Togo Shinonaga

Periodic nanostructures on titanium dioxide film produced using femtosecond laser with wavelengths of 388 nm and 775 nm.

Titanium dioxide (TiO2) film is an important biomaterial used to improve the biocompatibility of titanium (Ti). We have used a film coating method with an aerosol beam and femtosecond laser irradiation to form periodic structures on biomaterials for control of the cell spreading. The control of cell spreading on biomaterials is important for the development of advanced biomaterials. In this study, nanostructures with periods of 130 and 230 nm were formed on a film using a femtosecond laser with wavelengths of 388 and 775 nm, respectively. The nanostructure period on the film was 30% of the laser wavelengths. Periods produced with wavelengths of 388 and 775 nm were calculated using a surface plasmon polariton (SPP) model and the experimental results for both wavelengths were in the range of the calculated periods, which suggests that the mechanism for the formation of the periodic nanostructures on the film with a femtosecond laser was due to the excitation of SPPs.

Hierarchical periodic micro/nano-structures on nitinol and their influence on oriented endothelialization and anti-thrombosis

The applications of hierarchical micro/nano-structures, which possess properties of two-scale roughness, have been studied in various fields. In this study, hierarchical periodic micro/nano-structures were fabricated on nitinol, an equiatomic Ni-Ti alloy, using a femtosecond laser for the surface modification of intravascular stents. By controlling the laser fluence, two types of surfaces were developed: periodic nano- and micro/nano-structures. Evaluation of water contact angles indicated that the nano-surface was hydrophilic and the micro/nano-surface was hydrophobic. Endothelial cells aligned along the nano-structures on both surfaces, whereas platelets failed to adhere to the micro/nano-surface. Decorrelation between the responses of the two cell types and the results of water contact angle analysis were a result of the pinning effect. This is the first study to show the applicability of hierarchical periodic micro/nano-structures for surface modification of nitinol.

Variation of cell spreading on TiO2 film modified by 775 nm and 388 nm femtosecond laser irradiation

Titanium (Ti) is one of the most used biomaterials in metals. However, Ti is typically artificial materials. Thus, it is necessary for improving the biocompatibility of Ti. Recently, coating of the titanium dioxides (TiO2) film on Ti plate has been proposed to improve biocompatibility of Ti. We have developed coating method of the film on Ti plate with an aerosol beam. Periodic structures formation on biomaterials was also a useful method for improving the biocompatibility. Direction of cell spreading might be controlled along the grooves of periodic microstructures. In our previous study, periodic nanostructures were formed on the film by femtosecond laser irradiation at fundamental wave (775 nm). Period of the periodic nanostructures was about 230 nm. In cell test, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. Then, influence of the period of the periodic nanostructures on cell spreading has not been investigated yet. The period might be changed by changing the laser wavelength. In this study, the periodic nanostructures were created on the film with femtosecond laser at 775nm and 388 nm, respectively. After cell test, cell spreading along the grooves of the periodic nanostructures was observed on 775 nm and 388nm laser irradiated areas. Distribution of direction of cell spreading on laser irradiated area was also examined. These results suggested that controlling the cell spreading on periodic nanostructures with period of 230 nm was better than that with period of 130 nm.

Biocompatibility of titanium dioxide film modified by femtosecond laser irradiation

Titanium (Ti) is one of the most widely used for biomaterials, because of its excellent anti-corrosion and high mechanical properties. In addion to these properies, the bioactivity of Ti is required. Recently, coating of the titanium dioxide (TiO2) film on Ti plate surface is useful methods to obtain biocompatibility of Ti plate. If periodic nanostructures were formed on the film surface, direction of cell spreading might be controlled due to grooves direction. Then, femtosecond laser is one of the useful tools of periodic nanostructures formation. Peiriod of periodic nanostructures might be varied by changing the laser wavelength. In the experiments, the film was formed on Ti plate with an aerosol beam which was composed of submicron size TiO2 particles and helium gas. The film was irradiated with the femtosecond laser. Laser wavelengths of the laser was at 1044, 775 and 388 nm, respectively. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film by femtosecond laser irradiation at 1044, 775 and 388 nm, respectively. The period of the periodic nanostructures on the film produced by femtosecond laser irradiation at 1044, 775 and 388 nm was about 350, 230 and 130 nm, respectively. In the cell test, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. These results suggested that direction of cell spreading could be controlled by the periodic nanostructures formation

