U.S. patent application number 13/290929 was filed with the patent office on 2013-05-09 for method for forming bilayer patches.
This patent application is currently assigned to APPLIED SILICONE CORPORATION. The applicant listed for this patent is Nolan Pasko, R. Alastair Winn. Invention is credited to Nolan Pasko, R. Alastair Winn.
Application Number | 20130116783 13/290929 |
Document ID | / |
Family ID | 48224233 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130116783 |
Kind Code |
A1 |
Winn; R. Alastair ; et
al. |
May 9, 2013 |
METHOD FOR FORMING BILAYER PATCHES
Abstract
A method for injection molding thin materials (sub-millimeter)
having low green strength could make certain manufacturing
processes significantly more efficient yet has heretofore been
unavailable. Provided herein is a method that enables injection
molding of thin materials by using a mold with contact surfaces
having a low surface energy release agent disposed thereon. The low
surface energy release agent may be applied as a coating on a
conventional mold or the mold itself or just the contact surfaces
thereof may be formed of a low surface energy release material. The
method finds particular applicability in making special contour
patches for medical and cosmetic implants and prosthetics. A
preferred approach involves injection molding a thin layer of
unvulcanized material on a cold mold, injection molding a thin
layer of vulcanized material on a hot mold, transferring the
vulcanized layer to the unvulcanized layer on the cold mold, and
removing the combined layers.
Inventors: |
Winn; R. Alastair; (Santa
Barbara, CA) ; Pasko; Nolan; (Encinitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Winn; R. Alastair
Pasko; Nolan |
Santa Barbara
Encinitas |
CA
CA |
US
US |
|
|
Assignee: |
APPLIED SILICONE
CORPORATION
Santa Paula
CA
|
Family ID: |
48224233 |
Appl. No.: |
13/290929 |
Filed: |
November 7, 2011 |
Current U.S.
Class: |
623/8 ; 156/245;
428/411.1 |
Current CPC
Class: |
B32B 25/20 20130101;
B29C 45/0055 20130101; B29C 45/1615 20130101; B32B 2535/00
20130101; Y10T 428/31504 20150401; Y10T 428/31663 20150401; B32B
2556/00 20130101; B32B 2250/24 20130101; B32B 2305/72 20130101;
B29C 43/24 20130101; B29C 65/02 20130101; B32B 2250/02 20130101;
B32B 2305/77 20130101; B29C 33/58 20130101; B29K 2083/00 20130101;
B29L 2031/7532 20130101; B29C 33/56 20130101; A61F 2/12 20130101;
B29C 45/0001 20130101; B29C 2045/0058 20130101; B29C 45/1657
20130101; B32B 25/08 20130101; B32B 27/283 20130101 |
Class at
Publication: |
623/8 ; 156/245;
428/411.1 |
International
Class: |
A61F 2/12 20060101
A61F002/12; B32B 37/14 20060101 B32B037/14; B32B 9/04 20060101
B32B009/04; B29C 45/16 20060101 B29C045/16 |
Claims
1. A method of forming a patch, comprising: injection molding a
vulcanized polymer layer using a first mold plate; injection
molding a unvulcanized polymer layer using a second mold plate;
removing the vulcanized polymer layer from the first mold plate;
disposing the vulcanized polymer layer onto the unvulcanized layer
while the unvulcanized layer is still on the second mold plate.
compressing the vulcanized polymer layer and the unvulcanized
polymer layer until the vulcanized polymer layer adheres to the
unvulcanized layer to form a patch; and removing the patch from the
second mold plate.
2. The method of claim 1, wherein the second mold plate has a
contact surface upon which the unvulcanized polymer layer is formed
that is formed from a low surface energy material.
3. The method of claim 2, wherein the low surface energy material
is selected from the group consisting of polytetrafluoroethylene,
and polyvinylidene fluoride.
4. The method of claim 1, wherein the second mold plate has a
contact surface upon which the unvulcanized polymer layer is
formed, the contact surface formed from a release agent bonded to
the second mold plate.
5. The method of claim 4, wherein the release agent is a low
surface energy material.
6. The method of claim 5, wherein the release agent is a
fluorinated polymer.
7. The method of claim 5, wherein the release agent is selected
from the group consisting of polyvinylidene fluoride,
polyvinylidene chloride, and poly(p-xylylene).
8. The method of claim 1, further comprising applying a release
coating to a contact surface of the second mold plate upon which
the unvulcanized polymer layer is formed.
9. The method of claim 8, wherein the release coating is a
fluorinated polymer.
10. The method of claim 8, wherein the release agent is selected
from the group consisting of polyvinylidene fluoride,
polyvinylidene chloride, and poly(p-xylylene).
