Highly Sensitive Multifunctional Electronic Skin Based on Nanocellulose/MXene Composite Films with Good Electromagnetic Shielding Biocompatible Antibacterial Properties

Bionic learning in MXene-based actuators: An emerging frontier

Bionics offers valuable insights into the design and application of MXene-based soft actuators, which have garnered significant attention in the fields of flexible electronics and smart materials owing to their exceptional electrical conductivity, tunable interlayer spacing, and responsiveness to diverse external stimuli. This review begins with a comprehensive summary of the main response mechanisms of MXene-based soft actuators under various external stimuli. It presents a detailed analysis of the advantages and limitations of different actuation modes and discusses strategies for composite modification with other materials to enhance MXene performance under multi-stimulus conditions. Inspired by the sensory capabilities of animals and plants in nature, this work explores the potential for biomimetic design and identifies four key challenges for advancing the field: (1) the development of efficient and controllable material synthesis techniques, (2) the electrochemical stability and environmental robustness of devices, (3) the overall performance optimization of actuators, and (4) the nascent exploration of biomimetic learning mechanisms. Finally, future research directions are outlined, offering novel perspectives to promote the broader application of MXene-based soft actuators in biomimetic systems.

MXenes from MAX phases: synthesis, hybridization, and advances in supercapacitor applications

MXenes, which are essentially 2D layered structures composed of transition metal carbides and nitrides obtained from MAX phases, have gained substantial interest in the field of energy storage, especially for their potential as electrodes in supercapacitors due to their unique properties such as high electrical conductivity, large surface area, and tunable surface chemistry that enable efficient charge storage. However, their practical implementation is hindered by challenges like self-restacking, oxidation, and restricted ion transport within the layered structure. This review focuses on the synthesis process of MXenes from MAX phases, highlighting the different etching techniques employed and how they significantly influence the resulting MXene structure and subsequent electrochemical performance. It further highlights the hybridization of MXenes with carbon-based materials, conducting polymers, and metal oxides to enhance charge storage capacity, cyclic stability, and ion diffusion. The influence of dimensional structuring (1D, 2D, and 3D architectures) on electrochemical performance is critically analyzed, showcasing their role in optimizing electrolyte accessibility and energy density. Additionally, the review highlights that while MXene-based supercapacitors have seen significant advancements in terms of energy storage efficiency through various material combinations and fabrication techniques, key challenges like large-scale production, long-term stability, and compatibility with electrolytes still need to be addressed. Future research should prioritize developing scalable synthesis methods, optimizing hybrid material interactions, and investigating new electrolyte systems to fully realize the potential of MXene-based supercapacitors for commercial applications. This comprehensive review provides a roadmap for researchers aiming to bridge the gap between laboratory research and commercial supercapacitor applications.

Robust and ultra-thin nanocellulose/MXene composite film and its performance in efficient electricity-generation and sensing

The conversion of mechanical energy into electrical energy by triboelectric nanogenerators (TENG) has attracted attention in recent years, particularly in the field of wearable sensor. In this work, TEMPO-oxidized cellulose nanofibers (TOCNF) with carboxylate groups were compounded with MXene to serve as both the negative friction layer and the electrode in assembling a TENG with nylon. The synergistic effect between TOCNF and MXene was analyzed to disclose its influence on the performance of the as-prepared TENG. The MXene/TOCNF composite film, containing 50 wt% MXene, exhibited the best performance among all specimens, and the assembled TENG demonstrated excellent performance with an open-circuit voltage of 210 V, a short-circuit current of 0.84 μA, and a transferred charge of 8.6 nC. The excellent output performance might be attributed to the presence of carboxylate and F-containing groups in the composite film. This flexible TENG also functioned as a self-powered sensor, generating sensitive and stable signals in response to human motion and writing. This work verifies the simultaneous use of robust and flexible nanocellulose/MXene composite films as both the friction layer and electrode, which could spur the development of TENGs using sustainable and abundant cellulosic materials.

