United States Patent
`
`[191
`
`[11] Patent Number:
`
`4,570,271
`
`Sump
`‘
`[45] Date of Patent:
`Feb. 18, 1986
`
`
`[54] POROUS COATINGS FROM WIRE MESH
`FOR BONE IMPLANTS
`
`[75]
`Inventor: Kenneth R. Sump, Riehland, Wash.
`[731 Assignee Battene Develenment Corporation,
`Columbus, Ohxo
`[21] Appl. No.: 561,577
`[22] Filed:
`Dec. 14, 1983
`
`Related US. Application Data
`.
`_
`1
`Continuat1on-1n-part of Ser. No. 287,431, Jul. 27, 1981,
`abandoned.
`
`[63]
`
`Int. Cl.4 ................................................ A61F 1/24
`[51]
`[52] US. Cl. ................................... 623/18; 228/ 173.5;
`228/193
`[58] Field of Search .................... 228/178, 173 F, 182,
`223/193; 3/],91, 1,913
`
`[56]
`
`_
`References C'ted
`U.S. PATENT DOCUMENTS
`3,789,498
`2/1974 Cole .................................... 228/193
`
`4,038,703
`8/1977 Bokros .................... 3/1.91
`4,064,567 12/1977 Burstein et a1.
`...... 3/1.91
`4,088,258
`5/1978 Regalbuto ........................... 228/ 193
`
`4,245,769
`1/1981 Meginnis ............................ 228/193
`4,252,263
`2/1981 Houston .......... 228/193
`
`4,261,063
`4/1981 Blanquaert .
`........ 3/1.91
`4,315,591
`2/1982 Houston .............
`. 228/193
`2:322:33? 1371333 3222:;8?.f.‘.1.:::................:::: 37113}
`
`FOREIGN PATENT DOCUMENTS
`2029749 3/1980 United ngdom ................ 228/193
`Primary Examiner—Nicholas P. Godici
`Assistant Examiner—M. Jordan
`Attorney, Agent, or Firm—Wells, St. John & Roberts
`[57]
`ABSTRACT
`
`A method of coating areas of bone implant elements and
`the resulting implant having a porous coating are de-
`scribed. Preselected surface areas are covered by a
`preform made from continuous woven lengths of wire.
`The preform is compressed and heated to assure that
`diffusion bonding occurs between the wire surfaces and
`between the surface boundaries of the implant element
`and the wire surfaces in contact with it. Porosity is
`acmeved by contml 0f the “35““in V°ids between the
`bonded Wire Por‘i‘ms-
`
`9 Claims, 3 Drawing Figures
`
`
`
`Page 1 of 6
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`ZIMMER EXHIBIT 1017
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`ZIMMER EXHIBIT 1017
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`Page 1 of 6
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`

`

`U.S. Patent
`
`Feb. 18,1986
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`Sheetl of2
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`4,570,271
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` ._:R) u
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`Page 2 of 6
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`US. Patent
`
`Feb. 18,1986
`
`Sheet 2 of 2
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`4,570,271
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`Page 3 of 6
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`Page 3 of 6
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`

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`1
`
`4,570,271
`
`POROUS COATINGS FROM WIRE MESH FOR
`BONE IMPLANTS
`
`RELATED APPLICATIONS
`
`This is a continuation-in-part of application Ser. No.
`287,431, filed July 27, 1981, now abandoned.
`TECHNICAL FIELD
`
`This disclosure relates to the production of a porous
`coating about preselected metallic surface areas on bone
`implant elements for subsequent tissue ingrowth appli-
`cations. The coating is produced by compressing a pre-
`formed metallic cover of continuous wire mesh over the
`implafit surfaces to be coated. It requires adequate ap-
`plication of heat and pressure about the cover to assure
`sintering of the wires to one another and to the adjacent
`surface areas. The resulting porous coating has inter»
`connected pores through which hard or soft body tis-
`sues can grow to attach the bone implant element to
`bone.
