Smart Materials Research Articles

Mechanics-Switchable and Antiswelling Colloidal Hydrogels Inspired by the Cononsolvency Effect.

Stiffness switching hydrogels have been in high demand for intelligent devices, adhesion science, soft robotics, and flexible electronics. However, it is challenging to post-tune the mechanical properties of a hydrogel once the polymer network structure is formed. Inspired by the cononsolvency effect, we prepared a mechanics-switching colloidal hydrogel through the precipitation polymerization of methacrylamide in mixed dimethyl sulfoxide and water solvents. The colloidal network enables the hydrogels to simultaneously strengthen, stiffen, and toughen. The colloidal hydrogels not only display a broad spectrum of adjustable mechanical properties (ranging from 0.08 to 57.1 MPa) via solvent response but also accomplish reversible stiffness conversion through the solvent-tuned conformational adjustment of colloidal polymer networks, with the maximum modulus conversion reaching 1427, and exhibit solvent-responsive shape memory. Based on the stable and tight colloidal network, the hydrogels exhibit antiswelling properties in various aqueous solutions and solvents. The colloidal hydrogel would provide more possibilities in various applications, such as antiimpact protection, shape memory, electronic switches, and intelligent engineering materials. It is envisioned that this work will provide key opportunities in developing mechanics-switching and on-demand tuning of soft materials for tissue engineering, flexible electronics, and biomedical science.

4D printing of pH-responsive bilayer with programmable shape-shifting behaviour

4D printing of smart materials has seen remarkable advancements in the domain of biomedical devices, with a particular focus on developing responsive and adaptive programmable structures. In this work, we report the 4D printing of two solvent-responsive hydrogels forming a bilayer that undergoes bidirectional actuation depending on the pH of the solvent. A strong interlayer adhesion between the hydrogels is formed without subjecting either of their surfaces to any chemical modification. These hydrogels have an interfacial toughness of 71.8 J/m2 and undergoes no delamination during actuation inside a solvent. Conventionally, pH-responsive actuators are only limited to simple 2D films prepared by solvent casting. However, our work focuses on the design and fabrication of complex bilayer and patterned structures using Direct-Ink Writing (DIW) approach. These printed structures actuate upon immersion in a solvent medium, and the actuation is reversible in nature. The influence of programmable variables on the morphed structure was studied systematically by modifying the rheological properties (in the range of 102−105 Pa.s) and printing parameters (optimized at a printing speed of 5mm/sec, with the extrusion pressure of 5−6 bar and nozzle diameter of 0.5 mm) of the 3D printed bilayer structure. The physicochemical properties of the printable hydrogel ink were tuned such that the same structure can respond to both acidic and basic pH (with non-morphing point at pH 7), by altering the directionality of actuation. We have demonstrated the applications of these pH-responsive actuators in smart valves.

Precise Photochemical Post‐Processing of Molecular Crystals

Molecular crystals carry a great potential as new soft smart materials, with a plethora of recent examples overcoming the major obstacle of mechanical flexibility, and this research direction holds enormous potential to revolutionize optics, electronics, medicine, and space exploration. However, shaping organic crystals into desired shapes and sizes remains a major practical challenge due to the lack of control over the crystallization process, and the difficulties in mechanical post‐processing without introduction of defects that are usually imparted by their soft nature. Here we present an innovative approach that employs photochemical processing for precise and nondestructive cutting of a molecular crystal. Our proposed method uses light to post‐process crystals of the desired size and shape, similar to using light to cut other materials. This reaction induces strain, ensuring sharp cleavage without the need for melting or other processes. We further demonstrate the potential of this approach by producing crystals of arbitrary size, which can be used as controllable optical waveguides. Among other potential applications, this method can be used to prepare dynamic crystals, particularly those with aspect ratios crucial for mechanical deformation, such as flexible electronics, soft robotics, and sensing.

Precise Photochemical Post-Processing of Molecular Crystals.

Molecular crystals carry a great potential as new soft smart materials, with a plethora of recent examples overcoming the major obstacle of mechanical flexibility, and this research direction holds enormous potential to revolutionize optics, electronics, medicine, and space exploration. However, shaping organic crystals into desired shapes and sizes remains a major practical challenge due to the lack of control over the crystallization process, and the difficulties in mechanical post-processing without introduction of defects that are usually imparted by their soft nature. Here we present an innovative approach that employs photochemical processing for precise and nondestructive cutting of a molecular crystal. Our proposed method uses light to post-process crystals of the desired size and shape, similar to using light to cut other materials. This reaction induces strain, ensuring sharp cleavage without the need for melting or other processes. We further demonstrate the potential of this approach by producing crystals of arbitrary size, which can be used as controllable optical waveguides. Among other potential applications, this method can be used to prepare dynamic crystals, particularly those with aspect ratios crucial for mechanical deformation, such as flexible electronics, soft robotics, and sensing.

