Theoretical study of peculiarities of unstable longitudinal shear crack growth in sub-Rayleigh and supershear regimes

In the paper we present the results of the theoretical study of some fundamental aspects of mode II crack propagation in conventional sub-Rayleigh regime and transition to intersonic regime. It is shown that development of a sub-Rayleigh shear crack is determined in many respects by elastic vortex traveling ahead of the crack tip at a shear wave velocity. Formation of such a vortex helps to better understand the well-known phenomenon of acceleration of a shear crack towards the longitudinal wave velocity. Simulation results have shown that due to self-similarity of shear crack propagation the conditions of sub-Rayleigh to intersonic transition depend on dimensionless material and crack parameters. Two key dimensionless parameters are proposed

A molecular dynamic study of charged nanofilm interaction with negative lipid bilayer

Hydrophobic and functionalized nanoparticles of different sizes and shapes have a various biomedical application, in particular anticancer therapy. It is known that charged nanoparticles may bind lipids and membrane proteins as well as cause lipid bilayer disruption. We have performed preliminary molecular dynamic simulations to investigate the effect of positively charged synthetic nanofilm, imitating a fragment of the two-dimensional folded AlOOH structure, on the POPE/POPG lipid membrane. It has been shown that the synthetic nanofilm with frozen coordinates tightens the membrane and binds lipid headgroups. Furthermore, the presence of the positively charged nanofilm perturbs the cation concentration in the near-surface membrane region

Adsorption of charged protein residues on an inorganic nanosheet: Computer simulation of LDH interaction with ion channel

Quasi-two-dimensional and hybrid nanomaterials based on layered double hydroxides (LDH), cationic clays, layered oxyhydroxides and hydroxides of metals possess large specific surface area and strong electrostatic properties with permanent or pH-dependent electric charge. Such nanomaterials may impact cellular electrostatics, changing the ion balance, pH and membrane potential. Selective ion adsorption/exchange may alter the transmembrane electrochemical gradient, disrupting potential-dependent cellular processes. Cellular proteins as a rule have charged residues which can be effectively adsorbed on the surface of layered hydroxide based nanomaterials. The aim of this study is to attempt to shed some light on the possibility and mechanisms of protein “adhesion” an LDH nanosheet and to propose a new direction in anticancer medicine, based on physical impact and strong electrostatics. An unbiased molecular dynamics simulation was performed and the combined process free energy estimation (COPFEE) approach was used

Molecular Level in Silico Studies for Oncology. Direct Models Review

The combination of therapy and diagnostics in one process "theranostics" is a trend in a modern medicine, especially in oncology. Such an approach requires development and usage of multifunctional hybrid nanoparticles with a hierarchical structure. Numerical methods and mathematical models play a significant role in the design of the hierarchical nanoparticles and allow looking inside the nanoscale mechanisms of agent-cell interactions. The current position of in silico approach in biomedicine and oncology is discussed. The review of the molecular level in silico studies in oncology, which are using the direct models, is presented

Two-Dimensional Al Hydroxide Interaction with Cancerous Cell Membrane Building Units: Complexed Free Energy and Orientation Analysis

The application of hierarchical nanoparticles based on metal hydroxides in biomedicine, including anticancer therapy and medical imaging, is a rapidly developing field. Low-dimensional aluminum oxyhydroxide nanomaterials (AlOOH-NM) are quite promising base to develop hybrid theranostic nano-agents with core-shell architecture, which is determined by AlOOH-NMs physicochemical properties such as: large specific surface area, pH-dependent charge, amphoteric behavior, high surface density of polar groups capable to form non-covalent bonds, low or null cytotoxicity and biocompatibility. Characterization of the system behavior within interface between NM and plasmatic membrane is crucial for the understanding of nano-agent-cell interaction. In the present work the complex in silico study including the free energy estimation and orientation analysis of phosphatidylcholine (POPC) and phosphatidylethanolamine (POPE) lipids interacting with AlOOH nanosheet was conducted to understand the effect of such nanomaterial on cancerous cell plasmatic membrane

Theoretical investigation of influence of pore pressure on mechanical response of gas-filled permeable materials

