U.S. patent application number 11/119485 was filed with the patent office on 2005-11-10 for method of forming a mold and molding a micro-device.
This patent application is currently assigned to Becton, Dickinson and Company. Invention is credited to Lastovich, Alexander G..
Application Number | 20050247666 11/119485 |
Document ID | / |
Family ID | 30114489 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050247666 |
Kind Code |
A1 |
Lastovich, Alexander G. |
November 10, 2005 |
Method of forming a mold and molding a micro-device
Abstract
A method of forming a device including a plurality of micron or
sub-micron sized features is provided. A master having a surface
contour defining a plurality of features is provided. The surface
contour of the master is coated with at least one layer of material
to form a shell. The master is removed from the shell to form a
negative image of the surface contour in the shell. The negative
image in the shell is filled with material, for example,
polycarbonate, polyacrylic, or polystyrene, to form a device having
features substantially the same as the master. The negative image
may be filled using injection molding, compression molding,
embossing or any other compatible technique.
Inventors: |
Lastovich, Alexander G.;
(Raleigh, NC) |
Correspondence
Address: |
DAVID W. HIGHET, VP AND CHIEF IP COUNSEL
BECTON, DICKINSON AND COMPANY
1 BECTON DRIVE, MC 110
FRANKLIN LAKES
NJ
07417-1880
US
|
Assignee: |
Becton, Dickinson and
Company
Franklin Lakes
NJ
|
Family ID: |
30114489 |
Appl. No.: |
11/119485 |
Filed: |
April 29, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11119485 |
Apr 29, 2005 |
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10193317 |
Jul 12, 2002 |
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6899838 |
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Current U.S.
Class: |
216/52 |
Current CPC
Class: |
B29L 2031/756 20130101;
B29C 33/3842 20130101; B81B 1/006 20130101; B29C 2793/0045
20130101; B29C 33/42 20130101; B29C 2045/0094 20130101; B29L
2031/7544 20130101; A61B 17/205 20130101; B29C 45/0055
20130101 |
Class at
Publication: |
216/052 |
International
Class: |
B44C 001/22 |
Claims
I claim:
1. A method of forming a mold for a micro-device including an array
of microfeatures, comprising: providing a master having a surface
contour which includes skin penetration features; wherein said
surface contour of said master is formed by micro-machining;
covering the surface contour with a layer of material; removing the
master from the layer of material to form a negative image of the
master in the layer of material wherein the negative image is
fillable by a flowable process; filling the negative image
fluidically with a flowable material to form a device having
substantially the same features as the master; solidifying said
flowable material; and separating said device from said negative
image.
2. The method of claim 1, further comprising, coating the master
with a release film, before the covering of the surface contour, to
facilitate removal of the master.
3. The method of claim 1, further comprising, etching to remove the
master.
4. The method of claim 3, wherein the etchant is hydroxide.
5. The method of claim 1, wherein the layer of material is a
metal.
6. The method of claim 1, wherein the layer of material is
nickel.
7. The method of claim 1, wherein the master is sacrificed during
its removal.
8. The method of claim 1, wherein the negative image has at least
one structural feature of about 5 microns to about 250 microns in
one dimension.
9. The method of claim 1, wherein the negative image defines
recesses having a depth from its surface of about 5 microns to
about 250 microns.
10. The method of claim 9, wherein the recesses are arranged in an
array of uniformly spaced rows and columns to provide a density of
about 1 to about 100 of the recess per mm2.
11. The method of claim 1, wherein the master is formed from
silicon.
12. The method of claim 1, further comprising: individually forming
portions of the master from silicon; and connecting the portions
into a complete master.
13. The method of claim 1, wherein the layer of material is formed
via sintering.
14. The method of claim 1, wherein the layer of material has a
thickness of about 0.01-0.2 inches.
