研究者詳細 - 寺坂　宏一

Multicellular organisms demonstrate a hierarchical organization where multiple cells collectively form tissues, thereby enabling higher-order cooperative functionalities beyond the capabilities of individual cells. Drawing inspiration from this biological organization, assemblies of multiple protocells are developed to create novel functional materials with emergent higher-order cooperative functionalities. This paper presents new artificial tissues derived from multiple vesicles, which serve as protocellular models. These tissues are formed and manipulated through non-covalent interactions triggered by a salt bridge. Exhibiting pH-sensitive reversible formation and destruction under neutral conditions, these artificial vesicle tissues demonstrate three distinct higher-order cooperative functionalities: transportation of large cargoes, photo-induced contractions, and enhanced survivability against external threats. The rapid assembly and disassembly of these artificial tissues in response to pH variations enable controlled mechanical task performance. Additionally, the self-healing property of these artificial tissues indicates robustness against external mechanical damage. The research suggests that these vesicles can detect specific pH environments and spontaneously assemble into artificial tissues with advanced functionalities. This leads to the possibility of developing intelligent materials with high environmental specificity, particularly for applications in soft robotics.

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Extraction of 5-Hydroxymethylfurfural under Hydrogen Peroxide in Liquid–Liquid Slug Flow of Water / Methylisobutylketone Biphasic System and Effect of Hemin

Shimanouchi T., Sanagi S., Fujioka S., Terasaka K., Kimura Y.

Solvent Extraction Research and Development, Japan 31 （ 2 ） 67 - 75 2024年

ISSN 13417215

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微細なバブルに関するサイエンスの発展

寺坂宏一

表面と真空（日本表面真空学会） 66 （ 11 ） 629 - 630 2023年11月

研究論文（学術雑誌）

ファインバブルの基礎と食品工学への適用

寺坂宏一

食品機械装置（食品機械装置） 711 （ 11 ） 10 - 15 2023年11月

Photoinduced phase transition between vesicles and coacervates using low-molecular-weight catanionic amphiphiles

Kojima T., Terasaka K., Asakura K., Banno T.

Colloids and Surfaces A: Physicochemical and Engineering Aspects （Colloids and Surfaces A: Physicochemical and Engineering Aspects） 669 2023年07月

ISSN 09277757

Amphiphiles form various molecular self-assemblies in the aqueous phase, such as vesicles and coacervates, depending on molecular properties. Recently, phase transitions between vesicles and coacervates have drawn much attention because the switching between “closed” and “open” compartments could achieve the controllability of molecular sequestrations. We expect that the photoinduced drastic change in the molecular structure of catanionic amphiphiles comprising azobenzene-containing cationic amphiphiles (Azo) and anionic sodium dodecyl sulfate causes the transition. Self-assemblies prepared by a thin-film hydration method were observed using microscopy under UV and subsequent visible-light illumination. Additionally, investigation of selectivity for molecular sequestration and assay of enzymatic reactions in the self-assemblies were conducted. Photoinduced reversible phase transitions between vesicles and coacervates occurred owing to the photoisomerization of Azo. The formed coacervates had selectivity for molecular sequestration. Additionally, the transition achieved fusion of different vesicles via coacervates. Although coacervates are generally known to facilitate enzymatic reactions, the reactions were inhibited in the presence of the formed self-assemblies due to the deactivation of enzymes. Our results represent rapid and non-invasive systems of reversible vesicle–coacervate transitions. Furthermore, the findings provide a new aspect of coacervates in which catanionic low-molecular-weight amphiphiles could act as suppressors of chemical reactions.

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Ultrafine bubble generation by rapid condensation of mixed vapor of non-condensable gas and steam

Terasaka K., Taguchi K., Tetsuka T., Fujioka S.

