A Solid-Liquid Bicontinuous Fiber with Strain-Insensitive Ionic Conduction.

Stretchable ionic conductors are crucial for enabling advanced iontronic devices to operate under diverse deformation conditions. However, when employed as interconnects, existing ionic conductors struggle to maintain stable ionic conduction under strain, hindering high-fidelity signal transmission. Here, it is shown that strain-insensitive ionic conduction can be achieved by creating a solid-liquid bicontinuous microstructure. A bicontinuous fiber from polymerization-induced phase separation, which contains a solid elastomer phase interpenetrated by a liquid ion-conducting phase, is fabricated. The spontaneous partitioning of dissolved salts leads to the formation of a robust self-wrinkled interface, fostering the development of highly tortuous ionic channels. Upon stretch, these meandering ionic channels are straightened, effectively enhancing ionic conductivity to counteract the strain effect. Remarkably, the fiber retains highly stable ionic conduction till fracture, with only 7% resistance increase at 200% strain. This approach presents a promising avenue for designing durable ionic cables capable of signal transmission with minimal strain-induced distortion.

Entropy-Driven Design of Highly Impact-Stiffening Supramolecular Polymer Networks with Salt-Bridge Hydrogen Bonds.

Impact-stiffening materials that undergo a strain rate-induced soft-to-rigid transition hold great promise as soft armors in the protection of the human body and equipment. However, current impact-stiffening materials, such as polyborosiloxanes and shear-thickening fluids, often exhibit a limited impact-stiffening response. Herein, we propose a design strategy for fabricating highly impact-stiffening supramolecular polymer networks by leveraging high-entropy-penalty physical interactions. We synthesized a fully biobased supramolecular polymer comprising poly(α-thioctic acid) and arginine clusters, whose chain dynamics are governed by highly specific guanidinium-carboxylate salt-bridge hydrogen bonds. The resulting material exhibits an exceptional impact-stiffening response of ∼2100 times, transitioning from a soft dissipating state (21 kPa, 0.1 Hz) to a highly stiffened glassy state (45.3 MPa, 100 Hz) with increasing strain rates. Moreover, the material's high energy-dissipating and hot-melting properties bring excellent damping performance and easy hybridization with other scaffolds. This entropy-driven approach paves the way for the development of next-generation soft, sustainable, and impact-resistant materials.

A systematic review and meta-analysis of clinical efficacy of early and late rehabilitation interventions for ischemic stroke.

INTRODUCTION: At present, stroke has become the first cause of death and disability among Chinese adults. With the coming of the aging population in China, the disease burden brought by stroke will be increasingly aggravated. And stroke is a leading cause of disability. There is a golden plastic period after stroke, during which timely and safe intervention and rehabilitation therapy can effectively improve the disability status. However, there is still controversy about the duration of interventional rehabilitation after stroke. This study conducted a meta-analysis on the influence of intervention in early and late ischemic stroke rehabilitation. METHOD: Chinese language databases such as CNKI, Wanfang, and VIP, and English language databases such as Embase, PubMed, Web of Science, and The Cochrane Library were searched, and RCT related to early and late rehabilitation of ischemic stroke from the establishment of the database to October 2023 was collected. Review Manager 5.4.1 was used for relevant analysis. The main outcomes were Barthel Index or Modified Barthel Index, Fugl-Meyer Assessment scale, NIHSS, China Stroke Scale. Standardized Mean Difference (SMD) was used as an effective indicator of continuity variables, and the estimated interval was expressed by 95% confidence interval (CI). RESULTS: A total of 1908 patients were included in 16 studies. The results showed that, compared with late rehabilitation, early rehabilitation improved clinical efficacy. Barthel Index or Modified Barthel Index score was [SMD = 1.40, 95%CI(1.16,1.63), p < 0.001]; the score of Fugl-Meyer Assessment Scale was [SMD = 1.18, 95%Cl (0.85, 1.52), P < 0.001]; the score of NIHSS was [SMD= -0.44, 95% CI(-0.65, -0.24), P < 0.001]; the result of China Stroke Scale score was [SMD= -0.37, 95%CI(-0.56, -0.18), P < 0.001]. CONCLUSION: In comparison with late rehabilitation, early rehabilitation can significantly improve self-care abilities, daily activities, and neurological functions of ischemic stroke patients. TRIAL REGISTRATION: This meta-analysis has been registered with Prospero, and the registration number is CRD42022309911. The registration period is March 22, 2022.

Self-compliant ionic skin by leveraging hierarchical hydrogen bond association.

Robust interfacial compliance is essential for long-term physiological monitoring via skin-mountable ionic materials. Unfortunately, existing epidermal ionic skins are not compliant and durable enough to accommodate the time-varying deformations of convoluted skin surface, due to an imbalance in viscosity and elasticity. Here we introduce a self-compliant ionic skin that consistently works at the critical gel point state with almost equal viscosity and elasticity over a super-wide frequency range. The material is designed by leveraging hierarchical hydrogen bond association, allowing for the continuous release of polymer strands to create topological entanglements as complementary crosslinks. By embodying properties of rapid stress relaxation, softness, ionic conductivity, self-healability, flaw-insensitivity, self-adhesion, and water-resistance, this ionic skin fosters excellent interfacial compliance with cyclically deforming substrates, and facilitates the acquisition of high-fidelity electrophysiological signals with alleviated motion artifacts. The presented strategy is generalizable and could expand the applicability of epidermal ionic skins to more complex service conditions.

Peeling-Stiffening Self-Adhesive Ionogel with Superhigh Interfacial Toughness.

Self-adhesive materials that can directly adhere to diverse solid surfaces are indispensable in modern life and technologies. However, it remains a challenge to develop self-adhesive materials with strong adhesion while maintaining its intrinsic softness for efficient tackiness. Here, a peeling-stiffening self-adhesive ionogel that reconciles the seemingly contradictory properties of softness and strong adhesion is reported. The ionogel contains two ionophilic repeating units with distinct associating affinities, which allows to adaptively wet rough surface in the soft dissipating state for adhering, and to dramatically stiffen to the glassy state upon peeling. The corresponding modulus increases by 117 times driven by strain-rate-induced phase separation, which greatly suppresses crack propagation and results in a super high interfacial toughness of 8046 J m-2 . The self-adhesive ionogel is also transparent, self-healable, recyclable, and can be easily removed by simple moisture treatment. This strategy provides a new way to design high-performance self-adhesive materials for intelligent soft devices.

Human embryonic stem cells secrete macrophage migration inhibitory factor: A novel finding.

Macrophage migration inhibitory factor (MIF) is expressed in a variety of cells and participates in important biological mechanisms. However, few studies have reported whether MIF is expressed in human Embryonic stem cells (ESCs) and its effect on human ESCs. Two human ESCs cell lines, H1 and H9 were used. The expression of MIF and its receptors CD74, CD44, CXCR2, CXCR4 and CXCR7 were detected by an immunofluorescence assay, RT-qPCR and western blotting, respectively. The autocrine level of MIF was measured via enzyme-linked immunosorbent assay. The interaction between MIF and its main receptor was investigated by co-immunoprecipitation and confocal immunofluorescence microscopy. Finally, the effect of MIF on the proliferation and survival of human ESCs was preliminarily explored by incubating cells with exogenous MIF, MIF competitive ligand CXCL12 and MIF classic inhibitor ISO-1. We reported that MIF was highly expressed in H1 and H9 human ESCs. MIF was positively expressed in the cytoplasm, cell membrane and culture medium. Several surprising results emerge. The autosecreted concentration of MIF was 22 ng/mL, which was significantly higher than 2 ng/mL-6 ng/mL in normal human serum, and this was independent of cell culture time and cell number. Human ESCs mainly expressed the MIF receptors CXCR2 and CXCR7 rather than the classical receptor CD74. The protein receptor that interacts with MIF on human embryonic stem cells is CXCR7, and no evidence of interaction with CXCR2 was found. We found no evidence that MIF supports the proliferation and survival of human embryonic stem cells. In conclusion, we first found that MIF was highly expressed in human ESCs and at the same time highly expressed in associated receptors, suggesting that MIF mainly acts in an autocrine form in human ESCs.

Non-equilibrium-Growing Aesthetic Ionic Skin for Fingertip-Like Strain-Undisturbed Tactile Sensation and Texture Recognition.

Humans use periodically ridged fingertips to precisely perceive the characteristics of objects via ion-based fast- and slow-adaptive mechanotransduction. However, designing artificial ionic skins with fingertip-like tactile capabilities remains challenging because of the contradiction between structural compliance and pressure sensing accuracy (e.g., anti-interference from stretch and texture recognition). Inspired by the formation and modulus-contrast hierarchical structure of fingertips, an aesthetic ionic skin grown from a non-equilibrium Liesegang patterning process is introduced. This ionic skin with periodic stiff ridges embedded in a soft hydrogel matrix enables strain-undisturbed triboelectric dynamic pressure sensing as well as vibrotactile texture recognition. By coupling with another piezoresistive ionogel, an artificial tactile sensory system is further fabricated as a soft robotic skin to mimic the simultaneous fast- and slow-adaptive multimodal sensations of fingers in grasping actions. This approach may inspire the future design of high-performance ionic tactile sensors for intelligent applications in soft robotics and prosthetics.

Aqueous spinning of robust, self-healable, and crack-resistant hydrogel microfibers enabled by hydrogen bond nanoconfinement.

Robust damage-tolerant hydrogel fibers with high strength, crack resistance, and self-healing properties are indispensable for their long-term uses in soft machines and robots as load-bearing and actuating elements. However, current hydrogel fibers with inherent homogeneous structure are generally vulnerable to defects and cracks and thus local mechanical failure readily occurs across fiber normal. Here, inspired by spider spinning, we introduce a facile, energy-efficient aqueous pultrusion spinning process to continuously produce stiff yet extensible hydrogel microfibers at ambient conditions. The resulting microfibers are not only crack-insensitive but also rapidly heal the cracks in 30 s by moisture, owing to their structural nanoconfinement with hydrogen bond clusters embedded in an ionically complexed hygroscopic matrix. Moreover, the nanoconfined structure is highly energy-dissipating, moisture-sensitive but stable in water, leading to excellent damping and supercontraction properties. This work creates opportunities for the sustainable spinning of robust hydrogel-based fibrous materials towards diverse intelligent applications.

Highly Damping and Self-Healable Ionic Elastomer from Dynamic Phase Separation of Sticky Fluorinated Polymers.

Shock-induced low-frequency vibration damage is extremely harmful to bionic soft robots and machines that may incur the malfunction of fragile electronic elements. However, current skin-like self-healable ionic elastomers as the artificial sensing and protecting layer still lack the ability to dampen vibrations, due to their almost opposite design for molecular frictions to material's elasticity. Inspired by the two-phase structure of adipose tissue (the natural damping skin layer), here, a highly damping ionic elastomer with energy-dissipating nanophases embedded in an elastic matrix is introduced, which is formed by polymerization-induced dynamic phase separation of sticky fluorinated copolymers in the presence of lithium salts. Such a supramolecular design decouples the elastic and damping functions into two distinct phases, and thus reconciles a few intriguing properties including ionic conductivity, high stretchability, softness, strain-stiffening, elastic recovery, room-temperature self-healability, recyclability, and most importantly, record-high damping capacity at the human motion frequency range (loss factor tan δ > 1 at 0.1-50 Hz). This study opens the door for the artificial syntheses of high-performance damping ionic skins with robust sensing and protective applications in soft electronics and robotics.

Fatigue-free artificial ionic skin toughened by self-healable elastic nanomesh.

Robust ionic sensing materials that are both fatigue-resistant and self-healable like human skin are essential for soft electronics and robotics with extended service life. However, most existing self-healable artificial ionic skins produced on the basis of network reconfiguration suffer from a low fatigue threshold due to the easy fracture of low-energy amorphous polymer chains with susceptible crack propagation. Here we engineer a fatigue-free yet fully healable hybrid ionic skin toughened by a high-energy, self-healable elastic nanomesh, resembling the repairable nanofibrous interwoven structure of human skin. Such a design affords a superhigh fatigue threshold of 2950 J m-2 while maintaining skin-like compliance, stretchability, and strain-adaptive stiffening response. Moreover, nanofiber tension-induced moisture breathing of ionic matrix leads to a record-high strain-sensing gauge factor of 66.8, far exceeding previous intrinsically stretchable ionic conductors. This concept creates opportunities for designing durable ion-conducting materials that replicate the unparalleled combinatory properties of natural skins more precisely.

Entropy-Mediated Polymer-Cluster Interactions Enable Dramatic Thermal Stiffening Hydrogels for Mechanoadaptive Smart Fabrics.

Thermal stiffening materials that are naturally soft but adaptively self-strengthen upon heat are intriguing for load-bearing and self-protection applications at elevated temperatures. However, to simultaneously achieve high modulus change amplitude and high mechanical strength at the stiffened state remains challenging. Herein, entropy-mediated polymer-mineral cluster interactions are exploited to afford thermal stiffening hydrogels with a record-high storage modulus enhancement of 13 000 times covering a super wide regime from 1.3 kPa to 17 MPa. Such a dramatic thermal stiffening effect is ascribed to the transition from liquid-liquid to solid-liquid phase separations, and at the molecular level, driven by enhanced polymer-cluster interactions. The hydrogel is further processed into sheath-core fibers and smart fabrics, which demonstrate self-strengthening and self-powered sensing properties by co-weaving another liquid metal fiber as both the joule heater and triboelectric layer.

Intrinsically stretchable sheath-core ionic sensory fibers with well-regulated conformal and reprogrammable buckling.

Fiber-based intrinsically stretchable ionic conductors are appealing in the emerging imperceptible sensing devices with an ultrabroad working range, yet still suffer from a low strain sensitivity (gauge factor generally smaller than 3) as compared to electronic conductors. To circumvent this issue, here we report downsized superelastic sheath-core ionic sensory fibers with a fingerprint-like conformal buckling architecture. By delicately regulating the intermolecular interactions in the ionogel core and fluoroelastomer sheath as well as adjusting holding strains, the transparency and buckling density of the fiber are finely modulated. Heat to above 60 °C would further erase the formed buckles, enabling the encoded information of the fiber to be reprogrammable. Importantly, introducing conformal buckles are shown to bring about two-fold sensitivity enhancement of the sensory fibers, leading to a considerably high gauge factor of 10.1 for ionic strain sensors. Furthermore, the water droplet control ability of the buckled fibers with tunable wettability is also demonstrated, contributing to the versatility of the present sensory fibers which may gain promising applications in integrative electronics, optics, and microfluidics.

A Highly Robust Ionotronic Fiber with Unprecedented Mechanomodulation of Ionic Conduction.

Stretchable ionic conductors are appealing for tissue-like soft electronics, yet suffer from a tardy mechanoelectric response due to their poor modulation of ionic conduction arising from intrinsic homogeneous soft chain network. Here, a highly robust ionotronic fiber is designed by synergizing ionic liquid and liquid crystal elastomer with alternate rigid mesogen units and soft chain spacers, which shows an unprecedented strain-induced ionic conductivity boost (≈103 times enhanced as stretched to 2000% strain). Such a surprisingly high enhancement is attributed to the formation of microphase-separated low-tortuosity ion-conducting nanochannels guided by strain-induced emergence of aligned smectic mesophases, thus allowing for ultrafast ion transport that resembles the role of "swimming lanes." Intriguingly, the boosting conductivity even reverses Pouillet's Law-dictated resistance increase at certain strains, leading to unique waveform-discernible strain sensing. Moreover, the fiber retains thermal actuation properties with a maximum of 70% strain changes upon heating, and enables integrated self-perception and actuation. The findings offer a promising molecular engineering route to mechanically modulate the ion transport behavior of ionic conductors toward advanced ionotronic applications.

