An easily processable silver nanowires-dual-cellulose conductive paper for versatile flexible pressure sensors

Electronic skin based on natural biodegradable polymers for human motion monitoring

The wearability of the flexible electronic skin (e-skin) allows it to attach to the skin for human motion monitoring, which is essential for studying human motion and especially for assessing how well patients are recovering from rehabilitation therapy. However, the use of non-degradable synthetic materials in e-skin may raise skin safety concerns. Natural biodegradable polymers with advantages such as biodegradability, biocompatibility, sustainability, natural abundance, and low cost have the potential to be alternative materials for constructing flexible e-skin and applying them to human motion monitoring. This review summarizes the applications of natural biodegradable polymers in e-skin for human motion monitoring over the past three years, focusing on the discussion of cellulose, chitosan, silk fibroin, gelatin, and sodium alginate. Finally, we summarize the opportunities and challenges of e-skin based on natural biodegradable polymers. It is hoped that this review will provide insights for the future development of flexible e-skin in the field of human motion monitoring.

High-Performance Graphene Flexible Sensors for Pulse Monitoring and Human-Machine Interaction

Flexible sensors are of great interest due to their potential applications in human physiological signal monitoring, wearable devices, and healthcare. However, sensor devices employed for cardiovascular testing are normally bulky and expensive, which hamper wearability and point-of-care use. Herein, we report a simple method for preparing multifunctional flexible sensors using hydrazine hydrate (N2H4·H2O) as the reducing agent, graphene as the active material, and polyethylene (PE) tape as the encapsulation material. The flexible sensor produced with this method has a low detection limit of 100 mg, a fast response and recovery time of 40 and 20 ms, and shows no performance degradation even after up to 30,000 motion cycles. The sensors we have developed are capable of monitoring the pulse with relative accuracy, which presents an opportunity to replace bulky devices and normalize cardiovascular testing in the future. In order to further broaden the application field, the sensor is installed as a sensor array to recognize objects of different weights and shapes, showing that the sensor has excellent application potential in wearable artificial intelligence.

Nanocellulose-Enhanced, Easily Processable Cellulose-Based Flexible Pressure Sensor for Wearable Epidermal Sensing

Flexible pressure sensors (FPSs) based on biomass materials have gained considerable attention for their potential in wearable electronics, human-machine interaction, and environmental protection. Herein, flexible silver nanowire-dual-cellulose paper (SNdCP) containing common cellulose fibers, cellulose nanofibers (CNFs), and silver nanowires (AgNWs) for FPSs was assembled by a facile papermaking strategy. Compared with bacterial cellulose (BC) and cellulose nanocrystals (CNCs), CNFs possess better dimensions and reinforcement, which enables the composite paper to exhibit better mechanical properties (tensile stress of 164.65 MPa) and electrical conductivity (11600 S·m-1), providing more possibilities for FPSs. Benefiting from these advantages, we construct an easily processable and sensitive human-interactive FPS based on a composite paper with high sensitivity (0.050 kPa-1), fast response/recovery time (158/95 ms), and exceptional stability (>1000 bending cycles), capable of responding to finger motions, voice recognition, and human pulses; through further employment as the array unit and a control circuit, the observed highly adaptive mechano-electric transformability and functions are well maintained. Overall, a facile and versatile strategy with the potential to provide clues for the fabrication of cellulose-based FPSs with outstanding performance was introduced.

A highly sensitive flexible capacitive pressure sensor with hierarchical pyramid micro-structured PDMS-based dielectric layer for health monitoring

Herein, a flexible pressure sensor with high sensitivity was created using a dielectric layer featuring a hierarchical pyramid microstructure, both in simulation and fabrication. The capacitive pressure sensor comprises a hierarchically arranged dielectric layer made of polydimethylsiloxane (PDMS) with pyramid microstructures, positioned between copper electrodes at the top and bottom. The achievement of superior sensing performance is highly contingent upon the thickness of the dielectric layer, as indicated by both empirical findings and finite-element analysis. Specifically, the capacitive pressure sensor, featuring a dielectric layer thickness of 0.5 mm, exhibits a remarkable sensitivity of 0.77 kPa-1 within the pressure range below 1 kPa. It also demonstrates an impressive response time of 55 ms and recovery time of 42 ms, along with a low detection limit of 8 Pa. Furthermore, this sensor showcases exceptional stability and reproducibility with up to 1,000 cycles. Considering its exceptional achievements, the pressure sensor has been effectively utilized for monitoring physiological signals, sign language gestures, and vertical mechanical force exerted on objects. Additionally, a 5 × 5 sensor array was fabricated to accurately and precisely map the shape and position of objects. The pressure sensor with advanced performance shows broad potential in electronic skin applications.

Waterproof and ultrasensitive paper-based wearable strain/pressure sensor from carbon black/multilayer graphene/carboxymethyl cellulose composite

Huge electronic wastes motivated the flourishing of biodegradable electrically conductive cellulosic paper-based functional materials as flexible wearable devices. However, the relatively low sensitivity and unstable output in combination with poor wet strength under high moisture circumstances impeded the practical application. Herein, a superhydrophobic cellulosic paper with ultrahigh sensitivity was proposed by innovatively employing ionic sodium carboxymethyl cellulose (CMC) as bridge to reinforce the interfacial interaction between carbon black (CB) and multilayer graphene (MG) and SiO₂ nanoparticles as superhydrophobic layer. The resultant paper-based (PB) sensor displayed excellent strain sensing behaviors, wide working range (-1.0 %-1.0 %), ultrahigh sensitivity (gauge factor, GF = 70.2), and satisfied durability (>10,000 cycles). Moreover, the superhydrophobic surface offered well waterproof and self-cleaning properties, even stable running data without encapsulation under extremely high moisture conditions. Impressively, when the fabricated PB sensor was applied for electronic-skin (E-skin), the signal capture of spatial strain of E-skin upon bodily motion was breezily achieved. Thus, our work not only provides a new pathway for reinforcing the interfacial interaction of electrically conductive carbonaceous materials, but also promises a category of unprecedentedly superhydrophobic cellulosic paper-based strain sensors with ultra-sensitivity in human-machine interfaces field.

A bacterial cellulose-based separator with tunable pore size for lithium-ion batteries

Bacterial cellulose (BC) lithium-ion batteries separators possess outstanding thermal dimensional stability and electrolyte wettability, but theirs nano diameter and high aspect ratio lead to poor porosity and pore size uniformity of dense BC separators, limiting the Li⁺ transmission in the separators. In this paper, chitosan (CS) with different molecular weight was grafted onto BC (named OBCS), and a high-performance OBCS separator with excellent pore structure and tunable pore size was prepared by simple suction filtration. The spacing and dispersion uniformity of OBCS were improved by the CS grafted on BC surface, thus improving the pore structure and porosity of OBCS separators. The results showed that the obtained OBCS separators not only have excellent physicochemical properties, but also exhibit higher electrochemical performances than the commercial polypropylene (PP) separator. This work provides a new feasible strategy for improving the pore structure and porosity of nanocellulose separators.

Attapulgite Nanorods Incorporated MXene Lamellar Membranes for Enhanced Decontamination of Dye Wastewater

Due to its unique physical and chemical properties, MXene has recently attracted much attention as a promising candidate for wastewater treatment. However, the low water permeation flux of MXene membrane remains a challenge that has not been fully solved. In this study, attapulgite was used to increase the flux of MXene membrane through a facile one-pot method, during which the MXene nanosheets were self-assembled while being intercalated by the attapulgite nanorods to finally form the composite membranes. Under optimal conditions, an increase of water permeation flux of 97.31% could be observed, which was attributed to the broadened nano-channel upon the adequate intercalation of attapulgite nanorods. Its permeation flux and rejection rate for methylene blue (MB) were further studied for diverse applications. In contrast to bare MXene, the permeation flux increased by 61.72% with a still high rejection rate of 90.67%, owing to the size rejection. Overcoming a key technique barrier, this work successfully improved the water permeability of MXene by inserting attapulgite nanorods, heralding the exciting prospects of MXene-based lamellar membrane in dye wastewater treatment.

Mechanistic insights into morphological and chemical changes during benzenesulfonic acid pretreatment and simultaneous saccharification and fermentation process for ethanol production

The anatomical and histochemical characterization of pretreated substrates is essential for the further valorization of biomass during the biorefinery process. In this work, the benzenesulfonic acid (BA)-treated substrates were employed for simultaneous saccharification and fermentation (SSF) of ethanol for the first time. An ethanol yield of 50.36% was attained at 10% solids loading and 47.45 g/L of ethanol accumulated at 30 % solids loading. The dramatic improvements could result from the deconstruction of cell walls, which were evidenced by fluorescence microscope and confocal Raman microscopy spectra. Additionally, for a thorough comprehension of the inherent chemistry of lignin during the BA pretreatment, the changes in lignin structure features were identified for the first time by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). In summary, this study tried to probe the possibility of BA-treated Miscanthus for the SSF process and unveiled the mechanism of the efficient BA pretreatment.