Smart Materials Research Articles

Weavable, Reconfigurable Triboelectric Ferrofluid Fiber for Early Warning.

As communication technologies have become omnipresent, the prevalence of electromagnetic field (EMF) exposures poses possible health risks, particularly to vulnerable groups such as pregnant women. In response, we introduce a triboelectric ferrofluid fiber (TFF) that moves in response to EMF, thereby generating charge in a way that is self-powered. The TFF is flexible, stretchable (470%), and can be woven into fabrics. The TFF utilizes a soft-contact (ferrofluid-silicon rubber fiber) triboelectric core layer to enhance its sensitivity to EMF, enabling it to detect even minor electromagnetic fluctuations, such as those from cell phone typing. By integrating hydrogel electrodes that offer conductivity and minimal electromagnetic interference shielding, the TFF's sensitivity to magnetic fields is further amplified. Moreover, its open-circuit voltage output is increased by 50% compared to the conventional electrodes. Building on this technology, we designed a smart fabric for environmental early warning and potential real-time pulse monitoring, specifically tailored for the safety and healthcare needs of vulnerable groups. Finally, we developed a sensing and communication apparel (SCA) by integrating TFF into the apparel and exploring its capabilities in a wireless transmission of warning signals and long-distance NFC functionality.

In Situ Generation of Microwire Heterojunctions with Flexible Optical Waveguide and Hydration-Mediated Photochromism.

Flexible heterojunctions based on molecular systems are in high demand for applications in photonics, electronics, and smart materials, but fabrication challenges have hindered progress. Herein, we present an in situ approach to creating optical heterojunctions using hydration-mediated flexible molecular crystals. These hydrated multi-component molecular solids display strong blue emitting optical waveguides with minimal optical loss (0.005 dB/μm) and excellent flexibility (elastic modulus: 3.87 GPa). The water-mediated process enables the molecular microwires with tunable elastic and plastic deformation, as well as reversible uptake and release of lattice water, facilitating the formation of flexible heterojunctions. Spectral analysis and theoretical modeling reveal that these microwires exhibit both photochromism and color-tunable dual emission (fluorescence and phosphorescence), expanding their utility in photonic information encoding. Therefore, this work introduces a hydration-mediated molecular engineering strategy for fabricating crystalline heterojunctions with on-demand processability and controllable emission sequences, enabling optical signal manipulation at the micro/nanoscale.

Organelle-Specific Smart Supramolecular Materials for Bioimaging and Theranostics Application.

In cellular environments, certain synthetic molecules can form nanostructures via self-assembly, impacting molecular imaging, and biomedical applications. Control over the formation of these self-assembled nanostructures in subcellular organelle is challenging. By the action of stimuli, either present in the cellular environment or applied externally, in situ generation of molecular precursors can lead to accumulation and supramolecular nanostructure formation, resulting in efficient bioimaging. Here, we summarize smart fluorophore-based ordered nanostructure preparation at specific organelles for efficient bioimaging and therapeutic application towards cancer theranostics. We also present challenges and an outlook regarding intercellular self-assembly for theranostics application. Altogether, smart nanostructured materials with fluorescence read-outs at specific subcellular compartments would be beneficial in synthetic biology and precision therapeutics.

Textile electronics for ubiquitous health monitoring

Textile electronics for ubiquitous health monitoring

Hybrid Strategies for Enhancing the Multifunctionality of Smart Dynamic Molecular Crystal Materials.

Dynamic molecular crystals are an emerging class of smart engineering materials that possess unique ability to convert external energy into mechanical motion. Moreover, they have being considered as strong candidates for dynamic elements in applications such as flexible electronic devices, artificial muscles, sensors, and soft robots. However, the inherent defects of molecular crystals like brittleness, short-life and fatigue, have significantly impeded their practical applications. Inspired by the concept of "the whole is greater than the sum of its parts" in the field of biology, building stimuli-response composites materials can be regarded as one of the ways to break through the current limitations of dynamic molecular crystals. Moreover, the hybrid materials can exhibit new functionalities that cannot be achieved by a single object. In this review, the focus was placed on the analysis and discussion of various hybrid strategies and options, as well as the functionalities of hybrid dynamic molecular crystal materials and the important practical applications of composite materials, with the introduction of photomechanical molecular crystals and flexible molecular crystals as a starting point.Moreover, the efficiency, limitations, and advantages of different hybrid methods were compared and discussed.

