Active coacervate droplets are protocells that grow and resist Ostwald ripening

Salt-Bridge-Mediated Coacervate-to-Vesicle Transformation in Arginine-Rich Coacervates

Polypeptide-based liquid-liquid phase separation (LLPS) has received considerable attention as it governs the formation of membraneless organelles in cells. However, the detailed mechanistic understanding of how one of the most prevalent cationic amino acids in proteins, arginine, interacts with various biomolecules to induce phase separation and undergo morphogenesis remains to be resolved. Herein, we report the phase separation behavior and transformation of arginine-rich coacervates into vesicular structures upon introducing polyphosphates. Transformation into vesicles was shown to occur independent of the initial anionic counterparts and was driven by salt-bridge interactions between guanidinium groups of arginine residues and phosphates. We also investigate the role of intermolecular forces and ionic effects on the morphological transformation and further exploit their potential in the assembly of artificial tissue-like constructs. Overall, our findings underpin a unifying principle for vesicle transformation from arginine-rich coacervates and their potency for reconstituting hierarchical biological microcompartments.

Cytomimetic calcification in chemically self-regulated prototissues

The fabrication of cytomimetic materials capable of orchestrated and adaptive functions remains a significant challenge in bottom-up synthetic biology. Inspired by the cell/matrix integration of living bone, here we covalently tether distributed single populations of alkaline phosphatase-containing inorganic protocells (colloidosomes) onto a crosslinked organic network to establish viscoelastic tissue-like micro-composites. The prototissues are endogenously calcified with site-specific mineralization modalities involving selective intra-protocellular calcification, matrix-specific extra-protocellular calcification or gradient calcification. To mirror the interplay between osteoblasts and osteoclasts, we prepare integrated prototissues comprising a binary population of enzymatically active colloidosomes capable of endogenous calcification and decalcification and utilize chemical inputs to induce structural remodelling. Overall, our methodology opens a route to the chemically self-regulated calcification of homogeneous and gradient tissue-like mineral-matrix composites, advances the development of bottom-up synthetic biology in chemical materials research, and could provide potential opportunities in bioinspired tissue engineering, hydrogel technologies and bone biomimetics.

Peptide Coacervates: Formation, Mechanism, and Biological Applications

Biomolecular coacervates, dynamic compartments formed via liquid-liquid phase separation (LLPS), are essential for orchestrating intracellular processes and have emerged as versatile tools in bioengineering. Peptides, with their modular amino acid sequences, exhibit unique potential in coacervate design due to their ability to undergo LLPS while offering precise control over molecular architecture and environmental responsiveness. Their simplicity, synthetic accessibility, and tunability make peptide-based coacervates particularly attractive for biomedical and materials applications. However, the formation and stability of these systems depend on a delicate balance of intrinsic factors (e.g., sequence charge, hydrophobicity, and chain length) and extrinsic conditions (e.g., pH, ionic strength, and temperature), necessitating a deeper understanding of their interplay. This review synthesizes recent advances in the molecular mechanisms driving peptide coacervation, emphasizing how sequence design and environmental cues govern phase behavior. We further highlight groundbreaking applications, from drug delivery platforms to protocell mimics, and discuss strategies to translate mechanistic insights into functional materials. By bridging fundamental principles with innovative applications, this work aims to accelerate the development of peptide coacervates as programmable, multifunctional systems, offering a roadmap for next-generation biochemical technologies.

Multiphasic protein condensation governed by shape and valency

Liquid-liquid phase separation (LLPS) of biological macromolecules leads to the formation of various membraneless organelles. The multilayered and multiphasic form of LLPS can mediate complex cellular functions; however, the determinants of its topological features are not fully understood. Herein, we focus on synaptic proteins consisting of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its interacting partners and present a computational model that reproduces forms of LLPS, including a form of two-phase condensates, phase-in-phase (PIP) organization. The model analyses reveal that the PIP formation requires competitive binding between the proteins. The PIP forms only when CaMKII has high valency and a short linker length. Such CaMKII exhibits low surface tension, a modular structure, and slow diffusion, enabling it to stay in small biochemical domains for a long time, which is necessary for synaptic plasticity. Thus, the computational modeling reveals new structure-function relationships for CaMKII as a synaptic memory unit.

Light-Responsive Mononucleotide Coacervates

Liquid-liquid phase separation (LLPS) is central to the formation of biomolecular condensates in modern cells and is also explored as a mechanism for assembling protocells. Phase-separated droplets provide dynamic micro-environments that concentrate reactants, enhance reactions, and allow molecular exchange, essential for both cellular regulation, and adaptive compartmentalization. While modern cells achieve dynamic LLPS through enzymatic and metabolic pathways, protocells may be designed to harness external stimuli such as pH, temperature, redox potential, or light. However, existing studies of light-responsive coacervates rely on complex biomolecules, limiting their use as minimal platforms of energy-driven phase separation. Here, we develop a minimal system of light-responsive coacervates composed of low-molecular-weight species: mononucleotides and azobenzene-based amphiphiles with varying charge valency. These coacervates undergo reversible phase transitions through azobenzene photoisomerization, with their behavior governed by charge valency and nucleotide structure. We demonstrate that coacervates formed with high-valency azobenzenes remain stable under UV irradiation but exhibit significant property changes, while those with low-valency azobenzenes dissolve, enabling light-controlled nucleotide release. Additionally, we achieved hierarchical droplet organization and light-actuated biomolecular localization within multiphase systems. Overall, these findings establish a minimal platform for designing light-responsive synthetic protocells, providing insights into dynamic compartmentalization in de novo life-like systems.

Catalytically Active Coacervates Sustained Out-of-Equilibrium

Metabolically active membraneless organelles of extant biology have the capability to maintain their structure under nonequilibrium conditions by leveraging chemical reactions. Herein, we report active coacervates accessed via a mixture of minimal building blocks that featured π-electron rich short peptide, positively charged aldehyde, and a cyclic ketone under nonequilibrium conditions. Peptide bound with the aldehyde by a dynamic covalent bond and demixed to form coacervates through hydrophobic interactions. Importantly, the short-peptide could utilize its free amine (β-alanine) to catalyze C─C bond formation which eventually led to the depletion of one of the building blocks (aldehyde) via aldol reaction; an intrinsic catalytic role that helped the coacervate to suppress coalescence. Notably, under continuous additions (open system) of the depleting precursors, the active coacervates were able to demonstrate spatial stability for longer duration. This out-of-equilibrium behavior of phase separated droplets in presence of flux of building blocks is reminiscent of the active membraneless organelles seen in contemporary biochemistry.