15. A method of forming a device including a plurality of micron or
sub-micron sized features, the method comprising: providing a
master having a surface contour defining skin penetration features;
coating the surface contour of the master with at least one layer
of sinterable material; sintering said sinterable material;
removing the master from the layer of material to form a negative
image of the surface contour in the layer of material; forming a
mold insert from the negative image; filling the negative image
fluidically with a flowable material to form a device having
substantially the same features as the master; and separating said
device formed from said flowable material from the negative
image.
16. The method of claim 15, wherein the filling step further
comprises filling by injection molding.
17. The method of claim 16, wherein the injection molding is done
at a vacuum.
18. The method of claim 15, further comprising drilling holes in
the features of the device to form hollow micro-needles.
19. The method of claim 15, wherein the layer of material is at
least 0.07 inches thick.
20. The method of claim 15, wherein the layer of material is about
0.01 to about 0.2 inches thick.
21. The method of claim 15, further comprising, coating the master
with a release film, before the covering of the surface contour, to
facilitate removal of the master.
22. The method of claim 15, further comprising, etching to remove
the master.
23. The method of claim 15, wherein the layer of material is a
metal.
24. The method of claim 15, wherein the layer of material is
nickel.
25. The method of claim 16, further comprising removing residual
air during the injection molding.
26. The method of claim 15, further comprising forming vents in the
mold insert.
27. The method of claim 15, wherein the negative image is filled
with a polymer.
28. The method of claim 15, wherein the negative image is filled
with one of polyethylene, polypropylene, acrylic, cyclic olefinic
copolymers, polyamide, polystyrenes, polyester and
polycarbonate.
29. The method of claim 18, wherein the drilling is performed via
lasers.
30. The method of claim 15, wherein the master is formed by
micromachining.
31. The method of claim 15, wherein the filling step further
comprises: filling the negative image with a flowable powdered
metallic material; and sintering the powdered metallic material to
form the micro-device.
32. The method of claim 15, wherein the master is formed from
silicon.
33. The method of claim 32, further comprising: individually
forming portions of the master from silicon; and connecting the
portions into a complete master.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 10/193,317
filed Jul. 12, 2002, which is herein incorporated by reference in
its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of manufacturing a
device, and particularly, a micro-device. More particularly, the
invention is directed to a method of forming a mold for a
micro-device and molding a micro-device for medical use.
BACKGROUND OF THE INVENTION
[0003] There has been an increase in interest in processes for the
manufacture of small devices in the field of biological and
biochemical analysis. The manufacture of devices used for
analytical testing uses techniques similar to those used in the
electronics industry. Examples of these manufacturing techniques
include photolithography and wet chemical etching. The devices are
often made from solid substrates such as silicon and glass.
[0004] Microanalytical devices have been used for performing
various analytical reactions. For example, U.S. Pat. No. 5,498,392
to Wilding et al. discloses a mesoscale device having
microfabricated fluid channels and chambers in a solid substrate
for the performance of nucleic acid amplification reactions. U.S.
Pat. No. 5,304,487 to Wilding et al. discloses a mesoscale device
having a cell handling region for detecting an analyte in a sample.
The microchannels and chambers have a cross-sectional dimension
ranging from 0.1 micron to 500 microns. U.S. Pat. No. 5,885,470 to
Parce et al. discloses a microfluidic transport device made from a
polymeric substrate having fluid channels that can be a few microns
wide.
[0005] There has also been an increased interest in microneedle
injection for the transdermal delivery of various drugs. The
microneedle devices can have a plurality of microneedles with a
length of a few hundred microns. One example of a microneedle
device for delivering a drug to a patient is disclosed in U.S. Pat.
No. 5,879,326 to Godshall et al.
[0006] Microneedle drug delivery devices are able to penetrate the
stratum corneum of the skin with less irritation. The stratum
corneum is a complex structure of compacted keratinized cell
remnants having a thickness of about 10-30 microns and forms a
waterproof membrane to protect the body from invasion by various
substances and the outward migration of various compounds. The
delivery of drugs through the skin is enhanced by either increasing
the permeability of the skin or increasing the force or energy used
to direct the drugs through the skin.
