Highly Flexible, Self-Bonding, Self-Healing, and Conductive Soft Pressure Sensors Based on Dicarboxylic Cellulose Nanofiber Hydrogels.

Conductive hydrogels have gained a great deal of interest in the flexible electronics industry because of their remarkable inherent properties. However, a significant challenge remains for balancing hydrogel's conductivity, self-healing, and strength properties. Herein, double network ionic hydrogels were fabricated by concurrently introducing borax into dicarboxylic cellulose nanofiber (DCNFs) and polyacrylamide (PAM) hydrogels. The incorporation of borax provided a superabsorbent feature to the PAM/DCNF hydrogels (without borax) with the equilibrium water absorption rate increased from 552 to 1800% after 42 h. The compressive strength of the prepared hydrogel was 935 kPa compared to 132 kPa for the PAM hydrogel, with high cycling stability (stable after 1000 compression cycles with 50% strain). The hydrogel pressure sensor had a very sensitive response (gauge factor = 1.36) in the strain range from 10 to 80%, which made it possible to detect mechanical motion accurately and reliably. The developed hydrogels with high-performance, environmentally friendly properties are promising for use in future artificial skin and human-machine interface applications.

Catalytic Growth of Ultralong Graphene Nanoribbons on Insulating Substrates.

Graphene nanoribbons (GNRs) with widths of a few nanometers are promising candidates for future nanoelectronic applications due to their structurally tunable bandgaps, ultrahigh carrier mobilities, and exceptional stability. However, the direct growth of micrometer-long GNRs on insulating substrates, which is essential for the fabrication of nanoelectronic devices, remains an immense challenge. Here, the epitaxial growth of GNRs on an insulating hexagonal boron nitride (h-BN) substrate through nanoparticle-catalyzed chemical vapor deposition is reported. Ultranarrow GNRs with lengths of up to 10 µm are synthesized. Remarkably, the as-grown GNRs are crystallographically aligned with the h-BN substrate, forming 1D moiré superlattices. Scanning tunneling microscopy reveals an average width of 2 nm and a typical bandgap of ≈1 eV for similar GNRs grown on conducting graphite substrates. Fully atomistic computational simulations support the experimental results and reveal a competition between the formation of GNRs and carbon nanotubes during the nucleation stage, and van der Waals sliding of the GNRs on the h-BN substrate throughout the growth stage. This study provides a scalable, single-step method for growing micrometer-long narrow GNRs on insulating substrates, thus opening a route to explore the performance of high-quality GNR devices and the fundamental physics of 1D moiré superlattices.

High-density adherent culture of CHO cells using rolled scaffold bioreactor.

Rapid expansion of biopharmaceutical market calls for more efficient and reliable platforms to culture mammalian cells on a large scale. Stirred-tank bioreactors have been widely used for large-scale cell culture. However, it requires months of trials and errors to optimize culture conditions for each cell line. In this article, we extend our earlier studies on rolled scaffold (RS) bioreactors for high-density adherent cell culture and report two new implementations of RSs with greatly enhanced mass-manufacturability, termed as Mesh-RS and Fiber-RS. CHO-K1 cells were successfully expanded in Mesh-RS and Fiber-RS bioreactors with an average growth rate of 1.09 ± 0.04 1/day and 0.95 ± 0.07 1/day, which were higher than those reported in similar studies. Fiber-RS bioreactor exhibited a very high cell density of 72.8 × 106 cells/ml. Besides, a dialyzer was integrated into the RS bioreactor to remove cellular waste and to replenish nutrients without disturbing the cells. By collecting the dialyzed media separately, the dialysis efficiency was significantly improved. In conclusion, the developed RS bioreactor has a strong potential to provide a highly reliable and easily scalable platform for large-scale cell culture in the biopharmaceutical industry.

In-situ twistable bilayer graphene.

The electrical and optical properties of twisted bilayer graphene (tBLG) depend sensitively on the twist angle. To study the angle dependent properties of the tBLG, currently it is required fabrication of a large number of samples with systematically varied twist angles. Here, we demonstrate the construction of in-situ twistable bilayer graphene, in which the twist angle of the two graphene monolayers can be in-situ tuned continuously in a large range with high precision. The controlled tuning of the twist angle is confirmed by a combination of real-space and spectroscopic characterizations, including atomic force microscopy (AFM) identification of crystal lattice orientation, scanning near-field optical microscopy (SNOM) imaging of superlattice domain walls, and resonant Raman spectroscopy of the largely enhanced G-mode. The developed in-situ twistable homostructure devices enable systematic investigation of the twist angle effects in a single device, thus could largely advance the research of twistronics.

Direct imaging of interlayer-coupled symmetric and antisymmetric plasmon modes in graphene/hBN/graphene heterostructures.

Much of the richness and variety of physics today are based on coupling phenomena where multiple interacting systems hybridize into new ones with completely distinct attributes. Recent development in building van der Waals (vdWs) heterostructures from different 2D materials provides exciting possibilities in realizing novel coupling phenomena in a designable manner. Here, with a graphene/hBN/graphene heterostructure, we report near-field infrared nano-imaging of plasmon-plasmon coupling in two vertically separated graphene layers. Emergent symmetric and anti-symmetric coupling modes are directly observed simultaneously. Coupling and decoupling processes are systematically investigated with experiment, simulation and theory. The reported interlayer plasmon-plasmon coupling could serve as an extra degree of freedom to control light propagation at the deep sub-wavelength scale with low loss and provide exciting opportunities for optical chip integration.