Smart Materials Research Articles

Environmentally Friendly Protective Coating for Electrically Conductive Yarns Using in Smart Textiles

Current research focuses on advancements and breakthroughs in the realm of smart textiles, with applications spanning various industries such as medicine and education. For producing flexible smart textiles, electrically conductive yarns (EC) are needed to transmit signals or as part of sensor systems. Mostly, these EC consist of a polymer core with an outer metallized layer. Using EC in contact with skin requires high reliability and safety, and thus, the EC must maintain their functional properties on a long-term scale under a range of different stresses. The electrical properties of EC deteriorate under mechanical stress applied during production or in-use through damage to the yarn’s surface. At present, there are only partially feasible solutions to protect the metal-layer of the yarn surface. Hence, this paper presents a newly developed non-toxic coating (NTC) to protect the EC surface. The NTC consists of an aqueous emulsion with polypropylene wax and oxidized wax. To determine the long-term stability of the coating, the produced yarns undergo comprehensive evaluation using a range of analytical techniques. The aim is to identify the optimal coating by exploring different equipment and parameters. Additionally, it is various test methods to gauge the durability of the newly developed NTC used and ensure its reliability over time. To characterize the yarn properties before and after the coating, light microscopy (LM), washing processes, mechanical resistance tests and resistivity measurement are conducted.

Quantifying the Human Perception: Development and Characterization of Textile-Based Capacitive Strain and Pressure Sensors

In the research field of smart textiles, one main goal concerns quantifying environmental forces acting on the wearer's body since textiles, acting as the boundary between the two, are an excellent way of integrating sensors. Integrating strain and pressure sensors into wearables promises a simple way of monitoring a person's posture and forces acting on their body. Sensors relying on a capacitive measuring principle are highly suitable for this, as they are less sensitive to changes in temperature than resistive or inductive types. In this paper, textile-based capacitive sensors are produced by braiding conductive yarns with and without an electrically insulating TPU sheath. The produced sensors are analyzed in cyclic strain and compression tests. Moreover, their behavior under changing temperatures is tested to prove their resilience against environmental changes. To extend their capabilities from an integral measurement to a localized assessment of the strain, time-domain-reflectometry (TDR) is employed. Finally, the sensors are integrated into a flexible actuated bending beam, and their adoption for soft robotics is discussed. Strain is tested cyclically, showing good long-term stability. Pressure sensitivity is measured in a static compression test under increasing force. TDR is used to localize strain in two discreet sections of the sensor. Although strain could not be quantified through TDR, characteristic points in the measured response signal indicating the position of the strain were identified. Textile-based capacitive sensors are suitable for strain up to 10 % and pressure up to 8 N. The determined gauge factors are satisfactory, with strain sensors inherently having a higher gauge factor than pressure sensors. Furthermore, they display good long-term stability and no adverse reaction to changes in temperature. TDR is proven to provide localization of strain in flexible sensors.

Distributed sensing along fibers for smart clothing.

Textile sensors transform our everyday clothing into a means to track movement and biosignals in a completely unobtrusive way. One major hindrance to the adoption of "smart" clothing is the difficulty encountered with connections and space when scaling up the number of sensors. There is a lack of research addressing a key limitation in wearable electronics: Connections between rigid and textile elements are often unreliable, and they require interfacing sensors in a way incompatible with textile mass production methods. We introduce a prototype garment, compact readout circuit, and algorithm to measure localized strain along multiple regions of a fiber. We use a helical auxetic yarn sensor with tunable sensitivity along its length to selectively respond to strain signals. We demonstrate distributed sensing in clothing, monitoring arm joint angles from a single continuous fiber. Compared to optical motion capture, we achieve around five degrees error in reconstructing shoulder, elbow, and wrist joint angles.

Recent progress in tannin and lignin blended metal oxides and metal sulfides as smart materials for electrochemical sensor applications.

