Switchable tribology of ferroelectrics.

Switchable tribological properties of ferroelectrics offer an alternative route to visualize and control ferroelectric domains. Here, we observe the switchable friction and wear behavior of ferroelectrics using a nanoscale scanning probe-down domains have lower friction coefficients and show slower wear rates than up domains and can be used as smart masks. This asymmetry is enabled by flexoelectrically coupled polarization in the up and down domains under a sufficiently high contact force. Moreover, we determine that this polarization-sensitive tribological asymmetry is widely applicable across various ferroelectrics with different chemical compositions and crystalline symmetry. Finally, using this switchable tribology and multi-pass patterning with a domain-based dynamic smart mask, we demonstrate three-dimensional nanostructuring exploiting the asymmetric wear rates of up and down domains, which can, furthermore, be scaled up to technologically relevant (mm-cm) size. These findings demonstrate that ferroelectrics are electrically tunable tribological materials at the nanoscale for versatile applications.

Reducing Time to Discovery: Materials and Molecular Modeling, Imaging, Informatics, and Integration.

Multiscale and multimodal imaging of material structures and properties provides solid ground on which materials theory and design can flourish. Recently, KAIST announced 10 flagship research fields, which include KAIST Materials Revolution: Materials and Molecular Modeling, Imaging, Informatics and Integration (M3I3). The M3I3 initiative aims to reduce the time for the discovery, design and development of materials based on elucidating multiscale processing-structure-property relationship and materials hierarchy, which are to be quantified and understood through a combination of machine learning and scientific insights. In this review, we begin by introducing recent progress on related initiatives around the globe, such as the Materials Genome Initiative (U.S.), Materials Informatics (U.S.), the Materials Project (U.S.), the Open Quantum Materials Database (U.S.), Materials Research by Information Integration Initiative (Japan), Novel Materials Discovery (E.U.), the NOMAD repository (E.U.), Materials Scientific Data Sharing Network (China), Vom Materials Zur Innovation (Germany), and Creative Materials Discovery (Korea), and discuss the role of multiscale materials and molecular imaging combined with machine learning in realizing the vision of M3I3. Specifically, microscopies using photons, electrons, and physical probes will be revisited with a focus on the multiscale structural hierarchy, as well as structure-property relationships. Additionally, data mining from the literature combined with machine learning will be shown to be more efficient in finding the future direction of materials structures with improved properties than the classical approach. Examples of materials for applications in energy and information will be reviewed and discussed. A case study on the development of a Ni-Co-Mn cathode materials illustrates M3I3's approach to creating libraries of multiscale structure-property-processing relationships. We end with a future outlook toward recent developments in the field of M3I3.

Nanoscale effects of beverages on enamel surface of human teeth: An atomic force microscopy study.

Dental erosion has become a prevalence disease and attracted increasing attention worldwide. In this research, we quantitatively evaluate the mechanical and morphological changes in the very early stages of softening and weakening of human enamel surfaces induced by soft drinks using atomic force microscopy (AFM). With an increase of the immersion time in soft drinks, we found a significant increase of surface roughness (Rq) of the enamel surface. The prismatic structure of enamel was clearly observed after a 1-h immersion in Coca-Cola®, which shows its strong erosion effect. According to the elastic modulus mapping images obtained by AFM, a considerable decrease of elastic modulus (E) of enamel surface has been found as the enamel surface structures are etched away by soft drinks. A high surface roughness of enamel will result in a high chance of cavities due to easier bacterial adhesion on rougher surface, while a drastic deterioration of the mechanical properties of the enamel will weaken its protection property. Our findings show the serious influence of acidic drinks on enamel surface at the very beginning stage of etching process, which is quite meaningful for people to prevent dental erosion and keep dental health.

The effect of hypertonic saline on mRNA of proinflammatory cytokines in lipopolysaccharide-stimulated polymorphonuclear cells.

BACKGROUND: Hypertonic saline is often used to resuscitate patients experiencing shock. In such conditions, polymorphonuclear cells and Toll-like receptors (TLRs) form an essential part of early induced innate immunity. OBJECTIVE: To investigate the immunomodulatory effect of hypertonic saline on polymorphonuclear cells by evaluating the changes in TLR-4 receptors and proinflammatory cytokines. METHODS: Polymorphonuclear cells were isolated from whole blood using Polymorphprep (Axis-Shield, Oslo, Norway). The isolated polymorphonuclear cells were plated at a density of 1 × 10(6) cells/mL in 6-well flat-bottomed culture plates and were stimulated with 1 µg/mL lipopolysaccharide or N-formyl-methionyl-leucyl-phenylalanine. The stimulated polymorphonuclear cells were cultured in hypertonic saline at 10, 20, or 40 mmol/L above isotonicity. After that, the changes in TLR-4 and cytokines were measured by quantitative real-time polymerase chain reaction and flow cytometry. RESULTS: The level of TLR-4 mRNA expression decreased after stimulation with N-formyl-methionyl-leucyl-phenylalanine, but hypertonic saline did not affect the TLR-4 mRNA expression. TLR-4 mRNA expression was clearly induced upon stimulation with lipopolysaccharide, and the addition of hypertonic saline restored TLR-4 mRNA expression in polymorphonuclear cells. The interleukin-1ß mRNA expression was decreased in the hypertonic environment. On the other hand, the tumor necrosis factor-α value was not influenced by the addition of hypertonic saline. CONCLUSIONS: Hypertonic saline has an immunomodulatory effect on polymorphonuclear cells through the TLR-4 pathway, and the interleukin-1ß-associated pathway is influenced more by hypertonic saline than is the tumor necrosis factor-α-associated pathway.