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Liposomes, molecular self-assemblies resembling biological membranes, are a promising scaffold to investigate the physicochemical logic behind the complexity of living cells. Despite elaborate synthetic studies constructing cell-like chemical systems using liposomes, less attention has been paid to the proactive role of the membrane emerging as dynamics of the molecular self-assembly. This study investigated the liposomes containing anionic phospholipids by exposing them to steady flow conditions using a newly constructed automatic microfluidic observation platform. We demonstrated that the liposomes accumulated even macromolecules under the microfluidic condition without pore formation. By investigating the effect of composition of liposomes and visualizing negatively charged phospholipids upon the flow, we presumed that the external flow caused a compositional asymmetry of anionic phospholipids between the inner/outer leaflets, and the asymmetry enabled a rapid accumulation of those molecules against the concentration gradient. The current study opens new research interests regarding the nature of biological membranes under steady flow conditions.

Self-propelled droplets made of organic materials can be an influential candidate for understanding cell migration from the viewpoint of nonequilibrium physics and have attracted significant attention with regard to soft-matter-type rovers. Because self-propelled droplets are soft enough to be easily deformed, they should be useful as chemically artificial rovers that can move in small areas with many obstacles in water and can be applied as ‘motile’ carriers for exploring and curing of biological bodies or remediation of the natural environment. Here, we review recent research progress on designing self-propelled droplets of micrometer size.

Closed bilayer membranes of amphiphiles in water, termed vesicles, represent one of the promising models of primitive cellular compartments. Herein, we reviewed studies on the design and construction of vesicle-based cell models capable of sequential growth and division and their underlying analysis methods. We discussed the potential contribution of these studies to the universal understanding of the chemical/physical logics behind the steady reproduction of cellular membranes.

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.

Using water-floating 3D-printed models, we investigated the dynamics of camphor boats, which are composed of a one-holed board and a camphor grain, under constraint conditions where a rod hooks the camphor boat on the water surface. When a camphor boat was connected to a water-floating disk or another camphor boat through a rod, we found that regular dynamics of the camphor boat appear and depend on the mobility restriction of the disk, the rod length, and the position of a slit of the camphor boat. We performed numerical simulations to reproduce the observed motions with theoretical models including constraint conditions.

Flow cytometric analysis revealed that the redistribution of components of a hybrid vesicular system composed of amphiphilic nicotinamide and its reduced form occurred associated with the emergence of nonlamellar aggregates that emitted an enhanced blue emission together with a green emission due to exciplex formation.

As a supramolecular micromachine with information flow, a giant vesicle (GV)-based artificial cell that exhibits a linked proliferation between GV reproduction and internal DNA amplification has been explored in this study. The linked proliferation is controlled by a complex consisting of GV membrane-intruded DNA with acidic amphiphilic catalysts, working overall as a lipo-deoxyribozyme. Here, we investigated how a GV-based artificial cell containing this lipo-deoxyribozyme responds to diverse external and internal environments, changing its proliferative dynamics. We observed morphological changes (phenotypic expression) in GVs induced by the addition of membrane precursors with different intervals of addition (starvation periods). First, we focused on a new phenotype, the &ldquo, multiple tubulated&rdquo, form, which emerged after a long starvation period. Compared to other forms, the multiple tubulated form is characterized by a larger membrane surface with a heavily cationic charge. A second consideration is the effect of the chain length of encapsulated DNA on competitive proliferation. The competitive proliferation among three different species of artificial cells containing different lengths of DNA was investigated. The results clearly showed a distinct intervention in the proliferation dynamics of the artificial cells with each other. In this sense, our GV-based artificial cell can be regarded as an intelligent supramolecular machine responding to external and internal environments, providing a new concept for developing molecular machines and robotics.

In this manuscript, we report our ground-breaking result on development of artificial multicellular structures capable for neuron like spiking activity. These structures are self-growing ensembles of vesicles whose membranes are combinations of phospholipid and viscous amphipathic molecules. The vesicles grow from a porous gel, and an osmotic pressure difference between the interior of the gel and its surrounding drives the growth. The vesicles’ membranes have also incorporated pore forming proteins. The growing ensembles exhibit spike-like dynamics in electrical potential recorded on the electrodes inserted in the ensembles. We speculate that the spike-like electrical activity is due to the breaking and leaking of the compartments, fusion, and fission of the vesicles during the growth. We demonstrate the spontaneous growth of multi-cellular lipid compartments, which can also incorporate liposomes with membrane proteins, and their generation of an electrical spike-like signal. The bottom-up development of a multicellular artificial molecular system like this report would lead the transition of material's complexity toward information transfer emulating that of a nervous system. The evidence of neuromorphic electrical activity in multicellular systems of lipid vesicles is a promising indication of feasibility of future designs of self-growing artificial proto-brains. We, therefore, think that this manuscript should attract outstanding interest from the wide community of scientists, engineers and laymen, especially those interested in in artificial life, molecular computing, origins of life, artificial cell, molecular robotics, and synthetic biology.

