Flexible multilevel nonvolatile biocompatible memristor with high durability.

Current protein or glucose based biomemristors have low resistance-switching performance and require complex structural designs, significantly hindering the development of implantable memristor devices. It is imperative to discover novel candidate materials for biomemristor with high durability and excellent biosafety for implantable health monitoring. Herein, we initially demonstrate the resistance switching characteristics of a nonvolatile memristor in a configuration of Pt/AlOOH/ITO consisting of biocompatible AlOOH nanosheets sandwiched between a Indium Tin Oxides (ITO) electrode and a platinum (Pt) counter-electrode. The hydrothermally synthesized AlOOH nanosheets have excellent biocompatibility as confirmed through the Cell Counting Kit-8 (CCK-8) tests. Four discrete resistance levels are achieved in this assembled device in responsible to different compliance currents (ICC) for the set process, where the emerging multilevel states show high durability over 103 cycles, outperforming the protein-based biomemristors under similar conditions. The excellent performance of the Pt/AlOOH/ITO memristor is attributed to the significant role of hydrogen proton with pipe effect, as confirmed by both experimental results and density functional theory (DFT) analyses. The present results indicate the nonvolatile memristors with great potential as the next generation implantable multilevel resistive memories for long-term human health monitoring.

Dramatic improvement in the mechanical properties of polydopamine/polyacrylamide hydrogel mediated human amniotic membrane.

Human amniotic membrane (hAM) is a promising material for tissue engineering due to several benefits, including desirable biocompatibility, stem cell source, antibacterial activity, etc. However, because of its low elasticity, the clinical application of hAM is severely restricted. To solve this issue, we employed polydopamine/polyacrylamide (PDA/PAM) hydrogels to toughen hAM. The test results indicated that the PDA/PAM hydrogel can enhance the toughness of hAM dramatically due to the formation of abundant chemical bonds and the strong mechanical properties of the hydrogel itself. Compared to pure hAM, the break elongation and tensile strength of PDA/PAM-toughened hAM rose by 154.15 and 492.31%, respectively. And most importantly, the fracture toughness was almost 15 times higher than untreated hAM. In addition, the cytotoxicity of the PDA/PAM-coated hAM was not detected due to the superior biocompatibility of the chemicals used in the study. Treating hAM with adhesive hydrogels to increase its mechanical characteristics will further promote the application of hAM as a tissue engineering material.

Nanoscale pulverization effect in double-layered MOF-derived hierarchical G/Co@C composites for boosting electromagnetic wave dissipation.

Metal-organic frameworks (MOFs) have drawn a lot of interest as prospective starting points for highly effective electromagnetic wave (EMW) absorbers. However, the inevitable shrinkage and probable densification that occur during pyrolysis significantly reduce the microwave-loss capacity. A dual-layer MOF, ZIF-8@ZIF-67, is created and effectively decorated on graphene sheets as a solution to this problem. The shrinkage and densification were then suppressed by the subsequent pulverization effect between the two MOFs. Due to suitable compositions and specialized microstructures, G/Co@C exhibits excellent impedance matching and dissipates EMW by combining magnetic and dielectric loss. The maximum reflection loss of G/Co@C-7/paraffin is -55.0 dB at 5.8 GHz with just 7% filler. Therefore, the preparation of high-efficiency MOF-derived microwave absorbers by the pulverization effect is demonstrated to be an efficient strategy.

Bismaleimide bridged silsesquioxane aerogels with excellent heat resistance: effect of sol-gel solvent polarity.

Due to the poor heat-resistance and intrinsic weakness of the bridging moieties in aerogel matrixes, it remains greatly challenging to fabricate highly thermostable and toughened silsesquioxane aerogels. By utilizing bismaleimide as the bridging part and optimizing the solvent polarity, lightweight (ρ < 0.09 g cm-3), compressible (80% strain) and superhydrophobic (CA ≈ 150°) bismaleimide bridged silsesquioxane aerogels (BMIT-BSAs) are constructed. The microstructure and compressive modulus of BMIT-BSAs can be tuned by the sol-gel solvents with different polarities. Moreover, stable low-temperature wettability at -196 °C and a significantly increased initial deposition temperature of 336 °C for both N2 and O2 atmospheres were measured, demonstrating the wide temperature tolerance of BMIT-BSAs.

Polydopamine decoration on 3D graphene foam and its electromagnetic interference shielding properties.

3D graphene foam was recently demonstrated to exhibit excellent electromagnetic interference (EMI) shielding performance. In this work, we prepared 3D graphene foams by incorporating a surface modification process of graphene via self-polymerization of dopamine with a subsequent foaming process. The multiple roles played by polydopamine (PDA), including as nitrogen doping source and as an enhancement tool to achieve higher extent of reduction of the graphene through providing wider pathways and larger accessible surface areas were discussed in detail. Despite the presence of the PDA which acted as barriers among the graphene layers that hindered the electrons movement, the enhanced reduction of graphene sheets and the polarization effects introduced by PDA decoration compensated the negative effect of the barrier on EMI shielding effectiveness (SE). As a result, the PDA decorated 3D graphene foams showed improved EMI shielding effectiveness (SE) compared to PDA-free graphene foam (from 23.1 to 26.5dB). More significantly, the EMI shielding performance of the PDA decorated graphene foam was much superior to all existing carbon-based porous materials when the thickness of the specimen was considered.

Mechanical, tribological and biological properties of novel 45S5 Bioglass® composites reinforced with in situ reduced graphene oxide.

45S5 Bioglass® (45S5) is one of the most widely used biomaterials in ceramic-based bone graft substitutes by virtue of its excellent biocompatibility and bioactivity. However, the fracture toughness and wear resistance of 45S5 have to be improved to extend its applications in load bearing orthopedic implants. The current study reports the first use of graphene nanoplatelet (GNP) to enhance the fracture toughness and wear resistance of 45S5. Composite powders with four different loadings of graphene oxide (GO), i.e. 0, 0.1, 0.5 and 1wt%, were sintered by spark plasma sintering (SPS) at a relatively low temperature of 550°C, during which in situ thermal reduction of GO took place. It was found that by adding 0.5wt% GO to the 45S5 powder, the fracture toughness of the sintered pellets was increased by 130.2% while friction coefficient and specific wear rate were decreased by 21.3% and 62.0%, respectively. Furthermore, the viability of MG63 cells grown on the GNP-incorporated pellets was comparably high to that of the cells grown on the pure 45S5 pellets. As compared with the pure 45S5 leachates, the media conditioned by the GNP/45S5 pellets fabricated from the composite powder with 1wt% GO could enhance both the proliferation and viability of MG63 cells. It is thus envisioned that the GNP-reinforced 45S5 is a highly promising material for fabricating mechanically strong and biocompatible load-bearing bone implants.

Single-Step Process toward Achieving Superhydrophobic Reduced Graphene Oxide.

We report the first use of spark plasma sintering (SPS) as a single-step process to achieve superhydrophobic reduced graphene oxide (rGO). It was found that SPS was capable of converting smooth and electrically insulating graphene oxide (GO) sheets into highly electrically conductive rGO with minimum residual oxygen and hierarchical roughness which could be well retained after prolonged ultrasonication. At a temperature of 500 °C, which is lower than the conventional critical temperature for GO exfoliation, GO was successfully exfoliated, reduced, and hierarchically roughened. rGO fabricated by only 1 min of treatment at 1050 °C was superhydrophobic with a surface roughness (Ra) 10 times as large as that of GO as well as an extraordinarily high C:O ratio of 83.03 (atom %) and water contact angle of 153°. This demonstrates that SPS is a superior GO reduction technique, which enabled superhydrophobic rGO to be quickly and effectively achieved in one single step. Moreover, the superhydrophobic rGO fabricated by SPS showed an impressive bacterial antifouling and inactivation effect against Escherichia coli in both aqueous solution and the solid state. It is envisioned that the superhydrophobic rGO obtained in this study can be potentially used for a wide range of industrial and biomedical applications, such as the fabrication of self-cleaning and antibacterial surfaces.

In-grown structure of NiFe mixed metal oxides and CNT hybrid catalysts for oxygen evolution reaction.

This work reports a unique in-grown structure of a NiFe-MMO/CNT hybrid catalyst. This structure creates larger interfacial area and strong interaction between the NiFe-MMO catalyst and the CNT, which could promote charge transfer at the interface, and hence improve conductivity. This leads to outstanding electrochemical performance for oxygen evolution reaction.

Growth of silver nanocrystals on graphene by simultaneous reduction of graphene oxide and silver ions with a rapid and efficient one-step approach.

A rapid and efficient one-step approach to prepare graphene-Ag nanocomposites by simultaneous reduction of graphene oxide (GO) and silver ions with formaldehyde as the reducing agent within several minutes was demonstrated.