U.S. patent application number 16/510815 was filed with the patent office on 2019-11-07 for microneedle arrays formed from polymer films.
The applicant listed for this patent is TransDerm, Inc.. Invention is credited to Roger L. KASPAR, Tycho Speaker.
Application Number | 20190337197 16/510815 |
Document ID | / |
Family ID | 40342018 |
Filed Date | 2019-11-07 |
United States Patent
Application |
20190337197 |
Kind Code |
A1 |
KASPAR; Roger L. ; et
al. |
November 7, 2019 |
MICRONEEDLE ARRAYS FORMED FROM POLYMER FILMS
Abstract
An active agent can be administered transdermally to a patient
by using a transdermal patch that has microneedles that are
compositionally homogenous with a base layer. The transdermal patch
can contain an active agent that can be delivered to a skin surface
of a subject when the patch is applied.
Inventors: |
KASPAR; Roger L.; (Santa
Cruz, CA) ; Speaker; Tycho; (Santa Cruz, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TransDerm, Inc. |
Santa Cruz |
CA |
US |
|
|
Family ID: |
40342018 |
Appl. No.: |
16/510815 |
Filed: |
July 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13758872 |
Feb 4, 2013 |
10377062 |
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16510815 |
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12187268 |
Aug 6, 2008 |
8366677 |
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13758872 |
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60963725 |
Aug 6, 2007 |
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60994568 |
Sep 19, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29L 2031/7544 20130101;
B81C 1/00111 20130101; B29C 39/42 20130101; A61K 9/0021 20130101;
A61M 2037/0023 20130101; B29C 39/38 20130101; B29C 41/02 20130101;
A61M 2037/0061 20130101; A61M 2037/003 20130101; B29C 41/50
20130101; B29C 2059/023 20130101; A61M 37/0015 20130101; A61M
2037/0053 20130101; A61B 5/685 20130101; B81B 2201/055
20130101 |
International
Class: |
B29C 41/02 20060101
B29C041/02; B81C 1/00 20060101 B81C001/00; A61M 37/00 20060101
A61M037/00; A61B 5/00 20060101 A61B005/00; A61K 9/00 20060101
A61K009/00 |
Claims
1. A method of administering an active agent transdermally
comprising: providing a transdermal patch having a polymer base
layer with microneedles projecting from a surface thereof, wherein
the microneedles are compositionally homogenous with the polymer
base layer, and wherein said transdermal patch contains an active
agent; and applying said transdermal patch to a skin surface of a
subject.
2. The method of claim 1, wherein the active agent is delivered
over a sustained period of time.
3. The method of claim 1, wherein the polymer base layer of the
transdermal patch is removed from the skin surface of the subject
while leaving the microneedles embedded in the skin surface.
4. The method of claim 1, wherein the microneedles continue to
deliver the active agent after the polymer base layer is removed
from the skin surface of the subject.
5. The method of claim 4, wherein the microneedles are hollow.
6. The method of claim 1, wherein the microneedles are solid.
7. The method of claim 6, wherein the active agent is loaded onto
an exterior surface of the microneedles.
8. The method of claim 1, wherein an active agent is included in
the polymer base layer.
9. The method of claim 1, wherein the microneedles are regularly
spaced on the polymer base layer.
10. The method of claim 5, wherein the active agent is loaded into
the microneedles.
11. The method of claim 1, wherein the transdermal patch contains
two or more active agents.
12. The method of claim 1, wherein the active agent is incorporated
into the microneedles.
13. The method of claim 1, wherein the polymer is
bio-absorbable.
14. The method of claim 1, wherein the polymer is
biodegradable.
15. The method of claim 1, further comprising removing said
transdermal patch from the skin surface of a subject.
16. The method of claim 15, wherein the microneedles remain
embedded in the skin surface after removal of the transdermal
patch.
17. The method of claim 1, wherein the polymer base layer has a
thickness from about 0.5 mm to about 5 mm.
18. The method of claim 1, wherein the polymer is selected from the
group consisting of polyvinyl alcohol, polyacrylates, polymers of
ethylene-vinyl acetates, other acyl substituted cellulose acetates,
polyurethanes, polystyrenes, polyvinyl chloride, polyvinyl
fluoride, polyethylene oxide, chlorosulphonate polyolefins,
poly(vinyl imidazole), poly(valeric acid), poly butric acid, poly
lactides, polyglycolides, polyanhydrides, polyorthoesters,
polysaccharides, gelatin, and mixtures and copolymers thereof.
19. The method of claim 1, wherein the active agent is a nucleic
acid.
20. The method of claim 19, wherein the nucleic acid is single
stranded DNA, double stranded DNA, single stranded RNA, double
stranded RNA, or plasmid.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/758,872, filed on Feb. 4, 2013, which is a divisional
of U.S. patent application Ser. No. 12/187,268, filed on Aug. 6,
2008, now U.S. Pat. No. 8,366,677, which claims the benefit of U.S.
Provisional Application Ser. No. 60/963,725, filed Aug. 6, 2007,
and 60/994,568, filed Sep. 19, 2007, the entirety of each of which
is incorporated herein by reference.
BACKGROUND
[0002] This invention relates generally to the field of devices for
the transport of therapeutic or biological molecules into and
across skin tissue barriers, such as for drug delivery.
[0003] Drugs are commonly administered today through either the
oral, parenteral, or transdermal routes of administration. One
great challenge to transdermal administration is poor permeation of
the active agent through the skin. The rate of diffusion depends in
part on the size and hydrophilicity of the drug molecules and the
concentration gradient across the stratum corneum. Few drugs have
the necessary physiochemical properties to be effectively delivered
through the skin by passive diffusion, iontophoresis,
electroporation, ultrasound, chemical permeation enhancers, and
heat (so-called active systems) have been used in an attempt to
improve the rate of delivery. Furthermore, the combination of the
active agent, permeation enhancers, and certain carriers have been
used in order to try and achieve specific delivery profiles over a
desired duration.
SUMMARY
[0004] Accordingly, the present invention provides for transdermal
delivery devices as well as methods for their manufacture and use.
In one embodiment, a transdermal delivery device is provided. The
transdermal delivery device includes a polymer layer which has
microneedles projecting from one of its surfaces. The microneedles
are compositionally homogenous with the polymer base layer.
[0005] In another embodiment, a method for administering an active
agent transdermally is provided. First a transdermal delivery
device is provided. The transdermal device includes a polymer base
layer having microneedles projecting from one of its surfaces. The
microneedles are compositionally homogenous with the base polymer
layer. An active agent is also included in the transdermal delivery
device. The transdermal delivery device is applied to a skin
surface of a subject in order to deliver the active agent to the
subject.
