Corrosion Resistance and Biological Response to Nitinol Christine Trepanier

Transcription

1 Corrosion Resistance and Biological Response to Nitinol Christine Trepanier Nitinol Devices & Components, Fremont, CA

2 Outline 1. Background 2. Surface properties 3. Corrosion resistance 4. Biocompatibility Case Study: Effect of oxide layer composition on corrosion resistance and biocompatibility 5. Summary 2

3 Nitinol Composition 50.8% at. Nickel, Titanium 3

4 Biocompatibility Titanium Well accepted by the body. No clinical toxicity observed (Hildebrand, et al. 1998) Nickel Observed to be toxic (Denkhaus, et al and Barceloux, et al. 1999) Can trigger contact allergies ~ 10% ww population (women > men) (Schafer, et al., 2001) 4

5 Biocompatibility Surface properties Corrosion resistance 5

6 Biocompatibility Surface Properties Corrosion resistance 6

7 Thermal Oxidation of Nitinol Zhu, et al., Trepanier, et al, SMST 2003; Pelton, et al., Solid-to-Solid Transformations 2005" " 7

8 Surface Properties of Thermally Oxidized Nitinol 8

9 Surface Composition AES 70 Atomic concentration (%) Heat treatment 500 o C, 5 min Sputter Depth (A) Electropolished 9

10 Biocompatibility Surface properties Corrosion resistance 10

11 Localized Corrosion Resistance

12 Localized Corrosion Resistance

13 Localized Corrosion Acceptance criteria Predicate device Literature reference Corbett, Breakdown potential >600 mv vs SCE. E b vs E b -E r Tool to compare corrosion performance Tool to predict biocompatibility?

14 Localized Corrosion Resistance

15 Effect of Strain Strain Range up to ~10% during constrain In Vivo Strain Range Nitinol Implants ~1-2% Electropolished NiTi Thermally Oxidized NiTi Potential (mv Vs SCE) % strain 4% strain 8% strain 10% strain Current Density (10 x A/cm 2 ) Trepanier, et al., SMST 2003

16 Effect of Fretting on Localized Corrosion Breakdown Potential Pre- and Post- Fatigue Testing 316L stent post-fatigue & corrosion Breakdown Potential (mv vs SCE) Baseline Stainless Post-Fatigue SS Baseline NiTi Post-Fatigue NiTi NiTi stent post-fatigue & corrosion

17 Localized Corrosion

18 Uniform Corrosion Resistance

19 Effect of Surface Treatment on Uniform Corrosion 2 Months Immersion Study 37 C Hank s Solution, ph=7.4 Trepanier, et al., SFB

20 Acceptance Criteria Nickel Leaching Predicate device Literature reference US Pharmacopeia (USP) Permissible Daily Exposure (PDE) of 0.5 µg/kg/day. ~ 35µg/day (70kg person) Assumes daily excretion of Ni What about Localized effects? Effects of exposure route and type of nickel compound?

21 Effect of Fretting on Ion Release Nickel Ion Release Passivated and Non-Passivated Braided Nitinol device 1M and 10M cycles Fatigue Test 3000 Nickel ion Release (ppb) Passivated Non-passivated Fatigue Test Cycles (M) NDC Proprietary and Confidential 21

22 Biocompatibility Surface properties Corrosion resistance 22

23 Effect of Nitinol Oxide Layer Composition on Corrosion Resistance and Biocompatibility Stacey J. Sullivan, Maureen L. Dreher, Jiwen Zheng, Lynn Chen and Srinidhi Nagaraja 1 Daniel Madamba, Katie Miyashiro, Christine Trépanier 2 1 Food and Drug Administration, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Silver Spring, Maryland USA 2 Nitinol Devices & Components, Fremont, CA, USA

24 Goals & Materials Assess impact of oxide layer composition on: Localized corrosion resistance Uniform corrosion resistance Biocompatibility Group Target E b (vs SCE) Comments 1 >600 mv Complex Thermal oxide 2 >600 mv Passivated oxide mv Mechanical polish 4 <300 mv Posi>ve E b 5 <300 mv Nega>ve E b

25 Method q Identify processes to achieve target E b q Characterize Surface Properties via AES q Quantify Localized Corrosion Resistance ASTM F2129 q Quantify Uniform Corrosion Resistance, Nickel leaching 60 day study (1,2,3,5,7,14,21,30,45,60 days) q Animal study in progress Minipig implantation: left and right iliac arteries (24 animals implanted) Single and overlapped stent conditions (n=6/group) 6 month implantation period Periodic serum & urine nickel analysis Explanted stent (SEM) and artery (histopathology) analysis

26 Stent Processing Materials: Laser cut generic stents (ground and oxidized tubing) Group OT AF SP MP EP Tubing Oxidized Ground Removal of HAZ N/A Chemical Polishing Stress Relief 505 C 540 C 505 C 505 C 505 C Expansion 505 C 505 C 505 C 505 C 505 C A f Tuning 505 C 550 C 505 C 505 C 505 C Finishing Ultrasonic clean Ultrasonic clean Ultrasonic clean Etch Burnish Etch EP 26

27 Surface Topography Oxidized Tubing (OT) Salt Pot (SP) Air Furnace (AF) Thank You Mechanical Polish (MP) Electropolish (EP)

28 Oxide Layer Composition OT > 3500 nm AF ~130nm Thank You EP ~4nm SP ~420 nm MP ~4nm

29 Localized Corrosion Resistance Group OT AF SP MP EP Thank You E r (mv vs SCE) / / / / /- 62 E b (mv vs SCE) / /- 73 NB 832 +/- 256 NB

30 Correlation between Oxide Layer Thickness and Er 0 Oxide Layer Thickness (nm) Rest PotenNal (mv vs SCE) y = ln(x) R² =

31 Nickel Release As manufactured OT-NC SP-NC AF-NC MP-NC EP-NC Thank You 16,000 Cumulative Ni Release (ng) 14,000 12,000 10,000 8,000 6,000 4,000 2, Day

32 Nickel Release Post-Crimp OT-C SP-C AF-C MP-C EP-C Thank You 80,000 Cumulative Ni Release (ng) 70,000 60,000 50,000 40,000 30,000 20,000 10, Day

33 Correlation Oxide Layer Thickness and Nickel Release CumulaNve Nickel Release (ng) 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 Crimped Not Crimped y = 22.5x R² = y = 4.0x R² = Thank You Oxide Layer Thickness (nm)

34 Summary Surface Properties Formation of complex oxide layer during HT Thank You Ti oxide and Nickel-rich phases Localized & Uniform Corrosion Resistance Effect of outer surface layer Impact of deformation and fretting on corrosion resistance Acceptance criteria? Biocompatibility