Soft Materials Research Articles

Publisher Correction: Non-classical crystallization in soft and organic materials

Publisher Correction: Non-classical crystallization in soft and organic materials

Extremely durable electrical impedance tomography–based soft and ultrathin wearable e-skin for three-dimensional tactile interfaces

In the rapidly evolving field of human-machine interfaces (HMIs), high-resolution wearable electronic skin (e-skin) is essential for user interaction. However, traditional array-structured tactile interfaces require increased number of interconnects, while soft material–based computational methods have limited functionalities. Here, we introduce a thin and soft e-skin for tactile interfaces, offering high mapping capabilities through electrical impedance tomography (EIT). We employed an organic/inorganic hybrid structure with simple, cost-effective fabrication processes, ensuring flexibility and stability. The conductive and stretchable sensing domain includes a micropatterned multiwall carbon nanotube and elastomer composite. The skin-like tactile interface effectively detects pressure-induced conductivity changes, offering superior spatiotemporal resolution with fewer interconnects (pixel/interconnects >57). This EIT-based tactile interface discerns external pressures to a submillimeter degree and vertical deformations of a few hundred micrometers. It sustains stable functions under external damage or environmental changes, confirming its suitability for persistent wearable use. We demonstrate practical applications in real-time HMIs: handwriting recognition and drone control.

Salt Gradient-Induced Phoresis of Vesicles and Enhanced Membrane Fusion in a Crowded Milieu.

Phoresis of biocolloidal objects in response to chemical gradients is a matter of interest among diverse scientific disciplines owing to their importance in the spatiotemporal orchestration of biochemical processes. Although there are reports of soft matter transport/phoresis in the gradient of ions or salts in the aqueous system, their phoretic behavior in the presence of macromolecular crowder is largely unexplored. Notably, cellular cytoplasm is illustrated as a crowded milieu and thereby understanding biomolecular phoresis in the presence of polymeric macromolecules would endorse phoretic behavior in a biomimetic environment. Here, we report the phoresis-induced enhanced aggregation and fusion of vesicles in gradients of monovalent (NaCl) and divalent salt (MgCl2), in the presence of polymeric crowder, polyethylene glycol of molecular weight 400 (PEG 400). Apart from diffusiophoresis, depletion force plays a crucial factor in crowded environments to control localized vesicle aggregation in a salt gradient. This demonstration will potentially show the pathway to future research related to spatiotemporally correlated liposomal transport and membrane-dependent function (such as content mixing and signaling) in a physiologically relevant crowded environment.

Photothermalprogramming of magnetic soft materials for complex and reconfigurable 3D deformations

Photothermalprogramming of magnetic soft materials for complex and reconfigurable 3D deformations

Ionic Liquid Crystals as Chromogenic Materials

Ionic liquid crystals (ILCs), a class of soft matter materials whose properties can be tuned by the wise pairing of the cation and anion, have recently emerged as promising candidates for different applications, combining the characteristics of ionic liquids and liquid crystals. Among those potential uses, this review aims to cover chromogenic ILCs. In this context, examples of photo-, electro- and thermochromism based on ILCs are provided. Furthermore, thermotropic and lyotropic ionic liquid crystals are also summarised, including the most common chemical and phase structures, as well as the advantages of confining these materials. This manuscript also comprises the following main experimental techniques used to characterise ILCs: Differential Scanning Calorimetry (DSC), Polarised Optical Microscopy (POM) and X-Ray Powder Diffraction (XRD). Chromogenic ILCs can be interesting smart materials for energy and health purposes.

Explaining the spread in measurement of PDMS elastic properties: influence of test method and curing protocol.

Accuracy in the measurement of mechanical properties is essential for precision engineering and for the interrogation of composition-property relationships. Conventional methods of mechanical testing, such as uniaxial tension, compression, and nanoindentation, provide highly repeatable and reliable results for stiff materials, for which they were originally developed. However, when applied to the characterization of soft and biological materials, the same cannot be said, and the spread of reported properties of similar materials is vast. Polydimethylsiloxane (PDMS), commonly obtained from Dow as SYLGARD 184, is a ubiquitous such material, which has been integral to the rapid development of biocompatible microfluidic devices and flexible electronics in recent decades. However, reported shear moduli of this material range over 2 orders of magnitude for similar chemical compositions. Taking advantage of the increased mechanical scrutiny afforded to SYLGARD 184 in recent years, we combine both published and new experimental data obtained using 9 mechanical test methods. A statistical analysis then elucidates the significant bias induced by the test method itself, and distinguishes this bias from the influence of curing protocols on the mechanical properties. The goal of this work is thus two-fold: (i) it provides a quantitative understanding of the different factors that influence reported properties of this particular material, and (ii) it serves as a cautionary tale. As researchers in the field of mechanics strive to quantify the properties of increasingly complex soft and biological materials, converging on a standardized measurement of PDMS is a necessary first step.