[0006] In yet another embodiment, a method of manufacturing a
transdermal drug delivery device having a microneedle array is
provided. The method involves providing a substrate and then
applying a polymer solution to the substrate to form a base layer.
An exposed surface of the base layer is then disposed with a
textured surface or template having elevated points protruding
therefrom such that the elevated points contact the exposed surface
of the base layer. Exemplary textured surfaces include but are not
limited to arrays of metal pins or points as commonly used in
electronics or as on the surface of an ordinary rasp file. The
textured surface is then distanced from the exposed surface of the
base layer such that the elevated points draw out tube-like
projections from the exposed surface of the base layer. The base
layer and the tube-like projections can be dried to form
microneedle arrays. In some cases, the microneedles can be hollow.
In other embodiments, the microneedles may be solid. The
microneedle arrays can then be cut to form the transdermal drug
delivery device.
BRIEF DESCRIPTION OF DRAWINGS
[0007] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawings will be provided by the Office upon
request and payment of the necessary fee.
[0008] FIGS. 1A-1C show a microneedle array device showing relative
scale. FIG. 1A illustrates a microneedle array shown is supported
by a glass substrate, with a penny to show scale. Highly regular
arrays of hollow, dissolvable microneedles are formed from a
polymer solution film. The array shown has 248 microneedles in an 8
by 31 array, showing 2 or fewer defective needles. FIG. 1B shows a
close-up of the microneedles of an array clearly showing internal
channels in each needle. Solid needles are also possible, by
varying fabrication conditions. Bubbles in the base film are
similar to those believed to cause the hollows during the needle
forming process. The needle tips may be beveled at any angle by
trimming. FIG. 1C shows a needle loaded with fluorescein and under
UV illumination. Microneedle array delivery devices may be formed
with hollow needles suitable for loading with a variety of
materials ("cargo").
[0009] FIG. 2 shows a schematic of a microneedle array preparation.
Needles are prepared from a polymer (e.g. polyvinyl alcohol (PVA))
film by "drawing out," leaving a hollow tube. The ends are clipped
to give desired shape of needle end (and length). The resulting
hollow tubes are "charged" with an active ingredient, such as
nucleic acids (e.g. plasmid or siRNA). The cured (hardened)
microneedle array is inserted into the skin. In the aqueous
environment of the epidermis, the needles soften and deform, and
the inserted portion will separate (leaving the "charged" tips in
the epidermis) as the backing material is removed after an initial
application period. As the PVA solution dissolves, the cargo is
slowly released into the target epidermis.
[0010] FIGS. 3A and 3B show cross-sections of excised human skin
showing penetration by needles loaded with gentian violet. FIG. 3A
shows a microneedle delivery device loaded with gentian violet
solution as a visual reporter ("cargo") and was applied to fresh
human skin explant (resulting from an abdominoplasty procedure) and
then immediately placed into tissue freezing medium (OCT) and
cooled to -28.degree. C. The sample was sectioned at an angle
nearly parallel to the needle array geometry, allowing observation
of multiple needles. The delivery device backing material is
visible as a layer between the OCT and the skin sample. The left
needle is itself cross-sectioned, showing the gentian violet
solution loaded into the needle shaft. The middle needle appears to
penetrate both the stratum corneum and the epidermis, with the
needle tip in full contact with the dermis. A third needle (on the
right) is visible but is out of the focal plane. FIG. 3B shows the
gentian violet delivered to human epidermis and dermis using the
microneedles. The Gentian violet was detected using a fluorescent
microscope under red fluorescence filters (excitation 546 nm;
emission 580 nm). The skin section was stained with DAPI to allow
nuclei visualization.
[0011] FIGS. 4A-4C show in vivo imaging of individual microneedle
penetration sites and visualization in skin sections. FIG. 4A shows
localized fluorescence observed using the Xenogen IVIS 200 system
to view the left mouse footpad of a mouse to which had been applied
a microneedle array loaded with siGLO Red (a fluorescently-tagged
siRNA mimic, 0.05 .mu.g per needle). FIG. 4B shows fluorescence
microscopy of mouse footpad longitudinal skin sections. FIG. 4C
shows fluorescence microscopy of mouse footpad cross sections of
needles loaded with siGLO Red demonstrating delivery to the
epidermis. All sections were stained with DAPI to visualize nuclei
(bar=10 .mu.m).
[0012] FIGS. 5A-5F show several fluorescence microscopy images of
mouse footpad skin sections demonstrating siGLO Red
(fluorescently-labeled siRNA mimic) delivery to the epidermis (or
dermis) following administration using a loaded microneedle array.
FIGS. 5A and 5B show that lateral diffusion dominates the transport
of material outward from the delivery site (.about.90 min
timepoint), with comparatively little red fluorescence visible in
the dermis (bar=20 .mu.m). FIGS. 5C and 5D show that diffusion was
occasionally detected in both the dermis and epidermis (bar=10
.mu.m). FIGS. 5E and 5F where taken 30 min after application and
show that longer needles are able to deliver to the dermis. All
sections were stained with DAPI to visualize nuclei (bar=50
.mu.m).
[0013] FIGS. 6A and 6B show expression of fLuc reporter gene in
mouse ear and mouse footpad administered by a microneedle array
transdermal delivery device. FIG. 6A shows an ear on the right that
was "injected" with a needle array loaded with .about.50 .mu.L fLuc
expression plasmid (10 mg/mL in PBS) per needle. The ear on the
left was "injected" with the STMNA delivery device loaded with PBS
only. Needles were inserted into the ear for 20 min. After 24 h,
luciferase expression was determined following IP luciferin
injection by whole animal imaging using the Xenogen IVIS200 in vivo
system. FIG. 6B shows footpad delivery. Reproducibility of
microneedle array-mediated delivery of fLuc reporter plasmid was
assessed by treating multiple mice. Left footpads were treated with
microneedle arrays (12 needles) loaded with luciferase expression
plasmid. Luciferase expression is observed in the left footpads
following IP administration of luciferin, while right footpads,
which received microneedles loaded with PBS vehicle alone, do
not.
DETAILED DESCRIPTION
[0014] Before particular embodiments of the present invention are
disclosed and described, it is to be understood that this invention
is not limited to the particular process and materials disclosed
herein as such may vary to some degree. It is also to be understood
that the terminology used herein is used for the purpose of
describing particular embodiments only and is not intended to be
limiting.
[0015] In describing and claiming the present invention, the
following terminology will be used.
[0016] The singular forms "a," "an," and "the" include plural
referents unless the context clearly dictates otherwise. Thus, for
example, reference to "a microneedle" includes reference to one or
more microneedles, and reference to "the polymer" includes
reference to one or more polymers.