11. A patch formed by the process of claim 1.
12. A method of forming a layered patch, comprising: injection
molding an unvulcanized layer by molding the unvulcanized layer
against a first mold having a low surface energy contact surface;
forming a vulcanized layer; applying the vulcanized layer over the
unvulcanized layer while the unvulcanized layer is still on the
first mold; adhering the vulcanized layer to the unvulcanized
layer; removing the adhered vulcanized and unvulcanized layers from
the first mold; and cutting the adhered vulcanized and unvulcanized
layers into a desired shape for a patch.
13. The method of claim 12, wherein forming the vulcanized layer
includes injection molding.
14. The method of claim 12, wherein forming the vulcanized layer
includes calendering.
15. The method of claim 13, wherein forming the vulcanized layer
includes hot injections molding to cure and vulcanize the
vulcanized layer.
16. The method of claim 12, wherein injection molding the
unvulcanized layer includes using a cold injection molding
process.
17. The method of claim 12, wherein injection molding the
unvulcanized layer includes using a cold mold.
18. The method of claim 12, wherein the low energy surface of the
mold is created by coating a surface of the mold with low surface
energy material.
19. The method of claim 12, wherein the low energy surface of the
mold is created by bonding a release agent to a surface of the
mold.
20. The method of claim 12, wherein the mold having a low energy
surface is formed from a material having a low surface energy.
21. The method of claim 18, wherein the low surface energy material
is a fluorinated polymer.
22. The method of claim 21, wherein the low surface energy material
is polyvinylidene fluoride.
23. The method of claim 21, wherein the low surface energy material
is polyvinylidene chloride.
24. The method of claim 21, wherein the low surface energy material
is poly(p-xylylene).
25. The method of claim 21, wherein the low surface energy material
is polytetrafluoroethylene.
26. The method of claim 12, wherein forming the vulcanized layer
includes solvent casting.
27. The product formed using the process of claim 12.
28. The method of claim 12, wherein injection molding the
unvulcanized layer includes molding a contour into the unvulcanized
layer.
29. The method of claim 12, wherein injection molding the
unvulcanized layer includes molding forming means for providing an
insertion point in the patch for filling an implantable silicone
breast prosthesis with fluid.
30. The method of claim 29, wherein the fluid is a silicone
gel.
31. An implantable silicone breast prosthesis manufactured using
the process of claim 12.
Description
BACKGROUND
[0001] The present invention is generally directed to the
manufacture of medical devices. More specifically, the present
invention includes a system and method for manufacturing bilayer
adhesive patches that are to be bonded to a medical device that is
formed in such a manner that patching is required to complete the
manufacture of the device.
[0002] Current manufacturing processes to make many medical
implantable devices involve forming thin silicone elastomer shells
by dipping or molding a thin layer of silicone material on a male
mandrel. For example, in the manufacture of breast implants, the
outer silicone membrane is formed on a male mandrel. The membrane,
typically called a "shell," is removed from the mandrel by cutting
a small hole in the shell so that the shell can be removed from the
male mandrel without deforming or tearing the shell. Through the
hole, the surrounding edges of the shell can then be grasped to
stretch and peel the remainder of the shell from the male mandrel
more easily. After the shell is off of the mandrel the small circle
or hole must be patched to close the shell so as to provide full
containment integrity to the shell so that it may then be filled
with a filling material, such as a silicone gel.
[0003] Current processes of making bilayer patches for medical and
cosmetic implants and prosthetics are more difficult, costly, and
time-consuming than they need to be. Patches for devices such as
breast implants formed from silicone usually have a first layer
that is vulcanized, which is then applied to a second layer that is
unvulcanized.
[0004] Vulcanization generally refers to the process of
crosslinking the silicone polymer based material to form a dry,
non-adhering material with good elastomeric memory. The vulcanized
layer is thin, typically less than 0.5 mm and preferably less than
0.2 mm. Forming thin layers with sticky unvulcanized silicone
elastomer bases is difficult and typically done by calendering or
solvent based knife-coating, with subsequent devolatilization and
vulcanization on a sheet of base plastic such as Teflon.RTM. (sold
by DuPont), polyester or polyethylene.
[0005] The unvulcanized portion or layer of the bilayer patch,
typically less than 0.5 mm thick, is typically applied to the
vulcanized layer by calendering unvulcanized silicone into a thin
layer and then applying that layer to the vulcanized layer
described above. Calendering refers to the process of forming a
uniform thickness thin layer by pressing uncured malleable
elastomer systems between rotating cylinders or rollers. It is
difficult to peel thin layers off of the rollers used for
calendering without tearing or breaking the fragile thin
unvulcanized layer. Accordingly, this process often results in a
high loss factor. Alternatively, the unvulcanized layer can be
applied to the vulcanized layer by a solvent dispersion technique
and subsequently devolatilizing the assembly before proceeding with
applying the patch to the shell to close the opening cut into the
shell to remove shell from the mandrel. After the vulcanized and
unvulcanized layers are joined, they are typically supported on a
thin plastic sheet.
