U.S. patent application number 13/010929 was filed with the patent office on 2011-05-19 for soft prosthesis shell texturing method.
This patent application is currently assigned to ALLERGAN, INC.. Invention is credited to Loantrang Dang, Thomas E. Powell.
Application Number | 20110117267 13/010929 |
Document ID | / |
Family ID | 40588926 |
Filed Date | 2011-05-19 |
United States Patent
Application |
20110117267 |
Kind Code |
A1 |
Powell; Thomas E. ; et
al. |
May 19, 2011 |
Soft Prosthesis Shell Texturing Method
Abstract
A method of texturing a soft prosthetic implant shell, such as a
silicone breast implant shell. A soft prosthetic implant with a
textured external surface layer of silicone elastomer and having an
open-cell structure is made by adhering and then dissolving round
salt crystals. The resulting roughened surface has enhanced
physical properties relative to surfaces formed with angular salt
crystals. An implant having such a textured external surface layer
is expected to help prevent capsular contraction, to help prevent
scar formation, and to help in anchoring the implant within the
body.
Inventors: |
Powell; Thomas E.; (Santa
Barbara, CA) ; Dang; Loantrang; (Oxnard, CA) |
Assignee: |
ALLERGAN, INC.
Irvine
CA
|
Family ID: |
40588926 |
Appl. No.: |
13/010929 |
Filed: |
January 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12261939 |
Oct 30, 2008 |
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13010929 |
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60985489 |
Nov 5, 2007 |
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60991004 |
Nov 29, 2007 |
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Current U.S.
Class: |
427/2.24 |
Current CPC
Class: |
A61F 2/0077 20130101;
A61F 2002/0086 20130101; A61F 2/12 20130101 |
Class at
Publication: |
427/2.24 |
International
Class: |
B05D 3/10 20060101
B05D003/10 |
Claims
1. A process for forming a soft prosthetic implant, comprising:
forming a flexible shell; adhering on the exterior of the flexible
shell a substantially even distribution of rounded salt particles;
curing the flexible shell with the rounded salt particles adhered
thereto; and exposing the flexible shell to an aqueous solvent for
the rounded salt particles for a sufficient amount of time to
dissolve the rounded salt particles and form an open-pored
structure on the exterior of the flexible shell.
2. The process of claim 1, wherein the rounded salt particles are
sodium chloride crystals.
3. The process of claim 1, wherein the flexible shell is formed of
a silicone elastomer.
4. The process of claim 1 further comprising the step of applying a
tack coat layer to the flexible shell prior to the step of
adhering.
5. The process of claim 1, further comprising the step of applying
an overcoat to the distribution of rounded salt particles prior to
the step of curing.
6. The process of claim 1, wherein the rounded salt particles have
a maximum particle size range selected from a group of ranges
consisting of (1) a range between about 180 microns and about 425
microns, (2) a range between about 425 microns and about 850
microns, and (3) a range between about 850 microns and about 1450
microns.
7. The process of claim 6 wherein about 90% of the rounded salt
particles are in the selected particle size range.
8. The process of claim 1, wherein the prosthetic implant is a
breast implant and the flexible shell is shaped accordingly.
9. The process of claim 1, wherein the step of forming the flexible
shell comprises dipping a mandrel into a liquid dispersion of an
elastomeric material.
10. The process of claim 1, wherein the step of forming the
flexible shell comprises rotationally molding the shell.
11. The process of claim 1, wherein the step of adhering comprises
dipping the flexible shell into a liquid containing the rounded
salt particles.
12. The process of claim 11, further comprising the step of
applying a tack coat layer onto the flexible shell prior to the
step of dipping the flexible shell into a liquid containing the
rounded salt particles.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/261,939, filed Oct. 30, 2008, which claims the benefit
of U.S. Provisional Patent Application Ser. No. 60/985,489, filed
on Nov. 5, 2007 and U.S. Provisional Patent Application Ser. No.
