Ceramic Society of Japan Acta Medica Okayama 1348-6535 134 1 2026 Structure and acid resistance of fluoride-treated hydroxyapatite particles 31 37 EN Satoshi Hayakawa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Kazuki Ando Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Tomohiko Yoshioka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Topical fluoride is used in clinical dentistry to prevent dental caries. The primary reaction product formed on the tooth surface after topical fluoride application is calcium fluoride (CaF2). In this study, we investigated the effect of deposited CaF2 on the acid resistance of fluoride-treated hydroxyapatite (HAp). Commercial HAp particles were treated with two types of fluoride-containing acetic acid-sodium acetate (Ac-AcNa) buffer solutions, with and without the addition of phosphate ions. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses confirmed the formation of fluorine-substituted hydroxyapatite (F-HAp), along with a hydration layer containing calcium phosphate and CaF2. Phase composition analysis revealed that the presence of phosphate ions in the fluoride treatment solution reduced the amount of CaF2 deposited. Acid resistance evaluation and phase composition analysis indicated that the initial dissolution rate of the fluoride-treated HAp in Ac-AcNa buffer solutions decreased on surfaces densely covered with CaF2 particles. No potential conflict of interest relevant to this article was reported.

Ceramic Society of Japan Acta Medica Okayama 1348-6535 134 1 2026 Preparation of brookite-type titanium dioxide particle layer on titanium surfaces via hydrothermal treatment and evaluation of in vitro apatite-forming ability 24 30 EN Satoshi Hayakawa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yushi Nakamoto Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Seiya Kojima Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Noriyuki Nagaoka Advanced Research Center for Oral and Craniofacial Sciences, Okayama University Dental School Takuya Kataoka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Tomohiko Yoshioka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University In this study, we prepared a brookite-type titanium dioxide particle layer on the surface of titanium substrates via hydrothermal treatment in aqueous urea solutions containing sodium chloride (NaCl) and examined its in vitro apatite-forming ability. Increasing the urea concentration suppressed the formation of anatase-type titanium dioxide on the titanium substrate, forming a particle layer composed of pure brookite-type titanium dioxide. The size and packing density of brookite-type titanium dioxide particles formed on the titanium substrate increased with the NaCl concentration in a 7.0 mol·dm－3 urea solution. When titanium substrates hydrothermally treated in aqueous solutions of 7.0 mol·dm－3 urea and 2.0 mol·dm－3 NaCl were soaked in a simulated body fluid for various periods up to 7 d, the substrate surface was densely covered with hemispherical apatite particles (5.3 µm in diameter) within 3 d, indicating that the brookite-type titanium dioxide particle layer had an excellent apatite-forming ability comparable to that of the anatase-type titanium dioxide particle layer. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1613-6810 2025 Atomic-Level Insights into Thermal Carbonization of Ethynyl-Containing Boron Compounds e13537 EN Kentaro Ohkura Research Institute for Interdisciplinary Science, Okayama University Satoshi Hayakawa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Takahashi Graduate School of Environment Life Natural Science and Technology, Okayama University Ken Yamazaki Graduate School of Environment Life Natural Science and Technology, Okayama University Jun Kano Graduate School of Environment Life Natural Science and Technology, Okayama University Yuta Nishina Research Institute for Interdisciplinary Science, Okayama University This study reports the design, synthesis, and characterization of boron-doped carbon (BDC) derived from a triethynylborane-pyridine complex. Triethynylborane is stabilized by coordination with pyridine, facilitating its synthesis and handling in ambient conditions. The complex is subjected to thermal treatment at various temperatures to form BDC. Powder XRD and single-crystal XRD analyses reveal that BDC prepared at 200 °C retains an ordered structure, while higher temperatures induce alkyne structural changes without significant weight or surface area alterations. Coin cells are assembled using BDC as the anode, demonstrating unique Li-ion and Na-ion storage properties distinct from graphite. These results suggest that the BDC reflects the precursor's crystal structure, enabling novel electrochemical behavior. These findings offer insight into the development of advanced BDC materials for energy storage applications. No potential conflict of interest relevant to this article was reported.

Ceramic Society of Japan Acta Medica Okayama 1348-6535 133 9 2025 Preparation and structural characterization of nanoporous silica/magnesium(II)-whitlockite composite particles 555 561 EN Takuya Kataoka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Daiki Hirota Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Eiji Fujii Industrial Technology Center of Okayama Prefecture Tomohiko Yoshioka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satoshi Hayakawa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University The preparation of particles composed of nanoporous silica (NS) and Mg2+-whitlockite (Mg-WH) would provide valuable insights for designing particles for biomedical applications. In this study, NS and Mg-WH composite particles were successfully synthesized. The addition of chitosan during synthesis possibly promoted the crystallization of calcium phosphate phases in the composite particles. Pore size distribution analysis of the particles showed a maximum at 3.2 nm. Investigating the adsorption of methylene blue onto the particles in a phosphate buffer (pH 7.4) showed that the saturated adsorption amount of methylene blue on the particles was significantly higher than that on commercial hydroxyapatite. The composite particles provided important results for potential applications as drug carriers for bone regeneration and repair. No potential conflict of interest relevant to this article was reported.

