Engineering pH-Responsive, Self-Healing Vesicle-Type Artificial Tissues with Higher-Order Cooperative Functionalities.

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.

Bifurcation and Transposition of the Wicking Front of Binary Solutions Infiltrating into Chromatography Paper Associated with Their Evaporation.

Nonequilibrium fluid patterns, such as Marangoni contraction, coffee rings, and tears of wine, are generated in binary solutions spread on a substrate during their evaporation. In this study, we observed another type of nonequilibrium behavior exhibited by binary solutions as they infiltrate porous materials and undergo evaporation. A binary solution comprising hexane and ethanol was brought into contact with the chromatography paper to facilitate infiltration into the paper's pores. Because the experimental setup was in an open environment, infiltration and evaporation occurred simultaneously. The wicking front exhibited an initial rapid advancement, followed by subsequent receding and readvancing. Additionally, the bifurcation of the wicking front after the onset of its readvancement was confirmed by monitoring the temporal evolution of the spatial luminance distribution and temperature distribution on the surface of the chromatography paper. Chromatographic development of a hydrophilic dye was conducted in this experimental setup in an open environment. Additionally, it was confirmed that the receding and readvancing of the wicking front represented the transposition of the bifurcated wicking fronts.

Factors to control the alignment of surface-treated titanium dioxide powders to maximize performance of sunscreens.

OBJECTIVE: Titanium dioxide powders are contained in a large class of colour cosmetics and sunscreen formulas. When they are used, the formation of a uniform functional powder layer on the skin is an important factor to show their functionality, such as aesthetic and UV protection. Attempts were made to extract the factors that affect the UV shielding ability of the deposited powder layer. METHODS: Seven kinds of surface treatments were conducted on nano-sized titanium dioxide powder to modify the surface characteristics. Dispersion samples were prepared by mixing these powders with liquids, such as mixed solutions of cyclopentasiloxane, isododecane, coconuts alkane and dimethicone using a disperser and a bead mill. The dispersions were applied using an applicator on cellulose triacetate film, polycarbonate film and polymethyl pentene film. Laser microscope observation and micro-gloss glossmeter analysis were carried out to assess the flatness of the deposited powder layers, and the UV shielding ability was evaluated using SPF analyser. RESULTS: Factors whose influences on the structure and UV shielding ability of the deposited powder layer being analysed were pseudo-HLB of the powders, liquids for preparing the dispersions and material of the substrates. Higher UV shielding ability was attained when powders having pseudo-HLB at around 6 were employed independent from the kinds of liquids and substrates. Flatness of the deposited layer was found to enhance the UV shielding ability of the UV-B region, while that of the UV-A region was scarcely influenced by the flatness. Employing lower surface tension liquids for preparing the dispersions and materials exhibiting lower polar components of surface free energy as substrates tended to enhance the UV shielding ability. CONCLUSION: Surface treatments conducted on the powders in this study were found to change UV shielding ability, especially UV-B shielding ability, and the relation between pseudo-HLB and UV shielding ability was scarcely influenced by the kinds of liquids. Both surface tension of liquids and the polar component of surface free energy of substrates affected the UV shielding ability. It was suggested that pseudo-HLB calculated based on chemical structure becomes useful information to choose optimum surface treatment to make uniform powder alignment independent from the surrounding environment.