Our technologically advanced civilization has made sensors an essential component. They have potential uses in the pharmaceutical sector, clinical analysis, food quality control, environmental monitoring, and other areas. One of the most active fields of analytical chemistry research is the fabrication of electrochemical sensors. An intriguing area of electroanalytical chemistry is the modification of electrodes using polymeric films. Due to their benefits, which include high adhesion to the electrode surface, chemical stability of the coating, superior selectivity, sensitivity, and homogeneity in electrochemical deposition, polymer-modified electrodes have attracted a great deal of interest in the electroanalytical sector. Conducting polymers are an important material for sensing devices because of their fascinating features, which include high mechanical flexibility, electrical conductivity, and the capacity to be electrochemically converted between electronically insulating and conducting states. Tannin or lignin nanomaterials can be an inter-linker leading to flexible and functional polymeric networks. There is a continuing demand for fast and simple analytical methods for the determination of many clinically important biomarkers, food additives, environmental pollutants etc. This review in a comprehensive way summarizes and discusses the various metal oxide and sulfide-incorporated tannin and lignin scaffolds using electrochemical sensing and biosensing.

Cholesterol-substituted spiropyran: Photochromism, thermochromism, mechanochromism and its application in time-resolved information encryption

Organic multi-stimulus-responsive materials are widely used in anti-counterfeiting and information encryption due to their unique response characteristics and designability. However, progress in obtaining multi-stimulus-responsive smart materials has been very slow. Herein, a spiropyran derivative is constructed, which shows photochromic, thermochromic and mechanical photochromic properties, and has reversible absorption/luminescence adjustment ability. By introducing non-covalent interactions such as van der Waals force and hydrogen bond, this new molecule is more sensitive to external stimuli and exhibits better photochromic, mechanochromic and thermochromic properties with rapid speed and high contrast. Furthermore, these three stimulus responses can be completely restored to the initial state under white light irradiation. The reversible multiple response characteristics of this molecule make it possible to provide dynamic anti-counterfeiting and advanced information encryption capabilities. To demonstrate its application in advanced information encryption, powders treated with different stimuli are combined with fluorescent dyes to encrypt complex digital information. This work puts forward a new time-resolved encryption strategy, which provides important guidance for the development of time-resolved information security materials.

Shape‐Memory Alloy‐Based Auxetic Smart Metamaterials: Enabling Inherently Bidirectional Actuation

Auxetic metamaterials, characterized by their negative Poisson's ratio, have garnered significant interest in various fields due to their unique mechanical properties. This article presents a pioneering approach to the development of auxetic smart metamaterials using shape memory alloy (SMA) as the core material. As SMAs can be Joule heated to change between their low‐ and high‐temperature phases to trigger the actuation of the structure, the auxetic smart metamaterial can actively modify its shape and stiffness to produce bidirectional actuation with a single power input and using a single bias mechanical element. The proposed active auxetic metamaterial consists of an SMA plate patterned with auxetic cuts, creating hinges that modulate the deformation of the structure to produce an auxetic behavior. This work looks at the impact of different geometric parameters on the behavior of the structure, including its generated force, its maximum strain, and its Poisson's ratio. The study also investigates the effect of the number of segmented units, revealing that designs with more segmented units suffer from stress concentrations near attachment points, limiting their advantages. This article shows that smart materials can help imbue metamaterials such as auxetic metamaterials with active properties to facilitate their implementation in future robotic applications.

Evaluation and Trend of Smart Clothing Research: Visualization Analysis Based on Bibliometric Analysis and Quantitative Statistics

Evaluation and Trend of Smart Clothing Research: Visualization Analysis Based on Bibliometric Analysis and Quantitative Statistics

Synthesis and characterization of hydroxy propyl methyl Cellulose/Copper nanobiocomposites for antibacterial and antioxidant smart materials

The synthesis of hydroxy propyl methyl cellulose (HPMC) /copper nanobiocomposites adopting a microwave treatment. In this study, HPMC and copper nitrate at various concentration were mixed and subjected to varying microwave treatment times (10, 20, 30, 40, 50 and 60 s). UV–Vis spectroscopy was employed to analyse the physicochemical characteristics of HPMC/Copper nanobiocomposites, with a maximal absorbance at 380 nm, indicating the formation copper nanoparticles within the HPMC matrix. The interaction between copper nanoparticles and HPMC was further confirmed through FT-IR analysis. The SEM analysis displayed microporous structures ranging from 5 to 14 µm in diameter, with an average pore size of 7.0 ± 2.0 nm. The compositional analysis was done with EDS mapping. TEM analysis revealed spherical shaped copper nanoparticles/ HPMC with an average particle size about 2.5 nm. Remarkably, these nanobiocomposites exhibited a broad-spectrum antibacterial activity, displaying minimal inhibitory concentrations against both Gram-negative and Gram-positive bacterium. Significantly, the assessment of antibacterial activity in HPMC/copper nanobiocomposites demonstrated their efficacy against both Escherichia coli and Staphylococcus aureus. The antibacterial properties holds significant implications for their potential applications of HPMC/ copper nanobiocomposites in the fields of food packaging and biomedicine.

