Elena L. Kossovich

Hybrid coarse-grained/atomistic model of “chitosan + carbon nanostructures” composites

We present a new hybrid molecular dynamics model of chitosan oligomers which is constructed specifically for studying chitosan + carbon nanostructures composites, their structure and mechanical properties. The model is derived for application within the modified molecular mechanics force field AMBER. Method of virtual sites mapping allowed to retain hexagonal rings of chitosan backbone. Mass and structural disposition of virtual atoms has been found as function of joined groups’ atoms masses and coordinates. Geometrical parameters (e.g., bond length, valence angles, torsional angles and van der Waals distances) were found using semi-empirical methods. Parameters of interaction within the AMBER force field were estimated according to structural and energy characteristics of chitosan dimers and oligomers. Model has successfully passed multilevel verification based on comparison of its behaviour with atomistic chitosan within the same force field. It appeared that the model reproduces structural and energy characteristics of chitosan and its composites with carbon nanostructures. Moreover, it allows estimation of their mechanical properties. Dynamical characteristics of composite components are also well reproduced.

Predictive analysis of chitosan-based nanocomposite biopolymers elastic properties at nano- and microscale

Chitosan nanocomposites mechanical properties play a major role in usage of such materials for specific areas of application, mostly in medicine and development of ecologically-friendly production. Computer-based predictive modelling of such composites will reduce costs of their development. In this paper, a multiscale approach for structural characterization and evaluation of mechanical properties is proposed based on hybrid coarse-grained/all atom molecular dynamics. Chitosan films and fibers are constructed and studied in silico as well as chitosan composites with different types of randomly distributed reinforcing fillers (graphene nanoparticles, graphene oxide nanoparticles, carbon nanotubes, chitin nanoparticles). Young’s moduli are found for such composites, degrees of improvement of mechanical properties and size effects within the framework of proposed methodology are discussed.

Strain-hardening effect of graphene on a chain of the chitosan for the tissue engineering

We report the results of the chitosan dimer study, the mechanism of its interaction with the carbon nanostructures and also the mechanical properties of the chitosan/graphene, chitosan/nanotube complexes using the density function and the molecular dynamic methods. It was established that the physical adsorption of the chitosan with graphene is carried out by the Van der Waals interaction between the hexagonal links of the chitosan with the hexagonal cell of the atomic grid of graphene and nanotube.

Study of lipoproteins and arterial intima interaction based on arterial endothelial cells real geometrical structure

An original methodology is developed for scanning of the arterial intima morphology using the atomic force microscopy. The probing nanolaboratory NTEGRASpectra (NT-MDT, Russia) was itilized. The pictures of the coronary artery intima topology were obtained with the resolution of 1 nm. The 3D model of the ‘endothelial cell surface - low density lipoprotein (LDL)’ complex was constructed. Using the ANSYS software, the deformation of LDL particle was found as well as the stress distribution at the moment of the macromolecule and endothelial surface collision. The largest normal and tangential stresses are found in the area of LDL interaction with the surface. These stresses are 2.173 and 0.053 kPa, respectively. It was shown that the LDL structure is being highly strained, which leads to the molecule compression and crease. Therefore, one can conclude that at the moment of LDL entering the intercellular hiatus the macromolecule will be suffering the overall deformations and large modification of its structure.

Super strong nanoindentors for biomedical applications based on the bamboo-like nanotubes

The results of quantum-chemical analysis of elastic and strength properties of the bamboo-like tube are presented in this paper. For the first time the configuration of the thinnest stable bamboo-like tube was established. The bamboo-like nanotube breaking point is established to be under compression of 11GPa. Configuration of the nanoindentor based on symmetric and streamlined tip of the tube (15,15), presented in this work, provides perfect interaction between the nanoindentor tip and the tissue because tip has no sharp protruding pieces.

Mechanical Properties of Thin Films of Coals by Nanoindentation

In the current work, depth-sensing indentation tests were applied at different coals microcomponents in order to characterize their mechanical properties. To this end, three coals were chosen differing by their rank and properties. Thin transparent films of such coals were prepared as samples in order to use transmitted light microscopy to achieve exact positioning of indent probe in the zone occupied by specific coal microcomponent. Experimental procedures allowed obtaining load-displacement curves at different microcomponents. These curves revealed differences between microcomponent vitrinite behavior among coals of different types. Measured values of elastic moduli and hardness also proved that they variate with coal rank. It was concluded that matrix of coals (vitrinite microcomponent) transforms its mechanical properties with rank, whereas the inclusions properties do not change as significantly.

Finite Element Modeling of Atherosclerotic Plaque Evolution

In this paper we considered a time-dependent coupled problem of the low-density lipoproteins (LDL) diffusion into internal layers of the blood vessel, diffusion of macrophages and deformation of the vessel wall with endothelial defects. Solving of the problem in its axisymmetric formulation is performed using finite element (FE) package Comsol Multiphysics in the framework of joint working modes: Convection/Diffusion (for the LDL), Diffusion (for the LDL modified by macrophages, or foam cells), and Moving Mesh (for visualizing the wall deformation).

Mechanical properties of coal microcomponents under continuous indentation

The article reports data on continuous indentation of different rank black coal and anthracite. The test specimens are specially prepared, and their faces are differently oriented relative to their bedding planes. Different mechanical behavior of coal and anthracite microcomponents in different planes relative to bedding is identified, and relevant values of elasticity modulus and hardness are determined. The measurements exhibit spatial anisotropy of microlevel mechanical properties of vitrinite and inertinite.

Patient-specific system for prognosis of surgical treatment outcomes of human cardiovascular system

Object of study: Improvement of life quality of patients with high stroke risk ia the main goal for development of system for patient-specific modeling of cardiovascular system. This work is dedicated at increase of safety outcomes for surgical treatment of brain blood supply alterations. The objects of study are common carotid artery, internal and external carotid arteries and bulb. Methods: We estimated mechanical properties of carotid arteries tissues and patching materials utilized at angioplasty. We studied angioarchitecture features of arteries. We developed and clinically adapted computer biomechanical models, which are characterized by geometrical, physical and mechanical similarity with carotid artery in norm and with pathology (atherosclerosis, pathological tortuosity, and their combination). Results: Collaboration of practicing cardiovascular surgeons and specialists in the area of Mathematics and Mechanics allowed to successfully conduct finite-element modeling of surgical treatment taking into account various features of operation techniques and patching materials for a specific patient. Numerical experiment allowed to reveal factors leading to brain blood supply decrease and atherosclerosis development. Modeling of carotid artery reconstruction surgery for a specific patient on the basis of the constructed biomechanical model demonstrated the possibility of its application in clinical practice at approximation of numerical experiment to the real conditions.

Molecular dynamics study of phospholipid biomacromolecules using a coarse-grained model

We studied the phospholipid molecule structure, rigidity, rotary mobility and micelle aggregation process using a coarse-grained (CG) model. It was found that the phospholipid structure can be presented as a spring with a rigidity of 27.68 kN/m. The rotational frequency of such molecule equals to 0.9 GHz at the temperature of 293 K and increases up to 1.2 GHz at 309K. At the constant temperature the micelle aggregation time does not depend on number of interacting molecules. Along with the temperature increase, the aggregation time decreases. At lower temperatures the assembly process depends on distance between the adjacent molecules.