Design and fabrication of organic and polymeric soft materials exhibiting solvent-free isothermal changes in mechanical properties triggered by photostimulation are challenging. Here, we report dramatic changes in viscoelasticity of coumarin end-functionalized poly(dimethyl siloxane) with a branched macromolecular architecture under a solvent-free isothermal condition upon alternating irradiation of UV at the wavelength of 365 and 254 nm (UV365 and UV254). Significantly, it is disclosed that storage modulus (G′) was increased by a factor of more than 30000. Moreover, the subsequent UV254 irradiation caused sharp decrease in G′ and it became comparable to loss modulus. Furthermore, alternating irradiation of UV365 and UV254 caused repetitive increase and decrease in G′ of the material.

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.

The self-propelled behaviors of macroscopic inanimate objects at surfaces and interfaces are ubiquitous phenomena of fundamental interest in interface science. However, given the existence of a large variety of systems with their own inherent chemical properties, the kinematics of the self-propelled motion and the dynamics of the forces driving these systems often remain largely unknown. Here, we experimentally investigate the spontaneous motion of a sodium oleate tablet at a water-nitrobenzene interface, under nonequilibrium and global isothermal conditions, through measurements of the interfacial tension with the noninvasive, quasi-elastic laser scattering method. The sodium oleate tablet was self-propelled due to an imbalance in the interfacial tension induced by the inhomogeneous adsorption of oleate/oleic acid molecules. The kinetics of the self-propelled motion of a boat-shaped plastic sheet bearing sodium oleate tablets at a sodium oleate aqueous solution-nitrobenzene interface was also studied. The interfacial tension difference between the front and rear of the boat was quantitatively identified as the force pushing the boat forward, although the Marangoni flow due to the uneven distribution of the interfacial tension behind the boat tended to decelerate the motion.

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.

For the development of artificial cell-like machinery, liposomes encapsulating cytoskeletons have drawn much recent attention. However, there has been no report showing isothermally reversible morphological changes of liposomes containing cytoskeletons. We succeeded in reversibly changing the shape of cell-sized giant vesicles by controlling the polymerization/depolymerization state of cytoskeletal microtubules that were encapsulated in the vesicles using pressure changes. The result indicates that it is possible to manipulate artificial cell models composed of molecules such as lipids and proteins. The findings obtained in this study will be helpful in clarifying the details of cooperation between cytoskeletal dynamics and morphogenesis of biological membranes and in improving the design and construction of further advanced artificial cell-like machinery, such as drug-delivery systems. In addition, the experimental system used in this study can be applied to research to elucidate the adaptive strategy of living organisms to external stimuli and extreme conditions such as osmotic stress and high-pressure environments like the deep sea.

Surfactant-based film-forming curing compounds (SFCCs) are widely used to retain water on fresh concrete by forming multilayered films. However, the water-retaining mechanism is not yet fully understood; therefore, we aimed to clarify this mechanism, thereby potentially aiding in evaluating the effect of SFCC or to develop more effective SFCCs. It was confirmed that SFCC does not hinder the setting and hardening properties or strength development. Thus, we examined water evaporation from cement pastes on which SFCC was sprayed. Consequently, the water-retaining effect lasted up to 8 h, which indicating that 8 h after spraying SFCC is enough time for suppression of plastic cracking. We then observed the water surface on which SFCC was spread under a Brewster angle microscope and discovered that SFCC on the water surface forms continuous thin film and agglomerates. The water-retaining effect was higher when a continuous thin film was formed; thus, the observation of this thin film facilitated the evaluation of the effect of SFCC.

