I. V. Kirillova

Electrospun Chitosan Nanofiber Materials as Burn Dressing

Burn healing is one of the most important problems of modern surgery due to the high percentage of burns among other traumas, high lethality and disability after the treatment for burns of high surface area. Problem of the covering of large burned surfaces is still a challenge. In present study, a novel electrospun nanofibrous material is proposed as a new material for burn dressing. Versatility of electrospinning nanofiber manufacturing method allows developing various types of micro- and nanofiber materials from biocompatible and biodegradable polymers, including chitosan. Samples of chitosan nanofiber mats were created and tested as wound dressings for IIIa and IIIb degree burns. It is shown that chitosan nanofiber dressings provide effective absorbtion of exudate, ventilation of the wound, protection from infection and stimulate the process of skin tissue regeneration. Degradation of these materials prevents mechanical damage of wound during removing. The influence of thickness of materials on regenerative processes and degradation is studied. Mechanical properties of nanofiber mats are investigated.

Finite Element Model of the Patched Human Carotid

Introduction: The hemodynamic effects of carotid artery patching are not well known. Our objective was to develop a fluid-solid finite element model of the endarterectomized and patched carotid artery. Methods: Hyperelastic materials parameters were determined from studies of 8 cadaveric carotids. Blood flow characteristics were based on intraoperative data from a patient undergoing endarterectomy. Wall shear stress, cyclic strain and effective stress were computed as hemodynamic parameters with known association with endothelial injury, neointimal hyperplasia abd atherogenesis. Results: Low wall shear stress, high cyclic strain and high effective stress were identified diffusely in the carotid bulb, at the margins around the patch and in the flow divider. Conclusion: Endarterectomy and Polytetrafluoroethylene patching produce considerable abnormalities in the hemodynamics of the repaired carotid. Advanced mechanical modeling can be used to evaluate different carotid revascularization approaches to obtain optimized biomechanical and hemodynamic results for the care of patients with carotid bifurcation disease.

Dispersion of waves in a plane acoustic layer with flexible elastic walls

A plane acoustic layer bounded by elastic membranes is considered. Dispersion relations for symmetric and antisymmetric waves are derived. The limit behavior of dispersion curves is investigated for wave numbers tending to zero and to infinity. With the use of the resulting asymptotic expansions, the two-point Pade approximations are constructed. The orthogonality relations for eigenmodes are presented.

Asymptotic integration of the dynamic equations of the theory of elasticity for the case of thin shells

Abstract Asymptotic integration of the three-dimensional dynamic equations of the theory of elasticity is carried out for the case of thin shells. Specific features of the asymptotic properties of the stress-strain state (SSS) of the shell in dynamic problems are discussed. Limiting two-dimensional systems of equations are derived.

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.

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.

Biomechanical rationale of coronary artery bypass grafting of multivessel disease.

The biomechanical model of human coronary arteries was modified for improving the quality of diagnosis and surgical treatment for coronary heart disease. The problem of hemodynamics in the left coronary artery with multivessel bed disease – 45% stenosis of the anterior descending branch and 75% stenosis of the circumflex branch – was particularly considered. Numerical simulation of the coronary arterial bypass of the main trunk was carried out to estimate the functional condition of the coronary arteries after restoring myocardial blood supply by surgery.

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.

Hyperbolic Boundary Layers in Compound Cylindrical Shells

A survey of papers dealing with the mathematical modeling of transient wave propagation in compound and stiffened shell constructions by asymptotic methods based on exact three-dimensional elasticity equations can be found in [1]. Longitudinal actions of tangential and bending types are considered. An asymptotic model of wave propagation in a semi-infinite shell of rotation is used, which employs the two-dimensional Kirchhoff-Love (tangential and flexural) components, the solutions of the quasiplane problem of elasticity, the parabolic boundary layer near the quasifront, and the hyperbolic boundary layer near the expansion wave front. The boundary value contact problems for the incident, reflected, and transmitted waves are posed and solved on the basis of approximate theories for the corresponding components. If the boundary conditions are satisfied at the shell faces in the exact three-dimensional form in small neighborhoods of the shell end contact region, then the construction of the quasistatic boundary layer satisfying the boundary conditions together with the two-dimensional component is completed. Methods proposed for solving boundary value problems by using integral transforms and asymptotic approaches to their inversion are described. But the methods developed for constructing hyperbolic boundary layers near the wave fronts are not described in [1].The present paper supplements the materials presented in [1] with the description of hyperbolic boundary layers for all types of shell face actions including the case of NW-type forces, which have not yet been described.

The deflection of a carbon composite carbon nanotube / graphene using molecular dynamics simulation

For the first time, the dependence of the bending force on the transverse displacement of atoms in the center of the composite material consisting of graphene and parallel oriented zigzag nanotubes was studied. Mathematical modeling of the action of the needle of the atomic force microscope was carried out using the single-layer armchair carbon nanotube. Armchair nanotubes are convenient for using them as a needle of an atomic force microscope, because their edges are not sharpened (unlike zigzag tubes). Consequently, armchair nanotubes will cause minimal damage upon contact with the investigation object. The geometric parameters of the composite was revealed under the action of the bending force of 6μN.