Toward Design Principles for Biomolecular Condensates for Metabolic Pathways

Biology uses membrane-less organelles or biomolecular condensates as dynamic reaction compartments that can form or dissolve to regulate biochemical pathways. This has led to a flurry of research aiming to design new synthetic organelles that function as reaction crucibles for enzymes and biomolecular cascades in biotechnology. The mechanisms by which a condensate can enhance multistep biochemical processes including mass action, tuning the chemical environment, scaffolding and metabolic channelling is reviewed. These mechanisms are not inherently beneficial for the rate of enzymatic processes but can also inhibit a reaction. Similarly, some aspects of condensates are likely intrinsically inhibitory including retardation of diffusion, where the net effect of a condensate will be a trade-off between inhibitory and stimulatory effects. It is discussed which generalizable conclusions can be drawn so far and how close it is to design principles for condensates for enzyme cascades in microbial cell factories including which reactions are likely to be enhanced by condensates and which type of condensate will be suited for which reaction.

Adaptive ATP-induced molecular condensation in membranized protocells

Liquid-liquid phase separation (LLPS) has been achieved in various cytomimetic (protocell) models, but controlling molecular condensation using noninert crowders to systematically alter protocell function remains challenging. Intracellular ATP levels influence protein-protein interactions, and dysregulation of ATP can alter cellular crowding dynamics, thereby disrupting the normal formation or dissolution of condensates. Here, we develop a membranized protocell model capable of endogenous LLPS and liquid-gel-like phase separation through precise manipulation of intermolecular interactions within semipermeable polysaccharide-based microcapsules (polysaccharidosomes, P-somes), prepared using microtemplate-guided assembly. We demonstrate that intraprotocellular diffusion-mediated LLPS can be extended into the liquid-gel-like domain by the uptake of the biologically active crowder ATP, resulting in a range of modalities dependent on the fine-tuning of molecular condensation. Endogenous enzyme activity in these crowded polysaccharidosomes is enhanced compared to free enzymes in solution, though this enhancement diminishes at higher levels of intraprotocellular condensation. Additionally, increased molecular crowding inhibits intraprotocell DNA strand displacement reactions. Our findings introduce an expedient and optimized approach to the batch construction of membranized protocell models with controllable molecular crowding and functional diversity. Our mix-incubate-wash protocol for inducing endogenous LLPS in membranized protocells offers potential applications in microreactor technology, environmental sensing, and the delivery and sustained release of therapeutics.

Temperature-Responsive Zwitterionic Polymers That Undergo UCST-Type Liquid-Liquid Phase Separation under Physiological Ionic Strength

Associative phase separation (complex coacervation) in liquid-liquid phase separation (LLPS) involves the separation of multiple substances into concentrated and dilute phases by electrostatic interactions. Simple phase separation (simple coacervation) occurs when the hydrophilicity and hydrophobicity of a single molecule change dramatically in response to a specific stimulus. Simple coacervation arises from the lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-type phase separations in aqueous media containing temperature-responsive polymers. LCST- and UCST-type LLPSs induce droplet formation at temperatures above the LCST and below the UCST, respectively. Although there have been several studies on the UCST-type LLPS of temperature-responsive polymers in water, only a few temperature-responsive polymers that exhibit UCST-type LLPS in aqueous media with physiological ionic strength have been reported. In this study, we synthesized temperature-responsive zwitterionic polymers, exhibiting UCST-type LLPS in physiological ionic strength, by copolymerizing two types of zwitterionic monomers─sulfabetaine (SaB) having ammonium and sulfate groups and sulfobetaine (SB) having ammonium and sulfonate groups─in aqueous media with various ionic strengths. The resulting zwitterionic copolymers, P(SaB-co-SB)s, exhibited a cloud point (CP) characterized by a transition from turbidity to transparency as the temperature increased in a buffer with physiological ionic strength. The CP of P(SaB-co-SB) shifted from lower to higher temperatures as the SaB content increased. Microscopic observation showed that P(SaB-co-SB) underwent UCST-type LLPS to form coacervate droplets even in a buffer solution with physiological ionic strength at temperatures lower than the CP; however, the coacervates dissolved above the CP, unlike general UCST-type temperature-responsive polymers. The CPs of the P(SaB-co-SB)s under physiological ionic strength varied with the SaB content and ionic strength of the copolymerization medium. UCST-type LLPSs were induced by strong dipole-dipole interactions between SaB units at physiological ionic strength.

Programmable Coacervate Droplets via Reaction-Coupled Liquid-Liquid Phase Separation (LLPS) and Competitive Inhibition

Membraneless biomolecular condensates formed by liquid-liquid phase separation (LLPS) are crucial for many spatiotemporal biological functions. Designing synthetic mimics to emulate and understand LLPS is an active area of research, which has led to the development of coacervate droplets through elegant bioinspired designs. However, recent interest in this field has shifted toward designing programmable coacervates to impart spatiotemporal control over these liquid phases. Herein, we demonstrate the programming of LLPS in synthetic systems by employing concepts of competitive binding and reaction-coupled assembly involving dynamic covalent bonds. Our results utilize small building blocks that follow a simple coacervation mechanism, distinguishing this approach from previously reported programmable complex coacervates, which often rely on reaction-controlled generation of one of the components. We introduce these concepts using dynamic covalent bonds (boronate esters) and small chromophoric building blocks appended with terminal boronic acid groups. Upon reaction with substrates (monosaccharides), these building blocks form molecular structures resembling "sticker-and-spacer" designs for coacervation, leading to a reaction-driven, temporally controlled LLPS process. The differential reactivity of various monosaccharides, combined with the reversibility of dynamic bonds, enables competitive binding-driven control over the growth, inhibition, and dissolution of the coacervation process, offering new strategies for programmable LLPS that are reminiscent of protein-induced inhibition in biomolecular condensates. Detailed spectroscopic probing and kinetic analyses provide mechanistic insights into the reaction-coupled and autocatalytic growth processes, revealing the glucose-selective nature of this coacervation system. Finally, coupling dynamic covalent reactions with temporal pH modulation results in transient coacervation, which can be visualized by using confocal microscopy. We anticipate that this approach will pave the way for designing coacervate droplets with novel biorelevant emergent properties.

Acetylation of Short Glycopeptides Enables Phase Separation

Liquid-liquid phase separation (LLPS) of biomacromolecules is crucial for regulating cellular functions. To explore their molecular mechanisms, peptide-based coacervates mimicking natural proteins have been developed, but the role of side chain modifications such as glycosylation remains underexplored. Here, we demonstrate that acetylation of short glycopeptides can induce pH- and concentration-dependent phase separation, while removing acetyl groups abolishes this behavior. Circular dichroism spectroscopy revealed a strong link between peptide structural ordering and the phase separation propensity. Peptides capable of forming liquid droplets displayed a significant ellipticity change at 205 nm upon changing solution pH. Moreover, these peptide coacervates can interact with cells and enhance the antiproliferative property of doxorubicin. Therefore, this work highlights the critical role of O-acetylation in LLPS and provides a valuable tool for studying the parameters regulating LLPS and its implications in cellular processes.

