SURFACE ALLOYED MEDICAL IMPLANT

Abstract

A medical implant is disclosed. The medical implant includes: a first biocompatible metal forming a substrate (210, 310, 410), a second biocompatible metal diffused into the first biocompatible metal to form an biocompatible alloy surface (220, 314, 414), the alloy surface further including a diffusion hardening species, wherein the diffusion hardening species may be carbon, nitrogen, oxygen, boron, or any combination thereof. A method of forming a medical implant is also disclosed. The method includes the steps of: providing a first biocompatible metal or alloy that forms a substrate (210, 310, 410), providing a second biocompatible metal or alloy, diffusing the second biocompatible metal into the first biocompatible metal to form an alloy layer (220, 314, 414), removing excess second metal material from the substrate to expose the alloy layer, and diffusion hardening the alloy layer.

Claims

1. An implant, comprising: a substrate; and a surface alloyed zone formed in the substrate, the surface alloyed zone including a surface alloyed hardened zone and a surface alloyed non-hardened zone, the surface alloyed hardened zone including at least one diffusion hardening material and the surface alloyed non-hardened zone having no diffusion hardening material.

2. The implant of claim 1, wherein the surface alloyed zone forms at least one surface of the substrate.

3. The implant of claim 1, wherein the surface alloyed hardened zone is formed by diffusion of the at least one diffusion hardening material into the substrate.

4. The implant of claim 3, wherein the surface alloyed non-hardened zone is formed by preventing diffusion of the at least one diffusion hardening material into the substrate.

5. The implant of claim 4, wherein the diffusion is performed in a vacuum of less than 10.sup.−4 Torr and in the temperature range of approximately 600 degrees C. to approximately 1200 degrees C.

6. The implant of claim 1, wherein the surface alloyed zone is formed in a presence of a gas, the gas being at least one of the following: carbon, oxygen, nitrogen, and any combinations thereof.

7. The implant of claim 1, wherein the surface alloyed zone is formed in a presence of an inert gas, the inert gas being at least one of the following: argon, helium, krypton, neon, nitrogen, and any combinations thereof.

8. The implant of claim 1, wherein the surface alloyed hardened zone is an oxide layer.

9. The implant of claim 8, wherein the oxide layer has a thickness of approximately 25 micron.

10. The implant of claim 1, wherein the surface alloyed hardened zone is formed by at least one of the following: oxidation, nitriding, carburizing, and any combination thereof.

11. The implant of claim 1, wherein the surface alloyed hardened zone is formed at approximately 600 degrees C.

12. The implant of claim 1, wherein the substrate is at least one of the following: a cobalt chrome substrate, a titanium substrate, a titanium alloy substrate, a stainless steel substrate, a zirconium substrate, a zirconium alloy substrate, and any combinations thereof.

13. The implant of claim 12, wherein the surface alloyed zone is formed by infusion into the substrate at least one of the following: zirconium, cobalt, chromium, titanium, niobium, aluminum, vanadium, and any combinations thereof.

14. The implant of claim 1, wherein the surface alloyed zone has a thickness of between approximately 2 microns to approximately 2000 microns.

15. An implant formed by a method comprising: forming a surface alloyed zone in a substrate, the forming of the surface alloyed zone including: forming a surface alloyed hardened zone by diffusing at least one diffusion hardening material into the substrate; and forming a surface alloyed non-hardened zone by preventing diffusing of the at least one diffusion hardening material into the substrate, the surface alloyed non-hardened zone including no diffusion hardening material.

16. The implant of claim 15, wherein the forming of the surface alloyed zone includes forming the surface alloyed zone in a presence of a gas, the gas being at least one of the following: carbon, oxygen, nitrogen, and any combinations thereof.

17. The implant of claim 15, wherein the forming of the surface alloyed zone includes forming the surface alloyed zone in a presence of an inert gas, the inert gas being at least one of the following: argon, helium, krypton, neon, nitrogen, and any combinations thereof.

