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We report here finite element analysis of the mechanical behavior of aortic valve implant support frames. The material fatigue strength and the effects of annealing on the frames were assessed. The von Mises stresses arising during production processing in the lamellae of the end sections were found to have amplitudes close to the critical (ultimate tensile strength). Annealing reduced the maximum stress by 14.8–23.3% compared to non–annealed samples. Annealed support frames are expected to display more satisfactory material fatigue strength characteristics under the same alternating cyclic stresses.

The aimof the study was an in vitro hydrodynamic study of the developed prosthetic heart valve of the second generation, designed to carry out an implantation using «valve-in-valve» method.Material and methods.Prototypes of the developed prosthesis were studied under simulated physiological conditions of the heart using a Vivitro Labs pulse duplicator (Canada) in a comparative aspect with «UniLine» clinical commercial aortic valve bioprosthesis (Russia). Samples were tested by simulating sutureless implantation procedure.Results. The developed valves showed satisfactory hydrodynamic characteristics – for all cases of «implantation» from the position of the average trans-prosthetic gradient (6.1–11.1 mm Hg) and the effective orifice area (1.60–1.81 cm2 ). The analysis of the regurgitation fraction allowed us to determine the optimal sizes for implantation using «valvein-valve» method, which subsequently will form the basis of sizing guidelines for size selection. A qualitative analysis of the leaflet’s work demonstrated the presence of slight asymmetry for a number of prostheses – in case of mismatch of sizes when simulating «valve-in-valve» procedure.Conclusion. The tests demonstrate the viability of the developed design from the standpoint of hydrodynamic efficiency and determines the basic rules of selecting a prosthesis for reimplantation relative to the primary valve.

Aim: to assess the contribution of primary tissue failure, calcification, bacterial contamination and pannus to bioprosthetic valve dysfunction. Materials and methods . To evaluate degenerative changes of the «UniLine» bioprosthesis explanted from the mitral position with macroscopic examination, light and scanning electron microscopy, and micro-computed tomography (micro-CT). Light microscopy was used to analyze cell composition, the presence of bacteria, the localization of calcific deposits and recipient cells. Scanning electron microscopy allowed confirming the presence of bacteria. Micro-CT was used to evaluate the deformation of the bioprosthetic elements, the distribution of calcific deposits and their volume in the valve tissue. Results. The presence of pannus, calcification, primary tissue failure and bacterial contamination were found among the causes leading to bioprosthetic dysfunction. Prosthetic leaflets showed pannus growth from the inflow tract. Excessive circumferential pannus extended into outflow tract. Calcific deposits were mostly localized in the commissural zone and the central portion of the leaflets. The total volume of calcification accounted for 1/3 of the bioprosthetic tissue component. The relationship between calcification and stress-strain properties of the bioprosthetic elements has been indicated. The asymmetric deformation of the bioprosthetic stent frame and leaflets with 1.5-fold thickening of the last has been found. The areas with loose and fragmented collagen and elastic fibers contained red blood cells and neutrophils. Endothelial cells and fibroblastic cells were present in the outer surface layers. There were no signs of calcification in the areas accumulating cells and bacteria. Conclusion. We can assume that primary tissue failure, calcification, bacterial contamination and pannus independently contribute to the onset of bioprosthetic heart valve dysfunction.

