Russian Journal of Biomechanics

This study is aimed at creation of 3-D geometrical and mechanical finite-element models of the cornea and numerical analysis of its stress-strain state and mechanical behavior under conditions of intraocular pressure and external air jet pressure when diagnosing patients at different stages of keratoconus as well as after treatment with corneal collagen cross-linking. There is created a geometrical model of the cornea in a form of spatial segment of thin-shell convex structure where shell thickness is variable and form of anterior and posterior surfaces is determined arbitrarily by extrapolation of experimental data of corneal topographic study of a specific patient with keratotopograph Pentacam AXL. Material, used for emulation of the cornea, is regarded as heterogeneous, isotropic and nonlinearly elastic. Its coefficients of rigidity are assigned basing on the known experimental data and are adjusted by correlation of parameters on corneal deformation under airflow impulse resulting from numerical modeling and their true estimation by noncontact tonometer Corvis ST. To describe airflow impact occurring in course of tonometry a distributed impulse strain, with parameters corresponding to the settings of airflow impulse of the applied equipment, is effectuated to a part of anterior surface of the emulated shell. If ectatic process is present adjacent to the corneal region in question, local segments with diminishing coefficients of rigidity (from periphery to the center) are applied. Dimensions, form, place, quantity of such regions and character of rigidity decrease inside them are derived from solution of inverse problems aimed at minimization of difference between the results of emulation and experimental measurement of keratotopometric and deformational parameters in specific points of the cornea. To simulate corneal collagen crosslinking procedure, an additional circular zone with enhanced rigidity coefficients is provided. Modification of rigidity characteristics by depth and radius of this zone, is set in accordance with experimental data on photosensitive agent distribution in course of its diffusion within the cornea and flux density of UV emission.

The recent decade is known for changes in approaches to malignant tumor treatment. It has become known that a tumor is a heterogeneous agglomeration of cancer cells and can develop different spatial structures for collective invasion and migration over the course of its evolution Cancer cell budding at the invasive front of a tumor is one of the processes which determine its malignant nature. A new approach to tumor and its manifested effects in its evolution should be examined both with the medical methods and the methods of mathematical modeling. The methods of mathematical modeling applied in studies of malignant entities help observe the processes in their dynamics running during tumor growth. We develop a mathematical model of heterogeneous invasive carcinoma growth. The model derives from the model of a cell with its individual dynamics that enables us to describe the object under analysis in detail to some extent. Modeling reproduces the effect of budding during the growth of a cribriform carcinoma. This has been qualitatively compared with the results of clinical studies of histological sections. We also measured quantitative characteristics, the index of epithelial-mesenchymal transition which is compared with a cell phenotype in epithelial tissue. The paper shows dynamics in the development of cells-buds, their migration near the tumor front, and amoeboid migration in epithelial tissue. The paper also describes the development of a second tumor source triggered by the mesenchymal-epithelial transition. The results of the study demonstrate the dynamics in the development of malignant entities and their inherent effects.

The aim of teaching the canoeing technique is to develop effective motor patterns ensuring the stability and reliability of the results regardless of the conditions for movement realization. The paper presents an algorithm for automated assessment of the stability of the motor pattern of canoe paddlers based on the amplitude-time analysis of muscle electromyography profiles. New diagnostic indicators of physical and technical readiness of canoeing paddlers have been proposed: the coefficient of stability of the muscle activity and the coefficient of stability of the temporal structure of the stroke. The studies of the stability of the motor pattern of first class canoe paddlers ( n = 16) have been carried out under different conditions of movements using the paddling ergometer: covering a distance of 250 m with maximum power of movements (test 1) and covering a distance of 250 m with maximum pace of movements (test 2). It has been found that first class canoe paddlers are characterized by a high stability of the muscular activity (on average more than 86 %) and high stability of the temporal structure of strokes (more than 93 %), regardless of the power and pace of movements. Moreover, the research has revealed a tendency for increase in the stability of muscular activity of the paddlers with increasing training experience ( r = 0,70 for the mode of maximum power of movements, r = 0,73 for the mode of maximum pace of movements).

The antropoid model of three mobile links that can change their configuration due to internal steering forces and the mobile surface reactions with the specified motion is considered in the article. The first bottom link simulates shin, the second link simulates hip, and the third link simulates the body with the head. The proposed model differs from the existing ones in utilization of angles between links. In the preceding studies of anthropoid dynamics simulation, the angles are usually calculated from a particular assigned direction - either vertical or horizontal. This approach, however, is inconsistent with the musculoskeletal system biomechanics of anthropoid, exoskeleton, or anthropomorphic robot. The positions of their links are specified by the angles between the links. This approach of specifying the angles makes the system of differential equations, describing the proposed model motion, more complicated in comparison with the models where the angles are calculated from the assigned direction. The local mobile systems of coordinates are fixed with the corresponding links and are used for deriving the motion equations. The programmed motion corresponding to the specified law of generalized coordinates change is considered. The corresponding controlling forces are figured out as the result of the forward problem solution. The link control is simulated with the piecewise step function. The impact of the passive exoskeleton own mass is considered. The spinning rotors impact of the active exoskeleton’s electric drives on the dynamics of human-exoskeleton biomechanical system is studied. The energy consumption in each drive is estimated. The entire cycle of anthropoid dynamics simulation on the movable base in different motion modes is conducted. The value of the obtained results lies in the fact that the proposed model can be used directly in creating anthropomorphic robots and exoskeletons.

Digital transformation of the algorithm of implant prosthetics includes the following steps: planning the spatial position of implants in the jawbone; making a surgical guide for real positioning of the virtual localization of implants; taking an optical impression; creation of a framework and/or the implant prosthesis itself. However, the above digital chain lacks an important step of creating a new dynamic stereotype of the patient's masticatory apparatus biomechanics that should take into account its individual characteristics. In this situation, a digital workflow can help with the reconstruction of the biomechanics of the masticatory apparatus. The aim of the study was the clinical testing of the digital workflow for reconstructing the biomechanics of the masticatory apparatus in implant-supported prosthetics in edentulous patients. Digital modeling of the occlusal surface of artificial dentition was carried out in 82 patients (28 men, 54 women) aged 54 to 83 years (mean age 73.9 ± 4.9 years). In this case, the electronic axiograph CADIAX 3 diagnostic (GAMMA Dental), virtual articulators GAMMA Reference SL and AmannGirrbach Artex CR in the Exocad galway 3.0 and Zirkonzahn.Software program were used. X-ray cephalometric analysis was also used, which was carried out in the GAMMA and OrthoLine programs. The following stages have been introduced into the technological chain of prosthodontic treatment: digital registration of the lower jaw biomechanics in combination with the spatial construction of the occlusal plane with X-ray cephalometric analysis; manufacturing of the final prosthesis copying it according to the temporary CAD/CAM prosthesis, with digital axiography, in particular, digital modeling of the occlusal surface of artificial teeth. This approach, providing a high survival rate of supporting implants (97 %) and implant prostheses (98.1 %), ease of use, contributed to the achievement of a high level of patient quality of life (scores on the GOHAI scale after treatment = 56.5 ± 10.0) associated with prosthetics.