Tough and Strain-Sensitive Organohydrogels Based on MXene and PEDOT/PSS and Their Effects on Mechanical Properties and Strain-Sensing Performance.

Conductive hydrogels have shown promising application prospects in the field of flexible sensors, but they often suffer from poor mechanical properties, low sensitivity, and lack of frost resistance. Herein, we report a tough, highly sensitive, and antifreeze strain sensor assembled from a conductive organohydrogel composed of a dual-cross-linked polyacrylamide and poly(vinyl alcohol) (PVA) network, as well as MXene nanosheets as nanofillers and poly(3,4-ethylenedioxythiophene)-doped poly(styrenesulfonate) (PEDOT/PSS) as the main conducting component (PPMP-OH organohydrogel). The tensile strength and toughness of PPMP-OH had been greatly enhanced by MXene nanosheets due to the mechanical reinforcement of MXene nanosheets, as well as various strong noncovalent interactions formed in the organohydrogels. The PPM1P-OH organohydrogels showed a tensile strength of 1.48 MPa at 772% and a toughness of 5.59 MJ/m3. Moreover, the conductivity and strain-sensing performance of PPMP-OH were significantly improved by PEDOT/PSS, which can form hydrogen bonds with PVA and electrostatic interactions with MXene. This was greatly beneficial for constructing a uniformly distributed and stable 3D conductive network and helped to obtain strain-dependent resistance of PPMP-OH. The strain sensors assembled from PPMP1-OH exhibited a high sensitivity of 5.16, a wide range of detectable strains up to 500%, and a short response time of 122 ms, which can effectively detect various physiological activities of the human body with high stability. In addition, the corresponding pressure sensor array also showed high sensitivity in identifying pressure magnitude and position.

Bottom-Up Construction of Electrochemically Active Living Filters: From Graphene Oxide Mediated Formation of Bacterial Cables to 3D Assembly of Hierarchical Architectures.

Living composites comprising of both biotic and abiotic modules are shifting the paradigm of materials science, yet challenges remain in effectively converging their distinctive structural and functional attributes. Here we present a bottom-up hybridization strategy to construct functionally coherent, electrochemically active biohybrids with optimal mass/charge transport, mechanical integrity, and biocatalytic performance. This biohybrid can overcome several key limitations of traditional biocarrier designs and demonstrate superior efficiency in metabolizing low-concentration toxic ions with minimal environmental impact. Overall, this work exemplifies a biointegration strategy that complements existing synthetic biology toolsets to further expand the range of material attributes and functionalities.

Enhanced activity and stability of papain by covalent immobilization on porous magnetic nanoparticles.

Papain enzyme was successfully immobilized by covalent bonding onto biocompatible Fe3O4/SF nanoparticles, which were prepared with the soft template of silk fibroin (SF). The optimized immobilization condition is pH6.0, hydrolysis time of 60min, and an enzyme/support ratio of 10.0mg/g. Compared with free papain, the immobilized papain exhibits a high effective activity, broader working pH and temperature. This immobilized papain can be separated from the solution by the external magnetic field for cyclic utilization, and 70% of initial activity was retained after eight consecutive operations while completely loss of proteolytic activity for the free papain. Furthermore, the immobilized papain maintained 85% of their initial activity after being stored for 28days. Kinetic parameters, maximum reaction rate (Vmax) and Michaelis constant (Km) of immobilized papain, were determined as 4.95mg/l·min and 0.23mg/ml, larger than its free counterpart. All the results above indicated that the immobilized papain onto magnetic Fe3O4/SF nanoparticles would have potential industrial and medical applications.

Sensitive detection of dopamine via leucodopaminechrome on polyacrylic acid-coated ceria nanorods.

The major hurdle in detection of dopamine (DA) by electro-analysis is the presence of physiological interferents with a similar oxidation potential of DA. The conventional method is to enlarge the difference of their oxidation potentials. Here, we report an unconventional method to detect DA via leucodopaminechrome on CeO2 nanorods. Leucodopaminechrome is produced from the cyclization of dopamine-quinone, a product of two-electron oxidation of DA. Thus, its concentration is proportional to the DA concentration. Determining DA is demonstrated by measuring the reduction current of leucodopaminechrome on CeO2 nanorods. CeO2 nanorods demonstrate high electrocatalytic activity for reduction of leucodopaminechrome with a low potential at -0.27 V. The low detection potential of leucodopaminechrome can avoid the interference from ascorbic acid (AA) and uric acid (UA). Therefore, detecting DA via leucodopaminechrome is an effective method to avoid interference from AA and UA, and the suggested biosensor also displays good reproducibility and stability.

Facile synthesis of the Ti3+ self-doped TiO2-graphene nanosheet composites with enhanced photocatalysis.

This study developed a facile approach for preparing Ti(3+) self-doped TiO2-graphene photocatalyst by a one-step vacuum activation technology involved a relative lower temperature, which could be activated by the visible light owing to the synergistic effect among Ti(3+) doping, some new intersurface bonds generation and graphene oxide reduction. Compared with the traditional methods, the vacuum activation involves a low temperature and low-costing, which can achieve the reduction of GO, the self doping of Ti(3+) in TiO2 and the loading of TiO2 nanoparticles on GR surface at the same time. These resulting TiO2-graphene composites show the high photodegradation rate of MO, high hydrogen evolution activity and excellent IPCE in the visible light irradiation. The facile vacuum activation method can provide an effective and practical approach to improve the performance of TiO2-graphene and other metal oxides-graphene towards their practical photocatalytic applications.

Silk-regulated hierarchical hollow magnetite/carbon nanocomposite spheroids for lithium-ion battery anodes.

Hierarchical olive-like structured carbon-Fe3O4 nanocomposite particles composed of a hollow interior and a carbon coated surface are prepared by a facile, silk protein-assisted hydrothermal method. Silk nanofibers as templates and carbon precursors first regulate the formation of hollow Fe2O3 microspheres and then they are converted into carbon by a reduction process into Fe3O4. This process significantly simplifies the fabrication and carbon coating processes to form complex hollow structures. When tested as anode materials for lithium-ion batteries, these hollow carbon-coated particles exhibit high capacity (900 mAh g(-1)), excellent cycle stability (180 cycles) and rate performance due to their unique hierarchical hollow structure and carbon coating.

Reversible hydrogel-solution system of silk with high beta-sheet content.

Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The ß-sheet-rich natural nanofiber units of about 10-50 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of ß-sheet-rich silk nanofibers about 10-20 nm in diameter is reported here, where these nanofibers formed into "flowing hydrogels" at 0.5-2% solutions and could be transformed back into the solution state at lower concentrations, even with a high ß-sheet content. This is in contrast with other silk processed materials, where significant ß-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting ß-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above -50 mV) than previous silk materials which tend to be below -30 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of ß-sheet-rich silk nanofibers, resulting in reversible hydrogel-solution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of ß-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature.

One-step synthesis of biocompatible magnetite/silk fibroin core-shell nanoparticles.

A one-step hydrothermal process with silk fibroin (SF) nanofibers as the template and coating was developed to synthesize core-shell magnetite/SF nanoparticles with limited controllable sizes. The Fe3O4 nanoparticles gradually aggregated into nanospheres with sizes increased from 120 to 500 nm by increasing the SF content in the reaction system. The magnetic properties and biocompatibility of Fe3O4/SF nanoparticles, as well as their functional ability with antibodies are also discussed to assess their possible applications in MRI and bio-separation. Compared to previous two-step processes, our one-step method provides a simpler and more cost-effective approach to prepare biocompatible core-shell magnetite nanoparticles.