Patent Description:
<CIT>describes a uniformly expandable mold formed with a continuous surface defining a three-dimensional pattern for replicating an article. The relative pressure between the inside of the mold and the outside controls the area of the surface to change the size of the three-dimensional pattern without distorting the relative dimensional relationship of the component segments forming the pattern whereby material may be deposited on the mold surface with the mold expanded to a desired size. The pressure differential is increased to increase the size of the mold and stretch the layer already deposited thereon. A second, dissimilar layer is bonded to the first layer while it is stretched. When the article is removed from the mold, a state of relative expansive/compressive tension is created at the bond interface between the first and second layers which forces the material of one layer to enter voids in the other layer to seal defects.

<CIT> describes a method of forming an implant including providing a preformed shell formed from at least one cured elastomeric layer. The preformed shell includes an outer surface, an inner surface, and an opening for accessing an interior volume of the preformed shell. The method further includes expanding the preformed shell to an expanded state, in which the interior volume is greater than the interior volume of the preformed shell at a time of forming the preformed shell and forming an inner zone having at least one inner elastomeric layer on at least a portion of the inner surface of the preformed shell, while the shell is in the expanded state, thereby forming a multi-zone shell. The method further includes reducing the interior volume of the multi-zone shell, thereby contracting the at least one inner elastomeric layer of the inner zone and causing texturing of the at least one inner elastomeric layer.

Prosthetic implants, such as tissue expanders, are typically used to replace or augment body tissue. In the case of the female breast, it may become necessary to remove some or all of the mammary gland and surrounding tissue in order to treat breast cancer. This surgery typically leaves a void that can be filled with an implantable breast prosthesis that supports surrounding tissue and provides a normal body appearance, thereby eliminating much of the shock and depression that often follows breast cancer surgeries. Implantable breast prostheses are also used for breast augmentation procedures.

Tissue expanders are a type of implantable devices that are placed beneath the skin and then gradually inflated to stretch the overlying tissue. Tissue expanders are commonly used to either create a pocket for receiving a permanent prosthesis or to generate an increased skin surface area in anticipation of the new skin being utilized for grafting or reconstruction. After implantation, a solution, such as saline, is periodically injected into the tissue expander to increase the volume of the expander. Between injections, the surrounding skin is permitted to stretch and grow to create the increased skin surface. The solution (e.g., saline solution) may also be withdrawn from the tissue expander to reduce its volume.

Implantable prostheses and tissue expanders are usually formed of a shell of an elastomeric material (e.g., a silicone shell). Such devices are typically manufactured by dipping an appropriately sized and shaped mandrel into a biocompatible elastomer, such as silicone. Once the shell has been formed, it is removed from the mandrel. The dip-molding process results in the formation of a shell that has a mandrel opening, e.g., a circular hole, in one of its faces. The mandrel opening is subsequently covered with a patch that seals the hole to form a fluid impervious implant shell. The patch may be attached to the implant shell using silicone elastomers or other similar biocompatible elastomers.

Tissue expanders typically have integrated injection ports that are used for expanding shells. Over as period of time, a fluid, such as saline, is introduced through the injection ports to fill and expand the shells in order to enlarge the breast pocket. A potential failure mode for a mammary implant is accidental puncture of the shell outside the injection port, thereby resulting in fluid leaks and deflation of the shell, which may require another operation to remove and/or replace the tissue expander.

There have been many efforts directed to making mammary implants. For example, <CIT>, assigned to Mentor Worldwide LLC, teaches a surgical prosthesis having a textured exterior surface formed of non-absorbent material, which is substantially free of pores and interstices. The device is usable for mammary and other implants. As shown in <FIG> of the '<NUM> patent, an unpatched surgical prosthesis, such as for use as a mammary implant, is stretched over a flat or low curvature disk having a circular, oval or other suitable shaped cross-section. The majority of the exterior surface of the prosthesis is located on the upper side of the disk. A layer or multiple layers of unvulcanized or partially vulcanized silicone with a total thickness of <NUM> inches to <NUM> inches covers the upper surface of the prosthesis. The silicone covering is disposed across almost the entire exterior surface of the prosthesis such that no seam will appear visible at the top or substantially any of the sides of the finished prosthesis. The silicone covering is covered with a porous or textured medium, such as foam, a perforated screen or a specially molded form having a textured surface of the particular desired design and topography. The entire assembly including the disk, prosthesis, silicone layer and porous or textured medium is then compressed using either cold or hot compressive platens. After compression, the platens are removed and the medium is also removed leaving a texturized imprint in the silicone layer. The prosthesis with the imprinted texturized silicone layer is then removed from the disk and the prosthesis with the imprinted silicone layer is cured at vulcanizing temperatures.

There have been many efforts directed to providing implantable prostheses that are designed to prevent fluid leaks. For example, <CIT>, assigned to Mentor Worldwide LLC, teaches a mammary prosthesis having a self-sealing area in the upper pole region of the anterior face. The self-sealing area is greater than that of a traditional filling port, and reduces the severity of the consequences of an inadvertent puncture by a hypodermic needle during the filling process. In addition, the self-sealing area is thicker than the material in the other areas of the prosthesis, causing fluid introduced to the prosthesis to stay in the lower pole region of the prosthesis, making the shape of the prosthesis appear more like that of a natural breast.

<CIT>, assigned to Ethicon, Inc. of Somerville, New Jersey, teaches an expandable implant including an implant shell having an opening and a valve assembly for closing the opening. The valve assembly has a first elastic patch, and a second elastic patch juxtaposed with the first elastic patch. A major face of the first elastic patch opposes a major face of the second elastic patch. The opposing major faces have a bonded area in which the opposing faces are joined together and an unbonded area in which the opposing major faces are not joined together and are free to move away from one another. A plug is disposed between the opposing major faces. A first opening extends through the first elastic patch and a second opening extends through the second elastic patch. The first and second openings are offset from one another and the unbonded area defines an elongated channel extending between the first and second openings.