Ceramic Society of Japan Acta Medica Okayama 1348-6535 133 1 2025 Comparative study of the effects of fluoride treatment with cyclic variations in pH on the structures of stoichiometric, calcium-deficient, and carbonated hydroxyapatites 15 24 EN Satoshi Hayakawa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yu Okada Graduate School of Natural Science and Technology, Okayama University Tomohiko Yoshioka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University The primary objective of this study was to analyze the effects of fluoride treatment with cyclic variations in pH on the structure of stoichiometric hydroxyapatite (HAp), calcium-deficient HAp (CDHAp), and carbonated HAp (CHAp) powders. The structures of HAp, CDHAp, and CHAp before and after fluoride treatment were investigated using X-ray diffraction, Fourier-transform infrared, Raman, and nuclear magnetic resonance spectroscopic analyses. The fluoride treatment with cyclic variations in pH increased the calcium deficiency in HAp and CHAp but decreased in CDHAp. During fluoride treatment, fluoridated CDHAp or fluoridated calcium-deficient CHAp was formed on the surface of the HAp samples via dissolution and crystal growth, accompanied by the selective elution of component ions and partial substitution of OH－ groups in the HAp hexagonal lattice with F－ ions. No evidence of the formation of Ca(OH)2 and OH－ groups outside the HAp crystal lattice was obtained. A new perspective on the formation of structured water at the surface termination of the OH columns (disordered region), with possible interactions with adsorbed water molecules or nonspecifically adsorbed F－ ions was provided. The top surface of the fluoridated CDHAp consisted of an amorphous fluoride-rich hydrated layer, which included calcium phosphate and CaF2. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 0928-0707 112 2 2024 Electrochemically assisted sol-gel deposition of bioactive gels for biomedical applications 419 424 EN Tomohiko Yoshioka Biomaterials Laboratory, Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Miyamoto Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satoshi Hayakawa Biomaterials Laboratory, Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University So far, the sol-gel process has been available to prepare precursor gels of bioactive glasses with various compositions. In this report, we described a novel coating method of bioactive gels on a titanium substrate where the sol-gel transition is controlled by applying external electric fields. The application of a constant current of 10 mA/cm2 in an acidic sol containing pre-hydrolyzed tetraethoxysilane, calcium nitrate, and ammonium dihydrogen phosphate led to the deposition of gels on the titanium cathodes due to the generation of OH– by water electrolysis as a catalyst of the sol-gel transition. The obtained gels, which were characterized to be amorphous and consisted of Si, Ca, and P, covered the titanium substrates as a coating. The bioactivity of the gels deposited was confirmed by soaking in a simulated body fluid (SBF) up to 7 days, suggesting that the electrochemically assisted sol-gel process is promising for providing bioactive coatings on metallic implants. No potential conflict of interest relevant to this article was reported.

Nature Acta Medica Okayama 2045-2322 10 1 2020 Three-dimensional observation and analysis of remineralization in dentinal caries lesions 4387 EN Kumiko Yoshihara Okayama University, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Department of Pathology & Experimental Medicine Noriyuki Nagaoka Okayama University Dental School, Advanced Research Center for Oral and Craniofacial Sciences Akiko Nakamura National Institute for Materials Science Toru Hara National Institute for Materials Science Satoshi Hayakawa Okayama University, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Biomaterials Laboratory Yasuhiro Yoshida Hokkaido University, Faculty of Dental Medicine, Department of Biomaterials and Bioengineering Meerbeek, Bart Van Meerbeek KU Leuven (University of Leuven), Department of Oral Health Research, BIOMAT & UZ Leuven (University Hospitals Leuven) The remineralization mechanism in dental caries lesions is not completely understood. This study reports on ultrastructural and chemical changes observed within arrested caries lesions. Carious human teeth were observed using scanning electron microscopy (SEM) and focused-ion-beam (FIB)-SEM. The crystals detected in the caries lesions were characterized by transmission electron microscopy (TEM), along with chemical element mapping using energy-dispersive spectroscopy (EDS)-STEM. FIB-SEM 3D reconstructions revealed a severely damaged dentin surface abundantly covered by bacteria. Although the dentin tubules were clogged up to a depth of 100 mu m, bacterial invasion into dentin tubules was not observed. TEM crystal analysis and EDS-STEM revealed the presence of Ca and P, as well as of Mg within the HAp crystals deposited inside the dentin tubules. It was concluded that extensive remineralization with deposition of Mg-HAp crystals had occurred in dentin tubules of caries-arrested dentin. Understanding the natural remineralization process is thought to be helpful for developing clinical biomimetic remineralization protocols. No potential conflict of interest relevant to this article was reported.