Formulation of Epoxy Prepregs, Synthesization Parameters, and Resin Impregnation Approaches—A Comprehensive Review

Prepregs are resin-impregnated, expensive composites mainly limited to high-end applications within the aeronautical, defense, automotive, and energy sectors. Prepreg technology is mainly protected by trade secrets, resulting in limited studies on prepreg resin matrix development and recent advancements. Three key parameters for epoxy resin matrix development including B-staging, viscosity, and tackiness, and their control strategies are discussed in detail. The B-stage is defined as the partially cured stage of epoxy prepregs and is extremely important for prepreg layup, pot life, and final performances. The three key parameters are interrelated and accurately controlled, and, hence, resin development plays a huge role in the prepreg development process. This review also discusses the measuring techniques of the parameters in detail. Based on the resin impregnation techniques and B-stage control, two approaches are proposed to develop the prepreg resin formulations: conventional resin impregnation and viscosity-controlled resin impregnation. The approaches would be extremely useful, especially for advancing beyond the existing prepreg applications and developing smart materials and functional composites through advanced resin modification strategies.

On nonlinear 3D electro-elastic numerical modeling of two-phase inhomogeneous FG piezocomposites reinforced with GNPs

The novelty here comes from not only the perfect nonlinear three-dimensional (3D) electro-elasticity investigation but also the mixed material itself. The literature widely showed mechanical assessments on the piezoelectric structures; however, a lack of nonlinear three-dimensional elasticity studies has been witnessed on these kinds of smart materials. Therefore, a nonlinear 3D elasticity-piezoelectricity coupling is considered in this study. What is more, this research brings about an era in the field of sensing manufacturing such as sensors and actuators by proposing the construction of these devices in an advanced composite framework. The piezoelectric medium can be electro-mechanically improved with the aggregation of graphene platelets/nanoplatelets (GPLs/GNPs) based on the functionally graded (FG) composition. The assumption for such a smart composite has been made to provide higher flexibility smart tools while their elastic strength can also get further. To accomplish this, the derivation of a rigorous mathematical model has come out for a transversely isotropic inhomogeneous FG-piezoelectric beam-like sensor/actuator using 3D kinematic displacements, geometrically nonlinear strains, Lagrange technique, 3D stress-strains tensors, linear elastic material, and in particular Halpin-Tsai micro-mechanic model. Numerical modeling has been built by the generalized differential quadrature (GDQ) technique. A comprehensive parametric study has also been established for intelligent FG beams.

Photon localization transition in a magnetorheological fluid

We investigate photon transport in magnetically tunable fluids, specifically magnetic nanofluids and magnetorheological fluids (MRFs). Our study focuses on the statistical analysis of light transport in these fluids, with a particular focus on earlier theoretical proposals related to the possibility of Anderson localization in these systems. We employ a well-known mesoscopic quantifier, the generalized conductance, to assess the domain of light transport in these systems. Magnetic nanofluids, which contain nanometer-sized magnetite particles, exhibit weak scattering with no substantial consequence on conductance, regardless of the applied magnetic field. In contrast, magnetorheological fluids, a bidispersion of micrometer-sized magnetizable spheres in a magnetic nanofluid, show a decrease in conductance to values below unity as the magnetic field strength increases. This decrease occurs at the magnetic-field-induced photonic bandgap in MRFs, which plays a crucial role in the localization process and is characterized by reduced transmitted intensity, altered speckle patterns, and significant changes in intensity statistics. Our findings also highlight the temporal evolution of field-induced speckles, where the initial high correlation decreases over time, and the correlation width widens indicating that the duration of sustained correlation enhances as the system reaches equilibrium. Consequently, the evolution of field-induced scatterers in MRFs significantly emulates light localization effects as the system attains equilibrium. This study concludes that our system is a prime candidate to observe possible strong localization in a magnetically tunable, dissipative complex system. Such systems hold potential applications in optical switching, adaptive optics, and smart materials design through controlled light manipulation using external magnetic fields.