`
`10
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`15
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`20
`
`BACKGROUND ART
`
`25
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`30
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`35
`
`4o
`
`U.S. Pat. No. 3,852,045 to Wheeler, Sump, and Kara-
`gianes discloses a porous metallic material including a
`network of interconnected voids or pores. It is formed
`on a surgical prosthetic device for tissue ingrowth pur-
`poses. The voids or pores about the resulting surface
`areas are produced in the coating material by use of a
`composite material including expendable void formers.
`The described composite material is treated by high
`energy rate forming pressures to densify its structure
`prior to removal of the expendable void former. Sub-
`stantial
`thicknesses of the void coating on substrate
`metallic elements is disclosed.
`While the products resulting from the systems taught
`in US. Pat. No. 3,852,045 have performed satisfacto-
`rily, the practical application of the system is severely
`limited by both the expense and availability of equip-
`ment for the required high energy rate forming steps.
`Furthermore, such steps are of questionable value when
`attempting to produce a relatively thin porous coating
`on implant elements, since the high pressures to which
`the elements would be subjected might result in struc-
`tural damage to them.
`US. Pat. No. 3,986,550 to Restaker et al describes
`prosthetic devices having porous sections. It discusses
`prior efforts to use consolidated metal powders to pro-
`duce porous metals for this purpose, but dismisses them
`as being brittle and having unacceptable toughness. The
`patent specifically describes a process for producing a
`porous section by use of short fiber strands. The strands
`are molded and sintered to interconnect the metal fi-
`bers. It states that by repressing procedures, external
`dimensions of the coated prosthesis can be precisely
`regulated to the excavation in the receiving bone so that
`a zero clearance fit is achieved. It describes that long
`wire lengths give more interlock and better molded
`strengths, but notes that the longer the wire, the more
`difficult it is to feed into dies. No mention is made of 60
`preforming the wires or using wire mesh of any type.
`An article published in the Journal of Bone and Joint
`Surgery, Volume 53-A, No. 1, January, 1971, Pages 101
`through 114, titled “Sintered Fiber Metal Deposits as a
`Basis for Attachment of Implants to Bone”, by Galante
`et al, also describes the molding and sintering of short
`metal fibers for production of implant materials. It con-
`tains a review of available literature publications relat-
`
`45
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`50
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`Page 4 of 6
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`2
`ing to porous elements of this type, including open pore
`materials derived from powders consolidated and
`shaped in molding dies under pressure. The article dis-
`closes coating of cylinders by pressing fiber sleeves to
`form them separately, but the sleeves discussed are
`produced from individual kinked lengths of wires. This
`would appear to expose fiber ends at
`the resulting
`coated surface and would produce a surface that would
`include discontinuities and lack desired uniformity.
`Also, individual fibers pressed in a random mat would
`not result
`in a coating having uniform porosity or
`strength.
`According to the present invention, relatively thin
`porous metallic coatings are produced about selected
`surface area configurations on a bone implant element
`by performing a sleeve or surface covering from a wire
`mesh produced from continuous lengths of wire. The
`mesh is preferably knitted, braided, wound or woven in
`some manner to produce a uniform mesh structure
`which, when pressed, will have relatively uniform po-
`rosity in the resulting voids that are formed between the
`wires. The wires are made from a material either identi-
`cal to or metallurgically compatible with the metallic
`surface being coated. They are heated and pressed in
`place about the surface to effect diffusion bonding be-
`tween engaged wire sections as well as between the
`surface area and the wire surfaces in contact with it.
`
`DISCLOSURE OF INVENTION
`
`The present method for producing a porous coating
`on a preselected metallic surface area of a bone implant
`element for tissue ingrowth applications comprises the
`step of first overlaying the area with a multi-layer cov-
`ering comprising a continuous metallic wire mesh. The
`covering is compressed against the preselected surface
`area. Compression is required during the heating step,
`and can be accomplished prior to heating as well. The
`preselected surface area and covering are then heated to
`maintain an elevated temperature at which diffusion
`bonding occurs in the materials. The resulting coating
`will have a surface configuration complementary to the
`mold in which it is compressed. Controlled porosity
`throughout the coating results from the uniform spacing
`between the wires in the initial preform. The degree of
`compression will control the ultimate amount of poros-
`ity in the final coating.
`It is an object of this disclosure to achieve controlled
`pore size and morphology in a porous coating without
`requiring the use of high energy rate forming pressures.