18. The implant of claim 15, the method further comprising removing at least a portion of the at least one diffusion hardening material.

19. The implant of claim 18, wherein the removing includes at least one of the following: grinding, tumbling, glass-beading, shot-peening, grit blasting, polishing, sanding, abrasive slurry, and any combination thereof.

20. A method, comprising: providing a substrate; diffusing at least one diffusion hardening material into the substrate to form at least a portion of surface alloyed zone, the surface alloyed zone including: a surface alloyed hardened zone including the at least one diffusion hardening material; and a surface alloyed non-hardened zone not including the at least one diffusion hardening material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the written description serve to explain the principles, characteristics, and features of the invention. In the drawings:

[0072] FIG. 1 is a schematic of an oxidized zirconium sample.

[0073] FIG. 2 illustrates a hardness profile an oxidized zirconium sample.

[0074] FIG. 3 illustrates the depth of titanium diffusion in a sample of Zr-2.5Nb alloy surface alloyed with titanium.

[0075] FIG. 4 is a metallographic image of a Zr-2.5Nb sample surface alloyed with titanium and then oxidized.

[0076] FIG. 5 is a schematic of a cobalt chrome surface alloyed with zirconium and subsequently oxidized.

[0077] FIG. 6 is a schematic of a zirconium alloy surface alloyed with titanium and subsequently oxidized.

[0078] FIG. 7 is a schematic of a hip implant.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0079] The following description of the depicted embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0080] As used herein, “a” or “an” means one or more. Unless otherwise indicated, the singular contains the plural and the plural contains the singular.

[0081] As used herein, the term “alloy” means a metallic solid solution. The term “surface alloy” is defined as an alloy in which one or more alloying species is present in a surface and a near-surface region in a greater concentration than in the bulk substrate. As such, the surface and the near-surface region include one or more “surface alloy species.” Thus, a bulk sample of Zr-2.5Nb is an alloy of zirconium having niobium at 2.5% throughout. If that same sample is then surface alloyed with titanium such that titanium is present in greater concentration in the surface and the near-surface region than in the substrate, the sample is an “alloy” and has a “surface alloy.”

[0082] As used herein, “zirconium alloy” is defined broadly, and includes alloys having at least 5% (w/w) zirconium. The alloys can be of zirconium, titanium, hafnium and niobium. The alloys can be polycrystalline or amorphous or single crystals or combinations of same.

[0083] The “surface alloyed zone” is defined as the surface and the near-surface region that comprises one or more surface alloying metallic species. In some embodiments, the surface alloyed zone region may be about one to about five percent of the thickness of the substrate, and more particularly from about one to about two percent of the thickness of the substrate. In some embodiments, the surface alloyed zone may have a thickness from about 10 microns to about 2000 microns. For example, if the substrate is 10 mm thick then the surface alloyed zone may be as thick as 2 mm. In one particular embodiment, the surface alloyed zone may have a thickness from about 10 microns to about 100 microns.

[0084] The “diffusion hardened zone” is defined as the surface alloyed zone that comprises one or more diffusion hardening species. Examples of diffusion hardening species include carbon, oxygen, nitrogen, boron, or any combination thereof. The diffusion hardened zone has hardness at least 1.1 times greater than the substrate hardness. Where a composition has been both surface alloyed with one or more alloying species and diffusion hardened with one or more diffusion hardening species, the region that comprises both a diffusion hardening species and a surface-alloying metal is defined as the “surface alloyed/hardened zone.” In many embodiments of the present invention, the diffusion hardening is performed such that any diffusion hardening species do not extend as far into the substrate as do the surface alloying species. The region at depths that comprises only surface alloying species but no diffusion hardening species is defined as the “surface alloyed/non-hardened zone.” In such cases, the surface alloyed zone comprises both the surface alloyed/hardened zone and the surface alloyed/non-hardened zone.