The paper is devoted to theoretical investigation of the influence of gas pore pressure on the characteristics of mechanical response of gas-filled permeable materials and media. Investigation was based on computer-aided simulation by hybrid cellular automaton method. Mechanical response of the model gas-filled samples of young brown coal under unconfined (in absence of constraint) and constrained conditions was investigated. The simulation results showed that increase of the pore pressure of the gas acting on the solid skeleton leads to decrease in materials strength. This is due to the fact that the gas pressure makes an additional contribution to integral pressure acting in volume of the loaded medium. Consequences of this are earlier beginning of plastic deformation and fracture of the material. It should be noted that in the constrained conditions decreasing of material strength with increasing gas pore pressure has more pronounced nonlinear character, in comparison with similar tests for unconfined samples. This is due to the fact that loading of constrained material is accompanied by its massive cracking and, consequently, by a grater decrease of the strength characteristics of the medium

The computer-aided simulation of deformation and fracture of water-saturated elastic porous material with hybrid cellular automaton method

A method of numerical simulation of liquid-saturated porous media, that represents a combination of particle method and finite-difference method, namely, the hybrid cellular automaton method was proposed. It allows taking into account inelastic deformations, dilation and fracture of solid skeleton as well as the influence of pore pressure on the stress state of the skeleton and the redistribution of a liquid in filtration volume of porous medium. The method was applied to study the influence of viscous compressible liquid in pores of material on its strength and fracture. It has been shown that the strength of brittle liquid-saturated specimens depends on the material properties and the geometry of porosity, the physical-mechanical properties of the liquid etc. The latter shows the topicality of application of numerical methods to study and predict strength properties of fluid-saturated media under loading

On the role of scales in elastomer friction

The paper is devoted to a general analysis of friction of elastomers from the point of view of scales contributing to the force of friction. We argue that-contrary to the wide spread opinion-elastomer friction is not a multiscale phenomenon, but is governed mostly by the interplay of only two scales-the largest and the smallest scales of roughness of the contacting bodies. This is illustrated by analyzing the main ideas of the theory of elastomer friction based on the paradigm of Greenwood, Tabor and Grosch. The same conclusions can be obtained from the widely used contact theory proposed by Persson

Influence of crystallographic orientation on the response of copper crystallites to nanoindentation

Molecular dynamics simulation was performed to study the features of nucleation and development of plastic deformation in copper crystallites in nanoindentation with different crystallographic orientations of their loaded surface: (011), (001), and (111). Atomic interaction was described by a potential constructed in terms of the embedded atom method. It is shown that behavior of the crystallite reaction force correlates well with a change in the fraction of atoms involved in local structural rearrangements. The generation of local structural changes decreases the slope of the crystallite reaction force curve or results in an extremum due to internal stress relaxation. Analysis of structural changes in the material being indented demonstrates that the orientation of its loaded surface greatly affects the features of nucleation and development of plastic deformation

Iron oxide and gold nanoparticles in cancer therapy

Continuous research activities in the field of nanomedicine in the past decade have, to a great extent, been focused on nanoparticle technologies for cancer therapy. Gold and iron oxide nanoparticles (NP) are two of the most studied inorganic nanomaterials due to their unique optical and magnetic properties. Both types of NPs are emerging as promising systems for anti-tumor drug delivery and for nanoparticle-mediated thermal therapy of cancer. In thermal therapy, localized heating inside tumors or in proximity of tumor cells can be induced, for example, with Au NPs by radiofrequency ablation heating or conversion of photon energy (photothermal therapy) and in iron oxide magnetic NPs by heat generation through relaxation in an alternating magnetic field (magnetic hyperthermia). Furthermore, the superparamagnetic properties of iron oxide nanoparticles have led to their use as potent MRI (magnetic resonance imaging) contrast agents. Surface modification/coating can produce NPs with tailored and desired properties, such as enhanced blood circulation time, stability, biocompatibility and water solubility. To target nanoparticles to specific tumor cells, NPs should be conjugated with targeting moieties on the surface which bind to receptors or other molecular structures on the cell surface. The article presents several approaches to enhancing the specificity of Au and iron oxide nanoparticles for tumor tissue by appropriate surface modification/functionalization, as well as the effect of these treatments on the saturation magnetization value of iron oxide NPs. The use of other nanoparticles and nanostructures in cancer treatment is also briefly reviewed