記述言語：英語   掲載種別：研究論文（学術雑誌）

Physically crosslinked hydrogels with thixotropic properties attract considerable attention in the biomedical research field because their self‐healing nature is useful in cell encapsulation, as injectable gels, and as bioinks for three‐dimensional (3D) bioprinting. Here, we report the formation of thixotropic hydrogels containing nanofibers of double‐hydrophobic elastin‐like polypeptides (ELPs). The hydrogels are obtained with the double‐hydrophobic ELPs at 0.5 wt%, the concentration of which is an order of magnitude lower than those for previously reported ELP hydrogels. Although the kinetics of hydrogel formation is slower for the double‐hydrophobic ELP with a cell-binding sequence, the storage moduli G’ of mature hydrogels are similar regardless of the presence of a cell‐binding sequence. Reversible gel–sol transitions are demonstrated in step‐strain rheological measurements. The degree of recovery of the storage modulus G’ after the removal of high shear stress is improved by chemical crosslinking of nanofibers when intermolecular crosslinking is successful. This work would provide deeper insight into the structure–property relationships of the self‐assembling polypeptides and a better design strategy for hydrogels with desired viscoelastic properties.

DOI： 10.3390/ijms22084104

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Tearable and fillable implants are used to facilitate surgery. The use of implants that can generate heat and release a drug in response to an exogenous trigger, such as an alternating magnetic field (AMF), can facilitate on-demand combined thermal treatment and chemotherapy via remote operation. In this study, we fabricated tearable sponges composed of collagen, magnetite nanoparticles, and anticancer drugs. Crosslinking of the sponges by heating for 6 h completely suppressed undesirable drug release in saline at 37 °C but allowed drug release at 45 °C. The sponges generated heat immediately after AMF application and raised the cell culture medium temperature from 37 to 45 °C within 15 min. Heat generation was controlled by switching the AMF on and off. Furthermore, in response to heat generation, drug release from the sponges could be induced and moderated. Thus, remote-controlled heat generation and drug release were achieved by switching the AMF on and off. The sponges destroyed tumor cells when AMF was applied for 15 min but not when AMF was absent. The tearing and filling properties of the sponges may be useful for the surgical repair of bone and tissue defects. Moreover, these sponges, along with AMF application, can facilitate combined thermal therapy and chemotherapy.

DOI： 10.3390/MA13163637

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記述言語：英語   掲載種別：研究論文（学術雑誌）

<p>Octacalcium phosphate (OCP), which has a layered structure composed of an apatitic layer and a hydrated layer, is a precursor of hydroxyapatite (HAp). Although the topotactic transformation of OCP to HAp is a well-known phenomenon, its mechanism remains unclear. In this study, to clarify the role of the OCP hydrated layer in the mentioned transformation, we investigated the behavior of the transformation of OCP with hydrated layers of different thicknesses to HAp under hydrothermal conditions. We used three types of samples: plain OCP (Pure-OCP), OCP with incorporated succinate ions (Suc-OCP), and OCP with incorporated suberate ions (Sub-OCP). We found that all three OCP types transformed topotactically into HAp. The order of reactivity was Sub-OCP > Suc-OCP > Pure-OCP, which corresponds to the thickness of the hydrated layer. Since the transformation involves a compositional change, our finding implies that the hydrated layer acts as a diffusion (mass transfer) passage for dicarboxylate ions and hydrogen phosphate ions located within it, which move outside the crystal during the topotactic transformation. Our results thus contribute to a better understanding of the topotactic transformation mechanism of OCPs to HAp.</p>

DOI： 10.1246/bcsj.20200031

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CiNii Article

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Driven by the emergence of colloidal semiconductor quantum dots (QDs) of tunable emission wavelengths, characteristic of exciton absorption peaks, outstanding photostability and solution processability in device fabrication have become a key tool in the development of nanomedicine and optoelectronics. Diamond cubic crystalline silicon (Si) QDs, with a diameter larger than 2 nm, terminated with hydrogen atoms are known to exhibit bulk-inherited spin and valley properties. Herein, we demonstrate a newly discovered size region of Si QDs, in which a fast radiative recombination on the order of hundreds of picoseconds is responsible for photoluminescence (PL). Despite retaining a crystallographic structure like the bulk, controlling their diameters in the 1.1-1.7 nm range realizes the strong PL with continuous spectral tunability in the 530-580 nm window, the narrow spectral line widths without emission tails, and the fast relaxation of photogenerated carriers. In contrast, QDs with diameters greater than 1.8 nm display the decay times on the microsecond order as well as the previous Si QDs. In addition to the five-orders-of-magnitude variation in the PL decay time, a systematic study on the temperature dependence of PL properties suggests that the energy structure of the smaller QDs does not retain an indirect band gap character. It is discussed that a 1.7 nm diameter is critical to undergo changes in energy structure from bulky to molecular configurations.

