Excellent Elasticity Research Articles

Matching combination of amorphous ionic hydrogel with elastic fabric enables integrated properties for wearable sensing

The combination of hydrogels and fabrics opens up significant opportunities for flexible materials, particularly in biomedicine and wearable technology. However, the weak interface caused by insufficient interactions between the different phases and the substantial modulus mismatch limit their broader application. In this research, flexible and amorphous polyvinyl alcohol (PVA) hydrogels were integrated with polar and elastic fabrics to create multifunctional composites via in-situ freeze-thawing technology. First, by incorporating antifreeze inorganic salts into the precursor solution, we effectively suppressed ice crystal growth during the cooling process, promoting a uniform and loosely aligned PVA chain structure. This led to the formation of an amorphous crosslinked network while simultaneously releasing free hydroxyl groups. These hydroxyl groups facilitate the formation of robust interfaces within the composite. In addition, an elastic fabric composed of a polyester-polyurethane fiber blend was selected. The polyester fibers, rich in carbonyl groups along their polymer chains, form strong hydrogen bonds with the free hydroxyl groups from the PVA hydrogel, creating a highly resilient interface. The polyurethane fibers contribute to a lower Young's modulus, as well as excellent elasticity and ductility, reducing the fabric's inherent stiffness and mitigating fiber pull-out failure. Further, the incorporation of CaCl2 not only created an environment rich in free ions, but also provided the amorphous structure with increasing spacing between adjacent polymer chains, facilitating the transportation of ions. Therefore, the composite exhibits adept sensing capabilities for intricate human body movements, fostering auspicious prospects in smart sensor applications.

Highly Elastic, Fatigue-Resistant, and Antifreezing MXene Functionalized Organohydrogels as Flexible Pressure Sensors for Human Motion Monitoring.

Conductive organohydrogels-based flexible pressure sensors have gained considerable attention in health monitoring, artificial skin, and human-computer interaction due to their excellent biocompatibility, wearability, and versatility. However, hydrogels' unsatisfactory mechanical and unstable electrical properties hinder their comprehensive application. Herein, an elastic, fatigue-resistant, and antifreezing poly(vinyl alcohol) (PVA)/lipoic acid (LA) organohydrogel with a double-network structure and reversible cross-linking interactions has been designed, and MXene as a conductive filler is functionalized into organohydrogel to further enhance the diverse sensing performance of flexible pressure sensors. The as-fabricated MXene-based PVA/LA organohydrogels (PLBM) exhibit stable fatigue resistance for over 450 cycles under 40% compressive strain, excellent elasticity, antifreezing properties (<-20 °C), and degradability. Furthermore, the pressure sensors based on the PLBM organohydrogels show a fast response time (62 ms), high sensitivity (S = 0.0402 kPa-1), and excellent stability (over 1000 cycles). The exceptional performance enables the sensors to monitor human movements, such as joint flexion and throat swallowing. Moreover, the sensors integrating with the one-dimensional convolutional neural networks and the long-short-term memory networks deep learning algorithms have been developed to recognize letters with a 93.75% accuracy, representing enormous potential in monitoring human motion and human-computer interaction.

Fabrication and characterization of UV-curable thiol-functionalized siloxane elastomers with enhanced adhesion for flexible substrates

The rapid advancement of flexible and wearable devices has increased the demand for substrate materials with excellent elasticity, biocompatibility, and transparency. Polydimethylsiloxane (PDMS) is widely used in these applications due to its advantageous properties. However, its inherently low surface energy limits its adhesion in high-stretchability contexts. To address this issue, various surface modification techniques have been developed, but these methods often alter the intrinsic properties of PDMS or introduce complexities in the manufacturing process. This study proposes elastomers based on ultraviolet (UV)-curable siloxane resins, which retain outstanding flexibility and transparency while significantly enhancing adhesion properties. UV-curable siloxanes were synthesized to prepare elastomers that were evaluated for their mechanical, thermal, and surface properties in comparison with PDMS. Results indicate that the prepared elastomers can be rapidly cured under UV exposure, achieving storage moduli 6 and 37 times higher than those of PDMS at 25°C and 100°C, respectively. Furthermore, thermal conductivity improved by 60%, and the coefficient of thermal expansion was reduced by 26%, demonstrating superior mechanical stability across diverse conditions. Adhesion properties were also markedly enhanced, as shown by peel-test adhesion strength that was 7 times greater than that of conventional PDMS.

Durable flame retardant and UV-resistant coating for Poly (ethylene terephthalate) fabric with recyclability and reusability

Poly (ethylene terephthalate) (PET)fabric is widely used in our lives due to its excellent mechanical strength, high elasticity, wrinkle resistance, and anti-abrasion. However, the inflammability and droplets produced during combustion restricted its application. Herein, a novel PET fabric with fire resistance, anti-dripping, and UV resistance is proposed to resolve this problem. Firstly, the finishing agent (AAD) was synthesized using adipoyl chloride, 9-anthracenemethanol, and diethyl(hydroxymethyl)phosphonate. Then AAD was introduced to the surface of PET fabric by dip-pad-cure process. The limiting oxygen index (LOI) value of AAD-treated PET enhanced to 23.8% from 19.3%. Besides, the fabric passed the vertical burning test (VBT) with no droplets generated. The fabric could still pass the VBT and maintain an LOI value of 23.3% after washing. Meanwhile, the AAD-treated PET fabric showed outstanding UV resistance with a high UPF value of 4318.27. The breaking force of AAD-treated PET was also improved. More importantly, the AAD coating could be easily removed from the fabric using dichloromethane and recycled using a rotary evaporator with a recovery rate of 98.6%. The recycled AAD could also recoated on the PET fabric to impart similar properties. This work proposed a novel strategy to prepare durable flame retardant and UV-resistant PET fabrics with recyclability.

Mechanical Behaviors of Orthogonal Spiral Metal Skeleton–Polyurethane Elastomer Composites under Complex Loading Modes

Herein, a novel material design strategy is proposed: an interpenetrating composite composed of a woven orthogonal spiral metal skeleton and polyurethane (PU) elastomer. This interpenetrating composite combines rigidity and flexibility, exhibiting excellent elasticity and deformation recovery. The deformation behavior and mechanical properties of the composites under various loading conditions are investigated through experiments and numerical simulations. Different degrees of warping behaviors occur in composites with various structural parameters under uniaxial tension. Alternating rotations and double spiral arrangements can significantly limit the warping phenomenon, with a maximum reduction of 78%. The bending load capacity is regularly increased by increasing the wire diameter and decreasing the pitch. Increasing the number of loaded spiral wires enhances the bending load capacity of the composites. Uniaxial compression tests demonstrate that the composites have excellent load‐carrying capacity and strain recovery, with compressive strength 1.5 times that of pure PU. Cyclic compression tests further illustrate the excellent energy consumption capacity and stability of the composites. Overall, the introduction of orthogonal spiral skeletons into the composites demonstrates the potential to achieve enhanced load‐carrying capacity and large strain recovery simultaneously.

Cellulose acetate-decorated and siloxane-modified hydrophobic melamine foam with excellent selectivity and durability for efficient oil/water separation

The construction of hydrophobic porous adsorption materials, which are cost-effective, green, stable, and efficient, are urgently demanded for the large-scale and effective oily wastewater treatment. Herein, a facile and low-cost two-step fabrication strategy of hydrophobic melamine foam (MF) was demonstrated, including cellulose acetate (CA) decoration and siloxane modification. Cellulose acetate initially assembled on the skeleton of MF with the aid of hydrogen bond formation between the hydroxyl groups of CA and imimo groups of MF. At an optimal concentration of CA, the as-prepared composite foam (CA/MF) exhibited good hydrophobicity. To further improve the oil/water selectivity, the above foam was enhanced by chemical vapor deposition (CVD) of methyltrimethoxysilane (MTMS). The successful silicification reaction between CA/MF and MTMS decreased the surface energy and improved the surface topological structure, leading to excellent hydrophobicity (water contact angle of 147.4°) and superoliophilicty. Such hydrophobized cellulose acetate/melamine foam (H-CA/MF) presented low density, favorable porosity (97.78%), and distinguished pore volume (88.66 mL/g), leading to a high oil adsorption capacity of up to 56.6 g/g. Due to the excellent mechanical elasticity of H-CA/MF, the oil absorption and recovery can be achieved easily by a simple manual adsorption-squeezing method and lab-made pump-assisted separation device with satisfactory recyclability. Moreover, H-CA/MF displayed marvelous stability and environmental adaptability in different harsh environment, further enlarging its practical application scenarios. Along with the green and cost-effective preparation process, the present study provides a facile strategy to fabricate hydrophobized melamine-based foam, which is of great significance for scalable and efficient oil/water separation.

Earth-abundant, low-cost raw micro-silicon enabled by mechanically strengthened binder for high-capacity and long-life battery electrode

Nano-structured silicon materials with high capacity, are currently being gradually commercialized and composited with graphite in high-energy batteries, although their fabrication cost is rather high. However, the low-cost micro-silicon materials are always criticized and discarded in batteries due to the severe particle-to-electrode crack and huge volume change. Herein, inspired by the human ligament, a cross-linked binder with greatly enhanced mechanical properties is designed and fabricated to stabilize micro-silicon anodes. This biomimetic polymer can not only act as flexible “fibrils” in ligament, to adapt the high-volume change of silicon anode; but also act as “proteoglycan” in ligament to firmly hold these flexible fibrils and proactively constrain stress concentration of silicon anode. The combination of “soft to hard” hierarchical structure would endow binders with excellent elasticity and toughness. The pure micro-Si (5∼10 μm) electrodes with PSB binder exhibit high initial coulombic efficiency (ICE) of 93.3 % and favorable reversible capacity of ∼1500 mAh g−1 at 4000 mA g−1 after 600 cycles. Furthermore, the PSB binder also enables the μSi/GR//NCM811 full cell with 91.4 % capacity retention over 200 cycles. This functional PSB binders provide inspiration for constructing μSi anodes with high-ICE, high reversible capacity, and long-cycling life.

Load‐Bearing Structure Inspired Cellulose‐Based Aerogel With High Resilience and Water Tolerance

AbstractCellulose‐based aerogels possess satisfactory sustainability, porosity, and resilience, which are promising materials to replace traditional petroleum‐based foams. However, the viscous aggregation formed between hydrophilic fibers and the pore collapse caused by weak support force pose challenges for their further applications. Here, a load‐bearing structure‐inspired cellulose‐based aerogel is innovatively developed with excellent elasticity and water tolerance through surface‐interface modulation. Specifically, cellulose and polyvinyl alcohol (PVA) form interwoven skeletons by non‐directional freeze drying. Crucially, the rhamnolipid surfactant assists in forming stable and uniform bubbles, and drives the regularization of frame structure during the freezing process, promoting the construction of refined mechanical structures. Besides, the interfacial enhancement by esterification reaction of citric acid and the encapsulation by hydrophobic silane via chemical vapor deposition endow aerogels with better resilience and water tolerance. The as‐prepared aerogels can withstand intensive compression cycle tests and possess the ability to rebound over 10 times underwater. Even after 12 h wet treatment, the strain and stress loss respectively decrease by ≈55.5% and ≈14% compare with the initial unregulated aerogels after 500 cycles of 80% compression. Surprisingly, they have excellent cushioning performance beyond expanded polystyrene (EPS) and expanded polyethylene (EPE) in simulated road transportation packaging applications, indicating their potential in new‐generation cushioning materials.

Damaging effect of fine grinding treatment on the microstructure of polyurea elastomer modifier used in asphalt binder

The excellent elasticity and strength of polyurea elastomer could provide good potential in asphalt modification. In this paper, PUA materials were prepared by spraying and crushing technology. Using liquid nitrogen, PUA was ground into powders of different particle sizes. The size composition and characteristics of PUA powder were analyzed using laser particle size analyzer. The functional microstructures were identified through laser confocal scanning microscopy. The damaging effect of grinding on functional microstructures was investigated. The impact of PUA on the rheological property of asphalt was determined. The results showed that the size distribution of PUA powders presents the normal distribution characteristic, and the size distribution of 0.3 mm, 0.15 mm, and 0.075 mm PUA powders have intersection. The spherical microstructure distributed independently in PUA particle and some spherical microstructure distributed in the triangular shape. The width/length ratio of characteristic microstructure in 0.15 mm and 0.075 mm PUA powder were increased, which supposed that the spherical microstructure had been damaged by grinding effect. PUA could reduce the cumulative deformation of asphalt when suffering from repeated loads.

Energy Dissipation and Toughening of Covalent Networks via a Sacrificial Conformation Approach.

Covalent polymer networks find wide utility in diverse engineering applications owing to their desirable stiffness and resilience. However, the rigid covalent chemical structure between crosslinking points imposes limitations on enhancing their toughness. Although the incorporation of sacrificial chemical bonds has shown promise in improving toughness through energy dissipation, composite networks struggle to maintain both rapid recovery and stiffness. Consequently, a significant challenge persists in achieving a covalent network that combines high strength, stiffness, toughness, and fast recovery performance. To address this challenge, we propose a novel sacrificial structure termed "sacrificial conformation." In this approach, β-cyclodextrin is covalently embedded into the network skeleton as the sacrificial conformation element. Compared to traditional covalent networks (LCN), well-designed cyclodextrin-embedded covalent network (CCN) exhibit a 100-fold increase in Young's modulus and a 60-fold increase in toughness. Importantly, CCN maintains excellent elasticity, ensuring swift recovery after deformation. This sacrificial conformational strategy enables efficient energy dissipation without necessitating the rupture of chemical bonds, thereby overcoming the limitations of traditional approaches. This advancement holds great promise for the design and fabrication of advanced elastomers and hydrogels with superior mechanical properties and dynamic behavior.

Energy Dissipation and Toughening of Covalent Networks via a Sacrificial Conformation Approach

Covalent polymer networks find wide utility in diverse engineering applications owing to their desirable stiffness and resilience. However, the rigid covalent chemical structure between crosslinking points imposes limitations on enhancing their toughness. Although the incorporation of sacrificial chemical bonds has shown promise in improving toughness through energy dissipation, composite networks struggle to maintain both rapid recovery and stiffness. Consequently, a significant challenge persists in achieving a covalent network that combines high strength, stiffness, toughness, and fast recovery performance. To address this challenge, we propose a novel sacrificial structure termed "sacrificial conformation." In this approach, β‐cyclodextrin is covalently embedded into the network skeleton as the sacrificial conformation element. Compared to traditional covalent networks (LCN), well‐designed cyclodextrin‐embedded covalent network (CCN) exhibit a 100‐fold increase in Young's modulus and a 60‐fold increase in toughness. Importantly, CCN maintains excellent elasticity, ensuring swift recovery after deformation. This sacrificial conformational strategy enables efficient energy dissipation without necessitating the rupture of chemical bonds, thereby overcoming the limitations of traditional approaches. This advancement holds great promise for the design and fabrication of advanced elastomers and hydrogels with superior mechanical properties and dynamic behavior.

Reusable superhydrophobic fluorinated cellulose-graphene composite aerogels for selective oil absorption

Although some progress had been made in the adsorption of graphene aerogels, more research was needed on their elasticity and recyclability. In this paper, a superhydrophobic fluorinated cellulose and graphene composite aerogel (FCGA) was prepared by a simple two-step impregnation method. Firstly, nano-cellulose was introduced into the graphene aerogel to inhibit the excessive accumulation of graphene lamellae and increase the specific surface area. The surface of the composite aerogel was then impregnated with silanol and fluorinated functional groups by a two-step impregnation method, resulting in a superhydrophobic aerogel with remarkable elasticity. The introduction of cellulose and silane provided the aerogel with excellent elasticity and recovery from cyclic adsorption. The successful grafting of the fluorophobic groups of PFDMS onto the graphene oxide strengthened the framework of the graphene aerogel, making FCGA a good candidate for repeated selective oil absorption. It could be restored to the original height after compression to 50% and 80% strain decompression. FCGA could efficiently absorb oil in water and had a high organic adsorption capacity. And the adsorption capacity of different oils/organic solvents reached 22,480 mg/g∼36,700 mg/g. Its absorption efficiency remained above 98.5% under distillation cycles. Due to its high elasticity, it retained more than 90% of its cyclic adsorption capacity through the squeeze cycle. As a simple, low-cost recovery method, its reusability was already better than most known adsorption elastic materials. The prepared composite aerogel had the advantages of simple preparation, low density (0.014 g/cm3), superhydrophobicity (water contact angle 153.3°), excellent adsorption properties, and recyclability. Therefore, FCGA had a very promising application in circulating selective oil absorption.

Enhancing refrigerated chicken breasts preservation: Novel composite hydrogels incorporated with antimicrobial peptides, bacterial cellulose, and polyvinyl alcohol

Microbial contamination annually leads to substantial food resource loss. Effective food packaging can mitigate food contamination and waste, yet conventional materials such as plastics often lack bacteriostatic activity. This study aimed to synthesise FengycinA-M3@bacterial cellulose@polyvinyl alcohol composite hydrogels via dual cross-linking with hydrogen and borate bonding, with the goal of enhancing antibacterial properties and prolonging the preservation period of refrigerated chicken breast. The composite hydrogel was subjected to comprehensive characterisation for structural, mechanical, water absorption, slow peptide release, antimicrobial capacity, biocompatibility, and chicken breast freshness preservation. The results showed that the composite hydrogel had a porous network structure and excellent gel elasticity and biocompatibility. It was effective in inhibiting Staphylococcus aureus and Escherichia coli, and prolonged the storage time of frozen chicken breast for up to 12 days. These findings emphasise the potential of hydrogel food packaging to prolong storage periods and its suitability for food industry applications due to ease of manufacture.

Designing Isocyanate‐Containing Elastomeric Electrolytes for Antioxidative Interphases in 4.7 V Solid‐State Lithium Metal Batteries

AbstractTo facilitate the use of solid polymer electrolytes (SPEs) with high‐nickel (Ni) cathodes in high‐voltage lithium (Li) metal batteries (LMBs), it is crucial to address the challenges of low oxidative stability and the formation of vulnerable interphases. In this study, isocyanate groups (−N═C═O) are incorporated to develop an SPE with a bi‐continuous structure, consisting of elastomeric and plastic crystal phases. This rationally designed SPE exhibits high ionic conductivity (0.9 × 10−3 S cm−1 at 25 °C), excellent elasticity (elongation at break of 330%), and enhanced oxidative stability (over 4.8 V vs. Li/Li⁺). A full cell, incorporating this SPE with a thin Li foil of 40 µm, and a high‐Ni LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode operating at 4.7 V vs. Li/Li⁺, demonstrates excellent cyclability, retaining 70% of its initial capacity after 200 cycles under a high C‐rate of 1C at 25 °C. The extended cycling of isocyanate‐containing SPE at 4.7 V vs. Li/Li⁺ is attributed to robust and compact inorganic‐rich interphases enabled by antioxidative −N−C═O components, as well as uniform Li deposition attributed to the bi‐continuous structured SPE. This study suggests that the isocyanate‐containing SPE system is a promising candidate for high‐voltage solid‐state LMBs by constructing stable interphases.

Bidirectional Elastic PTFE Small Diameter Artificial Blood Vessel Grafts and Surface Antithrombotic Functionalized Construction.

Expanded polytetrafluoroethylene (ePTFE) failed to achieve clinical application in the field of small-diameter blood vessels due to its lack of elasticity in the circumferential direction and high stiffness. Excellent multidirectional elasticity and dynamic compliance matching with natural blood vessels are important means to solve the problem of acute thrombosis and poor long-term patency. Herein, novel PTFE spinning blood vessels were prepared by the PTFE emulsion electrospinning process, which not only presented good bidirectional elasticity but also promoted the adhesion and proliferation of endothelial cells and induced the contractile expression of SMCs. And, a PTFE-shish and aminated polycaprolactone (PCL)-kebab structure has been developed that converted the chemically inert PTFE surface into a drug-loading platform for the multifunctionalization of PTFE vascular grafts. It provides novel preparation methods for the application of new bidirectional elastic small-diameter artificial blood vessels and their surface functionalization construction.

Kapok/regenerated cellulose based carbon aerogel prepared at a low-temperature carbonization for oil/water separation

With the requirement of sustainable development in modern society, selective filtration and separation of oils and organic solvents from polluted wastewater is a critical and very important goal. Herein, a novel hydrophobic and oleophilic cellulose-based carbon aerogel composed of kapok fiber/regenerated cellulose was prepared at a low-temperature carbonization technique (300 ℃) directly using kapok and hardwood pulp as raw material, the N-methyl N-oxide monohydrate (NMMO·H2O) as a green cellulose solvent, and NH4H2PO4 (ADP) as a carbonization promotor, which is denoted as AX-KRCA(AX: A indicates the ADP used, x is the concentration of ADP solution (g/L)) The regenerated cellulose (RC) was converted from hardwood pulp via NMMO·H2O treatment, and further combined with kapok fiber to form a 3D porous structure. By adding ADP, AX-KRCA can be rapidly dehydrated into carbon at 300 ℃, which not only saves energy consumption but also retains the basic form of kapok fiber and regenerated cellulose, making it have excellent compressibility, elasticity, and fatigue resistance. The ultra-light porous AX-KRCA samples can be an efficient oil/water adsorbent, with an adsorption capacity from 98.0 to 232.1 g g−1 for various oils, and can maintain 87.3 % adsorption capacity after 20 cycles and 99.6 % separation efficiency after 5 times of filtration.

Fabrication cellulose/epoxy sponge via surface embedding for efficient and continuously oil/water separation

Discharging oily waste into environment have caused sever water, soil and air pollution. Mechanical compressible polymeric sponges show great potential in oil/water separation through adsorbing/filtering. However, most of these developed sponges were intermittent/manually in oil/water separation and the fabrication always complex. Herein, we developed superwetting sponge by embedding a handful amount of cellulose at the surface of sponge skeleton and delivered excellent mechanical elasticity and robustness. The cellulose/epoxy sponge (embedding 0.33 w% cellulose) can be compressed to 60 % strain with 60 kPa stress and returned to its original shape after 50 times cyclic strain-stress tests. Increasing the embedding amount generated adverse effects on mechanical elasticity and porosity. The as-fabricated cellulose/epoxy sponge showed high separation efficiency (94–99 %) on various oil/water mixtures and showed stable cyclic separation efficiency (>94 %). The optimized cellulose/epoxy sponge was placed into designed separator to separate dispersed oils showing satisfactory total organic carbon removal efficiency (56.63 %) and the inject flow rate showed adverse effects on separation efficiency. Surface embedding is feasible for fabrication mechanical elastic and robust superwetting sponge. The sponge separator showed high separation efficiency of dispersed oil indicating the great of potential polymeric sponge in practical application.

Polyurethane infused with heparin capped silver nanoparticles dressing for wound healing application: Synthesis, characterization and antimicrobial studies

Burn and diabetic wounds present significant challenges due to their complex nature, delayed healing, pain, and high susceptibility to bacterial infections. In this study, we developed and evaluated polyurethae (PU) nanofibers embedded with heparin-functionalized silver nanoparticles (hep-AgNPs) using an electrospinning technique. The choice to functionalize silver nanoparticles with heparin was based on heparin's established role in modulating inflammation and promoting angiogenesis. The electrospun nanofibers exhibited smooth, bead-free morphology with diameters ranging from 300 to 500 nm and demonstrated a sustained release of silver over seven days, offering continuous antimicrobial protection.Mechanical testing of the nanofibers revealed excellent strength and elasticity, making them well-suited for flexible wound dressings. The nanofibers also showed superior water absorption, fluid retention, and controlled water vapor transmission, essential for maintaining a moist wound environment conducive to healing. In vitro biocompatibility assays confirmed that the PU/hep-AgNPs bandages were non-toxic to keratinocytes and fibroblasts and significantly accelerated wound closure, as evidenced by scratch assays. The nanofibrous bandages also exhibited potent antibacterial activity against Staphylococcus aureus and Salmonella Typhimurium, two common wound pathogens.Overall, our findings demonstrate that PU/hep-AgNPs nanofibrous bandages are a promising candidate for chronic wound healing. They combine excellent biocompatibility, anti-inflammatory properties, and strong antimicrobial activity, which collectively contribute to faster wound healing and reduced risk of infection.

Precipitation behavior and performance evolution of cold-rolled cu-Ti-Fe alloy during heat treatment

The CuTi alloy is extensively utilized for its high strength, excellent elasticity, and processability. Heat treatment processes are crucial for affecting the microstructure and properties. The effects of different aging processes on the microstructure and properties of cold-rolled Cu-Ti-Fe alloy were investigated, and the heat treatment parameters were optimized. The results show that the cold-rolled Cu-Ti-Fe alloy exhibits excellent comprehensive performance at 450 °C for 2 h, with the hardness of 342.2 HV, the electrical conductivity of 16.1 % IACS, and the tensile strength of 1051 MPa. The aggregation of solute atoms occurs in the early stages of aging. The uniformly distributed β'-Cu4Ti phase precipitates at peak aging, which has a coherent relationship with the matrix. The precipitation of Ti atoms enhances the electrical conductivity of the alloy, and the movement of dislocations is prevented by precipitates, increasing the strength. During the over-aging stage, the precipitates transform into β-Cu4Ti phases, losing complete coherency with the matrix. The coarsening of precipitates leads to the softening of the Cu-Ti-Fe alloy. Theoretical calculation results indicate that the thermal diffusion ability of solute atoms is the strongest and precipitates completely when the alloy aged at 450 °C. The precipitation strengthening mechanism plays a significant role in improving the strength.

Dynamically crosslinked poly(vinyl alcohol)/borax strain sensors for organ motion monitoring

Wearable electronic sensing devices can detect various physiological responses and subtle changes in the skin in real time for the early detection and treatment of potential health problems or diseases. Among them, flexible hydrogel-based sensors are attracting much attention because they can monitor human movements and physiological signals. However, developing hydrogel-based sensors with rapid self-healing, self-adhesion, excellent conductivity and sensitivity characteristics remains a challenge. In this study, a hydrogel with a dynamic reversible network structure was developed using poly(vinyl alcohol) (PVA), hyaluronic acid (HA), borax, and tannic acid (TA). Multiple hydrogen bonds resulting from abundant hydroxyl groups in the hydrogel composed of borax, PVA, and TA improved the self-healing ability of the hydrogel, and the conductivity of this system (∼0.62 S/m) was improved upon immersion in NaCl. The optimum hydrogel exhibited excellent elasticity (∼941 %), biocompatibility, and demonstrated adhesion to porcine skin (dry: 5.3 kPa; wet: 2 kPa) without external stimulation in air and underwater environments. In addition, the fabricated hydrogels exhibited excellent sensitivity (∼300 % strain, gauge factor (GF) = 2.86; 300–900 % strain, GF = 4.95), allowing them to detect and distinguish various large and small human movements. Hydrogels that exhibited stable electrical signals even after 500 cycles were obtained, and the PBHT-N hydrogels were implanted into rabbit hearts to verify their applicability as strain sensors for effective real-time heart rate monitoring during rapid body movement.