Aim. To assess the contribution of pannus and calcification to the development of bioprosthetic valve dysfunction after tricuspid valve replacement in a pediatric patient.Materials and methods. A 3-month-old patient presented with tricuspid valve dysplasia and grade 4 tricuspid insufficiency underwent tricuspid valve replacement with the bioprosthesis «PeriCor» (ZAO «NeoKor», Russian Federation). The patient at the age of 6 years required a redo tricuspid valve replacement 5 years 8 months after initial surgery. Degenerative changes of the dysfunctional bioprosthetic valve explanted from the tricuspid position were assessed using macroscopic description and light microscopy. Cellular composition, the presence of bacteria, colocalization of calcifications with recipient cells were analyzed. The distribution of calcifications and their volume in the biomaterial tissue were estimated using microcomputer tomography imaging (micro-CT).Results. Bioprosthetic valve dysfunction was mainly caused by the pannus formation which was shown to encapsulate the anterior leaflet, resulting in its total failure and severe stenosis (reduced effective orifice area). There were no signs of ruptures and perforations in the valve tissues found. All leaflets were shown to contain predominantly fibroblastic cells and single blood cells, mainly located in the surface layers of the leaflets in the regions without any signs of calcification. Bacteria staining was negative for all types of the studied biomaterials. Calcifications were present in all xeno-tissue elements of the explanted bioprosthesis (i.e. leaflets, aortic segment, and pericardium). In addition, calcifications were also found in pannus growing during a functioning bioprosthetic valve. Calcifications were predominantly located in the co-optation and commissure zones of the leaflets. Importantly, massive calcifications were observed around the bioprosthetic stent frame. The total volume of calcification accounted for 1/3 of the biological component of the bioprosthesis (729 mm3).Conclusion. According to the data obtained in this study, we may conclude that the primary cause of the bioprosthesis failure was the growth of connective tissues, resulting in pannus-related dysfunction, rather than severe calcification of all bioprosthetic components. One may assume that bioprosthetic dysfunction is related to the peculiarity of the inflammatory response of the preschool patient. However, this typeof dysfunctions requires further investigation.

The paper describes the features of in silico simulation of fluid flows of variable viscosity in the study of prosthetic heart valves. Computer modeling and its verification were performed on the example of the bioprosthesis "UniLine" (Russia) used in modern cardio-surgical practice. A spatial model of the object of investigation was obtained by the method of computer microtomography, followed by the reconstruction of the primitive grid in two-dimensional sections. In the numerical experiment, the immersed boundary method was used. Herein the interaction of a solid and a liquid as well as the impact of mechanics of deformation of the elements of the prosthesis, such as the winged apparatus, were taken into account. Verification of the calculation algorithm was performed in the pulsating flow setup in conditions of simulating the physiological parameters of hydrodynamics similar to those used in silico. In general, the results of the simulation are consistent with the quantitative and qualitative data of the hydrodynamic experiment. Thus, in the numerical simulation, a pressure gradient of 3.0 ± 1.1 mmHg was obtained, an effective orifice area of 2.8 cm2, a regurgitation volume of 0.1 ml/min. The experimental evaluation has shown the similar indicators: 6.5 ± 3.6 mmHg, 2.3 ± 0.6 cm2, 3.1 ± 1.7 ml/min, respectively. The described method demonstrates its promise and can be used in design and research tasks.

Aim. We analysed the geometry and dynamics of the annulus fibrosus of the mitral valve in normal conditions, with mitral regurgitation of degenerative and ischaemic aetiology based on three-dimensional echocardiography with subsequent mathematical processing.Methods. We included the data of transesophageal three-dimensional echocardiography of 50 patients in the following three groups: 10 patients with degenerative regurgitation, 10 patients with ischaemic mitral regurgitation and 30 patients in the ‘normal’ group without mitral valve pathology. Transesophageal echocardiography was performed using an iE33 expert level equipment (Philips, USA), to quantitatively analyse the anterior-posterior diameter, anterolateral-posterior median diameter, intercommissural diameter, three-dimensional circumference of mitral valve, two-dimensional height of the coaptation zone, leaf height, maximum height, front and back angles of the valves, nonplanar angle, planarity coefficient and ellipticity coefficient. The measurements were performed for both the phases of the cardiac cycle, the period of expulsion of systole and the period of diastole filling, corresponding to the closed and open states of the valve. In addition, the treated data sets were processed in the QLAB programme (Philips, USA) where sets of points describing the geometry of the mitral valve were obtained. Thereafter, we used the in-house algorithm in the MATLAB R2015a environment (MathWorks, Massachusetts, USA). Mathematical models of the anatomy of the annulus rings were obtained for all the three studied groups.Results. A functional study of the mitral valve showed a similar nature of changes in the geometric features of the annulus fibrosus for both the pathologies. The dynamic performance of the fibrous rings during systole-diastole cycle significantly differed among the studied groups. We present the equations for the averaged models of the annulus fibrosus of the groups analysed in the study that can be used in design, verification and computer modelling problems.Conclusion. Pathological changes in the geometry of the mitral valve during ischaemic and degenerative regurgitation work on a similar principle, although there are aetiological differences. However, these pathologies differ when the changes in the geometry of the dynamics of ‘systole-diastole’ are analysed that warrant the use of different approaches and devices for their correction.Received 5 November 2020. Revised 12 December 2020. Accepted 22 December 2020.Funding: The work is supported by a grant of the President of the Russian Federation No. 075-15-2020-067.Conflict of interest: Authors declare no conflict of interest.Author contributionsConception and study design: E.A. Ovcharenko, L.S. BarbarashData collection and analysis: K.Yu. Klyshnikov, I.N. Sizova, N.V. KondyukovaStatistical analysis: K.Yu. KlyshnikovDrafting the article: E.A. Ovcharenko, K.Yu. KlyshnikovCritical revision of the article: E.A. Ovcharenko, K.Yu. Klyshnikov, I.N. Sizova, N.V. KondyukovaFinal approval of the version to be published: E.A. Ovcharenko, K.Yu. Klyshnikov, I.N. Sizova, N.V. Kondyukova, L.S. Barbarash

