Flame-Retardant PEDOT:PSS/LDHs/Leather Flexible Strain Sensor for Human Motion Detection

A Flexible Leather-Based Sensor via the Dual In Situ Growth of Conductive Materials for Human Motion Detection

Natural leather, with its mechanical strength, flexibility, and wearing comfort, is an ideal substrate material for wearable sensors. Currently, leather-based piezoresistive sensors still suffer from poor uniformity of conductive networks and weak interfacial interactions between conductive materials and leather, which limit their performance. Herein, it was innovatively proposed that polypyrrole (PPy) and silver nanoparticles (AgNPs) were sequentially grown in situ on the surface of collagen fibers (CFs). Then, the tanning process was carried out to produce a leather-based flexible wearable sensor (PPy/AgNPs-LBPS) with excellent conductivity, hydrothermal, and environmental stability. Specifically, the dual in situ growth and tanning process ensured the uniform penetration and distribution of conductive materials in leather substrates. Meanwhile, the hydrogen bonds between the conductive materials and CFs provided a firm combination to prevent the dropping of conductive materials. The synergistic effect of PPy and AgNPs enhanced the sensing performance of PPy/AgNPs-LBPS. It exhibited high sensitivity (0.65 kPa-1 and 3.76), a wide detection range (0-80 kPa and 0-100%), and fast response capability. These characteristics enabled PPy/AgNPs-LBPS to monitor subtle activities and large-scale movements of the human body in real time, as well as tactile perception. This thesis provides a new idea for the intelligent design of traditional leather materials, multidimensional perception in electronic skin, and advancements in artificial intelligence.

Organohydrogel Based Electronic Skin Reinforced by Dual-Mode Conduction and Hierarchical Collagen Fibers Skeleton

Collagen fiber skeleton from animal skin is an ideal substrate for electronic skin (e-skin). However, the interface mismatch between conductive materials and skeleton and the monotonicity of conductive network still hinder its creation. Herein, a novel collagen fiber-based e-skin with dual-mode conduction of NaCl and conductive spheres (IECS) is accomplished by loading organohydrogel into the skeleton via "permeation and self-assembly". The resulting interpenetrating network produces a 3D continuous, conductive pathway and strong interface interaction with high-density hydrogen bonding, thus exhibiting excellent strength (24.5 MPa), conductivity (14.82 S m-1), sensing performance (sensitivity of 16.64), and environmental stability. The physical structure (3D skeleton, interpenetrating network) and chemical interaction (interface interaction, salting-out) achieve energy dissipation. Meanwhile, the sensitivity is enhanced by dual-mode conduction, conductive sphere array, and deformation amplification induced by collagen fibers. Additionally, the strong bonding ability between glycerin and collagen fibers with water molecules provides anti-freezing and moisture-retention characteristics. Thus, the strategic synergy of compositional and structural design makes IECS a promising force-sensing part of piezoresistive sensor for human movement, pulse frequency, cipher transmission, and pressure distribution. In short, IECS presents a multifunctional platform for the invention of high-performance e-skin with on-demand property, which offers great application potential in wearable electronics.

Citric Acid and Polyvinyl Alcohol Induced PEDOT: PSS with Enhanced Electrical Conductivity and Stretchability for Eco-Friendly, Self-Healable, Wearable Organic Thermoelectrics

Poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) is a promising material for organic thermoelectric (TE) applications. However, it is challenging to achieve PEDOT: PSS composites with stretchable, self-healable, and high TE performance. Furthermore, some existing self-healing TE materials employ toxic reagents, posing risks to human health and the environment. In this study, a novel intrinsically self-healable and wearable composite is developed by incorporating environmentally friendly, highly biocompatible, and biodegradable materials of polyvinyl alcohol (PVA) and citric acid (CA) into PEDOT: PSS. This results in the formation of double hydrogen bonding networks among CA, PVA, and PEDOT: PSS, inducing microstructure alignment and leading to simultaneous enhancements in both TE performance and stretchability. The resulting composites exhibit a high electrical conductivity and power factor of 259.3 ± 11.7 S·cm-1, 6.9 ± 0.4 µW·m-1·K-2, along with a tensile strain up to 68%. Furthermore, the composites display impressive self-healing ability, with 84% recovery in electrical conductivity and an 85% recovery in tensile strain. Additionally, the temperature and strain sensors based on the PEDOT: PSS/PVA/CA are prepared, which exhibit high resolution suitable for human-machine interaction and wearable devices. This work provides a reliable and robust solution for the development of environmentally friendly, self-healing and wearable TE thermoelectrics.

Achieving High Ionic Conductivity and Mechanical Strength by a Leather Gel Electrolyte for Flexible Zinc-Ion Batteries

The continuous advancement in the field of flexible and wearable electronics has led to increased research interest in safe, low-cost, and flexible zinc-ion batteries, particularly with a focus on flexible electrolytes. In this study, we present a leather gel electrolyte (LGE) that offers robust mechanical properties and an excellent electrochemical performance. LGE exhibits an ionic conductivity of 1.36 × 10-2 S cm-1 and achieves a capacity of 303.7 mAh g-1 in flexible zinc-manganese dioxide batteries. Even after 1000 cycles, the capacity retention remains above 90%, demonstrating outstanding performance in protecting the zinc anode. Furthermore, such a flexible battery shows good resistance to damage due to the strong mechanical strength originating from leather. Notably, LGE utilizes green and sustainable leather as a raw material, making it a promising option for sustainable flexible devices.

A Self-Healing Conductive Elastomer Based on a Polymerizable Deep Eutectic Solvent

Conductive elastomers are extensively used in electronics; however, they are prone to mechanical damage, have shortened service life, and cause environmental pollution and resource waste under the influence of external factors. Therefore, conductive elastomers with rapid self-healing properties are crucial for solving these problems. To that end, a conductive elastomer based on a polymerizable deep eutectic solvent as the matrix is developed in this study. The contents of certain small molecules and conductive particles are adjusted to yield a conductive elastomer with excellent comprehensive performance. The elastomer exhibited noteworthy fracture strength (15.7 MPa), ultrahigh fracture elongation (2400%), excellent light transmittance (95.6%), and remarkable self-healing characteristics, with complete electrical healing achieved within 0.6 s, ≈63% strain, and ≈64% stress recovered within 1 min, and healing efficiency close to 99% realized within 24 h. By leveraging these properties, the elastomer is used to construct a sensor that exhibited a gauge factor of ≈0.574 in the strain range 0-2400% and excellent stability. Moreover, the CCK-8 toxicity test and fluorescence staining experiment have demonstrated that conductive elastomers have excellent cell compatibility and also have excellent potential in the field of biomedicine. In particular, the sensor is effectively applied in human motion detection, health monitoring.

Increasing Functionality of Fish Leather by Chemical Surface Modifications

Fish skin is a by-product of the fishing industry, which has become a significant environmental pollutant in recent years. Therefore, there is an emerging interest in developing novel technologies to utilize fish skin as a versatile raw material for the clothing and biomedical industries. Most research on finishing procedures is conducted on cattle leather, and practically very limited information on fish leather finishing is found in the literature. We have developed three functional surface finishing treatments on chromium (CL)- and vegetable (VL)- tanned salmon leather. These treatments include hydrophobic, oil repellent, and electro-conductive ones. The hydroxyl functional groups present on the surface of the leather were covalently grafted with bi-functional aliphatic small molecule, 10-undecenoylchloride (UC), by esterification reaction forming hydrophobic coating. The surface hydrophobicity was further increased via covalent binding of perfluorodecanethiol (PFDT) to the double bond end-groups of the UC-modified leather via thiol-ene click chemistry conditions. The oleophobic coating was successfully developed using synthesized fluorinated silica nanoparticles (FSN) and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), showing oil repellency with a contact angle of about 100° for soybean oil and n-hexadecane. The electrically conductive coating was realized by the incorporation of conjugated polymer, polyaniline (PANI), via in situ polymerization method. The treated leather exhibited surface resistivity of about 5.2 (Log (Ω/square)), much lower than untreated leather with a resistivity of 11.4 (Log (Ω/square)).

Robust and flexible smart silk/PEDOT conductive fibers as wearable sensor for personal health management and information transmission

Flexible highly conductive fibers have attracted much attention due to their great potential in the field of wearable electronic devices. In this work, silk/PEDOT conductive fibers with a resistivity of 1.73 Ω·cm were obtained by oxidizing Ce3+ with H2O2 under alkaline conditions to produce CeO2 and further promote the in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of silk fibers. The morphology and chemical composition of the silk/PEDOT conductive fibers were characterized and the results confirmed that a large amount of polythiophene was synthesized and deposited on the surface of silk fibers. The conductivity and electrochemical property stability of the silk/PEDOT conductive fibers were evaluated by soaping and organic solvent immersion, and the conductive silk fibers exhibited excellent environmental stability and durability. The silk/PEDOT conductive fibers show good pressure sensing and strain sensing performance, which exhibits high sensitivity, fast response and cyclability, and have excellent applications in personal health monitoring, human-machine information transmission, etc.

Fabrication and characterization of highly sensitive flexible strain sensor based on biodegradable gelatin nanocomposites and double strain layered structures with crack for gesture recognition

Flexible sensors have attracted extensive attention in the field of human-computer interaction. However, it is still a challenging task to realize accuracy gesture recognition with flexible sensor, which requires sensor not only have high sensitivity, but also have appropriate strain detection range. Here, a high gauge factor flexible sensor (gauge factor ∼ 1296 under 12-20 % strain) based on crack structure is reported. The sensor is made of a biodegradable and stretchable gelatin composite combined with fabric bases, with good repeatability (6000 cycles) and a fast response (60 ms). Because of the double-layer structure, it has a suitable detection range (20 % strain). The sensor is manufactured by a screen-printing process, and it has been used to make data gloves and has realized 9 gestures recognition with machine learning algorithm (99.6 % accuracy). In general, this study offers a wearable gestures recognition scheme through the proposed sensor.

Washable PEDOT:PSS Coated Polyester with Submicron Sized Fibers for Wearable Technologies

The use of non-metallic conductive yarns in wearable technologies like smart textiles requires compliant washable fibers that can withstand domestic washing without losing their conductive properties. A one-pot coating with PEDOT:PSS conductive polymers was applied to polyester submicron fibers, increasing the water resistance and washability under various domestic washing conditions. Plasma treatment of the untreated samples improved the anchoring of the coating to the fibers, producing smooth and homogeneous coatings. The primary doping of PEDOT:PSS with ethylene glycol (EG), dimethyl sulfoxide (DMSO), and a non-ionic surfactant as well as the secondary doping of the composite fibers improved the sheet resistance at room temperature. The as-obtained composite materials showed similar mechanical properties as the parent fibers, indicating that the coating and post-treatment do not affect the overall mechanical property of the composite. The performance of the composites under different temperature and humidity conditions and washability using the standardized ISO 6330:2012 procedure for domestic washing and drying showed that the obtained composites are good candidates for reliable washable wearable technologies, such as all-organic washable Joule heaters in functional textiles.

Leather for flexible multifunctional bio-based materials: a review

Nowadays, diverse leather usage conditions and increasing demands from consumers challenge the leather industry. Traditional leather manufacturing is facing long-term challenges, including low-value threshold, confined application fields, and environmental issues. Leather inherits all the biomimetic properties of natural skin such as flexibility, sanitation, cold resistance, biocompatibility, biodegradability, and other cross-domain functions, achieving unremitting attention in multi-functional bio-based materials. Series of researches have been devoted to creating and developing leather-based flexible multi-functional bio-materials, including antibacterial leather, conductive leather, flame-retardant leather, self-cleaning leather, aromatic leather, and electromagnetic shielding leather. In this review, we provide a comprehensive overview of the commonly used leather-based functional materials. Furthermore, the possible challenges for the development of functional leathers are proposed, and expected development directions of leather-based functional materials are discussed. This review may promote and inspire the emerging preparation and applications of leather for flexible functional bio-based materials.

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