Shape-memory NiTi with two-dimensional networks of micro-channels.
A process was developed for fabricating arrays of micro-channels in shape-memory NiTi for bone implant applications, with a tailorable internal architecture expected to improve biomechanical compatibility and osseointegration. Ni-51.4 at.% Ti with 24-34 vol.% porosity was fabricated by electrochemical dissolution of parallel layers of steel wire meshes embedded within a NiTi matrix during hot pressing of NiTi powders. The resulting NiTi structures exhibit parallel layers of orthogonally interconnected micro-channels with 350-400 μm diameters that exactly replicate the steel meshes. When low-carbon steel wires are used, iron diffuses into the surrounding NiTi during the densification step, creating a Fe-enriched zone near the wires. For high-carbon steel wires, TiC forms at the steel/NiTi interface and inhibits iron diffusion but also depletes some titanium from the adjacent NiTi. In both cases, the NiTi regions near the micro-channels exhibit altered phase transformation characteristics. These NiTi structures with replicated networks of micro-channels have excellent potential as bone implants and scaffolds given: (i) the versatility in channel size, shape, fraction and spatial arrangement; (ii) their low stiffness (15-26 GPa), close to 12-17 GPa for cortical bone; (iii) their high compressive strength (420-600 MPa at 8-9% strain); and (iv) their excellent compressive strain recovery (91-94% of an applied strain of 6%) by a combination of elasticity, superelasticity and the shape-memory effect.
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
Anselm J
AJ
Neurohr
David C
DC
Dunand
D002152:Calorimetry, Differential Scanning; D002244:Carbon; D019245:Compressive Strength; D004548:Elasticity; D044085:Microfluidics / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D044367:Phase Transition; D011208:Powders; D011312:Pressure; D014025:Titanium / Q000737:chemistry*
D011208:Powders; C040654:titanium nickelide; D002244:Carbon; D009532:Nickel; D014025:Titanium