Ryota Tamate

Transporting millimeter-sized droplets on a surface is fundamental for droplet fluidics, which requires minimization of droplet sticking and energy input. One promising strategy is tethering the self-propelling ability to droplets on nonsticking surfaces. Self-propulsion is achieved by forming a gradient structure on the substrate. Typically, the gradient is highly directional and nonreprogrammable, making the regulation of transport challenging. Here, we report that droplets are self-propelled from the edge to the center of the substrate. The substrate surface is covered with a stabilized lubricant that exhibits droplet slipperiness. Near the substrate edge, a lubricant thickness gradient forms, which self-propels the droplet. This property enabled the regulated self-propulsion of droplets by spatiotemporal edge-shape design. The edge shape determines the direction of the droplet’s self-propulsion. Moreover, the in situ edge appearance/disappearance, achieved by separating/connecting two neighboring coated substrates, enabled the regulation of self-propelling timing because the lubricant gradient structure is reconfigurable. We demonstrate droplets’ self-climbing, upside-down self-propulsion, in situ stop-and-go motion, two-droplet attractive motion, and reconfigurable two-dimensional droplet motion. We also demonstrate that the sliding droplet on the zigzag-shaped substrate moves along with the substrate’s shape due to edge self-propulsion. These droplet manipulations require no special devices, making them increasingly accessible.

Solid polymer electrolytes (SPEs) are polymer-based, flexible, and nonflammable electrolytes, making them promising candidates for developing highly stretchable electrochemical devices. However, in conventional designs, toughness improvement is typically coupled with an increase in stiffness. This coupling often arises from the introduction of thermally reversible crystals (TRCs) of polymer, resulting in high stiffness, brittleness, and poor conformability to electrodes. In this study, we develop a material design strategy to decouple toughness from stiffness in SPEs using strain-induced crystallization (SIC) in a homogeneous four-branched poly(ethylene glycol) (Tetra-PEG) network. SIC significantly enhances the toughness without increasing the stiffness, enabling the formation of soft, tough, and stretchable SPEs. Building on this decoupled platform, stiffness was reintroduced through TRCs of PEG, yielding SPEs that were both stiff and highly fracture-resistant. Importantly, upon heating, these materials exhibited thermoplastic behavior, which improved their conformability to metal electrodes. Consequently, Li|Tetra-PEG SPE|Li symmetric cells exhibited reversible lithium plating and stripping with stable long-term cycling. Overall, the proposed design strategy effectively decouples toughness from stiffness, thereby overcoming the conventional trade-offs in SPEs.

Shape memory ion gels comprising ultrahigh molecular weight polymers and ionic liquids are fabricated via a facile one-pot polymerisation, delivering outstanding shape-memory functions, including triple shape-memory behaviour and shape reprogramming.

Inspired by living systems, hierarchical materials have been developed to integrate multiple levels of organization, enabling complex behaviors to emerge from interactions among simpler components. However, understanding how dynamic behaviors are transduced across hierarchical levels in synthetic materials remains a major challenge. Here, we demonstrate the cross-hierarchical transduction of dynamic behaviors in life-like autonomous materials by investigating self-oscillating colloidosomes as a model system. Self-oscillating colloidosomes are composed of self-oscillating microgels, which exhibit autonomous flocculation/dispersion oscillation driven by a self-promoted Belousov-Zhabotinsky reaction at certain temperatures. We identified chemomechanical transduction across hierarchical levels in self-oscillating colloidosomes under out-of-equilibrium conditions. The self-oscillating colloidosomes exhibited swelling/deswelling or shape deformation oscillations in a stochastic manner, originating from flocculation/dispersion oscillations at the microgel level. We found that the choice between these two oscillation modes is determined by the oscillation modes of their constituent self-oscillating microgels. These findings pave the way for the cross-hierarchical design of chemically powered autonomous materials.

Reversible sol–gel transitions are difficult to achieve in conventional water‐swollen hydrogels in open aqueous environments, because polymer chains dissolve or diffuse once the network disassembles. Here, we present a proof‐of‐concept to overcome this limitation by introducing a water‐immiscible and non‐cytotoxic ionic liquid (IL) phase that confines polymer networks and prevents dissolution during reversible phase transitions. We report a photoreversible ion gel that crosses the rheological boundary (tan δ ∼ 1) under light, enabling reversible sol–gel switching within this closed IL environment. The material integrates an ABC triblock copolymer, P(AzoAm‐ r ‐NIPAm)‐ b ‐PBuA‐ b ‐PSt, with a solvent‐quality‐tunable blend of non‐cytotoxic ILs ([P4,4,4,1][TFSI]/[P8,8,8,8][TFSI]). The photoresponsive A‐block, P(AzoAm‐ r ‐NIPAm), exhibits a polarity‐dependent solubility change with the cis / trans isomerization of azobenzene, providing a reversible light‐controlled self‐assembly. Time‐resolved rheology confirmed repeated crossings of tan δ = 1 under alternating UV–vis illumination at 52°C. The switching mechanism is governed by the lifetime of reversible junctions, consistent with transient network theory. In addition, hMSCs adhered to and spread on the ion gel at 37°C, indicating the cytocompatibility of the ion gel itself. This light‐programmable, water‐immiscible ion gel has the potential to provide a reversible liquid‐solid mechanical cue for next‐generation mechanobiology.

Cell culture at liquid|liquid interfaces has attracted attention in mechanobiology. A visible-light-responsive polymer solution in a non-cytotoxic ionic liquid reversibly switches viscoelasticity, offering a new platform for liquid cell scaffolds.

In this study, ion gels are developed that simultaneously exhibit exceptional stiffness and fracture resistance through the synergistic effects of physical entanglements and hydrogen bonding between polymer chains within an ionic liquid matrix. Through radical copolymerization conducted in an ionic liquid under extremely low initiator concentrations, ultrahigh molecular weight polymers in situ with nearly complete monomer conversion are successfully synthesized. This strategy enabled the one‐pot synthesis of physically crosslinked polymer gels composed of abundant entanglements and hydrogen bonds between polymer chains. Notably, it is demonstrated that the synergy between physical entanglements arising from ultrahigh molecular weight polymer chains and noncovalent hydrogen bonding enables the simultaneous enhancement of mechanical properties that typically exhibit trade‐off relationships, such as stiffness, toughness, and fracture resistance. Consequently, the synthesized ion gels exhibited outstanding mechanical performances, ranking among the best previously reported tough polymer gels, while maintaining a favorable balance between ionic conductivity and mechanical strength. These findings underscore the broader significance of the approach, indicating that the integration of physical entanglements and reversible interactions offers a generalized pathway to mechanically robust materials across various polymer systems.

Droplets are highly mobile on lubricant-infused surfaces when droplet−lubricant phases are immiscible, and lubricant layer is stable. Recent studies have shown that the high droplet mobility is due to the absence of three-phase contact line friction by oleoplaning of the droplets on the lubricant layer. In this state, dynamic friction arises primarily from viscous dissipation in the lubricant around the droplet. Classical Landau–Levich–Derjaguin (LLD) law suggests that the friction force is proportional to the two-thirds power of the capillary number, and the lubricant thickness effect is not included. Here, we discovered that increased lubricant thickness enhances the droplet's mobility on lubricant-infused surfaces. This finding is unexpected, as a thicker lubricant layer would typically increase the potential volume for viscous dissipation. We formed stable lubricant layers of varying thicknesses ranging from tens to hundreds of micrometers on a “nanometrically smooth” base layer to remove the influence of surface texture. The droplet friction force on the different lubricant thickness surfaces is measured using the cantilever method. While all surfaces follow the LLD law, the friction force significantly decreases with increasing the lubricant thicknesses. The possible reason is the decrement of the energy dissipation at the lubricant ridge with the thickness. We propose a modified friction model incorporating the thickness dependence with the classical law, offering deeper insight into droplet friction dynamics on the lubricant-infused surfaces. In practical terms, reducing droplet friction enhances transport efficiency, contributing to advancements in fluidic systems and liquid-repellent applications.