WO1999017816A1

WO1999017816A1 - An expanded ptfe covered space-filling implant

Info

Publication number: WO1999017816A1
Application number: PCT/US1998/020797
Authority: WO
Inventors: Stanislaw L. Zukowski
Original assignee: Gore Enterprise Holdings, Inc.
Priority date: 1997-10-03
Filing date: 1998-10-02
Publication date: 1999-04-15
Also published as: AU9783498A

Abstract

An ePTFE-covered elastomer shape intended to serve as a space filling implant for use in plastic surgery. Methods of making are also described. The implant offers a much reduced risk of migration by virtue of its ePTFE covering wherein the ePTFE is provided with a desired pore size appropriate to provide for tissue attachment and to allow for subsequent removal of the implant without excessive tissue trauma resulting from excessive tissue ingrowth and attachment. The pore size may be selected to accommodate these contrary requirements of ingrowth and removability. Different surfaces of the implant may be provided with ePTFE coverings of different porosity if different degrees of attachment on the different surfaces are desired. The overall hardness of the implant may be controlled by selecting an elastomer material of desired durometer for the core of the implant.

Description

TITLE OF THE INVENTION

AN EXPANDED PTFE COVERED SPACE-FILLING IMPLANT

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a regular application based upon United States Provisional Patent Application No 60/060,903 filed October 3, 1997

FIELD OF THE INVENTION

The present invention relates to the field of space-filling implants useful in plastic surgery

BACKGROUND

The field of plastic surgery has long used various materials to fill space subcutaneously The most often used material has been silicone elastomer which is reasonably biocompatible and relatively inexpensively molded or otherwise shaped as desired for these applications It is frequently used, for example, in the reconstruction of chins and zygomatic arches It is most commonly used in non-porous forms having smooth curved exterior surfaces These forms are prone to migration beneath the skin unless specific additional attachment means are used such as suturing to adjacent tissue Various methods have been proposed in attempts to improve tissue attachment to the surface of the implantable shapes intended for space filling as well as to try to improve on the biocompatibility of the silicone shapes used previously While tissue attachment is desirable for implant stability in order to prevent migration, it must be approached cautiously in that the implant should be removable without causing substantial trauma to surrounding tissue in the event of any circumstance that might necessitate removal

US Patents 3,992,725 and 4,129,470 to Homsy describe porous implants of carbon fibers and polytetrafluoroethylene resin for various space-filling applications The porous nature of the material is intended to allow for tissue ingrowth The material composition is specified to have a critical surface tension of at least 35 dynes per centimeter In use these implants have proven to be less than ideally biocompatible Berman et al , (The Use of GORE-TEX E-PTFE bonded to Silicone Rubber as an Alloplastic Implant Material, Laryngoscope, Vol 96, No 5, May 1986) describe the use of expanded polytetrafluoroethylene (hereinafter ePTFE) bonded to silicone rubber sheet material as a prosthetic implant material The implants tested were in the form of composite sheets of about 0 25 cm thickness in the form of 1 mm thick expanded PTFE sheets bonded to both sides of a 0 02 inch (0 5 mm) thick silicone sheet Samples implanted for three months in rabbits produced good results, with reduced capsule formation comparing favorably with cartilage control samples

Brauman, US Patent 4 820,303, teaches the use of various materials including ePTFE for covering breast prostheses The covering material is attached with an adhesive material to a silicone envelope containing a soft gel or liquid filling The result is a compliant and flexible space-filling implant

A disadvantage of ePTFE used alone as a space filling implant is that it is relatively soft and compressible, when compressed, the porous ePTFE does not readily recover but rather remains in a compressed state The softness of the material prevents it from being readily shapeable in that when used in thicknesses greater those of its more conventional sheet forms (e g , thicknesses greater than about 1 mm) it is extremely difficult to cut with a blade for shaping A sharp blade does not readily cut the soft material but rather causes it to indent and compress under the blade edge Kranzler and Sharber, US Patent 5,098 779 describe ePTFE space-filling implants made carvable by impregnating the void space of the material with a resorbable material which renders the resulting composite adequately rigid for carving Over time immediately following implantation the resorbable material is taken up by the surrounding tissue allowing the tissue to ingrow into the void space of the ePTFE An alternative carvable form of ePTFE for space-filling is described by Sharber et al (W0 95/22359) in the form of ePTFE sheets laminated together with alternating layers of an adhesive material which results in increased rigidity and consequent carvabi ty