[0006] Regardless of how the vulcanized silicone layer and
unvulcanized silicone layer used to form the patch are combined,
once combined both sides are typically covered with a thin layer of
a thermoplastic polymer such as polyethylene. The polyethylene
covered bilayer sandwich is then cut into the desired size and
shape for the patch.
[0007] Consistent with current modern manufacturing procedures, the
patches are then transferred to another work area in which an
assembler manually peels off the polyethylene coating and applies
the patch to the shell by placing in into the shell, vulcanized
side away from the hole and unvulcanized side facing the hole.
Vulcanization and bonding are typically achieved by applying heat
and pressure to the assembly.
[0008] Another technique that has been investigated for the
manufacture of thin patches is the use of injection molding to form
the patch. Injection molding of silicone elastomers and plastics is
common practice and a well-developed art, though it may also be
used for other materials. A wide variety of products are
manufactured using injection molding, which vary greatly in their
size, shape, complexity, and application.
[0009] "Green strength," a measure of tack, deformability, elastic
memory and malleability of the unvulcanized silicone elastomer base
is a relevant limiting factor to injection molding. Moderate green
strength silicone materials typically used in forming silicone
elastomer shells do not easily lend themselves to typical mixing
systems such as two roll milling (calendering) or pumpable paste
static mixer systems.
[0010] Green strength can be a good indication of processing
behavior and a moderate to high green strength is desirable in
processing operations in which it is important to maintain the
integrity of a shape piece of material, particularly for the
unvulcanized layer.
[0011] Thick preforms of high green strength unvulcanized silicone,
typically formed by continuous extrusion and chopping, are commonly
used in industrial processes. However, injection molding of thin
preforms having moderate green strength and tack is not known to
have been done before commercially for this application on account
of the adhesion between a thin preform of unvulcanized silicone and
common mold materials (e.g. aluminum or steel) being too strong to
provide a reliable release that preserves the integrity of the thin
preform upon removal from the mold. Injection molding of thin
preforms is not commercially practical when losses due to the
preforms being damaged, deformed, or partially stuck to the mold
are too costly.
[0012] There is a need for an improved method for forming thin
bilayer silicone patches that is less expensive, less labor and
time intensive, and that reduces the loss factor of material waste.
For example, the traditional process of removing the polyethylene
coating is tedious and transporting the patches from one work
station to the next for processing creates delays, inefficiencies,
and increased costs for labor and facilities. It would be desirable
to provide an improved method for forming implant and prosthetic
patches in which the patch assembler is able to mold the patches on
demand at a single work station. It would be especially desirable
to provide a method for injection molding of thin preforms that
preserves the integrity of the preforms upon removal from the mold.
The present invention satisfies these and other needs.
SUMMARY OF THE INVENTION
[0013] In its most general aspect, the present invention provides a
process for molding patches for medical and cosmetic implants and
prosthetics more efficiently with less material and economic waste.
The method provides several improvements over current techniques
used in the art of manufacturing patches. For example, the method
avoids problems inherent in calendering very thin materials as are
required to form the patches.
[0014] In a more specific aspect, the present invention provides a
way to injection mold unvulcanized and mating vulcanized preforms
of very thin materials of low green strength while preserving their
integrity upon removal from the mold. According to one aspect of
the present invention, this is accomplished by first spraying a
mold, including a conventional mold, with a low surface energy
release agent that coats the mold and facilitates removal of the
preform from it. According to another aspect of the present
invention, this is accomplished by using molds in which the
portions of the mold that make contact with the preform are formed
of different materials than are conventionally used, for example,
low surface energy plastics rather than aluminum or steel.
Non-contact portions of the mold may or may not still be formed of
conventional materials including aluminum or steel.
[0015] In another aspect, the present invention provides a process
for combining the layers that makeup a patch, specifically the
unvulcanized layer and the vulcanized layer. Such a bilayer
assembly may be used as formed or subsequently cut into a desired
patch shape. In one aspect, patches are molded on demand at a
single work station, eliminating the steps of combination through
calendering or rolling squeegee technique, coating, and
peeling.
[0016] Another aspect of the present invention provides a process
through which the vulcanized layer may be transferred directly to
the unvulcanized layer while the unvulcanized layer remains on a
cold mold. The combined layers are together peeled off the cold
mold.