[0007] One method of delivering drugs through the skin is by
forming micropores or cuts through the stratum corneum. By
penetrating the stratum corneum and delivering the drug to the skin
in or below the stratum corneum, many drugs can be effectively
administered. The devices for penetrating the stratum corneum
generally include a plurality of micron size needles or blades
having a length to penetrate the stratum corneum without passing
completely through the epidermis. Examples of these devices are
disclosed in U.S. Pat. No. 5,879,326 to Godshall et al.; U.S. Pat.
No. 5,250,023 to Lee et al.; and WO 97/48440.
[0008] These devices are usually made from silicon or other metals
using etching methods. For example, U.S. Pat. No. 6,312,612 to
Sherman describes a method of forming a microneedle array using
MEMS technology and standard microfabrication techniques. Although
effective, the resulting microneedle devices are expensive to
manufacture and are difficult to produce in large numbers. Thus,
there have been recent efforts to form micro-devices from
polymers.
[0009] The '612 patent to Sherman also describes a method of
forming micro-devices from a polymer. A mold base having a number
of micropillars extending therefrom is formed by
microelectrode-discharge machining or by photolithographic
processing. A thin layer of polymer is arranged on top of the
micropillars. The layer of polymer is heated so it deforms around
the micropillars, forming micro-devices. The
microelectrode-discharge machining or photolithographic processing
used to form the mold are time consuming and expensive
processes.
[0010] U.S. Pat. No. 6,331,266 to Powell et al. describes a process
to form a molded micro-device from polymers. In particular Powell
et al. describe a method for forming a micro-device from plastic by
injection molding, compression molding, or embossing. The method of
Powell et al. focuses on forming the micro-device from a mold, and
not the creation of the mold itself.
[0011] U.S. Pat. No. 5,250,023 to Lee et al. describes a polymer
micromold and fabrication process for the mold. A mold assembly
with micro-sized features is formed. The mold assembly has a hollow
portion that is fabricated from a sacrificial mandrel. The mandrel
is surface-treated and coated to form an outer shell. The mandrel
is then etched away leaving the outer shell as the mold. The
process described in Lee et al. can only produce a singular hollow
mold at a time. The mold created is used in conjunction with
polymer extrusion in which polymer is passed through the hollow
mold.
[0012] The prior methods and apparatus for the manufacture of
micro-devices for medical use have exhibited some success but are
generally time consuming and expensive. For example, the process of
Lee et al. can only form a mold for a singular device. Accordingly,
a continuing need exists in the industry for an improved method for
the manufacture of micro-devices.
SUMMARY OF THE INVENTION
[0013] The present invention is directed to a method of
manufacturing devices, such as, micro-devices for medical and other
uses. The method and apparatus of the invention are suitable for
molding plastic devices having micron and submicron features. The
medical micro-devices are devices having channels, needles, points
or other structural features having dimensions ranging from less
than 1 micron to several hundred microns in length or width.
Examples of micro-devices that can be molded in accordance with the
present invention include analytical microchannel devices,
microneedles, pipettes and the like. Analytical microchannel
devices, for example, can include microchannels having a diameter
ranging from about 0.5 microns to about 500 microns.
[0014] In one embodiment of the invention, the micro-device is used
for penetrating or abrading the stratum corneum of the skin and for
the transdermal delivery of a substance, such as a drug or
pharmaceutical agent, through the abraded area. The device includes
a plurality of microprotrusions for abrading and preparing a
delivery site on the skin to enhance the delivery of a substance
through the stratum corneum of the skin to a sufficient depth where
the substance can be absorbed and utilized by the body.