Taylor & Francis Acta Medica Okayama 2187-0764 7 1 2019 Accelerated induction of in vitro apatite formation by parallel alignment of hydrothermally oxidized titanium substrates separated by sub-millimeter gaps 90 100 EN Satoshi Hayakawa Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Keigo Okamoto Biomaterials Laboratory, Graduate School of Natural Science and Technology, Okayama University Tomohiko Yoshioka Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Although autoclaving is a common sterilization method for biomedical devices, the ability to induce deposition of apatite particles on hydrothermally treated titanium is still not fully realized. This is because the induction ability is too weak to be evaluated via in vitro apatite formation in Kokubo's simulated body fluid (SBF) by the conventional immersion method, i.e. using samples with open and smooth surface. This study reports on the surface structure of hydrothermally treated titanium and the ability to induce deposition of apatite particles on the surface of parallel confined spaces separated by sub-millimeter gaps in Kokubo's SBF. Thin-film X-ray diffraction and analyses using Fourier transform infra-red (FT-IR) spectroscopy and Raman spectroscopy revealed that a nano-crystalline anatase-type titanium oxide layer was formed on titanium substrates after hydrothermal treatment at 150 degrees C for 2 h. When growth of the titanium oxide layer was moderately suppressed, the hydrothermally treated titanium surface exhibited a characteristic interference color, silver or gold, which does not impair the esthetic appearance of the titanium-based implant. The ability to induce deposition of apatite particles on hydrothermally treated titanium was remarkably amplified by parallel alignment of substrates separated by sub-millimeter gaps. No potential conflict of interest relevant to this article was reported.

Taylor & Francis Acta Medica Okayama 2019 Comparative study of in vitro apatite-forming abilities of highly ordered rutile nanorod arrays fabricated on cpTi and Ti6Al4V alloys EN Xingzhu Liu Biomaterials Laboratory, Graduate School of Natural Science and Technology, Okayama University Tomohiko Yoshioka Biomaterials Laboratory, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satoshi Hayakawa Biomaterials Laboratory, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University The surfaces of commercially available pure titanium (cpTi) and Ti6Al4V alloy specimens were modified to form highly ordered rutile nanorod arrays by chemical treatment and subsequent aging treatment. The densities of the rutile rods were (1.04 +/- 0.06) x10(3) and (0.70 +/- 0.10) x10(3) mu m(-2) for the cpTi and Ti6Al4V alloy specimens, respectively. Both the rutile nanorod arrays on the cpTi and Ti6Al4V alloy specimens deposited apatite particles when soaked in simulated body fluid (SBF) for one day. After soaking for various other periods, scanning electron microscopy images and thin-film X-ray diffraction patterns of these specimens showed that the cpTi specimens exhibited a superior rate of apatite nucleation and favored the formation of numerous apatite particles with larger diameter. This superior apatite-forming ability of the cpTi specimens can be attributed to the dense, thick titania layers with higher rutile nanorod density on their surfaces. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 36 2 2002 Preparation of alginic acid layers on solid substrates for biomedical applications 67 72 EN Tomohiko Yoshioka Kanji Tsuru Satoshi Hayakawa Akiyoshi Osaka 10.18926/47027 Alginic acid was immobilized on γ-aminopropyltriethoxysilane-coated glass as a model substrate since an alginic acid layer was known to prevent cell adhesion. The surface was characterized with X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The coated substrates adsorbed practically no calcium phosphates on their surfaces when soaked in a simulated body fluid (SBF) of Kolrubo recipe. Since calcium ions are one of the factors for blood clotting, the present alginic acid coating is one of the candidates to improve blood compatibility of clinical materials. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 36 1 2001 Improvement of Biocompatibility of Silicone Elastomer by Surface Modification 117 121 EN Yuki Shirosaki Kanji Tsuru Satoshi Hayakawa Akiyoshi Osaka Seisuke Takashima 10.18926/47005 γ-Methacryloxypropyltrimethoxysilane (γ-MPS) was grafted to silicone due to emulsion polymerization to induce Si-OH groups, in order to provide silicone with bioactivity spontaneous deposition of apatite in body fluid and to improve cytocompatibility. Apatite deposited on the grafted silicone within 7 days of soaking in 1.5 times as concentrated as the Kokubo solution. Osteoblastic cells (MC3T3-E1) were cultured on the specimens up to 7 days. After 5 days of culture, the number of MC3T3-E1 cells on the grafted specimen was much greater than that on the original specimen. These results indicated that the biocompatibility of silicone elastomer was improved by the grafting γ-MPS. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Apatite Formation on Electrochemically Treated Titanium 79 84 EN Akiyoshi Osaka Satoshi Hayakawa Kanji Tsuru 10.18926/19677 A titanium oxide gel was electrochemically prepared on Ti with a cell consisting of Ti as the working electrode, Pt as the counter one, AgCl as the reference one, and an aqueous solution of 0.1 mol/L Ca(NO(3))(2) as the electrolyte solution. The Ti electrode was kept at 9.5V for 1 hr for oxidation and subsequently kept at-3.0V for 10 min (Ca9.5-3.0):calcium ions were expected to be adsorbed at the latter treatment. Other Ti specimen was kept at -3.0V for 10 min (Ca-3.0). Both specimens were found so bioactive as to deposit apatite in 12 hr (Ca9.5-3.0) and in 1 day (Ca-3.0) when soaked in a simulated body fluid (Kokubo solution). Calcium carbonate detected on the surface of Ca9.5-3.0 caused no harmful effects on spontaneous deposition of apatite in the fluid. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 31 2 1997 Bioactive Calcium Borosilicate Glasses for Enameling Titanium 45 51 EN Akiyoshi Osaka Satoshi Hayakawa Chikara Ohtsuki 10.18926/19596 The thermal expansion coefficient of some bioactive glasses in the system CaO-SiO(2)-B(2)O(3) were adjusted to be similar to that of titanium by controlling the composition. A glass of composition 45CaO･30SiO(2)･25B(2)O(3) was selected among those as the enameling glass. A slurry was prepared by mixing the glass powder and ethanal to be developed on titanium and heated at 740℃ for 30 min. Thus treated specimen was soaked in a simulated body fluid (Kokubo solutiion). FT-IR reflection and thin film X-ray diffraction analyses indicated apatite formation on the glass coating layer within 12 h of soaking in the fluid. Thus titanium could be provided with bioactivity due to the enameling. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 31 2 1997 Bioactivity of Nb(V) and Ta(V)-Doped Calcium Silicate Glasses 39 44 EN Satoshi Hayakawa Chikara Ohtsuki Akiyoshi Osaka 10.18926/19594 Nb(2)O(5)-and Ta(2)O(5)-doped calcium si1icate glasses were soaked for various periods in a simulated body fluid(Kokubo solution) up to 30 days. Apatite formation ability of the surface of these glasses were investigated with thin-film X-ray diffraction and FT-IR reflection spectroscopy. The effects of these additive oxides on the bioactivity of CaO･SiO(2) based glass were discussed. A small amount of Nb(2)O(5) and Ta(2)O(5) suppressed the rate of silica hydrogel layer formation and the apatite formation on the surface of the glasses. The rate of the apatite nucleation on the surface of Nb(2)O(5)-doped calcium silicate glass was slower than that on the surface of Ta(2)O(5)-doped calcium silicate glass. It was concluded that the decrease in the apatite forming ability of calcium silicate glasses by these additive oxides is attributed to the suppression of formation of silica hydrogel layer which plays an important role in apatite nucleation. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 34 1-2 2000 Cytocompatibility of Silicone Elastomer Treated with Hydrogenperoxide Containing Tantalum Chloride 39 43 EN Satoshi Hayakawa Yuki Shirosaki Takeshi Yabuta Kanji Tsuru Akiyoshi Osaka 10.18926/15363 Silicone elastomer was chemically treated at 60℃ for 7 days with 30 wt% H(2)O(2) solutions with or without TaCl(5) and soaked for various periods in a simulated body fluid(Kokubo solution) up to 21 days. Apatite formation ability of the surface of the silicone elastomer specimens was investigated with thin-film X-ray diffraction and FT-IR reflection spectroscopy. These silicone specimens did not deposit apatite or calcium phosphates, irrespective of chemical treatment. Osteoblast-like cells (MC3T3-El) derived from mouse were cultured on the specimens at 36.5℃ under 5%C0(2) and 95% humidity. Similar degree of proliferation of cells was observed at 7 days among three specimens, while the no treatment specimen after incubation for 5 days showed a lower degree of proliferation than the silicone treated with 30 wt% H(2)O(2) solutions with or without TaCl(5). Alkaline phosphatase activity of the cells proliferated on the no treatment specimen was lower than those of the silicone treated with 30 wt% H(2)O(2) solutions with or without TaCl(5). These results indicate that the cytotoxicity of the silicone could be improved by the chemical treatment with 30 wt% H(2)O(2) solutions with or without TaCl(5). No potential conflict of interest relevant to this article was reported.