Russian Journal of Biomechanics

The mechanical response of the eye to cornea loading by wide flat stamps of different weights (Maklakoff elastotonometry) is studied in the case of artificially created strong inhomogeneity of the elastic properties of the cornea, which is formed due to vision correction surgery. The weakening of the cornea in the apical region or in the peripheral annular zone that lies a short distance from the sclera but is not adjacent to it is considered. The first case corresponds to correction of myopia and the second one to that of hyperopia. The cornea is modeled by a momentless, linearly elastic surface and the scleral region by an elastic reservoir that responds to changes in volume by changes in pressure. Within this representation, the mechanical properties of the cornea are characterized by the effective stiffness, a parameter that reflects both the elastic properties of the cornea material and the corneal thickness. It is shown that for moderate corneal stiffness the dependence of the tonometric pressure on the tonometer weight remains, similar to the case of homogeneous cornea, almost linear, which makes it possible to introduce the pressure difference coefficient as the slope of the corresponding straight line. The dependence of this coefficient on parameters that characterize the distribution of the elastic properties of the cornea is studied for various true pressures and scleral stiffnesses. The corneal inhomogeneity effect turned out to be qualitatively different for apical and peripheral weakening but insignificant. In the latter case, the effect is less expressed and, moreover, practically indiscernible. Thus, for operated eyes with moderately stiff corneas, the earlier developed methods of clinical estimation of elastotonometry results can be used.

Breastfeeding, due to its nutritional and immunological aspects, is the best source of food for a newborn. In a situation where it is not possible to breastfeed her baby, for example, when the mother has returned to work or is otherwise temporarily separated from her baby, it is necessary for her to express breast milk for storage and use during the period of separation. Also, if infant is unable to effectively draw out the milk, for example, due to premature birth, illness, or underdeveloped nursing reflex, it may be necessary to express the milk from the mother’s breast using a breast pump. To achieve lactation success before a suckling can ensure the effective extraction of milk, breast pumps must meet specific mechanical requirements. However, the parameters of the vacuum stimuli by which milk is produced remain non-optimized. A method was developed to compare the amount of milk ejected by vacuum pulses of different amplitudes. Milk was ejected during one session alternately by series of vacuum pulses of different amplitudes into separate containers in the same woman. In order to minimize the influence of reflex pressure increase in the gland duct system on milk excretion, the vacuum stimuli with the help of a special switch were grouped into a series of 4 vacuum pulses periodically following each other with a duration of 4 s series. In addition, to increase the accuracy of measuring the amount of milk at the end of each series of vacuum pulses, an additional vacuum pulse was introduced, with the help of which an air flow in the direction of the milk collectors was created, contributing to the removal of milk residues from the conductive paths of the switch. It was found that for most nursing women the optimal amplitude of the vacuum is about 190 mm Hg.

One of the main factors of environmental pollution is oil and petroleum products, which annual global emissions resulting from multiple accidents and leaks amount tens of thousands of tons. The problem of oil pollution of water resources has acquired a threatening scope due to a growing offshore oil production and transportation of petroleum products by sea and river transport. An effective way to eliminate the oil pollution of water environments is bioremediation using hydrocarbon-oxidizing microorganisms, in particular actinobacteria of the genus Rhodococcus . We studied the adsorption dynamics of Rhodococcus ruber IEGM 231 cells at the interface between bacterial suspension and liquid hydrocarbon ( n -hexadecane or n -dodecane). As a result, mathematical modelling of the initial stage of biofilm formation was performed based on thermodynamic description of cell cluster formation and destruction. The first developed biomechanical model of the surface (interfacial) tension time dependence is phenomenological, it describes the experimental graphs of the corresponding dependence obtained by high-precision tensiometry at different optical densities of bacterial suspensions. The second microlevel model is based on the theory of saturation of the bacterial adsorption layer and the biofilm formation at the hydrocarbon-water interface. In this model, a theoretical explanation of the revealed oscillatory dynamics of interfacial tension is proposed, thus relating to the measuring ring passages through the formed biofilm and the random nature of cell cluster formation-destruction to achieve thermodynamically stable state of the system.

Numerical study of unsteady three-dimensional flow in the constructed from clinical data model of stenotic common carotid artery with physiological maximum tortuosity has been carried out. It is established that the maximum intensity of the secondary flow is observed in Dean vortices, but not in swirling (one-vortex) flow; this circumstance should be taken into account, in particular, for conducting clinical measurements. The maximum wall shear stresses, that are dangerous because of possible damage to artery wall, are observed at a distance of 2-3 stenotic vessel diameters behind of stenosis on the external (relative to the center of the radius of curvature) side of the artery and increase with degree of stenosis. The minimum wall shear stresses that are dangerous from the point of view of atherosclerosis are observed on the inner side of the artery and their location is shifted to the end of the cervical segment of artery with increasing of degree of stenosis.

Taxis is a natural response that a living organism has towards stimuli such as gravity (gravitaxis), light (phototaxis), or chemical substances (chemotaxis), etc. Thermotaxis is the motion of a microorganism towards or away from a thermal stimulus, which generates a thermotactic pattern in nature. Examples include the motion of Dictyostelium slugs , the thermoregulation of honeybees, the behavior of roundworms (specifically Caenorhabditis elegans ), the behavior of human and animal sperm, and how colloidal particles act. Multiple mathematical models were suggested to deal with thermotaxis. The main goal of this paper is to predict the onset of thermotactic convection in fluid medium by using the linear stability analysis. Biological systems are known as the most common systems, where thermotactic patterns generated by living organisms could happen. This category of taxis takes place in a variety of directional motion of microorganisms, having the common sense of motion under the gradient-stimuli and can be generalized mathematically under the form of gradient-based taxis. The results from linear stability analysis show that the thermotactic convection is analogous to the classical thermal convection created by a constant temperature, when the Peclet number is small, and there exists an important overstability condition, when the microorganism cell diffusivity is greater than the thermal diffusivity. The promising future study from this analysis will rely on the application to the harmful algal blossoming.

The results of works about modern materials for implantation in dentistry are presented. Approaches to evaluate the performance efficiency of dental implants, both for single restoration, and for the complete restoration of the entire jaw, with a permanent prosthesis are considered. New forms of implants are being developed, new materials are being used, as well as methods of implantation in the field of dental implantology. In this regard, experts in the field of dentistry often turn to mechanics to evaluate the load-bearing capacity of biomechanical structures. The arising problems don’t belong to the number of formalizable problems that can be solved analytically and require the description in three-dimensional form. Therefore, numerical solutions must be used to solve them. The finite element method is the most convenient and often applicable. In this regard, there has been an increase in the number of publications devoted to the determination of the stress-strain state, both prostheses and bone tissue in the area of their fixation. The review of modern articles and books devoted to current researches and trends in the field of dental biomechanics is given.

This article discusses the beginning of scientific and practical path of Academician, Doctor of Medical Sciences, Professor Gavriil Abramovich Ilizarov, the establishment of the transosseous compression-distraction osteosynthesis on its early stage with respect to V.I. Stetsula and V.P. Shtin the scientists of Sverdlovsk (Yekaterinburg) Institute of reconstructive surgery by the method of transosseous compression-distraction osteosynthesis (1957), Sverdlovsk institute of reconstructive surgery (1959); and the scientist’s contribution into the development of the world community.