Skin-inspired bimodal pressure sensor for static and dynamic intelligent interactive perception system

With the rapid development of flexible pressure sensors, it is difficult for single-function devices to meet the demands of complex intelligent interactive scenarios. In this paper, a skin-inspired single electrode triboelectric nanogenerator (S-TENG)-ionic capacitive pressure sensor (IPS) bimodal pressure sensor with a top-down stacked structure is developed. The designed sensor not only exhibits high sensitivity, wide pressure detection range, fast response/recovery time, and long-term durability, but also detects external dynamic and static mechanical responses. Based on these superiorities, the designed sensor has been successfully applied in three practical intelligent interactive scenarios, including a music player system using IPS perception array, an intelligent handwriting perception system using S-TENG, and an intelligent material and shape perception system constructed by a bimodal pressure perception array. Expectably, the proposed bimodal pressure sensor can realize intelligent interactive perception in complex application scenarios, which provides a new paradigm for next generation of flexible pressure sensors.

Biphenyl or naphthalene-modified fluorene fluorogenic molecules with different solid-state emission and mechanofluorochromic behaviors

The preparation of three-color mechanofluorochromic molecules is of crucial importance in the development of mechanically responsive smart materials with multicolor switching feature. Unfortunately, the related mechano-responsive luminogenic compounds are rare. In this work, four fluorene derivatives, which contain various sites of biphenyl or naphthalene, were synthesized. Interestingly, compounds 1–4 exhibited diverse high-brightness solid-state fluorescence and observable fluorescent changes in response to mechanical force stimulus. For fluorophor 1 in the solid state, upon light grinding, an orange-yellow to yellow-green mechanofluorochromic transition with the notable blue shift of 85 nm was noticed, and the yellow-green to yellow bathochromic mechanofluorochromic response was observed after vigorous grinding. Therefore, fluorogen 1 showcased an unfrequent bidirectional tricolored mechanofluorochromism with a blue shift followed by a red shift. As for luminogens 2–4 exhibited diverse two-color reversible red-shifted mechanofluorochromic responses. Furthermore, their mechanochromic emissive mechanisms of 1–4 were investigated by X-ray powder diffraction tests.

Novel Easy‐to‐Synthesize Hydrazine Multi‐channel Detection and Adsorption Materials

Comprehensive SummaryHydrazine hydrate (DH) is a widely used chemical agent, but it is highly toxic. Thus, the development of low‐cost and easy‐to‐prepare materials for the detection and adsorption of DH is very significant. Herein, a novel and easy‐to‐prepare supramolecular smart material based on bisquinoline‐functionalized naphthalene diimide (DQ8) has been designed and synthesized. In the DQ8, the synergistic effect between quinoline and naphthalene diimide groups has been employed to improve the selectivity and sensitivity for binding of DH. The DQ8‐based crystalline porous material (DQ8‐CPM) can simultaneously detect and adsorb DH and produce noticeable fluorescence color changes after adsorption of DH vapor. More significantly, the DQ8‐CPM shows nice recycling performance on DH detection and adsorption. Meanwhile, a smart gel based on DQ8 (DQ8‐G) shows multi‐channel response for DH through color, fluorescence, and state changes. The DQ8 shows high selectivity and sensitivity for DH. The detection limit of DQ8 for DH is 8.6 × 10–7 mol/L. According to the investigation of the DH binding and response mechanism, the synergistic effect between quinoline and naphthalene diimide groups plays an important role in the DH response process. It's a simple and feasible way to develop materials for detection and adsorption of DH through synergistic effects.