[0017] As used herein, the term "about" is used to provide
flexibility to a numerical range endpoint by providing that a given
value may be "a little above" or "a little below" the endpoint.
[0018] The term "subject" refers to a mammal that may benefit from
the administration using a transdermal device or method of this
invention. Examples of subjects include humans, and other animals
such as horses, pigs, cattle, dogs, cats, rabbits, and aquatic
mammals.
[0019] As used herein, the term "active agent" or "drug" are used
interchangeably and refer to a pharmacologically active substance
or composition.
[0020] The term "transdermal" refers to the route of administration
that facilitates transfer of a drug into and/or through a skin
surface wherein a transdermal composition is administered to the
skin surface.
[0021] As used herein, the term "substantially" refers to the
complete or nearly complete extent or degree of an action,
characteristic, property, state, structure, item, or result.
[0022] As used herein, sequences, compounds, formulations, delivery
mechanisms, or other items may be presented in a common list for
convenience.
[0023] However, these lists should be construed as though each
member of the list is individually identified as a separate and
unique member. Thus, no individual member of such list should be
construed as a de facto equivalent of any other member of the same
list solely based on their presentation in a common group without
indications to the contrary.
[0024] Concentrations, amounts, and other numerical data may be
expressed or presented herein in a range format. It is to be
understood that such a range format is used merely for convenience
and brevity and thus should be interpreted flexibly to include not
only the numerical values explicitly recited as the limits of the
range, but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. As an illustration, a
numerical range of "about 0.5 to 10 g" should be interpreted to
include not only the explicitly recited values of about 0.5 g to
about 10.0 g, but also include individual values and sub-ranges
within the indicated range. Thus, included in this numerical range
are individual values such as 2, 5, and 7, and sub-ranges such as
from 2 to 8, 4 to 6, etc. This same principle applies to ranges
reciting only one numerical value. Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0025] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill in the art to which this invention belongs. Although
any methods, devices and materials similar or equivalent to those
described herein can be used in the practice or testing of the
invention, representative methods, devices, and materials are
described below.
[0026] As discussed above, the present invention provides
transdermal delivery devices as well as associated methods of
manufacture and use. In one embodiment, a transdermal delivery
device is provided. The transdermal delivery device includes a
polymer layer which has microneedles projecting from one of its
surfaces. The microneedles are compositionally homogenous with the
polymer base layer.
[0027] The polymer which forms the polymeric layer and the
microneedles can be selected from a variety of polymers known in
the transdermal drug delivery arts. In one embodiment, the polymer
can be bio-absorbable or biodegradable. Non-limiting examples
include polyvinyl alcohol (PVA), polyacrylates, polymers of
ethylene-vinyl acetates, and other acyl substituted cellulose
acetates, polyurethanes, polystyrenes, polyvinyl chloride,
polyvinyl fluoride, polyethylene oxide, chlorosulphonate
polyolefins, poly(vinyl imidazole), poly(valeric acid), poly
butyric acid, poly lactides, polyglycolides, polyanhydrides,
polyorthoesters, polysaccharides, gelatin, and the like, mixtures,
and copolymers thereof. In one embodiment, the polymer can be an
adhesive polymer. In a preferred embodiment, the polymer is
polyvinyl alcohol.
[0028] Depending on the type of polymer selected, the concentration
of the polymer used can be varied in order to obtain the desired
microneedle forming properties. In one embodiment, the
concentration of the polymeric solution which is used to form the
polymeric base layer and the microneedles can have a polymer
concentration of from 1 wt % to 50 wt %. In a one embodiment, the
polymer can be polyvinyl alcohol and the concentration in the
polymeric solution can be 20 wt %.
[0029] The microneedles of the microneedle arrays are made from the
same material as the polymer base thereby making them
compositionally homogenous with the polymer base. The microneedles
can be oriented at an angle to the polymer base or they can be
configured to be perpendicular to the polymer base. It is
preferable that the microneedles are oriented perpendicularly to
the polymer base in order to facilitate insertion of the needles
into skin surface by pressure normal to the surface. It is also
possible to produce and provide a microneedle array which has
microneedles with different angular configurations or different
needle lengths. In one embodiment, the microneedles can have a
length of from about 10 m to about 10000 m. In another embodiment,
the microneedles can have a length of from about 50 m to about 1000
m. In another embodiment, the microneedles can have a length of
from about 75 m to about 500 m.
[0030] Depending on the active agent or drug being delivered as
well as the desired length of time of delivery, and the polymer
used to form the microneedles, the microneedles can be configured
to soften or dissolve such that they detach and are left in
embedded in the skin. When the microneedles are configured to be
left in a subject even after removal of the polymer base layer, the
polymer can be a biodegradable or bio-absorbable polymer.
Microneedles which are detached and left embedded in the skin can
provide sustained or extended release of the active agent being
delivered by the needles. In one embodiment, formed needles can be
further loaded by momentarily contacting the needle tips to a
second polymer solution, which may contain an active agent. When
the needles are withdrawn, a residue of the second polymer solution
remains on the tips, or within the tip of the hollow portion of the
needles. If this second polymer solution possesses lower
water-solubility characteristics that differ from the primary
polymer composing the needles, the tip represents a payload that is
deposited when the microneedle detaches in the skin, in a manner
similar to a harpoon tip. The lower solubility of the payload tip
may provide an extended release characteristic if an active agent
is incorporated into the tip polymer.
[0031] The microneedles can be manufactured to be hollow or solid.
When the microneedles are hollow, an active agent or active agent
composition can be loaded into the hollow portion of the
microneedle which can then be delivered by the needle to a subject.
The term "hollow" refers to a region in the interior of the
microneedle having a diameter which is sufficient in size to allow
the passage of liquid or solid materials into or through the
microneedle. The hollow portions of the needle can, but are not
required to, extend throughout all or a portion of the needle. In
one embodiment, the hollow region can have an opening at the tip of
the microneedle. When the microneedles are solid, an active agent
or active agent composition can be loaded onto the exterior surface
of the microneedle. Hollow needles can be potentially loaded with
larger quantities of active agent payload than is possible for
solid needles of the same dimension.
[0032] The microneedle arrays contained in the transdermal devices
of the present invention can be configured to deliver a wide
variety of active agents including active agents intended for
topical, local, and/or systemic delivery. Generally, any drug or
active agent which can be effectively delivered transdermally can
be delivered using the microneedle arrays of the present invention.
In one embodiment, the active agent can be nucleic acid material,
including but not limited to single or double stranded DNA/RNA,
plasmids, or the like.
[0033] The active agents can be loaded or incorporated into the
microneedle arrays in a number of ways. In one embodiment, the
active agent can be loaded into the hollow region of the needle.
