Flexible Ti3C2Tx MXene/PANI/Bacterial Cellulose Aerogel for e-Skins and Gas Sensing

Ultra-High Performance Fibrous Ammonia Sensor with Full Degradability

Although portable sensors with real-time NH3 detection capability have been extensively investigated, the development and preparation of fibrous degradable NH3 sensors combining properties including high lightweight and flexibility, high integrability, eco-friendliness, as well as excellent sensing performances still remains a great challenge. In this work, through fabricating a multicomponent aerogel fiber with three-dimensional mesoporous structure, we developed a fully degradable fibrous NH3 sensor with super high sensing performances including high sensitivity (an ultrahigh response of 807% at 100 ppm of NH3), rapid response speed (the response and recovery time are 24.1 and 2.2 s respectively at 100 ppm of NH3), good selectivity, and ultralow trace levels of NH3 monitoring capability (1 ppb). Taking advantage of its great sensing performance, we fabricated an NH3 alert system by integrating the aerogel fiber with an alarm circuit for NH3 leakage warning and food spoilage alerting.

Directional fabrication of an ultra-light and porous bacterial nanocellulose/MXene composite aerogel for efficient thermal management

Global warming has intensified extreme weather events, necessitating advanced thermal management systems to protect human health. Due to its unique properties of increasing phonon scattering at interlayer interfaces and wide spectral absorption, MXene has great potential in thermal management. However, the self-stacking tendency of MXene caused by hydrogen bonding and van der Waals force limits its further application. Herein, we have successfully fabricated an ultra-light (0.011 g cm-3) three-dimensional (3D) bacterial nanocellulose (BNC)/MXene aerogel (BM) through directional freezing. The BNC serves as scaffolds, offering a porous structure with ultra-low thermal conductivity (0.038 W m-1 K-1), high porosity (99.33 %), and excellent insulation (ΔT of 164 at 200 °C). Additionally, the BM aerogel shows remarkable photo-thermal conversion efficiency (98 % solar absorption, 0.25-2.5 μm), quick thermal response (88 °C in 10 s), and thermal stability (89 °C sustained after 120 min). These multifunctional properties make the BM aerogel a potential candidate for advanced thermal management in response to global climate challenges.

Neuromorphic devices for electronic skin applications

Neuromorphic devices represent an important advancement in technology, drawing inspiration from the intricate and efficient mechanisms of the human brain. This review paper elucidates the diverse landscape of neuromorphic electronic skin (e-skin) technologies while highlighting their numerous applications. Here, neuromorphic devices for e-skin are classified as two types of direct neuromorphic e-skins combining both neuromorphic devices and sensors, and indirect e-skins separating neuromorphic devices and sensors. In direct neuromorphic e-skins, there are developing devices like memristor-based neuromorphic devices with sensors and transistor-based neuromorphic devices with sensors. On the other hand, indirect types are demonstrated as separated neuromorphic and sensor parts systems through the various interfacing structures. It also describes recent neuromorphic developments in artificial neural networks (ANNs), deep neural networks (DNNs), and convolutional neural networks (CNNs), for the real-time interpretation of sensory data. Moreover, it introduces multimodal sensory feedback, soft and flexible e-skins, and more intuitive human-machine interfaces. This review examines various applications, including smart textiles for the development of next-generation wearable bioelectronics, brain-sensing interfaces that enhance tactile perception, and the integration of human-machine interfaces aimed at replicating the biological sensorimotor loop, which can improve health monitoring and biomedical applications. Additionally, the review also highlights the potential of neuromorphic e-skin in human-robot interaction, particularly in the context of continuous prosthetic control and robotics. Through this analysis, the paper provides insights into current advancements, identifies key challenges, and suggests future research directions for optimizing neuromorphic e-skin devices and expanding their practical implementation.

Advances in cellulose-based self-powered ammonia sensors

Ammonia sensors are widely used across applications in food monitoring, environmental surveillance, and medical research, where high safety standards are essential. Cellulose-based materials are particularly well-suited to meet these stringent requirements, with significant potential for innovation due to their biodegradability and biocompatibility. Of the various cellulose-based ammonia sensors available, self-powered sensors, especially those based on triboelectric nanogenerators (TENGs), stand out for their unique advantages, including the absence of an external power supply, environmental sustainability, and ease of integration. This review offers a detailed overview of the integration of cellulose-based materials with ammonia-sensitive components, highlighting their ease of processing and modification. It further classifies and compares cellulose-based ammonia sensors based on their sensing mechanisms, emphasizing TENG-based sensors specifically. The review concludes with a summary of current applications and explores optimization strategies. Finally, it discusses future opportunities and challenges for cellulose-based self-powered ammonia sensors and provides valuable insights into ongoing innovation and potential.

