Abstract
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.
Original language | English (US) |
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Pages (from-to) | 1862-1872 |
Number of pages | 11 |
Journal | Acta Biomaterialia |
Volume | 7 |
Issue number | 4 |
DOIs | |
State | Published - Apr 2011 |
Funding
This research was supported by the National Science Foundation (NSF) through Grant DMR-0505772 and the Initiative for Sustainability and Energy at Northwestern (ISEN). A.J.N. also gratefully acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Postgraduate Scholarship. The authors thank Dr. Bing Ye (Northwestern University) for his assistance with powder densification.
Keywords
- Nickel titanium
- Nitinol
- Porous
- Shape memory
- Space-holder
ASJC Scopus subject areas
- Molecular Biology
- Biochemistry
- Biotechnology
- Biomedical Engineering
- Biomaterials