Deep learning reduces sensor requirements for gust rejection on a small uncrewed aerial vehicle morphing wing

Uncrewed aerial vehicles are integral to a smart city framework, but the dynamic environments above and within urban settings are dangerous for autonomous flight. Wind gusts caused by the uneven landscape jeopardize safe and effective aircraft operation. Birds rapidly reject gusts by changing their wing shape, but current gust alleviation methods for aircraft still use discrete control surfaces. Additionally, modern gust alleviation controllers challenge small uncrewed aerial vehicle power constraints by relying on extensive sensing networks and computationally expensive modeling. Here we show end-to-end deep reinforcement learning forgoing state inference to efficiently alleviate gusts on a smart material camber-morphing wing. In a series of wind tunnel gust experiments at the University of Michigan, trained controllers reduced gust impact by 84% from on-board pressure signals. Notably, gust alleviation using signals from only three pressure taps was statistically indistinguishable from using six pressure tap signals. By efficiently rejecting environmental perturbations, reduced-sensor fly-by-feel controllers open the door to small uncrewed aerial vehicle missions in cities.

Stereo Camera Setup for 360° Digital Image Correlation to Reveal Smart Structures of Hakea Fruits.

About forty years after its first application, digital image correlation (DIC) has become an established method for measuring surface displacements and deformations of objects under stress. To date, DIC has been used in a variety of in vitro and in vivo studies to biomechanically characterise biological samples in order to reveal biomimetic principles. However, when surfaces of samples strongly deform or twist, they cannot be thoroughly traced. To overcome this challenge, different DIC setups have been developed to provide additional sensor perspectives and, thus, capture larger parts of an object's surface. Herein, we discuss current solutions for this multi-perspective DIC, and we present our own approach to a 360° DIC system based on a single stereo-camera setup. Using this setup, we are able to characterise the desiccation-driven opening mechanism of two woody Hakea fruits over their entire surfaces. Both the breaking mechanism and the actuation of the two valves in predominantly dead plant material are models for smart materials. Based on these results, an evaluation of the setup for 360° DIC regarding its use in deducing biomimetic principles is given. Furthermore, we propose a way to improve and apply the method for future measurements.

Two birds with one stone: High electromagnetic interference shielding effectiveness and high thermal conductivity of ternary polyvinyl alcohol/graphene/ carbonyl iron nanocomposite films

Gaining brilliant flexible, easily-processable, bendable, low-density and high electrical conductivity (σ) materials with an excellent electromagnetic-interference (EMI) shielding performance is urgently needed in the fields of aerospace, aircraft, military, wearable and portable electronic industries. Therefore, the growing desire towards miniaturizing and developing high-frequency electronics is increasing incredibly today and grabbing much attention, however, they cause extreme heat accumulation and EM radiations that affect their performances as well as their hazardous effects on human health. So, polymer nanocomposites with high thermal conductivity (k) and EMI shielding effectiveness (SE) synchronously are urgently required to consume the generated heat and blocks the EM waves. Herein, poly(vinyl alcohol)/graphene nanosheets/carbonyl iron (PVA/GRx/CIR0.1-x) nanocomposite films are introduced as a new alternative candidate for EMI shielding applications with high in-plane k//, high mechanical functions, and EMI SET performance. The synergistic effect of GR and CIR on EMI shielding functions, thermal stability, mechanical properties, electrical features, and surface morphology has been explored. The increase in GR(x) amounts provides continuous GR layers and dense networks for conducting electrons and heats, provides the films with an admirable k// and total SE (SET) synchronously. Particularly, the PVA/GR0.08/CIR0.02 films have shown an σ of 1.72 Sm−1, a large SET of 32.94 dB and a specific SE (SSE/t) of 4365 dBcm2g−1 due to the mutual role (effect) of both high electrical conductive graphene and high magnetic carbonyl iron in cancelling the magnetic and electric fields of the incident EM waves. Moreover, the layered structure of GR endows films with a high k// of 3.62±0.11 W/(m·K), which is 14-fold larger than that of green PVA. The high compatibility and fine dispersion of GR/CIR fillers endow the films with a high Young modulus of 2.16 GPa, which is 7-fold larger than that of green PVA. This work suggests a novel and feasible scheme for producing high EMI shielding and high thermal conductive polymeric films, which will have huge prospects in advanced technology such as electromagnetic (microwave) interference shielding, wearable, biological, smart fabrics, military technologies and electronic equipments.

