Medical Devices and Prostheses

XPS or ESCA Surface Analysis:

  • Measure quantitative surface elemental composition
  • Identify surface contaminants
  • Measure effects of surface treatments of vascular stent surfaces
  • Determine surface oxide character since alloy oxides may differ greatly in composition dependent upon processing (Nitinol Stents, Stainless Steel Tubing, CoCrMo Alloy)
  • Examine oxide composition changes with depth by using argon ion etching (Nitinol Stents, Stainless Steel Tubing, CoCrMo Alloy)
  • Identify composition of stains and discolorations
  • Determine the real chemistry of multi-phase TiN coatings (TiO2, TiC, TiOx(OH)4-2x, titanium oxynitrides)
  • Examine brazed joints and electrical connections for proper composition at surfaces
  • Check ceramic electrical insulators for composition and surface contaminants
  • Determine cause of braze wetting problems
  • Identify corrosion product deposit chemistries on hip and knee explants including bone mineral and polypeptide components

 SEM/EDX Analysis:

  • Determine cause and location of crack initiation for stent failures in flexure testing
  • Examine device surfaces for microcracking
  • Examine surface oxides for evidence of non-uniformity
  • Check for fretting or scratches due to rubbing surfaces such as may occur on vascular stents
  • Examine brazed electrical or hermetic seals for problems
  • Determine nature and point of failure initiation of dental files in elastic torque testing
  • Distinguish organic matter on metal devices using backscatter detection mode imaging

 Differential Scanning Calorimetry or DSC:

  • Determine glass transition temperature of polymeric materials and measure energy of transition
  • Determine temperature of crystalline phase melting and measure energy of transition
  • Compare relative volumes of crystalline versus amorphous phases in polymers
  • Measure temperatures of austenitic and martinsitic transitions in Nitinol

 FTIR Infrared Spectroscopy:

  • Identify polymer material
  • Verify polymer is as-specified
  • Check whether polymer has degraded due to aging or cleaning/sterilization procedures
  • Solve packaging problems
  • Address printing problems on packaging and devices

 Electrochemistry and Corrosion Testing:

  • Cyclic potentiodynamic polarization to determine the corrosion susceptibility of small implant devices, ASTM F2129
  • Electrochemical reactivation to detect sensitization of AISI type 304 and 304L stainless steels, ASTM G108; also modifications for other alloys
  • Pitting or crevice corrosion of metallic surgical implant materials, ASTM F746

 

Analysis of Corrosion Deposit on Hip Explant

Corrosion Deposit on Hip Explant

Analysis of the light green and off-white corrosion deposit on the CoCrMo alloy hip implant shown above on the femoral stem just below the taper fitted to the head was carried out by XPS to determine its chemistry.  Similar corrosion product was found inside the head of the hip implant as well when it was removed from the patient.

The deposit was primarily a combination of chromium phosphate and chromium oxide with bone minerals and polypeptides, though many other compounds of chromium, molybdenum, and cobalt were also identified.  In most environments, chromium oxide concentrations at the surface provide good corrosion resistance, but chromium is not as resistant to phosphate attack as cobalt and molybdenum are in the CoCrMo alloy, so the corrosion product has much more chromium in it than it has cobalt or molybdenum.

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