[0085] As used herein, “ceramic” is defined as a chemical compound of a metal (or a metal constituent in an alloy) and one or more non-metals, including carbon, oxygen, nitrogen, boron, and combinations thereof. While the preferred embodiment of the ceramic of the present invention is an oxide, the ceramic of the present invention includes oxides, carbides, nitrides, borides, and any combination thereof. As used herein, “ceramic layer” is defined as a stratum of material consisting of ceramic which forms a part of a greater material. As used herein, the term “ceramic coating” refers to a surface transformed layer, surface film, surface oxide, nitride, carbide, boride (or combination thereof) present on the alloy or metal substrate.

[0086] As used herein, “biocompatible metal or biocompatible alloy” is defined as the individual metals or metal combinations (alloy) that are currently used in orthopedic industry. An example of biocompatible metal is pure titanium or pure zirconium with any additional metals less than 1 wt %. Examples of biocompatible alloys include cobalt-chromium-molybdenum, titanium-aluminum-vanadium, nickel-titanium and zirconium-niobium. The other biocompatible alloys that are referred in this invention are the alloys that are made from either zirconium or titanium or tantalum or niobium or hafnium or combination thereof.

[0087] In one embodiment of the invention, the composition that comprises the implant is made by a process that includes the steps of providing a first metal that forms a substrate, diffusing a second metal into the metal substrate, removing excess coating material from the first metal to provide an alloyed surface of the substrate, and hardening the alloyed surface. As examples, the first metal may be made of cobalt chrome, titanium, titanium alloy, stainless steel, zirconium, or zirconium alloy. As examples, the second metal may be made of zirconium, cobalt, chromium, titanium, niobium, aluminum, vanadium, or combinations thereof. As examples, the excess coating material may be removed by grinding, tumbling, glass-beading, shot-peening, grit blasting, polishing, sanding, or through the use of abrasive slurry. The hardening step may include treating the surface in an atmosphere of oxygen, carbon, nitrogen, boron, or any combination thereof.

[0088] In one particular embodiment of the invention, a substrate of a biocompatible alloy, such as Zr-2.5Nb, has a surface characterized by a ceramic layer that includes zirconium and titanium. The thickness of the ceramic layer is generally from about 1 micron to about 100 microns.

[0089] In one particular method, commercially pure titanium powder is laid on or placed upon a surface of an Zr-2.5Nb alloy sample. The sample and the titanium powder are then heated to about 800 degrees C. for about 10 hours in vacuum, which may be, as an example, less than about 10.sup.−4 torr. After the treatment, the sample is cooled to room temperature and the excess titanium surface powder is removed. This results in a surface alloy on the substrate, which is illustrated in a metallographic image in FIG. 3. The embodiment depicted in FIG. 3 illustrates a composition in cross-section having a substrate 210 and a surface alloyed zone 220. It should be noted that based on the metallographic image it appears that there is a distinct boundary between the substrate 210 and the surface alloyed zone 220. However, those having ordinary skill in the art would understand that such a distinct boundary does not exist. The titanium concentration gradually changes from the surface alloyed zone 220 to the substrate 210, even though metallographically it is not visible.

[0090] Thereafter, the sample with the alloyed surface may be hardened. For example, the alloy surface may be diffusion hardened, such as by oxidization at about 600 degrees C. for about one hour and 15 minutes. Those having ordinary skill in the art would understand that nitriding, carburizing, or other similar treatments may equally be used. The alloy surface after oxidation is illustrated by the metallographic image in FIG. 4. The embodiment depicted in FIG. 4 illustrates a composition in cross-section having the substrate 210, the surface alloyed/non-hardened zone 220, and a surface alloyed/hardened zone 230. In the depicted embodiment, the surface alloyed/hardened zone 230 is an oxide layer. In the embodiment depicted in FIG. 4, the oxidation process provides an approximately 25 micron thick oxide on the surface. This is significant as the titanium diffusion into the substrate provides a surface that forms a thicker oxide than that could be achieved otherwise on a Zr-2.5Nb substrate without such Ti alloyed region. For a non-alloyed surface, the oxide thickness generally would be about five to six microns in thickness.