An Exploration of Parents’ Preference for Young Children's Smart Textile Products

The topic of smart textiles has made substantial progress and garnered great interest. Nevertheless, studies are scarce regarding consumer attitudes and acceptability of these items. There is a lack of consumer studies specifically targeting the market for smart textiles designed for young children. This research seeks to close this disparity by investigating parents’ requirements and criteria when choosing smart fabrics intended for younger children. Surveys were administered to parents who had at least one child under the age of three. A nationwide sample was enlisted, yielding 267 valid responses. The results emphasized that safety is the most important factor for parents, regardless of their demographic characteristics. Parents who had previous exposure to smart textile items placed a higher emphasis on performance rather than pricing, in contrast to parents who did not have such exposure. The study additionally gathered and condensed product concepts and recommendations for subsequent product enhancement.

Strong and Stable Woody Triboelectric Materials Enabled by Biphase Blocking.

Driven by the "Internet of Everything" (IoE) vision, the demand for smart materials is growing. Wood, one of the most abundant and renewable resources, has long been a staple in construction and furnishing applications. To further expand its application range, this study developed a high-strength, stable wood-based triboelectric material through a synergistic biphasic mechanism. The in situ growth of flame retardants and the formation of a dense char layer significantly enhanced the fire resistance of the wood-based triboelectric material, reducing the heat release rate (HRR) by 95.4% and total heat release (THR) by 94.2%. The dense laminate structure provided an excellent impact toughness (126 kJ m-2). As a smart sensor, the wood-based triboelectric material demonstrated the ability to recognize human motion states and trajectories, exhibiting great potential for applications in smart homes. This study provides valuable insights for exploring the potential applications of wood as a smart material.

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

AbstractDiarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens up an entire new structure and property space expanding the versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached in up to 87 % upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state also serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of our aza‐diarylethene in a materials application.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Experimental study of magnetorheological fluids under large periodic deformations

Abstract Magnetorheological (MR) fluids are smart materials whose properties can be controlled by a magnetic field. They are used in a variety of applications with tailored operating parameters, facilitating broad and relatively straightforward implementation and control of the functional properties of these systems.

The aim of the study was to determine the variation in shear stress of MR fluids under varying shear deformation directions and different magnetic field induction levels. The experiments were carried out with the use of three commercially available fluids: MRF-122EG, MRF-132DG, and MRF-140CG, which primarily differ in the volumetric fraction of ferromagnetic particles. These fluids are designed for use in mechanical energy dissipation devices clutches, and brakes are characterized by high stability and a broad controllability range.

The experiments were performed using a rotational rheometer with a parallel plate measuring system to examine shear stress variability during both the deformation and rest phases. The study applied relatively large deformations, exceeding the linear viscoelastic range and the deformation corresponding to the yield point.

The test results revealed variations in the shear stress values across successive loading cycles, as well as fluctuations during the rest phase. It was also found that, depending on magnetic field induction level (i.e., the level of fluid magnetization), the rest period could result in either a decrease (relaxation) or an increase (hardening) in shear stress values. These findings have practical significance, particularly for MR fluid devices operating in shear mode.

QuPath Edu and OpenMicroanatomy: Open‐source virtual microscopy tools for medical education

AbstractVirtual microscopy is becoming increasingly common in both medical education and routine clinical practice. Virtual microscopy software is typically designed either for (1) training students in anatomy, histology, and histopathology, or (2) quantitative analysis—but not both simultaneously. QuPath is one of the most widely used software applications for histopathology image analysis in research and provides a comprehensive set of computational tools to evaluate histology slides. We have enhanced QuPath by developing a new extension, QuPath Edu, which adapts the software to function as an intuitive microanatomy learning environment. Additionally, we have created an entirely new, complementary software platform called OpenMicroanatomy, which provides an alternative way to access QuPath Edu teaching content through a web interface. These tools have been used in teaching of first year medical and dentistry students at the University of Oulu Medical Faculty, and we conducted a user survey for the Class of 2023 to assess the usability and student experience. In general, the introduced annotation and quiz features were appreciated by the students and the system usability of OpenMicroanatomy was considered excellent (SUS score 84.8). Together, these freely available tools enable teachers to develop and deploy innovative training material for anatomy, histopathology, quantitative analysis, and artificial intelligence in a wide range of contexts. This unique combination can provide the next generation of students with essential multidisciplinary skills.