Peptide-mediated liquid-liquid phase separation and biomolecular condensates

Liquid-liquid phase separation (LLPS) is a cornerstone of cellular organization, driving the formation of biomolecular condensates that regulate diverse biological processes and inspire innovative applications. This review explores the molecular mechanisms underlying peptide-mediated LLPS, emphasizing the roles of intermolecular interactions such as hydrophobic effects, electrostatic interactions, and π-π stacking in phase separation. The influence of environmental factors, such as pH, temperature, ionic strength, and molecular crowding on the stability and dynamics of peptide coacervates is examined, highlighting their tunable properties. Additionally, the unique physicochemical properties of peptide coacervates, including their viscoelastic behavior, interfacial dynamics, and stimuli-responsiveness, are discussed in the context of their biological relevance and engineering potential. Peptide coacervates are emerging as versatile platforms in biotechnology and medicine, particularly in drug delivery, tissue engineering, and synthetic biology. By integrating fundamental insights with practical applications, this review underscores the potential of peptide-mediated LLPS as a transformative tool for advancing science and healthcare.

Interfacing bacterial microcompartment shell proteins with genetically encoded condensates

Condensates formed by liquid-liquid phase separation are promising candidates for the development of synthetic cells and organelles. Here, we show that bacterial microcompartment shell proteins from Haliangium ochraceum (BMC-H) assemble into coatings on the surfaces of protein condensates formed by tandem RGG-RGG domains, an engineered construct derived from the intrinsically disordered region of the RNA helicase LAF-1. WT BMC-H proteins formed higher-order assemblies within RGG-RGG droplets; however, engineered BMC-H variants fused to RGG truncations formed coatings on droplet surfaces. These intrinsically disordered tags controlled the interaction with the condensed phase based on their length and sequence, and one of the designs, BMC-H-T2, assembled preferentially on the surface of the droplet and prevented droplet coalescence. The formation of the coatings is dependent on the pH and protein concentration; once formed, the coatings are stable and do not exchange with the dilute phase. Coated droplets could sequester and concentrate folded proteins, including TEV protease, with selectivity similar to uncoated droplets. Addition of TEV protease to coated droplets resulted in the digestion of RGG-RGG to RGG and a decrease in droplet diameter, but not in the dissolution of the coatings. BMC shell protein-coated protein condensates are entirely encodable and provide a way to control the properties of liquid-liquid phase-separated compartments in the context of synthetic biology.

Self-growing protocell models in aqueous two-phase system induced by internal DNA replication reaction

The bottom-up reconstitution of self-growing artificial cells is a critical milestone toward realizing autonomy and evolvability. However, building artificial cells that exhibit self-growth coupled with internal replication of gene-encoding DNA has not been achieved yet. Here, we report self-growing artificial cell models based on dextran-rich droplets in an aqueous two-phase system of poly(ethylene glycol) (PEG) and dextran (DEX). Motivated by the finding that DNA induces the generation of DEX-rich droplets, we integrate DNA amplification system with DEX-rich droplets, which exhibited active self-growth. We implement the protocells with cell-free transcription-translation systems coupled with DNA amplification/replication, which also show active self-growth. Considering the simplicities in terms of the chemical composition and the mechanism, these results underscore the potential of DEX droplets as a foundational platform for engineering protocells, giving implications for the emergence of protocells under prebiotic conditions.

Synthetic Biomolecular Condensates: Phase-Separation Control, Cytomimetic Modelling and Emerging Biomedical Potential

Liquid-liquid phase separation towards the formation of synthetic coacervate droplets represents a rapidly advancing frontier in the fields of synthetic biology, material science, and biomedicine. These artificial constructures mimic the biophysical principles and dynamic features of natural biomolecular condensates that are pivotal for cellular regulation and organization. Via adapting biological concepts, synthetic condensates with dynamic phase-separation control provide crucial insights into the fundamental cell processes and regulation of complex biological pathways. They are increasingly designed with the ability to display more complex and ambitious cell-like features and behaviors, which offer innovative solutions for cytomimetic modeling and engineering active materials with sophisticated functions. In this minireview, we highlight recent advancements in the design and construction of synthetic coacervate droplets; including their biomimicry structure and organization to replicate life-like properties and behaviors, and the dynamic control towards engineering active coacervates. Moreover, we highlight the unique applications of synthetic coacervates as catalytic centers and promising delivery vehicles, so that these biomimicry assemblies can be translated into practical applications.

Insights into the Mechanism of Protein Loading by Chain-Length Asymmetric Complex Coacervates

The study of the phase behavior of polyelectrolyte complex coacervates has attracted significant attention in recent years due to their potential use as membrane-less organelles, microreactors, and drug delivery platforms. In this work, we investigate the mechanism of protein loading in chain-length asymmetric complex coacervates composed of a polyelectrolyte and an oppositely charged multivalent ion. Unlike the symmetric case (polycation + polyanion), we show that protein loading is highly selective based on the protein's net charge: only proteins with charges opposite to the polyelectrolyte can be loaded. Through a series of systematic experiments, we identified that the protein loading process relies on the formation of a neutral three-component coacervate in which both the protein and the multivalent ion serve as complexing agents for the polyelectrolyte. Lastly, we demonstrated that this mechanism extends to the sequestration of other charged small molecules, offering valuable insights into designing functional multicomponent coacervates.

Microscopic and stochastic simulations of chemically active droplets

Biomolecular condensates play a central role in the spatial organization of living matter. Their formation is now well understood as a form of liquid-liquid phase separation that occurs very far from equilibrium. For instance, they can be modeled as active droplets, where the combination of molecular interactions and chemical reactions result in microphase separation. However, so far, models of chemically active droplets are spatially continuous and deterministic. Therefore, the relationship between the microscopic parameters of the models and some crucial properties of active droplets (such as their polydispersity, their shape anisotropy, or their typical lifetime) is yet to be established. In this work, we address this question computationally, using Brownian dynamics simulations of chemically active droplets: the building blocks are represented explicitly as particles that interact with attractive or repulsive interactions, depending on whether they are in a droplet-forming state or not. Thanks to this microscopic and stochastic view of the problem, we reveal how driving the system away from equilibrium in a controlled way determines the fluctuations and dynamics of active emulsions.

Separation of sticker-spacer energetics governs the coalescence of metastable condensates

Biological condensates often emerge as a multidroplet state and never coalesce into one large droplet within the experimental timespan. Previous work revealed that the sticker-spacer architecture of biopolymers may dynamically stabilize the multidroplet state. Here, we simulate the condensate coalescence using metadynamics approach and reveal two distinct physical mechanisms underlying the fusion of droplets. Condensates made of sticker-spacer polymers readily undergo a kinetic arrest when stickers exhibit slow exchange while fast exchanging stickers at similar levels of saturation allow merger to equilibrium states. On the other hand, condensates composed of homopolymers fuse readily until they reach a threshold density. Increase in entropy upon intercondensate mixing of chains drives the fusion of sticker-spacer chains. We map the range of mechanisms of kinetic arrest from slow sticker exchange dynamics to density mediated in terms of energetic separation of stickers and spacers. Our predictions appear to be in qualitative agreement with recent experiments probing dynamic nature of protein-RNA condensates.

