Double roughness structure, the origin of the lotus effect of natural lotus leaf, was successfully reproduced on a diarylethene microcrystalline surface. Static superwater-repellency and dynamic water-drop-bouncing were observed on the surface, in the manner of natural lotus leaves. Double roughness structure was essential for water-drop-bouncing. This ability was not observed on a single roughness microcrystalline surface showing the lotus effect of the same diarylethene derivative. The double roughness structure was reversibly controlled by alternating irradiation with UV and visible light.

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Apatite-coated silicon wafers are expected to be utilized for novel biosensors or implants. However, the mechanism and optimum conditions for the formation of an apatite layer on silicon wafer surfaces are unclear. Herein, we examined the effect of pretreating silicon wafers with titanium sputtering and weak alkali aqueous solutions before immersing them in a simulated body fluid (SBF). A week after immersion, silicon wafer surfaces coated with thin titanium layers were covered by hemispherical apatite particles that were produced in a heterogeneous nucleation reaction, whereas untreated silicon wafer surfaces were covered by spherical particles that were produced in a homogeneous reaction. Pretreatment of titanium-coated silicon wafers with 0.1 M NaOH aqueous solution assured heterogeneous apatite formation. Both titanium-coated and untreated silicon wafers were fully covered by the apatite layer after soaking in the SBF for 23 weeks. These findings show that pretreatment of silicon wafers with titanium sputtering and weak alkali aqueous solution is effective for obtaining apatite-coated silicon wafers.

We prepared an apatite/polymer composite material with a fractal surface by transferring the hierarchical rough surface of a plaster replica onto calcium phosphate paste and immersing the paste in a buffer. The rough structure (fractal dimension: 2.3) accelerated the spreading and penetration of a water droplet placed on the surface. This material can be applied in dental implants and texture testers.