Objectives for Public Workshop - Cardiovascular Metallic Implants: Corrosion, Surface Characterization, and Nickel Leaching, March 8-9, 2012

Workshop Objective:

To provide a forum for the discussion of:

1. The various methods that are used for corrosion assessments, surface characterization techniques, and nickel leach testing used to evaluate the suitability of metallic cardiovascular implant devices.
2. The limitations of each of these tests to predict actual in-vivo performance.
3. The need, utility, and circumstances when each test is needed
4. The potential testing paradigms, including what should be used as acceptance criteria for each test.

Session Objectives:

• Purpose of Testing (intro)
• Identify what testing has been done before
• What has been learned from previous testing
• Utility and limitations of testing
• Moving forward (testing considerations, knowledge gaps)

Schedule:

Day 1

• Intro 15 min
• 4-4.5 hr corrosion
• 2.0 hr surface characterization

Day 2

• 4 hr nickel leach/tox
• 3 hr summary

Session 1 – Corrosion (4-4.5hrs)

Objectives:

1. Identify the types of corrosion testing commonly performed. (15 min max including intro)
2. Identify what has been learned from previous corrosion testing; describe the relevance of corrosion testing. (60 min)
   • 2.1. Discuss whether corrosion testing has been predictive of in vivo corrosion (from animal studies or patient explants)
   • 2.2. Identify the in vivo driving forces for corrosion
3. Discuss interpretation of results and proposed acceptance criteria for ASTM F2129. (75min)
   • 3.1. Discuss interpretation of Er values
   • 3.2. Discuss value of Eb-Er vs Eb as acceptance criteria.
   • 3.3. Discuss whether specific Eb or Eb-Er values are universally appropriate.
   • 3.4. Discuss the significance of repassivation potential
   • 3.5. Discuss any other corrosion testing concerns
4. Moving Forward: Discuss how corrosion should be assessed moving forward. (90 min)
   • 4.1. Discuss whether ASTM F2129 is a sufficient assessment of clinically relevant corrosion.
     • 4.1.1. If not:
       • 4.1.1.1. Discuss whether it is possible to modify F2129 to be more clinically relevant (e.g. acceptance criteria)
       • 4.1.1.2. Discuss what is a sufficient assessment of clinically relevant corrosion.
   • 4.2. Discuss the utility of galvanic corrosion testing.
   • 4.3. Potential modifications to current testing methodologies and assessments.
     • 4.3.1. Identify best practices for F2129 testing
     • 4.3.2. Identify best practices for galvanic corrosion testing

Session 2 – Surface Characterization of Nickel-Containing Alloys (2.0hrs)

Objectives:

1. Identify commonly used methods to characterize the surface (passivation) layer of metal implant materials. Describe the respective benefits and drawback of each of current surface characterization techniques/methodologies, based on your experience as well as theoretical/practical considerations. (30 min)
2. Discuss the relevance of surface characterization (30 min)
• 2.1. Discuss potential structure-property relationships for each alloy.
• 2.2. Identify key surface characteristics for each alloy:
3. Moving Forward: Discuss potential implications for surface characterization (60 min)
• 3.1. Discuss whether surface characterization testing is needed in general
• 3.1.1. If not, discuss when it is needed (e.g. “poor” ASTM F2129 test results, fractures)
• 3.1.2. Discuss whether surface characterization testing can be used to obviate the need for other tests, and if so which ones and under what conditions.
• 3.2. Discuss whether acceptance criteria for surface chemistry and depth characteristics can or should be established for Auger, XPS, and FIB-SEM.
• 3.3. Discuss the potential benefits to perform surface microstructure quality control on final devices.

Session 3 – Nickel Leach and Toxicity (4hrs)

Objectives:

1. Discuss the consequences of nickel exposure (60 min)
• 1.1. Discuss the general biological response to/toxicity of nickel
• 1.2. Discuss clinical findings related to nickel tox
2. Discuss in vitro nickel leach testing (60 min)
• 2.1. Discuss what has been learned from in vitro nickel leach testing
• 2.2. Discuss the limitations of in vitro testing
• 2.3. Discuss best practices for in vitro nickel leach testing
3. Discuss in vivo nickel release assessment (30 min)
• 3.1. Identify animal and clinical approaches to evaluate nickel release.
• 3.2. Discuss what has been learned from in vivo nickel leach testing
• 3.3. Discuss the limitations of in vivo nickel assessment
4. Discuss in vitro – in vivo correlation of nickel release and patient exposure (30 min)
5. Discuss acceptable levels of nickel exposure (30 min)
6. Moving Forward: Identify knowledge gaps (30 min)

Session 4 – Testing Paradigm (3hrs)

Objective: Identify testing paradigms

Guiding Questions:

1. Corrosion testing:
   1. Currently, ASTM F2129 is generally needed to assess pitting/crevice corrosion.
      1. Is ASTM F2129 a sufficient assessment of clinically relevant corrosion?
      2. If not,
         1. Is there a way to modify F2129 to be more clinically relevant (e.g. acceptance criteria)
         2. Are there other assessments in lieu of or in addition to ASTM F2129 to assess clinically relevant corrosion? a)
   2. Under what conditions is galvanic corrosion (ASTM G71) needed?
      1. If ASTM F2129 results are “good” is galvanic corrosion testing needed?
2. Surface characterization:
   1. Is surface characterization testing needed in general?
   2. If not, when is it needed? (e.g. “poor” ASTM F2129 test results, fractures)
   3. Can surface characterization testing be used to obviate the need for other tests, and if so which ones and under what conditions?
3. Nickel leach
   1. Under what conditions is in vitro nickel leach testing needed (e.g. “poor” ASTM F2129 test results, fractures, “poor” surface characteristics)?
      1. Should open circuit potential be performed in tandem with in vitro nickel leach testing?
   2. Under what conditions is in vivo nickel leach testing needed?

Potential Tests for consideration:
Pitting/crevice corrosion (ASTM F2129)
Galvanic corrosion
Surface characterization
Animal testing
Ni leach (in vitro and/or in vivo)
Open circuit potential
(fretting/fatigue)