Zirconia ceramics are used extensively as dental restorative materials because of their excellent mechanical properties and biocompatibility. However, their surface functionalities, which include anti-bacterial and anti-corrosion properties, still require further improvement. Inspired by nature, superhydrophobic surfaces with micro/nanostructures and a low surface energy have received considerable attention for their outstanding self-cleaning, anti-bacterial, and anti-corrosion properties. In recent years, laser surface texturing has been demonstrated as an effective method for fabricating superhydrophobic zirconia ceramic surfaces. However, post-process treatment methods, including long-term storage in air, heat treatment, and silane reagent immersion, are either time-consuming or toxic. There is therefore a need to develop a time-efficient, low-cost, and ecological laser-based technique for fabricating superhydrophobic zirconia ceramic surfaces.

Commercially available zirconia ceramic (Y-TZP), a zirconia-toughened ceramic prepared with yttrium oxide (Y₂O₃) as the stabilizer with excellent mechanical properties and biocompatibility, was used as the experimental material. Laser surface-texturing experiments employed a laser marking machine equipped with a 355 nm UV laser source (Fig. 1). Upon laser surface texturing, the laser-textured zirconia ceramic surface immediately became superhydrophilic. To achieve the wettability transition, a mixture of 25 μL dimethyl silicone oil (volume fraction 0.4%) and isopropyl alcohol (volume fraction 99.6%) was dripped onto the surface of the laser-textured zirconia ceramic sample. The sample was then placed onto a 200 ℃ hot plate for 10 min. For surface characterizations, the surface topography and chemical composition of the laser-textured zirconia ceramic surface were first examined using confocal laser-scanning microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Then, the wettability of the laser-textured zirconia ceramic surface was evaluated using a contact-angle goniometer equipped with a high-resolution CMOS camera. The long-term durability and self-cleaning properties of the superhydrophobic zirconia ceramic surface were characterized by tape peeling and self-cleaning experiments.

Careful experimental investigations and analysis revealed several key findings: (1) Laser surface texturing induced periodically arrayed surface micro/nanostructures on the zirconia ceramic substrates. By regulating the laser processing parameters, periodic columnar structures or microgrooves with different densities were fabricated (Fig. 2), indicating that the laser-induced surface structure can be well controlled. (2) The surface chemistry analysis show that the laser texturing process oxidized the zirconia ceramic surface while also forming a periodic surface structure. After the mixed solution of silicone oil and isopropyl alcohol dripping and heat treatment, an increase in the carbon and silicon contents was detectable. This result indicates that hydrophobic functional groups, including —CH₂—, —CH₃, and CC, as well as a silicon-based thin film should have been absorbed and deposited onto the laser-textured zirconia ceramic surface, rendering the laser-textured zirconia ceramic surface superhydrophobic after the treatment (Fig. 4). (3) The measured contact angle shows that the untreated zirconia ceramic surface was intrinsically hydrophilic (contact angle 80.4°±2.4°). Immediately upon laser texturing, the zirconia ceramic surfaces became superhydrophilic with a saturated Wenzel regime (contact angle 0°). After mixed solution of silicone oil and isopropyl alcohol dripping and heat treatment, all the laser-textured zirconia surfaces turned superhydrophobic (Fig. 5) with a contact angle of 153.8°±1.2°. (4) The wettability and adhesion of the zirconia ceramic surface can be adjusted by controlling the laser parameters (Fig. 7). For scanning speeds in the range 10-200 mm/s, micro/nanostructures with different densities can be induced by laser surface texturing. At low scanning speeds, a highly adhesive superhydrophobic surface can be prepared using the hybrid process (laser processing+silicone oil modification+heat treatment). As the scanning speed increases, the zirconia ceramic surface displays superhydrophobicity with low adhesion. (5) Long-term storage in air, tape peeling tests, and self-cleaning experiments indicate that a superhydrophobic zirconia ceramic surface prepared with 50 mm/s scanning speed and 100 μm line spacing exhibits excellent stability, durability, and self-cleaning properties (Figs. 9 and 10).

This study developed a convenient and efficient laser-based surface-texturing method to modulate and control the surface functionalities of zirconia ceramic. Laser texturing generated periodic surface structures and oxidized the zirconia ceramic surface, while the subsequent mixed solution of silicone oil and isopropyl alcohol dripping and heat treatment accelerated the absorption of hydrophobic airborne organic compounds and deposited a silicon-based thin film on the laser-textured zirconia ceramic surface. Careful experimental validation and analyses reveal that the surface structure, chemical composition, and wettability can be well controlled and regulated using this method. Furthermore, laser parameters significantly affect the wettability of zirconia ceramic surface. The laser scanning speed and line spacing must be controlled within a certain range to ensure the superhydrophobicity and adhesion of the zirconia ceramic surface. The fabricated surface also displays good self-cleaning performance, stability in air, and resilience to tape peeling. This method will provide a feasible and highly efficient solution for regulating and controlling the surface functionalities of zirconia ceramic, opening the way for more practical and important applications.