Solvent-free isothermal tuning of viscoelasticity of polymer materials is important for an emerging photochemical molding technology and photoreversible adhesives. In this study we designed a four-armed star-shaped poly(butyl acrylate, BA) oligomer having four coumarin end groups. The irradiation of UV at the wavelength of 365 nm (UV365) to the viscous poly(BA) oligomer under a solvent-free condition produced a solid network material along with the progress of dimerization reaction with coumarin end groups. The subsequent irradiation of UV at the wavelength of 254 nm (UV254) caused dimer dissociation reaction to attain change in the mixing degree of star and network architectures in the material. Moreover, viscoelasticity of the network material was tunable by repetitive UV365 and UV254 irradiations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

The characteristic amoeboid behavior of an oil droplet (decane with dissolved palmitic acid) on an aqueous phase containing a surfactant (stearyltrimethylammonium chloride) has been investigated and discussed. The formation and motion of assemblies of molecular aggregates were observed with the aid of a range of particle tracers. The quasi-elastic laser scattering method was employed to measure the surface tension of the aqueous phase as a function of time. From those measurements we found that the amoeboid behavior occurs in three stages. First, molecular aggregates formed at the oil-water interface and subsequently spread and absorbed at the aqueous surface thanks to a convective flow due to the Marangoni effect. In the second stage, the whole aqueous surface was saturated with those molecular aggregates and a phase transition to a liquid condensed monolayer membrane occurred. Finally, domains formed at the bottom of the oil droplet with permeable boundaries composed of branch-shaped assemblies of molecular aggregates. Blebs grew in those parts of the oil droplet rim with high accumulation of molecular aggregates.

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.

In investigations of the emergence of protocells at the origin of life, repeatable and continuous supply of molecules and ions into the closed lipid bilayer membrane (liposome) is one of the fundamental challenges. Demonstrating an abiotic process to accumulate substances into preformed liposomes against the concentration gradient can provide a clue. Here we show that, without proteins, cell-sized liposomes under hydrodynamic environment repeatedly permeate small molecules and ions, including an analogue of adenosine triphosphate, even against the concentration gradient. The mechanism underlying this accumulation of the molecules and ions is shown to involve their unique partitioning at the liposomal membrane under forced external flow in a constrained space. This abiotic mechanism to accumulate substances inside of the liposomal compartment without light could provide an energetically up-hill process for protocells as a critical step toward the contemporary cells. How small molecules could have accumulated within hypothetical protocells on the early Earth is an open question. Here automated microfluidic experiments provide evidence for abiotic accumulation of small molecules within cell-sized liposomes under hydrodynamic flow evoking a surface-mediated mechanism.

DNA is an essential carrier of sequence-based genetic information for all life today. However, the chemical and physical properties of DNA may also affect the structure and dynamics of a vesicle-based model protocell in which it is encapsulated. To test these effects, we constructed a polyethylene glycol-grafted giant vesicle system capable of undergoing growth and division. The system incorporates a specific interaction between DNA and lipophilic catalysts as well as components of PCR. We found that vesicle division depends on the length of the encapsulated DNA, and the self-assembly of an internal supramolecular catalyst possibly leads to the direct causal relationship between DNA length and the capacity of the vesicle to self-reproduce. These results may help elucidate how nucleic acids could have functioned in the division of prebiotic protocells.

Lipid-coated microbubbles (MBs) with an indocyanine green (ICG) derivative were fabricated for ultrasound and near-infrared (NIR) fluorescence dual imaging. We characterized the NIR-fluorescence intensity, stability and viscoelastic properties of the encapsulating lipid shell, focusing on the influence of the ICG derivative and lipid compositions. In terms of the NIR fluorescence intensity, the fluorescence intensity of the MBs (with the ICG derivative) was significantly affected by the lipid composition of the MB shell. Regarding the contrast agent used for ultrasound imaging, the stability of the MBs and viscoelastic properties of shell also depended on the lipid compositions, while the incorporation of the ICG derivative into the MB shells had a negligible effect. The performance of this contrast agent for ultrasound and NIR fluorescence dual-imaging exhibited a significant trade-off relationship for the lipid composition.

A tetracyanoquaterthienoquinoid (TCT4Q)-based field effect transistor is characterized by the ambipolar transfer characteristics and the facile shift of the threshold voltage induced by the bias stress. The trapping and detrapping kinetics of charge carriers was investigated in detail by the temperature dependence of the decay of source-drain current (ISD). We found a repeatable formation of a molecular floating gate is derived from a ‘charge carrier-and-gate’ cycle comprising four stages, trapping of mobile carriers, formation of a floating gate, induction of oppositely charged mobile carriers, and recombination between mobile and trapped carriers to restore the initial state.

The self-reproduction of supramolecular assemblies based on the synthesis and self-assembly of building blocks is a critical step towards the construction of chemical systems with autonomous, adaptive, and propagation properties. In this report, we demonstrate that giant vesicles can grow and produce daughter vesicles by synthesizing and incorporating phospholipids in situ from ad-hoc precursors. Our model involves acyl chain elongation via copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition reaction and the ensuing production of synthetic phospholipids to induce budding and division. In addition, the growth and budding of giant vesicles were compatible with the encapsulation and transfer of macromolecules as large as lambda phage DNA to the buds. This chemical system provides a useful model towards the implementation of cell-like compartments capable of propagation and transport of biological materials.