DOI： 10.1021/acs.nanolett.9b03157

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Ceramic biomaterials that promote bone tissue regeneration are vital in the treatment of various bone-degenerative diseases and have stimulated intense bioceramic-related research. Salts of the calcium ion and phosphate esters (SCPE) can be transformed into calcium phosphate in aqueous environments containing alkaline phosphatase (ALP). Inspired by the formation process of hydroxyapatite (HAp) in our bones, these SCPEs are promising novel ceramic biomaterials showing a biomolecule-responsive function for bone repairing applications, because our bone tissues contain ALP. In this study, the behaviour of calcium phenylphosphate (CaPP), a typical SCPE, under conditions mimicking an in vivo environment were investigated. A simulated body fluid (SBF) modified with ALP was used as reaction media. The transformation from CaPP to HAp in the SBF containing ALP occurred, while no reaction occurred without ALP present. The transformation process of CaPP can be concluded as follows: first, soaked CaPP dissolves into the SBF and forms calcium ions and phenylphosphate ions. Subsequently, phosphate ions are generated by hydrolysis of phenylphosphate ions. This hydrolytic reaction is mediated by ALP. Finally, HAp is formed by the reaction of calcium, phosphate, and hydroxide ions in the SBF. Interestingly, the transformation reaction of CaPP occurred under conditions outside the optimal pH ranges for ALP. The findings of this study demonstrate that SCPEs are good candidates for a new class of ceramic biomaterials that respond to trigger biomolecules, namely ALP, in this case. This journal is

DOI： 10.1039/d0ma00600a

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Elastin-like polypeptides (ELPs) are promising candidates for fabricating tissue-engineering scaffolds that mimic the extracellular environment of elastic tissues. We have developed a “double-hydrophobic” block ELP, GPG, inspired by non-uniform distribution of two different hydrophobic domains in natural elastin. GPG has a block sequence of (VGGVG)5-(VPGXG)25-(VGGVG)5 that self-assembles to form nanofibers in water. Functional derivatives of GPG with appended amino acid motifs can also form nanofibers, a display of the block sequence’s robust self-assembling properties. However, how the block length affects fiber formation has never been clarified. This study focuses on the synthesis and characterization of a novel ELP, GPPG, in which the central sequence (VPGVG)25 is repeated twice by a short linker sequence. The self-assembly behavior and the resultant nanostructures of GPG and GPPG were when compared through circular dichroism spectroscopy, atomic force microscopy, and transmission electron microscopy. Dynamic rheology measurements revealed that the nanofiber dispersions of both GPG and GPPG at an extremely low concentration (0.034 wt%) exhibited solid-like behavior with storage modulus G′ > loss modulus G” over wide range of angular frequencies, which was most probably due to the high aspect ratio of the nanofibers that leads to the flocculation of nanofibers in the dispersion.

DOI： 10.3390/ijms20246262

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Block copolymer-mediated self-assembly of colloidal nanoparticles has attracted great attention for the fabrication of a wide variety of nanoparticle arrays. We have previously shown that silica nanospheres (SNSs) 15 nm in diameter assemble into ring-like nanostructures in the presence of amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (EOVE-MOVE) in an aqueous phase. Here, the effects of particle size of SNSs on this polymer-mediated self-assembly are studied systematically using scanning electron microscopy to observe SNSs of seven different sizes between 13 to 42 nm. SNSs of 13, 16, 19, and 21 nm in diameter assemble into nanorings in the presence of EOVE-MOVE. In contrast, larger SNSs of 26, 34, and 42 nm aggregate heavily, form chain-like networks, and remain dispersed, respectively, instead of forming ring-like nanostructures. The assembly trend for 26-42 nm-SNSs agrees with that expected from the increased colloidal stability for larger particles. Time-course observation for the assembled morphology of 16 nm-SNSs reveals that the nanorings, once formed, assemble further into network-like structures, as if the nanorings behave as building units for higher-order assembly. This indicates that the ring-like assembly is a fast process that can proceed onto random colloidal aggregation. Detailed analysis of nanoring structures revealed that the average number of SNSs comprising one ring decreased from 5.0 to 3.1 with increasing the SNS size from 13 to 21 nm. A change in the number of ring members was also observed when the length of EOVE-MOVE varied while the size of SNSs was fixed. Dynamic light scattering measurements and atomic force microscopy confirmed the SNSs/polymer composite structures. We hypothesize that a stable composite morphology may exist that is influenced by both the size of SNSs and the polymer molecular structures.