60/991,004, filed on Nov. 29, 2007, the disclosure of each of these
three applications incorporated in its entirety by this
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to soft prosthetic implants
and, more particularly, to methods of texturing the exterior
surface of such implants, for instance breast implants, to produce
an open-cell texture on the outer surface.
BACKGROUND OF THE INVENTION
[0003] Implantable prostheses are commonly used to replace or
augment body tissue. In the case of breast cancer, it is sometimes
necessary to remove some or all of the mammary gland and
surrounding tissue, which creates a void that can be filled with an
implantable prosthesis. The implant serves to support surrounding
tissue and to maintain the appearance of the body. The restoration
of the normal appearance of the body has an extremely beneficial
psychological effect on post-operative patients, eliminating much
of the shock and depression that often follows extensive surgical
procedures. Implantable prostheses are also used more generally for
restoring the normal appearance of soft tissue in various areas of
the body, such as the buttocks, chin, calf, etc.
[0004] Soft implantable prostheses typically include a relatively
thin and quite flexible envelope or shell made of vulcanized
(cured) silicone elastomer. The shell is filled either with a
silicone gel or with a normal saline solution. The filling of the
shell takes place before or after the shell is inserted through an
incision in the patient.
[0005] The development of implants having textured outer surfaces
reflects an attempt to prevent the contraction of the fibrous outer
capsule that forms around the implant, which tends to render an
implant spherical, painful and aesthetically undesirable. Layers of
polyether, polyester or polyurethane foam material have been
applied to the back sides of mammary prostheses so that
fibrous-tissue could grow into the material and thereby anchor
prosthesis securely to the chest wall. However, possible problems
exist with foam materials, which may degrade in the body over a
period of time, and the effectiveness of these materials for
preventing capsular contracture may disappear as they degrade.
[0006] Despite many advances in the construction of soft prosthetic
implants, there remains a need for better methods for texturing
surfaces of implants.
SUMMARY OF THE INVENTION
[0007] The present invention provides processes for forming soft
prosthetic implants having textured surfaces and implants formed by
said processes. The processes generally comprise the steps of
forming a flexible shell, adhering on the exterior of the flexible
shell a distribution of rounded particles, curing the flexible
shell with the rounded particles adhered thereto, and causing or
allowing the rounded particles to be removed from the shell thereby
leaving impressions of the particles in the shell to create an
open-pored structure on a surface thereof.
[0008] In one embodiment, the flexible shell is formed of a
silicone elastomer. For instance, the flexible shell may be formed
of a plurality of layers of different silicone elastomers, or the
flexible shell may be formed of a single homogeneous layer of a
silicone elastomer.
[0009] The step of forming the flexible shell may comprise dipping
a mandrel into a liquid dispersion of elastomeric material.
Alternatively, the step of forming comprises rotational
molding.
[0010] In one embodiment, the step of adhering comprises dipping
the flexible shell into a liquid containing the rounded particles,
for example, a liquid dispersion or emulsion of rounded particles,
for example, rounded salt crystals. Prior to the step of dipping
the flexible shell, the process may also include applying a tack
coat layer onto the flexible shell.
[0011] In one aspect, the rounded particles comprise rounded
crystals of sodium chloride and the solvent is an aqueous
composition, for example, water. In other embodiments, the rounded
particles comprise rounded sugar particles. In other embodiments,
the rounded particles comprise a suitable solid material which is
provided in a rounded particulate form, and which is capable of
being adhered to a shell, for example, an uncured elastomer shell,
and is capable of being dissolved, for example, using a solvent,
thereby leaving open, rounded pores in the shell.
[0012] In one embodiment, the rounded particles used in accordance
with the invention have a substantially uniform particle size of
between about 150 microns and about 1450 microns. More
specifically, the particles have a maximum particle size range
selected from a group of ranges consisting of (1) a range between
about 180 microns and about 425 microns, (2) a range between about
425 microns and about 850 microns, and (3) a range between about
850 microns and about 1450 microns. In one embodiment, about 90% of
the particles are in the selected particle size range.
