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Currently, aortic valve (AV) disease is the most common reason for heart valve surgery. The gold standard of care for people with aortic pathology is thought to be AV replacement. The issue of prosthesis selection has always been important. Although mechanical prosthesis are robust, lifelong anticoagulation medication is necessary due to the significant risk of thromboembolic consequences. Biological prostheses have a flow structure that is similar to the physiological one, and as malfunction gradually sets in, scheduled recurrent surgery can be carried out. The purpose of this study is to evaluate the short- and long-term effects of biological prosthetic aortic valve replacement (AVR) in elderly individuals. The study included 198 patients with AV pathology [85 men (42.9%)/113 women (57.1%)]. The median age was 70 [66–73] years. There were 175 (88.4%) patients with degenerative AV, 5 (2.5%) with infective endocarditis, and 30 patients (15.2%) had bicuspid AV. The median follow-up period was 26.3±1.4 months. Hospital mortality was 4.5%. No wound complications were detected. Thirty-one patients died in the long-term period. The causes of lethality were: cardiovascular disease (13 patients), malignant neoplasm (5 patients), gastrointestinal disease (2 patients), urinary system disease (1 patient), COVID-19 (1 patient), unknown cause (9 patients). Thus, the five-year postoperative survival rate was 63%, respectively. Throughout the observation period, two patients (2.9%) underwent reoperation on AV. 97.1% of patients were free of reoperation after five years. The five-year survival rate was 63% due to the history of severe concomitant pathology and mean age of the patients of 70 years.

This paper deals with direct restorations of teeth with non-carious cervical lesions (NCCL). NCCL defects are capable of gradual growth and are accompanied by the degradation of the surrounding tissue. Direct restorative treatment, in which the cavity is filled with a cementing agent, is considered to be an accessible and common treatment option. The study included simulations of the teeth without lesions, the teeth with V and U lesions and the tooth-restorative system. Parameterised numerical tooth models were constructed. Two cases with defect depths of 0.8 mm and ~1.7 mm and three variants with fillet radii of the defect end of 0.1, 0.2 and 0.3 mm were considered. The effect of two biomaterials for restorations was studied, namely Herculite XRV (Kerr Corp, Orange, CA, USA) and Charisma (Heraeus Kulzer GmbH, Hanau, Germany). The models were deformed with a vertical load of 100 to 1000 N from the antagonist tooth. The tooth-restorative system was considered, taking into consideration the contact interaction in the interface areas with the tooth tissues. Within the limits of the research, the character of the distribution of the deformation characteristics and their dependence on the level of loading, the depth of the defect and the radius of the curvature of the “wedge” were established.

Endoprosthetics with plastic stents has been used to restore bile drainage through the percutaneous or endoscopic method since the late 1970s. The long-term results cannot be considered satisfactory due to the high incidence of jaundice recurrence which is caused by the occlusion of plastic stents with a biliary sludge (accumulation of cholesterol crystals, pigment crystals, bacteria and calcium salts). Cholesterol is considered to be the main component of biliary sludge that stimulates the reduction of the stent lumen. The average lifetime of stents is 3–6 months. Despite numerous experimental studies of the occlusion process, the optimal timing for the replacement of the biliary plastic stent has not been established. Too frequent replacement of the stent can lead to additional complications, so an individualized forecast of the stent’s lifetime for a particular patient is needed. In this paper, a model of the flow of lithogenic bile as a non-Newtonian fluid is developed taking into account the transport of particles describing the behavior of cholesterol crystals that accumulate on the inner surface of the stent, stimulating a decrease in its lumen. A correlation was found between cholesterol concentration and occlusion time based on the use of a specially developed iterative procedure. The results of the numerical computations show that individual parameters (age, gender, bile viscosity, cholesterol concentration) have a significant impact on the rate of occlusion of the stent.