DOI： 10.1021/acs.langmuir.8b00420

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Human body contains trace inorganic elements that play important roles in the regulation of vital reactions. Biomaterials releasing the trace inorganic elements are suggested to be beneficial for tissue reconstruction remedies. The authors focused on inorganic layered compounds that give drug-releasing system tailored by assembling nanosheet-like crystals of the compounds with inserting ions and macromolecules which promote tissue regeneration. In the present study, calcium silicate hydrate (C-S-H) was selected as the framework, and its preparation conditions via precipitation method were explored. Moreover, the incorporation behaviors of alkylammonium molecules into the C-S-H were evaluated by their simultaneous addition during the method. Agglomerates of nanosheet-like C-S-H were precipitated by introducing calcium nitrate aqueous solution into equimolar concentration of sodium silicate aqueous solution in a controlled manner. By soaking C-S-H into simulated body fluid, which mimicked the inorganic elemental composition of human blood plasma, bone-like apatite was precipitated on its surface. The incorporation of tetrabuthylammonium cations (TBA+) were conducted by the addition of its hydroxide into sodium silicate aqueous solution during the preparation. XRD pattern of the sample showed the broadening of a peak, attributed to the interlayer distances in a C-S-H crystal. These results suggested the introduction of TBA+ in the C-S-H.

DOI： 10.2497/jjspm.65.325

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In ceramic forming techniques high particles packing can provide better properties of the final ceramic products. The high quality of the material coupled with the shape complexity of the ceramic product is still challenging. The aim of this work was the optimization and preparation of the ceramic samples based on two alumina powders of different particle size (AA05: 0.5 μm and TM-DAR: 0.15 μm). Firstly, ceramic suspensions of 50vol.% solid loading and the volumetric ratio of AA05 to TM-DAR 1:1, 2:1, 3:1, 4:1, respectively have been prepared. The 2-carboxyethyl acrylate was applied as the new monomer limiting the negative effect of oxygen inhibition. Additionally, the cold isostatic pressing (CIP) was used in order to increase relative density of green bodies. The results of presented research have shown that samples with the ratio of AA05 to TM-DAR 2:1 were characterized by the highest green density (62%). Moreover, CIP process proved to be effective and increased the density of green bodies from 62% to 67%. The pore size distribution of the green bodies has been measured. Samples were sintered at different conditions (1400°C, 1450°C and 1500°C for 1h and 1300°C, 1400°C, 1450°C and 1500°C for 5h).

DOI： 10.24425/123817

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Siloxane-containing vaterite (SiV) microparticles were prepared with controlling the degree of aminopropyl-functionalization in the siloxane; they are aiming for applications as bone regenerative devices. The aim of this work was to evaluate the structure at siloxane/vaterite interphase and to control the solubility of particles by the structural tuning of siloxane. The particles were spherical with average diameters of 1.1–1.4 μm. Differential infrared spectrometry revealed the transformation of aminopropyl terminals in the siloxane into carbamate (NH-COO−) groups. Moreover, the vaterite crystallites in the particles were slightly oriented towards the (0 0 1) plane. These results describe the interphase structure, with the carbamate groups coordinating on the Ca2+ ion face in the (0 0 1) plane of neighbouring vaterite. Upon soaking in buffer solution, the particles exhibited a rapid initial release of Ca2+ ions within 30 min and of soluble silica within 2 h. The vaterite in this particle survived for more than 6 h. The chemical stability of the siloxane was enhanced by incorporating tetraethoxysilane-derived siloxane with fractions of 24 mol% or 50 mol%. This enhancement controlled the initial release of not only soluble silica but also Ca2+ ions.

DOI： 10.1016/j.apt.2017.03.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）

On the basis of the systematic study on temperature dependence of photoluminescence (PL) properties along with relaxation dynamics we revise a long-accepted mechanism for enhancing absolute PL quantum yields (QYs) of freestanding silicon nanocrystals (ncSi). A hydrogen-terminated ncSi (ncSi:H) of 2.1 nm was prepared by thermal disproportination of (HSiO 1.5) n, followed by hydrofluoric etching. Room-temperature PL QY of the ncSi:H increased twentyfold only by hydrosilylation of 1-octadecene (ncSi-OD). A combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PL QYs with the notable difference in surface structure between the ncSi:H and the ncSi-OD. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PL QY.

DOI： 10.1038/srep36951

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Functional near-IR (NIR) emitting nanoparticles (NPs) adapted for two-photon excitation fluorescence cell imaging were obtained starting from octadecyl-terminated silicon nanocrystals (ncSi-OD) of narrow photoluminescence (PL) spectra having no long emission tails, continuously tunable over the 700-1000 nm window, PL quantum yields exceeding 30%, and PL lifetimes of 300 μs or longer. These NPs, consisting of a Pluronic F127 shell and a core made up of assembled ncSi-OD kept apart by an octadecyl (OD) layer, were readily internalized into the cytosol, but not the nucleus, of NIH3T3 cells and were non-toxic. Asymmetrical field-flow fractionation (AF4) analysis was carried out to determine the size of the NPs in water. HiLyte Fluor 750 amine was linked via an amide link to NPs prepared with Pluronic-F127-COOH, as a first demonstration of functional NIR-emitting water dispersible ncSi-based nanoparticles.

DOI： 10.1039/c6nr01437b

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