[0013] Another aspect of the invention is a soft prosthetic breast
implant, formed by a process comprising the steps of forming a
flexible shell of silicone elastomer in the shape of a breast
implant, adhering on the exterior of the flexible shell a
substantially even distribution of rounded particles, curing the
flexible shell with the rounded particles adhered thereto, and
exposing the flexible shell to a suitable solvent for a sufficient
amount of time to dissolve the rounded particles thereby forming an
open-pored structure on the exterior of the flexible shell.
[0014] In one embodiment, at least one, for example, at least two,
for example all three of the physical properties of ultimate break
force, ultimate elongation, and ultimate tensile strength of an
implant formed in accordance with the present process is superior
to an implant made using substantially the same process and the
same materials except for conventional angular or non-rounded salt
crystals instead of rounded salt crystals.
[0015] The step of forming the flexible shell may comprise dipping
a mandrel into a liquid dispersion of a shell material, or
rotational molding. In one embodiment, the step of forming the
flexible shell comprises forming a shell with an opening and the
process further includes attaching a patch to cover the opening.
The patch may be an unvulcanized elastomer and is attached prior to
the step of curing. Alternatively, the step of forming the flexible
shell comprises forming a shell with an opening and the process
further includes attaching valve, for example, a one-way valve to
cover the opening. The rounded salt crystals may comprise sodium
chloride.
[0016] A further understanding of the nature and advantages of the
present invention are set forth in the following description and
claims, particularly when considered in conjunction with the
accompanying drawings in which like parts bear like reference
numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Features and advantages of the present invention will become
appreciated and the same become better understood with reference to
the specification, claims, and appended drawings wherein:
[0018] FIGS. 1A-1C show several steps in a process of dip-forming
the shell of a breast implant prosthesis;
[0019] FIG. 2 is a cross-sectional view through one portion of a
textured multi-layered breast implant prosthesis shell;
[0020] FIG. 3 is a cross-sectional view through one portion of a
textured single-layer breast implant prosthesis shell;
[0021] FIG. 4 is a magnified view of a sample of rounded salt
crystals used in the implant texturing process of the present
invention;
[0022] FIG. 5 is a magnified view of a sample of cubic salt
crystals used in conventional implant texturing processes of the
prior art;
[0023] FIGS. 6A and 6B are cross-sectional and plan views,
respectively, of a textured implant of the prior art;
[0024] FIGS. 7A and 7B are cross-sectional and plan views,
respectively, of another textured implant of the prior art; and
[0025] FIGS. 8A and 8B are cross-sectional and plan views,
respectively, of a textured implant in accordance with the present
invention.
DETAILED DESCRIPTION
[0026] The present invention provides a saline- or gel-filled soft
implant for prostheses and tissue expanders. The implant generally
comprises a shell, for example, a silicone elastomer shell, with a
textured surface. The primary application for such soft implants is
to reconstruct or augment the female breast. Other potential
applications are implants for the buttocks, testes, or calf, among
other body regions.
[0027] FIGS. 1A-1C illustrate one process for forming flexible
implant shells for implantable prostheses and tissue expanders,
involving dipping a suitably shaped mandrel 20 into a silicone
elastomer dispersion 22. Many such dispersions are used in the
field. Basically they contain a silicone elastomer and a solvent.
The silicone elastomer is typically polydimethylsiloxane,
polydiphenyl-siloxane or some combination of these two elastomers.
Typical solvents include xylene or trichloromethane. Different
manufacturers vary the type and amount of the ingredients in the
dispersion, the viscosity of the dispersion and the solid content
of the dispersion. Nonetheless, the present invention is expected
to be adaptable to have utility with a wide variety of silicone
rubber dispersions.
[0028] The mandrel 20 is withdrawn from the dispersion and the
excess silicone elastomer dispersion is allowed to drain from the
mandrel. After the excess dispersion has drained from the mandrel
at least a portion of the solvent is allowed to volatilize or
evaporate. Normally this is accomplished by flowing air over the
coated mandrel at a controlled temperature and humidity. Different
manufacturers use various quantities, velocities or directions of
air flow and set the temperature and humidity of the air at
different values. However, the desired result, driving off the
solvent, remains the same.