Grayscale stereolithography 3D printing of shape memory polymers for dual information encryption based on reconfigurable geometry and tunable optics

Dual information encryption such as geometry and transparency switching is highly desirable for preventing the leakage of confidential information and constructing a secure environment which has wide range of applications in privacy protection, anti-counterfeiting, and information security. However, it is still a challenge to develop a novel encrypted strategy and smart material to achieve credible protective capacity for stored information by a facile and programmed manner. Herein, integrating with arbitrary grayscale stereolithography, the hydrophilic ultraviolet (UV) curable shape memory polymers (HU-SMPs) with superior mechanical properties (the tensile strength of 29.39 MPa, elongation of 46.32 %, and the toughness of 1021.98 kJ.m−3) were prepared, which can be used for multifunctional information encryption. During the encrypted process, the HU-SMPs with the performances of high deformable and excellent shape memory behaviors can provide the preprogrammed morphological information and inevitable encryption, while the humidity-responsive of HU-SMPs capable of generating revisable transparency switching that can be encoded as the secondary information encryption. In this way, the dual encrypted information in the HU-SMPs is readable only after sequential shape recovery and fast hydration under heat-stimuli and humidity-stimuli. In addition, with the aid of digitally grayscale drawing, the secondary encrypted information is cyclically displayed and erasable due to the reversible hydration and dehydration process of HU-SMPs. Finally, the encrypted information is also can be permanently storage or decryption by the versatile post-processing methods of UV irradiation after and before decryption, respectively. In short, the design of HU-SMPs that compatible with grayscale digital light process (g-DLP)-based 3D printing, will motivates the future development of smart materials and provides a new insight into the information encrypt fields.

Embedded Sensors with 3D Printing Technology: Review.

Embedded sensors (ESs) are used in smart materials to enable continuous and permanent measurements of their structural integrity, while sensing technology involves developing sensors, sensory systems, or smart materials that monitor a wide range of properties of materials. Incorporating 3D-printed sensors into hosting structures has grown in popularity because of improved assembly processes, reduced system complexity, and lower fabrication costs. 3D-printed sensors can be embedded into structures and attached to surfaces through two methods: attaching to surfaces or embedding in 3D-printed sensors. We discussed various additive manufacturing techniques for fabricating sensors in this review. We also discussed the many strategies for manufacturing sensors using additive manufacturing, as well as how sensors are integrated into the manufacturing process. The review also explained the fundamental mechanisms used in sensors and their applications. The study demonstrated that embedded 3D printing sensors facilitate the development of additive sensor materials for smart goods and the Internet of Things.

Fabrication of reusable bioprotective nanofabric with passive nano-Ag/Joule thermal disinfection properties for real-time wireless fine biomotion and gesture sensing