[0017] In still another aspect, the present invention provides a
method of forming a patch that includes: forming a layer of an
unvulcanized material to a cold mold having contact surfaces
comprising a low surface energy release agent; applying a second
layer of a vulcanized material over the first layer of the cold
molded unvulcanized material while cold molded layer is still on
the cold injection mold; allowing the second vulcanized layer to
attach to the unvulcanized layer; removing the combined vulcanized
and unvulcanized layers from the cold injection mold; and cutting
the bilayer combination into a desired shape for a patch.
[0018] According to one aspect, the combination of the unvulcanized
layer attached to the vulcanized layer is less than 0.5 millimeter
thick. In another aspect, the unvulcanized layer is less than 0.5
millimeter thick. In still another aspect, the unvulcanized
material has a low green strength.
[0019] In still a further aspect, the vulcanized layer is formed by
calendering and subsequent crosslinking of the polymer material.
According to one aspect, the vulcanized layer is formed by
injection molding on a hot injection mold having contact surfaces
comprising a low surface energy release agent. According to still
another aspect, the vulcanized layer is less than 0.5 millimeter
thick.
[0020] In still another aspect, the contact surfaces comprising the
low surface energy release agent are formed by applying a coating
of the low surface energy release agent to the contact surfaces of
the hot or cold injection mold. According to another aspect, the
contact surfaces of the hot or cold injection mold are made of a
material that has a low surface energy.
[0021] In a further aspect, the low surface energy release agent is
a fluorinated polymer. In yet a further aspect, the low surface
energy release agent is polyvinylidene fluoride. In another aspect,
the low surface energy release agent is polyvinylidene chloride,
and in yet another aspect, the low surface energy release agent is
poly(p-xylylene). In still another further aspect, the low surface
energy release agent is polytetrafluoroethylene, and in yet another
aspect, the low surface energy release agent is a plastic.
[0022] In another aspect, the method further includes forming a
label or bar code on at least one layer that will be visible on the
patch. According to one aspect, the label is an identifying label
that may be used for tracking a manufacturing history of an implant
or prosthesis to which the patch is applied.
[0023] In still another aspect, the method further includes forming
an aperture in the patch through which a filler material may be
supplied to an implant or prosthesis upon which the patch is
applied, the aperture configured to be sealed after an implant or
prosthesis is filled.
[0024] In yet another aspect, the method includes forming special
contours on the patch designed to minimize the transition between
the edge of the hole in the shell and the edge of the patch.
[0025] In another aspect, the method includes forming special
contours on or in the patch to minimize the flow under pressure
between the outer edge of the patch and the edge of the hole in the
shell.
[0026] In still another aspect, the invention includes a method of
forming a patch, comprising: injection molding a vulcanized polymer
layer using a first mold plate; injection molding a unvulcanized
polymer layer using a second mold plate; removing the vulcanized
polymer layer from the first mold plate; disposing the vulcanized
polymer layer onto the unvulcanized layer while the unvulcanized
layer is still on the second mold plate. compressing the vulcanized
polymer layer and the unvulcanized polymer layer until the
vulcanized polymer layer adheres to the unvulcanized layer to form
a patch; and removing the patch from the second mold plate.
[0027] In an alternative aspect, the second mold plate has a
contact surface upon which the unvulcanized polymer layer is formed
that is formed from a low surface energy material. In another
aspect, the low surface energy material is selected from the group
consisting of polytetrafluoroethylene, and polyvinylidene
fluoride.
[0028] In yet another aspect, the second mold plate has a contact
surface upon which the unvulcanized polymer layer is formed, the
contact surface formed from a release agent bonded to the second
mold plate. In still another aspect, the release agent is a low
surface energy material. In another aspect, the release agent is a
fluorinated polymer. In yet another aspect, the release agent is
selected from the group consisting of polyvinylidene fluoride,
polyvinylidene chloride, and poly(p-xylylene).
[0029] In another aspect, the invention may include applying a
release coating to a contact surface of the second mold plate upon
which the unvulcanized polymer layer is formed. I an alternative
aspect, the release coating is a fluorinated polymer. In still
another alternative aspect, the release agent is selected from the
group consisting of polyvinylidene fluoride, polyvinylidene
chloride, and poly(p-xylylene).
[0030] In still another aspect, the invention includes forming a
layered patch, comprising: injection molding an unvulcanized layer
by molding the unvulcanized layer against a first mold having a low
surface energy contact surface; forming a vulcanized layer;
applying the vulcanized layer over the unvulcanized layer while the
unvulcanized layer is still on the first mold; adhering the
vulcanized layer to the unvulcanized layer; removing the adhered
vulcanized and unvulcanized layers from the first mold; and cutting
the adhered vulcanized and unvulcanized layers into a desired shape
for a patch.
