Superelastic Thin Film NiTi-Polymer-Composites and Sputtered Thin-walled Tubes

Abstract

Superelastic shape memory materials are of special interest in medical applications due to the large obtainable strains, the constant stress level and their biocompatibility. Superelastic NiTi- polymer-composites have the potential to be used for novel applications in orthodontics and medical instrumentation as well as in certain areas of mechanical engineering. Especially, using NiTi thin films these composites have the potential to substantially reduce those forces compared to conventional NiTi wires and tubes. In orthodontic applications lowering the forces during archwire treatment is of special importance due to tooth root resorption, which can be caused by the application of oversized forces. Furthermore, the use of superelastic materials or composites enables the application of constant forces independent of diminutive tooth movements during the therapy due to the superelastic plateau. Superelastic NiTi thin films have been fabricated by magnetron sputtering using extremely pure cast melted targets. Special heat treatments were performed for the adjustment of the superelastic properties and the transformation temperatures. A superelastic strain exceeding 4% at 36°C was obtained. In this paper the fabrication of superelastic NiTi thin walled tubes by magnetron sputtering is presented and their mechanical properties are compared to conventional wires and tubes in view of orthodontic applications.