The Balbiani body is formed by microtubule-controlled molecular condensation of Buc in early oogenesis

Vertebrate oocyte polarity has been observed for two centuries and is essential for embryonic axis formation and germline specification, yet its underlying mechanisms remain unknown. In oocyte polarization, critical RNA-protein (RNP) granules delivered to the oocyte's vegetal pole are stored by the Balbiani body (Bb), a membraneless organelle conserved across species from insects to humans. However, the mechanisms of Bb formation are still unclear. Here, we elucidate mechanisms of Bb formation in zebrafish through developmental biomolecular condensation. Using super-resolution microscopy, live imaging, biochemical, and genetic analyses in vivo, we demonstrate that Bb formation is driven by molecular condensation through phase separation of the essential intrinsically disordered protein Bucky ball (Buc). Live imaging, molecular analyses, and fluorescence recovery after photobleaching (FRAP) experiments in vivo reveal Buc-dependent changes in the Bb condensate's dynamics and apparent material properties, transitioning from liquid-like condensates to a solid-like stable compartment. Furthermore, we identify a multistep regulation by microtubules that controls Bb condensation: first through dynein-mediated trafficking of early condensing Buc granules, then by scaffolding condensed granules, likely through molecular crowding, and finally by caging the mature Bb to prevent overgrowth and maintain shape. These regulatory steps ensure the formation of a single intact Bb, which is considered essential for oocyte polarization and embryonic development. Our work offers insight into the long-standing question of the origins of embryonic polarity in non-mammalian vertebrates, supports a paradigm of cellular control over molecular condensation by microtubules, and highlights biomolecular condensation as a key process in female reproduction.

Quantification of Biomolecular Condensate Volume Reveals Network Swelling and Dissolution Regimes during Phase Transition

Accurate determination of biomolecular condensate volume reveals that destabilization of condensates can lead to either swelling or shrinking of condensates, giving fundamental insights into the regulation of the volume of cellular condensates. Determination of the volume of biomolecular condensates and coacervate protocells is essential to investigate their precise composition and impact on (bio)chemical reactions that are localized inside the condensates. It is not a straightforward task, as condensates have tiny volumes, are highly viscous, and are prone to wetting. Here, we examine different strategies to determine condensate volume and introduce two new methods, with which condensate volumes of 1 μL or less (volume fraction 0.4%) can be determined with a standard deviation of 0.03 μL. Using these methods, we show that the swelling or shrinking of condensates depends on the degree of physical cross-linking. These observations are supported by Flory-Huggins theory and can have profound effects on condensates in cell biology.

Approaching Dynamic Behaviors of Life through Systems Chemistry

The intricate interplay of metabolic reactions and molecular assembly in living systems enables spatiotemporally organization and gives rise to diverse dynamic behaviors that characterize life. Over the last decades, research efforts have increasingly focused on replicating the remarkable properties and characteristics of living systems, driving the rapid growth of systems chemistry. This young discipline which generally studies interacting molecular networks and emergent system-level properties, behaviors, and functions, offers new concepts and tools to tackle the complexity of life. In this review paper, we have explored seminal research and recent advancements in recreating dynamic behaviors of life with systems chemistry. We believe that the recreation of the dynamic behaviors of life through systems chemistry would set the initial steps to obtain synthetic life de novo.

Sticky Polyelectrolyte Shield for Enhancing Biological Half-Life of Growth Factors

Delivery of secretomes, which includes growth factors, cytokines, and mRNA, is critical in regenerative medicine for cell-to-cell communication. However, the harsh in vivo environment presents significant challenges for secretome delivery. Proteolytic enzymes shorten secretomes' half-lives, and secretomes tend to rapidly diffuse at defect sites. Therefore, a delivery system that ensures prolonged retention and enhanced therapeutic efficacy of secretomes is required. In this study, a Coating Optimized Drug Delivery Enhancement (COD2E) system, a coacervate composed of dopamine functionalized fucoidan and poly-l-lysine, was fabricated for secretome delivery. The dopamine modification significantly enhanced adhesive strength (>7-fold) compared to that of the neat coacervates, which enabled rapid (5 min) and uniform coating ability on collagen sponges. The COD2E system was able to encapsulate fibroblast growth factor (FGF2) and prolong the half-life of FGF2. Notably, its efficacy, demonstrated through a single application of FGF2 encapsulated COD2E on collagen sponge, in a wound model demonstrated a successful tissue repair. The COD2E system is an effective growth factor delivery vehicle since it can protect growth factors, has an antioxidant ability, adheres on various material surfaces, and is hemocompatible.

Enzymatic Reaction Network-Driven Polymerization-Induced Transient Coacervation

A living cell has a highly complex microenvironment whereas numerous enzyme-driven processes are active at once. These procedures are incredibly accurate and efficient, although comparable control has not yet been established in vitro. Here, we design an enzymatic reaction network (ERN) that combines antagonistic and orthogonal enzymatic networks to produce adjustable dynamics of ATP-fueled transient coacervation. Using horseradish peroxidase (HRP)-mediated Biocatalytic Atom Transfer Radical Polymerization (BioATRP), we synthesized poly(dimethylaminoethyl methacrylate), which subsequently formed coacervates with ATP. We rationally explored enzymatic control over coacervation and dissolution, using orthogonal and antagonistic enzyme pairs viz., alkaline phosphatase, Creatine phosphokinase, hexokinase, esterase, and urease. ATP-fuelled coacervates also demonstrate the enzymatic catalysis to prove its potential to be exploited as a cellular microreactor. Additionally, we developed ERN-polymerization-induced transient coacervation (ERN-PIC), with complete control over the system, polymerization, coacervation, and dissolution. Notably, the coacervation process itself determines functional properties, as seen in selective cargo uptake. The strategy offers cutting-edge biomimetic applications, and insights into cellular compartmentalization by bridging the gap between synthetic and biological systems. The development of temporally programmed coacervation is promising for the spatial arrangement of multienzyme cascades, and offers novel ideas on the architecture of artificial cells.

Shape transformations in peptide-DNA coacervates driven by enzyme-catalyzed deacetylation

Biomolecular condensates formed by liquid-liquid phase separation (LLPS) are important organizers of biochemistry in living cells. Condensate formation can be dynamically regulated, for example, by protein binding or enzymatic processes. However, how enzymatic reactions can influence condensate shape and control shape transformations is less well understood. Here, we design a model condensate that can be formed by the enzymatic deacetylation of a small peptide by sirtuin-3 in the presence of DNA. Interestingly, upon nucleation condensates initially form gel-like aggregates that gradually transform into spherical droplets, displaying fusion and wetting. This process is governed by sirtuin-3 concentration, as more enzyme results in a faster aggregate-to-liquid transformation of the condensates. The counterintuitive transformation of gel-like to liquid-like condensates with increasing interaction strength between the peptide and DNA is recapitulated by forming condensates with different peptides and nucleic acids at increasing salt concentrations. Close to the critical point where coacervates dissolve, gel-like aggregates are formed with short double stranded DNA, but not with single stranded DNA or weakly binding peptides, even though the coacervate salt resistance is similar. At lower salt concentrations the interaction strength increases, and spherical, liquid-like condensates are formed. We attribute this behavior to bending of the DNA by oppositely charged peptides, which becomes stronger as the system moves further into the two-phase region. Overall, this work shows that enzymes can induce shape transformations of condensates and that condensate material properties do not necessarily reveal their stability.

