Surface and near surface hardened medical implants

• US 5,372,660 A
• Filed: 08/26/1993
• Issued: 12/13/1994
• Est. Priority Date: 08/26/1993
• Status: Expired due to Term

• Current Assignee: Howmedica Osteonics Corp. (Stryker Corporation)
• Original Assignee: Smith & Nephew Richards Incorporated (Smith & Nephew PLC)
• Inventors: Poggie, Robert A., Davidson, James A., Mishra, Ajit K.
• Primary Examiner(s): Roy, Upendra
• Application Number:
  US08/112,612
• Time in Patent Office: 474 Days
• Field of Search: 148/421, 148/669, 420/417, 623/16, 623/18
• US Class Current: 148/421
• CPC Class Codes: A61F 2310/00023 Titanium or titanium-based alloys, e.g. Ti-Ni alloys
• CPC Class Codes: A61L 27/06 Titanium or titanium alloys
• CPC Class Codes: A61L 31/022 Metals or alloys
• CPC Class Codes: C22C 14/00 Alloys based on titanium
• CPC Class Codes: C23C 8/12 using elemental oxygen or ozone
• CPC Class Codes: C23C 8/16 using oxygen-containing compounds, e.g. water, carbon dioxide
• CPC Class Codes: Y10S 623/923 Bone

Abstract

Surface and near surface hardened medical implants are provided. These implants are fabricated from titanium alloys that contain an amount of zirconium sufficient to permit the formation of a significant amount of zirconium oxide at the surface of the implant to cause surface hardening. Further, the zirconium-containing titanium alloy implants are characterized in having an alloy core with an oxygen-rich layer surrounding the core, and a surface layer, overlying the oxygen-rich layer, including mixed oxides of the metals present in the alloy. A zirconium-rich interface may sometimes be present between the oxygen-rich layer and the mixed-oxide surface layer. The method of producing these surface hardened implants includes the steps of heating the implant in an oxygen containing environment at a temperature sufficient to allow oxygen to diffuse to and react with the implant surface and near surface.

Claims

1. A surface and near surface hardened implant of titanium alloys containing zirconium, comprising:

(a) a zirconium-containing titanium alloy core;

(b) a layer, surrounding the core, of oxygen-rich alloy solution; and

(c) a surface layer, overlying the oxygen-rich alloy layer, of mixed oxides of metals present in the alloy core.

2. The surface and near surface hardened implant of claim 1, wherein the layer of oxygen-rich alloy solution and surface layer of mixed oxides are formed by subjecting the zirconium-containing titanium alloy core to elevated temperatures in an environment able to provide oxygen and from which oxygen can diffuse into the surface of the alloy.

3. The surface and near surface hardened implant of claims 1 or 2, wherein said layer of oxygen-rich alloy is less than about 50 microns thick.

4. The surface and near surface hardened zirconium containing implant of claim 1, wherein the layers are formed at temperatures between about 200°

C. and about 1200°

C.

5. The implant of claim 1, wherein the heating is up to from about 200°

to about 700°

C.

6. The surface and near surface hardened zirconium containing implant of claim 2, further comprising a zirconium-rich interface between the oxygen-rich layer and the mixed-oxide surface layer.

7. The surface and near surface hardened zirconium containing implant of claim 2, wherein the layers are formed in an environment comprising oxygen-containing compounds which are partially composed of oxygen and that disassociate to produce oxygen at temperatures at which the layers form.

8. The surface and near surface hardened zirconium containing implant of claim 2, wherein the titanium alloy comprises:

titanium;

from about 10 wt. % to about 20 wt. % niobium; and

from about 0.5 wt. % to about 20 wt. % zirconium.

9. The surface and near surface hardened zirconium containing implant of claim 2, wherein the core metallic alloy comprises:

titanium;

from about 35 wt. % to about 50 wt. % niobium; and

from about 0.5 wt. % to about 20 wt. % zirconium.

