Jun 4, 1997 |
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60019714 |
Jun 13, 1996 |
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Current U.S.
Class: |
604/272 ;
604/132 |
Current CPC
Class: |
A61M 5/2046 20130101;
A61M 5/3291 20130101; A61M 5/2053 20130101 |
Class at
Publication: |
604/272 ;
604/132 |
International
Class: |
A61M 005/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 1996 |
IE |
960427 |
Claims
1. A needle for the delivery of a liquid to a subject, comprising a
shaft having an internal surface defining a longitudinally
extending internal bore open at one end thereof to receive a liquid
supply, the other end of the shaft being sharpened for penetration
of the skin of the subject, the shaft being provided with at least
one aperture in the form of a cut extending across the external
surface of the side of the shaft at a sufficient depth to establish
communication with the bore, wherein the external aperture area is
greater than the internal aperture area, said areas being defined
by the surface areas of the material removed between the external
and internal surfaces of the shaft, respectively.
2. A needle according to claim 1, wherein the sharpened end of the
needle is in the form of a bevelled or conical tip and the aperture
is formed by a linear cut made at an angle to the internal bore
which is greater than or equal to the angle between the bevelled or
conical surface and the longitudinal bore.
3. A needle according to claim 1 or 2, wherein the cut extends in a
direction approximately perpendicular to the longitudinal bore.
4. A needle according to any preceding claim, wherein the width of
the cut on the external surface of the shaft is greater than the
width of the cut on the internal surface of the shaft.
5. A needle according to claim 4, wherein the width of the cut on
the external surface of the shaft is at least twice the width of
the cut on the internal surface of the shaft.
6. A needle according to any preceding claim, wherein the shaft has
a C-shaped cross section at the locus of the aperture, defined by
the partial circumferences of the internal and external shaft
surfaces and by the aperture surfaces formed by the cut which
connect the internal and external shaft surfaces, said aperture
surfaces being co-planar.
7. A needle according to any preceding claim, wherein the shaft is
provided with a plurality of said apertures, each of which is
located a different distance from the sharpened end of the
needle.
8. A needle according to any preceding claim, wherein the ratio
between the external aperture area and the internal aperture area
is greater than or equal to the ratio between the external width of
the shaft and the internal width of the bore.
9. A needle according to any one of preceding claim, wherein the
depth of the cut relative to the external surface varies along the
length of the cut.
10. A needle according to claim 9, wherein the depth of the cut
increases from zero at either end of the cut to a maximum depth
towards the centre of the cut which is greater than or equal to the
thickness of the wall of the shaft at that point.
11. A needle according to claim 9, wherein the variation in the
depth of the cut results from a planar cut surface machined across
a curved external surface.
12. A needle according to any preceding claim, wherein the
sharpened end is provided with a terminal orifice to assist in
delivery of the liquid through the needle.
13. A needle according to any preceding claim, wherein the or each
aperture is formed by the operation of a grinder on the surface of
the shaft.
14. A needle according to any preceding claim, wherein the or each
aperture is formed by milling.
15. A needle according to any preceding claim, wherein the external
and internal surfaces of the needle are defined generally in
cross-section by two concentric circles.
16. A method of manufacturing a plurality of delivery needles,
comprising the steps of arranging a plurality of tubular shafts
having internal bores in a row in parallel with one another and
performing a machining operation across the row of shafts to create
at least one aperture in the external surface of the side of each
shaft at a sufficient depth to establish communication with the
bore of each shaft.
17. A method according to claim 16, wherein the machining operation
includes running a grinder across the row of shafts to grind a line
of grooves across the surfaces of the shafts, the grooves being
sufficiently deep to provide communication between the external
surfaces of the shafts and the internal bores of the shafts.
18. A method according to claim 17, wherein the process also
comprises the step of sharpening the shafts while they are arranged
in a row.
19. A liquid delivery device for delivering a liquid to a subject,
comprising a reservoir for the liquid, means for driving the liquid
from the reservoir to an outlet, and a delivery needle according to
any one of claims 1-15 in communication with the outlet.
20. A device according to claim 19, wherein the reservoir and
driving means are located in a housing which is provided with means
for attachment to the skin of the subject and wherein the delivery
needle protrudes from the housing in use such that it penetrates
the skin of the subject upon application of the device to allow
delivery of the liquid through said needle.
21. A device according to claim 19 or 20, wherein the delivery rate
of the device is calibrated according to the pressure exerted by
the driving means.
22. A needle for the delivery of a liquid to a subject,
substantially as hereinbefore described with reference to and as
illustrated in FIGS. 1-3, 4-8, 9-10 and 11-12 of the accompanying
Drawings.
23. A method of manufacturing a plurality of delivery needles,
substantially as hereinbefore described with reference to and as
illustrated in FIGS. 9-10 and 11-12 of the accompanying
Drawings.
24. A liquid delivery device, substantially as hereinbefore
described with reference to and as illustrated in FIG. 13 of the
accompanying Drawings.
Description
TECHNICAL FIELD
[0001] This invention relates to needles for the delivery of
liquids to human or animal subjects.
BACKGROUND ART
[0002] The standard needle used for subcutaneous or intramuscular
injections is in the form of a hollow shaft provided with a
sharpened open end. This type of needle has been found to be
unreliable in ensuring accurate delivery rates, in particular when
used in conjunction with an infusion pump or some other delivery
device which depends for delivery on the magnitude of pressure
applied to the liquid being delivered.
[0003] The lack of accuracy is thought to be due to the build up of
pressure at the delivery point which opposes the driving pressure
applied to the liquid.
[0004] Others have tried to combat the problem by designing needles
which were intended to avoid the problem of pressure build up
arising from the orifice becoming plugged by tissue on entry into
the skin.
[0005] U.S. Pat. No. 4,413,993 (Guttman), U.S. Pat. No. 4,790,830
(Hamacher), and U.S. Pat. No. 4,838,877 (Massau) each disclose a
hypodermic or intravenous delivery needle having one or more
apertures located on the side of the shaft removed from the
sharpened tip.
[0006] U.S. Pat. No. 2,748,769 (Huber) discloses a hypodermic
needle having a curved or bent tip cut in a plane that extends
along the side of the needle towards which the bend is made and
thereby providing an orifice which is not plugged by tissue upon
insertion into a subject, the curved surface being provided with an
auxiliary delivery orifice which ensures delivery when the main
orifice rests against a vein wall.
[0007] U.S. Pat. No. 3,076,457 (Copen) discloses a hypodermic
needle having an aperture at the tip and also having an opening
which extends along the side of the shaft for part of its
length.
[0008] None of these needles provides a satisfactory solution to
the problem of ensuring accurate delivery using a delivery device
in which the delivery rate depends on the generation of pressure,
because in each case, the problem which has been addressed has been
the provision of an additional orifice which will not become
plugged upon insertion or which will not rest against a vein wall.
While these problems must be addressed in designing a needle for
use with an automated drug delivery device, it has been found that
these factors alone do not account for the major variations in
delivery rate which occur when using a device which depends for
delivery on pressurising a supply of drug.
[0009] It has been found, when conducting tests of devices which
operate on the pressurised reservoir principle, that there are
large variations in the resistance to delivery into the skin not
only when comparing different subjects or different delivery sites
on the same subject (which could be accounted for by differences in
tissue composition at the delivery site), but also when the
resistance to delivery is monitored over time during a single test
at a single site.
[0010] If the resistance to delivery (i.e. the impedance to the
flow of drug) varies while the pressure effecting delivery remains
fixed, then clearly the delivery rate (which is dependent on the
difference in pressure between the reservoir and the delivery site)
will fluctuate. Clearly this has serious implications for the
delivery accuracy of such devices.
[0011] The best results in subcutaneous delivery tests of this type
are obtained when using a needle such as that disclosed by Huber or
by Copen (see above), wherein the aperture has a greater external
surface area than internal surface area. Without wishing to be
bound by any theoretical explanation, it is conjectured that the
major obstacle to ensuring accurate delivery rates is not that the
orifice becomes plugged, but rather that the difficulty arises from
poor absorption by the tissue adjacent to the orifice(s), and/or
from variations in the structure of the tissue at the orifice. This
means that the drug accumulates at the orifice and the pressure
builds up until absorption commences, since a given surface area of
tissue can only absorb a certain amount of drug at a given
pressure. In cases where the external aperture surface area is
increased relative to the internal aperture surface area, the
absorption (by a larger tissue area) is correspondingly better and
fluctuations are reduced.
[0012] Nevertheless, it is not practicable to replace conventional
delivery needles with needles of the type disclosed by Huber or
Copen because of the substantial difference in manufacturing cost
involved. A conventional delivery needle can be formed by cutting
hollow steel tubing to the correct length, and grinding or in some
other way machining the cut end to provide the necessary sharpness
for skin penetration. The thus formed tip is of course
automatically provided with a delivery orifice, and the needle is
inexpensive.
[0013] In order to manufacture a needle of the type disclosed in
any of the prior art documents referred to above, the initial steps
of creating a needle must first be followed, and then the
additional holes or orifices must be machined into the side of the
needle. In the case of small diameter needles such as needles
having an external diameter of less than 0.7 mm and an internal
diameter of less than 0.45 mm (approximately 22 gauge or higher),
this is a relatively complicated task when compared to the
preceding steps.
[0014] The orifice may have to be created by laser drilling a hole
at the correct point, by pressing a revolving disc cutter against
the curved surface of the Huber needle, or by removing a
quarter-cylinder length from the side of the shaft in the case of
the Copen needle (no indication is given by Copen as to how one
would go about creating the type of aperture disclosed). In all
cases, the operations require careful positioning of the needle
relative to the machining means, and a delicate machining of each
and every needle. The magnitude of the cost differential between
such needles and conventional needles arises from the differences
between the complexity of the manufacturing processes involved in
each type of needle.
[0015] It is an object of the present invention to provide a needle
which has improved delivery characteristics when connected to an
infusion system, and which can be manufactured cheaply and easily
in large numbers at the same time unlike the prior art needles
referred to above.
DISCLOSURE OF INVENTION
[0016] Accordingly, the invention provides a needle for the
delivery of a liquid to a subject, comprising a shaft having an
internal surface defining a longitudinally extending internal bore
open at one end thereof to receive a liquid supply, the other end
of the shaft being sharpened for penetration of the skin of the
subject, the shaft being provided with at least one aperture in the
form of a cut extending across the external surface of the side of
the shaft at a sufficient depth to establish communication with the
bore, wherein the external aperture area is greater than the
internal aperture area, said areas being defined by the surface
areas of the material removed between the external and internal
surfaces of the shaft, respectively.
[0017] Because the or each aperture is in the form of a cut
extending across the shaft, rather than a section removed along the
length of the shaft or a hole drilled into or through the shaft (as
in the prior art), the needle according to the present invention is
far easier to manufacture. It is as easy to manufacture a large
number of identical needles (by extending a cut across a plurality
of shafts at the same time) as to form a cut in a single
needle.
[0018] Additionally, the or each aperture thus formed has a larger
external surface area than internal surface area, so that the
needle delivers drug to a large area of tissue, thereby increasing
the capability of absorption. The improved delivery characteristics
of the needle will be illustrated below. In all needles where a
hole is drilled into the surface of the needle, the external
surface area (as defined above) is in fact less than the internal
surface area due to the greater curvature of the internal
surface.
[0019] Suitably, the sharpened end of the needle is in the form of
a bevelled or conical tip and the aperture is formed by a linear
cut made at an angle to the internal bore which is greater than or
equal to the angle between the bevelled or conical surface and the
longitudinal bore.
[0020] In a presently preferred embodiment, the cut extends in a
direction approximately perpendicular to the longitudinal bore.
[0021] This allows the aperture(s) to be formed at exactly the same
distance from the needle tip in a batch of needles by aligning the
ends of a row of parallel adjacent needles and machining a groove
or cut across the surface of the row, to form a series of identical
apertures in the aligned needles.
[0022] Suitably, the width of the cut on the external surface of
the shaft is greater than the width of the cut on the internal
surface of the shaft. Preferably, the width of the cut on the
external surface of the shaft is at least twice the width of the
cut on the internal surface of the shaft.
[0023] It is preferred to maximise the external width of the cut
relative to the internal width of the cut, so as to maximise the
ratio between external and internal aperture areas.
[0024] According to a preferred embodiment, the shaft has a
C-shaped cross section at the locus of the aperture, defined by the
partial circumferences of the internal and external shaft surfaces
and by the aperture surfaces formed by the cut which connect the
internal and external shaft surfaces, said aperture surfaces being
co-planar.
[0025] Such a cross-section can be obtained by manufacturing the
needles as described in detail below.
[0026] Preferably, the shaft is provided with a plurality of said
apertures, each of which is located a different distance from the
sharpened end of the needle.
[0027] The provision of a plurality of apertures increases the area
of tissue to which the needle can deliver. Additionally, the
apertures can be spaced along the length of the shaft to provide
more delivery sites. If a single aperture is provided on a needle,
all of the tissue at the aperture may have poor absorption. By
increasing the number of apertures, the probability that at least
one aperture will deliver to a site with improved absorption is
maximised.
[0028] Preferably, the ratio between the external aperture area and
the internal aperture area is greater than or equal to the ratio
between the external width of the shaft and the internal width of
the bore. In general, this provides a substantially larger external
aperture surface area.
[0029] Preferably, the depth of the cut relative to the external
surface varies along the length of the cut. Further, preferably,
the depth of the cut increases from zero at either end of the cut
to a maximum depth towards the centre of the cut which is greater
than or equal to the thickness of the wall of the shaft at that
point.
[0030] In a preferred embodiment, the variation in the depth of the
cut results from a planar cut surface machined across a curved
external surface. Nevertheless, it is also possible to provide a
curved machined cut across the external surface.
[0031] Suitably, the sharpened end is provided with a terminal
orifice to assist in delivery of the liquid through the needle.
[0032] Preferably, the or each aperture is formed by the operation
of a grinder on the surface of the shaft. Alternatively, the or
each aperture is formed by another machining operation such as
milling (although grinding is at present preferred due to lower
costs and the fact that it is not as likely to give rise to
difficulties such as chips being produced by the operation.
[0033] Preferably, the external and internal surfaces of the needle
are defined generally in cross-section by two concentric circles.
There is no strict necessity to use a circular needle with a
circular bore, however, other than the fact that the tubing for
such a needle is readily and cheaply available.
[0034] The invention also provides a method of manufacturing a
plurality of delivery needles, comprising the steps of arranging a
plurality of tubular shafts having internal bores in a row in
parallel with one another and performing a machining operation
across the row of shafts to create at least one aperture in the
external surface of the side of each shaft at a sufficient depth to
establish communication with the bore of each shaft.
[0035] It will be appreciated that this operation can be carried
out on scores or hundreds of needles simultaneously. The
manufacture of a batch of 200 needles according to the invention
can be completed in only a few seconds. To carry out the
manufacture of 200 of the prior art needles referred to above, on
the other hand, would take 200 times the length of time required to
carry out the machining operation for one needle, which does not
include the additional time involved in positioning each successive
needle in the correct position for machining.
[0036] Preferably, the machining operation includes running a
grinder across the row of shafts to grind a line of grooves across
the surfaces of the shafts, the grooves being sufficiently deep to
provide communication between the external surfaces of the shafts
and the internal bores of the shafts.
[0037] Optionally, the process also comprises the step of
sharpening the shafts while they are arranged in a row.
[0038] In addition, the invention provides a liquid delivery device
for delivering a liquid to a subject, comprising a reservoir for
the liquid, means for driving the liquid from the reservoir to an
outlet, and a delivery needle according to the invention in
communication with the outlet.
[0039] Suitably, in such a device, the reservoir and driving means
are located in a housing which is provided with means for
attachment to the skin of the subject and wherein the delivery
needle protrudes from the housing in use such that it penetrates
the skin of the subject upon application of the device to allow
delivery of the liquid through said needle.
[0040] Preferably, the delivery rate of the device is calibrated
according to the pressure exerted by the driving means. By
incorporating the needle according to the invention, such a device
is freed from the variations and fluctuations in delivery rate
which have otherwise been found to exist.
[0041] The invention will be further illustrated by the following
description of embodiments thereof, given by way of example only
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0042] FIG. 1 is a sectional elevation of a first embodiment of a
needle according to the invention;
[0043] FIG. 2 is a first perspective view of the needle of FIG.
1;
[0044] FIG. 3 is a second perspective view of the needle of FIG.
1;
[0045] FIG. 4 is a sectional elevation of a second embodiment of a
needle according to the invention;
[0046] FIG. 5 is a first perspective view of the material removed
to create the apertures in the needle of FIG. 4;
[0047] FIG. 6 is a second perspective view of the material removed
to create the apertures in the needle of FIG. 4;
[0048] FIG. 7 is a cross-sectional elevation of the needle of FIG.
4 at the locus of one of the apertures taken along the line VII-VII
in FIG. 4;
[0049] FIG. 8 is a front elevation of the needle of FIG. 4;
[0050] FIG. 9 is a plan view of a batch of needles during a step in
the manufacturing process;
[0051] FIG. 10 is a side elevation of one of the needles shown in
FIG. 9;
[0052] FIG. 11 is a front elevation of a third embodiment of a
needle according to the invention;
[0053] FIG. 12 is a plan view of a batch of needles similar to the
needle of FIG. 11, shown during a step in the manufacturing
process;
[0054] FIG. 13 is a sectional elevation of a drug delivery device
according to the invention;
[0055] FIG. 14 is a graph illustrating the variation in pressure
opposing delivery during a test of a known drug delivery device;
and
[0056] FIG. 15 is a graph illustrating the variation in pressure
opposing delivery during a test of a drug delivery device according
to the invention.
MODES FOR CARRYING OUT THE INVENTION
[0057] In FIG. 1 there is indicated, generally at 10, a needle
according to the invention. The needle 10 comprises a shaft 11
having an external surface 12 and an internal surface 13 which
defines a longitudinally extending internal bore 14.
[0058] The bore 14 is open at one end 15 to receive a supply of
drug for delivery (for example by connection to a drug pump or a
syringe) and the other end 16 of the needle is also open and is
sharpened with a bevelled tip 17 to penetrate the skin of a
subject.
[0059] The shaft 11 is provided with three identical apertures 18
spaced at intervals from the tip 17. The apertures 18 permit
communication between the internal bore 14 and the exterior of the
needle 10. Communication between the bore 14 and the exterior of
the needle 10 is also facilitated by a terminal orifice 19 at end
16 of the shaft.
[0060] Referring additionally to FIGS. 2 and 3, the needle 10 can
be seen in perspective views which show shaft 11, tip 17, apertures
18 and orifice 19. FIG. 3 illustrates the particular shape of the
apertures 18, each of which can be seen to be in the form of a cut
which extends across the shaft 11. The external surface area of
each aperture is approximately three times that of the internal
surface area of each aperture, thereby increasing the area of
tissue which is presented to each aperture upon penetration into
the skin of a subject.
[0061] Similar apertures can also be seen in FIG. 4, in which a
second embodiment of needle according to the invention, indicated
generally at 20, is shown. Needle 20 is identical to needle 10
(FIGS. 1-3) apart from the shape of the sharpened end 21 and from
the fact that the side of the needle is provided with five rather
than three apertures 22.
[0062] In needle 20, the sharpened end 21 is closed, i.e. the
internal bore 23 is only open at the top 24 of the needle 20 and at
the apertures 22. The number of apertures can be chosen to suit the
delivery rate which is required and the site into which the shaft
25 is to be inserted. A needle inserted into an area of tissue
which is rich in capillaries or into a vein will not require as
many apertures as a needle inserted into a site which is deficient
in blood vessels or a site at which the number of blood vessels
varies over small distances.
[0063] FIG. 5 illustrates the shape of the apertures 18,22 in the
needles 10,20 of FIGS. 1-3 and 4 by showing the shape of the
material 30 which is removed to give rise to the apertures 18,22.
FIG. 6 shows the material 30 from the opposite direction from which
it is viewed in FIG. 5. In comparing the two views it can be seen
that the surface area 31 (FIG. 5) of material removed from the
exterior surface 12 (see FIG. 1) of the needle is considerably
larger than the surface area 32 (FIG. 6) of material 30 removed
from the internal surface 13 (FIG. 1). This relates directly to the
area of tissue which is presented to the apertures 18,22 for
absorption of the liquid delivered in use.
[0064] Referring to FIG. 6, the end surface 33 of the material 30
is in a plane which makes an angle of 45.degree. with the plane of
the cut surfaces 34,35 which bridge what were originally the
interior and exterior surfaces of the shaft. This angled surface
assists in the insertion of the needle into the skin of the
subject, and it also serves to further increase the external
aperture surface area.
[0065] In FIG. 7, the shaft 25 of the needle 20 of FIG. 4 is viewed
in cross-section at the locus of one of the apertures 22. It can be
seen from this view that the shaft has a C-shaped cross-section at
this point defined by the partial external circumference 36 of the
shaft 25 at this point, the partial internal circumference 37 of
the shaft 25 at this point, and the co-planar cut surfaces 38,39
which are complementary to the cut surfaces 34,35 visible in FIG.
6.
[0066] For the purposes of clarity, FIG. 8 shows needle 20 in a
front elevation, from which the large external surface area of the
each aperture 22 is clearly visible. The aperture area is increased
by virtue of surface 40 (which is complementary to surface 33 in
FIG. 6) being angled at 45.degree. to the plane of the cut surfaces
38,39.
[0067] The method of manufacture of needles according to the
invention can be understood with reference to FIG. 9, which shows a
plurality of identical needles 50 aligned adjacent and parallel to
one another. The needles are clamped into this position and the
apertures in the sides of the needles are formed by machining a cut
across the row of needles using a cutting tool such as a grinder
51. Dotted lines 52 illustrate the path of the grinder, and
referring additionally to FIG. 10, the shape of the aperture 53
formed in a needle 50 can be equated with the path of the grinder
51. The bevelled tips 54 of the needles can be cut either before or
after the apertures are cut, or the tips can be cut at the same
time as the apertures, taking advantage of the fact that the
needles are already aligned and clamped into position.
[0068] In FIG. 11, there is indicated, generally at 60, a third
embodiment of needle according to the invention. In this
embodiment, apertures 61 are formed by machining a row of cuts
across the needle at an angle equal to the bevelled angle of the
tip 62. Dotted lines 63 indicate the parallel paths of the cutter
which creates the bevelled tip 62 and the apertures 61.
[0069] Referring additionally to FIG. 12, it can be seen that a
plurality of needles 60 can be aligned adjacent to and parallel
with one another but laterally displaced, and the ends 64 of the
needles 60 can be bevelled by cutting the needles along this row
(the path of the cutter again being indicated by dotted line 63.
The apertures 61 (FIG. 11) can then be cut along a parallel path
while the needles 60 are aligned as shown.
[0070] In FIG. 13, there is indicated, generally at 70, a liquid
delivery device according to the invention, which is suitable for
use as an automated drug delivery device. The device 70 comprises a
housing 71 containing a reservoir 72 which is filled with a drug by
injection into a filling port 73 sealed with a self-sealing plug
74. Reservoir 72 communicates with a delivery needle 75 identical
to the needle 10 illustrated in FIG. 1.
[0071] The housing 71 also houses a gas generation chamber 76
containing an electrolyte which generates a gas when a pair of
electrodes 77 is energised by power supplied by a battery 78.
Chamber 76 is separated from reservoir 72 by a displaceable
membrane 79 such that when the electrodes 77 are energised to
generate a gas, the chamber 76 expands and thereby forces membrane
79 downwards to expel the liquid contained in reservoir 72 out of
needle 75. Upon termination of delivery (when the reservoir 72 has
emptied) or in the event of a blockage, a diaphragm 80 is forced
upwards by the increased pressure in chamber 76 to lift a
conductive element 81 bridging a pair of contacts 82, thereby
breaking the circuit which is used to energise the electrodes.
[0072] The housing 71 is provided with a displaceable cover 83
provided with a snap mechanism 84 which allows it to snap between a
first position as shown (wherein the needle 75 is concealed) and a
second position wherein the cover 83 lies against the lower surface
85 of the housing 71. Two additional snap mechanisms (not shown)
are located at 120.degree. intervals around the periphery of the
(circular) housing 71 and cover 83. The cover 83 is provided with a
release liner 86 which is removed before use to reveal an adhesive
surface on the bottom of the cover 83.
[0073] In use, the release liner 86 is removed and the cover 83 is
placed against the skin of the subject (to which it adheres), and
the housing 71 is then pressed against the skin causing the cover
83 to snap towards the housing and thereby projecting the needle 75
into the skin of the subject. Needle 75 projects into the skin by 5
mm in this embodiment, and the apertures 18 lie approximately
2.5-4.5 mm below the surface of the skin. The battery 78 is
energised by a start button (not shown) and delivery commences as a
result of the generation of gas.
[0074] Because the subcutaneous (resistive) pressure, i.e. the
impedance to flow of the drug, is reduced as a result of the needle
design, the liquid can be pumped into the skin at a constant rate,
with less expenditure of energy than when a conventional needle is
used. The device shown is a relatively simple embodiment, and it
will be appreciated that the invention is in no way limited to this
device; in particular, more sophisticated devices in which the
delivery rate can be varied would benefit from the incorporation of
a needle according to the invention. Alternatively, the device
could utilise a driving means other than the generation of gas by
an electrolytic cell, and the skilled person will be aware of a
wide range of automated drug delivery devices in which the delivery
rate is dependent at least in part on the pressure opposing
delivery through a prior art needle.
[0075] In FIG. 14, there is plotted a series of measurements of
pressure opposing delivery from a device according to the invention
operating on the same delivery principle as the device of FIG. 13,
but in which a conventional bevelled delivery needle was used. The
pressure measurements are plotted in centimeters of water (10 cm
H.sub.2O=981 Pa), and the measurements were carried out over a
period of approximately seven hours using a pressure transducer
which transmitted the measured subcutaneous pressures to a data
logging apparatus. A series of 15 tests was carried out using a
standard delivery needle with six different volunteers, and it can
be seen that the pressure measurements fluctuated considerably. The
standard pattern followed is a steady build-up of pressure followed
by a sudden release, and this occurs to a greater or lesser extent
in the various tests. What this means in terms of drug delivery,
therefore, is that although the device is attempting to pump drug
at a constant rate, the subject receives a series of bursts of
drug.
[0076] In FIG. 15, one can see the results obtained when the same
test was repeated, except that a device according to the invention
was used (i.e. having a needle as illustrated in FIG. 1). The
fluctuations were practically eliminated indicating that the needle
caused the liquid to be absorbed constantly without building up at
the delivery site. Whereas the peak pressures experienced in the
tests illustrated in FIG. 14 were in many cases between 200 and 400
cm H.sub.2O (approximately 20-40 kPa or 0.2-0.4 atm), the tests in
FIG. 15 show that in all cases the pressure remained below 50 cm
H.sub.2O (approximately 5 kPa or 0.05 atm) and generally was less
than 25 cm H.sub.2O (approximately 2.5 kPa or 0.025 atm). In each
case, the tests were carried out on healthy adult volunteers under
controlled clinical trial conditions to ensure comparability and
reliability of results for evaluation of the invention.
* * * * *