Bridging the Gap Rather Than Filling the Entire Valley-Anatomic Insights When Treating the Medial Infraorbital Region.

The treatment of the medial infraorbital region also termed the tear trough has become increasingly popular by the use of soft tissue fillers in a minimally invasive approach using a cannula. A total of 246 tear troughs were injected and investigated originating from 123 study participants. The clinical outcome was evaluated 6 months after the treatment by independent observers based on standardized frontal images and the procedure was documented by ultrasound imaging. On average, 0.26 (0.1) cc [range: 0.08-0.32] of soft tissue filler material was injected per tear trough. Tear trough depth was before the treatment rated as 2.12 (0.4), whereas after the treatment it was 1.15 (0.4) (p < 0.001). Hyperpigmentation score was 2.19 (0.4) before the treatment, whereas after the treatment it was 1.31 (0.5) (p < 0.001). Intraorbital fat pseudo-prolapse severity was rated before the treatment 1.88 (0.7), whereas it was rated after the treatment 1.14 (0.3) (p < 0.001). Wrinkle severity of the lower eyelid was rated before the treatment 1.51 (0.6), whereas it was rated after the treatment 1.12 (0.3) (p < 0.001). The results of this retrospectively investigated case series revealed that the conducted injection technique for treating the tear trough for medial infraorbital hollowing with a cannula provided statistically significant clinical improvement with a limited adverse events profile. The technique utilized an injection approach which was perpendicularly oriented to the longitudinal axis of the tear trough thereby "bridging the gap instead of filling the entire valley."

Ferroelastic ionic organic crystals that self-heal to 95%

The realm of self-healing materials integrates chemical and physical mechanisms that prevent wear and fracturing and extend the operational lifetime. Unlike the favorable rheology of amorphous soft materials that facilitates efficient contact between fragments, the efficiency of recovery of atomistically ordered materials is restricted by slower interfacial mass transport and the need for ideal physical alignment, which limits their real-world application. We report drastic enhancements in efficiency and recovery time in the self-healing of anilinium bromide, challenging these limitations. Crystals of this material recovered up to 49% within seconds and up to 95% after 100 min via ferroelastic detwinning. The spatial evolution of strain during cracking and healing was measured in real time using digital image correlation. Favorable alignment and strong ionic bonding across the interface of partially fractured crystals facilitate self-healing. This study elevates organic crystals close to the best-in-class self-healing polymers and sets an approach for durable crystal-based optoelectronics.

Hierarchical Structure of Soft Materials Studied at Small-Angle Neutron Scattering Instrument, SANS-U

Hierarchical Structure of Soft Materials Studied at Small-Angle Neutron Scattering Instrument, SANS-U

Monte Carlo simulation of spatial frequency domain imaging for breast tumors during compression.

Near-infrared optical imaging methods have shown promise for monitoring response to neoadjuvant chemotherapy (NAC) for breast cancer, with endogenous contrast coming from oxy- and deoxyhemoglobin. Spatial frequency domain imaging (SFDI) could be used to detect this contrast in a low-cost and portable format, but it has limited imaging depth. It is possible that local tissue compression could be used to reduce the effective tumor depth. To evaluate the potential of SFDI for therapy response prediction, we aim to predict how changes to tumor size, stiffness, and hemoglobin concentration would be reflected in contrast measured by SFDI under tissue compression. Finite element analysis of compression on an inclusion-containing soft material is combined with Monte Carlo simulation to predict the measured optical contrast. When the effect of compression on blood volume is not considered, contrast gain from compression increases with the size and stiffness of the inclusion and decreases with the inclusion depth. With a model of reduction of blood volume from compression, compression reduces imaging contrast, an effect that is greater for larger inclusions and stiffer inclusions at shallower depths. This computational modeling study represents a first step toward tracking tumor changes induced by NAC using SFDI and local compression.

A Recyclable Ionogel with High Mechanical Robustness Based on Covalent Adaptable Networks.