Loading into the hollow regions can be done through capillary
action, a pressurized reservoir, or any other means which can be
used without damaging the microneedle array. One method of loading
the hollow needles can be to bring the needle tips into momentary
contact with a solution of an active agent in a volatile material
such as water or ethanol. When the tips touch the surface of an
appropriate liquid, the liquid can wet into the tips by capillary
action, and an aliquot is introduced into only the needle tip,
which is believed will produce the most efficient use of the active
agent, avoiding waste of material in the non-penetrating portion of
the array.
[0034] The active agent can also be incorporated into the
microneedle through incorporation into the polymer solution from
which the microneedle and the polymer base layer are formed. When
the active agent is incorporated into the microneedle in this
manner the active agent is also incorporated into the polymer base
layer. When the active agent is incorporated directly into the
polymer of the microneedle, the microneedles deliver the drug in a
similar manner as the matrix layer in traditional transdermal
matrix patches. However, the microneedles may provide the
additional benefit of providing local disruption of skin barrier
structures, facilitating the entry of drugs which might not
normally penetrate skin in a transdermal matrix patch delivery
system.
[0035] In another embodiment, the active agent(s) can be
incorporated into the microneedle by first loading an active agent
solution onto the protrusions of the textured surface or template
used to draw out the needles from the base layer. In this case, the
active agent(s) are typically observed to be localized in the
needle structure, with little or no migration into the base layer.
A variety of other methods of loading the needles may be apparent
to one of ordinary skill in the art to which this invention
belongs, and these methods may include contact with solutions, or
vapor or powder forms of active agent compositions. Choice of
methods by which needles are loaded may be dictated by the
particular active agents and details of the desired application for
that particular microneedle array product.
[0036] The microneedle arrays can be incorporated into a variety of
transdermal delivery devices such as transdermal patches. In one
aspect of the invention, the polymer base layer of the microneedle
array can be attached to a backing layer to form a transdermal
patch. In another aspect, the polymer base layer can be associated
with or attached to an active agent reservoir from which active
agent can be delivered through the microneedles to a subject. The
reservoir layer can be a liquid reservoir or a hydrogel reservoir
or any other reservoir type known in the arts so long as the
reservoir can adequately deliver the active agent to the
microneedles. Other material may also be incorporated into the
transdermal delivery devices of the present invention such as
permeation enhancers, controlled-release membranes, humectants,
emollients, and the like.
[0037] The microneedle arrays can be used as or incorporated into
transdermal delivery devices to administer active agents
transdermally. The microneedle arrays of the transdermal delivery
devices can be applied to a skin surface of a subject in order to
deliver the active agent to the subject. The administration can be
for a sustained or an extended period of time. Sustained delivery
of the active agent can be accomplished by using microneedle arrays
in which the microneedles can be detached and remain in the skin of
the subject even after removal of the rest of the transdermal
delivery device, including the polymer base layer. Microneedles
left in the skin of a subject act as active agent reservoirs and
can delivery active agent even after the transdermal delivery
device is removed.
[0038] The microneedle arrays used in the transdermal delivery
devices of the present invention can be made in any manner known in
the art so long as they comply with the other requirements set
forth above. One method of manufacturing or forming the microneedle
arrays is provided herein. The method involves providing a
substrate and then applying a polymer solution to the substrate to
form a base layer. An exposed surface of the base layer is then
disposed with a textured surface having elevated points protruding
there from such that the elevated points contact the exposed
surface of the base layer. The textured surface is then distanced
from the exposed surface of the base layer such that the elevated
points draw out hollow tube-like projections from the exposed
surface of the base layer. The textured surface can be made of any
material known in the field and can be configured in any manner
which allows it to contact the base layer and draw out the
microneedle protrusions as described herein. Once drawn out, the
microneedle protrusions can be sharpened or otherwise shaped using
any method known in the art.
[0039] The base layer and the hollow tube-like projections can be
dried to form microneedle arrays. The microneedle arrays can then
be cut to form the transdermal drug delivery device. Methods for
cutting or forming the transdermal drug delivery device are well
known in the art, including but not limited to die cutting or other
physical shearing, thermal melting, thermal degradation, laser
ablation, chemical degradation, dissolution, freeze fracture,
sonication of the template, or any other physical or chemical known
in the art. It is important to note that the manufacture of the
needles can be done in single batch or continuous batch methods.
When a continuous manufacturing method is used, any mechanized
means known in the art can be used. For example, the surface used
to draw out the microneedle protrusions could be a roller having
numerous rows of protrusions which are configured to contact and
draw out the microneedles from the base layer. Other mechanized and
automated manufacturing techniques and technologies used in the
manufacturing arts can be retrofitted and used in the production of
the microneedles of the present invention.
[0040] The substrates used in the manufacture of the microneedle
arrays can be any solid or porous material onto which a polymer
solution can be applied. Non-limiting examples of substrate layers
include glass, backing layer materials including woven and
non-woven material, etc.
[0041] As discussed above, a variety of polymers and polymer
solution concentrations can be used in order to form the
microneedles of the present invention. The polymer solution can be
applied to the substrate in order to form a polymer base layer. The
polymer base layer generally has a thickness from about 0.5 mm to
about 5 mm. In one embodiment, the polymer base layer can have a
thickness of from 0.5 mm to about 2 mm. In on embodiment, the
polymer base layer has a thickness of about 1 mm.
[0042] The textured surface which contacts the exposed surface of
the polymer base layer has raised regions or points which contact
the polymer base layer. The raised regions can be regularly spaced
on the textured surface in order to form regularly spaced
microneedles. The number of raised regions on the textured surface
and correspondingly the number of microneedles formed can be a
factor of the active agent or drug being delivered as well as the
amount or dosage of the active agent. Such a determination could be
made by one of ordinary skill in the art. FIG. 1 shows an array of
microneedles formed using the method described herein from a 30 wt
% polyvinyl alcohol solution.
[0043] The length of the microneedles formed is a function of the
distance that the textured surface is distanced or drawn away from
the polymer base layer. As discussed above, the microneedles can
have a length of from about 10 m to about 10000 m. FIG. 2 shows a
schematic of the drawing process which can be used to form the
microneedle arrays. After the microneedles are drawn or formed, the
polymer base layer and the microneedles of the array can be dried
by baking, blowing, other drying means, or combinations thereof. In
one embodiment, drying of the microneedles and the polymer base
layer can occur during the distancing step in which the
microneedles are formed. It is noted that when loading of the
microneedles occurs after the initial drying it can be desirable to
perform an additional drying or baking step subsequent to the
loading of the needles with an active agent composition. Baking the
needles at about 80.degree. C. for about 1 hour increases their
rigidity, forming microneedles sufficiently rigid to penetrate
through the stratum corneum and into deeper skin layers (FIG. 3).