[0015] According to an exemplary embodiment of the invention, a
method of forming a mold for a micro-device including an array of
micro-features is provided. A master or original micro-device
having a surface contour is provided. The surface contour of the
master is coated with a layer of material, the layer preferably
having a thickness of at least about 0.01-0.2 inches and preferably
0.07 inches or greater. The master is removed from the layer of
material to form a negative image of the master in the layer of
material. The negative image may then be used in a molding process
to form a positive image having features that are substantially the
same as the features of the master.
[0016] In one embodiment of the invention, the master is sacrificed
when it is removed from the layer of material. For example, the
master may be removed by etching. In another embodiment, the master
is coated with a release layer, before being coated with the layer
of material. The release layer facilitates removal of the master
from the negative image, preserving the master unharmed.
[0017] According to another embodiment of the invention, a method
of forming a device including a plurality of micron or sub-micron
sized features is provided. A master having a surface contour
defining a plurality of features is provided. The surface contour
of the master is coated with at least one layer of material to form
a shell. The master is removed from the shell to form a negative
image of the surface contour in the shell. The negative image in
the shell is substantially filled with material, for example,
polycarbonate, acrylic (cyro 1-40) LCP, cyclic olefinic copolymers
(COC), polystyrene, or other suitable structural plastic, to form a
device having features substantially the same as the master. Of
course, other types of materials may be used to fill the shell. The
negative image may be filled using injection molding, compression
molding, embossing or any other compatible technique.
[0018] In a further embodiment, the shell defines recesses having a
depth of about 5 microns to about 250 microns. The recesses may be
arranged in an array of uniformly spaced or non-uniformly spaced
rows and columns or other patterns, including random patterns, to
provide a density of about 1 to about 100 of the recess per
mm.sup.2. The shell is a negative or reverse image for molding the
features of the master, where the master can have recesses or peaks
on its surface contour ranging from about 0.5 micron to several
hundred microns in length.
[0019] The advantages and other salient features of the invention
will become apparent from the following detailed description which,
taken in conjunction with the annexed drawings, discloses preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The following is a brief description of the drawings, in
which:
[0021] FIG. 1 is a perspective view of a microabrader surface one
the embodiment of the invention;
[0022] FIG. 2 is a partial cross-sectional view of the
microabrader;
[0023] FIG. 3 is a top view of the microabrader in the embodiment
of FIG. 1 showing the tips of the microprotrusions;
[0024] FIG. 4 is a negative image formed according to one
embodiment of the invention;
[0025] FIG. 5 is a magnified view of the negative image of FIG. 4;
and
[0026] FIG. 6 is an exploded perspective view of a mold and mold
member for molding a microprotrusion device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] The present invention is directed to a method of
manufacturing a micro-device, such as a medical device, having a
plurality of micron or submicron size features. In one embodiment
the micro-device is a microabrader device for preparing the skin
for transdermally administering a substance to a patient or
withdrawing a substance from the body of a patient. The method of
this embodiment is able to form a mold for a device having a
plurality of micron size features, such as a microabrader device.
The device is molded from a polymeric material. The molding method,
such as injection molding, is able to produce a high volume of the
devices with micron or submicron size features in an inexpensive
manner and with a high degree of consistency. The mold is able to
withstand repeated use and the high pressures of the molding
process.
[0028] The molds formed by the method of the invention are
preferably used to mold devices that have micron or submicron size
details integrally molded therein. Examples of micro-devices that
can be molded by the method of the invention include medical and
analytical devices having micron size channels, conduits or
capillaries, surgical needles, prosthetic devices, implants and the
like. The method and molding apparatus are particularly suitable
for the molded medical devices having channels, recesses, needles,
protrusions or other structural elements having at least one
dimension ranging from about 0.5 micron to about 500 microns. The
illustrated embodiment relates to a microprotrusion device for
abrading the skin, although it will be understood that the
invention is not limited to microabrader or microprotrusion devices
and can be used to mold a variety of devices.