Piezoelectric Biopolymers: Advancements in Energy Harvesting and Biomedical Applications

Biodegradable piezoelectric polymers have emerged as a hot research focus in bioelectronics, energy-harvesting systems, and biomedical applications, as well as in sustainable future development. Biopolymers possess plenty of features which make them promising candidates for next-generation electronic technologies, including biocompatibility, degradability, and flexibility. This review discusses piezoelectric biopolymers, focusing on the relationship between coupling mechanisms, material structures, and piezoelectric performance. Processing techniques such as annealing, mechanical drawing, and poling are introduced and further studied in terms of achieving high piezoelectric performance. This work reviews the strategies for enhancing piezoelectric properties via molecular engineering, nano structuring, and the incorporation of additives. Furthermore, the applications of these biopolymers in energy harvesting and biomedicine are provided, with a discussion of their potential in degradable bioelectronic devices. There are still challenges in optimizing piezoelectric performance and ensuring stability. Our research is expected to provide an understanding of these challenges and help to achieve a wider application of piezoelectric biopolymers.

Interfacial modulation of Ti3C2Tx MXene using functionalized cellulose nanofibrils for enhanced electrochemical actuation

Electrochemical actuators (ECAs) with low voltage actuation and large deformation ranges generally require electrode materials with high ion kinetic energy transport, high charge storage, and excellent electrochemical-mechanical properties. However, the fabrication of such actuators remains a major challenge. In the present work, hybrid electroactive films were fabricated by self-assembling one-dimensional functionalized cellulose nanofibrils (CNFs) with two-dimensional MXene (Ti3C2Tx). The obtained ECA actuators fabricated by carboxymethylated cellulose nanofibrils (consisting of -CH2COO-surface groups) with Ti3C2Tx integrate excellent curvature (0.1041 mm-1), mechanical strength (21.68 MPa), a bending strain of 0.50 %, and a good actuation displacement of 9.3 mm at a low voltage range of -0.6 to 0.3 V. This may be attributed to the enlarged layer spacing (15.34 Å), which makes the embedding and transport of H+ easier, and excellent adaptivity of mechanical properties achieved by molecular-scaled strong hydrogen bonding, leading to better actuation performance. This study provides a potential research direction for the preparation of ECAs with large actuation deformation.

Robust and Environmentally Friendly MXene-Based Electronic Skin Enabling the Three Essential Functions of Natural Skin: Perception, Protection, and Thermoregulation

The development of electronic skin (e-skin) emulating the human skin's three essential functions (perception, protection, and thermoregulation) has great potential for human-machine interfaces and intelligent robotics. However, existing studies mainly focus on perception. This study presents a novel, eco-friendly, mechanically robust e-skin replicating human skin's three essential functions. The e-skin is composed of Ti3C2Tx MXene, polypyrrole, and bacterial cellulose nanofibers, where the MXene nanoflakes form the matrix, the bacterial cellulose nanofibers act as the filler, and the polypyrrole serves as a conductive "cross-linker". This design allows customization of the electrical conductivity, microarchitecture, and mechanical properties, integrating sensing (perception), EMI shielding (protection), and thermal management (thermoregulation). The optimal e-skin can effectively sense various motions (including minuscule artery pulses), achieve an EMI shielding efficiency of 63.32 dB at 78 μm thickness, and regulate temperature up to 129 °C in 30 s at 2.4 V, demonstrating its potential for smart robotics in complex scenarios.

MXene-based composites in smart wound healing and dressings

MXenes, a class of two-dimensional materials, exhibit considerable potential in wound healing and dressing applications due to their distinctive attributes, including biocompatibility, expansive specific surface area, hydrophilicity, excellent electrical conductivity, unique mechanical properties, facile surface functionalization, and tunable band gaps. These materials serve as a foundation for the development of advanced wound healing materials, offering multifunctional nanoplatforms with theranostic capabilities. Key advantages of MXene-based materials in wound healing and dressings encompass potent antibacterial properties, hemostatic potential, pro-proliferative attributes, photothermal effects, and facilitation of cell growth. So far, different types of MXene-based materials have been introduced with improved features for wound healing and dressing applications. This review covers the recent advancements in MXene-based wound healing and dressings, with a focus on their contributions to tissue regeneration, infection control, anti-inflammation, photothermal effects, and targeted therapeutic delivery. We also discussed the constraints and prospects for the future application of these nanocomposites in the context of wound healing/dressings.

Revolutionizing Infection Control: Harnessing MXene-Based Nanostructures for Versatile Antimicrobial Strategies and Healthcare Advancements

The escalating global health challenge posed by infections prompts the exploration of innovative solutions utilizing MXene-based nanostructures. Societally, the need for effective antimicrobial strategies is crucial for public health, while scientifically, MXenes present promising properties for therapeutic applications, necessitating scalable production and comprehensive characterization techniques. Here we review the versatile physicochemical properties of MXene materials for combatting microbial threats and their various synthesis methods, including etching and top-down or bottom-up techniques. Crucial characterization techniques such as XRD, Raman spectroscopy, SEM/TEM, FTIR, XPS, and BET analysis provide insightful structural and functional attributes. The review highlights MXenes' diverse antimicrobial mechanisms, spanning membrane disruption and oxidative stress induction, demonstrating efficacy against bacterial, viral, and fungal infections. Despite translational hurdles, MXene-based nanostructures offer broad-spectrum antimicrobial potential, with applications in drug delivery and diagnostics, presenting a promising path for advancing infection control in global healthcare.

Flexible and ultrasensitive piezoresistive electronic skin based on chitin/sulfonated carbon nanotube films

Wearable electronic skin has gained increasing popularity due to its remarkable properties of high flexibility, sensitivity, and lightweight, making it an ideal choice for detecting human physiological activity. In this study, we successfully prepared e-skin using regenerated chitin (RCH) and sulfonated carbon nanotubes (SCNTs). The e-skin demonstrated brilliant mechanical and sensing properties, exhibiting a sensitivity of 1.75 kPa-1 within the 0-5 kPa range and a fast response-recovery time of <10 ms. Furthermore, it displayed an ultra-low detection limit of 1.39 Pa (5 mg), exceptional stability (up to 11,000 cycles), and a remarkable mechanical strength, reaching up to 50 MPa. Moreover, the e-skin was fabricated through a simple and economical approach. With the popularity of micro sensing devices, the e-skin holds tremendous potential for various applications, including wearable electronic devices, health and sports monitoring, artificial intelligence and other fields.

Highly Electroactive Tissue Engineering Scaffolds Based on Nanocellulose/Sulfonated Carbon Nanotube Composite Hydrogels for Myocardial Tissue Repair

Myocardial infarction (MI) has been a serious threat to the health of modern people for a long time. The introduction of tissue engineering (TE) therapy into the treatment of MI is one of the most promising therapeutic schedules. Considering the intrinsic electrophysiological activity of cardiac tissue, we utilized 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with excellent biocompatibility as the substrate, and sulfonated carbon nanotubes (SCNTs) with remarkable conductivity and water dispersibility as the electrically active material, to prepare TOCN-SCNT composite hydrogels. By adjusting the content of SCNTs from 0 to 5 wt %, TOCN-SCNT hydrogels exhibited conductivity ranging from 5.2 × 10-6 to 6.2 × 10-2 S cm-1. Just with 1 wt % incorporation of SCNTs, the hydrogel played a role in promoting the adhesive growth and proliferation of cells. The hydrogel expressed higher Connexin 43 (Cx-43) and cardiac troponin-T proteins compared with controls, demonstrating great potential in constructing a myocardial TE scaffold.

Structure Design and Processing Strategies of MXene-Based Materials for Electromagnetic Interference Shielding

The development of new materials for electromagnetic interference (EMI) shielding is an important area of research, as it allows for the creation of more effective and high-efficient shielding solutions. In this sense, MXenes, a class of 2D transition metal carbides and nitrides have exhibited promising performances as EMI shielding materials. Electric conductivity, low density, and flexibility are some of the properties given by MXene materials, which make them very attractive in the field. Different processing techniques have been employed to produce MXene-based materials with EMI shielding properties. This review summarizes processes and the role of key parameters like the content of fillers and thickness in the desired EMI shielding performance. It also discusses the determination of power coefficients in defining the EMI shielding mechanism and the concept of green shielding materials, as well as their influence on the real application of a produced material. The review concludes with a summary of current challenges and prospects in the production of MXene materials as EMI shields.

Recent advance in biomass membranes: Fabrication, functional regulation, and antimicrobial applications

Both inorganic and polymeric membranes have been widely applied for antimicrobial applications. However, these membranes exhibit low biocompatibility, weak biodegradability, and potential toxicity to human being and environment. Biomass materials serve as excellent candidates for fabricating functional membranes to address these problems due to their unique physical, chemical, and biological properties. Here we present recent progress in the fabrication, functional regulation, and antimicrobial applications of various biomass-based membranes. We first introduce the types of biomass membranes and their fabrication methods, including the phase inversion, vacuum filtration, electrospinning, layer-by-layer self-assembly, and coating. Then, the strategies on functional regulation of biomass membranes by adding 0D, 1D, and 2D nanomaterials are presented and analyzed. In addition, antibacterial, antifungal, and antiviral applications of biomass-based functional membranes are summarized. Finally, potential development aspects of biomass membranes are discussed and prospected. This comprehensive review is valuable for guiding the design, synthesis, structural/functional tailoring, and sustainable utilization of biomass membranes.

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.

Advances in Biodegradable Electronic Skin: Material Progress and Recent Applications in Sensing, Robotics, and Human-Machine Interfaces

The rapid growth of the electronics industry and proliferation of electronic materials and telecommunications technologies has led to the release of a massive amount of untreated electronic waste (e-waste) into the environment. Consequently, catastrophic environmental damage at the microbiome level and serious human health diseases threaten the natural fate of the planet. Currently, the demand for wearable electronics for applications in personalized medicine, electronic skins (e-skins), and health monitoring is substantial and growing. Therefore, "green" characteristics such as biodegradability, self-healing, and biocompatibility ensure the future application of wearable electronics and e-skins in biomedical engineering and bioanalytical sciences. Leveraging the biodegradability, sustainability, and biocompatibility of natural materials will dramatically influence the fabrication of environmentally friendly e-skins and wearable electronics. Here, the molecular and structural characteristics of biological skins and artificial e-skins are discussed. The focus then turns to the biodegradable materials, including natural and synthetic-polymer-based materials, and their recent applications in the development of biodegradable e-skin in wearable sensors, robotics, and human-machine interfaces (HMIs). Finally, the main challenges and outlook regarding the preparation and application of biodegradable e-skins are critically discussed in a near-future scenario, which is expected to lead to the next generation of biodegradable e-skins.

Antibacterial Capability of MXene (Ti3C2Tx) to Produce PLA Active Contact Surfaces for Food Packaging Applications

The globalization of the market and the increase of the global population that requires a higher demand of food products superimposes a big challenge to ensure food safety. In this sense, a common strategy to extend the shelf life and save life of food products is by avoiding bacterial contamination. For this, the development of antibacterial contact surfaces is an urgent need to fulfil the above-mentioned strategy. In this work, the role of MXene (Ti₃C₂T_x) in providing antibacterial contact surfaces was studied through the creation of composite films from polylactic acid (PLA), as the chosen polymeric matrix. The developed PLA/MXene films maintained the thermal and mechanical properties of PLA and also presented the attractive antibacterial properties of MXene. The composites' behaviour against two representative foodborne bacteria was studied: Listeria mono-cytogenes and Salmonella enterica (representing Gram-positive and Gram-negative bacteria, respectively). The composites prevented bacterial growth, and in the case of Listeria only 0.5 wt.% of MXene was necessary to reach 99.9999% bactericidal activity (six log reductions), while against Salmonella, 5 wt.% was necessary to achieve 99.999% bactericidal activity (five log reductions). Cy-totoxicity tests with fHDF/TER166 cell line showed that none of the obtained materials were cytotoxic. These results make MXene particles promising candidates for their use as additives into a polymeric matrix, useful to fabricate antibacterial contact surfaces that could prove useful for the food packaging industry.

Low-Temperature Photothermal Therapy Based on Borneol-Containing Polymer-Modified MXene Nanosheets

Noninvasive photothermal therapy (PTT) is an emerging strategy for eliminating multidrug-resistant (MDR) bacteria that achieve sterilization by generating temperatures above 50 °C; however, such a high temperature also causes collateral damage to healthy tissues. In this study, we developed a low-temperature PTT based on borneol-containing polymer-modified MXene nanosheets (BPM) with bacteria-targeting capabilities. BPM was fabricated through the electrostatic coassembly of negatively charged two-dimensional MXene nanosheets (2DM) and positively charged quaternized α-(+)-borneol-poly(N,N-dimethyl ethyl methacrylate) (BPQ) polymers. Integrating BPQ with 2DM improved the stability of 2DM in physiological environments and enabled the bacterial membrane to be targeted due to the presence of a borneol group and the partially positive charge of BPQ. With the aid of near-infrared irradiation, BPM was able to effectively eliminate methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) through targeted photothermal hyperthermia. More importantly, BPM effectively eradicated more than 99.999% (>5 orders of magnitude) of MRSA by localized heating at a temperature that is safe for the human body (≤40 °C). Together, these findings suggest that BPM has good biocompatibility and that membrane-targeting low-temperature PTT could have great therapeutic potential against MDR infections.

Nanocellulose-Based Nanocomposites for Sustainable Applications: A Review

Nanocellulose has emerged in recent years as one of the most notable green materials available due to its numerous appealing factors, including its non-toxic nature, biodegradability, high aspect ratio, superior mechanical capabilities, remarkable optical properties, anisotropic shape, high mechanical strength, excellent biocompatibility and tailorable surface chemistry. It is proving to be a promising material in a range of applications pertinent to the material engineering to biomedical applications. In this review, recent advances in the preparation, modification, and emerging application of nanocellulose, especially cellulose nanocrystals (CNCs), are described and discussed based on the analysis of the latest investigations. This review presents an overview of general concepts in nanocellulose-based nanocomposites for sustainable applications. Beginning with a brief introduction of cellulose, nanocellulose sources, structural characteristics and the extraction process for those new to the area, we go on to more in-depth content. Following that, the research on techniques used to modify the surface properties of nanocellulose by functionalizing surface hydroxyl groups to impart desirable hydrophilic-hydrophobic balance, as well as their characteristics and functionalization strategies, were explained. The usage of nanocellulose in nanocomposites in versatile fields, as well as novel and foreseen markets of nanocellulose products, are also discussed. Finally, the difficulties, challenges and prospects of materials based on nanocellulose are then discussed in the last section for readers searching for future high-end eco-friendly functional materials.

Bioinspired MXene-Based User-Interactive Electronic Skin for Digital and Visual Dual-Channel Sensing

User-interactive electronic skin (e-skin) that could convert mechanical stimuli into distinguishable outputs displays tremendous potential for wearable devices and health care applications. However, the existing devices have the disadvantages such as complex integration procedure and lack of the intuitive signal display function. Here, we present a bioinspired user-interactive e-skin, which is simple in structure and can synchronously achieve digital electrical response and optical visualization upon external mechanical stimulus. The e-skin comprises a conductive layer with a carbon nanotubes/cellulose nanofibers/MXene nanohybrid network featuring remarkable electromechanical behaviors, and a stretchable elastomer layer, which is composed of silicone rubber and thermochromic pigments. Furthermore, the conductive nanohybrid network with outstanding Joule heating performance can generate controllable thermal energy under voltage input and then achieve the dynamic coloration of silicone-based elastomer. Especially, such an innovative fusion strategy of digital data and visual images enables the e-skin to monitor human activities with evermore intuition and accuracy. The simple design philosophy and reliable operation of the demonstrated e-skin are expected to provide an ideal platform for next-generation flexible electronics.