Use of increased air flow rates, or reduced pressure as in a vacuum
oven may decrease the temperature and curing time required.
[0044] While not wishing to be bound by any particular theory,
generally, the increased needle rigidity required for skin
penetration is understood to be a function of solvent evaporation
rather than a chemical transformation, and any process by which
solvent may be removed is understood to accelerate needle
hardening. Further, it is believed that the shape and structure of
the needles is highly dependent on the dynamics of the drying
process. The length of the needles is directly dependent upon the
distance to which the template is retracted from the surface of the
polymer film base layer from which the needles are pulled. However,
the rate at which the template is retracted and rate at which the
film dries act together to determine the morphology of the needles
formed. If the template is withdrawn too quickly relative to the
drying rate, the strand of polymer solution connecting each
template protrusion may be stretched beyond its capacity to flow
and deform, and the strand may fail, prematurely separating the
template protrusion from the film. If the drying rate is too fast
relative to the rate of retraction, the entire film surface may dry
to form an elastic film rather than an inelastically deformable or
flowable gel. If the film dries sufficiently to behave as an
elastic solid before the template protrusion is completely
withdrawn, the film may tear or separate from the substrate,
producing an unacceptably deformed or non-uniform needle array.
However, between these two extremes, lies a range of acceptable
drying rates relative to any particular rate of retraction of the
template protrusions from the base polymer solution film. In one
embodiment the template can be retracted from the base at a rate of
0.1 mm/s to 100 mm/s with a heated airflow drying the of 0.1 m/s to
10 m/s at a temperature of 0.degree. C. to 100.degree. C. In
another embodiment, the template can be retracted from the base at
a rate of 1 mm to 50 mm/s with a heated airflow drying the of 0.5
m/s to 7 m/s at a temperature of 20.degree. C. to 70.degree. C. In
yet another embodiment, the template can be retracted from the base
at a rate of 2 mm/s to 15 mm/s with a heated airflow drying the of
0.75 m/s to 5 m/s at a temperature of 25.degree. C. to 50.degree.
C.
[0045] When the drying rate of the polymer film is well matched to
the rate of template retraction in the present invention, the base
polymer film remains fluid and inelastically deformable, while the
strands formed between the template protrusions and the base film
dry more quickly than the base layer, and rapidly become inelastic,
which permits longer fiber-like needle structures to be drawn out
of the still wet film. In effect, the drier elastic portion of the
strand plays the role of the template projections relative to the
wetter inelastically deformable base layer. Without being limited
by any particular theory, it is believed that the strands dry more
quickly than the base layer primarily due to a large ratio of
drying surface area versus internal volume, as compared to the base
layer which has a lower drying surface area versus its internal
volume. Additionally, air flow patterns further away from the film
surface may very likely contribute to this effect, particularly if
drying is promoted by flowing air over the needles as they are
formed.
[0046] Any method may be used to promote or control the drying
process, including methods that use air flow, heat or cooling,
pressurization or vacuum, humidity, or any other method familiar to
those skilled in the art of polymer processing. Further, to the
extent that the polymer solution rheology or elasticity may be
influenced by factors other than simple drying, such as
temperature, chemistry, photochemical effects, sonic or vibrational
energy, or other methods known to those skilled in the art of
polymer processing, these methods may also reasonably be applied to
accomplish the same effects in the needle drawing process.
[0047] As the needles are drawn out from the base polymer layer as
described above, it is understood that as the surface of the base
film dries to form an elastic layer, this layer becomes more and
more pulled onto the strands being drawn from the film. If the air
flow is such that the surface of the base layer dries to relative
inelasticity in the last one or two millimeters of the template
withdrawal, it is deformed more substantially in these last
millimeters of withdrawal, to form a wider base. Surprisingly, it
is observed that the formation of this wider base is accompanied by
the formation of a hollow space within the needle. Without being
limited by any particular theory, it is believed that the tension
produced by the withdrawal of the protrusions from the film during
its transition to elastic behavior creates a region of lower
pressure between the drying surface and the wetter solution beneath
the film surface, and that this lower pressure induces evaporation
of some of the water of the solution to form a pocket rich in water
vapor. Independent of the actual cause or contents of the void
area, a hollow needle is the result.
[0048] Another aspect of the incorporation of the drying surface
into the needle base is that if an active agent is distributed only
upon the surface of the polymer solution layer. For example, by
applying a small quantity of a solution of the active agent within
a more volatile material such as ethanol, it is observed that a
disproportionate quantity of the active agent is incorporated into
the base of the needles. This is readily observed by use of a
colored active agent such as fluorescein.
EXAMPLES
Example 1--Production of Microneedle Array
[0049] Microneedle arrays were prepared according to the following
steps:
[0050] 1) A 0.3 gram aliquot of approximately 30% polyvinyl alcohol
[PVA](Spectrum Chemicals, Gardena, Calif.) solution in water was
spread in a uniform thin layer to cover approximately the entire
surface of a standard glass microscope slide (roughly 25 by 75
mm).
[0051] 2) A common rasp-type file was placed with the working
surface facing up on the laboratory bench, and the slide was
lowered PVA-side down, so that the PVA layer was brought into
contact with the file working surface. The slide was then gently
pressed down so as to wet the tips of the file points with the PVA
solution.
[0052] 3) A common hair dryer set to low was used to direct a
stream of approximately 60.degree. C. air flowing at approximately
4 m/s over the file and slide thus assembled from a distance of
about 1 foot, blowing horizontally along the laboratory bench
surface, with the intent to dry and heat the needles as they were
formed.
[0053] 4) Immediately after directing the warm air stream over the
work piece, the slide was carefully removed from the file by
lifting it straight up from the file surface to a height of
approximately 15 mm above the file points. The file was held in
place, so that it was not pulled up by adhesion to the slide. From
each file point, a hollow tube was drawn up from the film surface,
the hollow being formed from a bubble at the needle base,
apparently created or enhanced by the pulling action.
[0054] 5) The slide was kept positioned exactly over the file to
avoid flexion or distortion of the newly formed needle structures,
and the warm air stream was continued for about 10 minutes to dry
the needles and the PVA film from which they had been formed.
[0055] 6) The air stream was stopped, and the needles were cut off
of the file surface by running a standard single-edged razor blade
parallel to the file surface, just above the file rasp tips. The
needles were smoothly and easily sliced just above their point of
contact with the file rasp tips. The rasp tips were spaced such
that a regular array of needles was formed in the film in 8 columns
of 31 rows each, forming 248 needles, of which 2 were either bent
or deformed such that they appeared not useful as needles, and the
remaining 246 needles appeared capable.