Advances in Porous Structure Design for Enhanced Piezoelectric and Triboelectric Nanogenerators: A Comprehensive Review

AbstractPorous structures offer several key advantages in energy harvesting, making them highly effective for enhancing the performance of piezoelectric and triboelectric nanogenerators (PENG and TENG). Their high surface area‐to‐volume ratio improves charge accumulation and electrostatic induction, which are critical for efficient energy conversion. Additionally, their lightweight and flexible nature allows for easy integration into wearable and flexible electronics. These combined properties make porous materials a powerful solution for addressing the efficiency limitations that have traditionally restricted nanogenerators. Recognizing these benefits, this review focuses on the essential role that porous materials play in advancing PENG and TENG technologies. It examines a wide range of porous materials, including aerogels, nano‐porous films, sponges, and 2D materials, explaining how their unique structures contribute to higher energy harvesting efficiency. The review also explores recent breakthroughs in the development of these materials, demonstrating how they overcome performance challenges and open up new possibilities for practical applications. These advancements position porous nanogenerators as strong candidates for use in wearable electronics, smart textiles, and Internet of Things (IoT) devices. By exploring these innovations, the review underscores the importance of porous structures in driving the future of energy harvesting technologies.

An Organic Vapor-Responsive Actuator Based on a Novel Urea Macrocycle.

The mechanical actuation of smart materials has garnered considerable attention in biological and medical research due to their ability to mimic biological processes at both molecular level, such as conformational changes in individual compounds, and at the macroscopic level, where polymeric substrates respond to external stimuli. In this study, we present a polymeric composite incorporating a novel urea macrocycle as a filler, forming a soft actuator that responds to various organic solvent vapors. The underlying actuation mechanism is attributed to crystalline phase transition of urea macrocycle, driven by the host‒guest interactions with diverse guest molecules. This work provides valuable insights for advancing the design of supramolecular hosts in smart material applications.

Analysis and Prediction of Nonlinear Hysteretic Behaviors of Graphite Magnetorheological Grease at Different Temperatures.

Magnetorheological grease (MRG) is considered a promising alternative to magnetorheological fluids as a smart material because of its higher stability and less leakage. To enhance yield stresses in various applications, graphite is incorporated as an additive, resulting in graphite magnetorheological grease (GMRG). However, the nonlinear hysteresis properties of this new material and its prediction methods have not been investigated. Therefore, in this work, the nonlinear hysteretic properties of GMRG at different temperatures, magnetic fields, and frequencies are systematically investigated and compared with those of MRG. The results of rheological experiments show that graphite enhances the shear stress of GMRG in the hysteresis curve through its reinforcing effect on the magnetic chains. The strain hardening, elasticity, and viscosity of GMRG are enhanced, but an increase in temperature decreases this efficacy. A prediction model based on the particle swarm optimization neural network algorithm (PSO-BP) is also proposed to efficiently and accurately control the nonlinear behavior of GMRG in engineering. The hysteresis curves of GMRG under different external excitations are characterized and predicted by the particle swarm optimization neural network approach. The statistical results show that the PSO-BP-based hysteresis characteristic estimates have satisfactory accuracy. In the test data, the PSO-BP model demonstrates improvements in RMSE, MAE, and SMAPE by 19.5%, 20.6%, and 21.0%, respectively, compared to the conventional BP network, which maintains an R2 value exceeding 0.95. This method provides an efficient solution for researchers to carry out reliable performance prediction in work such as genetic engineering of materials and related engineering applications.

