Diffusion-hardened medical implant

• US 8,647,701 B2
• Filed: 06/27/2011
• Issued: 02/11/2014
• Est. Priority Date: 12/15/2005
• Status: Active Grant

• Current Assignee: Smith & Nephew Incorporated (Smith & Nephew PLC)
• Original Assignee: Smith & Nephew Incorporated (Smith & Nephew PLC)
• Inventors: Pawar, Vivek, Jani, Shilesh C., Weaver, Carolyn
• Primary Examiner(s): SELLMAN, CACHET I
• Application Number:
  US13/170,084
• Publication Number:
  US 20110320007A1
• Time in Patent Office: 960 Days
• Field of Search: 427/2.1, 427/2.26, 427/2.29, 148/277, 148/269, 148/284, 148/281
• US Class Current: 427/2.26
• CPC Class Codes: A61F 2/28 Bones joints A61F2/30
• CPC Class Codes: A61F 2/30767 Special external or bone-contacting surface, e.g. coating for improving bone ingrowth
• CPC Class Codes: A61F 2/3094 Designing or manufacturing processes
• CPC Class Codes: A61F 2/32 for the hip
• CPC Class Codes: A61F 2/38 for elbows or knees
• CPC Class Codes: A61F 2/44 for the spine, e.g. vertebrae, spinal discs
• CPC Class Codes: A61F 2002/30016 differing in hardness, e.g. Vickers, Shore, Brinell
• CPC Class Codes: A61F 2002/30922 Hardened surfaces
• CPC Class Codes: A61F 2002/30929 having at least two superposed coatings
• CPC Class Codes: A61F 2210/0076 multilayered, e.g. laminated structures
• CPC Class Codes: A61F 2250/0019 differing in hardness, e.g. Vickers, Shore, Brinell
• CPC Class Codes: A61F 2250/0041 differing in wear resistance
• 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 2310/00101 Molybdenum or Mo-based alloys
• CPC Class Codes: A61F 2310/00485 Coating made of zirconium or Zr-based alloys
• CPC Class Codes: A61F 2310/00592 Coating or prosthesis-covering structure made of ceramics or of ceramic-like compounds
• 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 2400/00 : Materials characterised by their function or physical properties
• CPC Class Codes: A61L 27/045 : Cobalt or cobalt alloys
• CPC Class Codes: A61L 27/047 : Other specific metals or alloys not covered by A61L27/042 - A61L27/045 or A61L27/06
• CPC Class Codes: A61L 27/06 : Titanium or titanium alloys
• CPC Class Codes: A61L 27/10 : Ceramics or glasses
• CPC Class Codes: A61L 27/30 : Inorganic materials
• CPC Class Codes: A61L 27/50 : Materials characterised by their function or physical properties , e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
• CPC Class Codes: C23C 8/12 : using elemental oxygen or ozone
• CPC Class Codes: C23C 8/80 : After-treatment
• CPC Class Codes: Y10T 428/12611 : Oxide-containing component

Abstract

Methods of making surface hardened medical implants comprising providing a biocompatible alloy with a surface comprising an oxide or nitride layer, diffusing at least a portion of the respective oxygen or nitrogen from the oxide or nitride layer the substrate for a period of time to form a diffusion hardened zone of desired thickness. The period of time is based at least on (1) the diffusivity of a diffusing specie in the oxide or nitride layer, (2) a desired hardness profile of at least a portion of said implant defined by a function selected from the group consisting of: an error function, an exponential function, a near uniform distribution function, and any sequential combination thereof, or (3) a desired thickness of said oxide or nitride layer to be retained.

Claims

1. A method of making a surface hardened medical implant comprising the steps of:

forming a medical implant of zirconium or zirconium alloy;

oxidizing or nitriding said implant at a temperature of from 500 degrees C. to 700 degrees C. to retain at least 0.1 microns of said oxide or nitride layer, to form at least 0.005 microns metallic hardened layer on top of said at least 0.1 microns thick oxide or nitride layer, and to form a diffusion zone having a thickness of at least 2 microns below said at least 0.1 microns thick oxide or nitride layer; and

wherein said treating step is performed for a period of time determined based at least on a desired thickness of the diffusion zone to be formed.

2. The method of claim 1, wherein the medical implant further comprises titanium, tantalum, niobium, hafnium, and any combination thereof.

3. The method of claim 1, wherein the oxide or nitride thickness before said step of treating said implant under vacuum or inert gas is from 2 to 15 microns.

4. The method of claim 1, wherein the oxide or nitride thickness after said step of treating said implant under vacuum or inert gas is from 0.1 to 10 microns.

5. The method of claim 1, wherein the thickness of the diffusion hardened zone is from 2 to 50 microns.

6. The method of claim 1 further comprising:

removing a portion of said metallic hardened layer.

7. A method of making a surface hardened medical implant comprising the steps of:

forming a medical implant of zirconium or zirconium alloy;

oxidizing or nitriding said implant at a temperature of from 500 degrees C. to 700 degrees C. to form an oxide or nitride layer having a thickness of at least 2 microns;

treating said implant under vacuum or inert gas at a temperature less than 700 degrees C. to retain at least 0.1 microns of said oxide or nitride layer, to form at least 0.005 microns metallic hardened layer on top of said at least 0.1 microns thick oxide or nitride layer, and to form a diffusion zone having a thickness of at least 2 microns below said at least 0.1 microns thick oxide or nitride layer; and

polishing the metallic hardened layer with mechanical, chemical, or electromechanical devices or substances;

wherein said treating step is performed for a period of time determined based at least on a desired thickness of said oxide or nitride layer to be retained.

8. The method of claim 7, wherein the medical implant further comprises titanium, tantalum, niobium, hafnium, and any combination thereof.

9. The method of claim 7, wherein the oxide or nitride thickness before said step of treating said implant under vacuum or inert gas is from 2 to 15 microns.

10. The method of claim 7, wherein the oxide or nitride thickness after said step of treating said implant under vacuum or inert gas is from 0.1 to 10 microns.

11. The method of claim 7, wherein the thickness of the diffusion hardened zone is from 2 to 50 microns.

12. The method of claim 7 further comprising:

removing a portion of said metallic hardened layer.