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Self-organization by the directed migration of components within a system is an important process in many applications, such as the unidirectional migration of motor proteins for transporting items to specific sites in a cell. This manuscript describes a class of functional polymeric molecules that have a set of instructions written by specific chemical moieties. These instructions allow the functional polymeric molecules to be used for autonomous synthesis of particles: particles with both functional core–shell structure and customizable shapes are fabricated for the first time. The functional polymeric molecules direct the large-scale migration of the liquid molecules to specific sites for forming the required customized structure of the particle, thus overcoming previous challenges of fabricating this class of particles. This first synthesis of this class of particles enables the development of novel applications: the concept of shape specificity for targeting sites. Both the basic structural properties (core–shell structure and customizable shape) are used in the specific applications of targeted drug delivery and imaging. The secure physical fit due to the complementary shapes enables the particles to remain locked in position for the targeting. Polymeric molecules are first shown to be highly capable of being encoded with instructions for autonomous synthesis of structured materials.

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Aqueous liquids can be charged effectively by a number of methods for many important applications. Organic liquids, however, cannot be charged effectively by existing methods due to their low conductivities, especially the insulating nonpolar organic liquids; hence, there has not been any significant application developed based on charged organic liquids. This study describes an effective fundamental strategy for charging organic liquids, including nonpolar organic liquids: static charge is simply mixed into the liquid. Analyses suggested that the charged species are molecular ions that reside in the bulk of the liquid after charging. This method is simple and general, and the amount and polarity of charge can be flexibly tunable. The effectiveness of this method gives rise to opportunities for the development of novel applications. Charged organic droplets are manipulated for the first time by an electric field for controlling organic reactions. Particles with charge embedded in their bulk matrices are fabricated for the first time (i.e., via polymerizing the liquid monomers mixed with static charge). The charge in this novel class of bulk-charged particles is stable and permanent, especially when compared to the typical surface-charged particles. Simultaneous bulk-charged and bulk-magnetic particles are fabricated for the first time via simply mixing both the static charge and magnetic nanoparticles into the liquid monomers. These highly versatile particles are responsive to both electric and magnetic fields for practical applications.

The amount of charge of a material has always been regarded as a property (or state) of materials and can be measured precisely and specifically. This study describes for the first time a fundamental physical–chemical phenomenon in which the amount of charge of a material is actually a variable—it depends on the shape of the material. Materials are shown to have continuously variable and reversible ranges of charge states by changing their shapes. The phenomenon was general for different shapes, transformations, materials, atmospheric conditions, and methods of charging. The change in charge was probably due to a dynamic exchange of charge from the material to the surrounding atmosphere as the shape changed via the reversible ionization and deposition of air molecules. Similar changes in charge were observed for self-actuating materials that changed their shapes autonomously. This fundamental relationship between geometry and electrostatics via chemistry is important for the broad range of applications related to the charge of flexible materials.

Static charge generated by contact electrification can cause a wide range of undesirable consequences in our lives and in industry (e.g., adhesion of particles on surfaces, damage to electronics, and explosions). It has, however, been challenging to develop methods to prevent charging due to the vast types of materials that charge easily by contact electrification and the frequent changes in process and environmental conditions. The most common method is to use conductive materials for dissipating charge away; however, it is ineffective for many circumstances. Here, we propose a general and effective materials framework that involves a two-level consideration for preparing noncharging materials: (1) the variation of the proportion of a two-material composite and (2) the extent of stretching the composite material. This materials strategy is achieved by infusing particles within a stretchable bulk material. Importantly, the preparation of the noncharging surface for (1) is based on a novel fundamental mechanism that involves combining an appropriate amount of a material (e.g., the particles) that tends to charge positively with another material (e.g., the bulk material) that tends to charge negatively. This mechanism does not rely on conductivity; both the contacting materials naturally prevent the generation of static charge even when only nonconductive materials are involved. When the composite material is stretchable, the change in proportion of the surface coverage of the particles allows the charging response to be changed. Therefore, the variation in composition and stretching provide a wide two-dimensional parameter space for achieving noncharging response for the vast range of contacting materials that are used in industry and our lives. In addition, stretchability allows the composite material to flexibly adapt to changes in process and environmental conditions. This stretchable composite material was also demonstrated to be capable of preventing the adhesion of particles and separating particles of different materials.