Repeatable topological transformation of polymers for the modulation of material functions is a challenge. We have developed a method for repeatedly resetting a cyclic macromolecular architecture to a linear architecture by photostimulation, namely, topology-reset execution (T-rex) based on the photochemistry of hexaarylbiimidazoles (HABIs). We synthesized cyclic poly(dimethylsiloxane)s (PDMSs) of various ring sizes with HABIs linked in the chains. UV irradiation of the cyclic PDMSs produced telechelic linear PDMSs with triphenylimidazolyl radical (TPIR) end groups. After termination of UV irradiation, end-to-end recyclization occurred by the recoupling of TPIRs. The cyclic PDMSs also responded to ultrasound, which decreased their molecular weight (MW) by site-specific cleavage of in-chain HABI moieties, and we are able to reset the MWs by subsequent phototriggered T-rex. Furthermore, T-rex enabled solvent-free switching of the rheological properties of the materials while retaining the liquid character of PDMS.

Although the mechanical properties and compositions of lipid bilayer membranes can change upon deformation, the fundamental relations between the composition, membrane tension and fluidity of membranes with little curvature have not yet been studied. In the current study, the membrane tension and the diffusion coefficients of free-standing black lipid membranes (BLMs), based on 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were observed by systematic control of the cholesterol concentration and the osmotic pressure with the laser-induced surface deformation (LISD) and fluorescence recovery after photobleaching (FRAP) techniques. When the osmotic pressure was raised and, therefore, the curvature became larger, both the membrane tension and the diffusion coefficients increased as well. On the other hand, when the cholesterol concentration was raised, the membrane tension increased whereas the diffusion coefficient decreased. The importance of the present results goes beyond this quantitative evaluation of the relation between the membrane tension and the fluidity, as it clarifies the changes in the fundamental properties of lipid bilayers upon natural fluctuations and perturbative deformation that were hitherto unknown.

Liposomes encapsulating cytoskeletons have drawn much recent attention to develop an artificial cell-like chemical-machinery; however, as far as we know, there has been no report showing isothermally reversible morphological changes of liposomes containing cytoskeletons because the sets of various regulatory factors, that is, their interacting proteins, are required to control the state of every reaction system of cytoskeletons. Here we focused on hydrostatic pressure to control the polymerization state of microtubules (MTs) within cell-sized giant liposomes (diameters ∼10 μm). MT is the cytoskeleton formed by the polymerization of tubulin, and cytoskeletal systems consisting of MTs are very dynamic and play many important roles in living cells, such as the morphogenesis of nerve cells and formation of the spindle apparatus during mitosis. Using real-time imaging with a high-pressure microscope, we examined the effects of hydrostatic pressure on the morphology of tubulin-encapsulating giant liposomes. At ambient pressure (0.1 MPa), many liposomes formed protrusions due to tubulin polymerization within them. When high pressure (60 MPa) was applied, the protrusions shrank within several tens of seconds. This process was repeatedly inducible (around three times), and after the pressure was released, the protrusions regenerated within several minutes. These deformation rates of the liposomes are close to the velocities of migrating or shape-changing living cells rather than the shortening and elongation rates of the single MTs, which have been previously measured. These results demonstrate that the elongation and shortening of protrusions of giant liposomes is repeatedly controllable by regulating the polymerization state of MTs within them by applying and releasing hydrostatic pressure., 細胞サイズの人工膜小胞を可逆的に繰り返し変形させられることに成功 (生体運動マシナリーを使った分子ロボット構築の可能性を実証). 京都大学プレスリリース. 2016-04-19.

The effects of halide ions on the acceptor phase in the chemical oscillation in donor/membrane/acceptor systems were examined. The transfer of cetyltrimethylammonium (CTA(+)) ions from the donor phase and their adsorption and desorption at the membrane/acceptor interface led to spontaneous, nonlinear oscillations of the electric potential. Chloride ions stabilized the adsorption of CTA(+) ions and gave rise to a large-amplitude, long-interval, and a long relaxation-time constant. On the contrary, iodide ions, which are more hydrophobic than chloride ions, demonstrated opposite results. This mechanism was proposed based on the simultaneous time-resolved measurements of the interfacial tensions at both the donor/membrane and membrane/acceptor interfaces and observation of the convective flow due to Marangoni instability.