Ti3C2Tx Composite Aerogels Enable Pressure Sensors for Dialect Speech Recognition Assisted by Deep Learning

Wearable pressure sensors capable of adhering comfortably to the skin hold great promise in sound detection. However, current intelligent speech assistants based on pressure sensors can only recognize standard languages, which hampers effective communication for non-standard language people. Here, we prepare an ultralight Ti3C2Tx MXene/chitosan/polyvinylidene difluoride composite aerogel with a detection range of 6.25 Pa-1200 kPa, rapid response/recovery time, and low hysteresis (13.69%). The wearable aerogel pressure sensor can detect speech information through the throat muscle vibrations without any interference, allowing for accurate recognition of six dialects (96.2% accuracy) and seven different words (96.6% accuracy) with the assistance of convolutional neural networks. This work represents a significant step forward in silent speech recognition for human-machine interaction and physiological signal monitoring.

Aerogels based on Bacterial Nanocellulose and their Applications

Microbial cellulose stands out for its exceptional characteristics in the form of biofilms formed by highly interlocked fibrils, namely, bacterial nanocellulose (BNC). Concurrently, bio-based aerogels are finding uses in innovative materials owing to their lightweight, high surface area, physical, mechanical, and thermal properties. In particular, bio-based aerogels based on BNC offer significant opportunities as alternatives to synthetic or mineral counterparts. BNC aerogels are proposed for diverse applications, ranging from sensors to medical devices, as well as thermal and electroactive systems. Due to the fibrous nanostructure of BNC and the micro-porosity of BNC aerogels, these materials enable the creation of tailored and specialized designs. Herein, a comprehensive review of BNC-based aerogels, their attributes, hierarchical, and multiscale features are provided. Their potential across various disciplines is highlighted, emphasizing their biocompatibility and suitability for physical and chemical modification. BNC aerogels are shown as feasible options to advance material science and foster sustainable solutions through biotechnology.

Hydrogels and Aerogels for Versatile Photo-/Electro-Chemical and Energy-Related Applications

The development of photo-/electro-chemical and flexible electronics has stimulated research in catalysis, informatics, biomedicine, energy conversion, and storage applications. Gels (e.g., aerogel, hydrogel) comprise a range of polymers with three-dimensional (3D) network structures, where hydrophilic polyacrylamide, polyvinyl alcohol, copolymers, and hydroxides are the most widely studied for hydrogels, whereas 3D graphene, carbon, organic, and inorganic networks are widely studied for aerogels. Encapsulation of functional species with hydrogel building blocks can modify the optoelectronic, physicochemical, and mechanical properties. In addition, aerogels are a set of nanoporous or microporous 3D networks that bridge the macro- and nano-world. Different architectures modulate properties and have been adopted as a backbone substrate, enriching active sites and surface areas for photo-/electro-chemical energy conversion and storage applications. Fabrication via sol-gel processes, module assembly, and template routes have responded to professionalized features and enhanced performance. This review presents the most studied hydrogel materials, the classification of aerogel materials, and their applications in flexible sensors, batteries, supercapacitors, catalysis, biomedical, thermal insulation, etc.

MXene Key Composites: A New Arena for Gas Sensors

With the development of science and technology, the scale of industrial production continues to grow, and the types and quantities of gas raw materials used in industrial production and produced during the production process are also constantly increasing. These gases include flammable and explosive gases, and even contain toxic gases. Therefore, it is very important and necessary for gas sensors to detect and monitor these gases quickly and accurately. In recent years, a new two-dimensional material called MXene has attracted widespread attention in various applications. Their abundant surface functional groups and sites, excellent current conductivity, tunable surface chemistry, and outstanding stability make them promising for gas sensor applications. Since the birth of MXene materials, researchers have utilized the efficient and convenient solution etching preparation, high flexibility, and easily functionalize MXene with other materials to prepare composites for gas sensing. This has opened a new chapter in high-performance gas sensing materials and provided a new approach for advanced sensor research. However, previous reviews on MXene-based composite materials in gas sensing only focused on the performance of gas sensing, without systematically explaining the gas sensing mechanisms generated by different gases, as well as summarizing and predicting the advantages and disadvantages of MXene-based composite materials. This article reviews the latest progress in the application of MXene-based composite materials in gas sensing. Firstly, a brief summary was given of the commonly used methods for preparing gas sensing device structures, followed by an introduction to the key attributes of MXene related to gas sensing performance. This article focuses on the performance of MXene-based composite materials used for gas sensing, such as MXene/graphene, MXene/Metal oxide, MXene/Transition metal sulfides (TMDs), MXene/Metal-organic framework (MOF), MXene/Polymer. It summarizes the advantages and disadvantages of MXene composite materials with different composites and discusses the possible gas sensing mechanisms of MXene-based composite materials for different gases. Finally, future directions and inroads of MXenes-based composites in gas sensing are presented and discussed.

Recent advances in wearable flexible electronic skin: types, power supply methods, and development prospects

In recent years, wearable e-skin has emerged as a prominent technology with a wide range of applications in healthcare, health surveillance, human-machine interface, and virtual reality. Inspired by the properties of human skin, arrayed wearable e-skin is a novel technology that offers multifunctional sensing capabilities. It can detect and quantify various stimuli, mimicking the human somatosensory system, and record a wide range of physical and physiological parameters in real time. By combining flexible electronic device units with a data acquisition system, specific functional sensors can be distributed in targeted areas to achieve high sensitivity, resolution, adjustable sensing range, and large-area expandability. This review provides a comprehensive overview of recent advances in wearable e-skin technology, including its development status, types of applications, power supply methods, and prospects for future development. The emphasis of current research is on enhancing the sensitivity and stability of sensors, improving the comfort and reliability of wearable devices, and developing intelligent data processing and application algorithms. This review aims to serve as a scientific reference for the intelligent development of wearable e-skin technology.

MXene-Based Elastomer Mimetic Stretchable Sensors: Design, Properties, and Applications

Flexible sensors based on MXene-polymer composites are highly prospective for next-generation wearable electronics used in human-machine interfaces. One of the motivating factors behind the progress of flexible sensors is the steady arrival of new conductive materials. MXenes, a new family of 2D nanomaterials, have been drawing attention since the last decade due to their high electronic conductivity, processability, mechanical robustness and chemical tunability. In this review, we encompass the fabrication of MXene-based polymeric nanocomposites, their structure-property relationship, and applications in the flexible sensor domain. Moreover, our discussion is not only limited to sensor design, their mechanism, and various modes of sensing platform, but also their future perspective and market throughout the world. With our article, we intend to fortify the bond between flexible matrices and MXenes thus promoting the swift advancement of flexible MXene-sensors for wearable technologies.

Advancements in MXene-based composites for electronic skins

MXenes are a class of two-dimensional (2D) materials that have gained significant attention in the field of electronic skins (E-skins). MXene-based composites offer several advantages for E-skins, including high electrical conductivity, mechanical flexibility, transparency, and chemical stability. Their mechanical flexibility allows for conformal integration onto various surfaces, enabling the creation of E-skins that can closely mimic human skin. In addition, their high surface area facilitates enhanced sensitivity and responsiveness to external stimuli, making them ideal for sensing applications. Notably, MXene-based composites can be integrated into E-skins to create sensors that can detect various stimuli, such as temperature, pressure, strain, and humidity. These sensors can be used for a wide range of applications, including health monitoring, robotics, and human-machine interfaces. However, challenges related to scalability, integration, and biocompatibility need to be addressed. One important challenge is achieving long-term stability under harsh conditions such as high humidity. MXenes are susceptible to oxidation, which can degrade their electrical and mechanical properties over time. Another crucial challenge is the scalability of MXene synthesis, as large-scale production methods need to be developed to meet the demand for commercial applications. Notably, the integration of MXenes with other components, such as energy storage devices or flexible electronics, requires further developments to ensure compatibility and optimize overall performance. By addressing issues related to material stability, mechanical flexibility, scalability, sensing performance, and power supply, MXene-based E-skins can develop the fields of healthcare monitoring/diagnostics, prosthetics, motion monitoring, wearable electronics, and human-robot interactions. The integration of MXenes with emerging technologies, such as artificial intelligence or internet of things, can unlock new functionalities and applications for E-skins, ranging from healthcare monitoring to virtual reality interfaces. This review aims to examine the challenges, advantages, and limitations of MXenes and their composites in E-skins, while also exploring the future prospects and potential advancements in this field.

"Visualization" Gas-Gas Sensors Based on High Performance Novel MXenes Materials

The detection of toxic, harmful, explosive, and volatile gases cannot be separated from gas sensors, and gas sensors are also used to monitor the greenhouse effect and air pollution. However, existing gas sensors remain with many drawbacks, such as lower sensitivity, lower selectivity, and unstable room temperature detection. Thus, there is an imperative need to find more suitable sensing materials. The emergence of a new 2D layered material MXenes has brought dawn to solve this problem. The multiple advantages of MXenes, namely high specific surface area, enriched terminal functionality groups, hydrophilicity, and good electrical conductivity, make them among the most prolific gas-sensing materials. Therefore, this review paper describes the current main synthesis methods of MXenes materials, and focuses on summarizing and organizing the latest research results of MXenes in gas sensing applications. It also introduces the possible gas sensing mechanisms of MXenes materials on NH3 , NO2 , CH3 , and volatile organic compounds (VOCs). In conclusion, it provides insight into the problems and upcoming challenges of MXenes materials for gas sensing.

Gas-Sensing Mechanisms and Performances of MXenes and MXene-Based Heterostructures

MXenes are a class of 2D transition-metal carbides, nitrides, and carbonitrides with exceptional properties, including substantial electrical and thermal conductivities, outstanding mechanical strength, and a considerable surface area, rendering them an appealing choice for gas sensors. This manuscript provides a comprehensive analysis of heterostructures based on MXenes employed in gas-sensing applications and focuses on addressing the limited understanding of the sensor mechanisms of MXene-based heterostructures while highlighting their potential to enhance gas-sensing performance. The manuscript begins with a broad overview of gas-sensing mechanisms in both pristine materials and MXene-based heterostructures. Subsequently, it explores various features of MXene-based heterostructures, including their composites with other materials and their prospects for gas-sensing applications. Additionally, the manuscript evaluates different engineering strategies for MXenes and compares their advantages to other materials while discussing the limitations of current state-of-the-art sensors. Ultimately, this review seeks to foster collaboration and knowledge exchange within the field, facilitating the development of high-performance gas sensors based on MXenes.

Synthesis, Properties, and Applications of Nanocomposite Materials Based on Bacterial Cellulose and MXene

MXene exhibits impressive characteristics, including flexibility, mechanical robustness, the capacity to cleanse liquids like water through MXene membranes, water-attracting nature, and effectiveness against bacteria. Additionally, bacterial cellulose (BC) exhibits remarkable qualities, including mechanical strength, water absorption, porosity, and biodegradability. The central hypothesis posits that the incorporation of both MXene and bacterial cellulose into the material will result in a remarkable synthesis of the attributes inherent to MXene and BC. In layered MXene/BC coatings, the presence of BC serves to separate the MXene layers and enhance the material's integrity through hydrogen bond interactions. This interaction contributes to achieving a high mechanical strength of this film. Introducing cellulose into one layer of multilayer MXene can increase the interlayer space and more efficient use of MXene. Composite materials utilizing MXene and BC have gained significant traction in sensor electronics due to the heightened sensitivity exhibited by these sensors compared to usual ones. Hydrogel wound healing bandages are also fabricated using composite materials based on MXene/BC. It is worth mentioning that MXene/BC composites are used to store energy in supercapacitors. And finally, MXene/BC-based composites have demonstrated high electromagnetic interference (EMI) shielding efficiency.

Ti3C2Tx/MXene Composite Aerogel Flexible Biosensor for Measuring Occlusal Force In Situ

Occlusal force is an important parameter for evaluating the function of the occlusal system. Traditional occlusal forces can only be measured qualitatively. Here, we report a flexible piezoresistive pressure sensor with high sensitivity and a wide measurement range for in situ occlusal force measurements through the articulating paper. The sensing layer of the flexible piezoresistive sensor is a 3D porous MXene composite aerogel, which is fabricated by vacuum freezing. The MXene piezoresistive sensor is composed of the interdigital electrodes, the sensing layer, the PI encapsulation layer, and an articulating paper encapsulation layer. The sensor shows perfect performance with high sensitivity (210.21 kPa-1), wide measurement range (∼420 kPa), and a fast response time (123 ms response time, 163 ms recovery time). The amplitude of the occlusal force, which varied with time, can be observed on the mobile phone through the wireless system with the Bluetooth module. This technique has broad application prospects in oral health. In this work, we propose a simple method and a new idea for manufacturing high-performance wearable bioelectronic sensors.

Multifunctional Bacterial Cellulose/Covalent Organic Framework Composite Membranes with Antifouling and Antibacterial Properties for Dye Separation

Covalent organic frameworks (COFs) have a wide application prospect in wastewater treatment because of their unique structure and properties; however, the preparation of pure COF membranes remains a great challenge by reason of the insolubility and unprocessability of COF powders formed at high temperature and high pressure. In this study, a continuous and defect-free bacterial cellulose/covalent organic framework composite membrane was prepared by using bacterial cellulose (BC) and a porphyrin-based COF with their unique structures and hydrogen bonding forces. The dye rejection rate of this composite membrane toward methyl green and congo red was up to 99%, and the permeance was about 195 L m^-2 h^-1 bar^-1. It showed excellent stability under different pH conditions, long-time filtration, and cyclic experimental conditions. In addition, the hydrophilicity and surface negativity of the BC/COF composite membrane made it have certain antifouling performance, and the flux recovery rate can reach 93.72%. More importantly, the composite membrane exhibited excellent antibacterial properties due to the doping of the porphyrin-based COF, and the survival rates of both Escherichia coli and Staphylococcus aureus were less than 1% after exposure to visible light. The self-supporting BC/COF composite membrane synthesized by this strategy also has outstanding antifouling and antibacterial properties, in addition to excellent dye separation effects, which greatly broaden the application of COF materials in water treatment.

Multifunctional microwave absorption materials of multiscale cobalt sulfide/diatoms co-doped carbon aerogel

Microwave absorption materials (MAMs) have attracted much attention for their potential applications in stealth technology and prevention of electromagnetic pollution problems. Multifunctional MAMs are highly demanded because they can be applied in harsh environments. Hence, based on multiscale manipulation of atomic engineering, nanostructure and microstructure, a multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel was preparedthrough the physical crosslinking of divalent ions, unidirectional freezing, kirkendall effect, and heteroatomic doping. The aerogel with a low density of 13.1 mg/mm³ has a unique "lamellar-pillar" network structure due to the growth of ice crystals during the preparation process. With the assistance of thiourea, the doping of N, S atoms and the construction of hollow cobalt sulfide are accomplished simultaneously. The ingenious integration facilitates the synergistic effect of conductive loss, defect polarization, interfacial polarization, and multiple scattering. The multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel had a maximum reflection loss of -51.96 dB and an effective absorption bandwidth of 6.4 GHz, which is higher than that of other reported MAMs. It is further verified through finite element simulation and experiments that the aerogel has an excellent microwave absorption properties. In addition, the aerogel has excellent thermal insulation and flame retardant properties. Therefore, the development of this aerogel can help to use MAMs in complex applications.

Recent advances in the hybridization of cellulose and semiconductors: Design, fabrication and emerging multidimensional applications: A review

Cellulose is a plentiful, biodegradable, renewable, and natural polymer in the world that can be widely utilized in the production of polymer nanocomposites. Cellulose is developed in nanomaterials owing to its remarkable inherent features of low density, non-toxicity, and affordability, as well as the amazing sample characteristics of strength and thermal stability. Recently, there has been a lot of interest in organic-inorganic composites because of their adaptable qualities. Cellulose and semiconductors have exciting properties, and new combinations of both materials may result in efficient functional hybrid composites with distinct properties. Lately, a huge study was reported on cellulose and semiconductor-based nanocomposites. In this review, we summarize the present research development in the preparation methods, structure, features, and possible applications of multifunctional cellulose and semiconductor-based nanocomposites. The cellulose/semiconductor based nanocomposites have massive potential applications in the areas of photodegradation of organic dyes, hydrogen production, metal removal, biomedical, and sensor applications. It is also assumed that this article will promote additional investigation and will establish innovative capabilities to enhance novel cellulose and semiconductor based nanocomposites with new and exciting applications.

Preparation of high elastic bacterial cellulose aerogel through thermochemical vapor deposition catalyzed by solid acid for oil-water separation

Oil pollution has caused more and more serious damages to the environment, especially to water. Oil and water separation technologies based on high-performance absorbing materials have attracted extensive attentions. Herein, elasticity-enhanced bacterial cellulose (BC) aerogel is synthesized for oil/water separation through thermochemical vapor deposition (CVD) catalyzed by 1, 2, 3, 4-butanetetracarboxylic acid (BTCA). BTCA has two functions, namely, esterification with BC and catalyzing CVD. The prepared aerogel could be recovered soon after being compressed and the elastic recovery was >90 % at set maximum deformation of 80 %. And, it also exhibits vigorous fatigue resistance with an elastic deformation of >80 % after 50 cycles. The high elastic and hydrophobic aerogel is very suitable for absorbing and desorbing oils by simple mechanical squeezing. The adsorption capacity for n-hexane and dichloroethane maintain 87 % and 81 % after 50 cycles, respectively, which implies robust reusability. Importantly, the CVD could also be catalyzed by other solid acids such as citric acid and vitamin C. This design and fabrication method offers a novel avenue for the preparation of hydrophobic bacterial cellulose aerogel with high elasticity.

Conductive bacterial cellulose: From drug delivery to flexible electronics

Bacterial cellulose (BC) is a chemically pure, non-toxic, and non-pyrogenic natural polymer with high mechanical strength and a complex fibrillar porous structure. Due to these unique biological and physical properties, BC has been amply used in the food industry and, to a somewhat lesser extent, in medicine and cosmetology. To expand its application the BC structure can be modified. This review presented some recent developments in electrically conductive BC-based composites. The as-synthesized BC is an excellent dielectric. Conductive polymers, graphene oxide, nanoparticles and other materials are used to provide it with conductive properties. Conductive bacterial cellulose (CBC) is currently investigated in numerous areas including electrically conductive scaffolds for tissue regeneration, implantable and wearable biointerfaces, flexible batteries, sensors, EMI shielding composites. However, there are several issues to be addressed before CBC composites can enter the market, namely, composite mechanical strength reduction, porosity decrease, change in chemical characteristics. Some of them can be addressed both at the stage of synthesis, biologically, or by adding (nano)materials with the required properties to the BC structure. We propose several solutions to meet the challenges and suggest some promising BC applications.

A review related to MXene preparation and its sensor arrays of electronic skins

MXenes have been flourishing over the last decade as a high-performance 2D material, which combines the advantages of high electrical conductivity, photothermal conversion, and easy dispersion. They have been used to create soft, highly conductive, self-healing, and tactile-simulating electronic skins (E-skins). However, these E-skins remain generally limited to one or two functions with a complex preparation process. Next-generation E-skins necessitate not only large-scale fabrication using simple and fast methods but also the integration of multiple sensing functions and signal analysis components in order to provide functionality that was not unattainable in the past. Starting with the synthesis of pure MXenes, we walk through the steps of designing MXene sensors, integrating electronic skin arrays, and determining the function of MXene-based electronic skins. We also summarise the problems with existing MXene-based E-skins and possible futuristic directions.

MXene-Based Nanomaterials for Multifunctional Applications

MXene is becoming a "rising star" material due to its versatility for a wide portfolio of applications, including electrochemical energy storage devices, electrocatalysis, sensors, biomedical applications, membranes, flexible and wearable devices, etc. As these applications promote increased interest in MXene research, summarizing the latest findings on this family of materials will help inform the scientific community. In this review, we first discuss the rapid evolutionary change in MXenes from the first reported M₂XT_x structure to the last reported M₅X₄T_x structure. The use of systematically modified synthesis routes, such as foreign atom intercalation, tuning precursor chemistry, etc., will be further discussed in the next section. Then, we review the applications of MXenes and their composites/hybrids for rapidly growing applications such as batteries, supercapacitors, electrocatalysts, sensors, biomedical, electromagnetic interference shielding, membranes, and flexible and wearable devices. More importantly, we notice that its excellent metallic conductivity with its hydrophilic nature distinguishes MXene from other materials, and its properties and applications can be further modified by surface functionalization. MXene composites/hybrids outperform pristine MXenes in many applications. In addition, a summary of the latest findings using MXene-based materials to overcome application-specific drawbacks is provided in the last few sections. We hope that the information provided in this review will help integrate lab-scale findings into commercially viable products.

Challenges of Emerging Wearable Sensors for Remote Monitoring toward Telemedicine Healthcare

Digitized telemedicine tools with the Internet of Things (IoT) started advancing into our daily lives and have been incorporated with commercial wearable gadgets for noninvasive remote health monitoring. The newly established tools have been steered toward a new era of decentralized healthcare. The advancement of a telemedicine wearable monitoring system has attracted enormous interest in the multimodal big data acquisition of real-time physiological and biochemical information via noninvasive methods for any health-related industries. The expectation of telemedicine wearable creation has been focused on early diagnosis of multiple diseases and minimizing the cost of high-tech and invasive treatments. However, only limited progress has been directed toward the development of telemedicine wearable sensors. This Perspective addresses the advancement of these wearable sensors that encounter multiple challenges on the forefront and technological gaps hampering the realization of health monitoring at molecular levels related to smart materials mostly limited to single use, issues of selectivity to analytes, low sensitivity to targets, miniaturization, and lack of artificial intelligence to perform multiple tasks and secure big data transfer. Sensor stability with minimized signal drift, on-body sensor reusability, and long-term continuous health monitoring provides key analytical challenges. This Perspective also focuses on, promotes, and highlights wearable sensors with a distinct capability to interconnect with telemedicine healthcare for physical sensing and multiplex sensing at deeper levels. Moreover, it points out some critical challenges in different material aspects and promotes what it will take to advance the current state-of-art wearable sensors for telemedicine healthcare. Ultimately, this Perspective is to draw attention to some potential blind spots of wearable technology development and to inspire further development of this integrated technology in mitigating multimorbidity in aging societies through health monitoring at molecular levels to identify signs of diseases.

2D materials: increscent quantum flatland with immense potential for applications

Quantum flatland i.e., the family of two dimensional (2D) quantum materials has become increscent and has already encompassed elemental atomic sheets (Xenes), 2D transition metal dichalcogenides (TMDCs), 2D metal nitrides/carbides/carbonitrides (MXenes), 2D metal oxides, 2D metal phosphides, 2D metal halides, 2D mixed oxides, etc. and still new members are being explored. Owing to the occurrence of various structural phases of each 2D material and each exhibiting a unique electronic structure; bestows distinct physical and chemical properties. In the early years, world record electronic mobility and fractional quantum Hall effect of graphene attracted attention. Thanks to excellent electronic mobility, and extreme sensitivity of their electronic structures towards the adjacent environment, 2D materials have been employed as various ultrafast precision sensors such as gas/fire/light/strain sensors and in trace-level molecular detectors and disease diagnosis. 2D materials, their doped versions, and their hetero layers and hybrids have been successfully employed in electronic/photonic/optoelectronic/spintronic and straintronic chips. In recent times, quantum behavior such as the existence of a superconducting phase in moiré hetero layers, the feasibility of hyperbolic photonic metamaterials, mechanical metamaterials with negative Poisson ratio, and potential usage in second/third harmonic generation and electromagnetic shields, etc. have raised the expectations further. High surface area, excellent young's moduli, and anchoring/coupling capability bolster hopes for their usage as nanofillers in polymers, glass, and soft metals. Even though lab-scale demonstrations have been showcased, large-scale applications such as solar cells, LEDs, flat panel displays, hybrid energy storage, catalysis (including water splitting and CO2 reduction), etc. will catch up. While new members of the flatland family will be invented, new methods of large-scale synthesis of defect-free crystals will be explored and novel applications will emerge, it is expected. Achieving a high level of in-plane doping in 2D materials without adding defects is a challenge to work on. Development of understanding of inter-layer coupling and its effects on electron injection/excited state electron transfer at the 2D-2D interfaces will lead to future generation heterolayer devices and sensors.

Intelligent Wearable Sensors Interconnected with Advanced Wound Dressing Bandages for Contactless Chronic Skin Monitoring: Artificial Intelligence for Predicting Tissue Regeneration

Toward the adoption of artificial intelligence-enabled wearable sensors interconnected with intelligent medical objects, this contactless multi-intelligent wearable technology provides a solution for healthcare to monitor hard-to-heal wounds and create optimal efficiencies for clinical professionals by minimizing the risk of disease infection. This article addressed a flexible artificial intelligence-guiding (FLEX-AI) wearable sensor that can be operated with a deep artificial neural network (deep ANN) algorithm for chronic wound monitoring via short-range communication toward a seamless, MXENE-attached, radio frequency-tuned, and wound dressing-integrated (SMART-WD) bandage. Based on a supervised training set of on-contact pH-responsive voltage output, the confusion matrix for healing-stage recognition from this deep ANN machine learning revealed an accuracy of 94.6% for the contactless measurement. The core analytical design of these smart bandages integrated wound dressing of poly(vinyl acrylic) gel@PANI/Cu₂O NPs for instigating pH-responsive current during the wound healing process. Effectively, a chip-free bandage tag was fabricated with a capacitive Mxene/PTFE electret and adhesive acrylic inductance to match the resonance frequency generated by the intelligent wearable antenna. Under zero-current electrochemical potential, the wound dressing attained a slope of -76 mV/pH. With the higher activation voltage applied toward the wound dressing electrodes, cuprous ions intercalated more into the hybrid PVA gel/PANI shell, resulting in an exponential increase of the two-terminal current response. The healing phase diagram was classified into regimes of fast-curing, slow-curing, and no-curing for skin disease treatment with corticosteroids. Ultimately, the near-field sensing technology offers adequate information for guiding treatment decisions as well as drug effectiveness for wound care.

Mechanically Robust and Elastic Graphene/Aramid Nanofiber/Polyaniline Nanotube Aerogels for Pressure Sensors

The preparation of graphene-based aerogels with excellent mechanical strength, elasticity, and compressibility is still a challenge. Herein, we demonstrate a robust, elastic, and lightweight graphene/aramid nanofiber/polyaniline nanotube (rGO/ANF/PANIT) aerogel that is prepared by mixing graphene oxide (GO), ANF, and PANIT dispersions, followed by thermal treatment at 90 °C, freeze-drying, and a low-temperature annealing process. The PANIT bonds the graphene sheets tightly, benefitting the formation of composite gels. The ANF tightly interconnects the graphene sheets and further reinforces the composite network framework significantly, hence endowing rGO/ANF/PANIT composite aerogels with robust mechanical property. The prepared aerogels present a low density of ∼12 mg cm^-3, high conductivity, good resilience, and high compressibility. The rGO/ANF/PANIT aerogels as pressure sensors exhibit a high sensitivity of 1.73 kPa^-1, low detection limit (40 Pa), wide detection range, and excellent compressive cycle stability, highlighting the promising applications in pressure-sensitive electrical devices, including medical health detection, wearable electronics, and intelligent packaging fields.

Assessment of Occlusal Force and Local Gas Release Using Degradable Bacterial Cellulose/Ti3C2Tx MXene Bioaerogel for Oral Healthcare

Dental diseases resulting from movement disorders and volatile gases are very common. The classic method for detecting occlusal force is effective; however, its function is one-time rather than real-time monitoring, and the technology is very time-consuming. Herein, we report a multifunctional, flexible, and degradable bacterial cellulose/Ti₃C₂T_x MXene bioaerogel for the accurate detection of occlusal force and early diagnosis of periodontal diseases. Combining the mechanical properties of MXene and the abundant functional groups of bacterial cellulose, 3D porous bioaerogels exhibit both pressure-sensitive and ammonia (NH₃)-sensitive responses. By integrating these substances into a flexible array, the resulting device can distinguish the intensity, location, and even the time sequence of the occlusion force; moreover, it can provide NH₃ gas and occlusion force response signals. Therefore, this technology is promising for both disease diagnosis and oral health. In addition, the introduction of a renewable biomaterial allows the bioaerogel to degrade completely using a low-concentration hydrogen peroxide solution, making the device environmentally friendly and satisfying the demands for sustainable development.