<CIT>, assigned to Ethicon, Inc. of Somerville, New Jersey, teaches a tissue expander having an outer shell configured to retain a fluid, and an injection dome having a self-sealing septum region arranged through the outer shell. The injection dome is adapted to accept a hypodermic needle in order to fill the outer shell with fluid. The injection dome has a self-sealing patch arranged around the injection dome and along the outer shell, which includes a first sheet having a first sheet perimeter and forming a first central opening, a second sheet having a second sheet perimeter and forming a second central opening, an outer washer arranged between the first and second sheets at the first sheet perimeter and the second sheet perimeter, and a second washer arranged between the first and second sheets at the first central opening and the second central opening. The first sheet and the second sheet bound an annular space formed between the outer washer and the inner washer. The annular space is filled with a self-sealing material, such as a hydrophobic material, having a viscosity which is sufficiently high to prevent the self-sealing material from flowing outside the annular space when either the first or second sheet is punctured with a hypodermic needle, but low enough in viscosity so that the self-sealing material flows to close a track made by a hypodermic needle that has punctured the first or second sheet. The self-sealing material may be liquid silicone rubber, cohesive gel, sensitive gel, or memory gel.

<CIT> and <CIT>, both assigned to ImplantAdjust, LLC or Point Roberts, Washington, disclose an adjustable implant for volumetrically altering, replacing, expanding, or augmenting tissues. The implant includes an elastomeric membrane enclosed or partially enclosed about a main chamber. The implant is adapted to expand when filled with a fluid. The membrane includes an outer zone formed from at least one outer elastomeric layer; an inner zone formed from at least one inner elastomeric layer; and a middle zone formed from at least one elastomeric middle layer that is positioned between a least a portion of the outer zone and at least a portion of the inner zone. The implant is configured so that the middle zone is under contraction from a contracting force provided by the outer zone or the inner zone.

In spite of the above advances, there remains a need for improved mammary implants, prosthetic implants, and tissue expanders having effective and reliable self-sealing capabilities incorporated therein. There also remains a need for mammary implants, prosthetic implants, and tissue expanders having self-sealing membranes, self-sealing sheets, and self-sealing shell constructions that do not leak when punctured with a needle, and that do not leak when expanded to target volumes and pressures.

The invention is set out in the enclosed claims. A method of making a self-sealing membrane for a prosthetic device includes applying tension to a first layer of a cured elastomeric material to stretch the first layer, and while the first layer remains stretched, applying a second layer of an uncured elastomeric material over a first major surface of the first layer, wherein the second layer of an uncured elastomeric material is applied to the first layer in sheet form, and curing the second layer of the elastomeric material.

After the second layer is cured, tension is released from the first layer whereupon the first layer returns to a non-stretched configuration for holding the second layer in contraction.

In one embodiment, the first layer is a shell for a prosthetic implant, and the applying tension step includes stretching the shell over a disk for exposing the first major surface.

In one embodiment, the disk has a flat major surface, and stretching the shell over the disk conforms the first major surface of the shell to the shape of the flat major surface of the disk.

In one embodiment, curing the second layer preferably includes applying heat to the second layer.

In one embodiment, the second layer may be compressed into the first major surface of the first layer, such as by using a press.

In one embodiment, the compressing step may occur during the applying heat step. In one embodiment, the compressing step may occur before the applying heat step.

In one embodiment, the method may include, while the first layer remains stretched, applying a third layer of an uncured elastomeric material over a second major surface of the first layer and curing the third layer of the elastomeric material.

In one embodiment, after the second and third layers are cured and the tension is released from the first layer, the first layer returns to the non-stretched configuration for holding the second and third layers in contraction.

In one embodiment, the first layer includes a cured silicone elastomer, and the second and third layers may include an uncured silicone elastomer.

In one embodiment, a fixture may be used for applying tension for stretching the first layer within a plane.

In one embodiment, curing the second and third layers may include applying heat to the second and third layers.

In one embodiment, the second and third layers may be compressed into the respective first and second major surfaces of the first layer.

In one embodiment, a self-sealing membrane for a prosthetic implant has a three-layer construction including a middle layer of an elastomeric material having first and second major surfaces, a first outer layer of an elastomeric material overlying the first major surface of the middle layer, and a second outer layer of an elastomeric material overlying the second major surface of the middle layer, whereby the middle layer of the elastomeric material holds the first and second outer layers of the elastomeric material in contraction.

In one embodiment, the self-sealing membrane is preferably secured to an inner surface of a silicone shell of a prosthetic implant.

In one embodiment, the self-sealing membrane preferably extends around an outer perimeter of an injection port of a prosthetic implant.

In one embodiment, the self-sealing membrane may be secured to a posterior region of a silicone shell of a prosthetic implant.

In one embodiment, the self-sealing membrane preferably defines a self-sealing base that covers an inner surface of the silicone shell at the posterior region of the silicone shell.

In one embodiment, a self-sealing sheet includes two or more of the self-sealing membranes having the three-layer construction disclosed herein.

In one embodiment, major surfaces of adjacent ones of the self-sealing membranes having the three-layer construction are laminated together.

In one embodiment, a self-sealing sheet may include a first self-sealing membrane having the three-layer construction, a second self-sealing membrane having the three-layer construction being laminated to an exposed major surface of the first self-sealing membrane, and a third self-sealing membrane having the three-layer construction being laminated to an exposed major surface of the second self-sealing membrane.

The self-sealing sheet having two of more of the self-sealing membranes having the three-layer construction may be incorporated into an injection port assembly of a prosthetic implant. In one embodiment, the self-sealing sheet may be disposed between an injection dome and a needle guard of an injection port assembly.

In one embodiment, a shell (e.g., a silicone shell) for a prosthetic implant (e.g., a tissue expander) preferably has self-sealing properties incorporated therein, which prevent the shell from leaking fluid when punctured by a needle or a sharp object.

In one embodiment, the shell has a two-layer construction with a first layer and a second layer, whereby the second layer is held in contraction by the first layer.

In one embodiment, the first layer may be formed by depositing and curing a biocompatible elastomeric shell layer (e.g., a silicone shell) on a three-dimensional (3D) tool, such as a mandrel. In a relaxed state (i.e., with no external forces exerted on the shell), the shell has an inherent interior three-dimensional (3D) volume and a two-dimensional (2D) surface area.

In one embodiment, the first layer may be a shell that is stretched in a plane so that the surface area of the shell is greater than the inherent surface area of the shell in the relaxed state, however, the encompassed volume of the stretched shell is less than the inherent 3D volume of the shell in the relaxed state. After the shell is stretched, the second layer of an uncured biocompatible elastomeric material (e.g., uncured silicone material) may be deposited onto the stretched shell and cured, while the shell is held in the stretched state. After curing of the second layer and release of the two-layer construction back to a relaxed state, the second layer is held in contraction by the first layer, resulting in the second layer being configured to contract and close any holes that may be formed in the two-layer construction (e.g., when a needle punctures the self-sealing structure).