This study carried out modeling of the contact between a pair of antagonist teeth with/without individual mouthguards with different geometric configurations. Comparisons of the stress–strain state of teeth interacting through a multilayer mouthguard EVA and multilayer mouthguards with an A-silicon interlayer were performed. The influence of the intermediate layer geometry of A-silicone in a multilayer mouthguard with an A-silicon interlayer on the stress–strain state of the human dentition was considered. The teeth geometry was obtained by computed tomography data and patient dental impressions. The contact 2D problem had a constant thickness, frictional contact deformation, and large deformations in the mouthguard. The strain–stress analysis of the biomechanical model was performed by elastoplastic stress–strain theory. Four geometric configurations of the mouthguard were considered within a wide range of functional loads varied from 50 to 300 N. The stress–strain distributions in a teeth pair during contact interaction at different levels of the physiological loads were obtained. The dependences of the maximum level of stress intensity and the plastic deformation intensity were established, and the contact parameters near the occlusion zone were considered. It was found that when using a multilayer mouthguard with an A-silicone interlayer, there is a significant decrease in the stress intensity level in the hard tissues of the teeth, more than eight and four times for the teeth of the upper and lower teeth, respectively.

In this work, a new approach to solving problems of optimal control of manufacture procedures for the production of silica optical fiber are proposed. The procedure of silica tubes alloying by the Modified Chemical Vapor Deposition (MCVD) method and optical fiber drawing from a preform are considered. The problems of optimal control are presented as problems of controlling distributed systems with objective functionals and controls of different types. Two problems are formulated and solved. The first of them is the problem of the temperature field optimizing in the silica tubes alloying process in controlling the consumption of the oxygen–hydrogen gas mixture (in the one- and two-dimensional statements), the second problem is the geometric optimization of fiber shape in controlling the drawing velocity of the finished fiber. In both problems, while using an analog to the method of Lagrange, the optimality systems in the form of differential problems in partial derivatives are obtained, as well as formulas for finding the optimal control functions in an explicit form. To acquire optimality systems, the qualities of lower semicontinuity, convexity, and objective functional coercivity are applied. The numerical realization of the obtained systems is conducted by using Comsol Multiphysics.

Hemodynamically significant patent ductus arteriosus (hsPDA) in premature newborns is associated with a risk of PDA-related morbidities. Classification into risk groups may have a clinical utility in cases of suspected hsPDA to decrease the need for echocardiograms and unnecessary treatment. This prospective observational study included 99 premature newborns with extremely low body weight, who had an echocardiogram performed within the first three days of life. Discriminant analysis was utilized to find the best combination of prognostic factors for evaluation of hsPDA. We used binary logistic regression analysis to predict the relationship between parameters and hsPDA. The cohort’s mean and standard deviation gestational age was 27.6 ± 2.55 weeks, the mean birth weight was 1015 ± 274 g. Forty-six (46.4%) infants had a PDA with a mean diameter of 2.78 mm. Median NT-pro-BNP levels were 17,600 pg/mL for infants with a PDA and 2773 pg/mL in the non-hsPDA group. The combination of prognostic factors of hsPDA in newborns of extremely low body weight on the third day of life was determined: NT-pro-BNP, Apgar score, Silverman–Anderson score (Se = 82%, Sp = 88%). A cut-off value of NT-pro-BNP of more than 8500 pg/mL can predict hsPDA (Se = 84%, Sp = 86%).

Background and Objectives: To propose a new classification of diabetic foot syndrome adapted for inclusion in the ICD-10 (the ICD-10 is the 10th revision of the International Statistical Classification of Diseases) and providing more reliable data on the number of clinical cases. Materials and Methods: A randomized controlled trial was performed. A total of 180 patients (36.6%) discharged from the hospital after surgical treatment and 312 patients (63.4%) who applied independently were observed and analysed. All patients had type 2 diabetes and were comparable in gender, age, duration of diabetes, area and nature of the wound defect. Results: We proposed to add the following to the existing ICD-10 and the emerging ICD-11 codes: Edf10.0—insulin-dependent diabetes mellitus with diabetic foot syndrome and Edf11.0—non-insulin-dependent diabetes mellitus with diabetic foot syndrome, where “df” is an acronym for diabetic foot. The new classification designates the seven most frequent areas of the lesion and five degrees of depth of soft tissue lesions. Conclusions: The proposed classification adapted for ICD-10 will enable the standardisation of diagnosis, providing a complete picture of this complication of diabetes mellitus, determining the number of amputations and their validity. Accurate statistics will allow for objective funding and timely preventive measures.

