Surface Quality of Incoming Nitinol Wire Used to Manufacture Braided Implants. Carolyn Lahti, R&D Materials Engineer

Transcription

1 Surface Quality of Incoming Nitinol Wire Used to Manufacture Braided Implants Carolyn Lahti, R&D Materials Engineer 1

2 Carolyn Lahti, R&D Metallurgical Engineer at Boston Scientific Materials Testing, Analysis, and Characterization (MTAC) B.S. in Materials Science and Engineering Michigan Technological University MTAC In-house service lab Analyze a wide variety of products Interventional Cardiology Peripheral Interventions 2

3 Nitinol Manufacturing Process Supplier surface finishing techniques: Mechanical finish Diamond draw (shiny polish) Sandblast (matte surface) Chemical finish Etch/pickle Electropolish (EP) Oxide surface Coating Plating Sent to customer Surface finishing: chemical etch, EP, passivation, coating The Methods of Preparation of Ti-Ni-X Alloys and Their Forming Radim Kocich, Ivo Szurman and Miroslav Kursa ( 3

4 Importance of Surface Quality Surface quality influences performance From Noll and Lipson, "Allowable Working Stresses", Society for Experimental Stress Analysis, Vol. III, no. 2, 1949 Compromising factors id=49609&taxid=1418! 4

5 Goal of Study Analyze the surface quality of incoming wire and EP material of nitinol wire Characterize and optimize EP 5

6 Surface Roughness Measurements Mechanical_filtering_of_surface_finish_trace.svg Ra: arithmetic average of absolute surface roughness values Rp: maximum peak height Rv: maximum valley depth Rz: average distance between the highest peak and lowest valley in each sampling length Ra Rp Rz Rv 6

7 Experimental Setup Mechanical micron wire 25 micron material removal (radial) Chemical Etch micron material removal (radial) Proprietary 5 High purity nitinol wire Supplier A Supplier B Supplier C Nitinol wire 7

8 SEM Images Incoming Material Mechanical Chemical Etch 356 micron wire 25 micron material removal (radial) 50 micron material removal (radial) Proprietary Supplier A Supplier B Supplier C 8

9 Surface Roughness Incoming Material Material Incoming Surface Condi4on Observa4ons Peak Rp (Rp) (μm) Valley Rv (Rp) (μm) Range Rz (Rz) (μm) Mean Ra (Ra) (μm) 1 Mechanically polished Heavy surface scratching Mechanically polished Mostly smooth Chemically etched Smooth with small draw lines Chemically etched Smooth with small defects Proprietary finish Smooth with small draw lines

10 SEM Images 25 µm Material Removal Mechanical Chemical Etch 356 micron wire 25 micron material removal (radial) 50 micron material removal (radial) Proprietary Supplier A Supplier B Supplier C 10

11 Surface Roughness 25 µm Material Removal Material Incoming Surface Condi4on Incoming Material Observa4ons Peak Rp (Rp) (μm) Valley Rv (Rp) (μm) Range Rz (Rz) (μm) Mean Ra (Ra) (μm) 1 Mechanically polished Heavy surface scratching 2 Mechanically polished Mostly smooth Chemically etched Smooth with small draw lines Chemically etched Smooth with small defects Proprietary finish Smooth with small draw lines

12 SEM Images 50 µm Material Removal Mechanical Chemical Etch 356 micron wire 25 micron material removal (radial) 50 micron material removal (radial) Proprietary Supplier A Supplier B Supplier C 12

13 Surface Roughness 50 µm Material Removal Material Incoming Surface Condi4on Incoming Material Observa4ons Peak Rp (Rp) (μm) Valley Rv (Rp) (μm) Range Rz (Rz) (μm) Mean Ra (Ra) (μm) 1 Mechanically polished Heavy surface scratching Mechanically polished Mostly smooth Chemically etched Smooth with small draw lines Chemically etched Smooth with small defects Proprietary finish Smooth with small draw lines

14 Max Peak to Valley Distance 14

15 Mean Surface Roughness 15

16 Summary Quantification of surface finish variation throughout a collection of suppliers was assessed via SEM and roughness measurements Large variation in incoming surface quality observed across the different suppliers and incoming surface finishes The same electropolishing process works for a broad range of nitinol materials and results in a smoother surface Overall, incoming condition was less critical to the final EP condition However, incoming condition may be important to processing wire prior to EP (i.e. winding wire over fixtures) Smoother surfaces from suppliers may allow for a reduction in material removed during EP 16