[0029] The microabrader devices made by the method of the present
invention are particularly suitable for use in preparing skin for
administering a pharmaceutical agent to a patient or withdrawing a
substance intradermally from a patient. As used herein, a
pharmaceutical agent includes a substance having biological
activity such as antibiotics, antiviral agents, analgesics,
anesthetics, anorexics, antiarthritics, antidepressants,
antihistamines, anti-inflammatory agents, antineoplastic agents,
vaccines (including DNA vaccines), and the like. Other substances
that can be delivered intradermally to a patient include naturally
occurring, synthesized or recombinantly produced proteins, peptides
and fragments thereof. Substances and agents withdrawn from the
body include analytes, drugs, glucose, body electrolytes, alcohol,
blood gases, and the like. The above substances are not meant to be
an exhaustive list and other substances suitable for delivery or
withdrawal will be apparent to those skilled in the art.
[0030] In one embodiment of the invention, the method is directed
to the manufacture of a microabrader for preparing the skin, and
particularly the stratum corneum, for enhancing the delivery of a
substance transdermally to a patient or for sampling various agents
from the patient. The microabrader device is moved or rubbed on the
skin to abrade and remove at least a portion of the stratum
corneum. An active or passive drug delivery device or sampling
device as known in the art is applied over the abraded area. As
used herein, the term microabrader refers to a device that can
abrade the skin to increase the permeability of the skin without
causing unacceptable skin irritation or compromising the skin
barrier to infectious agents.
[0031] In the illustrated embodiment shown in FIGS. 1 and 2, the
microabrader device 10 made by a method according to an embodiment
of the present invention includes a substantially planar body or
support 12 having a plurality of microprotrusions 14 extending from
the bottom surface of the support. The dimensions of the support 12
can vary depending on the length of the microprotrusions, the
number of microprotrusions in a given area and the amount of the
substance to be administered to the patient. Typically, the support
12 has a surface area of about 1-4 square centimeters (cm.sup.2).
In preferred embodiments, the support surface 12 has a surface area
of about 2 cm.sup.2.
[0032] As shown in FIGS. 1 and 2, the microprotrusions 14 are
integrally formed and attached to the surface of the support 12 and
extend substantially perpendicular to the plane of the support 12.
The microprotrusions 14 in the illustrated embodiment are arranged
in a plurality of rows and columns and are substantially spaced
apart a uniform distance. The microprotrusions 14 in this
embodiment have a generally pyramidal shape with sides 16 extending
to a tip 18. The sides 16 as shown have a generally concave surface
when viewed in cross-section and form a curved surface extending
from the support 12 to the tip 18. In the embodiment illustrated,
the microprotrusions are formed by four sides 16 of substantially
equal shape and dimension. As shown in FIGS. 2 and 3, each of the
sides 16 of the microprotrusions 14 have opposite side edges
contiguous with an adjacent side and form a scraping edge 22
extending outward from the support 12. The scraping edges 22 define
a generally triangular or trapezoidal scraping surface
corresponding to the shape of the side 16. In further embodiments,
the microprotrusions 14 can be formed with fewer or more sides.
Alternatively, the microprotrusions can be conical or cylindrical,
with conical or pointed tips. Additionally, the microprotrusions
can be arranged on the support 12 in a non-uniform manner.
[0033] The microprotrusions 14 shown terminate at blunt tips 18.
Generally, the tips 18 are substantially flat and parallel to the
support 14. Each tip 18 preferably forms a well defined, sharp edge
20 where it meets the sides 16. The edge 20 extends substantially
parallel to the support 12 and defines a scraping edge. In further
embodiments, the edge 20 can be slightly rounded to form a smooth
transition from the sides 16 to the tip 18.
[0034] The micro-devices, such as the microabrader device 10 and
the microprotrusions 14 can be made from a plastic material that is
preferably non-reactive with the substance being administered and
that can be used in various molding processes, and particularly
injection molding. Suitable plastic materials include, for example,
polyethylene, polypropylene, acrylic, cyclic olefinic copolymers
(COC), polyamides, polystyrenes, polyesters and polycarbonates,
filled or un-filled and copolymers thereof as known in the art.