Ionogels are an emerging class of soft materials for flexible electronics, with high ionic conductivity, low volatility, and mechanical stretchability. Recyclable ionogels are recently developed to address the sustainability crisis of current electronics, through the introduction of non-covalent bonds. However, this strategy sacrifices mechanical robustness and chemical stability, severely diminishing the potential for practical application. Here, covalent adaptable networks (CANs) are incorporated into ionogels, where dynamic covalent crosslinks endow high strength (11.3MPa tensile strength), stretchability (2396% elongation at break), elasticity (energy loss coefficient of 0.055 at 100% strain), and durability (5000 cycles of 150% strain). The reversible nature of CANs allows the ionogel to be closed-loop recyclable for up to ten times. Additionally, the ionogel is toughened by physical crosslinks between conducting ions and polymer networks, breaking the common dilemma in enhancing mechanical properties and electrical conductivity. The ionogel demonstrates robust strain sensing performance under harsh mechanical treatments and is applied for reconfigurable multimodal sensing based on its recyclability. This study provides insights into improving the mechanical and electrical properties of ionogels toward functionally reliable and environmentally sustainable bioelectronics.

Structural transitions in liquid semiconductor alloys: A molecular dynamics study with a neural network potential.

Liquid-liquid phase transitions hold a unique and profound significance within condensed matter physics. These transitions, while conceptually intriguing, often pose formidable computational challenges. However, recent advances in neural network (NN) potentials offer a promising avenue to effectively address these challenges. In this paper, we delve into the structural transitions of liquid CdTe, CdS, and their alloy systems using molecular dynamics simulations, harnessing the power of an NN potential named LaspNN. Our investigations encompass both pressure and temperature effects. Through our simulations, we uncover three primary liquid structures around melting points that emerge as pressure increases: tetrahedral, rock salt, and close-packed structures, which greatly resemble those of solid states. In the high-temperature regime, we observe the formation of Te chains and S dimers, providing a deeper understanding of the liquid's atomic arrangements. When examining CdSxTe1-x alloys, our findings indicate that a small substitution of S by Te atoms for S-rich alloys (x > 0.5) exhibits a structural transition much different from CdS, while a large substitution of Te by S atoms for Te-rich alloys (x < 0.5) barely exhibits a structural transition similar to CdTe. We construct a schematic diagram for liquid alloys that considers both temperature and pressure, providing a comprehensive overview of the alloy system's behavior. The local aggregation of Te atoms demonstrates a linear relationship with alloy composition x, whereas that of S atoms exhibits a nonlinear one, shedding light on the composition-dependent structural changes.

Structural Study of Aqueous Electrolyte Solution by MeV Liquid Electron Scattering.

The impact of ions on water has long been a subject of great interest, as it is closely tied to the hydration structure, dynamics, and properties of electrolyte solutions. Over centuries of investigation, the influence of ions on water's structure remains highly debated. Prevailing techniques, such as neutron and X-ray scattering, primarily focus on the microscopic structure of salt solutions at very high concentrations, mostly above 1 mol/L. In this study, we measured the structure of aqueous potassium iodide (KI) and potassium chloride (KCl) solutions using MeV liquid electron scattering (MeV-LES) across a concentration range of 0.10 to 0.75 mol/L. The obtained results provide detailed insights into the variations in ion-oxygen and oxygen-oxygen correlations as a function of concentration. The observed structural differences between KI and KCl solutions are in line with the structure maker/breaker theory, which suggests that iodide ions exert a more pronounced effect than chloride ions on disrupting the water shell. This work demonstrates the potency of MeV-LES for investigating the atomic structure in liquids, augmenting the modern analytical toolbox.

Electrical-Modulated Flexible Acoustic Metamaterial: Enhancing Low-Frequency Absorption via an Ionic Electroactive Polymer.

The growing concern over low-frequency noise pollution resulting from global industrialization has posed substantial challenges in noise attenuation. However, conventional acoustic metamaterials, with fixed geometries, offer limited flexibility in the frequency range adjustment once constructed. This research unveiled the promising potential of ionic electroactive polymers, particularly ionic polymer-metal composites (IPMCs), as a superior candidate to design tunable acoustic metamaterial due to its bidirectional energy conversion capabilities. The previously perceived limitations of the IPMC, including slow reaction and high energy expenditure, owning to its inherent sluggish intermediary ionic mass transport process, were astutely leveraged to expedite the attenuation of low-frequency sound energy. Both our experimental and simulation results elucidated that the IPMC can generate voltage potentials in response to acoustic pressure at frequencies significantly higher than those previously established. In addition, the peak absorption frequency can be effectively shifted by up to 45.7% with the application of a 4 V voltage. By further integration with a microperforated panel (MPP) structure, the developed metamaterial absorbers can achieve complete sound absorption, which was continuously tunable under minimal voltage stimulation across a wide frequency spectrum. In addition, a microslit structure IPMC metamaterial absorber was designed to realize modulation of the perforation rate, and the absorption peak can be shifted by up to 79.2%. These findings signify a pioneering application of ionic intelligent materials and may pave the way for further innovations of tunable low-frequency acoustic structures, ultimately advancing the pragmatic deployment of both soft intelligent materials and acoustic metamaterials.