[0029] It is also common for prostheses manufacturers to repeat
this dip and volatilize procedure a number of times so that a
number of layers are built up on the mandrel to reach a desired
shell thickness. A layered structure like most current silicone
elastomer shells can be made by sequentially dipping the mandrel in
different dispersions. Alternatively, the steps may be repeated in
a single dispersion 22 so that the finished product is a single
homogenous material or layer. That is, the dipping process may be
done in multiple stages or steps, each step adding more material,
yet the finished product exhibits no distinct layers and the entire
shell wall is homogenous or uniform in composition.
[0030] FIG. 3 illustrates in cross-section a portion of a textured
multi-layered implant of the present invention. A primary barrier
to fluid passage through the shell wall is provided by an inner
barrier layer 30. Two base coat layers 32, 34 lie radially inward
from the barrier layer 30. In some cases a single base coat layer
may be used. On the outer side of the barrier layer 30, three
further base coat layers 36, 38, 40 are provided, although again a
single outer layer may be used. Furthermore, outside of the outer
base coat layers 30-40, a tack coat layer 42, a layer of textured
crystals 44, and an overcoat layer 48 are provided. The absolute
thickness of the implant wall may vary but an exemplary average
thickness is about 0.456 mm (0.018 inches). The overall thickness
of the textured implant wall is somewhat greater than a similar
smooth-walled shell because of the extra layers.
[0031] Alternatively, FIG. 3 illustrates a cross-section of
textured single-layered implant shell wall 50 that is a homogeneous
silicone elastomer made entirely of a barrier material that
sterically retards permeation of the silicone gel through the
shell. The outer surface 52 of the barrier layer 50 is textured.
The implants made with the single layer 50 may be for implant in
the breast such that the entire flexible outer shell is shaped
accordingly, for instance in with a more flattened posterior side
and rounded anterior side.
[0032] In addition to the aforementioned dipping process, the
flexible shell for the prosthetic implant may be formed using a
molding process. For example, a rotational molding process such as
described in Schuessler, U.S. Pat. No. 6,602,452, may be used. The
process for forming texturing on the exterior surface is preferably
done using a dipping technique, but the formation of the flexible
shell may then be accomplished by one of a number of methods.
[0033] An exemplary process for forming a textured outer surface on
either a multi-layered shell as in FIG. 2 or a single-layered shell
as in FIG. 3 will now be described. After the mandrel 20 of FIGS.
1A-1C is raised out of the dispersion with what is to be the final
layer adhering thereto, this layer is allowed to stabilize. That
is, it is held until the final coating no longer flows freely. This
occurs as some of the solvent evaporates from the final coating,
raising its viscosity.
[0034] Again, it should be understood that alternative methods are
contemplated for forming the flexible shell prior to the texturing
process. The dip molding process advantageously results in the
flexible shell pre-mounted on a dipping mandrel, which can then be
used for the texturing process. However, if the flexible shell is
made by another technique, such as by rotational molding, it can
subsequently be mounted on a dipping mandrel and the process
continued in the same manner.
[0035] Once the flexible shell has been stabilized and mounted on
the mandrel, any loose fibers or particles are blown off of the
exterior of the shell with an anti-static air gun. A tack coat
layer is then applied. The tack coat layer may be sprayed on, or
may be applied by dipping the flexible shell on the mandrel into a
tack coat material, for example, a tack coat dispersion. The
operator immerses the flexible shell into the dispersion and
returns the mandrel to a rack for stabilization. The time required
for stabilization typically varies between about 5 and about 20
minutes. A suitable tack coat layer may be made using the same
material employed in the base layers.
[0036] After tack coat layer has been applied, rounded salt
particles are applied substantially evenly over the entire surface.
The solid particles may be applied manually by sprinkling them over
the surface while the mandrel is manipulated, or a machine
operating like a bead blaster or sand blaster could be used to
deliver a steady stream of solid particles at an adequate velocity
to the coating on the mandrel.
