Multiphase Reset Induced Reliable Dual-Mode Resistance Switching of the Ta/HfO2/RuO2 Memristor.

Higher functionality should be achieved within the device-level switching characteristics to secure the operational possibility of mixed-signal data processing within a memristive crossbar array. This work investigated electroforming-free Ta/HfO2/RuO2 resistive switching devices for digital- and analog-type applications through various structural and electrical analyses. The multiphase reset behavior, induced by the conducting filament modulation and oxygen vacancy generation (annihilation) in the HfO2 layer by interacting with the Ta (RuO2) electrode, was utilized for the switching mode change. Therefore, a single device can manifest stable binary switching between low and high resistance states for the digital mode and the precise 8-bit conductance modulation (256 resistance values) via an optimized pulse application for the analog mode. An in-depth analysis of the operation in different modes and comparing memristors with different electrode structures validate the proposed mechanism. The Ta/HfO2/RuO2 resistive switching device is feasible for a mixed-signal processable memristive array.

Highly parallel stateful Boolean logic gates based on aluminum-doped self-rectifying memristors in a vertical crossbar array structure.

The self-rectifying memristor with electronic bipolar resistive switching shows electroforming-free, highly rectifying properties and low operating power. Furthermore, configuring the memristors in a vertical array structure provides a higher memory density than in a planar array structure. These combined advantages can be exploited in in-memory computing, which may provide a new and efficient stateful logic gate with high parallelism compared to the conventional stateful logic gates in the planar array structure. The different switching mechanism compared to the previous logic gates based on filamentary-type switching is explained and exploited to realize the AND and OR Boolean logic gates. Since the AND and OR logic functions are the basic operations of sum-of-product (SoP) and product-of-sum (PoS) expressions, any canonical expression for Boolean logic can be implemented in the vertical crossbar array (CBA). Accordingly, the composite logic gate, such as an exclusive OR operation, is demonstrated. In addition, the implementation of the memristive priority encoder is proposed using parallel logic gates. Although the switching speed should be improved in further work, a higher parallelism with a larger number of layers in the vertical array structure can mitigate the low operation speed issue.

Lobeglitazone: A Novel Thiazolidinedione for the Management of Type 2 Diabetes Mellitus.

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and ß-cell dysfunction. Among available oral antidiabetic agents, only the thiazolidinediones (TZDs) primarily target insulin resistance. TZDs improve insulin sensitivity by activating peroxisome proliferator-activated receptor γ. Rosiglitazone and pioglitazone have been used widely for T2DM treatment due to their potent glycemic efficacy and low risk of hypoglycemia. However, their use has decreased because of side effects and safety issues, such as cardiovascular concerns and bladder cancer. Lobeglitazone (Chong Kun Dang Pharmaceutical Corporation), a novel TZD, was developed to meet the demands for an effective and safe TZD. Lobeglitazone shows similar glycemic efficacy to pioglitazone, with a lower effective dose, and favorable safety results. It also showed pleiotropic effects in preclinical and clinical studies. In this article, we summarize the pharmacologic, pharmacokinetic, and clinical characteristics of lobeglitazone.

Iron Gall Ink Revisited: In Situ Oxidation of Fe(II)-Tannin Complex for Fluidic-Interface Engineering.

The ancient wisdom found in iron gall ink guides this work to a simple but advanced solution to the molecular engineering of fluidic interfaces. The Fe(II)-tannin coordination complex, a precursor of the iron gall ink, transforms into interface-active Fe(III)-tannin species, by oxygen molecules, which form a self-assembled layer at the fluidic interface spontaneously but still controllably. Kinetic studies show that the oxidation rate is directed by the counteranion of Fe(II) precursor salts, and FeCl2 is found to be more effective than FeSO4 -an ingredient of iron gall ink-in the interfacial-film fabrication. The optimized protocol leads to the formation of micrometer-thick, free-standing films at the air-water interface by continuously generating Fe(III)-tannic acid complexes in situ. The durable films formed are transferable, self-healable, pliable, and postfunctionalizable, and are hardened further by transfer to the basic buffer. This O2 -instructed film formation can be applied to other fluidic interfaces that have high O2 level, demonstrated by emulsion stabilization and concurrent capsule formation at the oil-water interface with no aid of surfactants. The system, inspired by the iron gall ink, provides new vistas on interface engineering and related materials science.

Salt-Induced, Continuous Deposition of Supramolecular Iron(III)-Tannic Acid Complex.

One-step assembly of iron(III)-tannic acid (Fe3+-TA) complex forms nanothin (∼10 nm) films on various substrates within minutes. In this deposition scheme, however, the film does not grow continuously over time even though Fe3+-TA complex is still abundant in the coating solution. In this paper, we report that the salt addition dramatically changes the one-off coating characteristic to continuous one, and each salt has its optimum concentration ( CMFT) that produces maximum film thickness. For detailed investigation of the salt effects, we employed various salts, including LiCl, NaCl, KCl, CaCl2, SrCl2, BaCl2, NaBr, and NaNO3, and found that only cations played an important role in the continuous deposition of the Fe3+-TA complex, with smaller CMFT values for the cations of higher valency and larger size. On the basis of the results, we suggested that the positively charged cations screened the negative surface charges of Fe3+-TA complex particles, leading to coagulation and continuous deposition, further supported by the ζ-potential measurement and time-resolved dynamic light-scattering analysis.

Quantifying van der Waals Interactions in Layered Transition Metal Dichalcogenides from Pressure-Enhanced Valence Band Splitting.

van der Waals (vdW) forces, despite being relatively weak, hold the layers together in transition metal dichalcogenides (TMDs) and play a key role in their band structure evolution, hence profoundly affecting their physical properties. In this work, we experimentally probe the vdW interactions in MoS2 and other TMDs by measuring the valence band maximum (VBM) splitting (Δ) at K point as a function of pressure in a diamond anvil cell. As high pressure increases interlayer wave function coupling, the VBM splitting is enhanced in 2H-stacked MoS2 multilayers but, due to its specific geometry, not in 3R-stacked multilayers, hence allowing the interlayer contribution to be separated out of the total VBM splitting, as well as predicting a negative pressure (2.4 GPa) where the interlayer contribution vanishes. This negative pressure represents the threshold vdW interaction beyond which neighboring layers are electronically decoupled. This approach is compared to first-principles calculations and found to be widely applicable to other group-VI TMDs.

Artificial Spores: Immunoprotective Nanocoating of Red Blood Cells with Supramolecular Ferric Ion-Tannic Acid Complex.

The blood-type-mismatch problem, in addition to shortage of blood donation, in blood transfusion has prompted the researchers to develop universal blood that does not require blood typing. In this work, the "cell-in-shell" (i.e., artificial spore) approach is utilized to shield the immune-provoking epitopes on the surface of red blood cells (RBCs). Individual RBCs are successfully coated with supramolecular metal-organic coordination complex of ferric ion (FeIII) and tannic acid (TA). The use of isotonic saline (0.85% NaCl) is found to be critical in the formation of stable, reasonably thick (20 nm) shells on RBCs without any aggregation and hemolysis. The formed "RBC-in-shell" structures maintain their original shapes, and effectively attenuate the antibody-mediated agglutination. Moreover, the oxygen-carrying capability of RBCs is not deteriorated after shell formation. This work suggests a simple but fast method for generating immune-camouflaged RBCs, which would contribute to the development of universal blood.

Pressurizing Field-Effect Transistors of Few-Layer MoS2 in a Diamond Anvil Cell.

Hydrostatic pressure applied using diamond anvil cells (DAC) has been widely explored to modulate physical properties of materials by tuning their lattice degree of freedom. Independently, electrical field is able to tune the electronic degree of freedom of functional materials via, for example, the field-effect transistor (FET) configuration. Combining these two orthogonal approaches would allow discovery of new physical properties and phases going beyond the known phase space. Such experiments are, however, technically challenging and have not been demonstrated. Herein, we report a feasible strategy to prepare and measure FETs in a DAC by lithographically patterning the nanodevices onto the diamond culet. Multiple-terminal FETs were fabricated in the DAC using few-layer MoS2 and BN as the channel semiconductor and dielectric layer, respectively. It is found that the mobility, conductance, carrier concentration, and contact conductance of MoS2 can all be significantly enhanced with pressure. We expect that the approach could enable unprecedented ways to explore new phases and properties of materials under coupled mechano-electrostatic modulation.

Artificial Spores: Cytocompatible Coating of Living Cells with Plant-Derived Pyrogallol.

Cell nanoencapsulation, generating cell-in-shell structures ("artificial spores"), provides a chemical toolbox for controlling the cellular behaviors and functional characteristics of individual cells. Among the shell materials studied so far, naturally occurring polyphenolic compounds, including polydopamine and tannic acid, have intensively been employed in cell-surface engineering, because their material-independent coating property eliminates an extra priming step for inducing subsequent shell formation. Albeit successful in generating cell-in-shell structures, the coating of polyphenolic compounds generally requires alkaline conditions and/or high salt conditions, which are not compatible with certain cell types. In this work, we demonstrate that the nanocoating of individual cells with a plant-derived phenolic compound, pyrogallol (1,2,3-trihydroxybenzene), occurs at mildly alkaline pH of 7.8 in an isotonic buffer. Three different cell types (anucleate, microbial, and mammalian cells) are coated with pyrogallol without noticeable decrease in cell viability. The protocol developed in this work could be applied to other polyphenolic compounds, and, considering the many polyphenols identified as a coating material, provides an advanced chemical tool in cell-surface engineering.

A degradable polydopamine coating based on disulfide-exchange reaction.

Although the programmed degradation of biocompatible films finds applications in various fields including biomedical and bionanotechnological areas, coating methods have generally been limited to be substrate-specific, not applicable to any kinds of substrates. In this paper, we report a dopamine derivative, which allows for both universal coating of various substrates and stimuli-responsive film degradation, inspired by mussel-adhesive proteins. Two dopamine moieties are linked together by the disulfide bond, the cleavage of which enables the programmed film degradation. Mechanistic analysis of the degradable films indicates that the initial cleavage of the disulfide linkage causes rapid uptake of water molecules, hydrating the films, which leads to rapid degradation. Our substrate-independent coating of degradable films provides an advanced tool for drug delivery systems, tissue engineering, and anti-fouling strategies.

Control of Microbial Growth in Alginate/Polydopamine Core/Shell Microbeads.

Microbial microencapsulation not only protects microorganisms from harmful environments by physically isolating them from the outside media but also has the potential to tailor the release profile of the encapsulated cells. However, the microbial release has not yet been controlled tightly, leading to undesired detrimental exposure of microorganisms to the outside. In this work, we suggest a simple method for controlling the cell release by suppressing the microbial growth in the microbeads. Alginate microbeads, encapsulating yeast cells, were coated with ultrathin but robust polydopamine shells, and the resulting core/shell structures effectively reduced the growth rate, while maintaining the cell viability.

Cytoprotective alginate/polydopamine core/shell microcapsules in microbial encapsulation.

Chemical encapsulation of microbes in threedimensional polymeric microcapsules promises various applications, such as cell therapy and biosensors, and provides a basic platform for studying microbial communications. However, the cytoprotection of microbes in the microcapsules against external aggressors has been a major challenge in the field of microbial microencapsulation, because ionotropic hydrogels widely used for microencapsulation swell uncontrollably, and are physicochemically labile. Herein, we developed a simple polydopamine coating for obtaining cytoprotective capability of the alginate capsule that encapsulated Saccharomyces cerevisiae. The resulting alginate/ polydopamine core/shell capsule was mechanically tough, prevented gel swelling and cell leakage, and increased resistance against enzymatic attack and UV-C irradiation. We believe that this multifunctional core/shell structure will provide a practical tool for manipulating microorganisms inside the microcapsules.