Intelligent microwave absorption of VO2@PDA/RGO composites based on dynamic interfacial polarization performance

To design smart microwave-absorbing materials (MAMs), it is essential to adjust the corresponding electrical conductivity and dielectric parameters according to variable conditions. However, it is still challenging to concurrently adjust the effective absorbing intensity and frequency range in MAMs due to their interdependent constraints. Here, we developed intelligent MAMs by incorporating core–shell structure vanadium dioxide @ polydopamine (VO2@PDA) powders as polarization loss units, while the subwavelength-sized reduced graphene oxide microspheres (RGOms) were used as conduction loss units. When the temperature is higher than the metal–insulator phase transition temperature of the insulator state VO2 (M), the corresponding metal state VO2 (R) could be produced, which, therefore, contributes to an enhanced interfacial polarization loss due to the significant electrical performance differences between the VO2 (R) and the PDA shell. As an optimized result, the changes of the effective absorption frequency band (▵EAF) and reflection loss (▵RL) of the RV3 composite could be approximately 1.5 GHz and 24 dB, respectively, attributable to the phase transition of VO2. This study provides a novel approach for the adjustment of electromagnetic responses based on dynamic interfacial polarization performance, which offers broader prospects for developing next-generation smart electromagnetic absorption devices with both reversible microwave absorption frequency range and intensities.

Revolutionizing smart textiles: a comprehensive review of conductive ink printing for sustainable and adaptive wearable applications

Purpose The demand of species monitoring for the benefit of various sectors such as industrial, medicinal and ecological has surged rapidly in the recent past. Therefore, the purpose of this paper is to articulate the major developments in synthesizing conductive inks for the structurization of miniaturized as well as disposable or reusable electrochemical equipments. Design/methodology/approach This section is not applicable to a review paper. Findings Numerous times the need for the use point becomes significant for achieving accurate as well as swift quantification. As an alternate, the wearable and effectual reuseable electrochemical sensors are being practiced. The technique of fabricating devices using conductive inks encompasses novelty, as it provides flexibility in designing the electrodes. The increase in the popularity of inks development is governed by its features of simplicity, reduced cost and waste generation, high production and eco-friendly engineering procedures. Further, the electrochemistry aspects of conductive inks highlighting the importance of their compounds and binders has also been discussed emphasizing on the conductive materials. Originality/value This paper is an original review work. This paper will be helpful for manufacturers/researchers from smart wearable textile sector in envisaging innovative developing techniques of sensors as well as biosensors through conductive inks.

Piezoresistive, Piezocapacitive and Memcapacitive Silk Fibroin-Based Cement Mortars.

Water-stable proteins may offer a new field of applications in smart materials for buildings and infrastructures where hydraulic reactions are involved. In this study, cement mortars modified through water-soluble silk fibroin (SF) are proposed. Water-soluble SF obtained by redissolving SF films in phosphate buffer solution (PBS) showed the formation of a gel with the β sheet features of silk II. Electrical measurements of SF indicate that calcium ions are primarily involved in the conductivity mechanism. By exploiting the water solubility properties of silk II and Ca2+ ion transport phenomena as well as their trapping effect on water molecules, SF provides piezoresistive and piezocapacitive properties to cement mortars, thus enabling self-sensing of mechanical strain, which is quite attractive in structural health monitoring applications. The SF/cement-based composite introduces a capacitive gauge factor which surpasses the traditional resistive gauge factor reported in the literature by threefold. Cyclic voltammetry measurements demonstrated that the SF/cement mortars possessed memcapacitive behavior for positive potentials near +5 V, which was attributed to an interfacial charge build-up modulated by the SF concentration and the working electrode. Electrical square-biphasic excitation combined with cyclic compressive loads revealed memristive behavior during the unloading stages. These findings, along with the availability and sustainability of SF, pave the way for the design of novel multifunctional materials, particularly for applications in masonry and concrete structures.