Preferred polymers include COC and an acrylic available from CYRO
under the trade name L40. The length and thickness of the
microprotrusions are selected based on the particular substance
being administered and the thickness of the stratum corneum in the
location where the device is to be applied. The microprotrusions
can have a length of about 5 microns up to about 250 microns. The
microprotrusions in the illustrated embodiment have a generally
pyramidal shape and are perpendicular to the plane of the device.
The microprotrusions can be solid or hollow members.
[0035] As shown in FIGS. 2 and 3, the microprotrusions 14 for
microabrader 10 are typically spaced apart uniformly in rows and
columns to form an array. Typically, the rows of microprotrusions
are spaced in rows to provide a density of about 1 to about 10 per
millimeter (mm) and provide a needle density of about 1 to about
100 needles per mm.sup.2, although the molding method of the
described embodiment enables the spacing to be varied as
needed.
[0036] In one embodiment, the micro-devices of the invention are
manufactured by injection molding. An injection molding process for
micro-devices is described in U.S. Pat. No. 6,331,266 to Powell et
al. and is incorporated herein by reference. The molding method
described in Powell et al. uses a mold member having a positive
image of the device being manufactured. The mold member is filled
with a polymeric material to form a reverse or negative image of
the micro-device. The method of forming mold member having a
negative image according to the present invention can be combined
with the injection molding process described in Powell et al. to
form high quality micro-devices in an efficient manner.
[0037] In order to form the negative or reverse image used in the
molding process, a positive image is first needed. A master, for
example an original of a micro-device, provides the positive image.
The master is essentially an example of the desired finished
product. For example, the master in the described embodiment is
microabrader 10. As shown in FIGS. 1 and 2, the microabrader 10 has
a surface contour that defines its features, such as the
microprotrusions 14. The surface contour of the microabrader 10 is
preferably a contour of an outer or exterior surface. In general,
the master can have any shape or geometry. The microabrader 10 used
as a master is typically made from silicon. The master microabrader
can be made using techniques used to shape and form silicon
surfaces, for example, photolithography and wet etching methods
that are substantially the same as known by those skilled in the
art for producing electronic components. The silicon microabrader
can also be made using various micromachining processes that
typically use a micron-size diamond milling machine.
[0038] Additionally, techniques are provided for forming devices
that are not easily formed in silicon. A pattern that is not easily
formed in silicon to provide for edges arranged in un-symmetric
patterns may be formed by dividing patterns that are easy to form
in silicon into several sections. These sections are placed
together, such as glued together, to form the desired pattern. For
example, it is not easy to etch a rotational pattern in which the
edges of the protrusions are arranged to substantially face in a
circular pattern in silicon due to the crystal lattice structure of
the silicon. To overcome this limitation, the rotational structure
may be formed in sections, similar to pieces of a pie, that are
glued together to form the complete rotational pattern. This
complete pattern can then be used as the positive image. Thus, it
is possible to form a complete plastic version of a pattern that
cannot be formed complete in silicon. Other examples include
circular rings of protrusions arranged in tiers of varying heights
from a base, among others.
[0039] In order to form the negative image of the master, here
microabrader 10, the surface contour of the microabrader 10 is
covered with at least one layer of material. The layer of material
preferably does not cover interior surfaces of the
microabrader.
[0040] Although in some instances this may be desirable. The layer
of material creates a shell defining the negative image of the
microabrader 10. The layer of material can be provided over the
outer surface contour of the microabrader 10 via a plating process.
The layer of material may be formed from any metallic or other
suitable material. However, nickel is preferable since it has a
similar coefficient of expansion to that of steel which makes it
easy to use at the elevated temperatures present in molding
applications. When the layer of material comprises nickel, it may
be deposited over the master using Nickel Composite Tooling (NCT),
a plating technique. NCT is a trade name for a commercial process
available from Vintage Industries.