Sutureless implantation of the mitral valve bioprosthesis using the valve-in-valve method was performed on a large animal (sheep). According to the results of a two-stage implantation (primary implantation of a xenopericardial 26-mm framed bioprosthesis and reimplantation of the developed 23-mm bioprosthesis), minor changes in quantitative indicators were revealed: an increase in the transprosthetic gradient by 1.3 mm Hg and a decrease in the area of the mitral orifice by 21.6%. Considerable reduction in the intervention time by 18 min was achieved (by 40% in comparison with the primary prosthesis). The absence of adverse events in the animal and complications in the post-operative period, as well as physiological hemodynamic indicators indicate the safety of the developed medical device.

Aim: to evaluate the biomechanical remodeling of polymer grafts modified with vascular endothelial growth factor (VEGF) after implantation into rat abdominal aorta.Materials and methods. Vascular grafts of2 mmdiameter were fabricated by electrospinning from polycaprolactone (PCL) and a mixture of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and PCL. The grafts were modified with VEGF by biphasic electrospinning. Morphology of the grafts was assessed by scanning electron microscopy. Physico-mechanical properties of PCL and PHBV/PCL grafts were estimated using uniaxial tensile test and physiological circulating system equipped with state-of-theart ultrasound vascular wall tracking system. Physico-mechanical testing of PCL/VEGF and PHBV/PCL/VEGF was performed before and after implantation into rat abdominal aorta for 6 months. The modeling of coronary artery bypass grafting (CABG) was performed by finite element analysis for modified grafts.Results. Durability of PCL and PHBV/PCL grafts did not differ from that of human internal mammary artery; however, elasticity and stiffness of these grafts were higher compared to internal mammary artery. Viscoelastic properties of the grafts were comparable to those of native blood vessels. Modification of the grafts with VEGF reduced material stiffness. Six months postimplantation, PCL/VEGF and PHBV/PCL/VEGF were integrated with aortic tissue that induced changes in the physico-mechanical properties of the grafts similar to the native vessel. Biomechanical modeling confirmed the functioning of modified grafts in bypass position for CABG.Conclusion. PCL/VEGF and PHBV/PCL/VEGF grafts have satisfactory physico-mechanical properties and can be potentially used in the reconstruction of blood vessels.

Samples of commercial and noncommercial xenopericardial grafts of different origin and processing are analyzed. A full-scale test of uniaxial stretching of the material was used to evaluate the features of physical and mechanical properties of the samples, and a computer finite element method simulation was used to evaluate the degree of the object compression. The results were analyzed in terms of the capacity of selected pericardial grafts to serve as a valve apparatus of a transcatheter heart valve prosthesis.