[0031] In another aspect, the forming vulcanized layer includes
injection molding; in an alternative aspect forming the vulcanized
layer includes calendering; and in still another aspect, forming
the vulcanized layer includes hot injections molding to cure and
vulcanize the vulcanized layer.
[0032] In yet another aspect, injection molding the unvulcanized
layer includes using a cold injection molding process.
Alternatively, injection molding the unvulcanized layer includes
using a cold mold.
[0033] In still another aspect, the low energy surface of the mold
is created by coating a surface of the mold with low surface energy
material. In an alternative aspect, the low energy surface of the
mold is created by bonding a release agent to a surface of the
mold. In yet another aspect, the mold having a low energy surface
is formed from a material having a low surface energy. In one
alternative aspect, the low surface energy material is a
fluorinated polymer; in another alternative aspect, the low surface
energy material is polyvinylidene fluoride; in another alternative
aspect, the low surface energy material may be polyvinylidene
chloride, poly(p-xylylene), or polytetrafluoroethylene.
[0034] In yet another aspect, forming the vulcanized layer includes
solvent casting.
[0035] In another aspect, injection molding the unvulcanized layer
includes molding a contour into the unvulcanized layer. In still
another aspect, injection molding the unvulcanized layer includes
molding forming means for providing an insertion point in the patch
for filling an implantable silicone breast prosthesis with fluid.
In an alternative aspect, the fluid is a silicone gel.
[0036] In yet one more aspect, the present invention includes an
implantable silicone breast prosthesis manufactured using any of
the aspects of the invention set forth above. Alternatively, the
present includes a patch formed using any of the aspects of the
invention described previously.
[0037] Other features and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, which illustrate, by
way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a flow chart illustrating a prior art process of
making patches.
[0039] FIG. 2 is a flow chart illustrating a process of making
patches in accordance with an embodiment of the present
invention.
[0040] FIG. 3 shows a conventional injection mold, hot or cold,
being coated with a low surface energy release agent in accordance
with an embodiment of the present invention.
[0041] FIG. 4 shows an injection mold, hot or cold, having contact
portions made of a low surface energy release material in
accordance with an embodiment of the present invention.
[0042] FIG. 5 shows an injection mold, hot or cold, formed of a low
surface energy release material in accordance with an embodiment of
the present invention.
[0043] FIG. 6 is a cross-sectional view showing a vulcanized layer
being applied to a hot injection mold having a low surface energy
release material between the mold and the vulcanized layer.
[0044] FIG. 7 a cross-sectional view showing the vulcanized layer,
after removal from the hot injection mold, being transferred to and
applied over an unvulcanized layer on a cold injection mold, the
cold mold also having a low surface energy release material.
[0045] FIG. 8 a cross-sectional view showing the vulcanized layer
making contact with the unvulcanized layer on the cold injection
mold.
[0046] FIG. 9 a cross-sectional view showing the combination of the
vulcanized layer and the unvulcanized layer bonded together being
pulled off of the cold injection mold having a low surface energy
release material.
[0047] FIG. 10 is a graphical representation of one embodiment of a
process used to cut the combination of the vulcanized layer and the
unvulcanized layer into the desired shape for a patch and
application of the patch to the implant or prosthetic shell at a
single work station.
[0048] FIG. 11 is a graphical flow diagram illustrating the steps
of forming the layers through injection molding, combining the
layers, peeling the layers off the mold, cutting the combined
layers into a patch, and applying the patch to the implant all
being performed at a single work station.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] In one of its various embodiments, the present invention
provides a process of making patches for medical and cosmetic
implants and prosthetics in which the patches can be made on demand
and applied to the implant, prosthetic, or a shell thereof or
precursor thereto at a single workstation. This process reduces
material losses from calendering and saves labor and facilities
costs due to the elimination of coating (before cutting) and
peeling the coating off (after cutting) steps and the ability to
concentrate the process at a single workstation.
[0050] Another aspect of the invention involves coating the mold
material used to injection mold the layers that form the patch with
a low surface energy release agent in order to facilitate removal
of the layers given the low green strength and propensity for
adhesion of thin preform materials. The low surface energy release
agent may be, for example, a fluorinated polymer, polyvinylidene
fluoride, polyvinylidene chloride, poly(p-xylylene), and like
compositions.
[0051] Alternatively or additionally to coating the mold material
with a low surface energy release agent, the portions of the mold
that make contact with the preform material that forms the patch
layer ("contact portions"), may themselves be made of a selected
material to facilitate removal. For example, contact portions of
the mold may be made of a low surface energy plastic,
polytetrafluoroethylene (PTFE), polyvinylidene fluoride, or like
materials. Or, the entire mold may be made of one of these
materials mentioned above to facilitate removal of thin preforms
with low green strength and high adhesion.