Biomedical Potential of Cellulose: Current Trends and Future Directions

ABSTRACTThe exploration of cellulose, a natural polysaccharide derived from renewable biomass, has seen significant advancements in recent years due to its biocompatibility, biodegradability, and versatility. This review paper comprehensively covers the latest developments in cellulose and its derivatives as functional biomaterials for various biomedical applications. Emphasis is placed on the intrinsic properties of cellulose, such as its mechanical strength, thermal stability, and chemical modifiability, which enable its wide‐ranging use in drug delivery systems, wound dressings, tissue engineering, and biosensors. The article further delves into the modification techniques—such as oxidation, esterification, and etherification—that enhance cellulose's performance, allowing it to be fine‐tuned for specialized medical applications, including the creation of scaffolds for tissue regeneration and smart materials for responsive drug release. Additionally, the hybridization of cellulose with inorganic materials offers potential in developing materials with superior antimicrobial properties and improved mechanical characteristics. This review also addresses the challenges in cellulose processing, particularly concerning optimizing its structure for specific applications, while highlighting future opportunities in the field of personalized medicine and intelligent healthcare devices. By examining both the current innovations and future trends, this review highlights the growing importance of cellulose as a sustainable and versatile resource in the biomedical industry.

Multifunctional Roles of Iron Oxide Nanoparticles in a Reversible Shape‐Memory Composite

AbstractThe utilization of functional fillers in the development of composite materials has come a long way since its advent to improve physical, chemical, or mechanical properties of the base material. However, the heterogenous roles contributed by a single type of filler remain uncommon in this field. Here the endowment of various modifications to a 1,8‐octanediol/1,12‐dodecanedioic acid/citric acid (OD/DDA/CA) matrix through the incorporation of iron oxide nanoparticles (IONPs) is reported. Owing to the relaxation and hysteresis loss behaviors of IONPs when exposed to an alternating magnetic field (AMF), the composites demonstrate a magnetothermal response. Similarly, the excitation and relaxation of electrons in IONPs under near‐infrared light (NIR) enable photothermic‐responsiveness. In combination, two findings nurtured an observed shape‐memory effect when the samples are under actuation by these indirect stimuli, where a shape recovery ratio (≥98%) and reversible strain (≤7%) are recorded. Moreover, the catalytic role of IONPs aided transesterification in the covalent network, demonstrated by successful repeated cycles of shape reconfiguration of the samples. This work highlights the prospectives of multifunctional composite fillers in the exploration of bio‐derived composite smart materials.

A Bistate Intelligent Eutectogel Material with Water‐Regulated Stiffness for Diverse Designed Functionality

AbstractThe design of stiffness‐changeable synthetic materials that can mimic their biological counterparts in the production of adaptable structures and functions is highly important but remains challenging. Here, the development of a bioinspired intelligent material composed of a deep eutectic solvent (DES) and an ionically crosslinked polymer network that is capable of switching reversibly between hard plastic and soft elastic states in response to water is reported. The eutectogel stiffness can be dramatically switched and flexibly regulated by water, which can activate salt ionization and shield the ionic crosslink. This design principle is extensively applied to multiple polymers, producing a series of bistate materials that exhibit water‐regulated capabilities ranging from self‐healing, shape memory, remolding, antifreezing, anticompressing, and stretchability to conductivity. These bistate materials are used for diverse functions, such as performing mechanical tasks, sensing and monitoring human movements, lighting LEDs, and outputting signals. This work opens an avenue for the development of next‐generation stiffness‐changeable materials with diverse functionalities for various designed applications.

Swelling-Shrinking Behavior of a Hydrogel with a CO2-Switchable Volume Phase Transition Temperature.

Macromolecules exhibit rich phase behavior that may be exploited for advanced material design. In particular, the volume phase transition in certain crosslinked hydrogels is a key property controlling the transition between a collapsed/dehydrated and a swollen/hydrated state, thereby regulating the release and absorption of water via a temperature change. In this work, a simple and tunable system exhibiting a carbon dioxide (CO2)-switchable volume phase transition is introduced, which displays isothermal swelling-shrinking behavior that is activated by addition and removal of CO2, respectively. Through systematic compositional studies, shifts in phase transition temperatures of up to 8.6°C are measured upon CO2 exposure, which enables pronounced isothermal swelling in response to CO2, reaching up to a fivefold increase in mass. The shift in transition temperature and the extent of swelling are controlled by the hydrogel composition, thus enabling the transition temperature and swelling degree to be tuned a priori for a particular application. Controlled release experiments from these gels upon a CO2-induced phase transition suggest viability for drug delivery applications. It is anticipated that this work will motivate and expand efforts to exploit phase behavior for smart material development.