Different systems, devices and methods may be used for stretching the first layer of a self-sealing membrane to increase the surface area of the first layer. In one embodiment, the first layer (i.e., a silicone shell) is stretched over a flat disk, whereby the outer periphery of the shell wraps over the outer periphery of the disk to keep the shell in place on the disk. In a second embodiment, the first layer may be stretched by using biaxial and/or a multi-axial tensioning process for griping and stretching the first layer.

In one embodiment, the first layer is preferably stretched in different directions within a single plane.

In one embodiment, a prosthetic implant (e.g., tissue expander) may have one or more self-sealing membranes (e.g., elastomeric membranes) that are designed to prevent fluid leaks if an implant shell and/or the one or more self-sealing membranes are punctured by a needle.

In one embodiment, the self-sealing elastomeric membranes may be made of silicone materials, however, other elastomeric materials may be used for making the self-sealing membranes disclosed herein.

When designing, manufacturing and testing mammary implants, tissue expanders, and breast prostheses, the terminology "self-sealing" is defined as the ability of a material to seal after being punctured (e.g., by a filling needle) so as to prevent the filler material (e.g., saline; gel) within the implant from escaping, even when the implant is put under load. Self-sealing requirements for breast tissue expanders are defined in ASTM F1441-<NUM>.

In one embodiment, a method of making an implant (e.g., a breast tissue expander) having self-sealing capabilities preferably includes stretching a shell (e.g., a silicone shell) onto a substrate having a major, flat surface (i.e., a disk) to expose a flat, uniform surface on the shell.

In one embodiment, after being placed over the disk, the shell is stretched by the disk and has the exposed, flat, uniform surface that generally conforms to the shape of the underlying major, flat surface of the disk.

In one embodiment, with the shell stretched by the disc, a layer of an uncured biocompatible elastomeric material (e.g., unvulcanized polysiloxane elastomer) may be deposited onto the exposed, flat surface of the stretched shell. The layer of the uncured elastomeric material is desirably trimmed to the edge of the disk.

In one embodiment, the uncured elastomer layer (e.g., an uncured silicone layer) is cured on the shell, while the shell is being stretched by the stretching disk.

In one embodiment, the layer of the uncured elastomeric material may be cured during a pressing step, whereby platens are used to press the first and second layers together. In one embodiment, the platens may be heated. The heat preferably cures the second layer that has been added to the shell.

In one embodiment, the second layer that has been added to the shell may be cured by placing an assembly of the disk, the shell, and the uncured elastomer layer into an oven having temperatures that are adapted to cure the second layer.

In one embodiment, once the second layer is fully cured on the shell (i.e., the first layer), the shell and the cured second layer may be removed from the stretching disk. Upon removing the shell from the disk, the shell contracts back into its original shape.

The resulting seal-sealing membrane has a two-layer construction, whereby a second zone (i.e., the cured elastomeric layer) of the self-sealing membrane is held in contraction by a first zone (i.e., the shell). In one embodiment, the initial shell layer that was stretched over the disk holds the added elastomeric layer (i.e., the second zone) in contraction.

In one embodiment, the above-describe method requires the initial silicone shell layer to be elongated in a two-dimensional planar manner.

In one embodiment, a foam layer may be placed into the press prior to closing the platens of the press. In one embodiment, a foam layer is placed between the uncured elastomeric layer and the platen prior to closing the press for compressing the assembly of the first layer (e.g., the silicone shell) and the second layer (e.g., the uncured elastomeric layer).

In one embodiment, the volume of the shell is not significant in the process, and the process of making a self-sealing membrane does not require the volume to be greater during the stretched state (and upon application of the additional silicone sheeting) compared to its initial state. For example, in one embodiment, the surface area of the stretched shell may be <NUM>% to <NUM>% compared to its relaxed state, whereby the encompassed volume of the stretched shell may be <NUM>% to <NUM>% compared to its relaxed state.

In one embodiment, a self-sealing membrane may have a plurality of layers that are under contraction, which can be achieved by running the above-disclosed process multiple times.

For example, one layer can be added as described above, and a second layer can be added by inverting the shell, stretching the shell back onto the disk, and repeating the above-described process to add a second uncured elastomeric layer.

In one embodiment, a self-sealing membrane may include a three-layer construction including two outer layers under contraction and an intermediate layer that holds the two outer layers in contraction. In one embodiment, the self-sealing membrane having the three-layer construction may be achieved by using a modified stretching disk fixture that allows for the application of a first uncured elastomeric layer on a first major surface of a shell and the application of a second uncured elastomeric layer on a second major surface of the shell. In one embodiment, the shell is stretched as the first and second uncured elastomeric layers are applied to the shell, and the shell remains stretched as the first and second elastomeric layers are cured.

In one embodiment, when performing a process of applying layers of uncured elastomeric material multiple times, the stretching disks may be different sizes resulting in layers that have different levels of contraction. For example, an outermost layer of a self-sealing membrane may have the lowest amount of contraction and an innermost layer of the self-sealing membrane may have the highest amount of contraction, which may provide a "bottle-neck" mechanism for self-sealing. Furthermore, differential contraction between layers may result in a desired curvature of the curved membrane, despite the process being performed in a planar manner.

In one embodiment, a method of making an implant having self-sealing properties may include simultaneously stretching multiple shells onto a stretching disk, and using uncured elastomeric layers between the shells for bonding the adjacent shells together. As a result, contraction of the uncured elastomeric material layers, or differential contraction of the shells if they have different sizes, can result in the formation of a self-sealing implant or expander.

In one aspect which is not claimed, the uncured elastomeric material that is deposited onto a stretched shell does not have to be applied to the shell in sheet form. In one aspect which is not claimed, the uncured elastomeric material may be deposited using other processes such as spraying or dipping the uncured elastomeric material onto an exposed surface of a stretched shell.

In one embodiment, the consistency/durometer and thickness/amount of the one or more uncured elastomeric layers that are applied to a stretched shell may differ. In one embodiment, the stretched shell may have higher tensile stiffness than the uncured elastomeric layers in order to increase the amount of compression imparted in those layers.

In one embodiment, a biaxial tensioning process may be used for making a self-sealing membrane having first and second outer layers that are under contraction and an intermediate layer located between the first and second outer layers and that holds the first and second outer layers under contraction.

