Hitoshi Ishizawa

Histomorphometric evaluation of the thin hydroxyapatite layer formed through anodization followed by hydrothermal treatment

By the previously described method of electrochemical and hydrothermal reaction, a thin hydroxyapatite (HA) layer of 1 microm thickness was formed on machined, grit-blasted, and titanium plasma-sprayed implants, the surfaces of which were equipped with a gap zone of 0.15 mm in depth. These implants, together with HA and titanium plasma-sprayed implants as control materials, were placed in dog mandibles for 4 weeks. Histomorphometrical comparison was performed to examine the effects of the thin HA layer and the surface topography on bone formation. The roughened implants, especially the grit-blasted implants, were surrounded with thin bone newly formed along the rough surfaces and showed higher bone apposition than the smooth implants. The gap zone of the HA plasma-sprayed implant was repaired with new bone that had vertically extended from the surrounding bone. The thin HA layer had as much osteoconduction as a plasma-sprayed HA coating but showed significantly different bone response. The results suggest that bone formation on an HA film is affected by degradation in living tissue that is related to the crystallinity and the chemical composition of the HA film itself.

Preparation of high-performance optical coatings with fluoride nanoparticle films made from autoclaved sols.

An ultralow refractive index is very advantageous when one designs antireflective coatings. We successfully obtained high-quality MgF2 thin films with ultralow refractive indices from autoclaved sols prepared from magnesium acetate and hydrofluoric acid. The MgF2 films consist of nanosized particles, and they have high laser-exposure durability at 193 nm. The reflectance of the antireflective coating with five layers, of which the top layer is formed by our method, is lower than 0.6% in the incident angle range of 0 degrees - 60 degrees at 193 nm.

The effect on immunocytes of anodic oxide titanium after hydrothermal treatment.

All dental root implants come in contact with the oral epithelium, and many complex factors are found to arise in this region. In order to perform a successful dental root implantation, it is necessary to clarify the interaction of the dental root implant material with the host defense mechanisms involved in the specific and nonspecific immune responses to many antigens in oral bacteria and their components. Recently, focusing on developing the dental root implant, the Nikon Corporation improved the surface characteristics of pure titanium even further by developing a hydroxyapatite (HA) layer formed on an anodic titanium oxide film containing Ca and P via hydrothermal treatment (SA treatment). However, since little is known about the effect of SA-treated pure titanium (HA/Ti) on the defense mechanisms of the oral membrane epithelium, we investigated (1) the in vitro proliferation of murine splenic B lymphocytes on the surface of HA/Ti in the presence of three lipopolysaccharide (LPS) concentrations and (2) interleukin-1alpha (IL-1alpha) production by the reaction of human peripheral blood mononuclear cells (PBM cells) on the surface of HA/Ti under the same concentrations. After culture, murine splenic lymphocytes were measured by uptake of 3H-thymidine, and cytokine release (IL-1alpha) from PBM cells was measured by ELISA. Results showed that HA/Ti had hardly any effect on the LPS-induced proliferation of B lymphocytes and IL-1alpha production. In vitro investigations of the effects of HA/Ti on the LPS-induced proliferation of murine splenic B lymphocytes and IL-1alpha from PBM cells might be a useful way of elucidating the defense mechanism between implants and the oral epithelium.

Investigation of MgF2 optical thin films with ultralow refractive indices prepared from autoclaved sols.

We have successfully developed a process to form high quality MgF(2) thin films with ultralow refractive indices from autoclaved sols prepared from magnesium acetate and hydrofluoric acid. And we have confirmed that our porous MgF(2) coatings have not only high transmittance in the UV region but also high uniformity of film thickness. They can be uniformly formed on phiv 300 mm substrates as a single coating and as a hybrid coating with sublayers formed by physical vapor deposition. They are expected to be applied to various optics that need high transmittance in the UV region.

Preparation of MgF2-SiO2 thin films with a low refractive index by a solgel process.

Porous MgF(2)-SiO(2) thin films consisting of MgF(2) particles connected by an amorphous SiO(2) binder are prepared by a solgel process. The films have a low refractive index of 1.26, sufficient strength to withstand wiping by a cloth, and a high environmental resistance. The refractive index of the film can be controlled by changing the processing conditions. Films can be uniformly formed on curved substrates and at relatively low temperatures, such as 100 degrees C. The low refractive index of the film, which cannot be achieved by conventional dry processes, is effective in improving the performance of antireflective coatings.

High-performance antireflective coatings with a porous nanoparticle layer for visible wavelengths

Ghosts and flares are well-known problems that are caused by reflections from lens surfaces when we take photographs. It is more difficult to prevent such stray light in a digital camera than in a film camera because of high reflectance from the low-pass filter and diffraction from the image sensor. To prevent such stray light, we introduce an ultralow refractive index layer into the antireflective (AR) coatings. We used the solgel method to form porous fluoride layers with ultralow refractive indices, and we succeeded in developing a unique process to form AR coatings with superior performance.

Yb 3+ -doped CaF 2 -LaF 3 ceramics laser

Highly transparent ceramic is an attractive gain medium for high-power lasers due to its high fracture toughness, homogeneity, and size scalability. Here we report the first Yb³⁺-doped CaF₂-LaF₃ ceramics laser. Codoping of La³⁺ ion can reduce the formation of Yb²⁺ ions and enhance the laser efficiency. In the laser experiment, the maximum output power of 4.36 W and the maximum slope efficiency of 69.5% were obtained with a 3% La, 2% Yb sample and a 2% La, 1% Yb sample, respectively. Due to the combined properties of Yb:CaF₂ and a ceramic laser gain medium, Yb:CaF₂-LaF₃ ceramic is a promising gain medium for a high-power ultrashort pulse laser and amplifier.

Highly efficient Yb 3+ -doped CaF 2 -LaF 3 ceramic laser

We prepared transparent Yb:CaF<inf>2</inf>-LaF<inf>3</inf> ceramics with different combinations of doping concentrations of Yb³⁺ and La³⁺ and obtained CW laser operation with maximum output of 3.97 W. The maximum slope efficiency was as high as 73.1%.

New Antireflective Coatings with Porous Nanoparticle Layers for Visible Wavelengths

Recently, required performance levels of antireflective coatings are becoming higher in technical fields of camera lens. We succeeded in forming antireflective coatings with ultra-low refractive index layers and achieving superior performances by sol-gel method.