OBJECTIF: Les poudres de dioxyde de titane font partie d'une grande classe de cosmétiques de couleur et de formules d'écran solaire. Lorsqu'elles sont utilisées, la formation d'une couche de poudre fonctionnelle uniforme sur la peau est un facteur important pour démontrer leur mode d'action, qu'il s'agisse de l'aspect esthétique ou de la protection contre les UV. Des tentatives ont été faites pour extraire les facteurs qui altèrent la capacité de protection contre les UV de la couche de poudre déposée. MÉTHODES: Sept types de traitements de surface ont été effectués sur une poudre de dioxyde de titane de taille nanométrique pour modifier les caractéristiques de surface. Des échantillons de dispersion ont été préparés en mélangeant ces poudres avec des liquides, tels que des mélanges de cyclopentasiloxane, d'isododécane, d'alcane de noix de coco et de diméthicone, à l'aide d'un disperseur et d'un broyeur à billes. Les dispersions ont été appliquées avec un applicateur sur un film de triacétate de cellulose, un film de polycarbonate et un film de polyméthylpentène. Une observation au microscope laser ainsi qu'une analyse au micro-glossmètre ont été faites pour évaluer la planéité des couches de poudre déposées, et la capacité de protection contre les UV a été évaluée avec un analyseur SPF (indice de protection solaire). RÉSULTATS: Les facteurs qui influent sur la structure et la capacité de protection contre les UV de la couche de poudre déposée analysée étaient le pseudo-HLB (équilibre hydrophile/lipophile) des poudres, les liquides pour la préparation des dispersions et le matériau des substrats. Une meilleure capacité de protection contre les UV a été obtenue lorsque des poudres ayant un pseudo-HLB d'environ 6 étaient utilisées, indépendamment des types de liquides et de substrats. La planéité de la couche déposée s'est avérée améliorer la capacité de protection contre les UV de la région UV-B, alors qu'elle n'a eu que peu d'incidence sur celle de la région UV-A. L'utilisation de liquides à faible tension de surface pour préparer les dispersions et les matériaux présentant comme substrats des composants polaires inférieurs de l'énergie libre de surface avait tendance à améliorer la capacité de protection contre les UV. CONCLUSION: Les traitements de surface effectués sur les poudres dans cette étude ont montré qu'ils modifiaient la capacité de protection contre les UV, en particulier la capacité de protection contre les UV-B, et que la relation entre le pseudo-HLB et la capacité de protection contre les UV était peu influencée par les types de liquides. La tension de surface des liquides et le composant polaire de l'énergie libre de surface des substrats ont affecté la capacité de protection contre les UV. Il a été suggéré que le pseudo-HLB calculé en fonction de la structure chimique devient utile.

Self-Assembling Properties and Recovery Effects on Damaged Skin Cells of Chemically Synthesized Mannosylerythritol Lipids.

Mannosylerythritol lipids (MELs), which are one of the representative sugar-based biosurfactants (BSs) produced by microorganisms, have attracted much attention in various fields in the sustainable development goals (SDGs) era. However, they are inseparable mixtures with respect to the chain length of the fatty acids. In this study, self-assembling properties and structure-activity relationship (SAR) studies of recovery effects on damaged skin cells using chemically synthesized MELs were investigated. It was revealed, for the first time, that synthetic and homogeneous MELs exhibited significant self-assembling properties to form droplets or giant vesicles. In addition, a small difference in the length of the fatty acid chains of the MELs significantly affected their recovery effects on the damaged skin cells. MELs with medium or longer length alkyl chains exhibited much higher recovery effects than that of C18-ceramide NP.

Synthesis of Mannosylerythritol Lipid Analogues and their Self-Assembling Properties, Recovery Effects on Damaged Skin Cells, and Antibacterial Activity.

Synthesis of three types of purpose-designed mannosylerythritol lipid (MEL)-D analogues with decanoyl groups, ß-GlcEL-D, α-GlcEL-D, and α-MEL-D, was accomplished utilizing our boron-mediated aglycon delivery (BMAD) methods. Their self-assembling properties, recovery effects on damaged skin cells, and antibacterial activity were evaluated. It was revealed, for the first time, that α-GlcEL-D and α-MEL-D only generated giant vesicles, indicating that slight differences in the steric configuration of an erythritol moiety and fatty acyl chains affect the ability to form vesicles. Analogue α-MEL-D exhibited significant recovery effects on damaged skin cells. Furthermore, α-MEL-D exhibited antibacterial activity as high as that for MEL-D, indicating that α-MEL-D is a promising artificial sugar-based material candidate for enhancing the barrier function of the stratum corneum, superior to a known cosmetic ingredient, and possesses antibacterial activity.

Pathway-Dependent Phase Transitions of Supramolecular Self-assemblies Containing Cationic Amphiphiles with Azobenzene and Disulfide Groups.

There have been several attempts to construct supramolecular chemical systems that mimic the phase transitions in living systems. However, most of these phase transitions are one-to-one and induced by one stimulus or chemical; there have been few reports on the pathway-dependent phase transition of supramolecular self-assemblies in multi-step. To induce multistep phase transitions, molecular crystals were prepared that contained a cationic amphiphile bearing azobenzene and disulfide groups. A reducing agent caused the crystals to become vesicles, and adjacent, non-touching vesicles fused under UV and subsequent visible light. Adding a reducing agent to the worm-like aggregates that were generated after UV irradiation of the original crystals resulted in the growth of sheet-like aggregates. 1 H NMR and fluorescence anisotropy measurements showed that a series of phase transitions was induced by changes in the phase structures from molecular conversions of the reactive amphiphiles. The multiple pathway-dependent phase transitions of supramolecular self-assemblies can provide a methodology for developing new stimuli-responsive materials that exhibit the desirable properties under specific circumstances from a systems chemistry viewpoint.