In one embodiment, a method of making a self-sealing membrane preferably includes using a fixture for securing an outer periphery of an intermediate layer (e.g., a vulcanized silicone elastomer sheet) and expanding the size of the fixture for stretching the intermediate layer in orthogonal directions. In one embodiment, the intermediate layer is preferably stretched within a single plane so that the intermediate layer has first and second major surfaces that are flat.

In one embodiment, a first layer of an uncured elastomer (e.g., unvulcanized polysiloxane elastomer) may be applied to the first major surface of the intermediate layer, and a second layer of an uncured elastomer (e.g., unvulcanized polysiloxane elastomer) may be applied to the second major surface of the intermediate layer.

In one embodiment, the first and second uncured outer layers and the intermediate layer are desirably pressed together and the three-layer structure may be cured by using heat. In one embodiment, a press having platens may be used for pressing the three layers together. In one embodiment, the platens may be heated. In one embodiment, a roller may be used for applying pressure to the layers.

In one embodiment, once the three-layer construction is fully cured, the outer periphery of the intermediate layer may be released from the fixture, whereupon the intermediate layer returns to its original, non-stretched configuration.

In one embodiment, when the intermediate layer returns to its original, non-stretched configuration, the intermediate layer holds the first and second outer layers in contraction.

In one embodiment, a self-sealing sheet may include a plurality of self-sealing membranes, each self-sealing membrane having a three-layer construction. In one embodiment, adjacent self-sealing membranes, each having three layers, may be joined or laminated together, such as by using unvulcanized material (e.g., unvulcanized elastomeric sheets) between adjacent three-layer, self-sealing membranes.

In one embodiment, a plurality of differentially contracted silicone layers may be achieved by running the above-described process multiple times, or having a fixture that elongates multiple parallel vulcanized silicone elastomer sheets, with the ability to adhere unvulcanized material in between.

In one embodiment, a cured layer of elastomeric material (e.g., a silicone shell) may be stretched over a stretching disk having a curved surface. The stretched cured layer of elastomeric material preferably has an exposed surface that is curved to conform to the shape of the curved surface of the stretching disk. In one embodiment, an uncured elastomeric material is applied over the curved surface of the stretched, cured layer, whereupon the uncured material conforms to the curved shape of the stretched, cured layer. After curing, when the first layer is removed from the disk, the self-sealing membrane defines sheeting that is concave towards the side that was cured under greater elongation.

In one embodiment, the stretching process does not have to be square or rectangular in nature. In one embodiment, a stretching fixture may be circular for radially stretching the cured elastomeric layer (e.g., a silicone shell).

In one embodiment, a seal-sealing membrane has a three-layer construction in which the outer zones (e.g., first and second outer layers) are held in contraction by a middle zone (e.g., an intermediate layer).

In one embodiment, the self-sealing membrane may be used to cover a portion of shell of a prosthetic implant. In one embodiment, the self-sealing membrane may replace a reinforcement patch that is sold under the registered trademark BUFFERZONE® by Mentor Worldwide LLC of Irvine, California, and that is used as a port protector for injection ports of implantable medical devices such as tissue expanders and breast implants.

In one embodiment, the self-sealing membrane disclosed herein is more pliable and easier to fold that conventional bladder-style sealing mechanisms. In one embodiment, the self-sealing membrane has improve tensile properties due to the incorporation of the compressed layers, such as increased elongation to failure, increased ultimate breaking force, and increased tensile stiffness.

In one embodiment, the self-sealing membrane disclosed herein has a homogenous construction with self-sealing capabilities throughout the entire surface area of the self-sealing membrane.

In one embodiment, the self-sealing membrane disclosed herein is easier and faster to make because its construction does not require the use of silicone gel or viscous fluids.

In one embodiment, a self-sealing membrane may be used to cover an anterior region of a shell of a prosthetic implant, such as a tissue expander.

In one embodiment, a self-sealing membrane preferably surrounds the injection port or an injection zone of a tissue expander shell.

In one embodiment, a self-sealing membrane disclosed herein may be used for covering other regions of a shell of a prosthetic implant. For example, a tissue expander (e.g., a breast tissue expander) may have suture tabs located in a posterior region of a shell for securing the tissue expander to surrounding tissue. Thus, in one embodiment, a self-sealing membrane may cover a base, a base patch, a base patch having suture tabs, a posterior end and/or a posterior radius of a tissue expander to protect those areas of the shell that are at risk of accidental needle puncturing, specifically during fixation of the tissue expander to the surrounding tissue.

In one embodiment, the self-sealing membranes and self-sealing structures disclosed herein may be applied throughout a shell to ensure coverage and leak prevention in other desired regions.

In one embodiment, the self-sealing membranes and self-sealing structures disclosed herein may be continuously adjoined or form an overlapping patchwork of self-sealing sheeting that may be applied to cover an entire shell.

Standard injection ports used in breast tissue expanders typically use molded silicone as the self-sealing material, and typically rely on a combination of thickness and compression from the outer metal injection port assembly.

In one embodiment, a self-sealing membrane or self-sealing structure disclosed herein may be incorporated into an injection port of a tissue expander. The seal-sealing construction disclosed herein provides superior self-sealing properties when compared to an equivalent thickness of molded silicone, and therefore can also be used as the injection port material.

In one embodiment, the self-sealing capabilities of an injection port may be improved by using a plurality of the self-sealing membranes that are joined together, whereby the plurality of the joined self-sealing membranes are thinner than the typical, prior art molded silicone material for this use.

These and other preferred embodiments of the present patent application will be described in more detail herein.

Referring to <FIG>, in one embodiment, a system <NUM> for making a self-sealing membrane for a shell (e.g., a mammary implant) preferably includes a press <NUM> having a top platen <NUM> and a bottom platen <NUM> that opposes one another. In one embodiment, the system <NUM> preferably includes a disk <NUM> (i.e., a stretching disk) having a flat major surface and an outer edge <NUM> that extends around an outer periphery of the disk. In one embodiment, a shell <NUM> (e.g., a cured silicone shell) is stretched over the disk <NUM> to expose a flat major surface <NUM> of the shell <NUM> that overlies the flat major surface of the disk <NUM>.

In one embodiment, the shell <NUM> may be made using one or more of the systems, devices and methods disclosed in <CIT>, <CIT>, or U. Patent Application Publication No. <CIT>.