[0056] 7) The PVA film was removed from the glass substrate by
sliding a standard single-edged razor blade between the edge of the
film and the glass, which permitted a smooth separation, something
between peeling and slicing the film away from the glass.
[0057] 8) The needles were trimmed to a height of about 3 mm using
a pair of typical cuticle-type scissors purchased from the local
Longs Drugstore. Trimming was performed under an inspection
microscope to facilitate visualization of the small structures, and
the needle tips were cut at approximately 45 degrees to normal, to
form a sharp, beveled tip.
[0058] 9) Needles were loaded with pcDNA3.1 fLuc expression plasmid
(10 mg/ml) at approximately 200 ng/needle in phosphate buffer
solution (PBS) and then baked at 90.degree. C. in a typical
consumer toaster oven with the door open for about 60 minutes, then
cooled for 10 minutes. This baking step was performed to dry and
harden the needles to sufficient rigidity for skin penetration. A
similar control needle array was prepared using the carrier (PBS)
alone.
[0059] 10) The needle arrays (fLuc expression plasmid or PBS
control) were pressed into the ears of an anesthetized (isoflurane)
mouse using finger pressure for approximately 20 minutes at which
time the needle arrays were removed. The mice were allowed to sleep
for an additional 25 minutes.
[0060] 11) After 24 hours, the mouse was administered 100 .mu.l of
30 mg/ml luciferin by intraperitaneal injection. Following a 10
minute incubation to allow biodistribution of the luciferin, the
mice were anesthetized with isoflurane and imaged for 5 minutes
(light emission captured) using a Xenogen IVIS200 imaging system,
which showed unambiguous signal localized at the site of
microneedle administration, demonstrating expression of the
injected plasmid.
Example 2--Manufacture of a Loaded Microneedle Array
[0061] Microneedle arrays of the present invention were prepared as
set forth below:
[0062] 1) A solution of polyvinyl alcohol (PVA) (Spectrum Chemical,
Gardena, Calif.) is prepared by dissolving 19 grams of dry PVA in
81 grams of distilled water (DI) at 80 C for 24 hours, stirring the
thick solution manually every 3 hours after the first 12 hours. The
solution is transferred hot to suitable containers for subsequent
dispensing (such as two 50 mL plastic syringes) and cooled to room
temperature prior to use.
[0063] 2) A solution of Carboxymethylcellulose Sodium solution
(CMC) (Spectrum Chemical, Gardena, Calif.) is prepared by
dissolving 2 grams CMC in 98 grams of DI at 80 C for 24 hours,
stirring continuously on a hotplate/magnetic stirrer. The solution
is transferred to a glass jar with a screw cap and cooled to room
temperature before use.
[0064] 3) An ordinary microscope slide measuring 25 by 75 mm by 1
mm thick is coated with roughly 0.5 grams of the 2% CMC solution
described above by the following method. The microscope slide held
by forceps at one short (25 mm) edge, and dipped into the CMC
solution until roughly 55 mm are below the surface, with 20 mm
remaining unwetted by the CMC. The slide is withdrawn from the CMC
solution and one side is scraped off using a spatula or other
straight edge. The scraped side is then wiped against a laboratory
wipe or other absorbent material to dry and remove the majority of
CMC solution, leaving a roughly cleaned bottom face, with a top
face coated in the CMC solution. The slide is placed on a level
surface in an air stream of 3 m/s at 50.degree. C. until visibly
dry, roughly 15 minutes. The CMC solution is sufficiently fluid to
flow across the surface, producing a roughly uniform coating on the
slide. The dried layer produced by this method serves as a release
layer for the subsequent PVA coating to be applied for needle
formation. The final dried weight of the CMC film is approximately
0.01 g, and the film thickness is apparently thinner than 0.1 mm as
gauged by eye.
[0065] 4) A microscope slide that has been pre-treated with CMC as
described above is coated with PVA preparatory to forming needles
by the following procedure. A roughly 0.75 gram aliquot of an 19%
PVA solution is deposited on one end of a CMC pre-treated
microscope slide, and spread to a thickness of 0.5 mm using a
spatula or similar straight edge. A sufficiently uniform 0.5 mm
layer thickness is produced by the use of two 1.5 mm rails on
either side of the slide. The underlying dry CMC layer thickness is
apparently negligible compared to the thickness of the subsequent
PVA layer, and is not considered in the application thickness of
the PVA layer. The layer produced is roughly 40 by 25 mm wide, and
0.5 mm thick.
[0066] 5) The microscope slide coated with PVA solution described
above is mounted in a chuck or clamped to prevent it from moving.
By means of a motion control device such as a pneumatic actuator, a
template of rigid pins is brought into contact with the PVA
solution to a depth of at least 0.2 mm. Heated air is flowed across
the substrate and pins at approximately 35.degree. C. and 1.0 m/s
and the pins are permitted to remain in the drying film for about 5
seconds and then retracted 1 cm at a rate of about 5 mm/s. About
halfway through the retraction, after 10 seconds, an additional
airflow is introduced at 50.degree. C. and 2.0 m/s. The initial
effect of retracting the pins is to produce stringlike fibers from
the PVA solution. As the PVA solution is pulled from the base layer
by the pins, the airflow dries the thin fibers much more rapidly
than the base layer. However, when the airflow is increased halfway
through, the fibers dry much more rapidly, and the drying region is
understood to be much closer to the base layer, and a thicker fiber
results. Surprisingly, under the conditions described above, this
thicker fiber develops a void, likely due to heated water vapor,
and subsequent retraction of the pins results in formation of a
hollow tube rather than a sealed fiber. If the stronger heated
airflow is initiated too early, the base film dries too quickly and
sheets of PVA film are pulled away rather than discrete fibers,
even to the point of separating from the glass slide. If the
stronger heated airflow is not initiated, hollow fiber formation
does not occur reliably, and the solid form is the typical outcome.
The form of the needles is strongly influenced by the uniformity,
temperature, and rate of air flow, and these must be optimized to
produce reproducible desired results. The values provided here are
exemplar, and any particular apparatus may require slight
adjustments to these parameters.
[0067] 6) The stronger heated airflow is maintained for
approximately 15 minutes until the base PVA layer has dried to a
thickness of approximately 0.1 mm, and is an elastic solid rather
than a liquid. The array is preferably further dried at 25.degree.
C. for 24 hours at approximately 30-50% humidity, and then
separated from the glass substrate by use of a razor blade or
similar sharp implement. The CMC layer permits easy removal by this
method, and prevents the PVA from bonding more permanently to the
glass.