High-performance flexible sensor with rapidly adjustable sensitivity for wearable electronics

Despite numerous advances in sensor structural design, existing sensors still struggle to achieve rapidly adjustable sensitivity. Here, we utilized a structural design with alternating hard and soft sensor connections, and a lockout device to construct a sensitivity-adjustable sensor (AHS-L). Silicone rubber foams (SF) served as the flexible matrix for fabricating sensors with different hardnesses. Among them, the soft sensor (SRC-ACPF) retained the foam structure, and constructed dual conductive networks both within and on the pore walls, enhancing its resistance sensitivity with a gauge factor (GF) of up to 561.9. In contrast, the SF used in the hard sensor (ASR-PPS) featured a fingerprint-like structure. A conductive network was introduced on the pores and backfilled with liquid silicone rubber to achieve a “soft and hard” distinction from SRC-ACPF. The fingerprint-like structure induced stress concentration during stretching, resulting in high resistance sensitivity for ASR-PPS (GF up to 711.5). This microstructure also amplified contact signals, enabling ASR-PPS to realize intelligent material recognition. Notably, the alternating soft and hard structure of the AHS-L allowed the tensile deformation to be concentrated in the SRC-ACPF. Meanwhile, due to the initial resistance difference, the resistance change in SRC-ACPF has less effect on the overall resistance fluctuation of AHS-L than ASR-PPS. Therefore, a lockout device was introduced to limit the deformation of the SRC-ACPF, allowing the deformation pattern of the AHS-L to be tuned and enabling the sensitivity to be quickly adjusted from low (GF of 3.7 within 0–22% strain, 63.8 within 22–38% strain) to ultra-high (GF of 444.7 within 0–20% strain, 821.2 within 20–46% strain).

Enhanced anti-bacterial properties and thermal regulation via photothermal conversion with localized surface plasmon resonance effect in cotton fabrics

Enhanced anti-bacterial properties and thermal regulation are realized in cotton fabrics cross-linked with hybrid poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate-co-ethylene glycol methacrylate) nanogels containing gold nanoparticles (Au NPs), denoted as hybrid P(MA-co-MA300-co-EGMA)/Au nanogels. Pure P(MA-co-MA300-co-EGMA) nanogels are synthesized by emulsion polymerization as carriers and then embedded with Au NPs via in-situ reduction. By applying 1,2,3,4-butanetetracarboxylic acid as a cross-linker and changing the amount of hybrid P(MA-co-MA300-co-EGMA)/Au nanogels in solution, the weight gain ratios of hybrid nanogels on cotton fabrics are set as 10 % (CHN-10) and 20 % (CHN-20). Due to the densely packed structure of the hybrid nanogels on the surface, the localized surface plasmon resonance (LSPR) effect of the Au NPs improves the photothermal conversion capability and converts the absorbed light energy into thermal energy. Simply illuminating with visible light, the surface temperature of CHN-20 pronouncedly increases from 20.4 to 43.0 °C in 50 s. The increased local temperature induces the denaturation of protein and the death of bacteria on the surface. Thus, an illumination with visible light for 2 h results in an anti-bacterial rate for S. aureus of 100 % for CHN-20. Additionally, it presents an excellent thermal regulation capability via photothermal conversion and can be used for continuously maintaining human body temperature in cold areas. Because no additional chemical agents and external power source are required for the anti-bacterial properties and thermal regulation, the obtained cotton fabrics cross-linked with hybrid P(MA-co-MA300-co-EGMA)/Au nanogels are eco-friendly and suitable for smart textiles in daily wear.