In one embodiment, the shell <NUM> may be made by dipping or spraying a mandrel with a biocompatible, curable material such as silicone, polymers, polyurethane, silicone-polyurethane co-polymers, elastomers or combinations thereof. After application of the biocompatible, curable material to the mandrel, the curable material is allowed to cure and the cured shell is removed from the mandrel.

In one embodiment, the disk <NUM> may be made of materials such as polymers, metal, wood, stone, and ceramic.

In one embodiment, a layer <NUM> of an uncured material (e.g., an uncured elastomer; an unvulcanized polysiloxane elastomer; an uncured silicone layer) is preferably placed onto the exposed flat surface <NUM> of the stretched shell <NUM> and trimmed to the outer edge <NUM> of the stretching disk <NUM>. While the shell remains stretched over the stretching disk <NUM>, the uncured layer <NUM> is desirably cured.

In one embodiment, the combination of the shell <NUM> and the uncured layer <NUM> may be placed into the press <NUM> of the system <NUM> so that pressing forces may be applied to the subassembly of the shell <NUM> and the uncured layer <NUM>. The pressing forces are desirably applied by closing the press <NUM> by moving the top and bottom platens <NUM>, <NUM> toward one another to compress the combination of the shell <NUM> and the uncured layer <NUM>.

In one embodiment, during the pressing step, the top and bottom platens <NUM>, <NUM> may be heated for applying heat to the combination of the shell <NUM> and the uncured layer <NUM>. The heat preferably cures the uncured layer <NUM> for adhering the uncured layer to the expose flat surface <NUM> of the shell <NUM>.

In one embodiment, the stretching disk <NUM>, the stretched shell <NUM>, and the uncured layer <NUM> may be placed into an oven at an elevated temperature for curing the uncured layer <NUM> while the stretched shell <NUM> remains on the stretching disk <NUM>.

In one embodiment, heat may be applied directly to the assembly of the stretching disk <NUM>, the shell <NUM>, and the uncured layer <NUM> using heating elements such as one or more heat guns.

In one embodiment, once the uncured silicone layer <NUM> is fully cured for being adhered to the shell <NUM>, the shell <NUM> and the cured layer <NUM> form a seal-sealing membrane that may be removed from the stretching disk <NUM>. In one embodiment, due to the stretched state of the shell <NUM> on the stretching disk <NUM>, upon removal from the stretching disk <NUM>, the shell <NUM> portion of the self-sealing membrane contracts back into its original shape and the cured layer <NUM> is under contraction.

Referring to <FIG>, in one embodiment, a self-sealing membrane <NUM> has a two-layer construction including a second layer <NUM> (i.e., a second zone) that is held in contraction by a first layer <NUM> (i.e., a first zone). Thus, after being removed from the disk <NUM> (<FIG>), the shell layer <NUM> holds the added layer <NUM> in contraction.

Referring to <FIG>, in one embodiment, a mammary implant <NUM> may include the self-sealing membrane <NUM> shown and described above in <FIG>. The self-sealing membrane <NUM> may be made utilizing the system <NUM> shown and described above in <FIG>. In one embodiment, the self-sealing membrane <NUM> may cover the entire area of the mammary implant <NUM> or a portion of the mammary implant <NUM> (e.g., an area surrounding an injection port). In one embodiment, the self-sealing membrane <NUM> includes the initial silicone shell layer <NUM> that is in its normal, non-stretched state and the added elastomeric layer <NUM> that is under contraction.

Referring to <FIG>, in one embodiment, a self-sealing membrane may have a three-layer construction whereby first and second outer layers are held in contraction by an intermediate layer. In one embodiment, a system <NUM> for making a self-sealing membrane having first and second outer layers held in contraction by an intermediate, middle layer preferably includes two or more grips 208A, 208B that are adapted to grip the outer periphery of a vulcanized silicone sheet <NUM> for stretching the sheet <NUM>. In one embodiment, a first layer 216A of an unvulcanized polysiloxane elastomer 216A is applied over a first major face of the vulcanized, intermediate layer <NUM>, and a second layer 216B of an unvulcanized polysiloxane elastomer is applied over a second major face of the vulcanized, intermediate layer <NUM>. In one embodiment, while the intermediate layer <NUM> is stretched by the grips 208A, 208B, the first and second outer layers 216A, 216B are pressed together to form a three-layer construction and the first and second outer layers 216A, 216B are cured by using heat. Once the three-layer construction is fully cured, the grips 208A and 208B may be loosened for releasing the self-sealing membrane from the grips 208A, 208B. Once the self-sealing membrane is released from the grips, the intermediate layer <NUM> returns to its normal, non-stretched state and the first and second outer layers 216A and 216B are contracted by the intermediate layer <NUM>.

Referring to <FIG>, in one embodiment, a system <NUM> for making a self-sealing membrane having three layers preferably includes a frame <NUM> having four rails <NUM>, <NUM>, <NUM>, and <NUM> that are adapted to slide relative to one another for selectively modifying the size or area of the frame <NUM>. In one embodiment, each sliding rail preferably supports one or more grips <NUM> that are adapted to engage the outer perimeter of a vulcanized silicone layer <NUM>. In the particular embodiment shown in <FIG>, the system <NUM> includes a pair of grips <NUM> attached to each sliding rail <NUM>, <NUM>, <NUM>, and <NUM>. In one embodiment, the grips <NUM> desirably project inwardly toward one another from the outer perimeter of the frame <NUM>.

Referring to <FIG>, in one embodiment, the respective grips <NUM> include clamps <NUM> that are configured for clamping down onto the outer perimeter (e.g., outer edge) of the vulcanized silicone sheet <NUM>.

Referring to <FIG>, in one embodiment, the vulcanized silicone sheet <NUM> has a square or rectangular shape, and the sheet <NUM> may be stretched within a plane along X and Y axes. In one embodiment, the frame <NUM> is loosened so that the fourth sliding rail <NUM> may be moved along the X axis in the direction DIR1 for moving the fourth rail <NUM> away from the second rail <NUM> to stretch the vulcanized silicone layer <NUM> along the X axis. After the fourth rail <NUM> has been moved into the position shown in <FIG>, the frame <NUM> may be tightened to prevent the rails from shifting along the X axis, thereby maintaining the silicone layer <NUM> in the stretched configuration shown in <FIG>.