EP 0320170 teaches that ePTFE may be formed into shapes including compound curves such as domes

SUMMARY OF THE INVENTION

The present invention relates to a space-filling implant and a method of making The implant comprises a substantially solid, three-dimensional shape of elastomeπc material such as silicone, polyurethane or a fluoropolymer elastomer which is provided with a covering of expanded polytetrafluoroethylene over substantially the entire exterior surface of the implant By substantially solid is meant that the three-dimensional shape does not contain large void spaces (larger than 1 cm length) which might contain another material such as air, a liquid or a gel, and that the elastomeπc material is substantially solid (more solid than a gel) following curing of the elastomer during manufacture of the implant The elastomeπc material may be porous in that it may contain small void spaces Substantially the entire exterior surface of the implant means that the covering is applied over at least about 75% of the exterior surface area of the shape of elastomeπc material Preferably at least 80%, 85%, 90%, 95%, 98%, 99% or 99 9% of the surface area of the elastomeπc shape is covered Most preferably, 100% of the surface of the shape is covered by the ePTFE material The three-dimensional aspect refers to the shape of elastomeπc material being non-planar and of a relatively substantial (e g , greater than 1 mm) average thickness wherein average thickness is the average dimension between opposing surfaces of the shape in a direction perpendicular to the plane through the shape that is closest to the opposing surfaces of the shape For example, a thin layer of elastomer used to join two opposing layers of ePTFE is not contemplated within the present invention The elastomer should have a significant thickness and preferably being of asymmetric shape wherein the dimensions of the elastomeric shape are variable in at least one direction Contemplated shapes include, for example, shapes appropriate for noses and chins

While the ePTFE covering may be adhered to the surface of the elastomeric core by the use of an adhesive material such as medical grade silicone adhesive, it is preferred that the implant be formed by filling an ePTFE covering with the silicone core material under pressure sufficient to cause the silicone to interpenetrate the void spaces of the ePTFE adjacent to the interior surfaces of the ePTFE covering and finally curing the silicone The implant is thus fabricated without the use of a separate adhesive layer A preferred method of manufacture is thus to line the interior surfaces of the cavity of a mold or form with the ePTFE covering material, the cavity of the mold or form having the shape of the desired space-filling implant The ePTFE covering material is then filled under pressure with the elastomer which is preferably silicone, the pressure again being adequate to achieve interpenetration of the interior surfaces of the ePTFE with the silicone The silicone is then cured and the implant removed from the mold or form Any extraneous edge material may then be selectively cut away from the desired shape of the implant The result is an ePTFE covered space-filling implant that can be provided with rigidity as desired based on the durometer of elastomer material selected The ePTFE covering allows for a degree of _% tissue attachment and implant stability which can be controlled by using ePTFE of specifically controlled pore size The ePTFE covering material is preferred to have a thickness of between about 0 1 and 4 mm The ePTFE material is preferred to have mean fibril lengths ranging between about 5 and 50 microns and a density between about 0 25 and 0 75 g/cc ePTFE having fibril lengths of greater than about 25 microns may allow for substantial ingrowth and attachment while fibril lengths of 10 microns or less result in limited attachment which in turn enhances subsequent removability of the implant If desired, different surfaces of the implant may be provided with ePTFE coverings of different mean fibril lengths Mean fibril length is measured as taught by US Patent 5,747,128 at col 6, lines 19-37

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 describes a cross section of a space-filling implant of the present invention Figure 2 describes a cross sectional view of a mold having a cavity lined with ePTFE sheet material prior to filling with elastomer

Figure 3 describes the mold of Figure 2 after filling with elastomer Figure 4 describes the implant after removal from the mold and prior to trimming excess ePTFE edge material

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 describes a cross section of an implant 10 of the present invention comprising a substantially solid elastomeric core 13 provided with an ePTFE covering 1 1 The elastomeric core is preferably a medical grade silicone the fabrication of which is well known in the art It is available in different hardnesses or durometers, allowing the hardness and compliance of the resulting implant to be controlled Other elastomers may also be used when available in adequately pure and biocompatible forms, these may include polyurethanes and fluoroelastomers The ePTFE covering material covers substantially all surfaces of the elastomeric core This material is made as taught by US Patents 3,953,566 and 4,187,390 These patents teach that the pore size and fibril length (or distance between adjacent nodes) can be controlled by varying aspects of the manufacturing process, primarily the stretch rate It is available in a variety of forms commercially and is commonly manufactured as both tubes and sheets It has a history of use as an implantable material (primarily as a vascular graft material) with excellent biocompatibility For purposes of the present invention, the ePTFE may be used in either its sintered or unsintered states, sintering being the result of exposure to heat above the crystalline melt temperature of

PTFE The unsintered material is softer and more easily deformed, and may therefore be more easily used as a covering material appropriate for irregular shapes of the elastomeric core

Figure 2 describes a method of making the space-filling implant of the present invention wherein a mold or form 16 is provided, preferably in two separable halves 18 and 19 Mold 16 has a cavity which is provided with sheets of ePTFE 15 and 17 lining the inner surfaces of the cavity such that the edges of sheets 15 and 17 extend outward through and beyond the edges of the mold halves 18 and 19 where these edges are intended to mate together Optional port tubes 20A and 20B are preferably inserted at opposite ends of the mold halves prior to bringing the ePTEF sheet mold halves together, these are intended to provide access to the mold cavity for the injection of uncured elastomer and to allow the escape of air as indicated by arrows 21 and 23 Port tube 20B may be dispensed with by simply allowing air to escape from between the edges of ePTFE sheets 15 and 17 during the process of injecting elastomer into the mold cavity until it is full The injection is done under pressure adequate to cause the elastomer to escape from between the edges of the ePTFE sheets 15 and 17 where they come together around the edges of the mold halves 18 and 19, elastomer should be seen escaping through these edges for their full lengths Although the Figures indicate a horizontal orientation to the mold halves, it may be preferred to orient them vertically with port 20A located at the bottom of the mold cavity and port 20B at the top to aid in the escape of air from the mold and help insure that the elastomer core is substantially solid and free of air bubbles After completion of filling the mold cavity, port tubes 20A and 20B may be removed and the opposing mold halves brought firmly together as shown by Figure 3, wherein the edges of the ePTFE sheets are brought firmly together The substantially solid elastomer core 13 is then allowed to cure (to become substantially solid) by methods appropriate for the elastomer selected After curing the mold halves 18 and 19 are separated and the implant 10 removed as shown by Figure 4 The excess edge material of the ePTFE sheets 15 and 17 is then trimmed from the implant at lines 27 resulting in the finished implant shown by Figure 1

In a variation on the above-described method, ePTFE sheets 15 and 17 may be replaced by a tubular ePTFE form which form is preferably unsintered ePTFE The ePTFE tube may be placed into the mold and elastomer may be injected into the lumen of the ePTFE tube under pressure sufficient to fill the tube and cause deformation of the tube appropriate to allow the tube to conform to the shape of the cavity within the mold

In an alternative method, the elastomer core component 13 may be a commercially available silicone space-filling implant The ePTFE covering material 11 may be a tubular form of unsintered ePTFE which fits snugly over the silicone core 13, the tube being selected to have an inside diameter of about the same dimension of the largest diameter of the silicone core Silicone adhesive is applied to the exterior surfaces of the silicone core which is then inserted into the ePTFE tube Tension is applied to opposing ends of the ePTFE tube thereby causing it to neck down and conform to the exterior of the silicone core 13 Heat of less than the crystalline melt temperature of the PTFE may be used during this tensionmg step to better enable deformation of the ePTFE tube necessary for conformation to the surfaces of the silicone core This process may be augmented by the use of a mold in a similar fashion to that described above to ensure conformation of the ePTFE material to the silicone core Alternatively, ePTFE sheet materials may be used to cover the silicone space-filling implant which has been coated with an adhesive, again a split mold may be used to improve conformance of the ePTFE to the exterior of the silicone core

Other adhesives may be used such as thermoplastic sheet materials placed between the elastomer core and the ePTFE covering material Preferred materials include fluoπnated ethylene propylene (FEP) and perfluonnated alkoxy resin (PFA), heat and pressure are then used to activate these, again preferably with the use of a mold

Claims

claim

1 A space-filling implant comprising an elastomeric material formed into a three- dimensional, substantially solid shape wherein the shape has an exterior surface which is substantially covered with porous polytetrafluoroethylene

2 A space-filling implant according to claim 1 wherein the porous polytetrafluoroethylene is porous expanded polytetrafluoroethylene having a node and fibril microstructure

3 A space-filling implant according to claim 2 wherein the microstructure has a mean fibril length of between about 5 and 50 microns

4 A space-filling implant according to claim 3 wherein the porous polytetrafluoroethylene has a thickness between about 0 1 and 4 mm

5 A space-filling implant according to claim 1 wherein the porous polytetrafluoroethylene has a thickness between about 0 1 and 4 mm 6 A space filling implant according to claim 1 wherein the shape is entirely covered with porous polytetrafluoroethylene

7 A space filling implant according to claim 2 wherein the shape is entirely covered with porous polytetrafluoroethylene

8 A space filling implant according to claim 3 wherein the shape is entirely covered with porous polytetrafluoroethylene

9 A space filling implant according to claim 5 wherein the shape is entirely covered with porous polytetrafluoroethylene

10 A space-filling implant according to claim 1 wherein the elastomeric material comprises silicone 11 A space-filling implant according to claim 2 wherein the elastomeric material comprises silicone

12 A space-filling implant according to claim 3 wherein the elastomeric material comprises silicone

13 A space-filling implant according to claim 5 wherein the elastomeric material comprises silicone

14 A space-filling implant according to claim 1 wherein the elastomeric material comprises polyurethane

15 A space-filling implant according to claim 2 wherein the elastomeric material comprises polyurethane 16 A space-filling implant according to claim 3 wherein the elastomeric material comprises polyurethane 17 A space-filling implant according to claim 5 wherein the elastomeric material comprises polyurethane

18 A space-filling implant according to claim 1 wherein the elastomeric material comprises an elastic fluoropolymer

19 A space-filling implant according to claim 2 wherein the elastomeric material comprises an elastic fluoropolymer

20 A space-fϋlmg implant according to claim 3 wherein the elastomeric material comprises an elastic fluoropolymer 21 A space-filling implant according to claim 5 wherein the elastomeric material comprises an elastic fluoropolymer

22 A space-filling implant according to claim 2 wherein the shape as at least two different portions of the exterior surface wherein the two different portions have ePTFE coverings of different mean fibril lengths 23 A method of making a space-filling implant comprising a) providing a mold having a three-dimensional cavity with surfaces b) lining the surfaces of the cavity with a porous polytetrafluoroethylene material c) substantially filling any remaining space within the cavity with an elastomeric material, d) allowing the elastomeric material to cure, thereby creating a substantially solid, three-dimensional shape having a covering of porous polytetrafluoroethyelene, e) removing the shape from the cavity of the mold

24 A method according to claim 23 wherein the elastomeric material is silicone

25 A method of making a space-filling implant comprising a) obtaining a three-dimensional, substantially solid shape having an exterior surface wherein said shape comprises an elastomeric material, b) providing the shape with a covering of porous polytetrafluoroethylene which substantially covers the exteror surface of the shape

26 A method according to claim 25 wherein the covering is adhered to the exterior surface with an adhesive

27 A method according to claim 25 wherein the adhesive is a silicone adhesive