Extent of myosin penetration within the actin cortex regulates cell surface mechanics

In animal cells, shape is mostly determined by the actomyosin cortex, a thin cytoskeletal network underlying the plasma membrane. Myosin motors generate tension in the cortex, and tension gradients result in cellular deformations. As such, many cell morphogenesis studies have focused on the mechanisms controlling myosin activity and recruitment to the cortex. Here, we demonstrate using super-resolution microscopy that myosin does not always overlap with actin at the cortex, but remains restricted towards the cytoplasm in cells with low cortex tension. We propose that this restricted penetration results from steric hindrance, as myosin minifilaments are considerably larger than the cortical actin meshsize. We identify myosin activity and actin network architecture as key regulators of myosin penetration into the cortex, and show that increasing myosin penetration increases cortical tension. Our study reveals that the spatial coordination of myosin and actin at the cortex regulates cell surface mechanics, and unveils an important mechanism whereby myosin size controls its action by limiting minifilament penetration into the cortical actin network. More generally, our findings suggest that protein size could regulate function in dense cytoskeletal structures.

Lymph node tissue homeostasis and adaptation to immune challenge resolved by fibroblast network mechanics

Emergent physical properties of tissues are not readily understood by reductionist studies of their constituent cells. Here, we show molecular signals controlling cellular physical properties, collectively determining tissue mechanics of lymph nodes, an immunologically-relevant, adult mammalian tissue. Lymph nodes paradoxically maintain robust tissue architecture in homeostasis yet are continually poised for extensive tissue expansion upon immune challenge. We find that following immune challenge, cytoskeletal mechanics of a cellular meshwork of fibroblasts determine tissue tension independently of extracellular matrix scaffolds. We determine that CLEC-2/podoplanin signalling regulates the cell surface mechanics of fibroblasts, permitting cell elongation and interdigitation through expedited access to plasma membrane reservoirs. Increased tissue tension through the stromal meshwork gates the initiation of fibroblast proliferation, restoring homeostatic cellular ratios and tissue structure through expansion.

Study of operational properties of steel friction pairs with antifriction coating from copper alloys produced by electric spark alloying

Improving the reliability, durability and safety of operation of heavily loaded friction units is an urgent problem in physics, chemistry and surface mechanics. The tribotechnical characteristics of coatings made of bronzes BrAZhMts10-3-1.5 and BrMtsF3-6, applied by electrospark alloying on bushings made of structural steel 30KhGSN2A for operation under conditions of high contact pressure under friction without lubrication, have been investigated. Modes of coating deposition from the standpoint of tribology (the value of the electric discharge current in a pulse, the value of the longitudinal electrode feed per one rotation of the part, the rotation speed of the workpiece, the number of passes during processing, finishing of the coating) have been developed. It was found that when applying bronze BrMtsF3-6 to obtain a high-quality coating, the process must be performed in a protective atmosphere of argon to prevent phosphorus burnout. The tribotechnical efficiency of coatings when working under dry friction conditions is shown. For the steady-state wear mode, the friction coefficient is 0.10 – 0.13 at a pressure of 200 – 250 MPa, the wear resistance of coated steel is doubled. Steel with a bronze coating BrAZhMts10-3-1.5 has a higher bearing capacity, with BrMtsF3-6 coating — a higher antifriction. The ways of increasing the service life of steel-coated steel friction pair are analyzed.

Thickness Estimation of TiO2-Based Nanotubes Using X-Ray Diffraction Techniques

TiO2-based nanotubes are a very promising material with many applications in solar cells, biomedical devices, gas sensors, hydrogen generation, supercapacitors, and lithium batteries, among others. Nanotube thickness is a very important property since it is related to electronic and surface mechanics. In this sense, transmission electron microscopy (TEM) can be used. However, it can be difficult to acquire a good TEM image because the transversal section of the nanotubes needs to be visible. In this work, TiO2-based nanotubes obtained via hydrothermal synthesis were studied using X-ray line profile analysis. Scherrer and Single-Line methods provided consistent results for the thickness of the nanotubes (≃ 5 nm) when compared with TEM. Additionally, Single-Line method was also applied to estimate the microstrain. The advantage of using XRD is given by the fact that it is a quick and statistically significant analysis when compared with TEM. The results show that XRD can be used as a rapid and reliable alternative for the thickness estimation of nanotubes.