[0037] In one embodiment, the coated mandrel is dipped into a body
of the particles. In another embodiment, particle application is
accomplished by exposing the coated mandrel to a liquid dispersion
of the particles. It should be understood that the present
invention is not intended to be restricted to any one particular
method of applying the particles.
[0038] In one embodiment, a salt bath for coating the tacky
flexible shells is prepared by first procuring a quantity of
rounded salt crystals and sorting the crystals into a desired size
range. For example, unsorted rounded salt crystals are placed in a
shaker having a first sieve size (e.g. coarse sieve) and a second
sieve size (e.g. fine sieve). Larger salt crystals will be stopped
by the coarse sieve at the inlet of the salt shaker, while smaller
salt crystals will continue through both of the sieves. Crystals in
the desired size range are trapped between the sieves. In a
specific embodiment, the first sieve is a 14 mesh sieve and the
second sieve is a 20 mesh sieve. In another embodiment, the first
sieve is a 20 mesh sieve and the second sieve is a 40 mesh sieve.
In yet another embodiment, the first sieve is a 40 mesh sieve and
the second sieve is a 80 mesh sieve.
[0039] In one embodiment, the rounded particles used in accordance
with the invention have a substantially uniform particle size of
between about 150 microns and about 1450 microns.
[0040] In one embodiment, the rounded particles comprise or consist
of relatively fine grained particles. For example, in one
embodiment, the rounded particles have a maximum particle size of
at least about 150 microns, for example, the particles have a
maximum particle size in a range of between about 180 microns and
about 425 microns. For example, about 90% of the rounded particles
will be retained between a sieve having mesh size 80 and a sieve
having mesh size 40.
[0041] In another embodiment, the rounded particles comprise or
consist of relatively medium grained particles. For example, in one
embodiment, the rounded particles have a maximum particle size of
at least about 300 microns, for example, the particles have a
maximum particle size in a range of between about 425 microns and
about 850 microns. For example, about 90% of the particles will be
retained between a sieve having mesh size 40 and a sieve having
mesh size 20.
[0042] In yet another embodiment, the rounded particles comprise or
consist of relatively large grained particles. For example, in one
embodiment, the rounded particles have a maximum particle size of
at least about 800 microns, for example, the particles have a
maximum particle size in a range of between about 850 microns and
about 1450 microns. For example, about 90% of the particles will be
retained between a sieve having mesh size 20 and a sieve having
mesh size 14.
[0043] The size of the salt crystals can be selected by sorting a
bulk quantity of rounded salt crystals using a series of gradually
smaller meshes.
[0044] In accordance with one embodiment of the invention, the salt
crystals, for example, those having a particular size distribution
are then added to an aqueous salt bath prior to being applied to
the shell. The tacky flexible shells are immersed in the salt bath,
rotated for even coverage, removed, and then allowed to stabilize.
After a suitable period of stabilization, such as between about 5
minutes and about 20 minutes, the flexible shells may be dipped
into an overcoat dispersion. A suitable overcoat dispersion may
also be made using the same material employed in the base layers.
The flexible shells on the mandrels are then mounted on a rack and
allowed to volatilize for a sufficient time, such as, for example,
about 15 minutes.
[0045] In one embodiment, the entire silicone elastomer shell
structure is vulcanized or cured in an oven at elevated
temperatures. For example, the temperature of the oven is
maintained at a temperature between about 200.degree. F. and about
350.degree. F. for a curing time preferably between about 20
minutes and about 1 hour, 40 minutes.
[0046] Upon removal from the oven, the mandrel/shell assembly is
placed in a solvent for the solid particles, and the solid
particles are allowed to dissolve. The solvent is a material that
does not affect the structure or integrity of the silicone
elastomer. When the solid particles have dissolved, the assembly is
removed from the solvent and the solvent evaporated. The shell is
then removed from the mandrel. At this point, it is preferable to
place the shell in a solvent for the solid particles and gently
agitate it to ensure complete dissolution of all the solid
particles. Once the shell has been removed from the solvent, the
solvent evaporates or otherwise is removed from the shell.
