"Casein micelle -nanoparticle double cross-linking" triggered stable adhesive, tough CA/MWCNT/PAAm hydrogel wearable strain sensors, for human motion monitoring.

Flexible hydrogels have emerged as highly-desirable materials for wearable strain sensors. However, pristine biomass hydrogel systems are limited by their lack of stretchability, self-adhesion, and sensitivity. Here, a novel CA/MWCNT/PAAm double-network conductive hydrogel was developed through integrating casein (CA) micelles and multi-walled carbon nanotubes (MWCNT) into the polyacrylamide (PAAm) network. The resulting hydrogel displayed desired properties such as adhesiveness, toughness, self-healing, and near-infrared photothermal response. In this hybrid system, MWCNT were uniformly dispersed in the presence of casein micelles through hydrogen bonding and electrostatic interactions, favoring its role of nano reinforcement. Moreover, based on the "casein micelle-nanoparticle double cross-linking" mechanism and its double network structure, the prepared hydrogel showed high extensibility (2288 % ± 63 %), fast responsiveness (273 ± 5.13 ms), high sensitivity (GF = 12.46 ± 0.35), and a wide strain range (1-1000 %). Through consistent and repeated electrical inputs, this hydrogel was able to detect including large and small human movements, such as hand, leg, and swallowing motions. The results from this study provide a new way to fabricate bio-based hydrogel sensors with excellent mechanical and electrical properties.

Ultra-thin freestanding graphene films for efficient thermal insulation and electromagnetic interference shielding.

The preparation of freestanding graphene films by convenient and environmentally friendly preparation methods is still the focus of attention in various industrial fields. Here, we first select electrical conductivity, yield and defectivity as evaluation indicators and systematically explore the factors affecting the preparation of high-performance graphene by electrochemical exfoliation, then further post-process it under volume-limited conditions by microwave reduction. Finally, we obtained a self-supporting graphene film with an irregular interlayer structure but excellent performance. It is found that the electrolyte is ammonium sulfate, the concentration is 0.2 M, the voltage is 8 V, and the pH is 11, which were the optimal conditions for preparing low-oxidation graphene. The square resistance of the EG was 1.6 Ω sq-1, and the yield could be 65%. In addition, electrical conductivity and joule heat were significantly improved after microwave post-processing, especially its electromagnetic shielding performance with a shielding coefficient of 53 dB able to be achieved. At the same time, the thermal conductivity is as low as 0.05 W m-1 K-1. The mechanism for the improvement of electromagnetic shielding performance is that (1) microwave reduction effectively enhances the conductivity of the graphene sheet overlapping network; (2) the gas generated by the instantaneous high temperature causes a large number of void structures between the graphene layers, and the irregular interlayer stacking structure makes the reflective surface more disordered, thereby prolonging the reflection path of electromagnetic waves among layers. In summary, this simple and environmentally friendly preparation strategy has good practical application prospects for graphene film products in flexible wearables, intelligent electronic devices, and electromagnetic wave protection.

Multifunctional electrospun membranes with hydrophilic and hydrophobic gradients property for wound dressing.

Achieving sustained and stable release of macromolecular antibacterial agents and unidirectional transport of liquids in targeted environment is still a challenge to be addressed in the management of wounds with large amounts of tissue exudates. In this work, a multilayer electrospun membrane (ethylcellulose-ethylcellulose/gelatin-quercetin/Eudragit L-100/polyethylene glycol, EC-EC/Gel-Q/EL/PEG) was designed with hydrophobic-hydrophilic gradients and drug sustained-release properties controlled by self-pumping effect and prepared using sequential electrospinning technology. The capillary force of different layers in the multilayer membrane could be controlled by precisely tuning the polymer concentrations of the inner and middle layers to extract water directly from hydrophobic inner ethylcellulose (EC) layer to hydrophilic middle ethylcellulose/gelatin (EC/Gel) layer. The droplets could not penetrate the hydrophobic side, but the drug molecules in the outer layer quercetin-loaded Eudragit L-100 (Q/EL/PEG) membrane moved after absorbing a large amount of water. The drug release behavior of multilayer wound dressing mainly followed the Korsmeyer-Peppas model. This multifunctional electrospun membrane could rapidly drive the biofluid outflow, effectively block the invasion of external contaminants and continuously release anti-inflammatory drugs, without any obvious cytotoxicity to mouse fibroblast cells. Hence, the above results indicate the excellent therapeutic potential of the proposed biomaterial as a wound dressing for diabetic patients.

Self-Healing, Solvent-Free, Anti-Corrosion Coating Based on Skin-like Polyurethane/Carbon Nanotubes Composites with Real-Time Damage Monitoring.

Self-healing anti-corrosion materials are widely regarded as a promising long-term corrosion protection strategy, and this is even more significant if the damage can be monitored in real-time and consequently repaired. Inspired by the hierarchical structure of human skin, self-healing, solvent-free polyurethane/carbon nanotubes composites (SFPUHE-HTF-CNTs) with a skin-like bilayer structure were constructed. The SFPUHE-HTF-CNTs were composed of two layers, namely, a hydrophobic solvent-free polyurethane (SFPUHE-HTF) containing disulfide bonds and fluorinated polysiloxane chain segments consisting of a self-healing layer and CNTs with good electrical conductivity consisting of a corrosion protection layer, which also allowed for the real-time monitoring of damage. The results of corrosion protection experiments indicated that the SFPUHE-HTF-CNTs had a low corrosion current density (8.94 × 10-9 A·cm-2), a positive corrosion potential (-0.38 V), and a high impedance modulus (|Z| = 4.79 × 105 Ω·cm2). The impedance modulus could still reach 4.54 × 104 Ω·cm2 after self-healing, showing excellent self-healing properties for anti-corrosion protection. Synchronously, the SFPUHE-HTF-CNTs exhibited a satisfactory damage sensing performance, enabling the real-time monitoring of fractures at different sizes. This work realized the effective combination of self-healing with corrosion protection and damage detection functions through a bionic design, and revealed the green, and low-cost preparation of advanced composites, which have the advantage of scale production.

Improving stability and separation performance of graphene oxide/graphene nanofiltration membranes by adjusting the laminated regularity of stacking-sheets.

The laminated graphene oxide (GO) membranes are promising alternatives in the field of nanofiltration due to their unique stacked interlayer structure and controllable molecular transport channels. However, it is still challenging to obtain satisfactory physical stability and separation performance to meet its practical application. In this study, a novel GO/Gr (graphene) nanofiltration membrane with high stability was engineered by post-hot-pressure treatment, following forward pressure filtration. The impact of GO/Gr loading ratio of the composites nanofiltration membranes for the permeability, selectivity, hydrophilicity and physical stability was investigated. The GO/Gr nanofiltration membranes exhibited high stability and separation performance because of the enhanced regularity and smoothness of the overall stacking layers. It was demonstrated that the satisfactory permeability (12.8-20 L·m-2·h-1) of GO/Gr nanofiltration membranes could be achieved. Compared with the pure GO membranes, GO/Gr-0.5 membranes exhibited a higher Na2SO4, NaCl, MgCl2, and MgSO4 rejection rate of approximately 78.3%, 51.2%, 34.5% and 32.6%, respectively. Meanwhile, the rejection rate (99.5%, 99.9%, 97.3% and 98.6%) of composite membranes for Methylene blue, Congo red, Rhodamine B and Methyl orange could be achieved. This facile way reveals the potential of stacked GO/Gr membranes in developing GO-based nanofiltration membranes.