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Titanium (Ti) is widely used as biomaterial, for example artificial bone, joint etcetera. Femtosecond laser can be used to form periodic nanostructures on Ti surface, and the structures help to control cell elongation. The period of the periodic nanostructures on Ti under atmospheric condition is about 70 to 80% compared with the laser wavelength. However, the mechanism of periodic nanostructure formation by femtosecond laser irradiation has not been clarified yet. Thus, we focused on Surface Plasmon Polariton (SPP) model, which was proposed as a model for formation of periodic nanostructures by femtosecond laser irradiation. In this model, standing waves are generated on the material surface caused by excited electrons on the material surface by laser irradiation. The wavelength of the standing waves depends on the permittivity of the surrounding medium, and the period of the periodic nanostructures also depends on the wavelength of the standing waves. Therefore, it is considered that the period of the nanostructures varies by changing the permittivity at the laser irradiation interface2,3).In this study, a polyethylene terephthalate (PET) films which has permittivity of 3.0, and a polymethyl methacrylate (PMMA) films which has permittivity of 3.4 were contacted on Ti surface by using contact jig and then the femtosecond laser at a wavelength of 800 nm was irradiated to create periodic nanostructures. As a result, periodic nanostructures with a period of 440 nm was formed on Ti under PET adhesion condition, and periodic nanostructures with a period of 380 nm was formed on Ti under PMMA adhesion condition. On the other hand, periodic nanostructures with a period of 600 nm was formed on Ti under atmospheric condition. It was found that the period of periodic nanostructures can be controlled by changing the permittivity of the medium adhered to Ti.
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