[0047] Dissolving the solid particles leaves behind open pores,
voids or spaces in the surface of the shell. When applied, some of
the solid particles are partially exposed so that they can be acted
upon by the solvent. These exposed solid particles also provide a
way for the solvent to reach those solid particles beneath the
surface to dissolve them in turn. The result is an interconnected
structure of cells, some of which are open to the surface, in the
outer layer of the shell. The process described above produces a
shell like that shown in either FIG. 2 or 3. The shell has a thin
outer wall made of silicone elastomer with an opening therein at
the point where a support member connected to the mandrel 20, which
opening will subsequently be covered with a patch.
[0048] The present invention diverges from previous processes in
the make-up of the salt crystals used in the dispersion 22. Namely,
as seen in FIG. 4, rounded salt crystals 60 are shown over a
reference scale 62. In contrast to regular crystalline sodium
chloride 70, as seen against a scale 72 in FIG. 5, the rounded salt
crystals 60 have been appropriately processed to smooth any sharp
or non-rounded edges that are typically found on standard sodium
chloride crystals 70 (sometimes, termed "cubic salt crystals").
[0049] FIGS. 6A and 6B illustrate in magnified cross-section and
plan view, respectively, an implant shell 80 of the prior art
having texturing formed using conventional cubic salt crystals. The
shell 80 includes an inner wall 82 and an outer textured surface
84. This textured surface 84 is formed by applying cubic salt
crystals and then dissolving those crystals to leave an open-celled
porous surface. The relatively rough surface 84 is partly the
result of the angular salt crystals used in the formation process.
The particular texture illustrated is sold under the tradename
Biocell.RTM. surface texture by Allergan, Inc. of Irvine,
Calif.
[0050] FIGS. 7A and 7B illustrate in magnified cross-section and
plan view, respectively, another implant shell 90 of the prior art
having texturing formed using conventional cubic salt crystals. The
shell 90 includes an inner wall 92 and an outer textured surface
94. This textured surface 94 is formed by an embossing process that
imprints the texture on uncured silicone material. The particular
texture illustrated is sold under the tradename Siltex.RTM. surface
texture by Mentor Corp. of Santa Barbara, Calif.
[0051] Now with references to FIGS. 8A and 8B, a magnified
cross-section and plan view of an implant shell 100 of the present
invention having texturing formed using rounded salt crystals is
illustrated. The shell 100 includes an inner wall 102 and an outer
textured surface 104. This textured surface 104 is formed by
applying rounded salt crystals and then dissolving those crystals
to leave an open-celled, porous, textured surface, as explained
above. The textured surface 104 is somewhat smoother than those
made with angular salt crystals, as seen in FIGS. 6 and 7. Although
not shown in great detail, the pores or openings in the open-celled
surface 104 have smoother dividing walls and fewer angular
discontinuities than the pores or openings in conventionally
manufactured shells that are otherwise identical but use angular
salt crystals rather than rounded salt crystals. As will be shown,
this difference surprisingly leads to statistically significant
changes in overall shell strength.
[0052] In one embodiment, the rounded salt crystals are applied so
as to achieve a depth ranging from a portion of one crystal
diameter to a multiple of many crystal diameters. The crystals may
be embedded in the surface of the shell to a depth of from about
one to about three times the diameter of the crystals. Penetration
of the solid crystals depends upon the size of the crystals, the
thickness of the final uncured layer, the viscosity of the uncured
layer and the force with which the crystals are applied. These
parameters can be controlled to achieve a desired depth of
penetration. For example, if the last layer is relatively thick and
low in viscosity, less external force will be required on the solid
crystals to produce an acceptable pore depth.
[0053] Although standard sodium chloride is preferably used for the
rounded salt crystals, other salts may be suitable based on several
factors: (1) the salt should be economically available in the
desired particle sizes; (2) the salt should be nontoxic in case
some remains in the surface of the prosthesis; and (3) the salt
should be readily soluble in a solvent that is economically
available, nontoxic and does not dissolve the silicone
elastomer.