[0041] In another embodiment of the invention, the layer of
material can be provided over the outer surface contour of the
microabrader 10 via a sintering process. The master is coated with
a powdered metallic material, for example by immersing the master
in the powdered material. The powdered material is then sintered to
form the shell.
[0042] The shell is preferably formed at least about 0.01-0.2
inches thick and preferably about 0.07 inches or greater. A thick
shell provides a more robust negative image that can withstand the
high pressures generated during the subsequent molding process. A
thick shell also produces a mold with a longer working life.
Additionally, the thickness of the shell is chosen such that the
back of the shell can be machined to provide a generally flat
surface to mate with the cavity of the mold thus eliminating the
need to epoxy the shell into the mold.
[0043] After the layer of nickel or other material is applied to
the master, the master is removed from the layer of material
leaving a negative image of the master in the nickel shell. There
are several different ways in which the master can be removed from
the nickel layer. For example, the master can be removed by
etching, in which case the master is sacrificed during removal.
Alternatively, the master can be coated so that the master releases
from the shell substantially intact. The master can then be used to
create other negative images. For example, in a master with no
undercut, the mold cavity off the first master can be plated (for
example, electroforming or electroless-forming) to make a metal
master Multiple molds may then be created off this new master
allowing multiple cavities off the same silicon chip.
[0044] In some instances, even if a coating is provided on the
master, some of the master may remain in recesses defined by the
negative image. These remaining portions should be removed in order
for the negative image to produce faithful replicates of the
master. Thus an etching process, for example, KOH etching, may be
performed to remove the layer of the material from the shell
without damaging the underlying material, which in the embodiment
described, is nickel.
[0045] An example of a shell 30 defining a negative image of an
array of microprotrusions is shown in FIG. 4. The negative image in
the shell 30 defines a cavity, i.e., a mold cavity. The mold cavity
can be of any geometry or shape, as long as a master can be formed.
A master used to form microabrader 10 as described above typically
includes microprotrusions 14 spaced apart uniformly in rows and
columns to form an array. Typically, the rows of microprotrusions
are spaced in rows to provide a density of about 1 to about 10 per
millimeter (mm) and provide a needle density of about 1 to about
100 needles per mm.sup.2. Accordingly, the negative image includes
an array of recesses 32 that correspond the microprotrusions 14 on
the master microabrader 10. The recesses 32 have dimensions and a
density corresponding to that of the microprotrusions 14 on the
master. FIG. 5 is view of a single recess 32 for a microprotrusion
which show the high quality of the negative image attained by the
above-described process.
[0046] After the shell 30 is formed, it may undergo additional
processing before it is used as a mold. Gate features, venting
accesses, and sprue may be cut for the molding process.
Additionally, modifications may be made to add geometry to the
shell if desired. Features that are not present in the master, such
as edge bevels, can also be added.
[0047] After the shell is formed and processed, it can be used as a
mold to form micro-devices, here microabraders, by injection
molding. FIG. 6 shows a portion of a mold used during the injection
molding process. Only one half of the mold is shown in FIG. 6,
although another half of the mold is used during the molding
process, as is well-known the one of ordinary skill in the art. As
shown in FIG. 6, the shell 30 is attached to a mold section 52 in a
recess 66 by a suitable coupling device or a heat resistant
adhesive, such as an epoxy adhesive. In an alternative embodiment,
a screw or other fastener is used to secure the shell 30 in place.