[0052] Prior to bringing the layers together the vulcanized layer
is preferably formed by a hot injection mold while the unvulcanized
layer is preferably formed by a cold injection mold. The vulcanized
layer is then peeled off the hot injection mold and transferred to
and applied over the unvulcanized layer on the cold injection mold.
Once the layers are properly in contact with each other the
combination can be pulled from the cold injection mold.
[0053] The preferred patch is typically made from the combination
of a layer of 0.2 mm thick vulcanized silicone with a layer of 0.2
mm thick unvulcanized silicone. One desirable application for the
thin preform injection molding process is to make patches for
breast implants. For this application, the vulcanized layer is made
of a special silicone that is so sticky it must be solvent cast
into thin films or injection molded from solvent free paste.
[0054] The vulcanized layer may be transferred to the unvulcanized
while it is still hot from the curing process in order to promote
adhesion. The weight of the hotter vulcanized layer over the
unvulcanized layer may be enough to promote bonding and adhesion
between the two layers that will securely combine the layers with
time. However, light pressure may also be applied to encourage the
vulcanized and the unvulcanized layers to come together to form a
singular combination layer. Light pressure may be applied, for
example, by blowing air or an inert gas on the layers as the
vulcanized layer cools over the unvulcanized layer. The layers may
be allowed to rest together for up to, for example, but not limited
to, twenty (20) minutes to mate until they are securely attached to
each other.
[0055] The patches and methods of producing patches described
herein are suited for patching holes in a shell that is a precursor
to an implant. Typically, a hole is intentionally created in a
shell in order to more easily remove it from a mandrel on which it
is formed. After a shell is patched, filler material may be
injected into the implant shell through the patch to form a
completed implant ready for implantation. Or, in the case of some
implants and tissue expanders, the device may be inserted without
filler material or with less than the final amount of filler
material which can be added after implantation through a port in
the patch. Common filler materials for breast implants, for
example, include silicone gels and saline solutions.
[0056] Optionally, a label may be formed on the patch during the
molding process. The label may be two or three dimensional. The
label may be formed by painting onto a layer used to form the patch
or it may be embossed on a layer through surface topography
provided on the injection mold or mandrel used to form the patch.
The label may be an identifying label that provides tracking
information as to the manufacturing history of the implant that may
be useful in recognizing, reporting, and ameliorating any issues
that may arise due to particular implants. If each patch receives a
unique label, the label may be formed by a unique three-dimensional
identifier (e.g. a sticker, a magnet, etc.) that is applied to an
injection mold or mandrel before the patch is formed thereon such
that a three-dimensional design will be imprinted into the
patch.
[0057] To provide appropriate background to the process of patching
described herein, the process of fabricating implant shells is
outlined with a focus on shells for breast implants or mammary
prostheses. Breast implant shells are generally formed on
mushroom-shaped mandrels by applying a liquid dispersion of a
silicone elastomer to the mushroom-head structure of the mandrel.
The silicone dispersion used to form the shell may be applied by
any one of several methods including dipping or dip-molding,
rotational molding (see, for example, U.S. Pat. No. 6,602,452,
incorporated by reference herein in its entirety), spraying,
brushing, painting, and the like.
[0058] In many situations it is preferable that the mandrel have a
textured or porous surface that is transferable to the surface
texture of the shell. Implants having surface texture, variable
surface topography, or micropillars have been shown to provide
several post-implantation advantages inside a patient's body that
reduce post-surgical complications and improve a body's acceptance
and tolerance of the implant. See, for example, European Patent No.
0416846 and European Patent No. 0710468, both of which are
incorporated by reference herein in their entirety.
[0059] Exemplary materials for mandrels include a hard resinous
polymeric material such as epoxy or polyester (e.g. polyethylene
terephthalate), polyvinylidene fluoride, polyacetal (homo or
copolymer), polytetrafluoroethylene, perfluoroethylene or other
fluoropolymers. Mandrels may also be formed of inert metals such as
nickel or stainless steel, or ceramics.
[0060] In manufacturing the shell, the mandrel may be successively
coated with several layers of the shell material dispersion with
devolatilization to ensure silicone is deposited in the proper
thickness. After the desired number of layers of liquid shell
material are applied to the mandrel, the mandrel coated with shell
material is cured at elevated temperatures such as, for example, 90
to 250 degrees centigrade, depending on the particular polymers in
the dispersion, for 0.5 to 6 hours. The cured elastomer shell is
then allowed to cool on the mandrel before a hole is created in the
shell to peel it off the mandrel.
