Understanding Pitting Corrosion Acceptance Criteria Using ASTM F2129 and ASTM F3306

The in-vitro acceptance criteria from the pitting corrosion test method (ASTM F2129) that represents safe long term in-vivo performance of medical devices has been a subject of discussion for decades in the community. Despite numerous studies focused towards answering these questions (Rosenbloom 2007, Lonn 2015, Sullivan 2017), there is no consensus around the acceptance criteria that has been established in the industry. Historically, definitions of acceptance criteria have centered on breakdown potentials (Eb), though there has been debate in the literature regarding the use of Eb or Eb-Er. Most studies in this area (Rosenbloom 2007, Sullivan 2017), point to low Eb values (i.e. < 300mV) as concerning to long term in-vivo performance and typically, Ni-elution testing is recommended to further understand a device’s corrosion performance (FDA guidance document 17013-R1).

To investigate the relationship between F2129 and F3306 test methods, nitinol samples representing high and low Eb and Eb-Er values will be manufactured. F2129 testing will be conducted on as manufactured (i.e. t = 0) and incubated samples at relevant F3306 time points (e.g. after incubation at t = 24 hr, 3 days, 7 days, 15 days, etc.). Another set of samples will undergo metal ion elution testing per F3306, including visual inspection. Side by side analysis of F2129 and F3306 results will inform the impact of different Eb and Eb-Er sample groups on the corrosion performance. The results of this study may help inform acceptance criteria development for corrosion assessment of nitinol devices.