The frequent outbreaks of new infectious diseases, with increased difficulty in prevention and control, have raised higher requirements for bio-protective smart textiles. However, current wearable sensing materials face challenges with thermal and humidity comfort, bioprotection, reusability, self-disinfection, and wireless real-time sensing ability. Herein, an ultralight and breathable sandwich-structured interlayer nanofiber composite consisting of two outer microporous layers of polyimide nanofibers embedded with AgNPs (Ag@PINFs) and one nanoporous conductive layer (＜100 nm) of carbon nanotubes (CNTs) have been demonstrated by in-situ reduction, electrospinning, and suction filtration to improve the triboelectric output performance and impart passive/active self-disinfection abilities to triboelectric nanogenerators (TENGs). The TENG was designed with a triple bio-protection function. This included a passive physical barrier effect, nano-Ag active disinfection, and active Joule-heat disinfection function, which ensures the reusability of TENG. As-prepared TENG possessed the following advantages: (i) good moisture-penetrability; (ii) good water and blood penetration resistance (≥17.2 kPa; ≥7kpa); (iii) improved triboelectric output performances (∼1.6 W/m2 at Ag content of 500 mg/kg); (iv) ultrahigh UV resistance (UPF＞6480); (v) high particle and wet/dry microbial filtration performance (PFE = 99.95%; wet microbial penetration time＞75 min; penetrated dry microbial: lg(cfu)=0); (vi) active bactericidal abilities with killing rates of ∼100% against E. Coli and S. aureus at Ag content of ≥ 70 mg/kg; (vii) high Joule heat self-disinfection efficiency with killing rates of 100% at applied voltage of ≥ 5 V; (viii) a wireless real-time sensing ability to distinguish fine biomotion such as swallowing, coughing, and normal speech and shouting, as well as recognizing hand gesture by developed two/four-channel wearable wireless monitoring system (∼18 g). The TENG has trinity performances including bio-protection, self-disinfection, and wireless fine biomotion and gesture sensing, which has potential applications in medical field.

Moisture actuated cobalt alginate discoloration artificial muscle

Artificial muscles have the ability to sense changes in the external environment and generate rapid and significant contraction deformation or rotational motion. However, most artificial muscles are limited to a single form of deformation, and there are still great difficulties in achieving complex dual response modes. Herein, a novel artificial muscle made of cobalt alginate fiber with both rotational/contraction deformation and discoloration functions was successfully prepared by a simple wet spinning and directional twisting methods. The wet-sensitive color change performance is achieved by the formation of different hydrates of cobalt ions in varying humidity conditions, while rotational motion is induced by radial untwisting resulting from fiber swelling upon moisture absorption. In addition, the artificial muscle fiber exhibited a transition from blue to purple to red as the environmental humidity changes from 35 % to 85 %. When the fibers were exposed to water, the twisted fiber with a twist count of 2500 truns provided a rotational speed of over 2000 rpm, and the actuating and discoloration performance did not significantly decrease in 50 repeated cycle tests. This stable shape and color dual response artificial muscle can simulate traditional windmill devices, while also providing a new design idea for smart textiles and humidity visualization devices.

Waterproof, stretchable and wearable corrugated conductive carbon fiber strain sensors for underwater respiration monitoring and swimming instruction

Respiration is one of crucial vital signs, which can be used for health assessment and sports management. Flexible resistive strain sensors provide an opportunity to monitor personal respiratory behaviors in real time due to high sensitivity, good linearity and fast response. However, there are some critical issues with the resistive strain sensor, such as strain mismatch, poor contact properties and moisture sensitivity, which easily cause unexpected electrical response, limiting its application scenarios. Here, a novel stretchable carbon fiber strain sensor is developed by a simple structural design, which endow the device with a remarkable linearity (R2=0.99601 in 0–40 % tensile strain), excellent anti-jamming performance, long-term durability, and waterproofness. Moreover, a sophisticated wearable respiratory monitoring system is further developed, which can not only precisely distinguish diverse respiratory patterns to enhance the accuracy in early illness diagnosis but also remotely capture real-time breathing information during swimming for guiding swimming training. It demonstrates that our stretchable resistive strain sensor has an enormous application potential in wearable electronics and smart clothing for health monitoring and training guide.

