Search

The cationic polymerization of isobutylene and its block copolymerization with styrene using DiCumCl/TiCl4/2,6-lutidine initiating system has been studied in open conditions. It was shown that a higher concentration of proton trap is required in open conditions as compared to the glove box technique in order to have good control over molecular weight and polydispersity. Polyisobutylenes with Mn ≤ 50,000 g mol−1 and low polydispersity (Đ ≤ 1.2) were prepared at [Lu] = 12 mM. The synthesis of poly(styrene-block-isobutylene-block-styrene) triblock copolymer (SIBS) in open conditions required the addition of proton trap into two steps, half at the beginning of the reaction and the second half together with styrene. Following this protocol, a series of triblock copolymers with different length of central polyisobutylene block (from Mn = 20,000 g mol−1 to 50,000 g mol−1) and side polystyrene blocks (Mn = 4000 g mol−1–9000 g mol−1) with low polydispersity (Đ ≤ 1.25) were synthesized. High molecular SIBS (Mn &gt, 50,000 g mol−1) with low polydispersity (Đ &lt, 1.3) containing longer polystyrene blocks (Mn &gt, 6000 g mol−1) demonstrated higher tensile strength (~13.5 MPa).

Objective: to justify the design of a self-expanding transcatheter aortic valve prosthesis based on a biomaterial stabilized with ethylene glycol diglycidyl ether using numerical simulation and a series of field experiments with working prototypes to determine the consistency of the proposed design solutions.Material and methods. Numerical computer models of a developed aortic valve prosthesis intended for transcatheter implantation, as well as prototypes of the most promising concepts for a series of field tests, were used in the work. Computer 3D models were subjected to numerical analysis in the Abaqus/CAE environment (Dassault Systemes, France) based on the finite element method with iterative design optimization and repeated numerical experiments. Physical prototypes of the transcatheter prosthesis were subjected to a series of mechanical tests for axial and radial compression, as well as tests on a Vivitro hydrodynamic stand (Vivitro Labs, Canada) under simulated normal flow. All studies were carried out in a comparative aspect with a similar transcatheter aortic valve prosthesis (control), the CoreValve™ bioprosthesis (Medtronic, Inc., USA).Results. Computer simulation demonstrates the stress-strain state values that do not significantly exceed the critical levels (628 and 756 MPa versus the threshold value 1080 MPa) for two basic concepts of support frames. The fatigue strength based on the calculation of the mean and alternating stresses corresponding to normo- and hypertensive states based on the Goodman diagrams, did not reveal any evidence that the threshold values (destruction area after 200 million cycles) were exceeded. The hydrodynamic characteristics of working prototypes made on the basis of computer models correspond to the testing data of CoreValve™ clinical bioprosthesis: the effective orifice area was 1.97 cm2, the mean transprosthetic gradient was 8.9 mm Hg, the regurgitant volume was 2.2–4.1 mL per cycle depending on the prototype model.Conclusion. Generally, experiments carried out showed the consistency of the concepts, including from the point of view of implementation of the leaflet apparatus based on xenogeneic tissues treated with ethylene glycol diglycidyl ether.

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 goal of this study was to assess the patency rate for a reinforced vascular bioprosthesis with KemAngioProsthesis xenogenic cells (JSC NeoСor, Kemerovo) during its mechanical deformation. The complex of natural and numerical methods used in the work made it possible to determine the mechanical properties of the test objects. We used a pitch of the helix of 4 mm and a thickness of the thread of 0.3–0.5 mm. It is shown that the material properties of the vascular wall are anisotropic compared to the longitudinal and transverse directions under loading. Thus, the elastic moduli were 1.37 (0.90, 1.12, 1.44, and 1.72) MPa versus 0.80 (0.97, 1.23, 1.61, and 2.15) MPa, respectively; the statistical analysis showed significant differences of these moduli among layers (p < 0.05). Using the finite element method to select parameters for the reinforcing lining it was found that the patency rate for a vascular prosthesis depends nonlinearly on the number of spirals. It has been shown that the external polymeric reinforcing lining during its mechanical deformation can offer satisfying patency rates and outcomes, which is typical of infra-inguinal reconstructions, especially when compared to the original unreinforced product. Additionally, the introduction of reinforcement increases the radial stiffness of the prosthesis, which can potentially lead to a decrease in the risk of vascular wall aneurysms in the long term.

