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An important challenge in active matter lies in harnessing useful global work from entities that produce work locally, e.g., via self-propulsion. We investigate here the active matter version of a classical capillary rise effect, by considering a non-phase separated sediment of self-propelled Janus colloids in contact with a vertical wall. We provide experimental evidence of an unexpected and dynamic adsorption layer at the wall. Additionally, we develop a complementary numerical model that recapitulates the experimental observations. We show that an adhesive and aligning wall enhances the pre-existing polarity heterogeneity within the bulk, enabling polar active particles to climb up a wall against gravity, effectively powering a global flux. Such steady-state flux has no equivalent in a passive wetting layer.
Hybrid hydrogels are hydrogels that exhibit heterogeneity in the network architecture by means of chemical composition and/or microstructure. The different types of interactions, together with structural heterogeneity, which can be created on different length scales, determine the mechanical properties of the final material to a large extent. In this work, the microstructure–mechanical property relationships for a hybrid hydrogel that contains both electrostatic and covalent interactions are investigated. The hybrid hydrogel is composed of a microphase-separated polyelectrolyte complex network (PEC) made of poly(4-styrenesulfonate) and poly(diallyldimethylammonium chloride) within a soft and elastic polyacrylamide hydrogel network. The system exhibits a granular structure, which is attributed to the liquid–liquid phase separation into complex coacervate droplets induced by the polymerization and the subsequent crowding effect of the polyacrylamide chains. The coacervate droplets are further hardened into PEC granules upon desalting the hydrogel. The structure formation is confirmed by a combination of electron microscopic imaging and molecular dynamics simulations. The interpenetration of both networks is shown to enhance the toughness of the resulting hydrogels due to the dissipative behavior of the PEC through the rupture of electrostatic interactions. Upon cyclic loading–unloading, the hydrogels show recovery of up to 80% of their original dissipative behavior in less than 300 s of rest with limited plasticity. The granular architecture and the tough and self-recoverable properties of the designed hybrid networks make them good candidates for applications, such as shape-memory materials, actuators, biological tissue mimics, and elastic substrates for soft sensors.
Synthetic biology applies concepts from electrical engineering and information processing to endow cells with computational functionality. Transferring the underlying molecular components into materials and wiring them according to topologies inspired by electronic circuit boards has yielded materials systems that perform selected computational operations. However, the limited functionality of available building blocks is restricting the implementation of advanced information-processing circuits into materials. Here, a set of protease-based biohybrid modules the bioactivity of which can either be induced or inhibited is engineered. Guided by a quantitative mathematical model and following a design-build-test-learn (DBTL) cycle, the modules are wired according to circuit topologies inspired by electronic signal decoders, a fundamental motif in information processing. A 2-input/4-output binary decoder for the detection of two small molecules in a material framework that can perform regulated outputs in form of distinct protease activities is designed. The here demonstrated smart material system is strongly modular and can be used for biomolecular information processing for example in advanced biosensing or drug delivery applications.
Molecular optogenetics utilizes genetically encoded, light-responsive protein switches to control the function of molecular processes. Over the last two years, there have been notable advances in the development of novel optogenetic switches, their utilization in elucidating intricate signaling pathways, and their progress toward practical applications in biotechnological processes, material sciences, and therapeutic applications. In this review, we discuss these areas, offer insights into recent developments, and contemplate future directions.
The hierarchical design of the toe pad surface in geckos and its reversible adhesiveness have inspired material scientists for many years. Micro- and nano-patterned surfaces with impressive adhesive performance have been developed to mimic gecko's properties. While the adhesive performance achieved in some examples has surpassed living counterparts, the durability of the fabricated surfaces is limited and the capability to self-renew and restore function—inherent to biological systems—is unimaginable. Here the morphogenesis of gecko setae using skin samples from the Bibron´s gecko (Chondrodactylus bibronii) is studied. Gecko setae develop as specialized apical differentiation structures at a distinct cell–cell layer interface within the skin epidermis. A primary role for F-actin and microtubules as templating structural elements is necessary for the development of setae's hierarchical morphology, and a stabilization role of keratins and corneus beta proteins is identified. Setae grow from single cells in a bottom layer protruding into four neighboring cells in the upper layer. The resulting multicellular junction can play a role during shedding by facilitating fracture of the cell–cell interface and release of the high aspect ratio setae. The results contribute to the understanding of setae regeneration and may inspire future concepts to bioengineer self-renewable patterned adhesive surfaces.
Water-Driven Sol-Gel Transition in Native Cellulose/1-Ethyl-3-methylimidazolium Acetate Solutions
(2024)
The addition of water to native cellulose/1-ethyl-3-methylimidazolium acetate solutions catalyzes the formation of gels, where polymer chain–chain intermolecular associations act as cross-links. However, the relationship between water content (Wc), polymer concentration (Cp), and gel strength is still missing. This study provides the fundamentals to design water-induced gels. First, the sol–gel transition occurs exclusively in entangled solutions, while in unentangled ones, intramolecular associations hamper interchain cross-linking, preventing the gel formation. In entangled systems, the addition of water has a dual impact: at low water concentrations, the gel modulus is water-independent and controlled by entanglements. As water increases, more cross-links per chain than entanglements emerge, causing the modulus of the gel to scale as Gp ∼ Cp2Wc3.0±0.2. Immersing the solutions in water yields hydrogels with noncrystalline, aggregate-rich structures. Such water–ionic liquid exchange is examined via Raman, FTIR, and WAXS. Our findings provide avenues for designing biogels with desired rheological properties.
Electrochemical water desalination is an emerging technology known for its high efficiency and low energy consumption in removing ions from aqueous media. The present thesis begins by explaining the fundamentals of a typical electrochemical water desalination system and presenting relevant performance metrics. The significance and limitations of the latter metrics are then discussed based on the generations of the electrodes developed during the past few decades. This report seeks to expand the scope by investigating MXene (titanium carbide) as a purely pseudocapacitive material characterized by a capacitor-like electric response achieved through ion intercalation. Afterward, the merit of MXene when utilized as an electrode in electrochemical desalination is investigated for both single-salt and multi-salt aqueous solutions, ultimately establishing qualitative insights into the relationship between MXene properties and its electrochemical desalination behavior. Finally, the thesis goes beyond MXene and explores its sibling materials, such as MBene (transition metal boride), for lithium-ion battery electrodes. As another application of 2D nanolamellar materials at the water-energy nexus, we have explored MXene conversion into transition metal dichalcogenides by sulfidation heat treatment and its merit as electrodes for hydrogen electrocatalysis. These findings can contribute to developing more efficient and sustainable energy storage, conversion, and desalination technologies.
Extracellular vesicles (EVs) are lipid-membrane-enclosed particles released from cells, playing a pivotal role in cellular communication, particularly within the immune system. The fundamental molecular mechanisms through which EVs offer unique functionality for immunotherapeutic benefits are identified and reviewed. The focus is on three essential features, all rooted in the EV lipid membrane: immune receptor–ligand interactions at the EV membrane interface, the shielding of immunogenic cargo within the EVs, and the fusion of EVs with target cell membranes for direct cargo delivery. From this, how these distinct EV attributes, from their initial description and analysis in immune communication, have led to the development of novel immunotherapeutic strategies is traced. This review delves into how these strategies are applied in various immunotherapies, such as cancer immunotherapy, autoimmune diseases, infections, vaccinations, and graft-versus-host diseases, to modulate communication among different cell types for immune regulation. It is concluded by reviewing clinical trials involving EVs in immunotherapy that have effectively harnessed EVs' unique molecular mechanisms in clinical settings. Research and standardization efforts to maximize the potential impact of EVs on immunotherapy are further suggested.
Natural killer (NK) cells play a vital role in eliminating tumorigenic cells. Efficient locating and killing of target cells in complex three-dimensional (3D) environments are critical for their functions under physiological conditions. However, the role of mechanosensing in regulating NK-cell killing efficiency in physiologically relevant scenarios is poorly understood. Here, we report that the responsiveness of NK cells is regulated by tumor cell stiffness. NK-cell killing efficiency in 3D is impaired against softened tumor cells, whereas it is enhanced against stiffened tumor cells. Notably, the durations required for NK-cell killing and detachment are significantly shortened for stiffened tumor cells. Furthermore, we have identified PIEZO1 as the predominantly expressed mechanosensitive ion channel among the examined candidates in NK cells. Perturbation of PIEZO1 abolishes stiffness-dependent NK-cell responsiveness, significantly impairs the killing efficiency of NK cells in 3D, and substantially reduces NK-cell infiltration into 3D collagen matrices. Conversely, PIEZO1 activation enhances NK killing efficiency as well as infiltration. In conclusion, our findings demonstrate that PIEZO1-mediated mechanosensing is crucial for NK killing functions, highlighting the role of mechanosensing in NK-cell killing efficiency under 3D physiological conditions and the influence of environmental physical cues on NK-cell functions.
This study presents a novel approach to developing high-performance lithium-ion battery electrodes by loading titania-carbon hybrid spherogels with sulfur. The resulting hybrid materials combine high charge storage capacity, electrical conductivity, and core-shell morphology, enabling the development of next-generation battery electrodes. We obtained homogeneous carbon spheres caging crystalline titania particles and sulfur using a template-assisted sol-gel route and carefully treated the titania-loaded carbon spherogels with hydrogen sulfide. The carbon shells maintain their microporous hollow sphere morphology, allowing for efficient sulfur deposition while protecting the titania crystals. By adjusting the sulfur impregnation of the carbon sphere and varying the titania loading, we achieved excellent lithium storage properties by successfully cycling encapsulated sulfur in the sphere while benefiting from the lithiation of titania particles. Without adding a conductive component, the optimized material provided after 150 cycles at a specific current of 250 mA g–1 a specific capacity of 825 mAh g–1 with a Coulombic efficiency of 98%.