Simple, green, and energy-efficient methods for preparing electroactive materials used to generate and store renewable energy are important for a sustainable future. In this study, we showed that noble and certain non-noble metal nanoparticles can be deposited on graphite without the aid of any reducing agent. This method of reducing metal ions to metal nanoparticles by graphite involves only one step (i.e., immersion into a solution) and one chemical (i.e., a metal salt). Hence, the method is exceedingly simple, green, and does not require any energy input. Large amounts of metal nanoparticles are generated both on the surface and deep into the bulk of graphite (∼100 μm). Despite the simplicity of this method, the metal deposited on graphite showed good electrocatalytic performance for ethanol oxidation and oxygen evolution reactions and also functioned as electrodes for supercapacitors. This method is thus ideal for preparing electrocatalytic materials and electrochemical energy storage devices due to its simplicity and environmental sustainability. The simplicity of the method is due to the inherent reducing potential of graphite (i.e., a material that is generally perceived as inert). Results from analyses showed that functionalization of the reactive edges in the regions of defects allowed the graphite to serve as a reducing agent. Increasing the amount of defects (e.g., via chemical or simple mechanical treatments) is shown to be the fundamental principle for increasing the reactivity of graphite.

Soft untethered grippers and machines are emerging fields of research due to their wide range of desirable properties and capabilities over traditional hard robots. Stimuli-responsive hydrogels are naturally soft and untethered (i.e., they respond to a signal from the environment); however, they are not used as grippers due to the weak mechanical properties of the hydrogels. This manuscript describes the fabrication of a general class of stimuli-responsive grippers that are soft and untethered. Each gripper is composed of a stimuli-responsive hydrogel with a hole in the middle for gripping onto objects and a layer of coating around its sides. Importantly, these grippers exert surprisingly large gripping forces relative to their weights—∼10 000, which is the highest reported in the literature for a gripper. This high load-to-weight ratio is unexpected because the stimuli-responsive hydrogel is soft, not tethered to any external supply of energy, and fabricated by simple methods. The approach is general: high load-to-weight ratios were achieved for both pH- and temperature-responsive hydrogels. As soft grippers, they gripped onto objects of different shapes and sizes easily. A class of soft untethered machines can be fabricated by assembling these soft grippers with different modular blocks of stimuli-responsive hydrogels for performing complex operations.

Static charge on surfaces of materials is generated when two solid surfaces come into contact and are then separated. It is important to understand the phenomenon because the influence of static charge on surfaces is widely felt in our daily lives and can have a wide range of applications or undesirable effects in industry. Although the phenomenon has been observed since antiquity, the fundamental mechanism that underlies the generation of charge on insulating surfaces is still not known. After many decades of research, different mechanisms have been proposed, including electron and ion transfer. One other possibility has been discussed to a lesser extent: material transfer (i.e., the transfer of quantities of charged materials). This study seeks to investigate the significance of material transfer by correlating the amount of charge transferred and the amount of material transferred from one surface to another after contact. The investigation involved varying the degree of softness of a polymer (polydimethylsiloxane; PDMS), contact-charging it against another reference material, and analyzing the surfaces of the materials after contact. Results showed that when more material transferred, more charge was generated. An explanation for these results is that the surface of PDMS experienced heterolytic cleavage of bonds, which resulted in the generation of charge. When more cleavage of bonds occurred, more charge was generated, and more materials were transferred. Hence, material transfer seems to have an important contribution for the generation of charge by contact.

Surface charge on materials is important due to its wide range of consequences and applications in many industries (e.g., semiconductor). One important parameter needed for the design of devices and selection of materials is the polarity of charge of solid surfaces after the surfaces are charged by contact electrification. Currently, it is only known that one surface charges positively, whereas the other surface charges negatively after contact (i.e., in accordance to the law of conservation of charge). This manuscript describes a previously unreported anomalous charging behavior of a general class of materials: the inorganic materials. Both contacting inorganic materials charged either both positively (e.g., mica and NaCl) or both negatively (e.g., quartz and CaF2). A close monitoring of the charge in real time showed that charge was conserved immediately after contact; however, an active interaction of the separated surfaces and the surrounding atmosphere unexpectedly changed the polarity of one surface rapidly (e.g., 1 s), thus resulting in both positively or both negatively charged surfaces. This anomalous charging behavior fundamentally changes our understanding of the design of devices related to contact electrification of inorganic materials and the triboelectric series.

Nanostructured electrodes are at the forefront of advanced materials research, and have been studied extensively in the context of their potential applications in energy storage and conversion. Here, we report on the properties of core–shell (gold-polypyrrole) hybrid nanowires and their suitability as electrodes in electrochemical capacitors and as electrocatalysts. In general, the specific capacitance of electrochemical capacitors can be increased by faradaic reactions, but their charge transfer resistance impedes charge transport, decreasing the capacitance with increasing charge/discharge rate. The specific capacitance of the hybrid electrodes is enhanced due to the pseudocapacitance of the polypyrrole shells; moreover, the electrodes operate as an ideal capacitive element and maintain their specific capacitance even at fast charge/discharge rates of 4690 mA/cm3and 10 V/s. These rates far exceed those of other types of pseudocapacitors, and are even superior to electric double layer-based supercapacitors. The mechanisms behind these fast charge/discharge rates are elucidated by electrochemical impedance spectroscopy, and are ascribed to the reduced internal resistance associated with the fast charge transport ability of the gold nanowire cores, low ionic resistance of the polypyrrole shells, and enhanced electron transport across the nanowire’s junctions. Furthermore, the hybrid electrodes show great catalytic activity for ethanol electro-oxidation, comparable to bare gold nanowires, and the surface activity of gold cores is not affected by the polypyrrole coating. The electrodes exhibit improved stability for electrocatalysis during potential cycling. This study demonstrates that the gold-polypyrrole hybrid electrodes can store and deliver charge at fast rates, and that the polypyrrole shells of the nanowires extend the catalytic lifetime of the gold cores.

Static charge generated by contact electrification on surfaces can lead to many undesirable consequences such as a reduction in the efficiency of manufacturing processes, damage to equipment, and explosions. However, it is extremely challenging to avoid contact electrification because it is ubiquitous: almost all types of materials charge on contact. Here, we coated materials with naturally occurring polydopamine (PDA) and tannic acid (TA) for preparing noncharging surfaces. Importantly, these coatings are very versatile and can be coated on a wide range of materials, including metals, inorganic materials, semiconductors, and polymers. Once coated, the amount of charge generated was found to reduce dramatically at different humidities. The reduction in charge may be due to the radical-scavenging property of PDA and TA. This simple general approach is ideal for coating the vast variety of materials that need to resist charging by contact electrification.

Insensitivity: A series of molecules containing a common head group and body as well as structurally varied tail groups (‐R) has been used in junctions with the structure Ag/S(CH2)4CONH(CH2)2R//Ga2O3/EGaIn to study the rates of charge transport by tunneling. Changing the structure of R over a range of common aliphatic, aromatic, and heteroaromatic organic groups was found to not significantly influence the rate of tunneling (see plots; the dashed lines represent calibration standards).

Unempfindlich: Eine Serie von Molekülen mit gleicher Kopfgruppe und Kohlenstoffkette, aber unterschiedlichen Endgruppen R wurde in Kontakten vom Typ Ag/S(CH2)4CONH(CH2)2R//Ga2O3/EGaIn eingesetzt (siehe Bild), um die Geschwindigkeit des Ladungstransports durch Tunneln zu studieren. Ein Variieren zwischen aliphatischen, aromatischen und heteroaromatischen R hatte keinen signifikanten Einfluss auf die Tunnelgeschwindigkeit.

Hatte Thales Recht?Entgegen früheren Berichten kann es ohne Wasser zu einer Kontaktelektrifizierung kommen. Zugleich hilft Wasser, die entwickelten Ladungen zu stabilisieren. Wasserfreie Bedingungen wurden gewährleistet, indem alle Schritte unter Öl durchgeführt wurden.

Was Thales right about water?Contrary to previous reports, contact charging can occur in the absence of water. At the same time, water helps stabilize the developed charges. Water‐free conditions are realized by performing all experiments and charge measurements under oil‐immersion.

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Echt stark!Kern‐Schale‐ und Nanopartikelkristalle detektieren chemische und enzymatische Analyte mit einem verstärkten Mess‐Signal. Die Kristalle werden dabei zunächst wasserunlöslich gemacht, indem ihre Oberfläche mit Dithiolen vernetzt wird, die analytspezifische Gruppen tragen. Bei Zugabe des Analyten werden diese Gruppen gespalten, woraufhin die Kristalle Millionen intensiv farbiger Nanopartikel freisetzen (siehe Bild).

Chemical reactions make cells work only if the participating chemicals are delivered to desired locations in a timely and precise fashion. Most research to date has focused on activetransport mechanisms, although passive diffusion is often equally rapid and energetically less costly. Capitalizing on these advantages, cells have developed sophisticated reactiondiffusion RD systems that control a wide range of cellular functions—from chemotaxis and cell division, through signaling cascades and oscillations, to cell motility. These apparently diverse systems share many common features and are “wired” according to “generic” motifs such as nonlinear kinetics, autocatalysis, and feedback loops. Understanding the operation of these complex biochemical systems requires the analysis of pertinent transportkinetic equations or, at least on a qualitative level, of the characteristic times of the constituent subprocesses. Therefore, in reviewing the manifestations of cellular RD, we also describe basic theory of reactiondiffusion phenomena.

Chemische Reaktionen können Zellen nur am Leben erhalten, wenn die beteiligten Verbindungen an den erforderlichen Stellen zeitlich präzise angeliefert werden. Die meisten Forschungen haben sich bislang auf aktive Transportmechanismen konzentriert, obwohl die passive Diffusion oft gleich schnell ist und weniger Energie erfordert. Um die Vorteile dieser Transportform zu nutzen, haben die Zellen ausgeklügelte Reaktions‐Diffusions(RD)‐Systeme entwickelt, die zahlreiche zelluläre Funktionen kontrollieren – von Chemotaxis und Zellteilung über Signalkaskaden und ‐oszillationen bis hin zur Zellbeweglichkeit. Diese nur scheinbar unterschiedlichen Systeme sind nach allgemeinen Prinzipien aufgebaut und haben viele Gemeinsamkeiten. Wiederkehrende Elemente sind nichtlineare Kinetik, Autokatalyse und Rückkopplungsschleifen. Um die Funktion dieser komplexen (bio)chemischen Systeme zu verstehen, muss man die Transportkinetik‐Gleichungen analysieren oder die charakteristischen Zeiten der Teilprozesse zumindest qualitativ betrachten. Während wir Beispiele für zelluläre RD‐Systeme vorstellen, versuchen wir daher auch, den Leser mit den theoretischen Grundlagen der RD‐Phänomene vertraut zu machen.

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Using particles with different functionalities for treating cancer has many advantages over other methods (for example, better access to remote parts of the body); however, current chemical (for example, chemotherapy) and biological (for example, immunotherapy) methods still face many challenges. Here, we describe a fundamentally different approach: using the physical force of an expanding stimuli-responsive hydrogel to rupture cancer cells attached on its surface. Specifically, we coated temperature-responsive hydrogels with a layer of cell-adherent arginine-glycine-aspartate (RGD) peptides. The approach involved first allowing cancer cells to attach onto the surface of the hydrogels, and then applying a change in temperature. As the hydrogel underwent a chemical transformation and expanded due to the stimulus, the cancer cells attached to it ruptured. The results from staining the cells with trypan blue, observing them using SEM, and analyzing them using the MTT assay showed that both breast and lung cancer cells died after the hydrogel expanded; hence, we showed that this physical force from the expanding hydrogel is strong enough to rupture the cancer cells. In addition, the force derived from the expanding hydrogel was determined separately to be larger than that needed to rupture typical cells. This physical approach is conceptually simple, technically easy to implement, and potentially generalizable for rupturing a wide range of cells.

Review: cellular reaction‐diffusion systems, prokaryotes, eukaryotes, theory; 294 refs.

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