Temperature-Dependent Dynamics of Giant Vesicles Composed of Hydrolysable Lipids Having an Amide Linkage.

Various amphiphiles including surfactants and lipids have been designed and synthesized to improve and create new functionalities. In particular, the emergence of cell-like behaviors of giant vesicles (GVs) composed of synthetic lipids has drawn much attention in the development of chemical models for cells. The aim of this study was to measure temperature-dependent morphological changes of GVs induced by fragmentation and subsequent growth using hydrolysable cationic lipids having an amide linkage. Results from differential scanning calorimetry, fluorescence spectroscopy using an environment-responsive probe, and confocal Raman microscopy showed that the dynamics observed were due to changes in the vesicle membrane, including variation in the lipid composition, induced by thermal stimulation.

Start of Micrometer-Sized Oil Droplet Motion through Generation of Surfactants.

Self-propelled motion of micrometer-sized oil droplets in surfactant solution has drawn much attention as an example of nonlinear life-like dynamics under far-from-equilibrium conditions. The driving force of this motion is thought to be induced by Marangoni convection based on heterogeneity in the interfacial tension at the droplet surface. Here, to clarify the required conditions for the self-propelled motion of oil droplets, we have constructed a chemical system, where oil droplet motion is induced by the production of 1,2,3-triazole-containing surfactants through the Cu-catalyzed azide-alkyne cycloaddition reaction. From the results of the visualization and analysis of flow fields around the droplet, the motion of the droplets could be attributed to the formation of flow fields, which achieved sufficient strength caused by the in situ production of surfactants at the droplet surface.

Locomotion Mode of Micrometer-Sized Oil Droplets in Solutions of Cationic Surfactants Having Ester or Ether Linkages.

Micrometer-sized self-propelled oil droplets under a far-from-equilibrium condition have drawn much attention because of their potential as a dynamic model for the chemical machinery in living organisms. To clarify the effect of interactions between the system components (surfactant, oil, and water) on the locomotion mode of droplets, we investigated the behaviors of oil droplets composed of n-heptyloxybenzaldehyde (HBA) in solutions of cationic surfactants having or not having an ester or an ether linkage. It was observed that in solutions of cationic surfactants having an ester or an ether linkage, spherical HBA droplets self-propelled by changing their direction frequently. On the other hand, when this functional group is absent, a slow self-propelled motion of the oil droplets concurrent with the evolution of aggregates on their surface was observed. From the results of measurement of interfacial tension and assessment of self-emulsification, we determined that the attractive interactions of cationic surfactants without an ester or an ether linkage with HBA are stronger than those having the linkage. The difference in the locomotion mode of oil droplets is probably explained from the viewpoint of the interactions among the system components.

Self-Propelled Motion of Monodisperse Underwater Oil Droplets Formed by a Microfluidic Device.

We evaluated the speed profile of self-propelled underwater oil droplets comprising a hydrophobic aldehyde derivative in terms of their diameter and the surrounding surfactant concentration using a microfluidic device. We found that the speed of the oil droplets is dependent on not only the surfactant concentration but also the droplet size in a certain range of the surfactant concentration. This tendency is interpreted in terms of combination of the oil and surfactant affording spontaneous emulsification in addition to the Marangoni effect.

Self-Propelled Oil Droplets and Their Morphological Change to Giant Vesicles Induced by a Surfactant Solution at Low pH.

Unique dynamics using inanimate molecular assemblies based on soft matter have drawn much attention for demonstrating far-from-equilibrium chemical systems. However, there are no soft matter systems that exhibit a possible pathway linking the self-propelled oil droplets to formation of giant vesicles stimulated by low pH. In this study, we conceived an experimental oil-in-water emulsion system in which flocculated particles composed of a imine-containing oil transformed to spherical oil droplets that self-propelled and, after coming to rest, formed membranous figures. Finally, these figures became giant vesicles. From NMR, pH curves, and surface tension measurements, we determined that this far-from-equilibrium phenomenon was due to the acidic hydrolysis of the oil, which produced a benzaldehyde derivative as an oil component and a primary amine as a surfactant precursor, and the dynamic behavior of the hydrolytic products in the emulsion system. These findings afforded us a potential linkage between mobile droplet-based protocells and vesicle-based protocells stimulated by low pH.

Molecular System for the Division of Self-Propelled Oil Droplets by Component Feeding.