Femtosecond laser induced periodic nanostructures on titanium dioxide film for improving biocompatibility

Periodic nanostructures formation on Titanium dioxide (TiO2) film by scanning of femtosecond laser beam spot at fundamental and second harmonic wave is reported. Titanium (Ti) is one of the most widely used for biomaterials, because of its excellent anti-corrosion and high mechanical properties. However, Ti implant is typically artificial materials and has no biofunction. Hence, it is necessary for improving the bioactivity of Ti. Recently, coating of TiO2 film on Ti plate surface is useful methods to improve biocompatibility of Ti plate. Then, if periodic nanostructures were formed on the film surface, cell spreading might be controlled at one direction. We propose periodic nanostructures formation on TiO2 film by femtosecond laser irradiation. Cell spread could be controlled along the grooves of periodic nanostructures. In the experiments, the film was formed on Ti plate with an aerosol beam. A commercial femtosecond Ti : sapphire laser system was employed in our experiments. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film at fundamental and second harmonic wave. Periodic nanostructures were also produced on Ti plate with femtosecond laser. The period of periodic nanostructures on the film was much shorter than that on Ti plate. By cell test, there was a region of cell spreading along the grooves of periodic nanostructures on the film formed with femtosecond laser at fundamental wave. On bare film surface, cell spreading was observed at all direction. These results suggest that direction of cell spread could be controlled by periodic nanostructures formation on the film.

Study on clarification of large-Area eb irradiation phenomenon by electron track analysis

In large-area electron beam (EB) irradiation method, uniformly high energy density can be obtained without focusing the beam. Large-area EB can be used for melting and evaporating metal surface instantly. It was clarified that high efficient surface finishing of metal mold steels, ceramics and cemented carbides was possible by the large-area EB irradiation. Furthermore, the tip of convex shape was often rounded after large-area EB irradiation with remarkable material removal at the tip. This phenomenon is probably caused due to the heat accumulation and electrons concentration at the tip. However, electrons behavior near the workpiece surface during large-area EB irradiation has not yet been clarified. In this study, electron track analysis was conducted in order to clarify electrons behavior during large-area EB irradiation. At first, analytical model of the large-area EB irradiation apparatus was built. Then, the EB diameter on the workpiece surface was experimentally measured with different energy density in order to evaluate the accuracy of our analytical model. The calculated results of EB diameter were in good agreement with the experimental ones. In addition, the electrons concentration phenomenon at the tip of convex shape was clarified by calculating energy density distribution on the surface obtained with electron track analysis. The analytical results indicated that the energy density increased from edge to tip of convex shape, while the energy density was constant in the case of planar shape. Experimented results also showed that removal thickness increases with high relative permeability. These results were similar tendency to the energy density distribution. Therefore, electrons concentration on the tip could be simulated by the electron track analysis.

Effect of focusing condition on micro-welding characteristic of glass by ps pulsed laser

An ultra-short pulse laser can make it possible to absorb laser energy at the focusing point inside a glass by non-linear absorption, and micro-welding of glass can be expected without an intermediate layer and adhesive. However molten area is greatly affected by its focusing condition, because one part of this process is related to non-liner phenomena, which can be generated at high-energy intensity condition. Therefore, in this study, effect of focusing condition on micro-welding of borosilicate glass (D263) were experimentally investigated using an ultra-shot pulsed laser of 12.5ps. Molten area was observed by a highspeed video camera, and breaking stress of the weld glasses was evaluated. Tear’s shape of molten area was created by the periodic movement of absorption point up and down in coaxial direction of laser beam. A usage of optical system with the spherical aberration correction made it possible to create a large volume weld joint even at the same pulse energy, because absorption rate of laser energy increased. Small pulse interval led to increasing the absorption rate, which could create a large molten area stably. An optical system with the spherical aberration correction led to stabilizing the shape of molten area, which resulted in the reliable joint.An ultra-short pulse laser can make it possible to absorb laser energy at the focusing point inside a glass by non-linear absorption, and micro-welding of glass can be expected without an intermediate layer and adhesive. However molten area is greatly affected by its focusing condition, because one part of this process is related to non-liner phenomena, which can be generated at high-energy intensity condition. Therefore, in this study, effect of focusing condition on micro-welding of borosilicate glass (D263) were experimentally investigated using an ultra-shot pulsed laser of 12.5ps. Molten area was observed by a highspeed video camera, and breaking stress of the weld glasses was evaluated. Tear’s shape of molten area was created by the periodic movement of absorption point up and down in coaxial direction of laser beam. A usage of optical system with the spherical aberration correction made it possible to create a large volume weld joint even at the same pulse energy, because absorption rate of laser e...