[0061] As shown in FIG. 1, in accordance with the traditional
process 100 for forming patches for implant shells several steps
are required which take place across several separate works
stations. The process typically begins at Box 102 with the
calendering of vulcanized and unvulcanized layers used to form the
patches. The thin calendered layers are manually peeled off of the
rollers used for calendering at Box 104. It is not uncommon for
layers to be torn, damaged, or partially destroyed during this
peeling process and accordingly the loss rate is generally higher
than desirable and contributes to the inefficiency of the
traditional process.
[0062] Next, the calendered layers are spread onto a thin plastic
sheet at Box 106. The layers are then cured with heat under
pressure in Box 108.
[0063] The separately calendered and cured vulcanized and
unvulcanized layers are then combined together through further
calendering or by aligning the sheets which are then combined using
a rolling squeegee technique in Box 110. One or both sides of the
combined layer sandwich are then coated with a thermoplastic
polymer at Box 112. The thermoplastic polymer applied to cover the
combined layer sandwich may be, for example, polyethylene. However,
other thermoplastic polymers other than polyethylene may also be
used as a coating on the combined layer sandwich.
[0064] Subsequently, the thermoplastic polymer covered sandwich of
combined layers (one layer vulcanized, another layer unvulcanized)
is cut into the size and shape desired for an implant shell patch
at Box 114. The patches may then be transferred to another work
station in Box 116. At that work station, an assembler manually
peels the thermoplastic polymer cover off of the patch with
tweezers in Box 118. Finally, with the thermoplastic cover removed,
the patch is applied to a shell to form an implant using standard
heat and pressure techniques at Box 120.
[0065] As shown in FIG. 2, broadly and in general terms, in
accordance with the process 200 according to one of several
embodiments of the present invention, an unvulcanized materials is
injected into a mold assembly having a contact surface covered with
a low surface energy release agent at Box 202. The unvulcanized
layer is then injection molded on the injection mold at Box 204.
The injection mold used may be a cold injection mold or a hot
injection mold. Typically, the mold assembly used for injection
molding the unvulcanized layer is a cold injection mold.
[0066] At Box 206, a separate vulcanized layer is then applied over
the unvulcanized layer on the mold assembly. A period of time
should be allowed, and possibly also some physical pressure
applied, to allow the vulcanized layer to securely attach to the
unvulcanized layer on the mold in 208.
[0067] Once the two layers are firmly adhered to each other upon
the mold assembly used to injection mold the bottom unvulcanized
layer, the combination of layers is removed from the injection mold
at Box 210.
[0068] The combination of layers is then cut into the desired size
and shape for patches at Box 212. The patches are then applied to a
shell on demand in Box 214. Each of the above steps may be
performed at a single work station.
[0069] As shown in FIG. 3, in accordance with an embodiment 300 of
the present invention, a conventional injection mold, hot or cold,
is coated with a low surface energy release agent. The conventional
injection mold includes molded part 302, molten plastic 304, raw
plastic 306, clamping unit 308, mold assembly 310, injection unit
312, and injection molding machine 314. The enlarged view of the
mold assembly 310 illustrates using a sprayer 316 to apply a
coating 318 of a low surface energy release agent on the surface of
the mold assembly that will make contact with the molten plastic
304 to form a molded part 302. As shown in FIG. 4, the coating 318
of a low surface energy release agent has been applied upon all
contact surfaces of the mold assembly 310.
[0070] As shown in FIG. 5, in accordance with another embodiment of
the present invention, a conventional injection mold is modified
such that the mold assembly 310 is formed entirely of a material
418 that is a low surface energy release agent. Alternatively, the
mold assembly 310 may be formed such that all contact surfaces
include a material 418 that is a low surface energy release agent.
In either of these embodiments, a coating is not needed because the
mold assembly itself, or at least the contact surfaces thereof, are
already formed of a low surface energy release material.
[0071] As shown in FIG. 6, a heat curable and/or vulcanizable
material is injected into a hot injection mold assembly 311 upon
which a coating 318 of a low surface energy release agent has
already been applied. A vulcanized layer 502 is then formed by
curing and vulcanizing the vulcanizable material, such as a
silicone elastomer within the hot mold assembly.
[0072] As shown in FIG. 7 and FIG. 8, the vulcanized layer 502 from
the hot injection mold assembly 311 is transferred to a cold
injection mold assembly 313, upon which a coating 318 of a low
surface energy release agent has been applied, the cold injection
mold assembly 313 already having an unvulcanized layer 504 formed
thereon over which the vulcanized layer 502 is applied. The
unvulcanized layer 504 was formed by injecting a suitable material,
such as a silicone elastomer or its precursors, into a cold mold
assembly. The mold assembly is then opened up, and the vulcanized
layer 502 applied over the unvulcanized layer 504 while the
unvulcanized layer 504 remains in the mold assembly. Referring now
to FIG. 8, the thin vulcanized layer 502, conforms to the shape of
the mold and thus also to the shape of the unvulcanized layer 504.