[0091] FIG. 5 illustrates another embodiment of the invention. The embodiment depicted in FIG. 5 is a structure 300 having a substrate 310 and a surface alloyed zone 314. In FIG. 5, a mixture of oxides, nitrides, carbides or any combinations thereof covers a substrate of a biocompatible alloy, such as CoCr. The mixture may be formed by diffusing one or more of zirconium, titanium, cobalt and chromium into the substrate. The thickness of the mixed oxides is generally about 1 micron to about 100 microns. As an example of the first embodiment, a surface of a CoCr alloy is diffused with zirconium at high temperature using a conventional diffusion process. The alloy is then oxidized to form a zirconium oxide mixed with cobalt and chromium oxide on the surface of the CoCr alloy.

[0092] In another embodiment, a surface of a Ti-6Al-4V alloy is diffused with zirconium at high temperature using a conventional diffusion process. The alloy is then oxidized to form mixed oxides of titanium, zirconium, aluminum and potentially vanadium.

[0093] FIG. 6 illustrates yet another embodiment of the invention. The embodiment depicted in FIG. 6 is a structure 400 having a substrate 410 and a surface alloyed zone 414. In FIG. 6, a mixture of oxides, nitrides, carbides or any combinations thereof covers a substrate of zirconium alloy. For example, the mixture may be formed by diffusing titanium into a zirconium substrate. The thickness of the mixed oxides is generally from about 1 micron to about 100 microns. Then the entire sample is oxidized. Diffusion of titanium in the zirconium substrate results in the formation of a much thicker oxide on the surface than it would have formed otherwise on a non-alloyed zirconium surface. The treated alloy can then be further diffusion hardened with a vacuum treatment to increase the depth of hardening.

[0094] In another embodiment of the invention, chromium is diffused into a cobalt chrome substrate and then the surface is nitrided to form a chromium nitride or is oxidized to form chromium oxide.

[0095] In some embodiments of the invention, the alloyed surfaces may be oxidized or nitrided or carburized in-situ such as during the alloying process. In some embodiments of the invention, a medical implant may include an alloyed surface that has not been oxidized, nitrided, or carburized.

[0096] It should be noted that the diffusion process described here is a non-exhaustive, illustrative example of the formation of an alloyed surface. Other techniques such as use of lasers or any other focused energy source such as induction heating to heat or partially melt the surface and then alloy the surface simultaneously using a metal powder jet may be used to create such an alloyed surface. Such embodiments are within the scope of the present invention.

[0097] In some embodiments, an inert gas or a mixture of inert gasses may be used during the diffusion hardening process instead of carrying the process out in a vacuum. Inert gasses may include, but are not limited to, nitrogen, argon, helium, krypton and neon.

[0098] The new composition has application in medical implants of all varieties. One of the uses of such an article is a hip implant. FIG. 7 illustrates a hip prosthesis 510. The hip prosthesis 510 includes a stem 512, a femoral head 514, a liner 516, and a shell 518. The femoral head 514 is operatively connected to the stem 512, and the liner 516 is coupled to the shell 518. The stem 512 is adapted for mounting in a femur (not shown), and the shell 518 is adapted for mounting to an acetabulum (not shown). The femoral head 514 articulates against the liner 516. In this particular case, both femoral head 514 and liner 516 can be made of the composition described herein.

[0099] In some embodiments of the invention, only one of the articulating components is made from the composition described and the other articulating component is made from a biocompatible material.

[0100] The present composition is applicable for any and all medical implants, but in particular for articulating medical implants such as, but not limited to, hip, knee, shoulder, and elbow orthopedic implants. Vertebral implants are also amenable to the present invention. The present invention also finds applicability to any and all non-articulating medical implants.

[0101] In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained.

[0102] The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.

[0103] As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. For example, while FIG. 3 illustrates a substrate made from Zr-2.5Nb alloy, other substrate materials may equally be used. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.