Rational Design of Bio‐Inspired Peptide Electronic Materials toward Bionanotechnology: Strategies and Applications

AbstractBiologically inspired peptide‐based materials, as novel charge transport materials, have gained increasing interest in bioelectronics due to their remarkable electrical properties and inherent biocompatibility. Extensive studies have shown that peptides can self‐assemble into a variety of hierarchical nanostructures with unique physical properties through supramolecular interactions. Therefore, peptide‐based materials hold great promise for applications in emerging electronic fields such as sensing, energy harvesting, energy storage, and electronic transmission. Herein, this work proposes a review article to summarize the rational design and research progress of peptide‐based materials and devices in bioelectronics. This work first introduces the design strategies and assembly mechanism for constructing high‐performance peptide‐based electronic materials and devices. In the following part, the applications of peptide‐based electronic materials and devices are systematically classified and discussed, including sensors, piezoelectric nanogenerators, electrodes, and semiconductors. Finally, the remaining challenges and future perspectives of peptide‐based bioelectronic materials and devices are presented. This work believes that this review will provide inspiration and guidance for the design and development of innovative peptide‐based smart materials in the field of bioelectronics.

Shape Transformation of Polymer Vesicles.

Life activities, such as respiration, are accomplished through the continuous shape modulation of cells, tissues, and organs. Developing smart materials with shape-morphing capability is a pivotal step toward life-like systems and emerging technologies of wearable electronics, soft robotics, and biomimetic actuators. Drawing inspiration from cells, smart vesicular systems have been assembled to mimic the biological shape modulation. This would enable the understanding of cellular shape adaptation and guide the design of smart materials with shape-morphing capability. Polymer vesicles assembled by amphiphilic molecules are an example of remarkable vesicular systems. The chemical versatility, physical stability, and surface functionality promise their application in nanomedicine, nanoreactor, and biomimetic systems. However, it is difficult to drive polymer vesicles away from equilibrium to induce shape transformation due to the unfavorable energy landscapes caused by the low mobility of polymer chains and low permeability of the vesicular membrane. Extensive studies in the past decades have developed various methods including dialysis, chemical addition, temperature variation, polymerization, gas exchange, etc., to drive shape transformation. Polymer vesicles can now be engineered into a variety of nonspherical shapes. Despite the brilliant progress, most of the current studies regarding the shape transformation of polymer vesicles still lie in the trial-and-error stage. It is a grand challenge to predict and program the shape transformations of polymer vesicles. An in-depth understanding of the deformation pathway of polymer vesicles would facilitate the transition from the trial-and-error stage to the computing stage. In this Account, we introduce recent progress in the shape transformation of polymer vesicles. To provide an insightful analysis, the shape transformation of polymer vesicles is divided into basic and coupled deformation. First, we discuss the basic deformation of polymer vesicles with a focus on two deformation pathways: the oblate pathway and the prolate pathway. Strategies used to trigger different deformation pathways are introduced. Second, we discuss the origin of the selectivity of two deformation pathways and the strategies used to control the selectivity. Third, we discuss the coupled deformation of polymer vesicles with a focus on the switch and coupling of two basic deformation pathways. Last, we analyze the challenges and opportunities in the shape transformation of polymer vesicles. We envision that a systematic understanding of the deformation pathway would push the shape transformation of polymer vesicles from the trial-and-error stage to the computing stage. This would enable the prediction of deformation behaviors of nanoparticles in complex environments, like blood and interstitial tissue, and access to advanced architecture desirable for man-made applications.

Robust, self-healing AIE fluorescent supramolecular elastomers for smart anti-counterfeiting

Providing aggregation-induced emission (AIE) polyurethane with self-healing capability can increase the lifetime of the material and adapt it to multiple application scenarios, which is a huge challenge in the development of luminescent smart materials. Herein, a range of transparent fluorescence polyurethanes (FPUs) with prominent strength were designed and synthesized. The optimization of robust FPUs exhibits outstanding mechanical performance (33.5 MPa tensile strength, 120.2 MJ m−3 toughness) and self-healing ability (88.9 %, at 80 °C for 2 h). Furthermore, the aggregation of tetraphenylethylene structure in the hard segment causes the system to emit bright blue fluoresence. We successfully screen-printed designable patterns on the self-healing polyurethane substrates. The concealed patterns self-repair after damage, and can be clearly and robustly displayed under 365 nm light irradiation. The as-prepared multifunctional self-healing material, exhibiting stable AIE fluorescence, is anticipated to possess significant value in the domains of smart anti-counterfeiting materials, flexible display screens and intelligent optoelectronics.

AI Smart Materials for Enhancing Sucking Ability in Preterm Infants

AI Smart Materials for Enhancing Sucking Ability in Preterm Infants