Skin-like mechanoresponsive self-healing ionic elastomer from supramolecular zwitterionic network.

Stretchable ionic skins are intriguing in mimicking the versatile sensations of natural skins. However, for their applications in advanced electronics, good elastic recovery, self-healing, and more importantly, skin-like nonlinear mechanoresponse (strain-stiffening) are essential but can be rarely met in one material. Here we demonstrate a robust proton-conductive ionic skin design via introducing an entropy-driven supramolecular zwitterionic reorganizable network to the hydrogen-bonded polycarboxylic acid network. The design allows two dynamic networks with distinct interacting strength to sequentially debond with stretch, and the conflict among elasticity, self-healing, and strain-stiffening can be thus defeated. The representative polyacrylic acid/betaine elastomer exhibits high stretchability (1600% elongation), immense strain-stiffening (24-fold modulus enhancement), ~100% self-healing, excellent elasticity (97.9 ± 1.1% recovery ratio, <14% hysteresis), high transparency (99.7 ± 0.1%), moisture-preserving, anti-freezing (elastic at -40 °C), water reprocessibility, as well as easy-to-peel adhesion. The combined advantages make the present ionic elastomer very promising in wearable iontronic sensors for human-machine interfacing.

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing.

Highly conductive and stretchy fibers are crucial components for smart fabrics and wearable electronics. However, most of the existing fiber conductors are strain sensitive with deteriorated conductance upon stretching, and thus, a compromised strategy via introducing merely geometric distortion of conductive path is often used for stable conductance. Here, we report a coaxial wet-spinning process for continuously fabricating intrinsically stretchable, highly conductive yet conductance-stable, liquid metal sheath-core microfibers. The microfiber can be stretched up to 1170%, and upon fully activating the conductive path, a very high conductivity of 4.35 × 104 S/m and resistance change of only 4% at 200% strain are realized, arising from both stretch-induced channel opening and stretching out of tortuous serpentine conductive path of the percolating liquid metal network. Moreover, the microfibers can be easily woven into an everyday glove or fabric, acting as excellent joule heaters, electrothermochromic displays, and self-powered wearable sensors to monitor human activities.

Tuning the properties of hydrogels made from poly(acrylic acid) and calcium salts.

Hydrogels consisting of poly(acrylic acid) (PAA) and calcium ions are a promising class of materials with shapeable, stretchable and self-healing behaviour originating from the reversible and dynamic nature of the electrostatic and hydrogen bonds in the structure. In the dry state, such materials - referred to as "mineral plastics"- can be transparent, hard and flame-resistant, while addition of water will result in rehydration and complete recoverage of the initial gel-like state. These desirable characteristics strongly depend on the molar mass of the used type of PAA and the experimental conditions at which the hydrogels are prepared. In this work, we show how the macroscopic properties of the materials can be adjusted by controlling the initial concentration of dissolved PAA and/or its molecular weight, and how rheological measurements can be used to monitor the resulting physical properties. Furthermore, we have employed isothermal titration calorimetry (ITC) to investigate thermodynamic aspects of the hydrogel formation to gain a better understanding of the underlying mechanism(s). Our results reveal that, and explain why, PAA molar masses between 50 and 100 kDa are particulary suitable for the formation of hydrogels with optimized properties, thus establishing a rational basis for targeted design of such materials with tailor-made characteristics.

Distinct Cation-Anion Interactions in the UCST and LCST Behavior of Polyelectrolyte Complex Aqueous Solutions.

Polyelectrolyte complexes (PECs) are recently observed to possess diversified thermoresponsive phase transition behaviors in aqueous solutions. Herein, by adjusting the initial polymer concentrations (Cpi) of poly(styrenesulfonate) (PSS)/poly(diallyldimethylammonium) (PDADMA) PEC in the same saline solution, in addition to previously reported lower critical solution temperature (LCST), we experimentally observed the upper critical solution temperature (UCST)-type phase transition behavior of PSS/PDADMA PECs at a lower polymer concentration. As elucidated by temperature-dependent Raman spectroscopy and two-dimensional correlation analysis, at temperatures lower than UCST, more hydrophobic polyelectrolyte chains lead to a high proportion of contact ion pairs (CIPs), contributing to UCST-type solid-liquid phase transition; however, at higher concentrations of PEC, the less hydrophobic polyelectrolyte chains correspond to a higher proportion of solvent-separated ion pairs (SIPs), which enables the occurrence of LCST-type liquid-liquid phase transition. With the spectroscopic indicator of CIPs/SIPs peak ratio and monitoring the hydration state of polymer chains, the complex interplays of PSS/PDADMA PECs are hereby interpreted at the molecular level, which lays the mechanistic foundation for designing other thermoresponsive PEC assemblies.

Microdynamic changes of moisture-induced crystallization of amorphous calcium carbonate revealed via in situ FTIR spectroscopy.

Amorphous calcium carbonate (ACC) is the most important intermediate phase in the nucleation/crystallization process of CaCO3, and thus the proper interpretation of how ACC transforms into final crystals at the molecular level is crucial to understand various biomineralization phenomena. Herein, we successfully monitored the moisture-induced crystallization process of ACC via in situ FTIR spectroscopy, which is very sensitive to the specific changes of the different vibrational modes of carbonates and water molecules. In combination with the tools of perturbation correlation moving window and two-dimensional correlation spectroscopy, it is found that the driving force of ACC crystallization is the fracture of hydrogen bonds formed by H2OCO32-. The bending vibrations of carbonate are more sensitive to moisture permeation than the stretching modes, and the whole crystallization process can be divided into three sequential stages, i.e., the hydrated ACC first loses its structural water and converts to the dehydrated ACC, which then gradually transforms into vaterite, followed by the final growth of vaterite crystals. Anhydrous ACC microdomains are found to be already existing in the as-prepared ACCs.

Mineral plastic hydrogels from the cross-linking of polyacrylic acid and alkaline earth or transition metal ions.

Used polymer materials generate huge environmental problems nowadays. A new solution was recently provided by a physically cross-linked polyacrylic acid-based mineral plastic hydrogel, which is resistant in the anhydrous state and easily recyclable. Here we report that substituting the cross-linker by various cations and controlling the metal content can provide promising materials with analogous properties.

Colloidally Stable Monolayer Nanosheets with Colorimetric Responses.

Despite the discovery of chromogenic-layered materials for decades of years, fabrication of colloidally stable monolayer organic 2D nanosheets in aqueous media with colorimetric responses is still challenging. Herein reported is the first solution synthesis of chromic monolayer nanosheets via the topochemical polymerization of self-assembled amphiphilic diacetylenes in aqueous media. The polydiacetylene (PDA) nanosheets are ≈3-4 nm thick in solution and only ≈1.9 nm thick in the dried state, while the lateral size can reach several micrometers. Moreover, the aqueous stability endows PDA nanosheets with excellent processability, which can further assemble into films via vacuum filtration or act as an ink for high-resolution inkjet printing. The filtrated films and printed patterns exhibit fully reversible blue-to-red thermochromism, and the film also displays an interesting reversible colorimetric transition in response to near-infrared light, which is not reported for other PDA-only systems. The present colloidal PDA nanosheets should represent a new kind of chromic organic 2D nanomaterials that may be applied as novel building blocks for developing intelligent hybrid materials and may also find diverse sensing, display and/or anticounterfeiting applications.