Ultra high molecular weight polyethylene components treated to resist shearing and frictional wear

• US 6,171,343 B1
• Filed: 04/30/1997
• Issued: 01/09/2001
• Est. Priority Date: 03/29/1994
• Status: Expired due to Term

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Lankford, James Jr., Dearnaley, Geoffrey
• Primary Examiner(s): Prebilic, Paul B.
• Application Number:
  US08/846,673
• Time in Patent Office: 1,350 Days
• Field of Search: 623/1, 623/11, 623/12, 623/16-23, 623/1.49, 623/22.15, 623/22.23, 623/23.4, 623/23.58, 623/23.6, 623/23.61, 623/23.71, 623/926, 600/36
• US Class Current: 623/23.6
• CPC Class Codes: A61F 2/24 Heart valves ; Vascular valves, e.g. venous valves; Heart implants, e.g. passive devices for improving the function of the native valve or the heart muscle; Transmyocardial revascularisation [TMR] devices; Valves implantable in the body
• CPC Class Codes: A61F 2/30 Joints
• 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 2/468 Testing instruments for artificial joints for testing non-implantable prostheses A61F2/76
• CPC Class Codes: A61F 2002/30024 differing in coefficient of friction
• CPC Class Codes: A61F 2240/008 Means for testing implantable prostheses
• CPC Class Codes: A61F 2250/0021 differing in coefficient of friction
• 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 2310/00059 Chromium or Cr-based alloys
• CPC Class Codes: A61F 2310/00071 Nickel or Ni-based alloys
• 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 2310/00107 Palladium or Pd-based alloys
• CPC Class Codes: A61F 2310/00137 Tungsten or W-based alloys
• CPC Class Codes: A61F 2310/00149 Platinum or Pt-based alloys
• CPC Class Codes: A61F 2310/0058 Coating made of diamond or of diamond-like carbon DLC
• CPC Class Codes: A61L 27/16 obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: A61L 27/303 Carbon
• 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: A61L 33/025 : Carbon; Graphite
• CPC Class Codes: B29C 2071/0027 : Removing undesirable residual components, e.g. solvents, unreacted monomers
• CPC Class Codes: B29C 71/0009 : using liquids, e.g. solvents, swelling agents spectacle cases, e.g. for cleaning contact lenses A45C11/04; disinfecting or sterilising contact lenses A61L12/00, using liquid substances A61L2/20; cleaning involving the use of liquid in general B08B3/00; for hydrating contact lenses B29D11/00067
• CPC Class Codes: B29K 2023/0683 : UHMWPE, i.e. ultra high molecular weight polyethylene
• CPC Class Codes: C08J 7/02 : with solvents, e.g. swelling agents
• CPC Class Codes: C08L 23/06 : Polyethene
• CPC Class Codes: C23C 16/0209 : by heating
• CPC Class Codes: C23C 16/0272 : Deposition of sub-layers, e.g. to promote the adhesion of the main coating
• CPC Class Codes: C23C 16/26 : Deposition of carbon only
• CPC Class Codes: C23C 16/48 : by irradiation, e.g. photolysis, radiolysis, particle radiation
• CPC Class Codes: C23C 16/486 : using ion beam radiation
• CPC Class Codes: C23C 28/00 : Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
• CPC Class Codes: C23C 28/044 : coatings specially adapted for cutting tools or wear applications
• CPC Class Codes: C23C 28/046 : with at least one amorphous inorganic material layer, e.g. DLC, a-C:H, a-C:Me, the layer being doped or not
• CPC Class Codes: Y10S 623/92 : Method or apparatus for preparing or treating prosthetic
• CPC Class Codes: Y10S 623/923 : Bone
• CPC Class Codes: Y10S 623/926 : Synthetic

Abstract

The present invention provides methods for modifying surfaces made from metal alloy and/or UHMWPE, preferably surfaces which are frictionally engaged, e.g., in an orthopaedic implant. The methods of the present invention reduce the coefficient of friction of the metal alloy component, reduce the shearing of fibrils from the UHMWPE component, and reduce sub-surface fatigue in the UHMWPE component. The method involves solvent immersion of the UHMWPE component to remove short chains of polyethylene at or near the surface of the component, and to swell and toughen the subsurface of the component. The method also involves firmly coating the surface of the metal alloy component with an adherent layer of diamond-like carbon (“DLC”) by creating a metal-silicide interface at the surface of the metal alloy to permit firmer adhesion of DLC. Although the methods of the present invention are particularly useful in orthopaedic applications, the methods also can be used to treat similar components used in other applications.

Claims

1. An orthopaedic implant comprising a metal alloy component comprising

an amorphous carbon coating in frictional contact with a surface of a second component, said surface comprising ultra high molecular weight polyethylene, wherein said surface is substantially undamaged due to swelling and said surface is devoid of polyethylene fibrils that shear off during frictional wear for about one million cycles against a polished CoCr pin at a stress level equivalent to that induced by normal body loads at a total hip interface, wherein said surface is treated by a processing comprising:

immersing said surface in an organic solvent for a first amount of time and at a temperature sufficient to dissolve polyethylene fibrils that frictionally shear off during said frictional wear but insufficient to result in damage due to swelling of said ultra-high molecular weight polyethylene, said organic solvent being selected from the group consisting of an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic hydrocarbon, and a mixture thereof; and

exposing said ultra high molecular weight polyethylene component to a sufficient vacuum for a second amount of time sufficient to remove residual solvent

wherein said metal alloy component is coated with amorphous carbon by a process comprising;

heating said metal alloy component to a first temperature;

in a vacuum, condensing onto said metal alloy component silicon in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;

substantially simultaneously bombarding said outer layer with a first energetic beam of ions under conditions comprising a first energy, a first ion density, and a first amount of time, wherein said conditions and said first temperature are sufficient to form said inner bonding layer cohesively bonded to said outer layer;

condensing a carbon precursor onto said outer layer at a second temperature, a pressure, and for a second amount of time sufficient to form a film of precursor molecules on said outer layer, wherein said second temperature and said pressure are sufficiently low that said carbon precursor is not vaporized off of said component;

substantially simultaneously bombarding said carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner layer of silicon carbide cohesively bonded to an outer coating of amorphous carbon.

2. An orthopaedic component comprising a surface comprising ultra-high molecular weight polyethylene,

wherein said component is substantially undamaged due to swelling and said surface is devoid of polyethylene fibrils that shear off during frictional wear for about one million cycles against a polished CoCr pin at a stress level equivalent to that induced by normal body loads at a total hip interface

wherein said orthopaedic implant comprises a metal alloy component comprising a metal selected from the group consisting of cobalt, nickel, titanium, zirconium, chromium, molybdenum, tungsten, platinum, palladium, and combinations thereof, wherein said metal alloy component is coated with amorphous carbon by a process comprising:

heating said metal alloy component to a first temperature;

in a vacuum, condensing onto said metal alloy component silicon in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of said silicon;

substantially simultaneously bombarding said outer layer with a first energetic beam of ions under conditions comprising a first energy, a first ion density, and a first amount of time, wherein said conditions and said first temperature are sufficient to form said inner bonding layer cohesively bonded to said outer layer;

condensing a carbon precursor onto said outer layer at a second temperature, a pressure, and for a second amount of time sufficient to form a film of precursor molecules on said outer layer, wherein said second temperature and said pressure are sufficiently low that said carbon precursor is not vaporized off of said component;

substantially simultaneously bombarding said carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner layer of silicon carbide cohesively bonded to an outer coating of amorphous carbon.

3. An orthopaedic implant comprising a metal alloy component comprising an amorphous carbon coating in frictional contact with a surface of a second component, said surface comprising ultra high molecular weight polyethylene, wherein said surface is substantially undamaged due to swelling and said surface is devoid of polyethylene fibrils that shear off during frictional wear for about one million cycles against a polished CoCr pin at a stress level equivalent to that induced by normal body loads at a total hip interface wherein said amorphous carbon coating further comprises nitrogen ions implanted therein.

4. An orthopaedic implant comprising a metal alloy component comprising

an amorphous carbon coating in frictional contact with a surface of a second component, said surface comprising ultra high molecular weight polyethylene, wherein said surface is substantially undamaged due to swelling and said surface is devoid of polyethylene fibrils that shear off during frictional wear for about one million cycles against a polished CoCr pin at a stress level equivalent to that induced by normal body loads at a total hip interface, wherein said surface is treated by a process comprising:

immersing said surface in an organic solvent for a first amount of time and at a temperature sufficient to dissolve polyethylene fibrils that frictionally shear off during said frictional wear but insufficient to result in damage due to swelling of said ultra-high molecular weight polyethylene, said organic solvent being selected from the group consisting of an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic hydrocarbon, and a mixture thereof; and

exposing said ultra high molecular weight polyethylene component to a sufficient vacuum for a second amount of time sufficient to remove residual solvent

wherein said amorphous carbon coating further comprises nitrogen ions implanted therein.