The biocompatibility and mechanical properties of cylindrical NiTi thin films produced by magnetron sputtering

Superelastic nickel titanium shape memory alloys (NiTi–SMA) are of biomedical interest due to the large obtainable strains and the constant stress level. Production of NiTi–SMA thin films by magnetron sputtering was developed recently. NiTi sputtered tubes have a high potential for application as vascular implants, e.g. stents. Magnetron sputtering, three dimensional lithography and wet etching were used in order to produce Ti and NiTi stent devices (thickness: 5–15 μm; diameter: 1–5 mm). For tensile tests, specimens were prepared in radial and axial directions in order to compare the mechanical properties of the film in both directions. The specimens – produced for cell culture experiments – were incubated with human mesenchymal stem cells (hMSC) for 7 days. Cell viability was analyzed via fluorescence microscopy after live/dead staining of the cells. Cytokine release from cells was quantified via ELISA. Cylindrical NiTi films showed a strain up to 6%. Tensile parameters were identical for both directions. Best material properties were obtained for deposition and patterning in the amorphous state followed by an ex-situ crystallization using rapid thermal annealing in a high vacuum chamber. First biological tests of the Ti and NiTi–SMA samples showed promising results regarding viability and cytokine release of hMSC.