10. The surface and near surface hardened zirconium containing implant of claim 2, wherein the core metallic alloy comprises:

about 74 wt. % titanium;

about 13 wt. % niobium; and

about 13 wt. % zirconium.

11. The surface and near surface hardened zirconium containing implant of claim 2, wherein the layers and interface are formed by a process comprising:

(a) exposing the implant to an oxygen-containing environment;

(b) heating the implant up to about 500°

C. in about 1 to about 10 hours;

(c) thermally soaking the heated implant for about 2 to about 8 hours at about 500°

C.; and

(d) cooling the soaked implant to room temperature in about 1 to about 10 hours.

12. The implant of claim 5, wherein the environment comprises argon, oxygen, and water vapor.

13. The implant of claim 5, wherein the environment comprises a composition having chemically bound oxygen that is released for forming an oxide with elemental metal at implant substrate surfaces during the steps of heating and soaking.

14. The surface and near surface hardened zirconium containing implant of claim 7, wherein inert gases are used as a carrier medium for the oxygen-containing compounds.

15. The surface and near surface hardened zirconium containing implant of claim 10, wherein the heating is in a furnace continuously supplied with oxygen-containing gasses.

16. The surface and near surface hardened zirconium containing titanium implant of claims 1 or 2, wherein said layer of oxygen-rich alloy is less than about 20 microns thick.

17. The surface and near surface hardened zirconium containing implant of claims 1 or 2, wherein said surface layer of mixed-oxides is from about 0.1 to about 10 microns thick.

18. A surface hardened medical implant comprising a zirconium-containing titanium alloy, the surface hardened implant produced by a process comprising:

(a) subjecting zirconium-containing titanium implant substrate to an environment able to provide oxygen;

(b) heating the zirconium-containing implant substrate to a temperature that allows oxygen to diffuse into surfaces of said implant;

(c) soaking the zirconium-containing implant substrate at the temperature for a time sufficient to oxidize elemental metal at the surfaces of the implant substrate; and

(d) producing a hardened medical implant comprising a hard mixed-oxide surface layer on the zirconium-containing implant substrate and an oxygen-rich layer beneath said mixed oxide surface layer.

19. The implant of claim 18, wherein the zirconium-containing titanium alloy is selected from the group of alloys consisting of:

(i) titanium, about 10 to about 20 wt. % niobium, and about 0.5 to about 20 wt. % zirconium; and

(ii) titanium, about 35 to about 50 wt. % niobium, and about 0.5 to about 20 wt. % zirconium.

20. The implant of claim 19, wherein the mixed oxide layer is from about 0.1 to about 10 microns thick.

21. The implant of claim 19, wherein the oxygen-rich layer is from about 1 to about 50 microns thick.

22. A medical implant comprising a zirconium-containing core and a hard mixed oxide surface on said core, the implant produced by a process comprising:

(a) subjecting an implant substrate comprising a zirconium-containing titanium alloy to an environment able to provide oxygen for oxidizing elemental metal at surfaces of the substrate;

(b) heating the implant substrate in the environment to a temperature from about 200°

to about 1200°

C.;

(c) soaking the implant substrate at a temperature that permits oxidizing of elemental metal at substrate surfaces and diffusion of oxygen beneath the substrate surfaces; and

(d) producing a hard mixed-oxide surface layer on the zirconium-containing implant substrate and an oxygen-rich layer beneath said mixed oxide surface layer.

23. The medical implant of claim 22, wherein the zirconium-containing titanium alloy selected from the group consisting of:

(i) titanium, about 10 to about 20 wt. % niobium, and about 0.5 to about 20 wt. % zirconium; and

(ii) titanium, about 35 to about 50 wt. % niobium, and about 0.5 to about 20 wt. % zirconium.

24. The medical implant of claims 22 or 23, wherein the implant is selected from the group consisting of hip joint stems, femoral heads, knee femoral components, knee tibial components, bone plates, fixation screws, intramedullary nails, inner ear vent tubes, spinal plates, spinal disks, pelvic plates, dental implants, cardiovascular implants, and compression hip screws.