In recent years, patterned ultra-hydrophilic thin films have received attention because of their potential as bio-compatible surfaces for implants. However, mechanical properties of the studied surfaces are not sufficiently robust for the majority of applications. Via an ion-beam assisted deposition process, we have fabricated nanostructurally stabilized, pure cubic zirconia thin films possessing properties of hardness (16 GPa) and wettability, which are expected to benefit tribology and wear reduction. These transparent, zirconia coatings are maximally wettable by water and bovine calf serum, which is explained by the Wenzel model based on the nanotextured surface and surface energy.

The effect of aging on hydrophilic properties of cubic zirconia was determined by water contact angle (CA) measurements on samples stored in a laboratory environment from February of 2005 until now. Measurements for samples without any cleaning showed CA of around 90°, indicating surface adsorption of moisture, organic contaminants, and/or gases over time. A cleaning procedure consisting of sonication in organic solvents followed by calcination at temperatures ranging from 300°C to 600°C was found to effectively burn off residual organic contaminants, yielding CA about 10° to 20°. X-ray diffractometry and atomic force microscopy analysis of these samples revealed that the cleaning procedure induced no apparent changes in the crystal structure and nanotextured surface.

We conclude that the observed loss of ultra-hydrophilic properties was due to organic contaminants. Our results reveal a cleaning method for the long-term maintenance of the wettability of zirconia, making it a viable material for applications involving hard, hydrophilic surfaces, such as biomedical implants.