Russian Journal of Biomechanics

Cerebral vascular aneurysms are abnormalities present in 2-5% of the population. Aneurysm rupture often leads to the development of a hemorrhagic stroke. Among its consequences are disability and death. Despite this, preventive surgical treatment of aneurysms is not always justified, since it leads to serious postoperative complications. In this regard, there is the problem of developing and justifying reliable and convenient criteria for assessing the risk of aneurysm rupture. Aspect ratio (the ratio of the height of the aneurysm to the diameter of the neck) is the relative size of the aneurysms used to classify them as prone to rupture and not prone to rupture. This characteristic is also used as predictor of aneurysm rupture. In this paper, we carried out a series of numerical biomechanical calculations aimed at substantiating the critical value of the aspect ratio characterizing aneurysms prone to rupture. In the simulation, the average shear stresses on the aneurysm wall were compared for different aspect ratios from 0.5 to 2.25 with a step of 0.25 for asymmetric models and for aspect ratios from 0.5 to 2.1 with a step of 0.2 for symmetrical models. It was revealed that average wall shear stresses on the aneurysm significantly decrease when the aspect ratio is greater than critical. An abrupt decrease in the average wall shear stresses on the aneurysm with aspect ratio greater than the critical value was revealed.

Replacement of postoperative maxillary defect of oncological origin in patients with complete absence of teeth is a difficult task. Based on the results of mechanical tests of structural materials and computer simulation of the biomechanics of the jaw prosthesis-obturator, the authors created improved obturator designs with specified design characteristics, which ensured the effectiveness of dental orthopedic treatment of this category of patients.

Nowadays, the average life span of knee prosthesis used in total knee replacement is approximately 10 to 15 years. The prevention of failure for these implants has been a constant struggle for orthopaedic surgeons and engineers. The reason behind for implant failures includes wear, infection, instability and stiffness. The major causes of failure are wear and tear of prosthesis. The most common biomaterials used in total knee replacement rubbing against a mating component of ultra-high-molecular-weight polyethylene are titanium alloys Ti6AI4V and alloy CoCrMo. The main drawback is that implants are still restrained by tiny ultra-high molecular weight poly debris generated by long term friction between femoral component and polyethylene articulating surface. Hence, the attempt is made to reduce the wear rate by replacing with high wear-resisting biomaterial. This research investigated whether polyether ether ketone was the appropriate material for total knee replacement by examining wear performance against Ti6AI4V. The experiments are conducted with different loading and speeds. The results are optimized by developing the regression equation using analysis of variance.

The study from the position of theoretical mechanics discusses some aspects of the jump down of the “athlete-gymnast” (or the “robot-gymnast”) from the “crossbar”. We discuss all phases of the jump in the planar case. “Gymnast” body is modeled as three-links physical pendulum, however, after departing from the "crossbar" and lowering the “hands” model the dynamic system becomes two-links pendulum. For a two-links model in the regime of “kinematic” control, we deal with the process of lowering hands, free flight, the output of the “legs” on the frame (absolutely inelastic impact) and holding operation in support phase with the aim of vertical stabilize of the pendulum system. Mode “kinematic control” means the ability to instantly change the angle between the links of the body (in some limits). For each of the phases of movement, we found a convenient form of describing dynamical equations. These equations are based on the use as a variable momentum of the system relative to various points of the body or space. The order of this system of equations is lower than for the full order system. The stage of calm “gymnast” that occurs after the foot on the surface of the support, will also be examined on the basis of special system of equations of this type. It was shown, that we can use numerical analysis to build the region of controllability for transition of the two-links model in a state of stabilization, corresponding to the equality of the horizontal coordinate of the support foot and the center of gravity of the two-links pendulum system. The algorithm of stabilizing control is designed. The results of presented of the analysis of the problem allow us to construct a convenient approximate model of the phenomenon as a whole, and to use it to control a robotic counterpart. As an example, it is considered one of the cases of motion that corresponds to the anthropomorphic model.

Constant exposure to the environment, head trauma and shaking of ocular tissues result in damage and disorders of the eye. In the United States, trauma alone causes about 30 000 people each year to lose vision in one eye. The sclera soft tissue plays a vital role in protecting, maintaining the shape of the eye and regulating the intraocular pressure, and is closely linked with glaucoma. The aim of the study was to investigate and compare the mechanical response of sheep sclera soft tissue under equibiaxial tension as data from such studies are limited. The material parameters describing the mechanical behaviour were determined using the Fung and Choi-Vito models. Sheep eyes were transported in ice and tested in saline solution at a temperature 37 ºC using within 4 to 6 hours after slaughter. Sheep sclera tissue was found to be nonlinear and anisotropic with average anisotropy constants ( A ) of 0.69 and 0.74 for the Fung and Choi-Vito models, respectively. The coefficients of correlation ( R 2) between the experimental and hyperelastic models were found to be 0.98 and 0.95 respectively, with Fung model providing the best fit and more anisotropic behaviour than the Choi-Vito model.