It will be apparent to those skilled in the art that while the
process is described with reference to mold plates having a
particular shape formed therein, any shape may be molded into the
various layers, or the layers may be formed in such a manner that
they are essentially flat.
[0073] As shown in FIG. 9, the vulcanized layer 502 adheres to the
unvulcanized layer 504 on the cold injection mold 313, mating the
layers to each other. The bilayer assembly comprising vulcanized
layer 502 and unvulcanized layer 503 may then be peeled off of the
mold as illustrated, maintaining the integrity of the bilayer patch
assembly.
[0074] Referring now to FIG. 10, upon peeling the combined layers
off of the mold assembly, the adhered layers 602 can be used as
formed or cut into the desired shape and size for the implant shell
patches. A cutout section 604, or patch, of the combined layers is
then transferred over to an implant shell 700 on a mandrel 710 and
applied over a hole 720 in the shell. This entire process, from
cutting the adhered layers into sections to patching the hole in
the implant shell on a mandrel, can occur at a single work station
900.
[0075] FIG. 11 illustrates how all steps of the process from
forming the vulcanized layer on a hot injection mold assembly as in
FIG. 6, to transferring the vulcanized layer to an unvulcanized
layer on a cold injection mold assembly as in FIG. 7, to applying
the vulcanized layer over the unvulcanized layer already on the
cold injection mold as in FIG. 8, to peeling the adhered layers off
the cold injection mold assembly as in FIG. 9, to cutting the
adhered layers into patch sections and applying over a hole in an
implant shell on a mandrel as in FIG. 10, may be performed at a
single work station 900.
[0076] According to one embodiment, the injection molding process
used requires the use of an injection molding machine, raw
material, and a mold. The process outline that follows assumes
fabrication of a plastic part as a representative example but is
not intended as being limited to fabrication of plastic parts.
[0077] First, if the contact surfaces of the injection mold are not
composed of a low surface energy release material or the mold is
not formed of a low surface energy release material, the contact
surfaces of the mold should be coated with a low surface energy
release agent. Any known manner of coating the mold surfaces may be
used to apply the low surface energy release agent coating,
including painting on the coating, spraying on the coating, dipping
the mold into a solution of coating, condensing vapors of the
coating material onto the mold, and the like. Alternatively, the
release surface may be highly polished to facilitate release of the
material from the molds.
[0078] Next, the mixed unvulcanized silicone elastomer components
are loaded into the injection molding machine and then injected
into the preheated mold, where the silicone elastomer components
are cured and vulcanized into the final part. The process cycle for
injection molding is very short, typically between 2 seconds and 2
minutes.
[0079] The main stages of the injection molding process are well
known in the art and include clamping, injection, and ejection.
Clamping refers to the step of securely closing and locking the two
halves of the mold by the clamping unit prior to injection of any
material into the mold. In the injection stage, the material used
to form the molded object, which may be a viscous fluid like
material such as an uncured silicone, is fed into the injection
molding machine, and advanced towards the mold by the injection
unit. The molding material is generally is forced into the cavity
of the mold under high pressure to ensure proper filling of the
mold cavity.
[0080] The mold plates in the injection molding machine may be
heated or cooled, dependent upon the material being used and the
desired properties of the finished molded article. In one
embodiment of the present invention, the vulcanized layer is formed
by heating the mold plate to cure and vulcanize the silicone
material injected into the mold. The unvulcanized layer, in
contrast, is injected into a cold plate so that the silicone may
cure without vulcanizing.
[0081] In the ejection stage, the molded part or article, is often
ejected from the mold. This ejection process is not typically used
in the various embodiments of the present invention. Rather, the
thin vulcanized and unvulcanized silicone layers are carefully
peeled from the mold cavity.
[0082] As described previously, use of a low surface energy release
material for construction of the mold plates, or which is applied
to a standard metal mold plate, to promote release of the molded
article is particularly advantageous when forming the thin layers
of vulcanized and unvulcanized silicone of the present invention.
Use of such a release agent allows removal of the thin layers of
unvulcanized silicone having low green sheet from the molds while
reducing the incidence of damage to the layers during the removal
step.
[0083] Further, the use of injection molding apparatus and method
that provides for easy release of the vulcanized and unvulcanized
layers allows for the combination of multiple manufacturing steps
so that the entire process of manufacturing a patch may be carried
out at a single work station by a single operator. Such a process
provides for a reduction in product loss due to damage, increased
productivity and lower manufacturing costs.
[0084] The present invention is not limited to the embodiments
described above. Various changes and modifications can, of course,
be made, without departing from the scope and spirit of the present
invention. Additional advantages and modifications will readily
occur to those skilled in the art. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *