Electrically Fueled Active Supramolecular Materials

Harnessing the Hofmeister Effect for Dynamic Self-Assembly of Supramolecular Hydrogels

Dynamic regulation of intermolecular interactions is essential for the creation of dynamic supramolecular materials with lifelike self-regulating functions. Yet specific ion effect, which is known to possess potent effect on intermolecular interactions, has remained unexplored for such a purpose. Here, we demonstrate our access to dynamic self-assembly of supramolecular hydrogels by orchestrating the Hofmeister effect through a simple enzymatic reaction. The involved gelators containing carboxylate moieties self-assemble into hydrogel (Gel1) at acidic pH and dissolve at basic pH. We surprisingly find that the dissolved gelators at basic pH can be driven to self-assemble into hydrogel (Gel2) by kosmotropic ions through the disruption of gelator-water interactions. By coupling to the enzymatic hydrolysis of urea, Gel1 gradually disintegrates over time because of the production of basic NH3. However, interestingly, with the accumulation of kosmotropic ions, NH4 + and CO3 2-, the dissolved gelators are driven to self-assemble into Gel2, realizing a self-regulating gel-sol-gel transition process. The transition rate and stiffness of Gel2 are tunable by adjusting the concentrations of urea or urease. This work may shed light on the creation of lifelike self-regulating supramolecular materials using Hofmeister effect for many enticing applications such as ion-programmed biosensing and drug delivery.

Chemically-fueled phase transition of a redox-responsive polymer

In living systems, dynamic biomacromolecular assemblies are driven and regulated by energy dissipative chemical reaction networks, enabling various autonomous functions. Inspired by this biological principle, we report a chemically-fueled phase transition of a poly(N-isopropylacrylamide) (PNIPAAm)-based polymer bearing viologen units (P(NIPAAm-V)), wherein redox changes drive coil-to-globule phase transitions. Upon the addition of a reducing agent, viologen moieties in P(NIPAAm-V) are converted into their reduced state, resulting in enhanced hydrophobicity and polymer aggregation. Coexistence of a platinum catalyst couples these redox-driven structural changes to hydrogen evolution, which oxidizes the viologen radicals, thus restoring the polymer chains to their hydrated random coil state. As a result, transient polymer assemblies form and subsequently disassemble upon depletion of the reducing agent, leading to a temporally controlled out-of-equilibrium phase transition. Moreover, by tuning the platinum concentration and reaction temperature, we achieve precise control of both the size and lifetime of these assemblies. Notably, viologen moieties constitute only about 1% of the polymer repeating units, underscoring that chemically-fueled phase transition is efficient strategy for dynamically regulating molecular assemblies. These findings demonstrate that chemically-fueled phase transitions in redox-responsive polymers offer a promising blueprint for designing dynamic, biomimetic materials capable of spatiotemporally regulated structural transformations.

An Autonomously Liquefied Hydrogel Adhesive for Programmable Bioelectronic Interface

Hydrogel adhesives have many important applications in the fields of drug delivery, regenerative medicine, and bioelectronics. The detachment of hydrogel adhesives under the benign conditions is vital to the definitive surgical repair and implanted devices. Although stimuli-mediated detachment of hydrogel adhesives has been achieved, it is still a grand challenge to develop a transient adhesive with programmable adhesion and autonomous detachment from the substrate, especially the hairy skins. Here, we report a transient hydrogel adhesive driven by antagonistic enzyme reaction networks for programmable bioelectronic interface. The transient hydrogel shows tunable mechanical properties, adjustable adhesive strength, and autonomous sol-gel-sol transition with a programmable lifetime. Moreover, the transient hydrogel adhesive enables conformable and stable adhesion to various materials. In particular, the bioelectrode coated by the transient hydrogel adhesive allows to record stable and high-quality electromyogram, electrocardiogram, and electroencephalogram signals directly on the hairy skins without hair shaving. Notably, the autonomous liquefication of the hydrogel adhesives enables the easy removal of bioelectrode from hairy skins after usage without any noticeable damages to the hairy skins and electrode. This work paves a new avenue in the innovative development of hydrogel adhesives for the conformable and detachable bioelectronic interface.

Heterogeneously catalyzed supramolecular polymerization: essential roles of nucleation and fragmentation-induced autocatalysis in chiral transfer

The complexity of multi-component molecular assembly demands precise control strategies to enhance both efficiency and selectivity. Heterogeneous nucleation and the autocatalytic secondary pathway, as key regulatory strategies, have attracted widespread attention for their crucial roles in crystal growth and amyloid protein aggregation. Here, we apply a heterogeneous nucleation strategy to supramolecular polymer systems and report the first direct observation of surface-enrichment-induced primary nucleation and a spontaneous fragmentation-driven autocatalytic secondary process. A heterogeneous nucleating agent promotes primary nucleation, facilitating supramolecular chiral induction. The resulting chiral polymers undergo a catalytic cycle of fragmentation and re-growth at their termini, with the fragments also acting as seeds for nucleation and growth. These pathways play a crucial role in the polymerization process and are essential for chiral transfer and asymmetry amplification, enabling the achievement of maximum enantioselectivity with as little as 0.5% molar equivalent of the heterogeneous nucleating agent. Furthermore, we reveal the existence of an optimal equivalent in their catalytic kinetics, arising from a surface assembly mechanism. In this mechanism, monomers adsorbed on the surface of the heterogeneous nucleating agent assemble with those in solution, rather than through surface diffusion and assembly. This process resembles the surface-catalyzed Eley-Rideal mechanism. Our study highlights the potential of heterogeneous nucleation as an effective strategy for controlling supramolecular polymerization and offers new insights into its underlying mechanism.

Cryogenic Electron Microscopy Informed Molecular Dynamics Simulations to Investigate the Disulfide Hydrogel Self-Assembly

Disulfide hydrogels, derived from cysteine-based redox systems, exhibit active self-assembly properties driven by reversible disulfide bond formation, making them a versatile platform for dynamic material design. Detailed cryogenic electron microscopy (cryo-EM) analysis reveals a consistent fiber diameter of 5.4 nm for individual fibers. Using cryo-EM-informed radial positional restraints, all-atom molecular dynamics (MD) simulations are employed to reproduce fibers with dimensions closely matching experimental observations, validated further through simulated cryo-EM images. The MD simulations reveal that the disulfide gelator (CSSC) predominantly adopts an open conformation, with hydrogen bonds emerging as the key intermolecular force stabilizing the fibers. Notably, intermolecular interactions are found to be higher at 70% conversion to the disulfide gelator compared with 100%, comparable with past unrestrained simulations. Water molecules and solute-water hydrogen bonds are present throughout the fiber, indicating that the fiber remains hydrated. These findings underscore the potential role of the thiol precursor CSH in stabilizing the transient phase and highlight the importance of CSH-CSSC interplay. Herein, it provides novel insights into molecular mechanisms governing active self-assembly and offers strategies for designing tunable materials through controlled assembly conditions.

Transient colloidal crystals fueled by electrochemical reaction products

Conventional electric field directed colloidal assembly enables fabricating ordered structures but lacks temporal control over assembly state. Chemical reaction networks have been discovered that transiently assemble colloids; however, they have slow dynamics (hrs - days) and poor temporal tunability, utilize complex reagents, and produce kinetically trapped states. Here we demonstrate transient colloidal crystals that autonomously form, breakup, and reconstitute in response to an electrochemical reaction network driven by a time invariant electrical stimulus. Aqueous mixtures of micron sized colloids and para-benzoquinone (BQ) were subjected to superimposed oscillatory and steady electric potentials, i.e., multimode potentials, that induce electrokinetic flows around colloids and proton-coupled BQ redox reactions. Transient assembly states coincided with electrochemically generated pH spikes near the cathode. We demonstrate wide tunability of transient assembly state lifetimes over two orders of magnitude by modifying the electric potential and electrode separation. An electrochemical transport model showed that interaction of advancing acidic and alkaline pH fronts from anodic BQ oxidation and cathodic BQ reduction caused pH transients. We present theoretical and experimental evidence that indicates transient colloidal crystals were mediated by competition between opposing colloidal scale electrohydrodynamic and electroosmotic flows, the latter of which is pH dependent.

Light-Mediated Interconversion between a Foldamer and a Self-Replicator

Self-replicating molecules and well-defined folded macromolecules are of great significance in the emergence and evolution of life. How they may interconnect and affect each other remains largely elusive. Here, we demonstrate an abiotic system where a single building block can oligomerize to yield either a self-replicating molecule or a foldamer. Specifically, agitation of a disulfide-based dynamic combinatorial library at moderately elevated pH channels it selectively into a self-replicating hexamer assembled into fibers, after passing through a period where a 15-subunit macrocyclic foldamer existed transiently. Without mechanoagitation or at lower pH, the formation of hexamer fiber is suppressed, resulting in the accumulation of the 15mer foldamer. Foldamer and self-replicator can be interconverted in response to external stimuli, including agitation and a change in pH. Furthermore, upon the addition of a photoacid, the pH of the medium can be controlled by irradiation, driving the switching between replicator and foldamer and allowing a dissipative out-of-equilibrium state to be accessed, using light as a source of energy.

Microfluidic-Assisted Self-Assembly of Molecular Hydrogelator at Water-Water Interfaces for Continuous Fabrication of Supramolecular Microcapsules

Control over the self-assembly of small molecules at specific areas is of great interest for many high-tech applications, yet remains a formidable challenge. Here, how the self-assembly of hydrazone-based molecular hydrogelators can be specifically triggered at water-water interfaces for the continuous fabrication of supramolecular microcapsules by virtue of the microfluidic technique is demonstrated. The non-assembling hydrazide- and aldehyde-based hydrogelator precursors are distributed in two immiscible aqueous polymer solutions, respectively, through spontaneous phase separation. In the presence of catalysts, hydrazone-based hydrogelators rapidly form and self-assemble into hydrogel networks at the generated water-water interfaces. Relying on the microfluidic technique, microcapsules bearing a shell of supramolecular hydrogel are continuously produced. The obtained microcapsules can effectively load enzymes, enabling localized enzymatic growth of supramolecular fibrous supramolecular structures, reminiscent of the self-assembly of biological filaments within living cells. This work may contribute to the development of biomimetic supramolecular carriers for applications in biomedicine and fundamental research, for instance, the construction of protocells.

Chemical Reaction Steers Spatiotemporal Self-Assembly of Supramolecular Hydrogels

Supramolecular structures are widespread in living system, which are usually spatiotemporally regulated by sophisticated metabolic processes to enable vital biological functions. Inspired by living system, tremendous efforts have been made to realize spatiotemporal control over the self-assembly of supramolecular materials in synthetic scenario by coupling chemical reaction with molecular self-assembly process. In this review, we focused on the works related to supramolecular hydrogels that are regulated in space and time using chemical reaction. Firstly, we summarized how spatially controlled self-assembly of supramolecular hydrogels can be achieved via chemical reaction-instructed self-assembly, and the application of such a self-assembly methodology in biotherapy was discussed as well. Second, we reviewed dynamic supramolecular hydrogels dictated by chemical reaction networks that can evolve their structures and properties against time. Third, we discussed the recent progresses in the control of the self-assembly of supramolecular hydrogels in both space and time though a reaction-diffusion-coupled self-assembly approach. Finally, we provided a perspective on the further development of spatiotemporally controlled supramolecular hydrogels using chemical reaction in the future.

Non-equilibrium self-assembly for living matter-like properties

The soft and wet machines of life emerged as the spatially enclosed ensemble of biomolecules with replicating capabilities integrated with metabolic reaction cycles that operate at far-from-equilibrium. A thorough step-by-step synthetic integration of these elements, namely metabolic and replicative properties all confined and operating far-from-equilibrium, can set the stage from which we can ask questions related to the construction of chemical-based evolving systems with living matter-like properties - a monumental endeavour of systems chemistry. The overarching concept of this Review maps the discoveries on this possible integration of reaction networks, self-reproduction and compartmentalization under non-equilibrium conditions. We deconvolute the events of reaction networks and transient compartmentalization and extend the discussion towards self-reproducing systems that can be sustained under non-equilibrium conditions. Although enormous challenges lie ahead in terms of molecular diversity, information transfer, adaptation and selection that are required for open-ended evolution, emerging strategies to generate minimal metabolic cycles can extend our growing understanding of the chemical emergence of the biosphere of Earth.

Guiding Transient Peptide Assemblies with Structural Elements Embedded in Abiotic Phosphate Fuels

Despite great progress in the construction of non-equilibrium systems, most approaches do not consider the structure of the fuel as a critical element to control the processes. Herein, we show that the amino acid side chains (A, F, Nal) in the structure of abiotic phosphates can direct assembly and reactivity during transient structure formation. The fuels bind covalently to substrates and subsequently influence the structures in the assembly process. We focus on the ways in which the phosphate esters guide structure formation and how structures and reactivity cross regulate when constructing assemblies. Through the chemical functionalization of energy-rich aminoacyl phosphate esters, we are able to control the yield of esters and thioesters upon adding dipeptides containing tyrosine or cysteine residues. The structural elements around the phosphate esters guide the lifetime of the structures formed and their supramolecular assemblies. These properties can be further influenced by the peptide sequence of substrates, incorporating anionic, aliphatic and aromatic residues. Furthermore, we illustrate that oligomerization of esters can be initiated from a single aminoacyl phosphate ester incorporating a tyrosine residue (Y). These findings suggest that activated amino acids with varying reactivity and energy contents can pave the way for designing and fabricating structured fuels.

Enzymatic Reaction-Coupled, Cooperative Supramolecular Polymerization

Nature employs sophisticated mechanisms to precisely regulate self-assembly and functions within biological systems, exemplified by the formation of cytoskeletal filaments. Various enzymatic reactions and auxiliary proteins couple with the self-assembly process, meticulously regulating the length and functions of resulting macromolecular structures. In this context, we present a bioinspired, reaction-coupled approach for the controlled supramolecular polymerization in synthetic systems. To achieve this, we employ an enzymatic reaction that interfaces with the adenosine triphosphate (ATP)-templated supramolecular polymerization of naphthalene diimide monomers (NSG). Notably, the enzymatic production of ATP (template) plays a pivotal role in facilitating reaction-controlled, cooperative growth of the NSG monomers. This growth process, in turn, provides positive feedback to the enzymatic production of ATP, creating an ideal reaction-coupled assembly process. The success of this approach is further evident in the living-growth characteristic observed during seeding experiments, marking this method as the pioneering instance where reaction-coupled self-assembly precisely controls the growth kinetics and structural aspects of supramolecular polymers in a predictive manner, akin to biological systems.

Observing the Dynamics of an Electrochemically Driven Active Material with Liquid Electron Microscopy

Electrochemical liquid electron microscopy has revolutionized our understanding of nanomaterial dynamics by allowing for direct observation of their electrochemical production. This technique, primarily applied to inorganic materials, is now being used to explore the self-assembly dynamics of active molecular materials. Our study examines these dynamics across various scales, from the nanoscale behavior of individual fibers to the micrometer-scale hierarchical evolution of fiber clusters. To isolate the influences of the electron beam and electrical potential on material behavior, we conducted thorough beam-sample interaction analyses. Our findings reveal that the dynamics of these active materials at the nanoscale are shaped by their proximity to the electrode and the applied electrical current. By integrating electron microscopy observations with reaction-diffusion simulations, we uncover that local structures and their formation history play a crucial role in determining assembly rates. This suggests that the emergence of nonequilibrium structures can locally accelerate further structural development, offering insights into the behavior of active materials under electrochemical conditions.

Electrically Powered Dissipative Hydrogel Networks Reveal Transient Stiffness Properties for Out-of-Equilibrium Operations

Living systems use dissipative processes to enable precise spatiotemporal control over various functions, including the transient modulation of the stiffness of tissues, which, however, is challenging to achieve in soft materials. Here, we report a new platform to program hydrogel films with tunable, time-dependent mechanical properties under out-of-equilibrium conditions, powered by electricity. We show that the lifetime of the transient network of a surface-confined hydrogel film can be effectively controlled by programming the generation of an electrochemically oxidized mediator in the presence of a chemical or photoreducing agent in solution. It is, therefore, electrically possible to direct the transient stiffening or softening of the hydrogel film, enabling high modularity of the material functions with precise spatiotemporal control. Temporally controlled operations of the hydrogel films are demonstrated for the on-demand, dose-controlled release of multiple model protein payloads from electrode arrays using the present electrically powered dissipative system. This demonstration of electrically driven transient modulation of the stiffness properties of hydrogel films represents an important step toward the engineering of dissipative materials for developing future biomedical applications that can harness the temporal, adaptive properties of this new class of materials.

Emergence of Dynamic Instability by Hybridizing Synthetic Self-Assembled Dipeptide Fibers with Surfactant Micelles

Supramolecular chemistry currently faces the challenge of controlling nonequilibrium dynamics such as the dynamic instability of microtubules. In this study, we explored the emergence of dynamic instability through the hybridization of peptide-type supramolecular nanofibers with surfactant micelles. Using real-time confocal imaging, we discovered that the addition of micelles to nanofibers induced the simultaneous but asynchronous growth and shrinkage of nanofibers during which the total number of fibers decreased monotonically. This dynamic phenomenon unexpectedly persisted for 6 days and was driven not by chemical reactions but by noncovalent supramolecular interactions between peptide-type nanofibers and surfactant micelles. This study demonstrates a strategy for inducing autonomous supramolecular dynamics, which will open up possibilities for developing soft materials applicable to biomedicine and soft robotics.

Correlating electrochemical stimulus to structural change in liquid electron microscopy videos using the structural dissimilarity metric

In-situ liquid cell transmission electron microscopy (LCTEM) with electrical biasing capabilities has emerged as an invaluable tool for directly imaging electrode processes with high temporal and spatial resolution. However, accurately quantifying structural changes that occur on the electrode and subsequently correlating them to the applied stimulus remains challenging. Here, we present structural dissimilarity (DSSIM) analysis as segmentation-free video processing algorithm for locally detecting and quantifying structural change occurring in LCTEM videos. In this study, DSSIM analysis is applied to two in-situ LCTEM videos to demonstrate how to implement this algorithm and interpret the results. We show DSSIM analysis can be used as a visualization tool for qualitative data analysis by highlighting structural changes which are easily missed when viewing the raw data. Furthermore, we demonstrate how DSSIM analysis can serve as a quantitative metric and efficiently convert 3-dimensional microscopy videos to 1-dimenional plots which makes it easy to interpret and compare events occurring at different timepoints in a video. In the analyses presented here, DSSIM is used to directly correlate the magnitude and temporal scale of structural change to the features of the applied electrical bias. ImageJ, Python, and MATLAB programs, including a user-friendly interface and accompanying documentation, are published alongside this manuscript to make DSSIM analysis easily accessible to the scientific community.

Multiscale Molecular Dynamics Simulations of an Active Self-Assembling Material

Inspired by the adaptability observed in biological materials, self-assembly processes have attracted significant interest for their potential to yield novel materials with unique properties. However, experimental methods have often fallen short in capturing the molecular details of the assembly process. In this study, we employ a multiscale molecular dynamics simulation approach, complemented by NMR quantification, to investigate the mechanism of self-assembly in a redox-fueled bioinspired system. Contrary to conventional assumptions, we have uncovered a significant role played by the monomer precursor in the assembly process, with its presence varying with concentration and the extent of conversion of the monomer to the dimer. Experimental confirmation through NMR quantification underscores the concentration-dependent incorporation of monomers into the fibrous structures. Furthermore, our simulations also shed light on the diverse intermolecular interactions, including T-shaped and parallel π stacking, as well as hydrogen bonds, in stabilizing the aggregates. Overall, the open conformation of the dimer is preferred within these aggregates. However, inside the aggregates, the distribution of conformations shifts slightly to the closed conformation compared to on the surface. These findings contribute to the growing field of bioinspired materials science by providing valuable mechanistic and structural insights to guide the design and development of self-assembling materials with biomimetic functionalities.

Pumping Small Molecules Selectively through an Energy-Assisted Assembling Process at Nonequilibrium States

In living organisms, precise control over the spatial and temporal distribution of molecules, including pheromones, is crucial. This level of control is equally important for the development of artificial active materials. In this study, we successfully controlled the distribution of small molecules in the system at nonequilibrium states by actively transporting them, even against the apparent concentration gradient, with high selectivity. As a demonstration, in the aqueous solution of acid orange (AO7) and TMC10COOH, we found that AO7 molecules can coassemble with transient anhydride (TMC10CO)2O to form larger assemblies in the presence of chemical fuel 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide hydrochloride (EDC). This led to a decrease in local free AO7 concentration and caused AO7 molecules from other locations in the solution to move toward the assemblies. Consequently, AO7 accumulates at the location where EDC was injected. By continuously injecting EDC, we could maintain a stable high value of the apparent AO7 concentration at the injection point. We also observed that this process which operated at nonequilibrium states exhibited high selectivity.

Cell-Like Synthetic Supramolecular Soft Materials Realized in Multicomponent, Non-/Out-of-Equilibrium Dynamic Systems

Living cells are complex, nonequilibrium supramolecular systems capable of independently and/or cooperatively integrating multiple bio-supramolecules to execute intricate physiological functions that cannot be accomplished by individual biomolecules. These biological design strategies offer valuable insights for the development of synthetic supramolecular systems with spatially controlled hierarchical structures, which, importantly, exhibit cell-like responses and functions. The next grand challenge in supramolecular chemistry is to control the organization of multiple types of supramolecules in a single system, thus integrating the functions of these supramolecules in an orthogonal and/or cooperative manner. In this perspective, the recent progress in constructing multicomponent supramolecular soft materials through the hybridization of supramolecules, such as self-assembled nanofibers/gels and coacervates, with other functional molecules, including polymer gels and enzymes is highlighted. Moreover, results show that these materials exhibit bioinspired responses to stimuli, such as bidirectional rheological responses of supramolecular double-network hydrogels, temporal stimulus pattern-dependent responses of synthetic coacervates, and 3D hydrogel patterning in response to reaction-diffusion processes are presented. Autonomous active soft materials with cell-like responses and spatially controlled structures hold promise for diverse applications, including soft robotics with directional motion, point-of-care disease diagnosis, and tissue regeneration.

CryoEM reveals the complex self-assembly of a chemically driven disulfide hydrogel

Inspired by the adaptability of biological materials, a variety of synthetic, chemically driven self-assembly processes have been developed that result in the transient formation of supramolecular structures. These structures form through two simultaneous reactions, forward and backward, which generate and consume a molecule that undergoes self-assembly. The dynamics of these assembly processes have been shown to differ from conventional thermodynamically stable molecular assemblies. However, the evolution of nanoscale morphologies in chemically driven self-assembly and how they compare to conventional assemblies has not been resolved. Here, we use a chemically driven redox system to separately carry out the forward and backward reactions. We analyze the forward and backward reactions both sequentially and synchronously with time-resolved cryogenic transmission electron microscopy (cryoEM). Quantitative image analysis shows that the synchronous process is more complex and heterogeneous than the sequential process. Our key finding is that a thermodynamically unstable stacked nanorod phase, briefly observed in the backward reaction, is sustained for ∼6 hours in the synchronous process. Kinetic Monte Carlo modeling show that the synchronous process is driven by multiple cycles of assembly and disassembly. The collective data suggest that chemically driven self-assembly can create sustained morphologies not seen in thermodynamically stable assemblies by kinetically stabilizing transient intermediates. This finding provides plausible design principles to develop and optimize supramolecular materials with novel properties.

Solvent-Induced Transient Self-Assembly of Peptide Gels: Gelator-Solvent Reactions and Material Properties Correlation

Herein, we introduce a new methodology for designing transient organogels that offers tunability of the mechanical properties simply by matching the protective groups of the precursor to that of the solvent. We developed solvent-induced transient materials in which the solvent chemically participates in a set of reactions and actively supports the assembly event. The activation of a single precursor by an acid (accelerator) yields the formation of two distinct gelators and induces gelation. The interconversion cycle is supplied by the secondary solvent (originating from hydrolysis of the primary solvent by the accelerator), which then progressively solubilizes the gel network. We show that this gelation method offers a direct correlation between the mechanical and transient properties by modifying the chemical structure of the precursors and the presence of an accelerator in the system. Such a method paves the way for the design of self-abolishing and mechanically tunable materials for targeted purposes. The biocompatibility and versatility of amino acid-based gelators can offer a wide range of biomaterials for applications requiring a controllable and definite lifetime such as drug delivery platforms exhibiting a burst release or self-abolishing cell culture substrates.

Controllable and Reversible Assembly of Nanofiber from Natural Macromolecules via Protonation and Deprotonation

Nanofiber is the critical building block for many biological systems to perform various functions. Artificial assembly of molecules into nanofibers in a controllable and reversible manner will create "smart" functions to mimic those of their natural analogues and fabricate new functional materials, but remains an open challenge especially for nature macromolecules. Herein, the controllable and reversible assembly of nanofiber (CSNF) from natural macromolecules with oppositely charged groups are successfully realized by protonation and deprotonation of charged groups. By controlling the electrostatic interaction via protonation and deprotonation, the size and morphology of the assembled nanostructures can be precisely controlled. A strong electrostatic interaction contributes to large nanofiber with high strength, while poor electrostatic interaction produces finer nanofiber or nanoparticle. And especially, the assembly, disassembly, and reassembly of the nanofiber occurs reversibly through protonation and deprotonation, thereby paving a new way for precisely controlling the assembly process and structure of nanofiber. The reversible assembly allows the nanostructure to dynamically reorganize in response to subtle perturbation of environment. The as-prepared CSNF is mechanical strong and can be used as a nano building block to fabricate high-strength film, wire, and straw. This study offers many opportunities for the biomimetic synthesis of new functional materials.

Bio-Inspired Far-From-Equilibrium Hydrogels: Design Principles and Applications

Inspired from dynamic living systems that operate under out-of-equilibrium conditions in biology, developing supramolecular hydrogels with self-regulating and autonomously dynamic properties to further advance adaptive hydrogels with life-like behavior is important. This review presents recent progress of bio-inspired supramolecular hydrogels out-of-equilibrium. The principle of out-of-equilibrium self-assembly for creating bio-inspired hydrogels is discussed. Various design strategies have been identified, such as chemical-driven reaction cycles with feedback control and physically oscillatory systems. These strategies can be coupled with hydrogels to achieve temporal and spatial control over structural and mechanical properties as well as programmable lifetime. These studies open up huge opportunities for potential applications, such as fluidic guidance, information storage, drug delivery, actuators and more. Finally, we address the challenges ahead of us in the coming years, and future possibilities and prospects are identified.

Artificial Molecular Ratchets: Tools Enabling Endergonic Processes

Non-equilibrium chemical systems underpin multiple domains of contemporary interest, including supramolecular chemistry, molecular machines, systems chemistry, prebiotic chemistry, and energy transduction. Experimental chemists are now pioneering the realization of artificial systems that can harvest energy away from equilibrium. In this tutorial Review, we provide an overview of artificial molecular ratchets: the chemical mechanisms enabling energy absorption from the environment. By focusing on the mechanism type-rather than the application domain or energy source-we offer a unifying picture of seemingly disparate phenomena, which we hope will foster progress in this fascinating domain of science.

What Triggers the Dynamic Self-Assembly of Molecules and Materials?

Dynamic self-assembly has emerged as one of the reliable approaches to create complex materials with more life-like functions. In a typical dynamic self-assembly process, the external triggers activate the building blocks to initiate the assembly step to form transiently stable higher-order structures. These external triggers provide a constant supply of energy to maintain the transiently stable self-assembled states. The withdrawal or consumption of the trigger deactivates the building block in the aggregates, thereby initiating the disassembly step. A precise control over the interplay between the deterministic and nondeterministic forces is the key to achieving a dynamic self-assembly process. This demands the appropriate choice of building blocks as well as triggers, which has led to the development of a wide range of triggers in dynamic self-assembly. Through this Perspective, we intend to highlight the functional diversities, prospects, and challenges associated with different classes of "triggers" by bringing them under one platform. Such treatment will help us to identify the missing features and deduce a guideline for the development of ideal triggers. A few of the desirable features that a trigger should possess, along with probable ways to achieve them, are discussed, as well. In summary, the Perspective covers many intriguing aspects of triggers that can be helpful for researchers to achieve precise spatiotemporal control over various interparticle interactions, which is essential to obtaining the desired outcome from a dynamic self-assembly process.

Cyclic Macroscopic Assembly and Disassembly Driven by Ionic Strength Fuel: A Waste-Free Approach

Nonequilibrium assembling systems developed so far have relied on chemical fuels to drive the programmable pH cycles, redox reactions, and metastable bond formations. However, these methods often result in the unwanted accumulation of chemical waste. Herein, we present a novel strategy for achieving cyclic and waste-free nonequilibrium assembly and disassembly of macroscopic hydrogels, utilizing an ionic strength-mediated approach. Our strategy involves using ammonium carbonate as a chemical fuel to temporally regulate the attractions between oppositely charged hydrogels via ionic strength-controlled charge screening and hydrogel elasticity changes. This chemical fuel effectively mediates the assembly/disassembly processes and prevents waste accumulation, as ammonium carbonate can completely decompose into volatile chemical waste. The cyclic and reversible assembly process can be achieved without significant damping due to the self-clearance mechanism, as long as the chemical fuel is repeatedly supplied. This concept holds promise for creating macroscopic and microscopic nonequilibrium systems and self-adaptive materials.

Four distinct network patterns of supramolecular/polymer composite hydrogels controlled by formation kinetics and interfiber interactions

Synthetic composite hydrogels comprising supramolecular fibers and covalent polymers have attracted considerable attention because their properties are similar to biological connective tissues. However, an in-depth analysis of the network structures has not been performed. In this study, we discovered the composite network can be categorized into four distinct patterns regarding morphology and colocalization of the components using in situ, real-time confocal imaging. Time-lapse imaging of the network formation process reveals that the patterns are governed by two factors, the order of the network formation and the interactions between the two different fibers. Additionally, the imaging studies revealed a unique composite hydrogel undergoing dynamic network remodeling on the scale of a hundred micrometers to more than one millimeter. Such dynamic properties allow for fracture-induced artificial patterning of a network three dimensionally. This study introduces a valuable guideline to the design of hierarchical composite soft materials.

Waste-Free Fully Electrically Fueled Dissipative Self-Assembly System

The importance and prevalence of energy-fueled active materials in living systems have inspired the design of synthetic active materials using various fuels. However, several major limitations of current designs remain to be addressed, such as the accumulation of chemical wastes during the process, unsustainable active behavior, and the lack of precise spatiotemporal control. Here, we demonstrate a fully electrically fueled (e-fueled) active self-assembly material that can overcome the aforementioned limitations. Using an electrochemical setup with dual electrocatalysts, the anodic oxidation of one electrocatalyst (ferrocyanide, [Fe(CN)₆]^4-) creates a positive fuel to activate the self-assembly, while simultaneously, the cathodic reduction of the other electrocatalyst (methyl viologen, [MV]²⁺) generates a negative fuel triggering fiber disassembly. Due to the fully catalytic nature for the reaction networks, this fully e-fueled active material system does not generate any chemical waste, can sustain active behavior for an extended period when the electrical potential is maintained, and provides spatiotemporal control.

Electric, magnetic, and shear field-directed assembly of inorganic nanoparticles

Ordered assemblies of inorganic nanoparticles (NPs) have shown tremendous potential for wide applications due to their unique collective properties, which differ from those of individual NPs. Various assembly methods, such as external field-directed assembly, interfacial assembly, template assembly, biomolecular recognition-mediated assembly, confined assembly, and others, have been employed to generate ordered inorganic NP assemblies with hierarchical structures. Among them, the external field-directed assembly method is particularly fascinating, as it can remotely assemble NPs into well-ordered superstructures. Moreover, external fields (e.g., electric, magnetic, and shear fields) can introduce a local and/or global field intensity gradient, resulting in an additional force on NPs to drive their rotation and/or translation. Therefore, the external field-directed assembly of NPs becomes a robust method to fabricate well-defined functional materials with the desired optical, electronic, and magnetic properties, which have various applications in catalysis, sensing, disease diagnosis, energy conversion/storage, photonics, nano-floating-gate memory, and others. In this review, the effects of an electric field, magnetic field, and shear field on the organization of inorganic NPs are highlighted. The methods for controlling the well-ordered organization of inorganic NPs at different scales and their advantages are reviewed. Finally, future challenges and perspectives in this field are discussed.

Autonomous Non-Equilibrium Self-Assembly and Molecular Movements Powered by Electrical Energy

The ability to exploit energy autonomously is one of the hallmarks of life. Mastering such processes in artificial nanosystems can open technological opportunities. In the last decades, light- and chemically driven autonomous systems have been developed in relation to conformational motion and self-assembly, mostly in relation to molecular motors. In contrast, despite electrical energy being an attractive energy source to power nanosystems, its autonomous harnessing has received little attention. Herein we consider an operation mode that allows the autonomous exploitation of electrical energy by a self-assembling system. Threading and dethreading motions of a pseudorotaxane take place autonomously in solution, powered by the current flowing between the electrodes of a scanning electrochemical microscope. The underlying autonomous energy ratchet mechanism drives the self-assembly steps away from equilibrium with a higher energy efficiency compared to other autonomous systems. The strategy is general and might be extended to other redox-driven systems.

Sugar-Fueled Dissipative Living Materials

Dissipative behaviors in biology are fuel-driven processes controlled by living cells, and they shape the structural and functional complexities in biological materials. This concept has inspired the development of various forms of synthetic dissipative materials controlled by time-dependent consumption of chemical or physical fuels, such as reactive chemical species, light, and electricity. To date, synthetic living materials featuring dissipative behaviors directly controlled by the fuel consumption of their constituent cells is unprecedented. In this paper, we report a chemical fuel-driven dissipative behavior of living materials comprising Staphylococcus epidermidis and telechelic block copolymers. The macroscopic phase transition is controlled by d-glucose which serves a dual role of a competitive disassembling agent and a biological fuel source for living cells. Our work is a significant step toward constructing a synthetic dissipative living system and provides a new tool and knowledge to design emergent living materials.

Optimizing dynamical functions for speed with stochastic paths

Living systems are built from microscopic components that function dynamically; they generate work with molecular motors, assemble and disassemble structures such as microtubules, keep time with circadian clocks, and catalyze the replication of DNA. How do we implement these functions in synthetic nanostructured materials to execute them before the onset of dissipative losses? Answering this question requires a quantitative understanding of when we can improve performance and speed while minimizing the dissipative losses associated with operating in a fluctuating environment. Here, we show that there are four modalities for optimizing dynamical functions that can guide the design of nanoscale systems. We analyze Markov models that span the design space: a clock, ratchet, replicator, and self-assembling system. Using stochastic thermodynamics and an exact expression for path probabilities, we classify these models of dynamical functions based on the correlation of speed with dissipation and with the chosen performance metric. We also analyze random networks to identify the model features that affect their classification and the optimization of their functionality. Overall, our results show that the possible nonequilibrium paths can determine our ability to optimize the performance of dynamical functions, despite ever-present dissipation, when there is a need for speed.

Temporal Stimulus Patterns Drive Differentiation of a Synthetic Dipeptide-Based Coacervate

The fate of living cells often depends on their processing of temporally modulated information, such as the frequency and duration of various signals. Synthetic stimulus-responsive systems have been intensely studied for >50 years, but it is still challenging for chemists to create artificial systems that can decode dynamically oscillating stimuli and alter the systems' properties/functions because of the lack of sophisticated reaction networks that are comparable with biological signal transduction. Here, we report morphological differentiation of synthetic dipeptide-based coacervates in response to temporally distinct patterns of the light pulse. We designed a simple cationic diphenylalanine peptide derivative to enable the formation of coacervates. The coacervates concentrated an anionic methacrylate monomer and a photoinitiator, which provided a unique reaction environment and facilitated light-triggered radical polymerization─even in air. Pulsed light irradiation at 9.0 Hz (but not at 0.5 Hz) afforded anionic polymers. This dependence on the light pulse patterns is attributable to the competition of reactive radical intermediates between the methacrylate monomer and molecular oxygen. The temporal pulse pattern-dependent polymer formation enabled the coacervates to differentiate in terms of morphology and internal viscosity, with an ultrasensitive switch-like mode. Our achievements will facilitate the rational design of smart supramolecular soft materials and are insightful regarding the synthesis of sophisticated chemical cells.