Referring to <FIG>, in one embodiment, the frame <NUM> may be loosened so that the cured silicone layer <NUM> may be stretched along the Y axis in the direction DIR2. In one embodiment, the frame <NUM> is desirably loosened so that the first rail <NUM> may be slid away from the third rail <NUM> for stretching the cured silicone layer <NUM> along the Y axis. The frame <NUM> may then be tightened to prevent the rails from shifting along the Y axis, thereby maintaining the silicone layer <NUM> in the stretched configuration shown in <FIG> in which the cured silicone layer <NUM> is stretched along both the X and Y axes. In one embodiment, the frame <NUM> is desirably loosened so that the rails <NUM>, <NUM>, <NUM> and <NUM> can be moved in combination and simultaneously, after which the frame <NUM> is tightened thereby maintaining the silicone layer <NUM> in the stretched configuration shown in <FIG>, whereby the cured silicone layer <NUM> is stretched along both the X and Y axes. In one embodiment, the amount of stretching in the X and Y axes is the same to create a uniformly stretched silicone layer <NUM>. In one embodiment, the amount of stretching in the X and Y axes differs to achieve a non-uniform stretched layer having differing self-sealing properties, or different tensile properties along different directions. In one embodiment, rather than using a fixed frame <NUM>, a continuous calendaring process may be used to apply tension to a silicone layer <NUM>, while unvulcanized silicone layers 216A and 216B are applied to the major faces of the silicone layer <NUM>, and subsequently cured through an oven or conveyor belt heating system.

Referring to <FIG>, in one embodiment, a first unvulcanized silicone layer 216A may be applied over a first major surface of the stretched silicone layer <NUM> (<FIG>). The frame <NUM> may then be reversed to expose a second major surface of the stretched silicone layer. A second unvulcanized silicon layer 216B (<FIG>) may be applied over the exposed second major surface of the stretched silicone layer <NUM> (<FIG>).

Referring to <FIG>, in one embodiment, the first unvulcanized layer 216A may be applied over a first exposed major surface of the vulcanized layer <NUM> by gradually laying the first unvulcanized layer 216A onto the exposed, first major surface of the vulcanized layer <NUM>. The unvulcanized layer 216A is applied by gradually laying the layer 216A onto the exposed, first major surface of the vulcanized layer <NUM> in the direction indicated by the first arrow <NUM>, while concurrently pressing the layer 216A with fingers or blunt tooling aids toward the sides, in the lateral directions indicated by the second arrows <NUM> to remove air bubbles.

In one embodiment, after the first unvulcanized layer 216A has been applied over the vulcanized layer <NUM>, the frame <NUM> may be reversed to expose the second major surface of the vulcanized layer, whereupon the second unvulcanized layer 216B may be applied over the second major surface of the vulcanized layer <NUM>.

Referring to <FIG>, in one embodiment, a three-layer structure of the stretched vulcanized layer <NUM> and the two outer unvulcanized layers 216A, 216B may be placed onto a first polyurethane foam layer 242A that underlies the three-layer structure.

Referring to <FIG>, in one embodiment, a second polyurethane foam layer 242B may be placed on top of the three-layer structure shown in <FIG>. In one embodiment, the three-layer structure including the two foam layers 242A (<FIG>) and 242B may be placed into a press, such as the press <NUM> shown and described above in <FIG>. In one embodiment, the polyurethane foams may be used to apply a desired textured surface to the unvulcanized layers 216A, 216B. In one embodiment, the two polyurethane foams are used as buffering materials to apply more even distribution f compression forces during pressing.

Referring to <FIG>, in one embodiment, a metal roller <NUM> may be used as a tooling aide for pressing against the foam layers 242A (<FIG>) and 242B (<FIG>) for compressing the unvulcanized layers 216A, 216B (<FIG>) onto the stretched silicone layer <NUM> (<FIG>). The platens <NUM>, <NUM> shown and described above in <FIG> may also be used.

Referring to <FIG>, in one embodiment, after the second foam layer 242B has been pressed into the second unvulcanized layer 216B, the second foam layer 242B may be slowly peeled away to expose the second unvulcanized layer 216B. The frame <NUM> may be reversed so that the first foam layer 242A may be slowly peeled away to expose the first unvulcanized layer 216A.

Referring to <FIG>, in one embodiment, the second unvulcanized layer 216B is preferably cured while it remains on the second major surface of the stretched silicone layer <NUM>. In one embodiment, heat guns <NUM> may be utilized for curing the second unvulcanized layer 216B. In one embodiment, after the second unvulcanized layer 216B has been cured, the frame <NUM> may be flipped over for curing the first unvulcanized layer 216A that has been applied over the first major surface of the stretched silicone layer <NUM>.

Referring to <FIG>, in one embodiment, after the first and second outer layers 216A and 216B (<FIG>) have been cured (e.g., by using heat) over the respective first and second major surfaces of the stretched silicone layer <NUM>, the clamps <NUM> may be loosened for releasing the outer edges of the silicone sheet <NUM> from the grips <NUM> of the system <NUM>.

Referring to <FIG>, in one embodiment, the system <NUM> shown and described above in <FIG> may be utilized for making a self-sealing membrane <NUM> having three layers including an intermediate layer <NUM> of a silicone elastomer, and first and second outer layers 216A, 216B of a silicone elastomer that are held in contraction by the intermediate layer <NUM>.

Referring to <FIG> and <FIG>, in one embodiment, a breast tissue expander <NUM> may be similar to or include one or more of the structural elements disclosed in assigned <CIT>, assigned to Ethicon, Inc. of Somerville, New Jersey. In one embodiment, the breast tissue expander <NUM> preferably includes a shell <NUM> (e.g., a silicone shell) having an injection port assembly <NUM> with a self-sealing membrane that surrounds the injection port assembly. The self-sealing membrane may be similar to that shown and described above in <FIG> or <FIG>.

Referring to <FIG> and <FIG>, in one embodiment, the breast tissue expander <NUM> preferably includes a base patch <NUM> having one or more suture tabs <NUM> that may be utilized for suturing the breast tissue expander <NUM> to tissue. In one embodiment, the base patch <NUM> preferably covers a posterior region of the breast tissue expander <NUM>.

In one embodiment, the breast tissue expander <NUM> preferably includes a self-sealing base <NUM> having a raised rim <NUM> that is preferably secured to the inside of the shell <NUM>.

In one embodiment, the breast tissue expander <NUM> preferably includes the shell <NUM> (e.g., a silicone shell) having a mandrel opening <NUM> that is covered by the base patch <NUM>, and an injection port opening <NUM> that is adapted to receive an injection port assembly <NUM>.