Chemical Engineering Science （Chemical Engineering Science） 263 2022年12月

ISSN 00092509

Although the mechanism of ultrafine bubble generation has not yet been elucidated, we believe that the state of gas-saturated water before the generation of ultrafine bubbles is the most important factor in the mechanism of ultrafine bubble generation. Therefore, we proposed the hypothesis that the spatial distribution of dissolved gas molecules among the water molecules before the ultrafine bubble formation is stared has a significant effect on the formation of ultrafine bubble suspending water. Based on this hypothesis, we succeeded in generating ultrafine bubbles of sufficient number concentration in the condensate by rapidly condensing a well mixture of non-condensable gas and vapor by cooling. The number concentration of the generated ultrafine bubbles increased almost in proportion to the condensation rate of the vapor. Therefore, it was found that promoting the formation of bubble nuclei from dissolved gas molecules existing between water molecules in the condensate and suppressing bubble growth led to an increase in the number concentration of ultrafine bubbles. The principle of ultrafine bubble generation in this invention not only simplifies the generation of ultrafine bubble water but also enables the control of the number concentration of ultrafine bubbles in water.

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Enhanced enzyme stability and gas utilization by microbubble aeration applying microporous aerators

Thomas B., Ohde D., Matthes S., Bubenheim P., Terasaka K., Schlüter M., Liese A.

Catalysis Science and Technology （Catalysis Science and Technology） 13 （ 4 ） 1098 - 1110 2022年12月

研究論文（学術雑誌）, ISSN 20444753

During the optimization of processes in biocatalysis, the limitations of mass transfer and enzyme stability have to be overcome. To achieve these goals, aeration with microbubbles is advantageous by providing favorable properties, which include high gas utility, low-pressure drop, and reduced foam formation. In this study, the influences of microbubble, classic sub-millibubble and macrobubble aeration on enzyme stability and gas utility are compared. Using five enzymes, the half-life was investigated by comparing the microbubble aeration with a 2 μm porous sintered frit to the macrobubble aeration with a 5 mm open pipe, both adjusted to provide a constant kLa of 160 h−1. Furthermore, the half-life of a glucose oxidase was investigated by variation of the kLa in the range of 40 to 350 h−1 and the mode of the aeration system comparing the 2 μm and 10 μm sintered frit as well as the 5 mm open pipe. In both experimental set-ups, it was demonstrated that the aeration with microbubbles using the 2 μm sintered frit was beneficial for reaching high levels of enzyme stability. From this, we discovered that the interfacial area renewal rate plays an important role in the process of enzyme deactivation, which changes depending on the aeration mode.

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超純水中の空気ウルトラファインバブルの保存、輸送、濃縮、希釈及び除去

寺坂宏一, 田中俊也

混相流（日本混相流学会） 36 （ 1 ） 4 - 11 2022年04月

研究論文（学術雑誌）, 共著, 筆頭著者

鉄道各所へのウルトラファインバブル水の応用* （ブラシ洗浄機による洗浄効果とクロス拭き時の摩擦低減効果）

鈴木隆起, 赤対秀明, 秦隆志, 西内悠祐, 多田佳織, 早水庸隆, 藤井貴敏, 氷室昭三, 寺坂宏一

混相流（日本混相流学会） 36 （ 1 ） 28 - 35 2022年04月

研究論文（学術雑誌）, 最終著者

Microbubble generation with rapid dissolution of ammonia (NH<inf>3</inf>)-hydrogen (H<inf>2</inf>) mixed gas fed from a nozzle into water

Kobayashi T., Fujioka S., Tanaka S., Terasaka K.

Chemical Engineering Science （Chemical Engineering Science） 248 2022年02月

ISSN 00092509

Because of their useful characteristics, microbubbles attracted much interest in industry and medicine. In this study, we developed a novel method of generating microbubbles through the chemical absorption of ammonia (NH3). By using an ultrahigh-speed camera, consecutive images of bubble formation were captured, and the microbubble generation mechanism was investigated. The effects of the gas flow rate and ammonia concentration in the liquid phase on the size of the microbubbles were examined. The hydrogen (H2) gas flow rate was found not to demonstrate a significant effect on the bubble diameter. The diameter of the microbubbles increased as the superficial velocity of the gas mixture (NH3 – H2) decreased.

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Unique properties of fine bubbles in the electrochemical reduction of carbon dioxide using boron-doped diamond electrodes

Tomisaki M., Natsui K., Fujioka S., Terasaka K., Einaga Y.

