BNNT vs. CNT: influence of structural defects on damping characteristics of nanocomposites.

The viscoelastic damping of nanocomposites reinforced with BNNTs and CNTs was compared. MD simulations revealed that the interfacial damping of pristine-CNT was superior to that of pristine-BNNT. The contrasting effects of structural defects were elucidated using interfacial adhesion, interphase, and overlapping phonon density of states in the nanotubes and polymers.

Mesoscale Simulation of Polymer Pyrolysis by Coarse-Grained Molecular Dynamics: A Parametric Study.

Full comprehension of the pyrolysis of polymer materials is crucial for the design and application of thermal protection systems; however, it involves complex phenomena at different spatial and temporal scales. To bridge the gap between the abundant atomistic simulations and continuum modeling in the literature, we perform a novel mesoscale study of the pyrolysis process using coarse-grained molecular dynamics (CG MD) simulations. Polyethylene (PE) consisting of united atoms including implicit hydrogen is considered a model polymer, and the configurational change of PE in thermal degradation is modeled by applying the bond-breaking phenomenon based on bond energy or bond length criteria. A cook-off simulation is implemented to optimize the heuristic protocol of bond dissociation by comparing the reaction products with a ReaxFF simulation. The aerobic hyperthermal pyrolysis under oxygen bombardment is simulated at a large scale of hundreds of nanometers to observe the intricate phenomena occurring from the surface to the depth inside the material. The intrinsic thermal durability of the model polymer at extreme conditions with and without oxygen environment can be effectively simulated from the proposed mesoscale simulation to predict important thermal degradation properties required for continuum-scale pyrolysis and ablation simulations. This work serves as an initial investigation of polymer pyrolysis at the mesoscale and helps understand the concept at a larger scale.

Piezoelectric and dielectric constants of topologically defected boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) form a promising low-dimensional piezoelectric material that may be used for multifunctional energy-harvesting nanopiezoelectronic devices. The piezoelectric and dielectric constants of a single-walled BNNT are determined via a molecular dynamics simulation with several Tersoff-like potential models and Born effective charges. The effect of Stone-Wales (SW) defects on the electroelastic behavior of BNNTs is considered, owing to their importance in determining the multifunctionality of BNNTs. Both solid and hollow cylinder structures are considered as equivalent continuous tubular structures that represent the BNNT in terms of electroelasticity. Direct and reverse piezoelectricity of the BNNTs are simulated by applying elastic strain and a constant electric field along the longitudinal direction of each tube, respectively. The initial polarization of the BNNTs changes, owing to the rotation of boron and nitrogen atoms. The Tersoff potential model considered herein predicts an increase in the dielectric constant with the SW defect, which is attributable to the opposite electric displacement of nitrogen and boron atoms under an electric field. It is also observed that the elastic modulus of BNNTs is degraded by the SW defect. However, the piezoelectric constants of the BNNTs either increase or decrease as the SW defect accumulates, exhibiting a strong dependency on the applied Tersoff potential model. The performance of each Tersoff potential model in describing the geometry of the SW defect and the effect of a change in polarization and electric displacement on the electroelasticity of BNNTs is discussed. The results herein offer a deep insight into the application of BNNTs to nanopiezoelectronics and a guideline to designing the optimal BNNT composition and topology for multifunctional energy-harvesting nanocomposites.

Ethyl Gallate Isolated from Castanopsis cuspidata var. sieboldii Branches Inhibits Melanogenesis and Promotes Autophagy in B16F10 Cells.

The Castanopsis cuspidata var. sieboldii (CCS) plant grows predominantly in temperate regions of Asian countries, such as South Korea. Research on CCS has so far concentrated on the nutritional analysis, antioxidant activity, and anti-inflammation properties of its branches. However, the isolation of compounds and structural elucidation of effective single molecules remain unexplored, necessitating further exploration of CCS branches. Therefore, this study demonstrates the antioxidant and antimelanogenic activity of a single substance of ethyl gallate (EG) isolated from CCS branch extracts. Notably, the antimelanogenic (whitening) activity of EG extracted from CCS branches remains unexplored. Tyrosinase inhibition, kinetic enzyme assays, and molecular docking studies were conducted using mushroom tyrosinase in order to examine the antioxidant mechanism and antimelanin activity of EG in B16F10 melanoma cells. Nontoxic EG concentrations were found to be below 5 µg/mL. While EG significantly reduced the levels of whitening-associated proteins, p-CREB, and p-PKA, it dose-dependently inhibited the expression of TYR, TRP-1, TRP-2, and transcription factor (MITF). In addition, EG downregulated melanogenetic gene expression and activated autophagy signals. Therefore, EG extracted from CCS branches could serve as a novel functional cosmetic material with antimelanogenic and autophagy-enhancing activity.

Gastric Hyperplastic Polyp Causing Upper Gastrointestinal Hemorrhage and Severe Anemia in a Dog.

An 11-year-old castrated male Shih Tzu was referred for lethargy and melena. The hematocrit level was 18.8% (normal range: 36-56%), indicating severe anemia. Abdominal ultrasound revealed a round-to-oval-shaped mass in the stomach. Computed tomography (CT) revealed an intraluminal mass (17 × 12 × 15 mm) cranial to the pyloric antrum. After obtaining informed consent from the owner, exploratory laparotomy and subsequent gastrostomy were performed, showing an ulcerated mass potentially responsible for the severe anemia. A lump of hair was firmly attached to the ulcerated surface of the mass. After complete removal of the mass, the anemia resolved spontaneously. Histological examination revealed that the mass was a gastric hyperplastic polyp. At the 6-month follow-up, the dog was healthy with a normal hematocrit level. Gastric hyperplastic polyps are tumor-like lesions arising from the mucosal surface of the stomach, and projecting into the lumen. They can appear in any part of the stomach, and are usually found incidentally during gastric endoscopy or necropsy. The clinical signs include chronic occult blood loss, abdominal pain, and gastric tract obstruction. Gastric polyps causing acute blood loss anemia have rarely been reported in human medicine. To our knowledge, this is the first report describing a gastric hyperplastic polyp that caused severe anemia because of acute blood loss in a dog.

Nomilin from Yuzu Seed Has In Vitro Antioxidant Activity and Downregulates Melanogenesis in B16F10 Melanoma Cells through the PKA/CREB Signaling Pathway.

Yuzu (Citrus junos) is a citrus plant native to Asian countries, including Korea, Japan, and China. Yuzu peel and seed contain abundant vitamin C, citric acid, and polyphenols. Although the antioxidative and antimelanogenic activities of other citrus fruits and yuzu extract have been reported, the tyrosinase inhibitory activity of the limonoid aglycone contained in yuzu seed extract is unknown. We separated yuzu seeds into the husk, shell, and meal and evaluated antioxidant activity of each. The limonoid glucoside fraction of the husk identified nomilin, a novel tyrosinase inhibitor. We performed tyrosinase inhibitory activity and noncompetitive inhibition assays and docking studies to determine nomilin binding sites. Furthermore, we evaluated the antioxidative mechanism and antimelanogenic activity of nomilin in B16F10 melanoma cells. The concentration of nomilin that did not show toxicity was <100 µg/mL. Nomilin suppressed protein expression of TYR, TRP-1, TRP-2, and microphthalmia-associated transcription factor (MITF) in a concentration-dependent manner. Nomilin significantly reduced the levels of p-CREB and p-PKA at the protein level and decreased the levels of skin-whitening-related factors MITF, tyrosinase, TRP-1, and TRP-2 at the mRNA level in a concentration-dependent manner. Thus, nomilin from yuzu seed husk can be used as a skin-whitening agent in cosmetics.

Bamboo Lignin Fractions with In Vitro Tyrosinase Inhibition Activity Downregulate Melanogenesis in B16F10 Cells via PKA/CREB Signaling Pathway.

Cosmetic ingredients originating from natural resources have garnered considerable attention, and the demand for whitening ingredients is increasing, particularly in Asian countries. Lignin is a natural phenolic biopolymer significantly effective as a natural sunscreen, as its ultraviolet protection efficacy ranges from 250 to 400 nm. However, using different types of lignin as cosmetic ingredients is difficult owing to the heterogeneity of lignin and the lack of in vitro and in vivo safety and efficacy data. Thus, steam-exploded lignin (SEL) was prepared from bamboo, fractionated via successive organic solvent extraction, and sequentially fractionated using ethyl acetate, methanol, and acetone to investigate its potential as a natural whitening material. Gel permeation chromatography showed that the molecular weight of acetone-soluble and acetone-insoluble SEL fractions were the lowest and the highest, respectively. Monomer structures of the four lignin fractions were elucidated using 1H, 13C, and 2D heteronuclear single quantum coherence nuclear magnetic resonance and pyrolysis gas chromatography/mass spectrometry. The antioxidant and tyrosinase inhibition activities of the four fractions were compared. The methanol-soluble SEL fraction (SEL-F2) showed the highest antioxidant activity (except 2,2-diphenyl-1-picrylhydrazyl scavenging activity), and the enzyme inhibition kinetics were confirmed. In this study, the expression pattern of the anti-melanogenic-related proteins by SEL-F2 was confirmed for the first time via the protein kinase A (PKA)/cAMP-response element-binding (CREB) protein signaling pathway in B16F10 melanoma cells. Thus, SEL may serve as a valuable cosmetic whitening ingredient.

Understanding Covalent Grafting of Nanotubes onto Polymer Nanocomposites: Molecular Dynamics Simulation Study.

Here, we systematically interrogate the effects of grafting single-walled (SWNT) and multi-walled carbon nanotubes (MWNT) to polymer matrices by using molecular dynamics (MD) simulations. We specifically investigate key material properties that include interfacial load transfer, alteration of nanotube properties, and dispersion of nanotubes in the polymer matrix. Simulations are conducted on a periodic unit cell model of the nanocomposite with a straight carbon nanotube and an amorphous polyethylene terephthalate (PET) matrix. For each type of nanotube, either 0%, 1.55%, or 3.1% of the carbon atoms in the outermost nanotubes are covalently grafted onto the carbon atoms of the PET matrix. Stress-strain curves and the elastic moduli of nanotubes and nanocomposites are determined based on the density of covalent grafting. Covalent grafting promotes two rivalling effects with respect to altering nanotube properties, and improvements in interfacial load transfer in the nanocomposites are clearly observed. The enhanced interface enables external loads applied to the nanocomposites to be efficiently transferred to the grafted nanotubes. Covalent functionalization of the nanotube surface with PET molecules can alter the solubility of nanotubes and improve dispersibility. Finally, we discuss the current limitations and challenges in using molecular modelling strategies to accurately predict properties on the nanotube and polymers systems studied here.

Novel Quercetin Derivative of 3,7-Dioleylquercetin Shows Less Toxicity and Highly Potent Tyrosinase Inhibition Activity.

Quercetin is a well-known plant flavonol and antioxidant; however, there has been some debate regarding the efficacy and safety of native quercetin as a skin-whitening agent via tyrosinase inhibition. Several researchers have synthesized quercetin derivatives as low-toxicity antioxidants and whitening agents. However, no suitable quercetin derivatives have been reported to date. In this study, a novel quercetin derivative was synthesized by the SN2 reaction using quercetin and oleyl bromide. The relationship between the structures and activities of quercetin derivatives as anti-melanogenic agents was assessed using in vitro enzyme kinetics, molecular docking, and quenching studies; cell line experiments; and in vivo zebrafish model studies. Novel 3,7-dioleylquercetin (OQ) exhibited a low cytotoxic concentration level at >100 µg/mL (125 µM), which is five times less toxic than native quercetin. The inhibition mechanism showed that OQ is a competitive inhibitor, similar to native quercetin. Expression of tyrosinase, tyrosinase-related protein 1 (TRP-1) and tyrosinase-related protein 2 (TRP-2), and microphthalmia-associated transcription factor was inhibited in B16F10 melanoma cell lines. mRNA transcription levels of tyrosinase, TRP-1, and TRP-2 decreased in a dose-dependent manner. Melanin formation was confirmed in the zebrafish model using quercetin derivatives. Therefore, OQ might be a valuable asset for the development of novel skin-whitening agents.

Elastic stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.

The filler size-dependent elastic stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in elastic stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface.