Flexible Materials Research Articles

Development of flexible electrothermal fabrics based on silver-nanowire-modified polyacrylonitrile nanofiber yarns for wearable heating applications

This paper describes the development of advanced electrothermal fabric constructed from electrospun polyacrylonitrile (PAN) nanofiber yarns, modified with silver nanowires (AgNWs) and polyethylenimine (PEI). The nanofiber yarns, with an average diameter of 53.7 µm, were woven into fabrics using conventional textile fabrication techniques. The incorporation of PEI significantly improved the hydrophilicity of the fabric, thereby enhancing the adhesion of the AgNWs and boosting the electrical conductivity of the fabric. Electrothermal characterization revealed that the fabric demonstrated a rapid heating response, reaching a steady-state temperature of approximately 37.5°C within 35 s under an applied voltage of 1.2 V. A strong linear correlation ( R2 = 0.999) was observed between the steady-state temperature and the applied power, indicating the potential for precise thermal management at low operating voltages. The AgNW–PEI–PAN nanofiber yarn fabric shows great promise as a flexible, efficient electrothermal material for applications in wearable technologies and smart textiles.

In Vitro Evaluation of the Fracture Strength among Three Different Denture Base Materials

Failure in the form of denture fracture is commonly encountered by both removable prosthodontics wearers and dentists, it is mainly attributed to material properties, technical features, stresses while in function or due to impact as a consequence of dropping the dentures. Traditionally, Heat-Polymerized Polymethylmethacrylate (PMMA) has been the gold standard for denture bases due to its ease of processing and acceptable mechanical properties. However, newer materials, injectable flexible nylon-based resin and CAD/CAM Polyether ether Ketone (PEEK) denture bases are being introduced with claims of superior strength and durability. The aim of this study was to investigate the fracture strength of three commonly used denture base materials in Libya, which may aid in selecting the best material for a given application and predicting potential material behavior under load when holding the durability of the material in mind. A total of 36 samples were tested. These samples were divided into three groups, with 12 samples each: Group I heat polymerized acrylic resin PMMA, group II Injectable flexible nylon-based resin and group III CAD/CAM (PEEK). The fracture strength test was carried out on a universal testing machine at a crosshead speed of 5 mm/min. The results were analyzed using ANOVA, and multiple comparisons were undertaken using Tukey’s HSD test. Statistical significance was set at P ≤ 0.001. The result of this study shows there were significant differences in the fracture strength among the three groups (P< 0.001). Moreover, CAD/CAM (PEEK) denture base material exhibited significantly the highest fracture strength (234.17N ± 13.5) whereas the least fracture strength value was measured with Injectable flexible nylon-based resin denture base material (75.25N±10.5). The study concluded that, within the limitations of this study, the results demonstrate that CAD/CAM (PEEK) outperforms Injectable flexible nylon-based resin and heat polymerized acrylic denture base materials in terms of the fracture strength, supporting its potential as an advanced material for denture construction. However, further clinical studies are recommended.

Flexible material handling system for multi-load autonomous mobile robots in manufacturing environments: a hierarchical reinforcement learning approach

The increasing complexity of customer demands has led to the implementation of flexible job-shop scheduling and automated material handling systems across manufacturing sectors. In particular, advances in robotic technology have made autonomous mobile robots (AMRs) essential for material handling tasks within these sectors. The capability of free movement, path planning, and loading multiple work-in-processes (WIPs) can significantly enhance the efficiency of material handling operations. However, the full flexibility of AMRs cannot be utilised when their decisions regarding the sequence of loading and unloading multiple WIPs are made by specific rule-based operations, resulting in inefficiencies in the throughput of WIPs in manufacturing environments. To address this inefficiency, we introduce a hierarchical reinforcement learning algorithm to optimise material handling with AMRs, thereby maximising the throughput of WIPs. In this approach, a graph attention network (GAT) serves as an encoder for the hierarchical reinforcement learning (HRL) input, effectively capturing the complex relationships between different nodes. Computational experiments demonstrate that our approach enhances the efficiency of the material handling system more effectively than existing rule-based methods.

