Arresting the surface oxidation kinetics of bilayer 1T'-MoTe2by sulphur passivation.

MoTe2garnered much attention among 2D materials due to stable polymorphs with distinctive structural and electronic properties. Among the polymorphs, 1T'-MoTe2in bulk form is type-II Weyl semimetal while, in monolayer form is a quantum spin Hall insulator. Thus, it is suitable for a wide variety of applications. Nevertheless, 1T'-MoTe2degrades within a few hours when exposed to the atmosphere and causes hindrances in device fabrication. Here the degradation kinetics of CVD-synthesized 1T'-MoTe2was investigated using Raman spectroscopy, XPS, and microscopic characterizations. The degradation rate of as-grown 1T'-MoTe2obtained was 9.2 × 10-3min-1. Further, we prevented the degradation of 1T'-MoTe2by introducing a thin coating of S that encapsulates the flakes. 1T'-MoTe2flakes showed stability for several days when covered using sulphur, indicating 25 times enhanced structural stability.

Transforming friction: unveiling sliding-induced phase transitions in CVD-grown WS2 monolayers under single-asperity sliding nanocontacts.

Transition metal dichalcogenides (TMDs) exhibit diverse properties across different phases, making them promising materials for various engineering applications. In the present work, we employed a comprehensive approach, combining experimental investigations and computational simulations to elucidate the remarkable tunable frictional characteristics of chemical vapor deposition (CVD) grown WS2 monolayers through the sliding-induced transitions between the 1H and 1T' phases. Our atomic force microscopy (AFM) measurements reveal a significant contrast in friction between the two phases, with the 1H phase displaying higher friction (∼52%) than the 1T' phase. Surprisingly, under repeated scanning at constant stress, the friction of the 1H phase decreases, eventually matching the lower friction values of the 1T' phase. It was observed that the phase transformation is irreversible and is strongly dependent on contact stresses and is accelerated as the contact stress is increased by increasing the applied normal load. Molecular dynamics (MD) simulations provide further insights into the phase transition mechanism, highlighting the role of localized lateral stress and strain induced by sliding an AFM tip on the 1H phase. The simulations confirm that sliding induced localized lateral strain plays a crucial role in the phase transition, ultimately resulting in a decrease in friction. Moreover, our simulations unveil an intriguing connection between friction, potential energy surfaces, and the localized lateral strain during the phase transformation process. Our findings not only offer insights into the tribological properties of TMD materials but also open new possibilities for tailoring their performance in various applications where reducing friction and wear is crucial.

Biodegradable IPN hydrogel beads of pectin and grafted alginate for controlled delivery of diclofenac sodium.

A novel diclofenac sodium (DS) loaded interpenetrating polymer network (IPN) beads of pectin and hydrolyzed polyacrylamide-graft-sodium alginate (PAAm-g-SA) was developed through ionotropic gelation and covalent cross-linking. The graft copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting, alkaline hydrolysis, and characterization of beads were confirmed by Fourier transforms infrared spectroscopy. The crystalline structure of drug after encapsulation into IPN beads were evaluated by differential scanning colorimetry and X-ray diffraction analyses. DS encapsulation was up to 96.45 %. The effect of hydrolyzed graft copolymer/pectin ratios and glutaraldehyde concentration on drug release in acidic and phosphate buffer solutions were investigated. The release of drug was significantly increased with increase of pH. The release of drug depends on the extent of cross-linking. The results indicated that IPN beads of hydrolyzed PAAm-g-SA and pectin could be used for sustained release of DS.

Heteroatomic stitching of broken WS2 monolayer with enhanced surface potential.