[0068] 7) The array of needles prepared as described above is
separated from the template pin array by slicing the needles with a
razor blade. It is convenient to slice the needles close to the
template pins to leave minimal PVA residue on the pin array, which
may be rapidly cleaned by immersion in water at 80.degree. C. The
needles are then manually trimmed with miniature shear-type
scissors, such as manicure scissors, to produce needles of a
desired length and tip-bevel. After an initial 24 hour 25.degree.
C. drying time, needles and backing material are easily cut, and
very flexible, although resilient. It is easier to cut the needles
before further drying, but not required.
[0069] Steps 8-10 may be included in the original manufacture or
can be performed at a later time.
[0070] 8) Needles may be loaded by bringing the needle tips into
contact with a solution of the desired payload, or any liquid form
of the payload. Lower viscosity (such as ethanolic) 1-100 cSt
solutions are most easily loaded, but higher viscosity up to around
1000 cSt aqueous solutions of macromolecules may also be loaded by
this method. A preferred method of loading individual needles is to
use a plastic dispensing pipette tip or similar, which permits
entry of the needle into the tip, but inhibits the tendency of
solution surface tension to wet across the PVA base layer, and
impedes evaporation of the payload solution from the dispenser.
Multiple needles can be loaded simultaneously by use of multiple
tips spaced at intervals aligned with needle spacing.
[0071] 9) After loading, the PVA matrix forming the needle
structures frequently becomes hydrated and softens. In order to
prepare the needles for use in injecting the payload material,
further drying is required. This drying may be accomplished by
simple heating in an airflow, but to prevent degradation of
sensitive biological molecules it is useful to use a vacuum oven.
Typically 12 hours drying at -20 lbs vacuum and 50.degree. C.
produces highly rigid needles that are useful for injection.
[0072] 10) If the payload in the needles was introduced in aqueous
solution, the sharp tips of the cut needles may be solubilized in
the loading process, and the final dried form may show rounding of
the initially sharp tip. In such case, it is useful to re-trim the
needle tips to produce a freshly cut sharp edge following the final
drying step.
Example 3--Loading Hollow Microneedles with an Active Agent
[0073] Hollow microneedles, such as those formed by the method of
Examples 1 or 2 can be loaded with an active agent. A method of
loading such hollow needles is to bring the needle tips into
momentary contact with a solution of an active agent in a volatile
material such as water or ethanol. When the tips touch the surface
of an appropriate liquid, the liquid can wet into the tips by
capillary action, and an aliquot is introduced into only the needle
tip, which is believed will produce the most efficient use of the
active agent, avoiding waste of material in the non-penetrating
portion of the array. After loading, the needles can be baked at
about 100.degree. C. for about 1 hour to increase their rigidity,
and they have been found to be sufficiently rigid to penetrate
through the stratum corneum and into deeper skin layers.
[0074] When the needles are significantly hydrated, they frequently
soften to a flexible, rubbery state, retaining their basic shape
and orientation, but no longer sufficiently rigid to penetrate
skin. Longer exposure to solvent can potentially deform or dissolve
the needles, but the short exposure to the low volumes used for
loading does not typically produce that result. If the needles are
rubbery after loading, a second dehydration process is required to
produce sufficient rigidity and hardness for skin penetration.
Generally this takes place through baking at around 100.degree. C.
for 1 hour, but it is expected that desiccation by a drying agent,
reduced pressure, or any other process would achieve a similar
effect.
Example 4--Identification of Polymers for Use in Preparing
Microneedles
[0075] Aqueous solution concentrations (10-50% weight/volume or
maximum flowable at 25.degree. C.) of various USP polymer materials
acceptable for parenteral use for fiber-extrusion/draw
characteristics using a standardized air flow of 5 cfm at
50.degree. C. were prepared. Suitability for fiber draw can be
determined by capability of the polymer solution to form a stable,
reproducible nascent fiber structure of at least 1 cm (various
polymers are expected to require different working speeds under
arbitrary conditions, but a suitable candidate material should
exhibit this minimum capability). Polymers to be tested include,
but not limited to, the following: alginic acid,
carboxymethylcellulose, hydroxypropylmethylcellulose, gelatin, guar
gum, gum acacia, polyacrylic acid, polyvinyl alcohol, and
polyvinylpyrrolidone, all available from Spectrum Chemical
(Gardena, Calif.).
Example 5--Identification of Possible Solution Concentrations
[0076] The solutions of Example 3 were tested to determine which of
the solution has the best dry film qualities. Amounts of each of
the solutions can be formed on glass substrates to form films
having 1 mm film thickness over a 25 mm by 75 mm area. The films
are then dried by baking at 90.degree. C. for 1 hour and inspected
for bubble formation, which is an indicator of the relative water
permeability of the drying film surface. The films are then cooled,
and the cooled films are then qualitatively ranked regarding the
following characteristics: difficulty of removal from glass
substrate, ductility, brittleness and stiffness. Any materials that
produce films that are insufficiently rigid to span a 5 cm gap
unsupported can be deemed unsuitable. The films are also
qualitatively ranked by resistance to shear and slice cutting by
standard scissors and by razor blade, providing an indication of
working resistance and film toughness.
Example 6--Testing of the Dissolution of the Films
[0077] Films identified in Example 4 are tested and quantitatively
ranked with regard to their dissolution rate. Materials that
produce films that completely dissolve within 10 seconds are
generally not as desirable. Time to non-rigidity and time to
flowability are recorded as a possible basis for predicting needle
solution dynamics expected after injection.
Example 7--Testing Polymer Solutions for Needle Formation
[0078] Films of each solution are prepared as in Example 4, and
template protrusions (8 columns by 31 rows of points) are contacted
and withdrawn in a standard airflow of 50 cfm at 50.degree. C.,
using a draw speed appropriate to each material as identified in
Example 3. Resulting arrays will be evaluated with respect to
needle dimensions and morphology, with preference given to
straight, tapered, hollow needles with tip cross-sectional area
being approximately 10% of the base cross-sectional area. Candidate
material is selected, based on quality of needle array, further
qualified by dissolution and rigidity characteristics relative to
other materials and by subjective evaluation of
ease-of-workability.
Example 8--Identification of Optimal Needle Formation
Conditions
[0079] Test solutions of 20%, 30%, 40%, and 50% (or maximum
flowable at 25.degree. C.) concentration are prepared for use in
needle drawing as in Example 6 under several airflow conditions
including 1) 50 cfm at 50.degree. C., 2) 100 cfm at 500, and 3) 50
cfm at 80.degree. C. The relative draw speed required for optimal
needle formation under each airflow condition, 5 replicates, is
observed and recorded. This data identifies a rough process
concentration, temperature, and airflow window. Conditions capable
of good needle characteristics with maximum draw speed will be
selected as optimal.
