Cortical stiffness of keratinocytes measured by lateral indentation with optical tweezers

Keratin intermediate filaments are the principal structural element of epithelial cells. Their importance in providing bulk cellular stiffness is well recognized, but their role in the mechanics of cell cortex is less understood. In this study, we therefore compared the cortical stiffness of three keratinocyte lines: primary wild type cells (NHEK2), immortalized wild type cells (NEB1) and immortalized mutant cells (KEB7). The cortical stiffness was measured by lateral indentation of cells with AOD-steered optical tweezers without employing any moving mechanical elements. The method was validated on fixed cells and Cytochalasin-D treated cells to ensure that the observed variations in stiffness within a single cell line were not a consequence of low measurement precision. The measurements of the cortical stiffness showed that primary wild type cells were significantly stiffer than immortalized wild type cells, which was also detected in previous studies of bulk elasticity. In addition, a small difference between the mutant and the wild type cells was detected, showing that mutation of keratin impacts also the cell cortex. Thus, our results indicate that the role of keratins in cortical stiffness is not negligible and call for further investigation of the mechanical interactions between keratins and elements of the cell cortex.

Cortical stiffness of keratinocytes measured by lateral indentation with optical tweezers

Keratin intermediate filaments are the principal structural element of epithelial cells. Their importance in providing bulk cellular stiffness is well recognized, but their role in the mechanics of cell cortex is less understood. In this study, we therefore compared the cortical stiffness of three keratinocyte lines: primary wild type cells (NHEK2), immortalized wild type cells (NEB1) and immortalized mutant cells (KEB7). The cortical stiffness was measured by lateral indentation of cells with AOD-steered optical tweezers without employing any moving mechanical elements. The method was validated on fixed cells and Cytochalasin-D treated cells to ensure that the observed variations in stiffness within a single cell line were not a consequence of low measurement precision. The measurements of the cortical stiffness showed that primary wild type cells were significantly stiffer than immortalized wild type cells, which was also detected in previous studies of bulk elasticity. In addition, a small difference between the mutant and the wild type cells was detected, showing that mutation of keratin impacts also the cell cortex. Thus, our results indicate that the role of keratins in cortical stiffness is not negligible and call for further investigation of the mechanical interactions between keratins and elements of the cell cortex.

Spatiotemporal Dynamics of Frictional Systems: The Interplay of Interfacial Friction and Bulk Elasticity

Frictional interfaces are abundant in natural and engineering systems, and predicting their behavior still poses challenges of prime scientific and technological importance. At the heart of these challenges lies the inherent coupling between the interfacial constitutive relation—the macroscopic friction law—and the bulk elasticity of the bodies that form the frictional interface. In this feature paper, we discuss the generic properties of a minimal macroscopic friction law and the many ways in which its coupling to bulk elasticity gives rise to rich spatiotemporal frictional dynamics. We first present the widely used rate-and-state friction constitutive framework, discuss its power and limitations, and propose extensions that are supported by experimental data. We then discuss how bulk elasticity couples different parts of the interface, and how the range and nature of this interaction are affected by the system’s geometry. Finally, in light of the coupling between interfacial and bulk physics, we discuss basic phenomena in spatially extended frictional systems, including the stability of homogeneous sliding, the onset of sliding motion and a wide variety of propagating frictional modes (e.g., rupture fronts, healing fronts and slip pulses). Overall, the results presented and discussed in this feature paper highlight the inseparable roles played by interfacial and bulk physics in spatially extended frictional systems.

INVESTIGATION OF THE EFFECT OF ATTENUATION OF ELASTIC LONGITUDINAL WAVES IN CAST IRON WITH FLAKE GRAPHITE ON THE CHARACTERISTICS OF SIGNALS DURING ULTRASONIC TESTING

The model of estimation of damping coefficient of elastic longitudinal waves in cast iron with flake graphite due to their Rayleigh and phase scattering on graphite inclusions, considering the deviation of the modulus of bulk elasticity of the phases of cast iron (metal base and graphite) from the mean value, is developed according to the theory of Mason. At the same time, the characteristics of cast iron used for calculations include the value of the longitudinal wave velocity, the mass content of graphite inclusions and their average size. In the process of studying the effect of attenuation of elastic longitudinal waves in cast iron with flake graphite on the characteristics of signals with narrow, medium width and wide spectra, a difference in the nature of the spectra changes due to frequency-dependent attenuation depending on the nominal pulse frequencies, cast iron models and the distance traveled by the ultrasonic wave is established. It is shown that the shorter the pulse, the greater the shift of the spectrum maximum in the frequency range less than the nominal. The effect of attenuation of longitudinal waves in cast iron with flake graphite on the impulse directivity characteristic of the round piezoplate depending on the cast iron model and pulse spatial length is established. The expansion of pulse directivity characteristics with increasing of the distance traveled by the wave in cast iron is shown, the greater the wider the pulse spectrum.

Temperature Dependence of the Bulk Elasticity Modulus of Aliphatic Alcohols and Their Fluorinated Analogs

The density of some fluorinated and non-fluorinated normal monoatomic alcohols and the sound propagation velocity in them have been studied experimentally in a temperature interval of 293–363 K. The bulk modulus of elasticity is calculated, and its relation with the intermolecular interaction energy is analyzed. The energy of intermolecular interaction in fluorinated alcohols is shown to be lower than in their non-fluorinated analogs. The substitution of hydrogen atoms by fluorine ones in the molecules of aliphatic alcohols increases the equilibrium distance between the molecules.

Laws of volume elasticity in physical processes of the effect of T, P, H parameters on the lattice modifications, phase transitions, conductivity and magnetism

Analysis of the experimental results allows to single out the law of bulk elasticity that implies that the structural binding energy is formed by physical and chemical methods and transformed into elastic stresses that control lattice changes, formation of phase transitions, resistivity and magnetism in the course of physical processes under the effect of parameters. The laws of volume thermo-, baro-and magnetoelasticity are the determining factors in lattice modifications in the structure sites together with the composition variation.

Microscale mapping of extracellular matrix elasticity of mouse joint cartilage: an approach to extracting bulk elasticity of soft matter with surface roughness

Novel analysis and experimental methodology for extracting bulk elasticity from cartilage sections and other soft materials with surface roughness.