Coacervate Droplets as Biomimetic Models for Designing Cell-Like Microreactors

Coacervates are versatile compartments formed by liquid-liquid phase separation. Their dynamic behavior and molecularly crowded microenvironment make them ideal materials for creating cell-like systems such as synthetic cells and microreactors. Recently, combinations of synthetic and natural molecules have been exploited via simple or complex coacervation to create compartments that can be used to build hierarchical chemical systems with life-like properties. This review highlights recent advances in the design of coacervate compartments and their application as biomimetic compartments for the design of cell-like chemical reactors and cell mimicking systems. It first explores the variety of materials used for coacervation and the influence of their chemical structure on their controlled dynamic behavior. Then, the applications of coacervates as cell-like systems are reviewed, focusing on how they can be used as cell-like microreactors through their ability to sequester molecules and provide a distinct and regulatory microenvironment for chemical reactions in aqueous media.

Multiphase coacervates: mimicking complex cellular structures through liquid-liquid phase separation

Coacervate microdroplets, arising from liquid-liquid phase separation, have emerged as promising models for primary cells, demonstrating the ability to regulate biomolecular enrichment, create chemical gradients, accelerate confined reactions, and even express proteins. Notably, multiphase coacervation provides a robust framework to replicate hierarchically complex cellular structures, offering valuable insights into cellular organization and function. In this review, we explore the recent advancements in the study of multiphase coacervates, focusing on design strategies, underlying mechanisms, structural control, and their applications in biomimetics. These developments highlight the potential of multiphase coacervates as powerful tools in the field of synthetic biology and material science.

The Assembly of Miniaturized Droplets toward Functional Architectures

Recent explorations of bioengineering have generated new concepts and strategies for the processing of soft and functional materials. Droplet assembly techniques can address problems in the construction of extremely soft architectures by expanding the manufacturing capabilities using droplets containing liquid or hydrogels including weak hydrogels. This Perspective sets out to provide a brief overview of this growing field, and discusses the challenges and opportunities ahead. The study highlights the recent key advances of materials and architectures from hitherto effective droplet-assembly technologies, as well as the applications in biomedical and bioengineering fields from artificial tissues to bioreactors. It is envisaged that these assembled architectures, as nature-inspired models, will stimulate the discovery of biomaterials and miniaturized platforms for interdisciplinary research in health, biotechnology, and sustainability.

Nucleotide-mediated modulation of chemoselective protein functionalization in a liquid-like condensed phase

Liquid-like protein condensates are ubiquitous in cellular system and are increasingly recognized for their roles in physiological processes. Condensed phase harbors distinctive chemical microenvironment, markedly different than dilute aqueous phase. Herein, we demonstrate chemoselective modification pattern of nucleophilic canonical amino acid sidechains (namely - cysteine, tyrosine and lysine) of the protein towards 4-chloro-7-nitrobenzofurazan in the dilute and condensed phase. We also delineate how the effect of nucleotides and their in situ enzymatic dissociation temporally modulate the protein condensate's pH and the protein's corresponding chemoselective modification. We have shown that the pH of the condensate decreases in the presence of nucleoside triphosphate, whereas it increases in the presence of nucleoside monophosphates or phosphate ion. For instance, we find lysine-specific modification gets inhibited in the presence of adenosine triphosphate (ATP), but significantly enhanced in the presence of monophosphates. This feature enables us to gain temporal control over dynamic change in protein functionalization via enzymatic ATP hydrolysis. Overall, this work substantiates the alteration in pH-responsiveness of Brønsted basicity of a protein's ε-amine in the condensed phase. Furthermore, this environment sensitivity in chemoselective protein functionalization in condensed phase will be important in adaptable protein engineering to the chemical biology of protein phase separation.

Design of multi-responsive and actuating microgels toward on-demand drug release

Multifunctional colloidal microgels that exhibit stimuli-responsive behaviour and excellent biocompatibility have attracted particular attention for developing functional compartmentalized networks. Herein, a series of stimuli-responsive microgels (M0, M1, and M2) were designed through the copolymerization of di(ethylene glycol) methyl ether methacrylate (DEGMA) and methacrylic acid (MAA) monomers using hydroxy ethyl methacrylate-coupled azobenzene (HEMA-Az) and ethylene glycol dimetharylate (EGDMA) as crosslinkers. The behaviour of the microgels in response to temperature, pH, and light was thoroughly investigated using spectroscopic, microscopic, and light-scattering techniques. Interestingly, the microgels deswelled with an increase in temperature, decrease in pH, and under the irradiation of UV light. Such a reversible swelling/deswelling behaviour was exploited for microgel M2, which showed better photoactuation at pH 5 with a higher fluid pumping velocity. The actuating microgel M2 was optimized for loading the drug ciprofloxacin (Cf) to study its release at different temperature, pH, and light conditions. Microgel M2 exhibited photoresponsive Cf release at pH 5 and 37 °C, demonstrating its potential for application in on-demand drug release.

Theory and quantitative assessment of pH-responsive polyzwitterion-polyelectrolyte complexation

We introduce a theoretical framework to describe the pH-sensitive phase behavior of polyzwitterion-polyelectrolyte complex coacervates that reasonably captures the phenomenon from recent experimental observations. The polyzwitterion is described by a combinatorial sequence of the four states in which each zwitterionic monomer can occupy: dipolar, quasi-cationic, quasi-anionic, and fully neutralized. We explore the effects of various modifiable chemical and physical properties of the polymers-such as, pKa of the pH-active charged group on the zwitterion, equilibrium constant of salt condensation on the permanently charged group on the zwitterion, degrees of polymerization, hydrophobicity (via the Flory-Huggins interaction parameter), and dipole lengths-on the window of complexation across many stoichiometric mixing ratios of polyzwitterion and polyelectrolyte. The properties that determine the net charge of the polyzwitterion have the strongest effect on the pH range in which polyzwitterion-polyelectrolyte complexation occurs. We finish with general guidance for those interested in molecular design of polyzwitterion-polyelectrolyte complex coacervates and opportunities for future investigation.

Fractal-Dependent Growth of Solidlike Condensates

The phenomenon of droplet growth occurs in various industrial and natural processes. Recently, the discovery of liquidlike condensates within cells has sparked an increasing interest in understanding their growth behaviors. These condensates exhibit varying material properties that are closely related to many cellular functions and diseases, particularly during the phase transition from liquidlike droplets to solidlike aggregates. However, how the liquid-to-solid phase transition affects the growth of condensates remains largely unknown. In this study, we investigate the growth of peptide-RNA condensates, which behave as either liquidlike droplets or solidlike aggregates depending on the RNA sequences. Dynamic light scattering experiments show that solidlike condensates grow surprisingly faster, with their hydrodynamic diameters increasing over time as d_{h}(t)∼t^{1/2}, contrasting with d_{h}(t)∼t^{1/3} for liquidlike droplets. By combining theoretical analysis and simulations, we demonstrate that this accelerated growth is caused by the noncoalescence aggregation of solidlike condensates and thus formation of percolated swollen structures with a decreased fractal dimension. Moreover, we demonstrate that the accelerated growth can be slowed down by introducing agents that can revert solidlike condensates back to their liquidlike states, such as urea or specific RNAs. Together, our work reveals a fractal-dependent growth mechanism of condensates, with useful insights for understanding the aging of condensates and modulating their aggregation behaviors in synthetic and biological systems.

