Atomic force microscopy is a unique technique for probing the mechanical properties of nanostructures. Using the bending-based test method, one can measure the Young’s modulus of the material of a ...suspended object, a nanobridge. This article presents a new, improved version of the bending-based test method. A special algorithm is elaborated to establish the nanobridge span length and to identify the boundary conditions of the nanobridge fixation. In particular, to realize this algorithm we propose a model of the beam with transformable boundary conditions (between clamped and supported beam model cases) varied by the only fitting parameter. To illustrate the main features of the developed bending-based test method application, the Young’s modulus measurements of mineral chrysotile nanoscrolls, forming the nanobridges across the pores of a track membrane, are presented.
In atomic force microscopy, the interaction of a probe with a sample is usually controlled by the angle of cantilever bending at a selected point on it using an optical lever. Such control is not ...designed to record all three components of the interaction-force vector. It is possible to reveal these components and the result of the force action, i.e., the displacement vector of the “nondeformable” probe of an “ideal” cantilever, by additional measurements of the deformation (by the piezoresistive method) or the amount of bending (by the interferometry method) at a selected point, or the bending angle at one more point on the cantilever. In this paper, we present the results of analytical calculation of the optimal location of these points on a cantilever for six combinations of the above three methods, which reduces the measurement error of the components of the force and displacement vectors to a minimum.
The gene expression differs in the nuclei of normal and malignant mammalian cells, and transcription is a critical initial step, which defines the difference. The mechanical properties of ...transcriptionally active chromatin are still poorly understood. Recently we have probed transcriptionally active chromatin of the nuclei subjected to mechanical stress, by Atomic Force Microscopy (AFM) 1. Nonetheless, a systematic study of the phenomenon is needed.
Nuclei were deformed and studied by AFM. Non-deformed nuclei were studied by fluorescence confocal microscopy. Their transcriptional activity was studied by RNA electrophoresis.
The malignant nuclei under the study were stable to deformation and assembled of 100–300 nm beads-like units, while normal cell nuclei were prone to deformation. The difference in stability to deformation of the nuclei correlated with DNA supercoiling, and transcription-depended units were responsive to supercoils breakage. The inhibitors of the topoisomerases I and II disrupted supercoiling and made the malignant nucleus prone to deformation. Cell nuclei treatment with histone deacetylase inhibitors (HDACIs) preserved the mechanical stability of deformed malignant nuclei and, at the same time, made it possible to observe chromatin decondensation up to 20–60 nm units. The AFM results were supplemented with confocal microscopy and RNA electrophoresis data.
Self-assembly of transcriptionally active chromatin and its decondensation, driven by DNA supercoiling-dependent rigidity, was visualized by AFM in the mechanically deformed nuclei.
We demonstrated that supercoiled DNA defines the transcription mechanics, and hypothesized the nuclear mechanics in vivo should depend on the chromatin architecture.
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•Mechanically deformed normal and malignant cells nuclei were assessed by AFM.•The nuclei of the malignant cells revealed a landscape assembled from 100 to 300 nm beads-like rigid units.•Topoisomerases I and II inhibitors broke supercoils, making nuclear chromatin prone to deformation.•Chromatin decondensation, induced by HDACIs treatment, revealed ∼20 nm rigid units.•The landscape represented transcription events, dependent on the DNA supercoiling.
To improve the accuracy of atomic force microscopy in nanomechanical experiments, an analytical model is proposed to study the static interaction of a cantilever in contact with a sample. The model ...takes into account: the cantilever probe is clamped by the sample or slides along its surface, the geometric and mechanical characteristics of the sample and the cantilever, their relative orientation. The cantilever console bending and torsion angles as functions of the sample displacements in three orthogonal directions have been measured by atomic force microscopy with an optical beam deflection scheme.The measurements are in good agreement with the simulation.
Nuclear rigidity is traditionally associated with lamina and densely packed heterochromatin. Actively transcribed DNA is thought to be less densely packed. Currently, approaches for direct ...measurements of the transcriptionally active chromatin rigidity are quite limited.
Isolated nuclei were subjected to mechanical stress at 60 g and analyzed by Atomic Force Microscopy (AFM).
Nuclei of the normal fibroblast cells were completely flattened under mechanical stress, whereas nuclei of the cancerous HeLa were extremely resistant. In the deformed HeLa nuclei, AFM revealed a highly-branched landscape assembled of ~400 nm closed-packed globules and their structure was changing in response to external influence. Normal and cancerous cells' isolated nuclei were strikingly different by DNA resistance to applied mechanical stress. Paradoxically, more transcriptionally active and less optically dense chromatin of the nuclei of the cancerous cells demonstrated higher physical rigidity. A high concentration of the transcription inhibitor actinomycin D led to complete flattening of HeLa nuclei, that might be related to the relaxation of supercoiled DNA tending to deformation. At a low concentration of actinomycin D, we observed the intermediary formation of stochastically distributed nanoloops and nanofilaments with different shapes but constant width ~ 180 nm. We related this phenomenon with partial DNA relaxation, while non-relaxed DNA still remained rigid.
The resistance to deformation of nuclear chromatin correlates with fundamental biological processes in the cell nucleus, such as transcription, as assessed by AFM.
A new outlook to studying internal nuclei structure is proposed.
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•The method of the imaging of transcriptionally active chromatin by AFM via nuclei mechanical stress was proposed.•Nuclear DNA of normal or transcriptionally inactive cells nuclei was completely flattened under mechanical stress.•HeLa cells' nuclei were sustainable to deformation, revealing the globular higher-packed architecture of the supercoiled DNA.•Transcription inhibitor actinomycin D relaxed tensions of supercoiled DNA reducing its resistance to mechanical stress.•Our results demonstrate a relationship between nuclear mechanics and transcription.
A powder metallurgy process for manufacturing hard magnetic alloy Fe–30Cr–16Co (wt%) was optimized. An acceptable level of magnetic properties of the alloy was reached upon sintering within the ...temperature range 1100–1400 °C (with a maximum at 1350 °C; Br = 1.21 T, Нс = 54.6 kA/m, and (BH)max = 37.6 кJ/m3) and at an overall duration of thermal treatment of 15 h. Lowest magnetic properties (Br = 1.12 T, Нс = 48.6 kA/m, and (BH)max = 31.1 KJ/m3) were observed at 1100 °C most likely due to higher porosity of about 7%. After full thermal treatment with temperature of thermomagnetic stage, 670 °C, we observe the presence of non-magnetic σ-phase, which leads to a sharp drop in magnetic properties. Based on the magnetic measurements at intermediate stages it can be deduced that the σ-phase is formed during the 2nd stage of thermal treatment during cooling down from 670° to 580°C Significant ductility is observed upon material failure during compression tests; fracture strain (εf ∙100%), around 40%. Yield strength, compressive strength, and linear thermal expansion for obtained alloys are presented. The yield strength decreases with increasing sintering temperature within the range 1100–1400 °C due to grain growth.
•Good magnetic properties of Fe–30Cr–16Co alloy could be obtained at wide range of sintering temperatures.•A decisive role in σ-phase formation is played by the temperature interval between stages of thermal treatment.•The yield strength of Fe–30Cr–16Co alloy increases with decreasing sintering temperature.•According to linear thermal expansion studies material suitable for use in hardware.
In this paper, we study changes in the near-surface layers of corrugated Pt foils that are considered as multiscale diffraction gratings in the uniaxial tension process. The structure transformation ...and the ordering degree are analyzed at various stages of loading the samples up to their destruction. Using the concept of multifractal formalism, a criterion for the efficiency of using these foils is proposed.
The optimization of measurements of three spatial components of the probe–sample interaction force and the corresponding “ideal cantilever” displacement vector is considered. To determine these ...components using an atomic force microscope with the optical beam deflection scheme, it is necessary to measure the bending angles at least at two points on the rectangular cantilever, as well as the torsion angle at any of these points. It is proved analytically that one of the optimal points is the intersection of the probe axis with the cantilever plane. A technique for calculating the optimal position of the other point is developed. An experiment concerning mapping of the force and displacement vector is performed, and satisfactory agreement with the theory is achieved.
Present-day multimedia strongly rely on rewritable phase-change optical memories. We demonstrate that, different from the current consensus, Ge(2)Sb(2)Te(5), the material of choice in DVD-RAM, does ...not possess the rocksalt structure but more likely consists of well-defined rigid building blocks that are randomly oriented in space consistent with cubic symmetry. Laser-induced amorphization results in drastic shortening of covalent bonds and a decrease in the mean-square relative displacement, demonstrating a substantial increase in the degree of short-range ordering, in sharp contrast to the amorphization of typical covalently bonded solids. This novel order-disorder transition is due to an umbrella-flip of Ge atoms from an octahedral position into a tetrahedral position without rupture of strong covalent bonds. It is this unique two-state nature of the transformation that ensures fast DVD performance and repeatable switching over ten million cycles.
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