Unique dynamics using inanimate molecular assemblies have drawn a great amount of attention for demonstrating prebiomimetic molecular systems. For the construction of an organized logic combining two fundamental dynamics of life, we demonstrate here a molecular system that exhibits both division and self-propelled motion using oil droplets. The key molecule of this molecular system is a novel cationic surfactant containing a five-membered acetal moiety, and the molecular system can feed the self-propelled oil droplet composed of a benzaldehyde derivative and an alkanol. The division dynamics of the self-propelled oil droplets were observed through the hydrolysis of the cationic surfactant in bulk solution. The mechanism of the current dynamics is argued to be based on the supply of "fresh" oil components in the moving oil droplets, which is induced by the Marangoni instability. We consider this molecular system to be a prototype of self-reproducing inanimate molecular assembly exhibiting self-propelled motion.

Multiple-division of self-propelled oil droplets through acetal formation.

We demonstrate a novel system that exhibits both self-propelled motion and division of micrometer-sized oil droplets induced by chemical conversion of the system components. Such unique dynamics were observed in an oil-in-water emulsion of a benzaldehyde derivative, an alkanol and a cationic surfactant at a low pH.

pH-induced motion control of self-propelled oil droplets using a hydrolyzable gemini cationic surfactant.

Self-propelled motion of micrometer-sized substances has drawn much attention as an autonomous transportation system. One candidate vehicle is a chemically driven micrometer-sized oil droplet. However, to the best of our knowledge, there has been no report of a chemical reaction system controlling the three-dimensional motion of oil droplets underwater. In this study, we developed a molecular system that controlled the self-propelled motion of 4-heptyloxybenzaldehyde oil droplets by using novel gemini cationic surfactants containing carbonate linkages (2G12C). We found that, in emulsions containing sodium hydroxide, the motion time of the self-propelled oil droplets was longer in the presence of 2G12C than in the presence of gemini cationic surfactants without carbonate linkages. Moreover, in 2G12C solution, oil droplets at rest underwent unidirectional, self-propelled motion in a gradient field toward a higher concentration of sodium hydroxide. Even though they stopped within several seconds, they restarted in the same direction. 2G12C was gradually hydrolyzed under basic conditions to produce a pair of the corresponding monomeric surfactants, which exhibit different interfacial properties from 2G12C. The prolonged and restart motion of the oil droplets were explained by the increase in the heterogeneity of the interfacial tension of the oil droplets.

Induction for Self-Propelled Motion of Artificial Objects with/without Shape Anisotropy.

Motion is an essential feature of living systems. Microorganisms autonomously change their nature in response to slight changes in the surrounding environment induced by external stimuli and exhibit unique motion modes. Various self-propelled objects have been constructed to understand these behaviors. Towards achievement of such purpose, the precise settings of experimental conditions including fabrication of objects with a shape anisotropy have been made attempts in the field of active matter and supramolecular chemistry. This review describes the recent progress in inducing the self-propelled motion of artificial objects. If life-like dynamic behavior such as self-propelled motion can be designed and experimentally induced from molecular properties, it will be easier to control functions expressed as outputs. This will lead to not only a better understanding of the complex functions in living systems, but also the fabrication of exotic materials with life-like properties.

Spot Overtaking of Dyes of Their Chromatographic Development Associated with Solvent Evaporation.

Infiltration of binary solution of hexane and ethanol into chromatography paper associated with their evaporation was found to generate unexpected initial rapid advancement of wicking front followed by its receding and readvancing in our previous research. In the present study, paper chromatography development of hydrophobic dye, Sudan III, and hydrophilic dye, Acid Blue 9, was carried out using binary solutions of hexane and ethanol in open environment, allowing the developing solvent been evaporated. Sudan III was developed with initial rapid advancing wicking front, while Acid Blue 9 was scarcely developed. On the other hand, Acid Blue 9 was developed with the readvancing second wicking front, while the spot of Sudan III scarcely migrated. Thus, the unexpected illusional phenomenon, overtaking the spot of Sudan III by the spot of Acid Blue 9, was observed. The readvancement of the second wicking front was found to be enhanced as increasing the relative humidity in the environment. Surface temperature of the chromatography paper was measured during the chromatographic development in open environment to show that it became lower than the dew point when the experiments were carried out in relatively high humidity. Solubility of Sudan III in a binary solution of ethanol and water remarkably decreased as increasing the content of water. It was thus suggested that the water vapor condensation to induce water mixing into the mobile phase to decrease the solubility of Sudan III to inhibit its chromatographic development to realize the illusional spot overtaking of dyes of their chromatographic development associated with solvent evaporation.

Investigation on the Validity of in vitro Sun Protection Factor and Ultraviolet-A Protection Factor Evaluation Method for Sunscreen Samples.

Factors affecting the in vitro Sun Protection Factor (SPF) and Ultraviolet-A Protection Factor (UVA-PF) of sunscreens were analyzed for verifying the validity and reliability of the ISO24443 evaluation method. UV absorbance measurements by different spectrophotometers did not lead to the large difference in in vitro SPF/UVA-PF, although the UV absorbance determined by each spectrophotometer exhibited relatively large difference when it was larger than 2. On the other hand, relatively large difference was found in in vitro SPF/UVA-PF by utilizing European Cosmetic and Perfumery Association (Colipa) 1994 or UV-solar simulated radiation (UV-SSR) for the spectral irradiance. Appropriateness of employing the coefficient of adjustment for the determination of in vitro UVA-PF was also found to be reexamined.

Mode changes associated with oil droplet movement in solutions of gemini cationic surfactants.

Micrometer-sized self-propelled oil droplets in nonequilibrium systems have attracted much attention, since they form stable emulsions composed of oil, water, and surfactant which represent a primitive type of inanimate chemical machinery. In this work, we examined means of controlling the movement of oil droplets by studying the dynamics of n-heptyloxybenzaldehyde droplets in phosphate buffers containing alkanediyl-α,ω-bis(N-dodecyl-N,N-dimethylammonium bromide) (nG12) with either tetramethylene (4G12), octaethylene (8G12), or dodecamethylene (12G12) chains in the linker moiety. Significant differences in droplet dynamics were observed to be induced by changes in the linker structure of these gemini cationic surfactants. In a phosphate buffer containing 30 mM 4G12, self-propelled motion of droplets concurrent with the formation of molecular aggregates on their surfaces was observed, whereas the fusion of oil droplets was evident in both 8G12 and 12G12 solutions. We also determined that the surface activities and the extent of molecular self-assembly of the surfactants in phosphate buffer were strongly influenced by the alkyl chain length in the linker moiety. We therefore conclude that the surface activities of the gemini cationic surfactant have important effects on the oil-water interfacial tension of oil droplets and the formation of molecular aggregates and that both of these factors induce the unique movement of the droplets.

pH-Sensitive self-propelled motion of oil droplets in the presence of cationic surfactants containing hydrolyzable ester linkages.

Self-propelled oil droplets in a nonequilibrium system have drawn much attention as both a primitive type of inanimate chemical machinery and a dynamic model of the origin of life. Here, to create the pH-sensitive self-propelled motion of oil droplets, we synthesized cationic surfactants containing hydrolyzable ester linkages. We found that n-heptyloxybenzaldehyde oil droplets were self-propelled in the presence of ester-containing cationic surfactant. In basic solution prepared with sodium hydroxide, oil droplets moved as molecular aggregates formed on their surface. Moreover, the self-propelled motion in the presence of the hydrolyzable cationic surfactant lasted longer than that in the presence of nonhydrolyzable cationic surfactant. This is probably due to the production of a fatty acid by the hydrolysis of the ester-containing cationic surfactant and the subsequent neutralization of the fatty acid with sodium hydroxide. A complex surfactant was formed in the aqueous solution because of the cation and anion combination. Because such complex formation can induce both a decrease in the interfacial tension of the oil droplet and self-assembly with n-heptyloxybenzaldehyde and lauric acid in the aqueous dispersion, the prolonged movement of the oil droplet may be explained by the increase in heterogeneity of the interfacial tension of the oil droplet triggered by the hydrolysis of the ester-containing surfactant.

Construction of Supramolecular Systems That Achieve Lifelike Functions.

The Nobel Prize in Chemistry was awarded in 1987 and 2016 for research in supramolecular chemistry on the "development and use of molecules with structure-specific interactions of high selectivity" and the "design and production of molecular machines", respectively. This confirmed the explosive development of supramolecular chemistry. In addition, attempts have been made in systems chemistry to embody the complex functions of living organisms as artificial non-equilibrium chemical systems, which have not received much attention in supramolecular chemistry. In this review, we explain recent developments in supramolecular chemistry through four categories: stimuli-responsiveness, time evolution, dissipative self-assembly, and hierarchical expression of functions. We discuss the development of non-equilibrium supramolecular systems, including the use of molecules with precisely designed properties, to achieve functions found in life as a hierarchical chemical system.