Gallbladder disease is one of the most spread pathologies in the world. Despite the number of operations dealing with biliary surgery increases, the number of postoperative complications is also high. The aim of this study is to show the influence of the biliary system pathology on bile flow character and to numerically assess the effect of surgical operation (cholecystectomy) on the fluid dynamics in the extrahepatic biliary tree, and also to reveal the difference between 1-way and 2-way FSI algorithms on the results. Moreover, the bile viscosity and biliary tree geometry influence on the choledynamics were evaluated. Bile velocity, pressure, wall shear stress (WSS), displacements and von Mises stress distributions in the extrahepatic biliary tree are presented, and comparison is made between a healthy and a lithogenic bile. The patient-specific biliary tree model is created using magnetic resonance imaging (MRI) and imported in a commercial finite element analysis software. It is found that in the case of lithogenic bile, velocities have lower magnitude while pressures are higher. Furthermore, stress analysis of the bile ducts shows that the WSS distribution is found mostly prevailing in the common hepatic duct and common bile duct areas. It is shown that when it is necessary to evaluate the bile flow dynamics in urgent medical situations, 1-way analysis is acceptable. Nevertheless, 2-way FSI provides more accurate data, if necessary to evaluate the stress-strain state of bile ducts. The proposed model can be applied to medical practice to reduce the number of post-operative complications.

Cardiovascular surgery requires the use of state-of-the-art artificial materials. For example, microporous polytetrafluoroethylene grafts manufactured by Gore-Tex® are used for the treatment of cyanotic heart defects (i.e., modified Blalock–Taussig shunt). Significant mortality during this palliative operation has led surgeons to adopt mathematical models to eliminate complications by performing fluid–solid interaction (FSI) simulations. To proceed with FSI modeling, it is necessary to know either the mechanical properties of the aorta and graft or the rheological properties of blood. The properties of the aorta and blood can be found in the literature, but there are no data about the mechanical properties of Gore-Tex® grafts. Experimental studies were carried out on the mechanical properties vascular grafts adopted for modified pediatric Blalock–Taussig shunts. Parameters of two models (the five-parameter Mooney–Rivlin model and the three-parameter Yeoh model) were determined by uniaxial experimental curve fitting. The obtained data were used for patient-specific FSI modeling of local blood flow in the “aorta-modified Blalock–Taussig shunt–pulmonary artery” system in three different shunt locations: central, right, and left. The anisotropic model of the aortic material showed higher stress values at the peak moment of systole, which may be a key factor determining the strength characteristics of the aorta and pulmonary artery. Additionally, this mechanical parameter is important when installing a central shunt, since it is in the area of the central anastomosis that an increase in stress on the aortic wall is observed. According to computations, the anisotropic model shows smaller values for the displacements of both the aorta and the shunt, which in turn may affect the success of preoperative predictions. Thus, it can be concluded that the anisotropic properties of the aorta play an important role in preoperative modeling.

The biliary system consists of the biliary tree, gallbladder and major duodenal papilla. Soft tissues compliance plays important role in the bio-fluids transport. Particularly, bile flow disturbances due to bile duct wall motor function changes in the extra-hepatic ducts, from medicine point of view are called dyscinesia of biliary tract. Fluid motion in the elastic and compliant ducts can be described by different models (for example, Windkessel model, peristaltic fluid motion, FSI algorithm). Our approach is decomposition of the biliary system into three compartments (extra-hepatic biliary tree, gallbladder, major duodenal papilla). Bile flow in the extra-hepatic ducts is simulated using FSI algorithm. Bile flow in the gallbladder can be described as flow in the reservoir with compliant ducts using Windkessel model. Bile flow in the major duodenal papilla is considered as peristaltic fluid motion, because the wall contraction is really important factor of fluid motion in that segment. The coupling of these compartments is performed by boundary conditions. The biliary system geometry was obtained using MRI patient-specific data. It was confirmed that normal bile can be modeled as Newtonian fluid and lithogenic bile can be modeled as non-Newtonian fluid (Carreau fluid). Bile ducts were modeled as hyperelastic material.

The aim of this study is to improve treatment results and SSI prevention by differential usage of the contemporary suture materials and choice of proper suturing technique. To simulate suturing process and compared two suturing techniques, two FE models were developed. Finite-element analysis (FEA) was based on experimental data of contemporary commercial sutures and soft tissue properties. We applied obtained results for abdominal wall closure in rats and compared non-absorbable suture (capron) with absorbable suture (PDS Plus) for chosen technique. Cross-sections were examined by lighting electron microscope. Afterwards, the results of patients’ treatment are also presented. It was shown that running sew was more appropriate for aponeurosis suturing compared to interrupted sew. The optimal parameters of suturing techniques were computed. Single-row running sew by PDS Plus was proved to hold wound edges for 90 days with less inflammatory response compared to other suture in the result of histological analysis. Application of contemporary synthetic absorbable suture materials with antibacterial coating for laparotomic wounds closure and anastomosis decreases local inflammatory reaction and provides the successful tissue regeneration. Application of advanced SSI prophylactics algorithm was shown to decrease risk of post-operative suppurative complications from 14.2 to 1.6 %.

The paper presents an experimental study of pathological human bile taken from the gallbladder and bile ducts. The flow dependences were obtained for different types of bile from patients with the same pathology, but of different age and sex. The parameters of the Casson’s and Carreau’s equations were found for bile samples. Results on the hysteretic bile behavior at loading-unloading tests are also presented, which proved that the pathologic bile is a non-Newtonian thixotropic liquid. The viscosity of the gallbladder bile was shown to be higher compared to the duct bile. It was found that at higher shear stress the pathological bile behaves like Newtonian fluid, which is explained by reorientation of structural components. Moreover, some pathological bile flow in the biliary system CFD simulations were performed. The velocity and pressure distributions as well as flow rates in the biliary segments during the gallbladder refilling and emptying phases are obtained. The results of CFD simulations can be used for surgeons to assess the patient’s condition and choose an adequate treatment.

Bile is a biofluid produced by the liver and responsible in the duodenum. The object of present research is an investigation of the peristaltic bile flow in the papilla of Vater, which is the narrowest place in the biliary system (responsible for bile production, storing, and transport of the bile into the duodenum for fat digestion). Recently, the pathological bile was revealed to be the non-Newtonian thixotropic fluid. The present paper contains results of solution of problems devoted to the peristaltic flow of bile as Carreau’s fluid. Two cases were considered: bile flow in the duct with a stone and bile flow in the stenosed duct. Adopting the perturbation method, we obtained the analytical solutions for axial velocity, flow rate, and pressure. Moreover, the dependences of pressure drop on the flow rate were obtained. Developed mathematical model may be used for studying of such pathology as choledochopancreatic reflux (i.e. pathological flow of the gallbladder bile coming out the common bile duct through the Vater’s papilla ampoule into the pancreatic ducts instead of the duodenum). Adopting an assumption that the reflux occurrence corresponds to the case when the flow rate becomes less zero, the critical pressures were computed. The pressure rise magnitudes corresponding to reflux occurring conditions depending on various parameters (amplitude ratio, Weissenberg number, etc.) were obtained.

The aim of the present paper is to develop an analytical model for description of the pathological bile flow in the major duodenal papilla duct with a calculus. The problem is separated into two parts. The first part deals with determination of bile behaviour and constitutive relation parameters of the pathological bile. The viscosity vs. shear rate, the viscosity vs. time, and shear stress vs. shear rate dependences are obtained for different types of bile taken from patients of different age and sex. As a result, the approximation of curves described by the Casson equation was obtained. It was shown that the pathological bile is a thixotropic non-Newtonian fluid. The second part is directly related to modelling of the bile flow in the duct with a calculus. As a result of solving the problem, the bile velocity profile, flow rate vs. time, and bile pressure vs. calculus radius were obtained. The dependences obtained may play an important role in the assessment of an indication to operation.