Sub-nanometre thick two-dimensional (2D) materials suffer from severe cracking during the high temperature chemical vapour deposition growth process. The cracking can be utilised to generate more active edges. These active edges can be stitched with a homo- or hetero-material. While the direct growth of 2D-heterostructures is mostly limited to a small fraction of outer edges of monolayer flakes, the cracked monolayers can be utilised to produce a large fraction of heterostructures. Heterostructures are important for developing multifunctional components for nanoscale electronics and optoelectronics. In this work, we demonstrate the formation of WS2-MoS2 heterostructures in large fractions by atomic stitching of cracked WS2 monolayers with the sequential growth of MoS2. Aberration-corrected scanning transmission electron microscopy and Raman spectroscopy have been utillised to probe fine details on the stitched interface between WS2 and MoS2. Growth of MoS2 domains were observed to take place at the terminating edge of cracked WS2, which then merged to form MoS2 multilayers at the cracked site. Growth of MoS2 at the opposite edges of WS2 eventually results in a MoS2-MoS2 junction with a Σ = 7 tilt boundary. Kelvin probe force microscope (KPFM) measurement from the stitched region revealed that the work function of WS2 is ∼32.46 meV higher than that of MoS2, which also closely matches with the Fermi energy difference between these two materials. With the aid of an atomic force microscope and KPFM, the surface potential width at the stitched region was found to be ∼5 times higher than the actual width of the interface, confirming the modulation of properties near the interface.

Nanoscale friction and wear behavior of a CVD-grown aged WS2 monolayer: the role of wrinkles and surface chemistry.

Friction reduction by transition metal dichalcogenide (TMD) monolayers is well documented; however, wrinkle formation on the surface of TMDs takes place due to strain relaxation over time and leads to the deterioration of the tribological properties at a small scale. Herein, we report the role of wrinkles on the wear behavior of a chemical vapor deposition (CVD) grown aged WS2 monolayer and the comparison with wrinkle-free regions. Atomic force microscopy (AFM) was utilized to perform load-dependent experiments, and we noticed that the wear initiated near wrinkles resulted in the disintegration of the monolayer. In contrast, in the wrinkle-free regions, wear occurred at significantly higher loads, similar to that of freshly grown WS2, although the coefficient of friction (COF) was increased due to the changes in surface chemistry as a result of aging, which was confirmed using X-ray photoelectron spectroscopy (XPS). In the presence of wrinkles, a ten-fold reduction in the load-carrying capacity was observed compared to the wrinkle-free regions. Molecular dynamics (MD) simulations were used to corroborate experimental findings, which demonstrate the role of wrinkles in the initiation of wear due to the stress concentration under sliding nanocontacts near the wrinkles. In addition, simulations help establish a relationship between the adsorbed chemical species on the surface and increased COF.

Application of Selenium Nanoparticles in Localized Drug Targeting for Cancer Therapy.

BACKGROUND: Selenium nanoparticles (SeNPs) have gained a place in the biomedical field; they serve as chemotherapeutic agents for targeted drug delivery due to their capacity to exert distinct mechanisms of action on cancer and normal cells. The principle behind these mechanisms is the generation of reactive oxygen species (ROS), which accelerates apoptosis via the dysfunction of various pathways. SeNPs, when used in higher concentrations, induce toxicity; however, conjugation and surface functionalization are some techniques available to ameliorate their toxic nature as well as enhance their anticancer activity. OBJECTIVES: The primary goal of this analysis is to provide a thorough and systematic investigation into the use of various SeNPs in localized drug targeting for cancer therapy. This has been achieved by citing examples of numerous SeNPs and their use as a drug targeting agent for cancer therapy. METHODS: All relevant data and information about the various SeNPs for drug targeting in cancer therapy were gathered from various databases, including Science Direct, PubMed, Taylor and Francis imprints, American Chemical Society, Springer, Royal Society of Chemistry, and Google Scholar. RESULTS: SeNPs are explored due to their better biopharmaceutical properties and cytostatic behavior. Se, as an essential component of the enzyme glutathione peroxidase (GPx) and other seleno-chemical substances, might boost chemotherapeutic efficacy and protect tissues from cellular damage caused by ROS. SeNPs have the potential to set the stage for developing new strategies to treat malignancy. CONCLUSION: This review extensively analyzed the anticancer efficacy and functionalization strategies of SeNPs in drug delivery to cancer cells. In addition, this review highlights the mechanism of action of drug-loaded SeNPs to suppress the proliferation of cancer cells in different cell lines.

Interplay between Thermal Stress and Interface Binding on Fracture of WS2 Monolayer with Triangular Voids.

The defect engineering of two-dimensional (2D) materials has become a pivotal strategy for tuning the electrical and optical properties of the material. However, the reliable application of these atomically thin materials in practical devices require careful control of structural defects to avoid premature failure. Herein, a systematic investigation is presented to delineate the complex interactions among structural defects, the role of thermal mismatch between WS2 monolayer and different substrates, and their consequent effect on the fracture behavior of the monolayer. Detailed microscopic and Raman/PL spectroscopic observations enabled a direct correlation between thermal mismatch stress and crack patterns originating from the corner of faceted voids in the WS2 monolayer. Aberration-corrected STEM-HAADF imaging reveals the tensile strain localization around the faceted void corners. Density functional theory (DFT) simulations on interfacial interaction between the substrate (Silicon and sapphire -Al2O3) and monolayer WS2 revealed a binding energy between WS2 and Si substrate is 20 times higher than that with a sapphire substrate. This increased interfacial interaction in WS2 and substrate-aided thermal mismatch stress arising due to difference in thermal expansion coefficient to a maximum extent leading to fracture in monolayer WS2. Finite element simulations revealed the stress distribution near the void in the WS2 monolayer, where the maximum stress was concentrated at the void tip.

Spectrophotometric analysis of crown discoloration induced by two different sealers: An In vitro study.

CONTEXT: Endodontic materials have been assessed with regards to their potential for dental staining. AIMS: To evaluate the coronal discoloration effect of Apexit Plus and Resino Seal in mandibular premolars using spectrophotometer. SETTINGS AND DESIGN: The study design was original research. MATERIALS AND METHODS: Forty human single-rooted mandibular first premolar teeth were selected for the study. They were divided into four groups of ten specimens each. Group 1 - Apexit Plus sealer, Group 2 - Resino Seal sealer, Group 3 - positive control (Blood), and Group 4 - negative control (distilled water). Teeth were resected 3 mm below at cementoenamel junction. In all samples, access cavities were prepared, instrumented, and irrigated. Sealers were mixed and placed into the pulp chamber through cervical access and control groups were filled with blood and distilled water. Coronal orifices were sealed using self-cure glass ionomer cement. Samples were analyzed using spectrophotometer to determine the discoloration in each group at 10, 17, and 24 days interval. STATISTICAL ANALYSIS USED: Statistical analysis used Wilcoxon signed-rank test. RESULTS: All sealers used in the present study caused a progressive coronal discoloration over a time period of 17-24 days. There was statistically significant difference between resino seal sealer and apexit plus sealer , with resino seal showing greater coronal discoloration. CONCLUSION: Resino seal sealer has greater potential to cause discoloration of crown as compared to apexit plus sealer over a period of time.

Effectiveness of Three Different Irrigants - 17% Ethylenediaminetetraacetic Acid, Q-MIX, and Phytic Acid in Smear Layer Removal: A Comparative Scanning Electron Microscope Study.

BACKGROUND: Removal of smear layer from the root canal walls is important for long-standing endodontic success. AIM: The aim of this study is to evaluate and compare smear layer removing ability among 17% ethylenediaminetetraacetic acid (EDTA), Q-MIX, and phytic acid by scanning electron microscopy (SEM). MATERIALS AND METHODS: This in-vitro experimental study assessed smear layer removal using three different irrigants. Thirty single-rooted freshly extracted human permanent premolars were collected, disinfected, and decoronated to a standardized root length of 13 mm. Root canals were cleaned and shaped till F2 universal rotary protaper at working length 1 mm short of the apex. They were randomly divided into three groups, and final irrigation was done accordingly. Group 1 (n = 10): with 1 ml of 17% EDTA, Group 2 (n = 10): with 1 ml of Q-MIX, Group 3 (n = 10): with 1 ml of phytic acid. Samples were then longitudinally sectioned and evaluated under SEM at coronal, middle, and apical levels. STATISTICAL ANALYSIS: Two-way analysis of variance and Tukey's post hoc test were performed. The level of significance was set at 0.05. RESULTS: Smear layer removing ability among irrigants and sections in descending order: 17 EDTA > Q-MIX > phytic acid; coronal > middle > apical. CONCLUSION: 17% EDTA showed better and promising results followed by Q-MIX and then phytic acid.

In vitro evaluation of remineralization efficacy of different calcium- and fluoride-based delivery systems on artificially demineralized enamel surface.

BACKGROUND: Caries is the most common dental disease facing the world population. Caries can be prevented by remineralizing early enamel lesions. AIM: To evaluate remineralization efficacy of stannous fluoride (SnF2), casein phosphopeptide-amorphous calcium phosphate with fluoride (CPP-ACPF) and calcium sucrose phosphate (CaSP). MATERIALS AND METHODS: Fifty enamel samples were taken; they were divided into five groups (n = 10). Demineralization was carried out with Groups A, B, C, and E. Remineralization was carried out with Groups A, B, and C for 7 days using SnF2, CPP-ACPF, and CaSP, respectively. In Group D, no surface treatment was carried out, to mark as positive control whereas Group E was kept as negative control with only surface demineralization of enamel. Enamel microhardness was tested using Vickers's microhardness tester after 7 day remineralization regime. STATISTICAL ANALYSIS: One-way analysis of variance and post hoc Tukey tests were performed. RESULTS: The mean microhardness values in descending order: Positive control > SnF2> CaSP > CPP-ACPF > negative control. CONCLUSION: All remineralizing agents showed improved surface remineralization. However, complete remineralization did not occur within 7 days. SnF2 showed the highest potential for remineralization followed by CaSP and CPP-ACPF.

Comparative scanning electron microscopy evaluation of Canal Brushing technique, sonic activation, and master apical file for the removal of triple antibiotic paste from root canal (in vitro study).

AIMS: To compare and evaluate the effectiveness of Canal Brushing technique, sonic activation, and master apical file (MAF) for the removal of triple antibiotic paste (TAP) from root canal using scanning electron microscopy (SEM). MATERIALS AND METHODS: Twenty-two single rooted teeth were instrumented with ProTaper up to the size number F2 and dressed with TAP. TAP was removed with Canal Brush technique (Group I, n: 6), sonic (EndoActivator) (Group II, n: 6), and MAF (Group III, n: 6). Four teeth served as positive (n: 2) and negative (n: 2) controls. The roots were split in the buccolingual direction and prepared for SEM examination (×1000) at coronal, middle, and apical third. Three examiners evaluated the wall cleanliness. STATISTICAL ANALYSIS: Statistical analysis was performed by Kruskal-Wallis test and Wilcoxon rank sum test. RESULTS: Difference in cleanliness between three groups is statistically significant in cervical region only. Pairwise comparison in cervical region Canal Brush and sonic activation showed more removal of TAP than MAF. CONCLUSIONS: Canal Brush and sonic activation system showed better result than MAF in the cervical and middle third of canal. In the apical third, none of the techniques showed a better result. None of the techniques showed complete removal of TAP from the canal.

Alginate based hydrogel as a potential biopolymeric carrier for drug delivery and cell delivery systems: present status and applications.

Alginate is a non-toxic, biocompatible and biodegradable natural polymer with a number of peculiar physicochemical properties for which it has wide applications in drug delivery and cell delivery systems. Hydrogel formation can be obtained by interactions of anionic alginates with multivalent inorganic cations by simple ionotropic gelation method. Hydrophilic polymeric network of three dimensional cross linked structures of hydrogels absorb substantial amount of water or biological fluids. Among the numerous biomaterials used for hydrogel formation alginate has been and will continue to be one of the most important biomaterial. Therefore, in view of the vast literature support, we focus in this review on alginate - based hydrogel as drug delivery and cell delivery carriers for biomedical applications. Various properties of alginates, their hydrogels and also various techniques used for preparing alginate hydrogels have been reviewed.