In-situ isomerization and reversible self-assembly of photoresponsive polymeric colloidal molecules enabled by ON and OFF light control

Photocatalytic colloids enable light-triggered nonequilibrium interactions and are emerging as key components for the self-assembly of colloidal molecules (CMs) out of equilibrium. However, the material choices have largely been limited to inorganic substances and the potential for reconfiguring structures through dynamic light control remains underexplored, despite light being a convenient handle for tuning nonequilibrium interactions. Here, we introduce photoresponsive N,O-containing covalent organic polymer (NOCOP) colloids, which display multi-wavelength triggered fluorescence and switchable diffusiophoretic interactions with the addition of triethanolamine. Our system can form various flexible structures, including ABn-type molecules and linear chains. By varying the relative sizes of active to passive colloids, we significantly increase the structural diversity of A2B2-type molecules. Most importantly, we demonstrate in-situ transitions between different isomeric configurations and the reversible assembly of various structures, enabled by on-demand light ON and OFF control of diffusiophoretic interactions. Our work introduces a new photoresponsive colloidal system and a novel strategy for constructing and reconfiguring colloidal assemblies, with promising applications in microrobotics, optical devices, and smart materials.

A multichromotropic dinuclear copper(II) complex: Unveiling its structural and spectroscopic properties

A novel dinuclear copper(II) complex, [Cu₂L₂(μ-Cl)₂]Cl₂•4H₂O, was synthesized using a tetradentate hemilabile ligand, 3,3′-((pyridin-2-ylmethyl)azanediyl)dipropanamide (L). The complex was characterized by various spectroscopic techniques, including FT-IR, UV-Vis spectroscopy, elemental analysis, TG-DTA, and conductivity measurements. X-ray crystallography confirmed the formation of the binuclear complex, revealing a dicationic unit with distorted octahedral geometry at the copper centers, bridged by two chloride ions. The coordination environment around each copper ion includes two nitrogen and two oxygen donors from the ligand, along with the bridging chlorides. Notably, the complex exhibits significant chromotropism, including solvatochromism, halochromism, ionochromism, and thermochromism, which are attributed to the Jahn-Teller effect and the flexible coordination environment around the copper centers. Thermal analysis indicates the stability of the complex up to 118°C, with subsequent decomposition occurring in distinct stages. Hirshfeld surface analysis further elucidates the intermolecular interactions within the crystal lattice. Computational studies were conducted using Time Dependent Density Functional Theory (TD-DFT) to gain insights into the nature of the observed chromotropism. The computed absorption spectra closely matched the experimental data, validating the proposed electronic transitions responsible for the chromotropic behavior. The multifaceted chromotropic behavior of this complex highlights its potential applications in sensing technologies and smart materials. The study advances the understanding of chromotropism in metal complexes and provides insights into the design of responsive materials based on transition metal chemistry.

Multi-protection durable unidirectional water-transport fabric with personalized moisture and thermal management

Effective management of the microclimate interface of the human skin-fabric-external environment significantly contributes to enhancing the wearer’s comfort experience. In this paper, a fast sweat-absorbing anti-corrosion durable fabric was prepared based on fiber surface modification and textile structure design to improve the comfort and prolong the service life of fabrics. By the formation of self-assembled membranes (SAMS), silver-plated yarns with excellent oxidative resistance and hydrophobicity were obtained. A durable unidirectional water-transport fabric (DUWF) was received through a weft-double weave organization with hydrophobic silver-plated yarns as the inner weft and hydrophilic lyocell yarns as the outer weft. Spontaneous moisture conduction was achieved by the wettability gradient of two sets of weft threads and one set of warp threads in the thickness direction. DUWF had an electromagnetic shielding effect of over 65 dB, a unidirectional moisture transfer index of 863.33 %, an ultraviolet protection factor (UPF) of 2000, a fast- cooling capacity of 3.3 °C, and good long-term stability and repeatability. The multifunctional smart fabrics proposed in this paper enhance the moisture and heat manageability of conventional garments and pave the way for further research on comfortable protective clothing.

Preparation of photochromic microcapsules with a diarylethene and polyurethane/chitosan for smart textiles

In order to overcome the influences of external environment on the properties photochromic compounds and expend their applications fields, various photochromic microcapsules have been prepared. However, the effects of wall materials on the properties of photochromic compounds need to be further studied. In this study, two photochromic microcapsules were prepared with polyurethane/chitosan as wall materials and a diarylethene molecular as core material. The properties such as photochromism, fatigue resistance, the sealing, and thermal stability of the microcapsules were studied, and the effects of the wall materials on the photochromic properties of the diarylethene were also investigated. Furthermore, the prepared microcapsules have been successfully applied to cotton fabrics of photochromic smart textiles.

Superior Conductive, Large Diameter CNT Composite Yarn of Insulative Polymer: Inferences of a Unidirectional Compression‐Stretching Technique

ABSTRACTLarge diameter yet highly conductive Carbon Nanotube (CNT) yarn could have prospective control on high‐tech application field spanning from electronic devices to wearable textiles; although the development of such macroscopic CNTs is extremely challenging. Especially, while fabricating CNT composite yarn with polymer, insulative nature of polymeric materials inherently propagates poor electrical conductivity to CNT yarn. To address this, we have proposed an exciting approach to fabricate large dimension, highly conductive yet flexible CNT‐Thermoplastic Polyurethane (TPU) composite yarn through unidirectional compression‐stretching process. Our technique allowed TPU molecules to be well dispersed into inner and inter‐CNT bundles facilitating well flexibility while the simultaneous functions of pressure and tension allowed more closely packed CNTs network within densified CNT yarn reducing the inherent voids and contact resistance. The consequent yarn possessed high conductivity of 1613 S/cm, attractive mechanical performance (tensile strength 1.3 GPa, Young's modulus 12 GPa, toughness 100.75 MJ/m3), exceptional anti‐abrasive ability (up to 46,350 cycles) endowing its multidirectional adaptability for smart textiles. Moreover, the desirable E‐heating performance together with excellent electrical stability allows successful exploitation of the prepared CNT yarn as stretchable heater. Such amazing integrated characteristics may allow the resultant yarn to replace traditional carbon fiber in various high‐tech arena as well.

Biocomposite Scaffolds for Tissue Engineering: Materials, Fabrication Techniques and Future Directions.

Tissue engineering is an interdisciplinary field that combines materials, methods, and biological molecules to engineer newly formed tissues to replace or restore functional organs. Biomaterials-based scaffolds play a crucial role in developing new tissue by interacting with human cells. Tissue engineering scaffolds with ideal characteristics, namely, nontoxicity, biodegradability, and appropriate mechanical and surface properties, are vital for tissue regeneration applications. However, current biocomposite scaffolds face significant limitations, particularly in achieving structural durability, controlled degradation rates, and effective cellular integration. These qualities are essential for maintaining long-term functionality in vivo. Although commonly utilized biomaterials can provide physical and chemical properties needed for tissue regeneration, inadequate biomimetic properties, as well as insufficient interactions of cells-scaffolds interaction, still need to be improved for the application of tissue engineering in vivo. It is impossible to achieve some essential features using a single material, so combining two or more materials may accomplish the requirements. In order to achieve a proper scaffold design, a suitable fabrication technique and combination of biomaterials with controlled micro or nanostructures are needed to achieve the proper biological responses. This review emphasizes advancements in scaffold durability, biocompatibility, and cellular responsiveness. It focuses on natural and synthetic polymer combinations and innovative fabrication techniques. Developing stimulus-responsive 3D scaffolds is critical, as these scaffolds enhance cell adhesion and promote functional tissue formation while maintaining structural integrity over time. This review also highlights the natural polymers, smart materials, and recent advanced techniques currently used to create emerging scaffolds for tissue regeneration applications.

Biochemical Signal-Induced Supramolecular Hydrogelation for Structured Free-Standing Soft Material Formation.

Cells coordinate their activity and regulate biological processes in response to chemical signals. Mimicking natural processes, control over the formation of artificial supramolecular materials is of high interest for their application in biology and medicine. Supramolecular material that can form in response to chemical signals is important for the development of autonomously responsive materials. Herein, a supramolecular hydrogel system is reported enabling in situ generation of hydrogelators in response to a specific chemical signal. Using self-immolative chemistry, spatial control over the formation of supramolecular hydrogel material and structured free-standing hydrogel objects via providing H2O2 locally is demonstrated. In addition, a hybrid system is developed enabling in situ generation of the H2O2 by the action of an enzyme and glucose, providing an extra handle for the development of an intelligent soft material. This generic design should enable the use of various (chemical)stimuli that can be obtained via coupling different stimuli and various chemical and/or biological markers and appears a versatile approach for the design of smart artificial soft materials that can find application in theranostic purposes.