Electrochimica Acta （Electrochimica Acta） 389 2021年09月

ISSN 00134686

The electrochemical CO2 reduction on boron-doped diamond (BDD) electrodes in an aqueous solution with fine bubbles was studied. The overpotential decreased and the production of carbon monoxide was promoted in the CO2 reduction with fine bubbles compared to that without fine bubbles. It is suggested that fine bubbles in solution could facilitate the mass transport and also act as the catalyst for producing carbon monoxide. Potential-dependent in-situ attenuated total reflectance-infrared (ATR-IR) measurements confirmed the catalytic activity, showing that in solutions with CO2 fine bubbles the CO2•– intermediate or the CO2 molecules themselves become stabilized near the electrode and these can be adsorbed on the electrode surface more easily compared to using solutions without CO2 fine bubbles. The reported work is a first step in understanding the effects of fine bubbles in CO2 reduction reactions.

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Destabilization of ultrafine bubbles in water using indirect ultrasonic irradiation

Tanaka S., Kobayashi H., Ohuchi S., Terasaka K., Fujioka S.

Ultrasonics Sonochemistry （Ultrasonics Sonochemistry） 71 2021年03月

ISSN 13504177

© 2020 The Authors Ultrafine bubble (UFB) is a bubble with a diameter of less than 1 μm. Little attention has been paid to the defoaming and removal of UFBs. This study proposes a method to destabilize UFBs by using indirect ultrasonic irradiation. Besides, the destabilization mechanism of UFB was investigated. The ultrasonic frequency was 1.6 MHz and the dissipated power was 30 W. UFB dispersions were prepared using two different types of bubble generators: pressurized dissolution method and swirling liquid flow method. The effects of ultrasonic irradiation on the stability of UFBs were evaluated by particle tracking analysis (PTA) and electrophoretic zeta potential measurement. Results showed that the indirect ultrasonic irradiation for 30 min reduced the number concentration of UFBs by 90% regardless of the generation method. This destabilization was attributed to a decrease in the magnitude of zeta potential of UFBs due to the changes in pH and electrical conductivity. These changes in the electrochemical properties were caused by the formation of nitric acid. To study the destabilization mechanism, the pH of the UFB dispersions were modified by titration; the chemical and mechanical effects of ultrasound were separately examined. It was found that not only the chemical effect caused by the formation of nitric acid but also the mechanical effect contributed to the destabilization of UFB. Feasibility studies were also performed for UFBs in an aqueous surfactant solution and UFBs in a solid particle dispersion. The proposed method selectively destabilized UFBs in the solutions.

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Microbubble enhanced mass transfer efficiency of CO<inf>2</inf>capture utilizing aqueous triethanolamine for enzymatic resorcinol carboxylation

Ohde D., Thomas B., Matthes S., Tanaka S., Bubenheim P., Terasaka K., Schlüter M., Liese A.

RSC Advances （RSC Advances） 11 （ 7 ） 4087 - 4096 2021年01月

研究論文（学術雑誌）

The present study focuses on the aeration of aqueous triethanolamine acting as reaction medium for biocatalytic carboxylations. For enhancing mass transfer in a bubble column reactor, microbubble aeration is applied and compared to conventional macrobubble aeration. Application of a 0.5 μm porous sparger enables microbubble CO2 aeration with bubble size distributions below 150 μm in Sauter mean diameter, correlating with the highest measured mass transfer rates. During CO2 saturation of the aqueous triethanolamine, bubble size distributions changed according to the level of CO2 saturation. For microbubbles, less foaming was observed compared to macrobubble aeration by a 10 μm porous sparger. This microbubble effect is attributed to their accelerated dissolution assisted by the Laplace pressure lowering the amount of bubbles reaching the surface of the liquid. The experiments reveal that the rate of interfacial area generation, which is calculated based on measured bubble size distributions, influences the biocatalyst activity.

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Experimental study and prediction by computational fluid dynamics on self-induced sloshing due to bubble flow in a rectangular vessel

Aoki R., Fujioka S., Terasaka K.