Complex Pathways Drive Pluripotent Fmoc-Leucine Self-Assemblies

Nature uses complex self-assembly pathways to access distinct functional non-equilibrium self-assemblies. This remarkable ability to steer same set of biomolecules into different self-assembly states is done by avoiding thermodynamic pit. In synthetic systems, on demand control over 'Pathway Complexity' to access self-assemblies different from equilibrium structures remains challenging. Here we show versatile non-equilibrium assemblies of the same monomer via alternate assembly pathways. The assemblies nucleate using non-classical or classical nucleation routes into distinct metastable (transient hydrogels), kinetic (stable hydrogels) and thermodynamic structures [(poly)-crystals and 2D sheets]. Initial chemical and thermal inputs force the monomers to follow different assembly pathways and form soft-materials with distinct molecular arrangements than at equilibrium. In many cases, equilibrium structures act as thermodynamic sink which consume monomers from metastable structures giving transiently formed materials. This dynamics can be tuned chemically or thermally to slow down the dissolution of transient hydrogel, or skip the intermediate hydrogel altogether to reach final equilibrium assemblies. If required this metastable state can be kinetically trapped to give strong hydrogel stable over days. This method to control different self-assembly states can find potential use in similar biomimetic systems to access new materials for various applications.

Peptide-Based Biomimetic Condensates via Liquid-Liquid Phase Separation as Biomedical Delivery Vehicles

Biomolecular condensates are dynamic liquid droplets through intracellular liquid-liquid phase separation that function as membraneless organelles, which are highly involved in various complex cellular processes and functions. Artificial analogs formed via similar pathways that can be integrated with biological complexity and advanced functions have received tremendous research interest in the field of synthetic biology. The coacervate droplet-based compartments can partition and concentrate a wide range of solutes, which are regarded as attractive candidates for mimicking phase-separation behaviors and biophysical features of biomolecular condensates. The use of peptide-based materials as phase-separating components has advantages such as the diversity of amino acid residues and customized sequence design, which allows for programming their phase-separation behaviors and the physicochemical properties of the resulting compartments. In this Perspective, we highlight the recent advancements in the design and construction of biomimicry condensates from synthetic peptides relevant to intracellular phase-separating protein, with specific reference to their molecular design, self-assembly via phase separation, and biorelated applications, to envisage the use of peptide-based droplets as emerging biomedical delivery vehicles.

Polyphenol-stabilized coacervates for enzyme-triggered drug delivery

Stability issues in membrane-free coacervates have been addressed with coating strategies, but these approaches often compromise the permeability of the coacervate. Here we report a facile approach to maintain both stability and permeability using tannic acid and then demonstrate the value of this approach in enzyme-triggered drug release. First, we develop size-tunable coacervates via self-assembly of heparin glycosaminoglycan with tyrosine and arginine-based peptides. A thrombin-recognition site within the peptide building block results in heparin release upon thrombin proteolysis. Notably, polyphenols are integrated within the nano-coacervates to improve stability in biofluids. Phenolic crosslinking at the liquid-liquid interface enables nano-coacervates to maintain exceptional structural integrity across various environments. We discover a pivotal polyphenol threshold for preserving enzymatic activity alongside enhanced stability. The disassembly rate of the nano-coacervates increases as a function of thrombin activity, thus preventing a coagulation cascade. This polyphenol-based approach not only improves stability but also opens the way for applications in biomedicine, protease sensing, and bio-responsive drug delivery.

Did the exposure of coacervate droplets to rain make them the first stable protocells?

Membraneless coacervate microdroplets have long been proposed as model protocells as they can grow, divide, and concentrate RNA by natural partitioning. However, the rapid exchange of RNA between these compartments, along with their rapid fusion, both within minutes, means that individual droplets would be unable to maintain their separate genetic identities. Hence, Darwinian evolution would not be possible, and the population would be vulnerable to collapse due to the rapid spread of parasitic RNAs. In this study, we show that distilled water, mimicking rain/freshwater, leads to the formation of electrostatic crosslinks on the interface of coacervate droplets that not only suppress droplet fusion indefinitely but also allow the spatiotemporal compartmentalization of RNA on a timescale of days depending on the length and structure of RNA. We suggest that these nonfusing membraneless droplets could potentially act as protocells with the capacity to evolve compartmentalized ribozymes in prebiotic environments.

Minimal Peptide Sequences That Undergo Liquid-Liquid Phase Separation via Self-Coacervation or Complex Coacervation with ATP

The simple (self-)coacervation of the minimal tryptophan/arginine peptide sequences W2R2 and W3R3 was observed in salt-free aqueous solution. The phase diagrams were mapped using turbidimetry and optical microscopy, and the coacervate droplets were imaged using confocal microscopy complemented by cryo-TEM to image smaller droplets. The droplet size distribution and stability were probed using dynamic light scattering, and the droplet surface potential was obtained from zeta potential measurements. SAXS was used to elucidate the structure within the coacervate droplets, and circular dichroism spectroscopy was used to probe the conformation of the peptides, a characteristic signature for cation-π interactions being present under conditions of coacervation. These observations were rationalized using a simple model for the Rayleigh stability of charged coacervate droplets, along with atomistic molecular dynamics simulations which provide insight into stabilizing π-π stacking interactions of tryptophan as well as arginine-tryptophan cation-π interactions (which modulate the charge of the tryptophan π-electron system). Remarkably, the dipeptide WR did not show simple coacervation under the conditions examined, but complex coacervation was observed in mixtures with ATP (adenosine triphosphate). The electrostatically stabilized coacervation in this case provides a minimal model for peptide/nucleotide membraneless organelle formation. These are among the simplest model peptide systems observed to date able to undergo either simple or complex coacervation and are of future interest as protocell systems.

Acyl Phosphates as Chemically Fueled Building Blocks for Self-Sustaining Protocells

Lipids spontaneously assemble into vesicle-forming membranes. Such vesicles serve as compartments for even the simplest living systems. Vesicles have been extensively studied for constructing synthetic cells or as models for protocells-the cells hypothesized to have existed before life. These compartments exist almost always close to equilibrium. Life, however, exists out of equilibrium. In this work, we studied vesicle-based compartments regulated by a non-equilibrium chemical reaction network that converts activating agents. In this way, the compartments require a constant or periodic supply of activating agents to sustain themselves. Specifically, we use activating agents to condense carboxylates and phosphate esters into acyl phosphate-based lipids that form vesicles. These vesicles can only be sustained when condensing agents are present; without them, they decay. We demonstrate that the chemical reaction network can operate on prebiotic activating agents, opening the door to prebiotically plausible, self-sustainable protocells that compete for resources. In future work, such protocells should be endowed with a genotype, e.g., self-replicating RNA structures, to alter the protocell's behavior. Such protocells could enable Darwinian evolution in a prebiotically plausible chemical system.

Kinetically Controlled and Nonequilibrium Assembly of Block Copolymers in Solution

Covalent polymers are versatile macromolecules that have found widespread use in society. Contemporary methods of polymerization have made it possible to construct sequence polymers, including block copolymers, with high precision. Such copolymers assemble in solution when the blocks have differing solubilities. This produces nano- and microparticles of various shapes and sizes. While it is straightforward to draw an analogy between such amphiphilic block copolymers and phospholipids, these two classes of molecules show quite different assembly characteristics. In particular, block copolymers often assemble under kinetic control, thus producing nonequilibrium structures. This leads to a rich variety of behaviors being observed in block copolymer assembly, such as pathway dependence (e.g., thermal history), nonergodicity and responsiveness. The dynamics of polymer assemblies can be readily controlled using changes in environmental conditions and/or integrating functional groups situated on polymers with external chemical reactions. This perspective highlights that kinetic control is both pervasive and a useful attribute in the mechanics of block copolymer assembly. Recent examples are highlighted in order to show that toggling between static and dynamic behavior can be used to generate, manipulate and dismantle nonequilibrium states. New methods to control the kinetics of block copolymer assembly will provide endless unanticipated applications in materials science, biomimicry and medicine.

Droplet drinking in constrictions

Droplets generated through microfluidics serve as a common platform for assembling artificial cells, which are feasibly tailored using microfluidic methodology. The ability of natural cells to undergo shape changes, such as phagocytosis, is a typical characteristic that researchers aim to mimic in artificial cells. However, simulating the deformation behavior of natural cells within droplets is exceptionally challenging. Here, this study reports a pinocytosis-like phenomenon observed in droplets, termed "droplet drinking". When droplets traverse a capillary with constrictions, the shear force from the continuous-phase fluid induces relative motion within the droplets, creating concave regions at the rear. These regions facilitate engulfing of the continuous-phase fluid, resulting in the formation of multiple emulsions. This behavior is influenced by the capillary number, and the size of the ingested droplets is governed by the interfacial tension between the two phases. The production of multicore or multi-shell emulsions can be easily accomplished by making slight adjustments to the constrictions. Furthermore, this method demonstrates the integration of reactants into pre-existing droplets, facilitating biochemical reactions. This study presents a convenient approach for generating complex emulsions and an innovative strategy for studying deformation behavior in droplet-based artificial cells.

Fitness Landscapes and Evolution of Catalytic RNA

The relationship between genotype and phenotype, or the fitness landscape, is the foundation of genetic engineering and evolution. However, mapping fitness landscapes poses a major technical challenge due to the amount of quantifiable data that is required. Catalytic RNA is a special topic in the study of fitness landscapes due to its relatively small sequence space combined with its importance in synthetic biology. The combination of in vitro selection and high-throughput sequencing has recently provided empirical maps of both complete and local RNA fitness landscapes, but the astronomical size of sequence space limits purely experimental investigations. Next steps are likely to involve data-driven interpolation and extrapolation over sequence space using various machine learning techniques. We discuss recent progress in understanding RNA fitness landscapes, particularly with respect to protocells and machine representations of RNA. The confluence of technical advances may significantly impact synthetic biology in the near future.

Constrained dynamics of DNA oligonucleotides in phase-separated droplets

Understanding the dynamics of biomolecules in complex environments is crucial for elucidating the effect of condensed and heterogeneous environments on their functional properties. A relevant environment-and one that can also be mimicked easily in vitro-is that of phase-separated droplets. While phase-separated droplet systems have been shown to compartmentalize a wide range of functional biomolecules, the effects of internal structuration of droplets on the dynamics and mobility of internalized molecules remain poorly understood. Here, we use fluorescence correlation spectroscopy to measure the dynamics of short oligonucleotides encapsulated within two representative kinds of uncharged and charged phase-separated droplets. We find that the internal structuration controls the oligonucleotide dynamics in these droplets, revealed by measuring physical parameters at high spatiotemporal resolution. By varying oligonucleotide length and salt concentrations (and thereby charge screening), we found that the dynamics are significantly affected in the noncharged droplets compared to the charged system. Our work lays the foundation for unraveling and quantifying the physical parameters governing biomolecular transport in the condensed environment.

Programmable Enzymatic Reaction Network in Artificial Cell-Like Polymersomes

The ability to precisely control in vitro enzymatic reactions in synthetic cells plays a crucial role in the bottom-up design of artificial cell models that can recapitulate the key cellular features and functions such as metabolism. However, integration of enzymatic reactions has been limited to bulk or microfluidic emulsions without a membrane, lacking the ability to design more sophisticated higher-order artificial cell communities for reconstituting spatiotemporal biological information at multiple length scales. Herein, droplet microfluidics is utilized to synthesize artificial cell-like polymersomes with distinct molecular permeability for spatiotemporal control of enzymatic reactions driven by external signals and fuels. The presence of a competing reverse enzymatic reaction that depletes the active substrates is shown to enable demonstration of fuel-driven formation of sub-microcompartments within polymersomes as well as realization of out-of-equilibrium systems. In addition, the different permeability characteristics of polymersome membranes are exploited to successfully construct a programmable enzymatic reaction network that mimics cellular communication within a heterogeneous cell community through selective molecular transport.

Active droplets through enzyme-free, dynamic phosphorylation

Life continuously transduces energy to perform critical functions using energy stored in reactive molecules like ATP or NADH. ATP dynamically phosphorylates active sites on proteins and thereby regulates their function. Inspired by such machinery, regulating supramolecular functions using energy stored in reactive molecules has gained traction. Enzyme-free, synthetic systems that use dynamic phosphorylation to regulate supramolecular processes have not yet been reported, to our knowledge. Here, we show an enzyme-free reaction cycle that consumes the phosphorylating agent monoamidophosphate by transiently phosphorylating histidine and histidine-containing peptides. The phosphorylated species are labile and deactivate through hydrolysis. The cycle exhibits versatility and tunability, allowing for the dynamic phosphorylation of multiple precursors with a tunable half-life. Notably, we show the resulting phosphorylated products can regulate the peptide's phase separation, leading to active droplets that require the continuous conversion of fuel to sustain. The reaction cycle will be valuable as a model for biological phosphorylation but can also offer insights into protocell formation.

Phase-separated droplets swim to their dissolution

Biological macromolecules can condense into liquid domains. In cells, these condensates form membraneless organelles that can organize chemical reactions. However, little is known about the physical consequences of chemical activity in and around condensates. Working with model bovine serum albumin (BSA) condensates, we show that droplets swim along chemical gradients. Active BSA droplets loaded with urease swim toward each other. Passive BSA droplets show diverse responses to externally applied gradients of the enzyme's substrate and products. In all these cases, droplets swim toward solvent conditions that favor their dissolution. We call this behavior "dialytaxis", and expect it to be generic, as conditions which favor dissolution typically reduce interfacial tension, whose gradients are well-known to drive droplet motion through the Marangoni effect. These results could potentially suggest alternative physical mechanisms for active transport in living cells, and may enable the design of fluid micro-robots.

Controlled Supramolecular Polymerization via Bioinspired, Liquid-Liquid Phase Separation of Monomers

Dynamic supramolecular assemblies, driven by noncovalent interactions, pervade the biological realm. In the synthetic domain, their counterparts, supramolecular polymers, endowed with remarkable self-repair and adaptive traits, are often realized through bioinspired designs. Recently, controlled supramolecular polymerization strategies have emerged, drawing inspiration from protein self-assembly. A burgeoning area of research involves mimicking the liquid-liquid phase separation (LLPS) observed in proteins to create coacervate droplets and recognizing their significance in cellular organization and diverse functions. Herein, we introduce a novel perspective on synthetic coacervates, extending beyond their established role in synthetic biology as dynamic, membraneless phases to enable structural control in synthetic supramolecular polymers. Drawing parallels with the cooperative growth of amyloid fibrils through LLPS, we present metastable coacervate droplets as dormant monomer phases for controlled supramolecular polymerization. This is achieved via a π-conjugated monomer design that combines structural characteristics for both coacervation through its terminal ionic groups and one-dimensional growth via a π-conjugated core. This design leads to a unique temporal LLPS, resulting in a metastable coacervate phase, which subsequently undergoes one-dimensional growth via nucleation within the droplets. In-depth spectroscopic and microscopic characterization provides insights into the temporal evolution of disordered and ordered phases. Furthermore, to modulate the kinetics of liquid-to-solid transformation and to achieve precise control over the structural characteristics of the resulting supramolecular polymers, we invoke seeding in the droplets, showcasing living growth characteristics. Our work thus opens up new avenues in the exciting field of supramolecular polymerization, offering general design principles and controlled synthesis of precision self-assembled structures in confined environments.

Synergistic stabilization of garlic essential oil nanoemulsions by carboxymethyl chitosan/Tween 80 and application for coating preservation of chilled fresh pork

Garlic essential oil (GEO) is a potential natural antioxidant and antimicrobial agent for food preservation, but its intrinsic low water-solubility, high volatility and poor stability severely limit its application and promotion. In this work, we investigated the synergistic stabilization of the GEO-in-water nanoemulsion using carboxymethyl chitosan (CCS) and Tween 80 (TW 80). Additionally, the nanoemulsion was fabricated through high-pressure microfluidization and utilized for the coating-mediated preservation of chilled pork. The garlic essential oil nanoemulsion (GEON) with 3.0 % CCS and 3.0 % TW 80 exhibited more homogeneous droplet size (around 150 nm) and narrower size distribution, while maintained long-term stability with no significant change in size during 30 d storage. Compared with free GEO, the GEONs exhibited a higher scavenging capacity to DPPH and ABTS free radicals as well as higher inhibitory effects against Escherichia coli and Staphylococcus aureus, suggesting that the encapsulation of GEO in nanoemulsion considerably improved its antioxidant and antibacterial activities. Furthermore, the results of coating preservation experiments showed that the GEON coating effectively expanded the shelf-life of chilled fresh pork for approximately one week. Altogether, this study would guide the development of GEO-loaded nanoemulsions, and promote GEON as a promising alternative for coating preservation of chilled fresh meat.

Probing the surface charge of condensates using microelectrophoresis

Biomolecular condensates play an important role in cellular organization. Coacervates are commonly used models that mimic the physicochemical properties of biomolecular condensates. The surface of condensates plays a key role in governing molecular exchange between condensates, accumulation of species at the interface, and the stability of condensates against coalescence. However, most important surface properties, including the surface charge and zeta potential, remain poorly characterized and understood. The zeta potential of coacervates is often measured using laser doppler electrophoresis, which assumes a size-independent electrophoretic mobility. Here, we show that this assumption is incorrect for liquid-like condensates and present an alternative method to study the electrophoretic mobility of coacervates and in vitro condensate models by microelectrophoresis and single-particle tracking. Coacervates have a size-dependent electrophoretic mobility, originating from their fluid nature, from which a well-defined zeta potential is calculated. Interestingly, microelectrophoresis measurements reveal that polylysine chains are enriched at the surface of polylysine/polyaspartic acid complex coacervates, which causes the negatively charged protein ɑ-synuclein to adsorb and accumulate at the interface. Addition of ATP inverts the surface charge, displaces ɑ-synuclein from the surface and may help to suppress its interface-catalyzed aggregation. Together, these findings show how condensate surface charge can be measured and altered, making this microelectrophoresis platform combined with automated single-particle tracking a promising characterization technique for both biomolecular condensates and coacervate protocells.

Self-assembly of stabilized droplets from liquid-liquid phase separation for higher-order structures and functions

Dynamic microscale droplets produced by liquid-liquid phase separation (LLPS) have emerged as appealing biomaterials due to their remarkable features. However, the instability of droplets limits the construction of population-level structures with collective behaviors. Here we first provide a brief background of droplets in the context of materials properties. Subsequently, we discuss current strategies for stabilizing droplets including physical separation and chemical modulation. We also discuss the recent development of LLPS droplets for various applications such as synthetic cells and biomedical materials. Finally, we give insights on how stabilized droplets can self-assemble into higher-order structures displaying coordinated functions to fully exploit their potentials in bottom-up synthetic biology and biomedical applications.

Triple Adaptation of Constitutional Dynamic Networks of Imines in Response to Micellar Agents: Internal Uptake-Interfacial Localization-Shape Transition

Understanding the behavior of complex chemical reaction networks and how environmental conditions can modulate their organization as well as the associated outcomes may take advantage of the design of related artificial systems. Microenvironments with defined boundaries are of particular interest for their unique properties and prebiotic significance. Dynamic covalent libraries (DCvLs) and their underlying constitutional dynamic networks (CDNs) have been shown to be appropriate for studying adaptation to several processes, including compartmentalization. However, microcompartments (e.g., micelles) provide specific environments for the selective protection from interfering reactions such as hydrolysis and an enhanced chemical promiscuity due to the interface, governing different processes of network modulation. Different interactions between the micelles and the library constituents lead to dynamic sensing, resulting in different expressions of the network through pattern generation. The constituents integrated into the micelles are protected from hydrolysis and hence preferentially expressed in the network composition at the cost of constitutionally linked members. In the present work, micellar integration was observed for two processes: internal uptake based on hydrophobic forces and interfacial localization relying on attractive electrostatic interactions. The latter drives a complex triple adaptation of the network with feedback on the shape of the self-assembled entity. Our results demonstrate how microcompartments can enforce the expression of constituents of CDNs by reducing the hydrolysis of uptaken members, unravelling processes that govern the response of reactions networks. Such studies open the way toward using DCvLs and CDNs to understand the emergence of complexity within reaction networks by their interactions with microenvironments.