An Atomistic Level Investigation of the PFDTES-Graphene Interfacial Shear Strength and the Stick-Slip Mechanism.

1H,1H,2H,2H-Perfluorodecyltriethoxysilane (PFDTES) is the most widely used coating material with low surface energy and has the potential to be used as a dust-mitigating coating material during lunar landing missions. Graphene can be added to the PFDTES matrix to improve its mechanical properties. In this study, molecular dynamics simulations were performed to investigate the interfacial shear strength and friction mechanism between the PFDTES matrix and graphene. A systematic molecular dynamics (MD) simulation has been performed to calculate the interfacial shear strength of the PFDTES-graphene interface with considering the effect of graphene sliding velocity and vacancy defect density. For a pristine graphene layer with a size of 10 nm × 10 nm, the interfacial force between graphene and the PFDTES matrix is around 3 nN. Like other polymeric materials, the interfacial shear force exhibited stick-slip behavior under loading. The interfacial shear force will start to increase after the graphene starts sliding against the PFDTES matrix and reaches a stable plateau in a very short distance. It has been found that the influence of the interfacial shear strength from the sliding velocity of graphene is minimal. However, a significant increase in the interfacial shear strength has been observed after the graphene defect density increased; i.e., the magnitude of the shear force increased from 3 nN to around 14 nN after the defect density increased from 0% for pristine graphene to 40%. It has been found that vacancy defects will increase the fluctuation in the interfacial shear force, and it is due to not only the increased roughness near defects but also the stretched bonds in graphene under loading according to the distribution of the bond length. This study concluded that interfacial stick-slip behavior also exists in the PFDTES-graphene interface, and vacancy defects will have a significant improvement in the interfacial shear strength.

Corrigendum: BM-MSCs alleviate diabetic nephropathy in male rats by regulating ER stress, oxidative stress, inflammation, and apoptotic pathways.

[This corrects the article DOI: 10.3389/fphar.2023.1265230.].

BM-MSCs alleviate diabetic nephropathy in male rats by regulating ER stress, oxidative stress, inflammation, and apoptotic pathways.

Introduction: Diabetic nephropathy (DN), a chronic kidney disease, is a major cause of end-stage kidney disease worldwide. Mesenchymal stem cells (MSCs) have become a promising option to mitigate several diabetic complications. Methods: In this study, we evaluated the therapeutic potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) in a rat model of STZ-induced DN. After the confirmation of diabetes, rats were treated with BM-MSCs and sacrificed at week 12 after treatment. Results: Our results showed that STZ-induced DN rats had extensive histopathological changes, significant upregulation in mRNA expression of renal apoptotic markers, ER stress markers, inflammatory markers, fibronectin, and intermediate filament proteins, and reduction of positive immunostaining of PCNA and elevated P53 in kidney tissue compared to the control group. BM-MSC therapy significantly improved renal histopathological changes, reduced renal apoptosis, ER stress, inflammation, and intermediate filament proteins, as well as increased positive immunostaining of PCNA and reduced P53 in renal tissue compared to the STZ-induced DN group. Conclusion: In conclusion, our study indicates that BM-MSCs may have therapeutic potential for the treatment of DN and provide important insights into their potential use as a novel therapeutic approach for DN.

High current density electron wind forces in metallic graphene nanoribbons.

In this study electric current-induced wind forces on a unit lattice of a 10-dimer zigzag graphene nanoribbon (ZGNR) are calculated under different magnitudes of electric field and temperatures. Wind forces are calculated using a semi-classical method where quantum mechanics is integrated into ensemble Monte Carlo simulations by considering energy and momentum conservation in both the transverse and longitudinal directions of graphene nanoribbon (GNR) during the electron-phonon scattering process. First order perturbation theory using the deformation potential approximation was used in the calculation of the scattering rates. The results show that under the same electric field, Joule heating power in a 10-dimer ZGNR is around 3 magnitudes higher than that in metallic single-walled carbon nanotubes and the wind forces are 1 magnitude higher. According to the calculated results, the wind force in the 10-dimer ZNGR is in the order of 0.0073 eV Å-1 under 20 kV at 300 K and it is much lower than the fracture strength of ZGNR based on the results of molecular dynamics simulations. Thus the failure of GNR under an electric current is considered to be mainly due to the Joule heating.

Influence of defects on dissipative transport in graphene nanoribbons tunnel field-effect transistor.

The influence of point defects on the dissipative carrier transport of armchair graphene nanoribbon (GNR) tunnel field effect transistor (TFET) is studied by solving the self-consistent Born approximation problem using the extended lowest order expansion method. The simulation results show that by introducing point defects to the channel region of the armchair GNR-TFET, the OFF state phonon contribution to the carrier transport changes significantly compared with that of the pristine device. The presence of defect would introduce additional optical phonon mode of much higher energy, which facilitates the OFF state phonon-assisted band-to-band tunneling process in a broader energy range and contribute to the dissipative carrier transport. In the ON-state, where the direct source to drain tunneling is at maximum, the electron-phonon interaction has a negligible effect, which is similar to that of the pristine device. Moreover, different defect types and locations are examined, their influence on hole and electron transport are reported.

Anisotropy of Graphene Nanoflake Diamond Interface Frictional Properties.

Using molecular dynamics (MD) simulations, the frictional properties of the interface between graphene nanoflake and single crystalline diamond substrate have been investigated. The equilibrium distance between the graphene nanoflake and the diamond substrate has been evaluated at different temperatures. This study considered the effects of temperature and relative sliding angle between graphene and diamond. The equilibrium distance between graphene and the diamond substrate was between 3.34 Å at 0 K and 3.42 Å at 600 K, and it was close to the interlayer distance of graphite which was 3.35 Å. The friction force between graphene nanoflakes and the diamond substrate exhibited periodic stick-slip motion which is similar to the friction force within a graphene-Au interface. The friction coefficient of the graphene-single crystalline diamond interface was between 0.0042 and 0.0244, depending on the sliding direction and the temperature. Generally, the friction coefficient was lowest when a graphene flake was sliding along its armchair direction and the highest when it was sliding along its zigzag direction. The friction coefficient increased by up to 20% when the temperature rose from 300 K to 600 K, hence a contribution from temperature cannot be neglected. The findings in this study validate the super-lubricity between graphene and diamond and will shed light on understanding the mechanical behavior of graphene nanodevices when using single crystalline diamond as the substrate.