`Another object is to provide porosity in the coating
`sufficient for tissue ingrowth applications, while retain-
`ing adequate strength properties for practical use in
`surgery.
`Another object of this invention is to provide a prac-
`tical thin porous coating on metallic bone implant sur-
`faces which can retain complex surface configurations
`desired about the surfaces.
`Finally, an object of the invention is to develop a
`practical process using presently available techniques,
`equipment and raw materials.
`DESCRIPTION OF THE DRAWINGS
`
`A preferred and alternate embodiment of this inven-
`tion is illustrated in the accompanying drawings,
`in
`which:
`
`FIG. 1 is a perspective View of an implant element
`having porous coated surfaces.
`
`Page 4 of 6
`
`

`

`4,570,271
`
`4
`surface areas under controlled conditions prior to and
`during subsequent heating to achieve reproducible coat-
`ings on the manufactured bone implant elements or
`prosthesis. The selected compression system must be
`capable of accurately forming required complex surface
`areas typically required in prosthetic implants such as
`that illustrated in the drawings. While isostatic pressing
`might be used, the specific illustration shown in FIG. 3
`shows use of mechanical dies having two or more seg-
`ments for compression of the coating surface areas.
`The preform covering 14 and prosthesis 10 are placed
`within the complementary jaws 20 of a pressing die,
`with the die cavity surfaces overlying the preselected
`surface areas of the prosthesis to be coated. Initial press~
`ing is preferably accomplished without heating to com-
`pact the volume of the initially loose covering material.
`Such initial pressing in a die may eliminate the need for
`high temperature pressing devices. The compessed die
`might then be mechanically locked prior to loading it
`into a furnace for heating. This would maintain preform
`covering 14 under compression. The die jaws 20 and
`prosthesis are then subjected to heat within a furnace
`21. The degree of compression might be increased or
`decreased as a result of heating, dependent upon the
`thermal coefficients of the materials in the prosthesis,
`the preform and the jaws 20 of the die.
`Furnace 21 is preferably a vacuum furnace, since
`subjecting the preform 14 and prosthesis 10 to vacuum
`pressure during the heating step inhibits oxidation of the
`metallic alloys. Oxidation can also be minimized or
`prevented by heating the pressing die within a suitable
`inert atmosphere. The temperature of the prosthesis and
`preform must be raised to a level at which diffusion
`bonding between the prosthesis surface areas and the
`wires in contact with them and also between adjacent
`wire surfaces will be achieved at the compressive forces
`to which they are subjected. In the case of prosthetic
`surfaces and wire coatings made from Ti6A14V alloy,
`the temperature will be between 800° to 1400° C.
`The prosthesis and covering wires might be simulta-
`neously subjected to the application of pressure and
`heat within vacuum furnace 21 by movement of the
`jaws 20 as indicated by arrows 22. Compression of
`preform 14 will reduce the volume of the cover about
`the prosthesis surfaces to the desired coating thickness,
`which can be calculated with respect to wire size and
`density to achieve the resulting desired degree of poros-
`ity.
`The process is completed by removing the prosthesis
`10 from the pressing die. It should require no surface
`finishing. The resulting surface will be uniform
`throughout its area and will not include projecting wire
`ends or discontinuities. The use of continuous wire
`structures in the coating lends superior strength to the
`resulting coating beyond that which can be achieved by
`sintering of shorter wire lengths.
`In an experiment designed to demonstrate that a knit-
`ted wire sleeve could be gravity sintered over a core in
`a compressed condition, a knitted tubular sleeve of
`Monel was sinter bonded over a nickel core in a vacuum
`furnace at 1,000“ C. for two hours. The sleeve was
`knitted from 0.0045 inch diameter wire. The com-
`pressed sample had an outside diameter of 0.560 inches
`and an inside diameter of 0.480 inches. Monel and nickel
`materials were used in this experiment because of imme-
`diate availability, but the process is readily applicable to
`alloys typically used in prosthesis devices.
`
`5
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`3
`FIG. 2 is an enlarged fragmentary transverse sec-
`tional view taken substantially along line 2—-—2 in FIG. 1
`with a circled corner area further enlarged for illustra-
`tion; and
`FIG. 3 is an illustrative flow diagram illustrating the
`steps of the present process.