In one embodiment, a posterior region of the shell <NUM> that surrounds the mandrel opening <NUM> is desirably covered by the self-sealing base <NUM> to protect the posterior face and the posterior radius of the shell. In one embodiment, the raised rim <NUM> of the self-sealing base <NUM> preferably surrounds the posterior radius of the shell <NUM>. In one embodiment, a sealing washer similar to the base patch sealing washer <NUM> may be utilized for sealing and/or adhering the posterior face <NUM> of the self-sealing base <NUM> to the inner surface of the posterior face <NUM> of the shell <NUM>.

In one embodiment, the injection port assembly <NUM> preferably includes an injection dome <NUM> having a port base <NUM> and a sealing flange <NUM>, an injection dome sealing washer <NUM> having a central opening <NUM>, a needle guard <NUM> having a magnet <NUM>, and a self-sealing membrane <NUM> having a three-layer self-sealing construction as shown and described above in <FIG>. In one embodiment, the self-sealing membrane <NUM> desirably has a central opening <NUM> that is aligned with the injection port opening <NUM> of the shell <NUM>. In one embodiment, the central opening <NUM> of the self-sealing membrane <NUM> is adapted to receive the needle guard <NUM> and the port base <NUM> of the injection dome <NUM>.

Referring to <FIG>, the injection port assembly <NUM> is preferably adapted to be aligned with the injection port opening <NUM> of the shell <NUM>. In one embodiment, the self-sealing membrane <NUM> is preferably disposed inside the shell <NUM> and is secured to an inner surface of the shell <NUM> so that the opening <NUM> of the self-sealing membrane <NUM> is aligned with the injection port opening <NUM> of the shell <NUM>. In one embodiment, the needle guard <NUM> is preferably disposed within the central opening <NUM> of the self-sealing membrane <NUM> and the injection port opening <NUM> of the shell <NUM>.

In one embodiment, injection dome sealing washer <NUM> is preferably secured to the outer surface of the shell <NUM> with the central opening <NUM> of the injection dome sealing washer <NUM> aligned with the central opening <NUM> of the self-sealing membrane <NUM> and the injection port opening <NUM> of the shell <NUM>.

In one embodiment, after the self-sealing membrane <NUM> and the injection dome sealing washer <NUM> have been secured to the shell <NUM>, the shell material that surrounds the injection port opening <NUM> is preferably sandwiched between the self-sealing membrane <NUM> and the injection dome sealing washer <NUM>.

In one embodiment, prior to insertion into the central opening <NUM> of the self-sealing membrane <NUM>, the needle guard <NUM> and the injection dome <NUM> are assembled together to form a subassembly. In one embodiment, the injection dome <NUM> preferably includes the port base <NUM> and the sealing flange <NUM> that extends outside the diameter of the port base <NUM>. In one embodiment, when the injection dome <NUM>/needle guard <NUM> subassembly is assembled with the shell <NUM>, the needle guard <NUM> and the port base <NUM> of the injection dome <NUM> pass through the central opening <NUM> of the injection dome sealing washer <NUM> and the central opening <NUM> of the self-sealing membrane <NUM>, as well as the injection port opening <NUM> of the shell <NUM>. The sealing flange <NUM> of the injection dome <NUM> preferably overlies the outer surface of the shell <NUM> for engaging the injection dome sealing washer <NUM>, which is also secured to the outer surface of the shell <NUM>.

Referring to <FIG>, in one embodiment, the injection port assembly <NUM> is assembled with the shell <NUM> of the breast tissue expander <NUM> (<FIG>). The injection port assembly <NUM> preferably passes through the injection port opening <NUM> (<FIG>) of the shell <NUM>. In one embodiment, the self-sealing membrane <NUM> is secured to the inner surface of the shell <NUM> and surrounds the injection port opening <NUM> (<FIG>) of the shell <NUM>. The needle guard <NUM> is assembled with the injection dome <NUM> so that the needle guard <NUM> and the port base <NUM> of the injection dome pass through the central opening <NUM> (<FIG>) of the self-sealing membrane <NUM> as well as the injection port opening <NUM> (<FIG>) of the shell <NUM>. The magnet <NUM> is secured to an underside of the needle guard <NUM>. The sealing flange <NUM> of the injection dome <NUM> extends outwardly beyond the outer perimeter of the injection port opening <NUM> (<FIG>) of the shell <NUM>. The injection dome sealing washer <NUM> preferably secures an underside of the sealing flange <NUM> of the injection dome <NUM> to an outer surface of the shell <NUM>.

Referring to <FIG>, in one embodiment, the self-sealing membrane <NUM> preferably includes the three-layer construction shown and described above in <FIG>. In one embodiment, the self-sealing membrane preferably has the central opening <NUM> that is adapted to receive a needle guard and a base of an injection dome. As described above, the central opening <NUM> is preferably aligned with an injection port opening <NUM> (<FIG>) formed in a shell of a breast tissue expander. In one embodiment, the self-sealing membrane <NUM> preferably includes an inner washer <NUM> that surrounds the central opening <NUM> and an outer washer <NUM> that extends around the outer perimeter of the self-sealing membrane <NUM>. In one embodiment, the inner and outer washers <NUM>, <NUM> are preferably utilized for securing a top surface <NUM> of the self-sealing membrane <NUM> to an inner surface of a shell of a mammary implant. In one embodiment, the first and second sealing washers <NUM>, <NUM> may be replaced by a single washer that extends outwardly between the outer perimeter of the central opening <NUM> and the outer perimeter of the self-sealing membrane, and that completely covers the top surface <NUM> of the self-sealing membrane <NUM>.

Referring to <FIG>, in one embodiment, the self-sealing membrane <NUM> preferably includes a three-layer construction having an intermediate layer <NUM> that is sandwiched between first and second outer layers 316A and 316B. The first and second outer layers 316A and 316B are preferably held in contraction by the intermediate layer <NUM>. The outer sealing washer <NUM> preferably overlies the outer perimeter of the first outer layer 316A for securing the anterior face of the self-sealing membrane <NUM> to an inner surface of a shell of a breast tissue expander.