Journal of Chemical Engineering of Japan （Journal of Chemical Engineering of Japan） 54 （ 2 ） 51 - 57 2021年

ISSN 00219592

Self-induced sloshing is an oscillatory phenomenon of a free liquid surface due to the flow of a fluid. This phenomenon has been reported in some gas–liquid reactors, and it is important to predict and prevent its occurrence for the safe operation of the reactors. However, the fundamental knowledge on the self-induced sloshing by bubble flow, such as the frequency and amplitude, is insufficient, and the occurrence condition has not been clarified. The purpose of this study is to investigate the characteristics of self-induced sloshing by bubble flow experimentally. We attempt to reproduce self-induced sloshing by using computational fluid dynamics (CFD) and establish a CFD model for the prediction of the occurrence of self-induced sloshing. In the experiments, air bubbles were dispersed into a liquid from the bottom of a rectangular vessel. The effects of the air flow rate and static liquid height on the characteristics of self-induced sloshing were investigated experimentally by image analysis. The occurrence of self-induced sloshing was confirmed by increasing the airflow rate at a specific static liquid height. The amplitude reached a maximum at the static liquid height, where self-induced sloshing was most likely to occur, and the frequency decreased with increasing static liquid height. Next, in order to reproduce the self-induced sloshing through CFD, an appropriate drag model of the bubbles was selected. Although the amplitude was overestimated due to the absence of the foam layer, the predicted frequency agreed well with the experimental value. Finally, the movement of the circulation flow was analyzed, and its correlation with the self-induced sloshing was clarified.

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Characterization of water/organic biphasic system in liquid-liquid slug flow under hydrothermal conditions: Solvation, vorticity, and hydrophobicity

Shimanouchi T., Fujioka S., Tanifuji T., Yamamoto K., Terasaka K., Kimura Y.

Solvent Extraction Research and Development （Solvent Extraction Research and Development） 28 （ 1 ） 21 - 35 2021年

ISSN 13417215

The microcapillary was combined with the liquid-liquid slug flow to build the separation field. The partition behavior of seventeen kinds of substrates was investigated by using six kinds of water/organic biphasic systems under hydrothermal conditions (25 - 190° C at 10 MPa). The scale of hydrophobicity (HF) of water/organic biphasic system was estimated. The HF value for the biphasic system used here was comparable to the conventional aqueous two-phase systems and depended on the (de)solvation of substrates by water and organic solvent. Besides, the vortex field in the slug contributed to the enhanced mass transfer of substrates. Those results are available for the selection of water/organic biphasic system as the reactive separation of target materials.

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空気微細気泡A重油による高速ディーゼル機関の燃費とNOX低減

山下裕史,工藤達司,中武靖仁,田中大,川原秀夫,寺坂宏一,河原寛,後藤英親

日本マリンエンジニアリング学会誌 56 （ 4 ） 152 - 158 2021年

Comparative investigation of fine bubble and macrobubble aeration on gas utility and biotransformation productivity

Thomas B., Ohde D., Matthes S., Engelmann C., Bubenheim P., Terasaka K., Schlüter M., Liese A.

Biotechnology and Bioengineering （Biotechnology and Bioengineering） 118 （ 1 ） 130 - 141 2021年

研究論文（学術雑誌）, 共著, ISSN 00063592

The sufficient provision of oxygen is mandatory for enzymatic oxidations in aqueous solution, however, in process optimization this still is a bottleneck that cannot be overcome with the established methods of macrobubble aeration. Providing higher mass transfer performance through microbubble aerators, inefficient aeration can be overcome or improved. Investigating the mass transport performance in a model protein solution, the microbubble aeration results in higher kLa values related to the applied airstream in comparison with macrobubble aeration. Comparing the aerators at identical kLa of 160 and 60 1/h, the microbubble aeration is resulting in 25 and 44 times enhanced gas utility compared with aeration with macrobubbles. To prove the feasibility of microbubbles in biocatalysis, the productivity of a glucose oxidase catalyzed biotransformation is compared with macrobubble aeration as well as the gas-saving potential. In contrast to the expectation that the same productivities are achieved at identically applied kLa, microbubble aeration increased the gluconic acid productivity by 32% and resulted in 41.6 times higher oxygen utilization. The observed advantages of microbubble aeration are based on the large volume-specific interfacial area combined with a prolonged residence time, which results in a high mass transfer performance, less enzyme deactivation by foam formation, and reduced gas consumption. This makes microbubble aerators favorable for application in biocatalysis.

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