Surface hardened biocompatible metallic medical implants

• US 5,498,302 A
• Filed: 11/09/1994
• Issued: 03/12/1996
• Est. Priority Date: 02/07/1992
• Status: Expired due to Term

• Current Assignee: Howmedica Osteonics Corp. (Stryker Corporation)
• Original Assignee: Smith & Nephew Richards Incorporated (Smith & Nephew PLC)
• Inventors: Davidson, James A.
• Primary Examiner(s): KASTLER, SCOTT R
• Application Number:
  US08/337,665
• Time in Patent Office: 489 Days
• Field of Search: 148/316, 148/317, 148/421, 148/669
• US Class Current: 148/317
• CPC Class Codes: A61F 2/30767 Special external or bone-contacting surface, e.g. coating for improving bone ingrowth
• CPC Class Codes: A61F 2002/30922 Hardened surfaces
• CPC Class Codes: A61F 2310/00017 Iron- or Fe-based alloys, e.g. stainless steel
• CPC Class Codes: A61F 2310/00023 Titanium or titanium-based alloys, e.g. Ti-Ni alloys
• CPC Class Codes: A61F 2310/00029 Cobalt-based alloys, e.g. Co-Cr alloys or Vitallium
• CPC Class Codes: A61F 2310/00089 Zirconium or Zr-based alloys
• CPC Class Codes: A61F 2310/00598 Coating or prosthesis-covering structure made of compounds based on metal oxides or hydroxides
• CPC Class Codes: A61F 2310/00856 Coating or prosthesis-covering structure made of compounds based on metal nitrides
• CPC Class Codes: A61L 27/045 Cobalt or cobalt alloys
• CPC Class Codes: A61L 27/06 Titanium or titanium alloys
• CPC Class Codes: A61L 27/306 Other specific inorganic materials not covered by A61L27/303 - A61L27/32

Abstract

This invention provides surface hardened, abrasion resistant high strength, biocompatible metal medical implants, in particular, titanium alloy implants which do not include any elements which have been shown or suggested as having short term or long term potential adverse effect from a standpoint of biocompatibility. Further, the invention provides methods of strengthening and hardening the surfaces of other titanium, zirconium, and cobalt-based alloy implants with small concentrations of a metal solute such as zirconium, yttrium, tantalum, aluminum, silicon, chromium, or thorium via internal oxidation or nitridation. Alternatively, nitrogen, oxygen, or carbon can be diffused directly into the surface of the implants by interstitial hardening to further increase the surface abrasion resistance of these internally oxidized or internally nitridized implant metal or metal alloys.

Claims

1. A surface hardened metallic medical implant, the implant comprising:

a surface hardened metallic alloy implant body with surface hardness greater than about 40 Rockwell C, the hardened surface produced by a process comprising;

(i) selecting a metallic alloy containing less than about 2 wt. % of a metal solute different from and more readily nitridable than other elements of the metallic alloy implant body;

(ii) hardening the surface of the implant body by internal nitridation of a substantial proportion of the more readily nitridable solute at the surface of the implant while maintaining a metallic luster on the surface of the implant.

2. The surface hardened metallic medical implant of claim 1, wherein said implant body comprises about 85 wt. % titanium and about 15 wt. % niobium;

and the metal solute is selected from the group consisting of silicon, tantalum, and thorium.

3. The surface hardened metallic medical implant of claim 1, wherein the implant body comprises about 73 wt. % titanium, about 13 wt. % niobium, and about 13 wt. % zirconium;

and the metal solute is selected from the group consisting of silicon and thorium.

4. The surface hardened metallic medical implant of claim 1, wherein the implant body comprises Co-Cr-Mo alloy and the metal solute is selected from the group consisting of silicon, tantalum and thorium.

5. The surface hardened metallic medical implant of claim 1, wherein the implant body comprises Ti-6A1-4V;

and the metal solute is selected from the group consisting of silicon, tantalum, and thorium.

6. The surface hardened metallic medical implant of claim 1, wherein the metallic implant body is further hardened by diffusion into the metallic alloy of an element selected from the group consisting of nitrogen, oxygen, and carbon.