Referring to <FIG> and <FIG>, in one embodiment, a breast tissue expander <NUM> may be similar to or include one or more of the structural elements disclosed in <CIT>, assigned to Mentor Worldwide LLC, of Irvine, California. In one embodiment, the breast tissue expander <NUM> preferably includes a shell <NUM> with an injection port assembly <NUM> assembled around an injection port opening of the shell <NUM>. In one embodiment, the breast tissue expander <NUM> preferably includes a self-sealing membrane <NUM> as shown and described herein that surrounds an injection dome <NUM> of the injection port assembly <NUM>.

In one embodiment, the breast tissue expander <NUM> includes a seal-sealing base <NUM> having a raised rim <NUM> that extends between a posterior region of the shell <NUM> and a base patch <NUM>. In one embodiment, the self-sealing base <NUM> preferably includes the self-sealing structure disclosed herein for minimizing the risk of a leak if the self-sealing base <NUM> is punctured during a suturing operation.

Referring to <FIG>, in one embodiment, the injection port assembly <NUM> of the breast tissue expander <NUM> shown and described above in <FIG> and <FIG> preferably includes a self-sealing membrane <NUM> having a central opening <NUM>, a needle guard <NUM> having a magnet <NUM>, an injection dome <NUM> having a base <NUM> and a sealing flange <NUM>, and an injection dome sealing washer <NUM> having a central opening <NUM> that is adapted to receive the needle guard <NUM> and the base <NUM> of the injection dome <NUM>.

In one embodiment, when the self-sealing membrane <NUM> is assembled with an inner surface of a shell of a breast tissue expander, the anterior face <NUM> of the self-sealing membrane <NUM> is desirably secured to the inner surface of the shell. The injection dome sealing washer <NUM> is preferably secured to an outer surface of the shell and surrounds the central opening <NUM> of the self-sealing membrane <NUM>. The needle guard <NUM> passes through the central opening <NUM> of the injection dome sealing washer <NUM> and the central opening <NUM> of the self-sealing membrane <NUM>. The injection dome <NUM> is assembled with the shell by abutting a posterior face of the injection dome sealing flange <NUM> with the anterior face of the injection dome sealing washer <NUM>, whereupon the injection dome sealing flange <NUM> of the injection dome <NUM> overlies the outer surface of the shell of the breast tissue expander.

Referring to <FIG>, in one embodiment, a self-sealing sheet <NUM> for an implant may include two or more of the three-layer self-sealing membranes <NUM> shown and described above in <FIG>. In one embodiment, the self-sealing sheet <NUM> preferably includes three different self-sealing membranes 220A, 220B, and 220C that are joined together by unvulcanized sealing layers 595A and 595B that may be cured for adhering the three self-sealing membranes 220A, 220B, and 220C to one another.

Referring to <FIG>, in one embodiment, the self-sealing sheet <NUM> preferably includes a first self-sealing membrane 220A having first and second outer layers 516A and 516B that are held in contraction by an intermediate layer <NUM>. The self-sealing sheet <NUM> preferably includes a second self-sealing membrane 220B including first and second outer layers 516A' and 516B' that are held in contraction by intermediate layer <NUM>'. In one embodiment, the seal-sealing sheet <NUM> preferably includes a third self-sealing membrane having first and second outer layers 516A" and 516B" that are held in contraction by intermediate layer <NUM>". In one embodiment, the first and second self-sealing members 220A and 220B are joined together by an unvulcanized layer 595A that may be cured. In one embodiment, the second the third self-sealing membranes 220B and 220C are joined together by a second unvulcanized layer 595B that may be cured.

In one embodiment, the self-sealing sheet <NUM> shown in <FIG> and <FIG> may be incorporated anywhere on a mammary implant to close needle openings after the self-sealing sheet <NUM> has been punctured by a needle. In one embodiment, unvulcanized layers <NUM> are not required and a plurality of alternating layers of <NUM> may be constructed by stacking multiple alternating layers of cured silicone shells <NUM> and unvulcanized layers <NUM> (<FIG>). In one embodiment, unvulcanized layers <NUM> are not required and a plurality of alternating layers of <NUM> may be constructed by stacking multiple alternating layers of cured silicone shells <NUM> and unvulcanized layers <NUM> as in the process shown in <FIG>, or by stretching multiple layers of vulcanized silicone sheets <NUM> with alternating layers of unvulcanized silicone <NUM> as in the process shown in <FIG>.

Referring to <FIG> and <FIG>, in one embodiment, the self-sealing structure <NUM> shown and described above in <FIG> and <FIG> may be incorporated into an injection port assembly <NUM> that includes an injection dome <NUM> and a needle guard <NUM> having a magnet <NUM>.

Referring to <FIG>, in one embodiment, the self-sealing structure <NUM> is preferably secured to the upper end <NUM> of an outer wall <NUM> of the needle guard <NUM>. The self-sealing structure <NUM> preferably completely covers the opening at the upper end <NUM> of the outer wall <NUM> to completely seal an enclosed chamber <NUM> disposed between a bottom surface of the implant shell sealing structures <NUM> and a bottom wall <NUM> of the needle guard <NUM>.

<FIG> shows an injection port assembly <NUM> including the self-sealing sheet <NUM> and the needle guard <NUM> of <FIG> assembled with the injection dome <NUM> shown in <FIG> and <FIG>. The injection port assembly <NUM> may be inserted into an injection port opening of a shell of a breast tissue expander so that the sealing flange <NUM> of the injection dome <NUM> overlies the outer surface of the shell and the base <NUM> of the injection dome <NUM> passes through the injection port opening of the shell. In one embodiment, the base <NUM> of the injection dome <NUM> may also pass through the central opening of a self-sealing membrane as shown and described herein. In one embodiment, the anterior surface of the self-sealing structure <NUM> and the needle guard <NUM> of <FIG> may be attached directly to the inner surface of the shell without requiring an opening through the shell nor an opening through the self-sealing membrane.

Claim 1:
A method of making a self-sealing membrane for a prosthetic device comprising:
applying tension to a first layer (<NUM>, <NUM>) of a cured elastomeric material to stretch said first layer;
while said first layer remains stretched, applying a second layer (<NUM>, 216A) of an uncured elastomeric material over a first major surface (<NUM>) of said first layer, wherein the second layer of an uncured elastomeric material is applied to the first layer (<NUM>, <NUM>) in sheet form, and curing said second layer (<NUM>, 216A) of said elastomeric material;
after said second layer (<NUM>, 216A) is cured, releasing the tension from said first layer (<NUM>, <NUM>), wherein said first layer returns to a non-stretched configuration for holding said second layer in contraction.