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 mu m; 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. (C) 2012 Elsevier B.V. All rights reserved.