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`In compliance with the constitutional purpose of the
`Patent Laws “to promote the progress of science and
`useful arts” (Article 1, Section 8), applicant submits the
`following disclosure of the invention.
`FIGS. 1 and 2 generally illustrate a known configura—
`tion of a hip prosthesis 10. 51‘he prosthesis 10, which is a
`relatively common bone implant element used in surgi-
`cal repair of hip joints, includes an elongated shank 11
`intended to be inserted axially within a supporting bone
`structure. It is capped by a ball structure generally
`shown at 9. In most surgical installations of such a pros-
`thesis, the shank 11 is anchored to the bone structure by
`adhesives.
`As illustrated in FIGS. 1 and 2, the outer surfaces of
`the shank 11 are covered by a porous metallic coating
`12 that surrounds an inner solid metal substrate 13. The
`coating 12 is bonded to the substrate 13, and includes
`interconnected pores through which soft and hard liv-
`ing tissues can grow after implantation of the prosthesis
`10.
`
`‘
`
`,
`.
`
`The present process is initiated by cleaning and ma-
`.
`. chining of the preselected metallic surface areas upon
`which the coating is to be formed. Additionally, a pre-
`. form covering of continuous woven wire complemen-
`tary to the surfaces is produced by conventional multi-
`layer knitting, braiding, winding, weaving or other
`continuous wire processes. The preform covering is
`, generally shown in FIG. 3 at 14. It is formed to comple-
`ment the geometry of the surfaces to be covered by it.
`Its initial thickness will be governed by the desired final
`thickness of the coating and degree of compression to
`,_ which it is to be subjected in order to produce the re-
`quired final coating porosity.
`The preform covering 14 can be in the form of a
`sleeve, a complete cover, or a curved or flat pad shaped
`to overlie the surfaces involved. It should be produced
`from wires made of metallic material matching or com-
`patible with the surface area being coated.
`There are three alternatives available for effecting the
`required compression and diffusion bonding of preform
`covering 14. It can be subjected to cold compression
`followed by heating in locked dies. It can be subjected
`to cold compression followed by hot cbmpression. It
`can also be subjected to hot compression alone. In each
`instance, diffusion bonding is achieved by application of
`heat while the wires in the preform are under pressure.
`Bonding of all areas of contact of the wires is a result of
`active pressing, retention in compressed locked dies,
`thermal expansion forces within confining dies, or a
`combination of such factors.
`The first step in utilizing this process is to place the
`preform covering 14 about the areas on prosthesis 10
`which are to be coated. This can be accomplished exter-
`nally from any die system, or the preform covering 14
`can be first placed within a die and the prosthesis 10
`subsequently inserted within it. In either case, the pre-
`form covering 14 and prosthesis 10 are eventually
`loaded into a compression mold or die and subjected to
`compressive forces capable of accurately deforming the
`
`Page 5 of 6
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`Page 5 of 6
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`

`4,570,271
`
`5
`
`5
`The knitted sleeve was inserted into an aluminum
`oxide tube and the nickel core then driven into the
`center of the sleeve. This caused compression of the
`knitted wire sleeve. The sinter bonding was designed to
`sinter to the wires to themselves at each contact point
`and also to sinter the wire surfaces to the core surfaces
`where they will contact.
`The sample held its compressed shape when removed
`from the aluminum oxide tube. It did demonstrate the
`feasibility of the sintering step, although greater 10
`comressive force appears to be required for strength
`purposes. The porous metal density was about 20% of
`the total volume, but could be designed to be much
`greater.
`In applying the method to a prosthetic surface, unal- 15
`loyed titanium or Ti6A14V alloys will typically be
`used. Wires of these materials matching the substrate
`will be applied to the desired areas of the prosthesis by
`inserting a woven wire preform over the device. The
`wire preform will then be sintered bonded in place both 20
`to itself and to the device. During sinter bonding, the
`wire preform will be compressed. All porosity would be
`open porosity, with the size and shape being variable
`and within limits imposed by the weaving or knitting
`capability of the process used in production of the pre- 25
`form.