[0054] In one embodiment, the rounded salt particles are sodium
chloride crystals which are readily available in granulated form,
and can be processed into round crystals, for example, by an
industrial milling facility, including Central Salt & Marine
Chemicals Research Institute of Bhavnagar, India, a subsidiary of
the Council of Scientific & Industrial Research (CSIR), a
publicly funded industrial R&D organization in India. When
crystalline sodium chloride is used in accordance with the
invention, the solvent may comprise pure water. A person of
ordinary skill in the art will understand that a number of solid
and solvent pairs could be chosen in accordance with various
embodiments of the invention.
[0055] After finishing the shell according to the steps described
above, additional processing steps may be performed. For example,
the opening left by the dip molding process may be patched with
unvulcanized sheeting, for example, uncured silicone elastomer
sheeting. If the prosthesis is to be filled with silicone gel, this
gel may be added and cured, the filled prosthesis packaged, and the
packaged prosthesis sterilized. If the prosthesis is to be inflated
with a saline solution, a one-way valve is assembled and installed,
the prosthesis is post cured if required, and the prosthesis is
then cleaned, packaged and sterilized. A combination breast implant
prosthesis can also be made wherein a gel-filled sac is positioned
inside the shell to be surrounded by saline solution.
[0056] As mentioned above, the properties of an implant shell
having a texture formed with round salt crystals are statistically
superior to those formed using cubic salt crystals. This is
believed to be due to a reduction in stress concentrations, which
may be seen at the sharp corners formed using cubic salt
crystals.
[0057] To compare the different shells, standard tensile strength
specimens were cut from the shells and subjected to stress tests.
The comparison shell was a standard commercial textured shell of
the prior art sold under the tradename INAMED.RTM. BIOCELL.RTM.
Saline- or Silicone-Filled Breast Implants, by Allergan, Inc. of
Irvine, Calif. More specifically, random BIOCELL.RTM. shells formed
using the process described with reference to FIGS. 6A and 6B were
used for comparison. Sixty specimens from this group were cut using
an H2 die and tested for tensile strength. Table I below
illustrates the results.
TABLE-US-00001 TABLE I Test of Prior Art Commercial Textured Shells
Ultimate Break Ultimate Tensile Thickness Stress@ % elongation
(psi) force Elongation Strength (in) 50% 100% 200% 300% (lbf) (%)
(psi) Mean 0.0209 52.79 84.40 176.119 295.552 4.272 621.690 819.079
Std. 0.0021 3.54 5.79 11.985 19.723 0.511 32.227 42.482 Min 0.0170
44.49 70.49 147.73 250.188 3.439 552.016 752.760 Max 0.0260 63.89
102.77 213.868 355.503 5.802 707.647 912.512
[0058] Likewise, sixty specimens from a group of shells formed
using the process of the present invention were cut using an H2 die
and tested for tensile strength. Table II below illustrates the
results.
TABLE-US-00002 TABLE II Test of Shells Produced with Process of the
Present Invention Ultimate Break Ultimate Tensile Thickness Stress@
% elongation (psi) force Elongation Strength (in) 50% 100% 200%
300% (lbf) (%) (psi) Mean 0.0214 47.50 76.08 163.350 280.964 4.494
662.411 841.880 Std. 0.0013 2.18 3.74 7.811 12.474 0.328 20.845
33.806 Min 0.0190 42.52 68.33 147.318 252.912 3.617 591.457 761.376
Max 0.0250 52.20 84.29 179.215 305.826 5.528 705.347 934.60
[0059] These data show that test samples of similar thickness
formed by the methods of the present invention experience lower
stresses during elongation while the break force, ultimate
elongation, and tensile strengths are significantly higher.
Specifically, the mean thickness of the test samples formed in
accordance with present invention was 0.0214 inches, while the mean
thickness of the prior art test samples was 0.0209 inches, or
around a 2.3% difference. However, the mean ultimate break force
for samples of the present invention was more than 5% greater, the
mean ultimate elongation was more than 6% greater, and the mean
ultimate tensile strength was nearly 3% greater than samples of the
prior art. Given the number of samples (n=60), these differences
are somewhat surprising given the similar technique for forming the
shells and similar thicknesses. Applicants believe that the rounded
salt crystals form a smoother open-cell structure on the exterior
of the shells which reduces stress concentrations. As such, the
test results indicate other than an expected linear relationship
proportional to the difference in thickness.
[0060] It is also important to note the improvement in ultimate
elongation. The resulting 662% mean elongation for the sixty shells
tested is well past the level required by various regulatory bodies
around the word. In particular, the U.S. standard is 350% from ASTM
F703, Standard Specification for Implantable Breast Prostheses. In
Europe and elsewhere, the standard for elongation is set at 450% by
ISO 14607. The implant shells formed by the lost material technique
and rounded salt crystals satisfy these standards with greater
margins of confidence than ever before. It is believed that
changing from a cubic crystal with sharp corners and edges to the
rounded crystals where stress concentrations are more evenly
distributed helps statistically meet consensus performance breast
standards.
[0061] In addition, tests were conducted on shells that were formed
using the texturing process of the present invention both with
conventional cubic salt crystals and with the rounded salt crystals
disclosed herein. That is, instead of comparing the shells of the
present invention with existing commercial shells, new shells were
formed using the same process but with conventional angular or
cubic salt crystals.
[0062] Specifically, five shells textured with regular cubic salt
crystals were dip molded, and five shells textured with rounded
salt crystals were also dip molded. All the shells were subjected
to gel curing at 145.degree. C. for 8 hours, and then subjected to
a simulated sterilization at 127.degree. C. for 20.5 hours. Sixty
tensile strength specimens from each batch were cut with an H2 die
and tested. These results are shown in the following Tables III and
IV.
TABLE-US-00003 TABLE III Test of Textured Shells formed with Cubic
Salt Crystals Ultimate Break Ultimate Tensile Thickness Stress@ %
elongation (psi) force Elongation Strength (in) 100% 200% 300%
(lbf) (%) (psi) Mean 0.0197 108.44 245.196 427.548 3.157 574.394
1020.331 Std. 0.0012 4.32 9.455 15.716 0.253 22.905 50.407 Min
0.017 96.59 218.531 396.776 2.73 513.924 905.827 Max 0.022 119.34
270.61 471.472 3.781 616.102 1126.053
TABLE-US-00004 TABLE IV Test of Textured Shells formed with Rounded
Salt Crystals Ultimate Break Ultimate Tensile Thickness Stress@ %
elongation (psi) force Elongation Strength (in) 100% 200% 300%
(lbf) (%) (psi) Mean 0.0196 113.49 253.224 437.177 3.321 593.298
1076.807 Std. 0.0015 5.13 10.537 16.966 0.337 22.248 57.867 Min
0.015 102.42 232.879 401.088 2.189 543.156 926.505 Max 0.025 124.49
276.015 473.083 4.321 639.847 1181.189
[0063] Again, these data show that test samples of similar
thickness formed by the methods of the present invention experience
lower stresses during elongation while the break force, ultimate
elongation, and tensile strengths are significantly higher.
Specifically, the mean thickness of the test samples formed in
accordance with present invention was 0.0196 inches, while the mean
thickness of the prior art test samples was 0.0197 inches, or
around a 0.05% difference, with the samples made in accordance with
the present invention being thinner on average. However, the mean
ultimate break force for samples of the present invention was more
than 5% greater, the mean ultimate elongation was more than 3%
greater (and sufficient to meet global standards), and the mean
ultimate tensile strength was nearly 6% greater than samples of the
prior art. Given the number of samples (n=60) and the fact that the
shells were identically formed except for the shape of the salt
crystals, these differences are even more surprising than the
previous comparison. Once again, the test results indicate a
non-linear relationship relative to the difference in
thickness.
[0064] Although the invention has been described and illustrated
with a certain degree of particularity, it is understood that the
present disclosure has been made only by way of example, and that
numerous changes in the combination and arrangement of parts can be
resorted to by those skilled in the art without departing from the
scope of the invention, as hereinafter claimed.
* * * * *