So far stimuli‐responsive polymer gels and their application to smart materials have been widely studied; this research has contributed to progress in gel science and engineering. For their ...development as a novel biomimetic polymer, studies of polymers with an autonomous self‐oscillating function have been carried out since the first reports in 1996. The development of novel self‐oscillating polymers and gels have been successful utilizing the oscillating reaction, called the Belousov–Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self‐oscillating polymer is composed of a poly(N‐isopropylacrylamide) network in which the catalyst for the BZ reaction is covalently immobilized. In the presence of the reactants, the polymer undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes (in the case of gel) without any on–off switching of external stimuli. Potential applications of the self‐socillating polymers and gels include several kinds of functional material systems, such as biomimetic actuators and mass transport surface.
Novel self‐oscillating polymers and gels have been developed utilizing the oscillating reaction, called the Belousov–Zhabotinsky reaction. The polymer or gel undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes without any on–off switching of external stimuli. Several kinds of functional material systems utilizing self‐oscillating polymers or gel are expected; potential systems include biomimetic actuators and mass transport surfaces.
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In 1996, the author reported “self-oscillating” polymer gels that spontaneously repeat swelling–deswelling changes in a closed solution without any on–off switching by external stimuli, such as heart ...muscle. They have attracted considerable attention as a new type of gel with an autonomous function that is clearly different from conventional stimuli-responsive gels. The autonomy of the gel is provided by the design, which creates a dissipative structure in the material. The gel has an energy-conversion system involving an oscillatory chemical reaction (called the Belousov–Zhabotinsky (BZ) reaction), which allows periodic mechanical motion of the polymer chain. Since the first report, the author has systematically developed self-oscillating polymer gels from fundamental behavior to construction and demonstration of material systems for potential applications in biomimetic materials, such as autonomous soft actuators, automatic transport systems, and functional fluids exhibiting autonomous sol–gel oscillations similar to those of ameba. Recently, BZ gels with similar properties have sometimes been called “Yoshida gels”. In this review, the research developments and recent progress on self-oscillating polymer gels from the author’s group are summarized.In 1996, the author reported “self-oscillating” polymer gels that spontaneously repeat swelling–deswelling changes in a closed solution without any on–off switching by external stimuli, such as with heart muscle. The gel has an energy converting system provided by an oscillatory chemical reaction called the Belousov–Zhabotinsky (BZ) reaction, which induces periodic mechanical motion of the polymer chain. The author systematically developed self-oscillating polymer gels with approaches ranging from demonstrating fundamental behaviors to constructing material systems for potential applications in biomimetic materials such as autonomous soft actuators, automatic transport systems, and functional fluids causing autonomous sol-gel oscillations, as seen with amebas. In this review, these research developments and recent progress from the author’s group are summarized.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Himawari-8/9—a new generation of Japanese geostationary meteorological satellites-carry state-of-the-art optical sensors with significantly higher radiometric, spectral, and spatial resolution than ...those previously available in the geostationary orbit. They have 16 observation bands, and their spatial resolution is 0.5 or 1 km for visible and near-infrared bands and 2 km for infrared bands. These advantages, when combined with shortened revisit times (around 10 min for Full Disk and 2.5 min for sectored regions), provide new levels of capacity for the identification and tracking of rapidly changing weather phenomena and for the derivation of quantitative products. For example, fundamental cloud product is retrieved from observation data of Himawari-8 operationally. Based on the fundamental cloud product, Clear Sky Radiance and Atmospheric Motion Vector are processed for numerical weather prediction, and volcanic ash product and Aeolian dust product are created for disaster watching and environmental monitoring. Imageries from the satellites are distributed and disseminated to users via multiple paths, including Internet cloud services and communication satellite services.
The mevalonate pathway is a well-known metabolic route that provides biosynthetic precursors for myriad isoprenoids. An unexpected variety of the pathway has been discovered from recent studies on ...microorganisms, mainly on archaea. The most recently discovered example, called the "archaeal" mevalonate pathway, is a modified version of the canonical eukaryotic mevalonate pathway and was elucidated in our previous study using the hyperthermophilic archaeon
This pathway comprises four known enzymes that can produce mevalonate 5-phosphate from acetyl coenzyme A, two recently discovered enzymes designated phosphomevalonate dehydratase and anhydromevalonate phosphate decarboxylase, and two more known enzymes, i.e., isopentenyl phosphate kinase and isopentenyl pyrophosphate:dimethylallyl pyrophosphate isomerase. To show its wide distribution in archaea and to confirm if its enzyme configuration is identical among species, the putative genes of a lower portion of the pathway-from mevalonate to isopentenyl pyrophosphate-were isolated from the methanogenic archaeon
, which is taxonomically distant from
, and were introduced into an engineered
strain that produces lycopene, a red carotenoid pigment. Lycopene production, as a measure of isoprenoid productivity, was enhanced when the cells were grown semianaerobically with the supplementation of mevalonolactone, which demonstrates that the archaeal pathway can function in bacterial cells to convert mevalonate into isopentenyl pyrophosphate. Gene deletion and complementation analysis using the carotenogenic
strain suggests that both phosphomevalonate dehydratase and anhydromevalonate phosphate decarboxylase from
are required for the enhancement of lycopene production.
Two enzymes that have recently been identified from the hyperthermophilic archaeon
as components of the archaeal mevalonate pathway do not require ATP for their reactions. This pathway, therefore, might consume less energy than other mevalonate pathways to produce precursors for isoprenoids. Thus, the pathway might be applicable to metabolic engineering and production of valuable isoprenoids that have application as pharmaceuticals. The archaeal mevalonate pathway was successfully reconstructed in
cells by introducing several genes from the methanogenic or hyperthermophilic archaeon, which demonstrated that the pathway requires the same components even in distantly related archaeal species and can function in bacterial cells.
To realize a renewable energy society, a polymeric system for photoinduced hydrogen generation utilizing a copolymer containing an electron acceptor was designed. In this system, the redox changes of ...viologen introduced into poly(N‐isopropylacrylamide) cause cyclic conformational changes owing to the shifting of the phase transition temperature (PTT). The polymeric coil–globule transitions with hydrophilic/hydrophobic changes accelerate the electron transfer for hydrogen generation. In particular, hydrogen generation using visible‐light energy with high efficiency is achieved around the PTT. In contrast to conventional solution systems, our polymeric system enables efficient hydrogen generation in a close molecular arrangement without the aggregation of catalytic nanoparticles. The utilization of conformational changes will provide a new strategy for synthesizing artificial photosynthetic hydrogels that split water to generate both hydrogen and oxygen.
A polymeric system for photoinduced hydrogen generation utilizing a copolymer containing an electron acceptor was designed. The polymeric coil–globule transitions, with hydrophilic/hydrophobic changes, accelerate the electron transfer. In contrast to conventional solution systems, our polymeric system enables efficient hydrogen generation in a close molecular arrangement without the aggregation of catalytic nanoparticles.
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There is a growing demand for the use of machine learning (ML) to derive fast-to-evaluate surrogate models of materials properties. In recent years, a broad array of materials property databases have ...emerged as part of a digital transformation of materials science. However, recent technological advances in ML are not fully exploited because of the insufficient volume and diversity of materials data. An ML framework called “transfer learning” has considerable potential to overcome the problem of limited amounts of materials data. Transfer learning relies on the concept that various property types, such as physical, chemical, electronic, thermodynamic, and mechanical properties, are physically interrelated. For a given target property to be predicted from a limited supply of training data, models of related proxy properties are pretrained using sufficient data; these models capture common features relevant to the target task. Repurposing of such machine-acquired features on the target task yields outstanding prediction performance even with exceedingly small data sets, as if highly experienced human experts can make rational inferences even for considerably less experienced tasks. In this study, to facilitate widespread use of transfer learning, we develop a pretrained model library called XenonPy.MDL. In this first release, the library comprises more than 140 000 pretrained models for various properties of small molecules, polymers, and inorganic crystalline materials. Along with these pretrained models, we describe some outstanding successes of transfer learning in different scenarios such as building models with only dozens of materials data, increasing the ability of extrapolative prediction through a strategic model transfer, and so on. Remarkably, transfer learning has autonomously identified rather nontrivial transferability across different properties transcending the different disciplines of materials science; for example, our analysis has revealed underlying bridges between small molecules and polymers and between organic and inorganic chemistry.
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In recent years, there has been a rapid growth in the use of machine learning in material science. Conventionally, a trained predictive model describes a scalar output variable, such as ...thermodynamic, electronic, or mechanical properties, as a function of input descriptors that vectorize the compositional or structural features of any given material, such as molecules, chemical compositions, or crystalline systems. In machine learning of material data, on the other hand, the output variable is often given as a function. For example, when predicting the optical absorption spectrum of a molecule, the output variable is a spectral function defined in the wavelength domain. Alternatively, in predicting the microstructure of a polymer nanocomposite, the output variable is given as an image from an electron microscope, which can be represented as a two- or three-dimensional function in the image coordinate system. In this study, we consider two unified frameworks to handle such multidimensional or functional output regressions, which are applicable to a wide range of predictive analyses in material science. The first approach employs generative adversarial networks, which are known to exhibit outstanding performance in various computer vision tasks such as image generation, style transfer, and video generation. We also present another type of statistical modeling inspired by a statistical methodology referred to as functional data analysis. This is an extension of kernel regression to deal with functional outputs, and its simple mathematical structure makes it effective in modeling even with small amounts of data. We demonstrate the proposed methods through several case studies in materials science.
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In the field of polymer science, many kinds of polymeric material systems that show a sol-gel transition have been created. However, most systems are unidirectional stimuli-responsive systems that ...require physical signals such as a change in temperature. Here, we report on the design of a block copolymer solution that undergoes autonomous and periodic sol-gel transition under constant conditions without any on-off switching through external stimuli. The amplitude of this self-oscillation of the viscosity is about 2,000 mPa s. We also demonstrate an intermittent forward motion of a droplet of the polymer solution synchronized with the autonomous sol-gel transition. This polymer solution bears the potential to become the base for a type of slime-like soft robot that can transform its shape kaleidoscopically and move autonomously, which is associated with the living amoeba that moves forward by a repeated sol-gel transition.
Pattern formation in the reaction-diffusion systems for the ferrocyanide–iodate–sulfite reaction has been investigated. Previous studies have been conducted in a uniform medium. However, in this ...study, we reported the pattern formation in heterostructured gels with different network densities. The chemical states of the gel depend on the diffusivity, which in turn depends on the network density of the gel. Consequently, a pH pattern reflecting the heterostructured gel emerged. Furthermore, adjusting the condition produces novel patterns in the heterostructured gel.
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A large variety of synthetic vesicles has been created for potential engineering applications and as model systems which mimic living organisms. In most cases, the structure is designed to be ...thermodynamically stable. However, mimicking dynamic behaviors of living vesicles still remains undeveloped. Herein, we present a synthetic vesicle which shows autonomous disintegration–reconstruction cycles without any external stimuli and which is similar to those in living organisms, such as in the nuclear envelope and synaptic vesicles. The vesicle is composed of a diblock copolymer which has a hydrophilic and a thermosensitive segment. The thermosensitive segment includes a redox moiety that acts as a catalyst for an oscillatory chemical reaction and also controls the aggregation temperature of vesicles. Furthermore, autonomous fusion of vesicles is also observed during the cycles.
Making and breaking: Biomimetic self‐oscillating vesicles that undergo autonomous and cyclic structural changes between vesicles and unimers without any external stimuli were developed by using synthetic polymers.
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