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.

High-performance dielectric film capacitors based on cellulose/Al2O3 nanosheets/PVDF composites.

The design and preparation of novel renewable biomass-based dielectric composites have drawn great attention recently. Here, cellulose was dissolved in NaOH/urea aqueous solution, and Al2O3 nanosheets (AONS) synthesized by hydrothermal method were used as fillers. Then the regenerated cellulose (RC)-AONS dielectric composite films were prepared by regeneration, washing and drying. The two-dimensional AONS had a better effect on improving the dielectric constant and breakdown strength of the composites, so that the RC-AONS composite film with 5 wt% AONS content reached an energy density of 6.2 J/cm3 at 420 MV/m. Furthermore, in order to improve the dielectric energy storage properties of cellulose films in high humidity environment, the hydrophobic polyvinylidene fluoride (PVDF) was innovatively introduced to construct RC-AONS-PVDF composite films. The energy storage density of the prepared ternary composite films could reach 8.32 J/cm3 at 400 MV/m, which was 416 % improvement against that of the commercially biaxially oriented polypropylene (2 J/cm3), and could be cycled for >10,000 times under 200 MV/m. Concurrently, the water absorption of the composite film in humidity was effectively reduced. This work broadens the application prospect of biomass-based materials in the field of film dielectric capacitor.

TOCN/copper calcium titanate composite aerogel films as high-performance triboelectric materials for energy harvesting.

The development of high-performance cellulose-based triboelectric nanogenerators (TENG) has been a subject widely concerned by researchers. Here, we prepared a composite aerogel film based on TEMPO-oxidized cellulose nanofiber (TOCN) and copper calcium titanate (CaCu3Ti4O12, CCTO) nanoparticles. Under their comprehensive effects of the enhanced dielectric performance, the TOCN/CCTO-20 composite film with 20 % CCTO content based TENG device showed the best output performance of an open circuit voltage of 152 V, a short circuit current of 33.8 µA and a power density of 483 mW/m2, which were 3.37, 4.07 and 3.71 times higher than that of the pure TOCN based TENG device, respectively. In addition, effects of external force conditions, aerogel film size parameters and the agglomeration state of high filler content on the output performance were also studied. These results indicated that the TOCN/CCTO composite aerogel films can be used as efficient and low-cost cellulose-based triboelectric positive materials for energy harvesting.

Hydrangea-like nanocellulose microspheres with high dye adsorption and drug encapsulation prepared by emulsion method.

Currently, microspheres with high adsorption capacity play a crucial role in dye adsorption and drug loading. In this study, 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCN) could be used to form nanocellulose microspheres by the emulsion method. The prepared hydrangea-like nanocellulose microspheres presented a stable three-dimensional network porous structure and exhibited excellent adsorption properties. The TOCN microspheres had a high adsorption capacity for methylene blue (MB) and methyl orange (MO) with the optimal adsorption capacity of 412.1 mg g-1 and 286.5 mg g-1 under neutral conditions, respectively. The TOCN microspheres displayed excellent adsorption selectivity on MB/MO mixed dyes, which could be used to selectively adsorb MB. Besides, the encapsulation rate of the positively charged drug doxorubicin hydrochloride (DOX) was as high as 93 %, and the drug loading capacity was as high as 34.5 %. Overall, our prepared nanocellulose microspheres had great potential for application in dye adsorption and drug delivery systems.

Porous cellulose composite aerogel films with super piezoelectric properties for energy harvesting.

The piezoelectric effect is one of the most promising electromechanical coupling processes for mechanical energy conversion and energy harvesting. However, natural polymer based piezoelectric materials are of poor piezoelectric performance. we developed flexible porous piezoelectric aerogel films based on TEMPO-oxidized cellulose nanofibrils (TOCN) and MoS2 nanosheets. Those aerogel films possessed large specific surface areas and abundant mesopores. Moreover, they exhibited very good piezoelectric properties when a field strength of 20 MV/m was used to polarize MoS2 nanosheets and air in the mesopores. When assembled to piezoelectric nanogenerators (PENGs), a TOCN/MoS2 aerogel film PENG containing 6 wt% of MoS2 exhibited the best output performance. It generated an open circuit voltage of 42 V and a short-circuit current of 1.1 µA, a maximum area power density of 1.29 µW/cm2 and a maximum volume power density of 0.143 µW/cm3. These features enable them to be promising piezoelectric materials for energy harvesting.

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

Electronic skin has aroused extensive research interest due to high similarity with human skin. Realizing a multifunctional electronic skin that is highly consistent with skin functions and endowed with more other functions is now a more urgent need and important challenge. Here, we use 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized cellulose nanofibril (TOCN) dispersion and highly conductive Ti3C2TX dispersion to prepare TOCN/Ti3C2TX composite film through vacuum-assisted filtration. The obtained composite film imitating the nacre-like lamellar structure of natural shells has good mechanical properties (124.6 MPa of tensile strength). Meanwhile, the composite film also showed excellent electromagnetic shielding performance (36 dB), biocompatibility, and antibacterial properties. In addition, the piezoresistive sensor assembled from the composite film exhibited a high sensitivity (11.6 kPa-1), fast response and recovery time (≤10 ms), ultralow monitoring limit (0.2 Pa), and long-term stability (>10 000 cycles). It also could detect human daily activities such as finger bent, chewing, and so on.

Cellulose/BaTiO3 nanofiber dielectric films with enhanced energy density by interface modification with poly(dopamine).

Flexible electrostatic capacitors have many potential applications in modern electric power systems. In this study, flexible cellulose-based dielectric films were prepared by compositing regenerated cellulose (RC) and one-dimensional BaTiO3 nanofiber (BTNF) via a simple and environmentally friendly process. To improve compatibility and distributional homogeneity of the fillers/matrix, BTNF was surface modified by dopamine to prepare the poly(dopamine) modified BTNF (PDA@BTNF). The obtained RC/PDA@BTNF composite films (RC-PDA@BTNF) possessed higher dielectric constant and breakdown strength than those of the RC and RC/BTNF composite films. In particular, RC/PDA@BTNF composite films with 2 vol% PDA@BTNF (RC-2PDA@BTNF) exhibited a high discharged energy density of 17.1 J/cm3 at 520 MV/m, which exceeded 40 % compared with that of RC-2BTNF at 460 MV/m. Meanwhile, RC-2PDA@BTNF could continuously work for more than 10,000 times with a high efficiency of 91 %. Furthermore, the composite films could maintain good dielectric properties for a long time when stored in vacuum condition (under 0.3 atm). Therefore, these flexible cellulose-based dielectric materials are promising in the field of novel high-performance film dielectric capacitors.

Necklace-like ferroferric oxide (Fe3O4) nanoparticle/carbon nanofibril aerogels with enhanced lithium storage by carbonization of ferric alginate.

Theoretically, transition metal oxide/carbon nanofibril aerogels are promising candidates for lithium-ion battery anode materials as they combine the high stability and electrical conductivity of the carbon matrix and the high theoretical specific capacity of transition metal oxide (TMO). However, challenges still exist to embed TMO nanoparticles into thin carbon nanofibril absolutely and tightly, limiting further improvements in electrochemical performances of the composites. Herein, necklace-like Fe3O4/carbon nanofibril aerogel (Fe3O4/CNF) was constructed by crosslinking alginate with Fe3+, followed by carbonization of the obtained ferric alginate aerogel. Based on an "egg-box" helical structure resulting from strong coordination between the Fe3+ and the carboxylate groups of alginate, three-dimensional interconnected carbon aerogel was facilely fabricated with Fe3O4 nanoparticles (~11 nm in diameter) firmly embedded in ultrafine carbon nanofibrils (~18 nm in diameter), exhibiting a special necklace-like structure. Consequently, the composite exhibits a high reversible capacity and stability of 1176 mAh g-1 over 200 cycles at 1 A g-1 and a high rate performance of 615 mAh g-1 at 4 A g-1. These Fe3O4/CNF aerogels may have potential applications for enhanced lithium storage of electrochemical devices.

Chitin/MoS2 Nanosheet Dielectric Composite Films with Significantly Enhanced Discharge Energy Density and Efficiency.

High-performance dielectric nanomaterials have received increasing attention due to their important applications in the field of energy storage. Among various dielectric materials, polymer nanocomposite is one of the most promising candidates. However, the problems of environmental pollution caused by polymer-based dielectric materials have been extensively studied in recent years, which need to be solved urgently, leading to the search for new biodegradable dielectric materials. Herein, we report composite materials based on biodegradable and renewable chitin and molybdenum disulfide (MoS2) nanosheets for the first time. The MoS2 nanosheets were first fabricated by glycerol/urea system and then KOH/urea aqueous solution was used to directly dissolve chitin at low temperature together with the dispersion of the MoS2 nanosheets in a simple green process. The two-dimensional MoS2 nanosheets possess high polarization strength, and a large specific surface area can enhance the interfacial polarization with chitin; meanwhile, it can serve as a charge breakdown barrier to hinder the propagation of electrical tree branches. The results also show that the dielectric constant and breakdown strength of the chitin/MoS2 nanocomposites were increased, while the dielectric loss remained low. When the MoS2 content was 5 wt %, the charge and discharge efficiencies of the composite film were more than 80%, and the breakdown strength also reached 350 MV m-1, thus resulting in a high discharge energy density of 4.91 J cm-3, which was more than twice of the neat chitin (2.17 J cm-3). Furthermore, the nanocomposite films exhibited good thermal stability. Therefore, these chitin-based nanocomposite films are promising as high-performance biomass-based dielectric capacitors.

Carboxylated nanocellulose/poly(ethylene oxide) composite films as solid-solid phase-change materials for thermal energy storage.

Composite films of poly(ethylene oxide) (PEO) and 0%-20% surface-carboxylated cellulose nanofibrils (CNFs) were prepared by mixing the aqueous CNF dispersion and aqueous PEO solution at various weight ratios followed by casting and drying. The 20% CNF/PEO composite film was transparent, whereas the 100% PEO film was translucent. The addition of CNFs to the PEO matrix resulted in decreases of the crystallinity and crystal size of spherical PEO. The Young's modulus and tensile strength of the 100% PEO film were 0.2 GPa and 6.1 MPa, respectively, and remarkably increased to 2.4 GPa and 86 MPa, respectively, with the addition of 20% CNF. The CNF/PEO composite films had clear melting and crystallization temperatures in the heating and cooling processes, respectively. Nevertheless, the coefficients of thermal expansion at temperatures above the melting point of PEO significantly decreased with the CNF addition. The CNF/PEO composite films are therefore promising solid-solid phase-change materials for energy storage with high film dimensional stability.

Three-Dimensional Nanoporous Cellulose Gels as a Flexible Reinforcement Matrix for Polymer Nanocomposites.

With the world's focus on utilization of sustainable natural resources, the conversion of wood and plant fibers into cellulose nanowhiskers/nanofibers is essential for application of cellulose in polymer nanocomposites. Here, we present a novel fabrication method of polymer nanocomposites by in-situ polymerization of monomers in three-dimensionally nanoporous cellulose gels (NCG) prepared from aqueous alkali hydroxide/urea solution. The NCG have interconnected nanofibrillar cellulose network structure, resulting in high mechanical strength and size stability. Polymerization of the monomer gave P(MMA/BMA)/NCG, P(MMA/BA)/NCG nanocomposites with a volume fraction of NCG ranging from 15% to 78%. SEM, TEM, and XRD analyses show that the NCG are finely distributed and preserved well in the nanocomposites after polymerization. DMA analysis demonstrates a significant improvement in tensile storage modulus E' above the glass transition temperature; for instance, at 95 °C, E' is increased by over 4 orders of magnitude from 0.03 MPa of the P(MMA/BMA) up to 350 MPa of nanocomposites containing 15% v/v NCG. This reinforcement effect can be explained by the percolation model. The nanocomposites also show remarkable improvement in solvent resistance (swelling ratio of 1.3-2.2 in chloroform, acetone, and toluene), thermal stability (do not melt or decompose up to 300 °C), and low coefficients of thermal expansion (in-plane CTE of 15 ppm·K(-1)). These nanocomposites will have great promising applications in flexible display, packing, biomedical implants, and many others.

Dissolution of Wood Pulp in Aqueous NaOH/Urea Solution via Dilute Acid Pretreatment.

Wood pulps with certain amounts of lignin were successfully dissolved in aqueous NaOH/urea solution by subjecting them to the dilute acid pretreatment. After the acid hydrolysis, viscosity-average degree of polymerization (DPv) of the pulps decreased. The results revealed that both the DPv and lignin contents influenced the dissolved proportions of wood pulps. When they were not so high, the wood pulps could almost completely dissolve with dissolved proportions >90%. In particular, the acid-pretreated unbleached kraft pulp with DPv of about 500 and lignin content of 6.9% could dissolve in NaOH/urea solvent and achieve a maximum pulp concentration of 4 wt % in the obtained lignocellulose solution. Moreover, the acid-pretreated bleached thermomechanical pulp with a high lignin content of 14.2% also almost completely dissolved. The lignocellulose films prepared from these wood pulp/NaOH/urea solutions exhibited good transparency and bendability, thus maybe promising as new biobased materials.

In situ synthesis of robust conductive cellulose/polypyrrole composite aerogels and their potential application in nerve regeneration.

Nanostructured conductive polymers can offer analogous environments for extracellular matrix and induce cellular responses by electric stimulation, however, such materials often lack mechanical strength and tend to collapse under small stresses. We prepared electrically conductive nanoporous materials by coating nanoporous cellulose gels (NCG) with polypyrrole (PPy) nanoparticles, which were synthesized in situ from pyrrole monomers supplied as vapor. The resulting NCG/PPy composite hydrogels were converted to aerogels by drying with supercritical CO2, giving a density of 0.41-0.53 g cm(-3), nitrogen adsorption surface areas of 264-303 m(2) g(-1), and high mechanical strength. The NCG/PPy composite hydrogels exhibited an electrical conductivity of up to 0.08 S cm(-1). In vitro studies showed that the incorporation of PPy into an NCG enhances the adhesion and proliferation of PC12 cells. Electrical stimulation demonstrated that PC12 cells attached and extended longer neurites when cultured on NCG/PPy composite gels with DBSA dopant. These materials are promising candidates for applications in nerve regeneration, carbon capture, catalyst supports, and many others.