Correlation between preparation techniques and frictional properties of cellulose nanocrystals as additives in water-based lubricants

To explore the tribological characteristics of cellulose nanocrystals derived through various preparation techniques when utilized as additives in water-based lubricants, two types of cellulose nanocrystals (S-CNC and C-CNC) were chosen. These were produced via sulfuric acid hydrolysis and oxidation methods. The morphology and structural features were assessed through techniques such as Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), laser confocal Raman spectroscopy, elemental analysis, scanning electron microscopy (SEM), and laser particle size analysis. According to thermogravimetric analysis (TGA), the thermal stability of S-CNC is slightly superior to that of C-CNC. S-CNC exhibits liquid crystallinity when the concentration exceeds 0.5 %, whereas C-CNC does not display liquid crystallinity at any concentration tested. Further investigation was conducted on the frictional properties of the two types of CNCs using a UMT reciprocating friction tester. The results indicate that both types of CNC exhibit significant friction reduction properties at various additive concentrations, provided the addition does not exceed w=1 %. When below their respective liquid crystalline phase concentrations, the friction reduction performance of S-CNC is slightly inferior to that of C-CNC; however, when above the liquid crystalline phase concentration, the friction reduction performance of S-CNC surpasses that of C-CNC. The addition of w=0.5 % S-CNC leads to a relative reduction of 63.4 % in the friction coefficient compared to the base system. Analysis of the steel plate surface contact angle and post-wear surface suggests that the lubrication mechanism of CNC involves the adsorption of polar functional groups such as hydroxyl or carboxyl groups from the CNC structure onto the friction pair surface, forming a lubricating protective film to varying degrees. Additionally, the liquid crystalline structure of S-CNC facilitates the formation of an ordered lubricating film, further enhancing the frictional properties. These findings provide valuable insights into the application of nanocellulose crystals as lubricant additives.

Dual design strategy for carboxymethyl cellulose-polyaniline composite hydrogels as super-sensitive amphibious sensors

Conductive hydrogels as ideal candidate materials for flexible sensors have exhibited many promising applications. However, complex application environments, such as low temperatures or underwater conditions, have introduced new requirements for hydrogel sensors. Herein, a high-performance conductive hydrogel based on carboxymethyl cellulose-polyaniline (CMC-PANI) submicron spheres, poly (vinyl alcohol) (PVA) and phytic acid (PA) was designed and fabricated via a dual design strategy. CMC-PANI particles were introduced to not only empower the good electromechanical performance to the hydrogels, but also enhance the mechanical properties. The obtained hydrogel exhibited good mechanical property, anti-freezing, anti-swellable behavior and recyclable performance. Resistive-type strain sensors assembled by the prepared hydrogels exhibited high pressure sensitivity (34.17×10−2 kPa−1) and fast response time (100 ms), which can clearly detect the pulse beats. Moreover, the hydrogel sensors can achieve long-term stability, high sensitivity and fatigue resistance as an underwater sensor. Based on these favorable performances, the conductive polymer hydrogels may open up an enticing avenue for functional soft materials in health diagnostic and electronic components.

Evaluating Cryo-TEM Reconstruction Accuracy of Self-Assembled Polymer Nanostructures.

Cryogenic transmission electron microscopy (cryo-TEM) combined with single particle analysis (SPA) is an emerging imaging approach for soft materials. However, the accuracy of SPA-reconstructed nanostructures, particularly those formed by synthetic polymers, remains uncertain due to potential packing heterogeneity of the nanostructures. In this study, the combination of molecular dynamics (MD) simulations and image simulations is utilized to validate the accuracy of cryo-TEM 3D reconstructions of self-assembled polypeptoid fibril nanostructures. Using CryoSPARC software, image simulations, 2D classifications, ab initio reconstructions, and homogenous refinements are performed. By comparing the results with atomic models, the recovery of molecular details is assessed, heterogeneous structures are identified, and the influence of extraction location on the reconstructions is evaluated. These findings confirm the fidelity of single particle analysis in accurately resolving complex structural characteristics and heterogeneous structures, exhibiting its potential as a valuable tool for detailed structural analysis of synthetic polymers and soft materials.

Effect of combined treatments of hydrolysis and succinylation on the solubility and emulsion stability of rennet casein and micellar casein

Casein is the most abundant protein in milk with good emulsifying properties and bioavailability. However, the tight micellar structure of casein results in poor solubility. In the case of soft solid materials such as processed cheese, imitation cheese, yoghurt and protein-based oil-in-water emulsions, poor solubility directly affects the homogeneity and stability of the texture structure of such products, leading to a poor user experience. In this study, two protein modification techniques, hydrolysis and succinylation, were combined to improve the solubility of casein and the stability of its emulsions. The individual and combined effects of enzymatic hydrolysis and succinylation modification approaches on the stability of rennet casein (RC) and micellar casein (MC) emulsions were further explored. After double-treatment of casein with enzymatic hydrolysis and succinylation, the solubility of RC and MC was up to about 95 %, which was superior to that of single-treatment. Fourier transform infrared spectroscopy showed that the characteristic wave signals of the double-treated samples were located between the two single-treated samples, and that there may be an opposite effect between the two modifications. After 21 days of storage, the emulsions prepared from double-treated caseins still remained stable. The salt ionic stability and freeze-thaw stability were significantly improved, and the physical stability of MC was increased by nearly three times. The results explained the effects of enzymatic hydrolysis and succinylation on the functional properties of casein, provided a reference for the development of food systems based on oil-in-water emulsions, and offered a new idea for the wide application of succinylated casein.

Geometrical incompatibility regulated pattern selection and morphological evolution in growing spherical soft tissues

Surface morphological patterns are widely observed in natural systems, which are closely correlated to vital biological functions and inspire surface morphology designs in soft matter systems. Geometrical incompatibility widely exists in biological tissues across different length scales and plays an important role in growth-induced pattern selection and morphological evolution of soft tissues. However, the underlying physical mechanism of growth-induced pattern formation and post-buckling evolution in geometrically incompatible spherical soft tissues remain elusive. Here, the effect of geometrical incompatibility on the growth-induced pattern selection and post-buckling evolution are investigated through swelling experiment, theoretical analysis and numerical simulation. The results show that not only the instability pattern but also the instability threshold can be regulated by manipulating geometric incompatibility. Notably, when the geometrical incompatibility parameter exceeds a critical value, spontaneous instability is observed before growth. With continuous growth, the core–shell soft sphere buckles into a periodic buckyball pattern and evolves toward a bean-shaped pattern, and then undergoes a wrinkle-to-fold transition into a labyrinth topography. Our results demonstrate, both experimentally and theoretically, that geometrical incompatibility can guide the growth-induced pattern formation and morphological evolution effectively. This study not only enhances our understanding of the growth-induced pattern selection and morphological evolution in spherical soft tissues, but also provides an inspiring insight for the fabrication of morphological patterns on curved surfaces.

Stretchable supramolecular hydrogel with instantaneous self-healing for electromagnetic interference shielding control and sensing

Conductive hydrogels possess instantaneous self-healing and adhesive properties have generated great excitement in the fields of sensing and electromagnetic interference (EMI) shielding. In this study, we ingeniously designed hydrogel-based soft materials with high conductivity by using poly(vinyl alcohol) (PVA), positively charged Ti3C2Tx MXene and thioctic acid (TA) as source materials. Through concentration-induced ring-opening polymerization of TA monomers in an aqueous solution of potassium hydroxide (KOH), supramolecular poly(potassium thioctate) (poly(PT)) was obtained. Then, the multifunctional poly(PT)/PVA/p-MXene hydrogel with exceptional stretchability, substrate-adhesion and self-healing capability was achieved through abundant dynamic bonds, including disulfide bonds, hydrogen bonds, coordination bonds and electrostatic interactions. The hydrophobic main chains within poly(PT) provide robust protection against the oxidative degradation of MXene. This hydrogel shows outstanding strain sensing and extraordinary EMI shielding effectiveness (SE) of 48.56 dB caused by the inner structure, conductivity, and water content. Interestingly, the EMI SE can be regulated by reabsorbing moisture from the air, thereby enabling the reuse of dried hydrogel. Furthermore, the EMI SE can be dynamically modulated through controlled deformations, confirming the potential application for electromagnetic waves (EMWs) sensing. This innovative approach not only simplifies the fabrication of multifunctional materials but also expands the applications of adhesive hydrogels with conductivity.