Assessment of ultrathin yttria-stabilized zirconia foils for biomedical applications

Bulk yttria-stabilized zirconia is a well-studied material with various applications, in particular for biomedical devices. Interestingly, it is now possible to obtain thin stand-alone sheets (40 µm thick) of this material. We present a preliminary study dealing with the aging of these foils to determine whether they would be suitable for implantable neurostimulator housing. Accelerated hydrothermal aging experiments were performed at 134 °C and 2 bar. Various analyses of the material were carried out, especially by atomic force microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–visible-near-infrared spectroscopy. The results show that the foils maintain their integrity during simulated long-term in vivo experiments, which indicates that they are not prone to fast degradation. The observed monoclinic transformation initiates from the surface and propagates into the bulk, leading to two distinct observable parts within the sheet. The aged and the non-aged parts are separated by a limit almost linear and parallel to the surface. We also show that the micro-strains are not altered significantly after 5 h accelerated aging, and that the optical properties are not modified despite structural modifications. Although further work is needed, we have shown that foils of yttria-stabilized zirconia resist accelerated aging and are thus a promising material for the fabrication of ultrathin implantable devices.