Femtosecond laser induced periodic nanostructures and microstructures on ti plate for control of cell spreading

Periodic nanostructures and microstructures formation on Ti plate by scanning of femtosecond laser beam spot is reported. Femtosecond lasers are useful tools for creating periodic structures with the period in the range from nanoscale to microscale on metals. The periodic nanostructures and microstructures were formed on the Ti plate by femtosecond laser irradiation for scanning speed of 0.5 mm/s at laser fluence of 0.35 J/cm2. The periods of periodic nanostructures and microstructures on the Ti plate were about 600 nm and 10µm, respectively. The results in cell test suggest that cell was spread along the direction of the periodic nanostructures’ grooves.Periodic nanostructures and microstructures formation on Ti plate by scanning of femtosecond laser beam spot is reported. Femtosecond lasers are useful tools for creating periodic structures with the period in the range from nanoscale to microscale on metals. The periodic nanostructures and microstructures were formed on the Ti plate by femtosecond laser irradiation for scanning speed of 0.5 mm/s at laser fluence of 0.35 J/cm2. The periods of periodic nanostructures and microstructures on the Ti plate were about 600 nm and 10µm, respectively. The results in cell test suggest that cell was spread along the direction of the periodic nanostructures’ grooves.

Periodic nanostructure formation on pet with femtosecond laser for control of cell elongation

Laser irradiation is carried out to form periodic nanostructures on the plastic surface. For example, polyethylene terephthalate (PET) was used in this study. Periodic nanostructures formation on PET is formed with excimer laser, because PET scarcely absorbs the light in the visible and infrared ray wavelength range. However, periodic nanostructures formation on PET is able to form with visible or infrared laser by combining PET with Si. For laser fluence, 60 mJ/cm2 and scanning speed, 20 mm/s, period and depth of the periodic nanostructures produced by the new method were about 650 nm and 80 nm, respectively. Cell test was conducted to examine cell spreading on treated and untreated PET. By cell test, cells were attached to periodic nanostructures of PET. Cells elongations were caused parallel to the grooves of the periodic nanostructures.Laser irradiation is carried out to form periodic nanostructures on the plastic surface. For example, polyethylene terephthalate (PET) was used in this study. Periodic nanostructures formation on PET is formed with excimer laser, because PET scarcely absorbs the light in the visible and infrared ray wavelength range. However, periodic nanostructures formation on PET is able to form with visible or infrared laser by combining PET with Si. For laser fluence, 60 mJ/cm2 and scanning speed, 20 mm/s, period and depth of the periodic nanostructures produced by the new method were about 650 nm and 80 nm, respectively. Cell test was conducted to examine cell spreading on treated and untreated PET. By cell test, cells were attached to periodic nanostructures of PET. Cells elongations were caused parallel to the grooves of the periodic nanostructures.

Development of visible-light activated titanium dioxide films with femtosecond laser

Titanium dioxide (TiO2) has a variety of functions, but cannot be activated by visible-light illumination. It is importance to extend the activity of TiO2 into the visible-light, which comprises the larger portion of the room light. Therefore, the visible-light activated TiO2 is required. We developed it with the femtosecond laser irradiation. The TiO2 films irradiated with femtosecond laser were darkened without changing topography of the TiO2 film surface. In the visible-light photocataltic function measurements, the TiO2 films were evaluated with the acetaldehyde decomposition test. The concentration of acetaldehyde was decreased to over time. This result indicated that visible-light activated photocatalyst function of TiO2 films were generated by femtosecond laser irradiation.