Ceramic Society of Japan Acta Medica Okayama 1348-6535 134 9 2026 Preparation of chitosan/apatite composite particles with core–shell structure 676 681 EN Takuya Kataoka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ryo Ikeda 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 In this study, a novel sequential preparation process of core–shell particles with chitosan (CS) cores and hydroxyapatite (HAp) shells is presented. This process involved the formation of phosphorylated CS particles, followed by HAp precipitation. Importantly, the precipitation of HAp on the surface of phosphorylated CS was confirmed. Different CaCl2 concentrations during the HAp precipitation step resulted in different HAp contents in the particles. To confirm the formation of the core–shell structure, the particles were immersed in hydrochloric acid (pH 2) for 5, 10, and 30 min. Notably, samples with higher HAp content (59 wt % and 84 wt %) retained their core morphology after 30 min of immersion, whereas samples with lower HAp content (28 wt %) rapidly lost their morphology. These results indicate that higher HAp content contributes to improved morphological stability under acidic conditions, leading to the formation of more stable core–shell particles. Overall, these findings clarify the role of phosphorylated CS in inducing HAp precipitation and show that the proposed preparation process leads to the formation of CS/HAp core–shell structures. No potential conflict of interest relevant to this article was reported.

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.

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.

岡山大学大学院ヘルスシステム統合科学研究科 Acta Medica Okayama 2436-3227 2 2022 統合科学次世代研究会の活動報告 37 39 EN Tomohiko Yoshioka Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Haruka Hikasa Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University 10.18926/interdisciplinary/63470 No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0260-8774 292 2021 Crystallization characteristics of amorphous trehalose dried from alcohol 110325 EN Takanari Sekitoh Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Takashi Okamoto Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Akiho Fujioka Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Tomohiko Yoshioka Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Shinji Terui Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Imanaka Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Naoyuki Ishida Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Koreyoshi Imamura Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University Trehalose forms a glass that can be used to preserve labile substances under desiccation. The crystallization characteristics, namely crystallization temperature (Tcry) and isothermal crystallization behavior of amorphous trehalose, dried from alcohol (methanol, ethanol), was analyzed and the results were compared with those for the amorphous trehalose freeze-dried from water. The use of alcohol as a solvent lowered the Tcry from 184 ± 6 °C for the case of an aqueous solvent to 103 ± 5 °C/methanol and 120 ± 8 °C/ethanol. The formation of multiple forms of crystals and partial melting were suggested by the thermal analysis. Isothermal crystallization experiments showed that the alcohol-originated amorphous trehalose was eventually exclusively converted into β-form crystals. The induction period (tind) before the start of isothermal crystallization was markedly shortened when alcohol was used as the solvent compared to water. The tind values for various amorphous sugar samples including the alcohol-originated ones could be correlated with difference between Tcry and the sample temperature. 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.