Example 9--Identification of Optimal Pre-Bake Drying Conditions
[0080] Needle arrays as prepared and tested in Example 7 are tested
to identify optimal pre-bake drying times. After drawing, the
arrays are dried in place under airflow identical to the draw
process for various times. Arrays are then be dried at 5, 10, 20,
or 40 minutes under this airflow and separated from glass
substrates. Optimal drying conditions will be identified on the
basis of best substrate removal characteristics.
Example 10--Identification of Optimal Curing Conditions for Loaded
Microneedles
[0081] Microneedle arrays as described in Example 8 are manually
trimmed to 3 mm length, with 2 sets of the 8 columns each trimmed
at nominal tip bevels of 0 (flat), 30, 45, and 60 degrees. Needles
are then loaded with 5 .mu.L ethanolic solution of 2% Gentian
Violet (Spectrum Chemicals) and 5% fluorescein (Spectrum Chemicals)
(approximately 50 nL per needle). Groups of 5 arrays are
pre-weighed, baked at temperature of either 60.degree. C. or
80.degree. C., for 30, 40, 50, 60, or 70 minutes and weighed then
again. Needles are then qualitatively evaluated for rigidity for
each set, with optimal conditions identified as those producing
maximum rigidity with the shortest cure time. Any melting or
discoloration of arrays will cause this bake condition to be
rejected. Rigidity is expected to correlate with moisture loss,
indirectly measured by change in mass. Any needle arrays observed
to be insufficiently rigid are re-cured at the same temperature in
10 minute increments until minimum required rigidity is attained.
Curing temperature and duration are compared in the presence or
absence of a vacuum.
Example 11--Testing of Needle Penetration and Active Agent
Delivery
[0082] Needle array assemblies as described in Example 9 are
applied to human skin explants (resulting from abdominoplasties of
de-identified patients with informed consent) and left in the skin
for 1-60 min. Explants (with or without the needle array) are then
frozen in OCT and sectioned using a Leica Jung Frigocut 2800E
cryotome. Sections are then mounted on microscope slides using
Histomount (Sigma) with DAPI stain for visualization of nuclei.
Sections are analyzed for needle penetration and depostition of
fluorescein and gentian violet by brightfield and fluorescence
microscopy (Zeiss AXIO Observer A. 1).
Example 12--Delivery of Fluorescently-Labeled siRNA Using
Microneedles
[0083] Microneedle arrays are loaded with 10 mg/mL siGLO Red siRNA
(Dharmacon #D001830-02) or Cy3-labeled K6a siRNA in water as
described for fluorescent dyes in Example 9. The loaded microneedle
arrays are applied to human skin and left in the skin for 1-60 min.
Treated explants are frozen in OCT and sectioned (7-10 micron)
using a Leica Jung Frigocut 2800E cryotome. Sections are mounted on
microscope slides using Histomount (Sigma) with DAPI stain for
visualization of nuclei. Sections are analyzed for Cy3 expression
using Zeiss Axio Observer.A1 fluorescence microscope equipped with
the DAPI and DsRed filters.
Example 13--Penetration of Microneedles into Human Skin
[0084] A microneedle array in the transdermal delivery device
loaded with gentian violet solution was applied to fresh human skin
explant (resulting from abdominoplasty procedure) and immediately
placed into tissue freezing medium (OCT) and frozen to -28.degree.
C. The sample was sectioned at an angle nearly parallel to the
needle array geometry, and multiple needles were observed (FIG. 3).
In FIG. 3, the microneedle array transdermal delivery device
backing material is visible as a layer between the OCT and the skin
sample. The left needle is itself cross-sectioned, showing how the
violet solution was drawn into the needle shaft by capillary
action. The needle at picture center of FIG. 3 appears to penetrate
both the stratum corneum and the epidermis, with the needle tip in
full contact with the dermis. A third needle is visible at right
(out of the cut plane) and is apparently penetrating to a similar
depth.
Example 14--Administration of fLuc to a Mouse Ear Using Microneedle
Arrays
[0085] The ear on the right was "injected" with a microneedle array
transdermal delivery device loaded with -50 nL fLuc expression
plasmid (10 mg/mL in PBS) per needle. The left ear was "injected"
with a microneedle array transdermal delivery device loaded with
PBS only to act as a control. The microneedles were inserted into
the ear for 20 min. After 24 h, luciferase expression was
determined following IP luciferin injection by whole animal imaging
using the Xenogen IVIS200 in vivo system. FIG. 4 shows the
expression of fLuc reporter gene in the mouse ear.
Example 15--Fabrication of a Composite Tip Microneedle Array
[0086] A microneedle array was fabricated following a procedure
similar to that of Example 1, omitting step number 7, but otherwise
performing the procedure to step number 8, but not continuing to
step number 9. The microneedles were then momentarily contacted to
a solution of approximately 0.1% gentian violet in 2% aqueous
carboxymethylcellulose, by positioning the entire array of needle
tips to press into an approximately 500 m film of the gentian
violet solution spread on a supporting substrate parallel to the
substrate. Withdrawing the needles was observed to form smaller
"needles upon needles" of the gentian violet solution. Upon drying
as in step 9 of Example 1, these needles were observed to be of
comparable sharpness and rigidity to the needles of Example 1, and
would be expected to have different tip solubility characteristics.
Any of the exemplary polymers presented above are believed to be
suitable for forming such composite tips, which are expected to
show various solubility behaviors under conditions of use.
Example 16--Manufacture of Microneedle
[0087] A polymer coated substrate is contacted with a series of
pins and pins are allowed to remain in the polymer coating for a
period of about 5 seconds while a heated air (35.degree. C.) is
flowed across the substrate at a rate of about 1.0 m/s. The pins
are then retrated from the substrate at a rate of 5 mm/s to a
distance of about 1 cm. About halfway through the retraction
(approximately 10 seconds) an additional airflow is introduced
having a temperature of about 50.degree. C. and a rate of about 2.0
m/s.
[0088] It is to be understood that the above-described methods,
formulations, and experiments are only illustrative of preferred
embodiments of the present invention. Numerous modifications and
alternative arrangements may be devised by those skilled in the art
without departing from the spirit and scope of the present
invention and the appended claims are intended to cover such
modifications and arrangements.
[0089] Thus, while the present invention has been described above
with particularity and detail in connection with what is presently
deemed to be the most practical and preferred embodiments of the
invention, it will be apparent to those of ordinary skill in the
art that numerous modifications, including, but not limited to,
variations in size, materials, shape, form, function and manner of
operation, assembly and use may be made without departing from the
principles and concepts set forth herein.
* * * * *