RF Sputtered Nb-Doped MoS2 Thin Film for Effective Detection of NO2 Gas Molecules: Theoretical and Experimental Studies.

Doping plays a significant role in affecting the physical and chemical properties of two-dimensional (2D) dichalcogenide materials. Controllable doping is one of the major factors in the modification of the electronic and mechanical properties of 2D materials. MoS2 2D materials have gained significant attention in gas sensing owing to their high surface-to-volume ratio. However, low response and recovery time hinder their application in practical gas sensors. Herein, we report the enhanced gas response and recovery of Nb-doped MoS2 gas sensor synthesized through physical vapor deposition (PVD) toward NO2 at different temperatures. The electronic states of MoS2 and Nb-doped MOS2 monolayers grown by PVD were analyzed based on their work functions. Doping with Nb increases the work function of MoS2 and its electronic properties. The Nb-doped MoS2 showed an ultrafast response and recovery time of t rec = 30/85 s toward 5 ppm of NO2 at their optimal operating temperature (100 °C). The experimental results complement the electron difference density functional theory calculation, showing both physisorption and chemisorption of NO2 gas molecules on niobium substitution doping in MoS2.

Interfacial Ammonia Selectivity, Atmospheric Passivation, and Molecular Identification in Graphene-Nanopored Activated Carbon Molecular-Sieve Gas Sensors.

Graphene's inherent nonselectivity and strong atmospheric doping render most graphene-based sensors unsuitable for atmospheric applications in environmental monitoring of pollutants and breath detection of biomarkers for noninvasive medical diagnosis. Hence, demonstrations of graphene's gas sensitivity are often in inert environments such as nitrogen, consequently of little practical relevance. Herein, target gas sensing at the graphene-activated carbon interface of a graphene-nanopored activated carbon molecular-sieve sensor obtained via the postlithographic pyrolysis of Novolac resin residues on graphene nanoribbons is shown to simultaneously induce ammonia selectivity and atmospheric passivation of graphene. Consequently, 500 parts per trillion (ppt) ammonia sensitivity in atmospheric air is achieved with a response time of ∼3 s. The similar graphene and a-C workfunctions ensure that the ambipolar and gas-adsorption-induced charge transfer characteristics of pristine graphene are retained. Harnessing the van der Waals bonding memory and electrically tunable charge-transfer characteristics of the adsorbed molecules on the graphene channel, a molecular identification technique (charge neutrality point disparity) is developed and demonstrated to be suitable even at parts per billion (ppb) gas concentrations. The selectivity and atmospheric passivation induced by the graphene-activated carbon interface enable atmospheric applications of graphene sensors in environmental monitoring and noninvasive medical diagnosis.

Revisiting the Mechanism of Electric Field Sensing in Graphene Devices.

Electric field sensing has various real-life applications, such as early prediction of lightning. In this study, we effectively used graphene as an electric field sensor that can detect both positive and negative electric fields. The response of the sensor is recorded as the change in drain current under the application of an electric field. In addition, by systematic analysis, we established the mechanism of the graphene electric field sensor, and it is found to be different from the previously proposed one. The mechanism relies on the transfer of electrons between graphene and the traps at the SiO2/graphene interface. While the direction of charge transfer depends on the polarity of the applied electric field, the amount of charge transferred depends on the magnitude of the electric field. Such a charge transfer changes the carrier concentration in the graphene channel, which is reflected as the change in drain current.

In-situ electrical conductance measurement of suspended ultra-narrow graphene nanoribbons observed via transmission electron microscopy.

Graphene nanoribbon is an attractive material for nano-electronic devices, as their electrical transport performance can be controlled by their edge structures. However, in most cases, the electrical transport has been investigated only for graphene nanoribbons fabricated on a substrate, which hinders the appearance of intrinsic electrical transport due to screening effects. In this study, we developed special devices based on silicon chips for transmission electron microscopy to observe a monolayer graphene nanoribbon suspended between two gold electrodes. Moreover, with the development of an in-situ transmission electron microscopy holder, the current-voltage characteristics were achieved simultaneously with observing and modifying the structure. We found that the current-voltage characteristics differed between 1.5 nm-wide graphene nanoribbons with armchair and zigzag edge structures. The energy gap of the zigzag edge was more than two-fold larger than that of the armchair edge and exhibited an abrupt jump above a critical bias voltage in the differential conductance curve. Thus, our in-situ transmission electron microscopy method is promising for elucidating the structural dependence of electrical conduction in two-dimensional materials.

Innovative marking method using novel endoscopic clip equipped with fluorescent resin to locate gastric cancer.

An asymptomatic 76-year-old man presented to our department for the treatment of gastric cancer. Esophagogastroduodenoscopy revealed a superficial elevated lesion with an irregular central depression in the lower third of the stomach; this was confirmed to be adenocarcinoma by biopsy, while abdominal contrast-enhanced CT revealed no abnormal lesions. Based on the patient's clinical diagnosis of early gastric cancer, we planned laparoscopic gastrectomy with preoperative placement of four endoscopic marking clips equipped with indocyanine green-conjugated resin to determine the resection margin. During surgery, a dedicated laparoscopic system was used to detect indocyanine green fluorescence emitted by the clips and determine their precise position. The clips helped to identify an accurate resection line for the stomach, enabling accurate laparoscopic distal gastrectomy with regional lymphadenectomy. We successfully demonstrated the usefulness of clips with fluorescent resin for detecting gastric cancer in patients. We report the first case using the clips to accurately locate a site of interest.

Role of Scx+/Sox9+ cells as potential progenitor cells for postnatal supraspinatus enthesis formation and healing after injury in mice.

A multipotent cell population co-expressing a basic-helix-loop-helix transcription factor scleraxis (Scx) and SRY-box 9 (Sox9) has been shown to contribute to the establishment of entheses (tendon attachment sites) during mouse embryonic development. The present study aimed to investigate the involvement of Scx+/Sox9+ cells in the postnatal formation of fibrocartilaginous entheses and in the healing process after injury, using ScxGFP transgenic mice. We demonstrate that Scx+/Sox9+ cells are localized in layers at the insertion site during the postnatal formation of fibrocartilaginous entheses of supraspinatus tendon until postnatal 3 weeks. Further, these cells were rarely seen at postnatal 6 weeks, when mature fibrocartilaginous entheses were formed. Furthermore, we investigated the involvement of Scx+/Sox9+ cells in the healing process after supraspinatus tendon enthesis injury, comparing the responses of 20- and 3-week-old mice. In the healing process of 20-week-old mice with disorganized fibrovascular tissue in response to injury, a small number of Scx+/Sox9+ cells transiently appeared from 1 week after injury, but they were rarely seen at 4 weeks after injury. Meanwhile, in 3-week-old mice, a thin layer of fibrocartilaginous tissue with calcification was formed at healing enthesis at 4 weeks after injury. From 1 to 2 weeks after injury, more Scx+/Sox9+ cells, widely distributed at the injured site, were seen compared with the 20-week-old mice. At 4 weeks after injury, these cells were located near the surface of the recreated fibrocartilaginous layer. This spatiotemporal localization pattern of Scx+/Sox9+ cells at the injured enthesis in our 3-week-old mouse model was similar to that in postnatal fibrocartilaginous enthesis formation. These findings indicate that Scx+/Sox9+ cells may have a role as entheseal progenitor-like cells during postnatal maturation of fibrocartilaginous entheses and healing after injury in a manner similar to that seen in embryonic development.

Design of Graphene Phononic Crystals for Heat Phonon Engineering.

Controlling the heat transport and thermal conductivity through a material is of prime importance for thermoelectric applications. Phononic crystals, which are a nanostructured array of specially designed pores, can suppress heat transportation owing to the phonon wave interference, resulting in bandgap formation in their band structure. To control heat phonon propagation in thermoelectric devices, phononic crystals with a bandgap in the THz regime are desirable. In this study, we carried out simulation on snowflake shaped phononic crystal and obtained several phononic bandgaps in the THz regime, with the highest being at ≈2 THz. The phononic bandgap position and the width of the bandgap were found to be tunable by varying the neck-length of the snowflake structure. A unique bandgap map computed by varying the neck-length continuously provides enormous amounts of information as to the size and position of the phononic bandgap for various pore dimensions. We have also carried out transmission spectrum analysis and found good agreement with the band structure calculations. The pressure map visualized at various frequencies validates the effectiveness of snowflake shaped nano-pores in suppressing the phonons partially or completely, depending on the transmission probabilities.

Adsorbed Molecules as Interchangeable Dopants and Scatterers with a Van der Waals Bonding Memory in Graphene Sensors.

Molecular adsorption-induced doping and scattering play a central role in the detection mechanism of graphene gas sensors. However, while the doping contributions in electric field-enhanced gas sensing is well studied, an understanding of the effects of scattering is still lacking. In this work, the scattering contribution of the graphene-molecule van der Waals (vdW) complex is studied under various electric fields and the associated vdW bonding retention in the complex is investigated. We show that contrary to the generally opined view, doping does not always dominate the graphene-molecule vdW complex interaction and consequently the conductivity response in graphene sensors, rather the vdW complex interaction only shows doping-dominated interaction at zero electric fields while scattering increases with electric field modulation. The experimentally observed electric field-dependent scattering response agrees with electron difference density analysis from density functional theory (DFT) calculations, which shows that scattering is directly dependent on the electric field-induced molecular reorientation as well as the redistribution and delocalization of charge in the graphene-gas molecule vdW complex. Furthermore, "vdW bonding memory", i.e., retention of electric field-induced vdW bonding states after turning off the electric field, is observed and shown to result from the high binding energies of the vdW complexes, which are an order of magnitude higher than the sensing measurement thermal energy. This vdW bonding memory in the graphene-molecule complexes is important for the molecular identification of adsorbed gases based on their tunable charge transfer characteristics.

Novel endoscopic marking clip equipped with resin-conjugated fluorescent indocyanine green during laparoscopic surgery for gastrointestinal cancer.

PURPOSE: Intraoperative identification of the cancer location is often difficult to conduct during laparoscopic surgery, especially in early-stage cancers. This study aimed to investigate the feasibility and accuracy of a novel endoscopic clip resin-conjugated fluorescent indocyanine green during laparoscopic surgery for gastrointestinal cancer. METHODS: Preoperative placement of endoscopic marking clips equipped with resin-conjugated fluorescent indocyanine green was performed to determine the resection margin in eight patients with gastrointestinal cancer. During laparoscopic surgery, a dedicated laparoscopic system with a xenon light source was used to detect fluorescence. The evaluation determined whether the fluorescent from the clips was visualized during laparoscopic surgery. RESULTS: Fluorescent signal emitted from ICG in the resin of the clips was detected in six patients from the outer layer of the serosal surfaces of the gastrointestinal tract, and the clips aided in accurate resection line of the organ. There were no significant differences of age, gender, and BMI between the patients in whom we could and could not detect ICG fluorescence. CONCLUSIONS: The results demonstrated the usefulness of a novel clip-equipped fluorescent resin, which is a promising diagnostic tool to detect accurate tumor location during laparoscopic surgery.

Conductance Tunable Suspended Graphene Nanomesh by Helium Ion Beam Milling.

This paper demonstrates that the electrical properties of suspended graphene nanomesh (GNM) can be tuned by systematically changing the porosity with helium ion beam milling (HIBM). The porosity of the GNM is well-controlled by defining the pitch of the periodic nanopores. The defective region surrounding the individual nanopores after HIBM, which limits the minimum pitch achievable between nanopores for a certain dose, is investigated and reported. The exponential relationship between the thermal activation energy (EA) and the porosity is found in the GNM devices. Good EA tuneability observed from the GNMs provides a new approach to the transport gap engineering beyond the conventional nanoribbon method.

Reference values for the locomotive syndrome risk test quantifying mobility of 8681 adults aged 20-89 years: A cross-sectional nationwide study in Japan.

BACKGROUND: The locomotive syndrome risk test was developed to quantify the decrease in mobility among adults, which could eventually lead to disability. The purpose of this study was to establish reference values for the locomotive syndrome risk test for adults and investigate the influence of age and sex. METHODS: We analyzed 8681 independent community dwellers (3607 men, 5074 women). Data pertaining to locomotive syndrome risk test (the two-step test, the stand-up test, and the 25-question geriatric locomotive function scale [GLFS-25]) scores were collected from seven administrative areas of Japan. RESULTS: The reference values of the three test scores were generated and all three test scores gradually decreased among young-to-middle-aged individuals and rapidly decreased in individuals aged over 60 years. The stand-up test score began decreasing significantly from the age of 30 years. The trajectories of decrease in the two-step test score with age was slightly different between men and women especially among the middle-aged individuals. The two physical test scores were more sensitive to aging than the self-reported test score. CONCLUSION: The reference values generated in this study could be employed to determine whether an individual has mobility comparable to independent community dwellers of the same age and sex.

Dielectric-Screening Reduction-Induced Large Transport Gap in Suspended Sub-10 nm Graphene Nanoribbon Functional Devices.

The predicted quasiparticle energy gap of more than 1 eV in sub-6 nm graphene nanoribbons (GNRs) is elusive, as it is strongly suppressed by the substrate dielectric screening. The number of techniques that can produce suspended high-quality and electrically contacted GNRs is small. The helium ion beam milling technique is capable of achieving sub-5 nm patterning; however, the functional device fabrication and the electrical characteristics are not yet reported. Here, the electrical transport measurement of suspended ≈6 nm wide mono- and bilayer GNR functional devices is reported, which are obtained through sub-nanometer resolution helium ion beam milling with controlled total helium ion budget. The transport gap opening of 0.16-0.8 eV is observed at room temperature. The measured transport gap of the different edge orientated GNRs is in good agreement with first-principles simulation results. The enhanced electron-electron interaction and reduced dielectric screening in the suspended quasi-1D GNRs and anti-ferromagnetic coupling between opposite edges in the zigzag GNRs substantiate the observed large transport gap.

Electrically controlled valley states in bilayer graphene.

Valley current, a stable, dissipationless current, originates due to the emergence of Berry curvature in inversion symmetry broken systems. Several theoretical predictions and experimental observations have explored layer symmetry breaking in AB-stacked bilayer graphene due to long-range Coulomb interactions between the electrons. However, none of the experimental studies conducted so far have observed valley current in unbiased bilayer graphene, which makes it vital to study the Berry curvature in unbiased bilayer graphene. In this study, we observed a non-zero Berry curvature with opposite values at K and K' valleys, validating the argumentation of the asymmetry persistent in unbiased bilayer graphene. The magnitude, as well as the polarity of the Berry curvature, is tunable with the application of an out-of-plane electric field. These results are especially important because they can lead to the realization of a valley valve, in which the carriers from the K and K' valleys can be regulated with a gate at the centre of a bilayer graphene nanoribbon.

Presynaptic Dysfunction in Neurons Derived from Tay-Sachs iPSCs.

Tay-Sachs disease (TSD) is a GM2 gangliosidosis lysosomal storage disease caused by a loss of lysosomal hexosaminidase-A (HEXA) activity and characterized by progressive neurodegeneration due to the massive accumulation of GM2 ganglioside in the brain. Here, we generated iPSCs derived from patients with TSD, and found similar potential for neural differentiation between TSD-iPSCs and normal iPSCs, although neural progenitor cells (NPCs) derived from the TSD-iPSCs exhibited enlarged lysosomes and upregulation of the lysosomal marker, LAMP1, caused by the accumulation of GM2 ganglioside. The NPCs derived from TSD-iPSCs also had an increased incidence of oxidative stress-induced cell death. TSD-iPSC-derived neurons showed a decrease in exocytotic activity with the accumulation of GM2 ganglioside, suggesting deficient neurotransmission in TSD. Our findings demonstrated that NPCs and mature neurons derived from TSD-iPSCs are potentially useful cellular models of TSD and are useful for investigating the efficacy of drug candidates in the future.

Quantum Dot Formation in Controllably Doped Graphene Nanoribbon.

We introduce the controllable doping from hydrogen silsesquioxane (HSQ) to graphene by changing its electron-beam exposure dose. Using HSQ as the dopant, a fine-resolution electron-beam resist allows us to selectively dope graphene with an extremely high spatial resolution of a few nanometers. Therefore, we can design and demonstrate the single quantum dot (QD)-like transport in the graphene nanoribbon (GNR) with the opening of the energy gap. Moreover, we suggest a rough geometric design rule in which a relatively short and wide GNR is required for observing the single QD-like transport. We envisage that this method can be utilized for other materials and for other applications, such as p-n junctions and tunnel field-effect transistors.

Fibroblast Growth Factor 2 Enhances Tendon-to-Bone Healing in a Rat Rotator Cuff Repair of Chronic Tears.

BACKGROUND: The effects of fibroblast growth factor 2 (FGF-2) on healing after surgical repair of chronic rotator cuff (RC) tears remain unclear. HYPOTHESIS: FGF-2 enhances tenogenic healing response, leading to biomechanical and histological improvement of repaired chronic RC tears in rats. STUDY DESIGN: Controlled laboratory study. METHODS: Adult male Sprague-Dawley rats (n = 117) underwent unilateral surgery to refix the supraspinatus tendon to its insertion site 3 weeks after detachment. Animals were assigned to either the FGF-2 group or a control group. The effects of FGF-2 were assessed via biomechanical tests at 3 weeks after detachment and at 6 and 12 weeks postoperatively and were assessed histologically and immunohistochemically for proliferating cell nuclear antigen and mesenchymal stem cell (MSC)-related markers at 2, 6, and 12 weeks postoperatively. The expression of tendon/enthesis-related markers, including SRY-box 9 (Sox9), scleraxis (Scx), and tenomodulin (Tnmd), were assessed by real-time reverse transcription polymerase chain reaction, in situ hybridization, and immunohistochemistry. The effect of FGF-2 on comprehensive gene expressions at the healing site was evaluated by microarray analysis. RESULTS: The FGF-2 group showed a significant increase in mechanical strength at 6 and 12 weeks compared with control; the FGF-2 group also showed significantly higher histological scores at 12 weeks than control, indicating the presence of more mature tendon-like tissue. At 12 weeks, Scx and Tnmd expression increased significantly in the FGF-2 group, whereas no significant differences in Sox9 were found between groups over time. At 2 weeks, the percentage of positive cells expressing MSC-related markers increased in the FGF-2 group. Microarray analysis at 2 weeks after surgery showed that the expression of several growth factor genes and extracellular matrix-related genes was influenced by FGF-2 treatment. CONCLUSION: FGF-2 enhanced the formation of tough tendon-like tissues including an increase in Scx- or Tnmd-expressing cells at 12 weeks after surgical repair of chronic RC tears. The increase in mesenchymal progenitors and the changes in gene expression upon FGF-2 treatment in the early phase of healing appear to be related to a certain favorable microenvironment for tenogenic healing response of chronic RC tears. CLINICAL RELEVANCE: These findings may provide advantages in therapeutic strategies for patients with RC tears.

Fabry-Pérot resonances and a crossover to the quantum Hall regime in ballistic graphene quantum point contacts.

We report on the observation of quantum transport and interference in a graphene device that is attached with a pair of split gates to form an electrostatically-defined quantum point contact (QPC). In the low magnetic field regime, the resistance exhibited Fabry-Pérot (FP) resonances due to np'n(pn'p) cavities formed by the top gate. In the quantum Hall (QH) regime with a high magnetic field, the edge states governed the phenomena, presenting a unique condition where the edge channels of electrons and holes along a p-n junction acted as a solid-state analogue of a monochromatic light beam. We observed a crossover from the FP to QH regimes in ballistic graphene QPC under a magnetic field with varying temperatures. In particular, the collapse of the QH effect was elucidated as the magnetic field was decreased. Our high-mobility graphene device enabled observation of such quantum coherence effects up to several tens of kelvins. The presented device could serve as one of the key elements in future electronic quantum optic devices.

Matrix metalloproteinase promotes elastic fiber degradation in ligamentum flavum degeneration.

Ligamentum flavum (LF) hypertrophy in lumbar spinal canal stenosis (LSCS) is characterized by a loss of elastic fibers and fibrosis. Chronic inflammation is thought to be responsible for the histological change but the mechanism underlying elastic fiber degradation remains unclear. Given that matrix metalloproteinase (MMP)-2 and -9 have elastolytic activity and are partly regulated by inflammatory cytokines such as interleukin (IL)-6, in this study, we investigated whether MMPs mediate LF degeneration using 52 LF samples obtained during lumbar surgery, including 31 LSCS and 21 control specimens. We confirmed by histological analysis that the LSCS samples exhibited severe degenerative changes compared with the controls. We found that MMP-2 was upregulated in LF tissue from patients with LSCS at the mRNA and protein levels, whereas MMP-9 expression did not differ between the two groups. The MMP-2 level was positively correlated with LF thickness and negatively correlated with the area occupied by elastic fibers. IL-6 mRNA expression was also increased in LF tissue from patients with LSCS and positively correlated with that of MMP-2. Signal transducer and activator of transcription (STAT)3, a component of the IL-6 signaling pathway, was activated in hypertrophied LF tissues. Our in vitro experiments using fibroblasts from LF tissue revealed that IL-6 increased MMP-2 expression, secretion, and activation via induction of STAT3 signaling, and this effect was reversed by STAT3 inhibitor treatment. Moreover, elastin degradation was promoted by IL-6 stimulation in LF fibroblast culture medium. These results indicate that MMP-2 induction by IL-6/STAT3 signaling in LF fibroblasts can degrade elastic fibers, leading to LF degeneration in LSCS.

Enhanced Sodium Ion Storage in Interlayer Expanded Multiwall Carbon Nanotubes.

We report an effective approach of utilizing multiwalled carbon nanotubes (MWCNTs) as an active anode material in sodium ion batteries by expanding the interlayer distance in a few outer layers of multiwalled carbon nanotubes. The performance enhancement was investigated using a density functional tight binding (DFTB) molecular dynamics simulation. It is found that a sodium atom forms a stable bonding with the partially expanded MWCNT (PECNT) with the binding energy of -1.50 eV based on the density functional theory calculation with van der Waals correction, where a sodium atom is caged between the two carbon hexagons in the two consecutive MWCNTs. Wave function and charge density analyses show that this binding is physisorption in nature. This larger exothermic nature of binding energy favors the stable bonding between the PECNT and a sodium atom, and thereby, it helps to enhance the electrochemical performance. In the experimental works, partial opening of the MWCNT with the expanded interlayer has been designed by the well-known Hummer's method. It has been found that the introduction of functional groups causes a partial opening of the outer few layers of a MWCNT, with the inner core remaining undisturbed. The enhanced performance is due to an expanded interlayer of carbon nanotubes, which provide sufficient active sites for the sodium ions to adsorb as well as to intercalate into the carbon structure. The PECNT shows a high specific capacity of 510 mAh g-1 at a current density of 20 mA g-1, which is about 2.3 times the specific capacity obtained for a pristine MWCNT at the same current density. This specific capacity is higher when compared to other carbon-based materials. The PECNT also shows a satisfactory cyclic stability at a current density of 200 mA g-1 for 100 cycles. Based on our experimental and theoretical results, an alternative perspective for the storage of sodium ions in MWCNTs is proposed.

Mesenchymal stem cells derived from human iPS cells via mesoderm and neuroepithelium have different features and therapeutic potentials.

Mesenchymal stem cells (MSCs) isolated from adult human tissues are capable of proliferating in vitro and maintaining their multipotency, making them attractive cell sources for regenerative medicine. However, the availability and capability of self-renewal under current preparation regimes are limited. Induced pluripotent stem cells (iPSCs) now offer an alternative, similar cell source to MSCs. Herein, we established new methods for differentiating hiPSCs into MSCs via mesoderm-like and neuroepithelium-like cells. Both derived MSC populations exhibited self-renewal and multipotency, as well as therapeutic potential in mouse models of skin wounds, pressure ulcers, and osteoarthritis. Interestingly, the therapeutic effects differ between the two types of MSCs in the disease models, suggesting that the therapeutic effect depends on the cell origin. Our results provide valuable basic insights for the clinical application of such cells.