Review: Advanced Drive Technologies for Bionic Soft Robots

Abstract This article provides a comprehensive exploration of the current research landscape in the field of soft actuation technology applied to bio-inspired soft robots. In sharp contrast to their conventional rigid counterparts, bio-inspired soft robots are primarily constructed from flexible materials, conferring upon them remarkable adaptability and flexibility to execute a multitude of tasks in complex environments. However, the classification of their driving technology poses a significant challenge owing to the diverse array of employed driving mechanisms and materials. Here, we classify several common soft actuation methods from the perspectives of the sources of motion in bio-inspired soft robots and their bio-inspired objects, effectively filling the classification system of soft robots, especially bio-inspired soft robots. Then, we summarize the driving principles and structures of various common driving methods from the perspective of bionics, and discuss the latest developments in the field of soft robot actuation from the perspective of driving modalities and methodologies. We then discuss the application directions of bio-inspired soft robots and the latest developments in each direction. Finally, after an in-depth review of various soft bio-inspired robot driving technologies in recent years, we summarize the issues and challenges encountered in the advancement of soft robot actuation technology.

Valence State Hydrogen Channel Enhances Sustained and Controllable Electrocatalytic Hydrogen Evolution in Diabetic Skin Wound Healing

AbstractDiabetes significantly increases the risk of serious health issues, including prolonged skin inflammation and delayed wound healing, owing to inferior glucose control and suppression of the immune system. Although traditional hydrogen (H2) therapy is slightly effective, its ability to tailor the release of H2 on the skin is limited. Accordingly, this study proposed a novel strategy for electrocatalytic H2 release under neutral conditions to promote wound healing in diabetic mice and rabbit. Herein, a defect‐engineered cobalt phosphide (CoP) catalyst was designed by introducing a neutral single‐metal electrocatalytic Hydrogen valence state channel into CoP. By effectively regulating the formation and transfer of *H active species during the CoP catalytic process, a considerable enhancement in neutral electrocatalytic H2 evolution performance was achieved (−78.0 mV@‐10.0 mA cm−2). Based on this superior catalytic performance, we developed a flexible electrode (namely, CoP/flexible gold electrode made by screen printing (FGSP) by combining a convenient electrolysis platform with continuous electrolyte supply and FGSP, enabling customized H2 release and accelerating wound healing in diabetic mice and rabbits. Notably, the designed flexible electrode features adjustable dimensions, interchangeable substrates, and material adaptability, meeting the diverse needs of clinical and basic research and demonstrating significant potential for applications in clinical medicine.

RF communication between dual band implantable and on body antennas for biotelemetry application

This paper investigates two antennas for implantable communication, which are a wide-band, low-profile transmitting antenna with a circular polarization (CP) merit immersed in a lossy medium and a corresponding wide-band, low-profile receiving antenna with a linear polarization (LP) merit placed on human tissue. The first antenna is implantable inside a human body for sensing, monitoring, and transmitting various vital signs, while the second antenna acts as a nearby receiving end. These antennas work in the 2.4-2.4835 GHz and 5.725-5.875 GHz industrial, scientific, and medical (ISM) bands. The main features of the designed transmitting antenna are its simplicity, the wide-band characteristics, which preserve the detuning effect caused by environmental heterogeneity, and the CP property at both operational ISM bands. Moreover, for introducing an electrically small antenna footprint with proper performance, the implantable antenna is designed with an entire size of 25.4 (5 5 1.016) . This antenna is designed and dissected in a homogeneous skin model (HSM) as well as a three-layer phantom. On the other hand, the wide-band receiving antenna is designed on flexible material for patients’ comfort with a compact size of 134.6 () . In addition, the implantable antenna performance is evaluated in a chicken slab as well as a saline solution, while the on-body antenna is placed on the chicken slab to measure its reflection coefficient. The measured impedance BWs of the implantable antenna are 13.04 % and 33.2 % in the chicken slab while 19.5% and 25.2 % in the saline solution at the two ISM bands, respectively. While, the measured impedance BWs of the on-body antenna are 24% and 50.4 % at two operating ISM frequencies. Finally, the measured transmission coefficient between the two antennas is evaluated.

Synthesis of flexible form stable phase change materials with in-situ formed porous TiO2 for personal thermal management

Synthesis of flexible form stable phase change materials with in-situ formed porous TiO2 for personal thermal management

Liquid Metal-Based Conductive Nerve Guidance Conduit Combined With Electrical Stimulation Boosts Peripheral Nerve Repair.

The combination of nerve guide conduits (NGCs) and electrical stimulation (ES) is an effective treatment for peripheral nerve injury (PNI). Flexible conductive materials with mechanical properties similar to those of biological tissues have been shown to have better long-term biointegration and functionality than rigid conductive materials. In this study, liquid metal (LM)-based conductive polycaprolactone/gelatin/polypyrrole/LM (PCL/Gel/PPy/LM, PGPL) NGC was combined with exogenous ES to repair PNI. PGPL membranes had good hydrophilicity, degradability, and mechanical properties, and its conductivity reached 0.66 ± 0.02 S/m. Invitro studies showed that the combination of PGPL membranes and ES (2 Hz, 100 mV/cm, 30 min/d) could significantly increase the expression of neuromarkers and had a better pro-neural differentiation effect. Invivo studies demonstrated that PGPL NGCs in combination with ES (2 Hz, 200 mV/mm, 30 min/d) could effectively promote morphological reconstruction and functional recovery of the sciatic nerve in rats. At 3 months post-surgery, PGPL NGCs combined with ES restored the nerve conduction velocity to 73.85% ± 5.45% of the normal value. The LM-based NGCs prepared in this study could effectively repair long sciatic nerve defects, which may further expand the application of LM in the field of nerve tissue engineering.

Thermally-enhanced flexible phase change materials incorporating magnetically aligned boron nitride platelets for efficient thermal management

Thermally-enhanced flexible phase change materials incorporating magnetically aligned boron nitride platelets for efficient thermal management

Bioinspired Omnidirectional Interface Engineered Flexible Island for Highly Stretchable Electronics.

With the advancement of electronics, there is a growing need to effectively combine rigid, flexible, and stretchable materials to build hybrid electronics. However, the interfacial transition between rigid/flexible and stretchable substrates presents considerable challenges, mainly due to differences in elastic moduli, complicating their integration for practical usage. Here, bioinspired omnidirectional interfacial-engineered flexible islands (BOIEFI) are introduced for a robust transition from flexible to stretchable substrates. These BOIEFIs enable the creation of highly stretchable and durable hybrid substrates capable of withstanding diverse physical deformations such as stretching, twisting, and even poking. Inspired by plant roots, BOIEFIs are designed with primary and secondary root structures that provide flexible mechanical interlocking between substrates with different elastic moduli. Through experimental and computational methods, optimized BOIEFIs exhibit significantly enhanced stretchability and improved fatigue life. To demonstrate the broad applicability, light-emitting diodes (LEDs) are integrated into BOIEFIs to establish a stretchable display. In addition, a human-machine interface device with soft pressure sensors and an LED array is fabricated for the implementation of hybrid electronics. This approach facilitates the harmonious integration of rigid, flexible, and stretchable substrates, leading to the creation of soft, highly stretchable, and durable hybrid electronics.

Four-port flexible UWB-MIMO antenna with triple band-notched for wearable IoT applications

Abstract A four-port ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with three notch bands is proposed in this work. The antenna uses ultra-thin flexible material liquid crystal polymer (LCP) as the substrate. Four identical monopole radiators are designed in this proposed antenna system. The notch bands of the antenna are generated by adding complementary split ring resonator (CSRR) and ring branch. A cross-shaped stub is set in the center of the four antenna units to enhance the isolation. The measured bandwidth of the antenna is 2.54–10.69 GHz, filtering out three notch frequency bands of 2.81–3.85, 5.11–5.98, and 7.34–8.69 GHz. The isolation in the entire working frequency is better than 22 dB. The bent performances of the MIMO system and the specific absorption rate (SAR) value are analyzed. The low SAR values, low envelope correlation coefficient (<0.05), high diversity gain (>9.999), and stable gain of the proposed antenna indicate that in UWB-MIMO systems and wearable Internet of Things applications, it can be widely used.

Simulation Study Based on Experimental Flexible Composite Phase Change Material for Battery Thermal Management

With the application of new energy vehicles, lithium batteries generate a large amount of heat during operation, s-o batteries need effective thermal management. The traditional air cooling method has poor temperature control, which cannot meet the needs of thermal management. In this study, a new flexible composite phase change material (CPCM) is prepared. Experiments have shown that CPCM has good flexibility at 30 °C. The heat generation of the simulated battery is set according to the experimental heat generation. The thermal performance of CPCM with different thicknesses is analyzed by simulation comparison. The results show that the temperature control effect of air cooling with an air velocity of 3 m/s is comparable to that of the CPCM with a filling thickness of 4 mm. The maximum temperature of the lithium battery pack is 316.98 K. The combination of CPCM and air cooling has a good temperature control effect, which can control the temperature of the battery pack within 315.23 K. Meanwhile, the air cooling simulated in this study is the natural air cooling of the disturbed air during the operation of the electric vehicle. It has the advantages of no energy consumption, green and low carbon and efficient thermal management.

Recent trends in electro-microfluidic devices for wireless monitoring of biomarker levels

Wireless monitoring has emerged as a promising approach that enables real-time tracking of health, disease progression, and fitness, unlocking new possibilities for personalized healthcare. The review focuses on integrating electro-microfluidic (EM) devices with wireless technologies, revealing the potential for miniaturized, portable, and cost-effective systems. EM devices can noninvasively detect critical disease biomarkers such as metabolites, proteins, and pathogens. These advancements address the growing demand for accessible diagnostics, especially in resource-limited settings. Advancements in microfabrication techniques and biocompatible materials have enhanced the sensitivity, specificity, and ability of the devices to detect multiple biomarkers simultaneously, ensuring reliable performance in diverse applications. Incorporating Internet of Things frameworks further bridges the gap between laboratory diagnostics and point-of-care testing, enabling seamless data transmission and remote monitoring. Additionally, implementing flexible materials such as polymers, paper-based platforms, and textile-integrated designs has expanded the scope of devices to wearable applications, providing user comfort and convenience. These devices improve diagnostic accuracy and patient safety by enabling continuous health monitoring and early disease detection. The review highlights a comprehensive overview of the cutting-edge advancements in EM devices, emphasizing their transformative potential in making healthcare more accessible, efficient, and personalized.

Valence State Hydrogen Channel Enhances Sustained and Controllable Electrocatalytic Hydrogen Evolution in Diabetic Skin Wound Healing.

Diabetes significantly increases the risk of serious health issues, including prolonged skin inflammation and delayed wound healing, owing to inferior glucose control and suppression of the immune system. Although traditional hydrogen (H2) therapy is slightly effective, its ability to tailor the release of H2 on the skin is limited. Accordingly, this study proposed a novel strategy for electrocatalytic H2 release under neutral conditions to promote wound healing in diabetic mice and rabbit. Herein, a defect-engineered cobalt phosphide (CoP) catalyst was designed by introducing a neutral single-metal electrocatalytic Hydrogen valence state channel into CoP. By effectively regulating the formation and transfer of *H active species during the CoP catalytic process, a considerable enhancement in neutral electrocatalytic H2 evolution performance was achieved (-78.0 mV@-10.0 mA cm-2). Based on this superior catalytic performance, we developed a flexible electrode (namely, CoP/flexible gold electrode made by screen printing (FGSP) by combining a convenient electrolysis platform with continuous electrolyte supply and FGSP, enabling customized H2 release and accelerating wound healing in diabetic mice and rabbits. Notably, the designed flexible electrode features adjustable dimensions, interchangeable substrates, and material adaptability, meeting the diverse needs of clinical and basic research and demonstrating significant potential for applications in clinical medicine.

Construction strategies and recent advances of flexible EMI phase change composites

With the continuous development of small and medium-sized electronic devices, which bring convenience to people’s lives, electromagnetic wave (EMW) pollution has emerged as a significant issue. The development of materials with electromagnetic interference (EMI) shielding capabilities for protection against harmful radiation plays a vital role. Currently, a wide range of multifunctional, lightweight EMI shielding materials have been created to address various environmental requirements. However, a single EMI shielding material has been difficult to meet the requirements of high-speed transmission of electromagnetic radiation of electronic equipment because when such devices operate at high speeds, they typically generate elevated temperatures, and excessive electromagnetic radiation further exacerbates heat accumulation, reducing both efficiency and lifespan. Therefore, thermal management is essential to lower operating temperatures and ensure optimal performance. Phase change materials (PCMs) are known for storing a large amount of energy, and have significant potential in thermal management, so flexible EMI phase change composites (PCCs) have emerged. This review provides a detailed examination of flexible EMI shielding materials based on various fillers, the potential of flexible PCMs in thermal management, and the latest advancements in developing new lightweight EMI PCCs. Finally, we suggest some potential research directions for flexible EMI shielding PCCs, hoping to contribute to the rapid advancement of next-generation flexible electronics, human thermal management, and artificial intelligence.

Segmentation of tobacco shred point cloud and 3-D measurement based on improved PointNet++ network with DTC algorithm.

The three dimensions of the tobacco silk components (cut stem, tobacco silk, reconstituted tobacco shred, and expanded tobacco silk) of cigarettes directly affect cigarette combustibility; by accurately measuring the dimensions of different tobacco silks in cigarettes, it is possible to optimize combustibility and reduce the production of harmful substances. Identifying the components of tobacco shred in cigarettes is a prerequisite for three-dimensional measurement. The two-dimensional image method can identify the tobacco shred and measure its two-dimensional characteristics but cannot determine its thickness. This study therefore focuses on the identification of the tobacco shred and measuring it in three dimensions. The point cloud data of the upper and lower surfaces of tobacco shred are segmented using the improved three-dimensional point cloud segmentation model based on the PointNet++ network. This model combines the weighted cross-entropy loss function to enhance the classification effect, the cosine annealing algorithm to optimize the training process, and the improved k-nearest neighbors multi-scale grouping method to enhance the model's ability to segment the point cloud with complex morphology. Meanwhile, this study also proposes a dimension transformation calculation method for calculating the three dimensions of tobacco shred. The experimental results show that the precision and recall of the improved segmentation model increased from 84.27% and 83.63% to 95.13% and 97.68%, respectively; the relative errors of the length and width of tobacco shred were less than 5% and 7%, and the relative error of the standard gauge block thickness measurement reached 1.12%. This study also provides a new idea for implementing three-dimensional measurements of other flexible materials.

Self‐Cleaning of Fluorescent Polyester: Construction of Superhydrophobic Coatings by Surface Microsolubility Particle Semi Embedding Technology

ABSTRACTFluorescent materials are extensively utilized in anti‐counterfeiting and security applications, and surface cleanliness is crucial for preserving their functionality. This study presents a novel hydrophobic fluorescent coating characterized by a morphology in which particles are semi‐embedded and evenly dispersed within the primer. The coating was developed using an innovative method that involves spraying hydrophobic silica onto a microscopically dissolved fluorescent polyethylene terephthalate (PET) primer. The coating demonstrates superior hydrophobicity, with a water contact angle (WCA) of 165.0° ± 5.0° and a sliding angle of 3.0°, as well as an outstanding luminous intensity 541.4 mcd/m2. Due to strong primer and semi‐embedded particle binding, the coating shows good durability. After 80 wear treatment, the hydrophobic properties of the fluorescent coating were largely maintained. After 32 days of exposure to 0.68 W/m2 ultraviolet light, the contact angle decreased from 160.0° to 154.7° (with a sliding angle of 8.0°). In addition, the firmness, transparency, and self‐cleaning function of the coating can be effectively maintained. The coating in this work has solved the inherent problems of functionality, hydrophobicity, and durability in the coating field, and has a wide range of applications including flexible fabrics, road safety field, and building exterior materials.

The influence of the carbon nanofiller in the PDMS-based composites on the strain resistive effect

In this study flexible polymer nanocomposite material with different types of carbon nanotubes (CNTs) (single-walled CNT [SWCNT] or multi-walled CNT [MWCNT]) has been obtained for use in stretchable elements of flexible structures. The features of electrically conductive nanostructures and their distribution in the nanocomposite material have been studied using Raman spectrometer and scanning electron microscope, respectively. Setup for studying the functional characteristics of the nanocomposite material based on a testing machine has been developed. The setup ensures simultaneous measurement of the electrical resistance of the nanocomposite material under cyclic tension. The ultimate tensile strength of the polymer composite under 25% tension with different electrically conductive nanostructures has been determined. It has been exposed for a sample with MWCNT, the ultimate tensile strength is significantly lower. It has been revealed that the highest tensile strength had been achieved in composites at about 0.37 MPa. The strain sensitivity (gauge factor [GF]) of polydimethylsiloxane (PDMS)/MWCNT has higher GF value compared to PDMS/SWCNT. This shows a higher potential for using them as fillers for creating sensor systems based on nanocomposite conductive materials.

On-Demand Polymer Materials for Sustainability and Space.

Production of polymer material goods on-demand is a recurring science fiction element, but advances in chemistry and engineering have pushed it closer to reality. Experienced at a hobby scale by 3D printing enthusiasts and at an industrial level through rapid prototyping and modular manufacturing, the approach is on its way to further flexibility and high-performance material production. We review the advances in on-demand materials design as well as manufacturing, using examples in space exploration and sustainability, because these are cases where the value proposition for rapid changes in materials is strong. Despite the promising technological base for on-demand production, challenges still exist for commercial viability. We thus also review business strategy and private and public policy considerations for transitioning polymer materials markets to on-demand production. Combined analysis of the chemistry, manufacturing, and business/policy advances provides a more comprehensive picture of the status and remaining challenges.

Nanoarchitectonics of a Skin-Like Polymeric Hydrogel with High Anti-Swelling and Self-Adhesion Performance for Underwater Communication.

Hydrogels are flexible materials characterized by a 3D network structure, which possess high water content and adjustable physicochemical properties. They have found widespread applications in tissue engineering, electronic skin, drug delivery, flexible sensors, and photothermal therapy. However, hydrogel networks often exhibit swelling behavior in aqueous environments, which can result in structural degradation and a loss of gel performance. In this study, polyacrylic acid is utilized as the primary network structure with the incorporation of the natural polymer chitosan. Furthermore, a conductive hydrogel exhibiting good mechanical strength similar to human skin and excellent anti-swelling properties is developed by integrating phytic acid into the hydrogel network. The as-prepared hydrogels exhibited maximum swelling in pure water, achieving an equilibrium swelling rate of 15%. Additionally, a dopamine-grafted polyacrylic acid binder is synthesized through a coupling reaction to enhance the adhesion of the hydrogels to various substrates. The hydrogels demonstrated strong adhesion properties with different substrates. Whether in the air or underwater, the hydrogel sensor effectively monitors human movement behaviors. Furthermore, by utilizing the sensing signals to send Morse code, the hydrogel sensor can facilitate underwater communication. This type of hydrogel sensor is anticipated to play a significant role in wearable sensing applications and underwater communication.