The shell 30 placed against the surface of the mold section 52 and
secured in place. Typically, the shell 30 is attached to a face of
a bottom wall (not shown) of the recess 66. In further embodiments,
the shell 30 can be attached to a side wall 67 of the recess. The
shell 30 has a generally square shape complementing the shape of
the recess 66 and generally extends between the side walls 67 of
the recess 66 in the embodiment illustrated. In further
embodiments, the shell 30 can have a dimension less than the
dimension of the bottom wall. An upper face of the shell 30 defines
a surface 76 for forming and shaping the micro-device. The surface
76 of the shell 30 is contoured in the form of an impression of the
finished molded article. As described above, the surface 76 of the
shell 30 can have at least one recess, ridge or peak having a width
and/or height ranging from about 0.5 micron to about 500 microns
depending on the device being molded. In the embodiment
illustrated, the surface 76 of the shell has a plurality of
recesses 32, as shown in FIG. 5, corresponding to the desired shape
and dimensions of the microprotrusions for a microabrader device.
When molding a microprotrusion device, the recesses can have a
depth of about 5 to 250 microns and spaced to provide a density of
about 1 to 100 recesses per mm.sup.2. Accordingly, the surface 76
of the shell 30 is the reverse or impression of the molded
micro-device. In one embodiment, the shell 30 has a thickness of
about 0.01-0.2 inches thick and preferably about 0.07 inches or
greater.
[0048] After being appropriately mounted in the molding apparatus,
an injection molding process can be performed to make the
micro-device, for example, the process described in U.S. Pat. No.
6,331,266 to Powell et al. During the injection molding process,
the mold cavity is filled with a material, such as acrylic, COC,
polyamides, polystyrenes, polyesters or polycarbonates as known in
the art, to form the micro-device, i.e., microabrader. Either hot
or cold runners may be used to during the injection molding
process.
[0049] Due to the microstructure of the mold cavity, the recesses
of mold cavity are not always completely filled during the
injection molding process. Residual air can be present in the mold
cavity, forming air bubbles and preventing the fill material from
completely filling the recesses in the mold. The residual air in
the mold cavity should be removed during injection molding in order
to form the highest quality devices. Accordingly, the injection
molding can be performed under vacuum to remove any residual air in
the mold and to allow the polymer or other fill material to
completely enter the recesses of the mold. Additionally, the tips
of some or all of the peaks and recesses of the mold cavity may be
provided with a vent to allow the residual air to escape or other
venting procedures may be used to improve the filling of the
recesses. The venting procedures may be used independent from or in
conjunction with the vacuum processing.
[0050] FIG. 6 illustrates an example of a mold provided with vents.
A surface 80 of mold section 52 is provided with a number of vents
78. Here, the mold section 52 is comprised of a metal and the vents
78 are very slight indentations in the surface 80. The vents may be
formed by scraping away a very thin layer of the surface 80. The
vents 80 should be sized such that residual air may escape from the
recess 66, but the material used to fill the recess 66 does not
substantially enter the vents 80.
[0051] The molded device can also be made using other molding
processes. For example, a micro-device can be made by embossing a
thermoplastic substrate with a mold or platen. The mold is provided
with the impression of the desired molded micro-device. The device
is formed by pressing the mold under pressure against the plastic
substrate that has been heated to its softening temperature.
Alternatively, the mold is heated and pressed against the
thermoplastic substrate to mold the device.
[0052] In further embodiments, the device is formed by a
compression molding method. In the compression molding method, a
thermoplastic material, such as a powdered material, is placed in a
hollow mold having a molding surface. The mold is closed and the
powdered thermoplastic is compressed under high pressure and heated
to melt and consolidate the powder particles. The molded device is
then removed from the mold.
[0053] In another embodiment, the device is formed using a
sintering process. In the sintering process, a powdered metallic
material is placed in the hollow mold having the mold surface. The
powdered metallic material substantially fills the hollow mold.
Sintering is then performed to form a metallic device.
[0054] The microabrader formed according to the above processes
above may have solid microprotrusions. A subsequent process, such
as laser drilling, can be used to form hollow microprotrusions.
[0055] While several embodiments have been shown to illustrate the
present invention, it will be understood by those skilled in the
art that various changes and modifications can be made therein
without departing from the scope of the invention as defined in the
appended claims.
* * * * *