`
`6
`rial compatible with the material of the surface area
`and having a total material thickness equal to a
`desired preform coating thickness;
`the preselected
`compressing the covering against
`surface area by subjecting it to compressive forces
`capable of accurately deforming the surface areas
`of the covering to the desired coating thickness to
`achieve a reproducible porous coating; and
`heating the compressed covering while under pres-
`sure to an elevated temperature at which diffusion
`bonding occurs between all areas of contact be-
`tween the wires in the wire mesh and also between
`the surface area and all areas of contact of the wires
`that engage it.
`2. A method for producing a porous matrix coating
`directly bonded about a preselected metallic surface
`area of a bone implant element for tissue ingrowth ap-
`plications, comprising the following steps:
`overlaying the preselected surface area with a pre-
`form covering formed of a plurality of layers of
`continuous metallic wire mesh made from a mate-
`rial compatible with the material of the surface area
`and having a total material thickness equal to a
`desired preform coating thickness;
`the preselected
`compressing the covering against
`surface area by subjecting it to compressive forces
`capable of accurately deforming the surface areas
`of the covering to the desired coating thickness to
`achieve a reproducible porous coating; and
`heating the compressed covering while under pres-
`sure to an elevated temperature at which diffusion
`bonding occurs between all areas of contact be-
`tween the wires in the wire mesh and also between
`the surface area and all areas of contact of the wires
`that engage it to produce a porous coating having
`interconnected pores through which soft and hard
`living tissues can grow after implantation of the
`bone implant element.
`3. A method as set out in claim 2 wherein the preform
`covering is first compressed and molded to a shape
`complementary to the preselected surface area prior to
`the overlaying step.
`4. A method as set out in claim 3 wherein the preform
`covering is compressed and molded to a density that is
`approximately 15% to 50% of its theoretical solid den-
`sity and the wire diameter size is 100 to 200 microns.
`5. A method as set out in claim 2 further comprising
`the step of producing the preform covering by continu-
`ous woven wire processes.
`6. A method as set out in claim 3 further comprising
`the step of producing the preform covering by knitting
`continuous wires.
`7. A method as set out in claim 2 further comprising
`the step of producing the preform covering by braiding
`continuous wires.
`8. A method as set out in claim 2 further comprising
`the step of producing the preform covering by winding
`of continuous wires.
`9. A method as set out in claim 2 wherein the preform
`covering is initially compressed prior to the heating step
`and is held under pressure in a loaded die during the
`heating step.
`it
`It
`II!
`it
`*
`
`The compression of the preform during the sintering
`process, following assembly about the prosthesis,
`in-
`creases the coating density and promotes more bonding
`points. It is estimated that the compressed density will 30
`be between 15% to 50% of theoretical in the coating,
`using wire sizes between 100 to 200 microns in diame-
`ter.
`
`An advantage of using a preformed coating made
`from wire is that this permits use of a wrought product 35
`rather than a powder, as has been previously attempted.
`There is no expendable phase material to remove in
`order to achieve the required porosity and no chance of
`contamination of the coating by other materials. The
`process appears to be very economical. It permits subas- 40
`sembly of the prosthesis outside a die or mold when
`desired. The processing steps appear to be limited to a
`minimum number for comparable systems.
`In compliance with the statute, the invention has been
`described in language more or less specific as to struc- 45
`tural features. It is to be understood, however, that the
`invention is not limited to the specific features shown,
`since the means and construction herein disclosed com-
`prise a preferred form of putting the invention into
`effect. The invention is, therefore, claimed in any of its 50
`forms or modifications within the proper scope of the
`appended claims, appropriately interpreted in accor—
`dance with the doctrine of equivalents.
`I claim:
`
`1. A bone implant element for tissue ingrowth appli- 55
`cations having a porous matrix coating directly bonded
`to a preselected metallic surface area thereof, the coat-
`ing having interconnected pores through which soft
`and hard living tissues can grow after implantation of
`the bone implant element;
`the coating being produced by the following steps:
`overlaying the preselected surface area with a pre-
`form covering formed of a plurality of layers of
`continuous metallic wire mesh made from a mate-
`
`60
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`65
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`Page 6 of 6
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`Page 6 of 6
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