A three-dimensional unsteady periodic flow of blood in xenogenic vascular bioprostheses is simulated by computational fluid dynamics methods. The geometry of the computational domain is based on microtomographic scanning of bioprostheses. To set a variable pressure gradient causing an unsteady flow in the prostheses, personal-specific data of the Doppler echography of the blood flow of a particular patient are used. A comparative analysis of the velocity fields in the flow areas corresponding to three real samples of bioprostheses with multiple stenoses is carried out. In the zones of stenosis and outside of them, the distribution of the near-wall shear stress, which affects the risk factors for thrombosis in the prostheses, is analyzed. An algorithm for predicting the hemodynamic effects arising in vascular bioprostheses is proposed; the algorithm is based on the numerical modeling of the blood flow in these prostheses.

—A numerical evaluation was performed to assess the efficiency of reinforcement of small-diameter vascular grafts made of polymeric materials. Based on the finite-element analysis, an algorithm was developed to find the optimal parameters for the reinforcing layer and to evaluate its stress–strain state under conditions of longitudinal bending simulation. The findings may be useful for industrial and laboratory trials in studies of the strengthening properties of similar products.

Polymeric heart valves seem to be an attractive alternative to mechanical and biological prostheses as they are more durable, due to the superior properties of novel polymers, and have the biocompatibility and hemodynamics comparable to tissue substitutes. This study reports a comprehensive assessment of a nanocomposite based on the functionalised graphene oxide and poly(carbonate-urea)urethane with the trade name “Hastalex” in comparison with GORE-TEX, a commercial polymer routinely used for cardiovascular medical devices. Experimental data have proved that GORE-TEX has a 2.5-fold (longitudinal direction) and 3.5-fold (transverse direction) lower ultimate tensile strength in comparison with Hastalex (p

Aim: to evaluate the manipulative properties of the system being developed for cardiac valve re-operation on an in vitro bovine heart model.Material and methods. The prototype of the prosthesis being developed, mounted on the implant holder, as well as the dilatation balloon of its own design, were used as the objects of the study. The bioprosthesis «UniLine» of 21 mm size for the aortic position was chosen as the target site of implantation, which was established by the «classical» suture method. After that, the implantation of the tested device was carried out as a «valve in valve» and the quality of the installation and the combined operation of all the components of the re-prosthesis system were evaluated.Results. The test implantation demonstrated the consistency of the proposed method on the basis of balloon seamless fi xation, as well as high ergonomic characteristics: the average time of seamless implantation of the developed prototype on an in vitro animal heart model was 3 minutes versus the implantation of the «UniLine» bioprosthesis – 11 min, Implantation provided a reliable prosthesis The breaking force was 12.9 N, which is equivalent to a pressure of 279 mm Hg.

We examined a fiber formation from pristine and modified single-walled carbon nanotube (SWCNT) films using a recently developed wet pulling technique. Crucial phenomena in the wet pulling process are a folding of a solvent soaked SWCNT film due to the liquid surface tension and fiber densification during the solvent evaporation. It is shown that electrical characteristics of the as-produced fibers are determined by the type of the liquid employed in their formation, which defines the SWCNT packing degree. The obtained specific strength (0.6–0.8 N/tex), toughness (up to 127 J/g) and specific conductivity (0.5–1.2 kS·m2/kg) are in many cases comparable with published data for fibers produced by more resource-consuming methods. These, in combination with the simplicity of our method and high piezoresistive gauge factor of 14 (for untwisted fibers at a 1% elongation), make SWCNT fibers promising components in future applications of stretchable electronics and robotics.

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.

In this study, we incorporated carbon nanotubes (CNTs) into poly(styrene-block-isobutylene-block-styrene) (SIBS) to investigate the physical characteristics of the resulting nanocomposite and its cytotoxicity to endothelial cells. CNTs were dispersed in chloroform using sonication following the addition of a SIBS solution at different ratios. The resultant nanocomposite films were analyzed by X-ray microtomography, optical and scanning electron microscopy, tensile strength was examined by uniaxial tension testing, hydrophobicity was evaluated using a sessile drop technique, for cytotoxicity analysis, human umbilical vein endothelial cells were cultured on SIBS&ndash, CNTs for 3 days. We observed an uneven distribution of CNTs in the polymer matrix with sporadic bundles of interwoven nanotubes. Increasing the CNT content from 0 wt% to 8 wt% led to an increase in the tensile strength of SIBS films from 4.69 to 16.48 MPa. The engineering normal strain significantly decreased in 1 wt% SIBS&ndash, CNT films in comparison with the unmodified samples, whereas a further increase in the CNT content did not significantly affect this parameter. The incorporation of CNT into the SIBS matrix resulted in increased hydrophilicity, whereas no cytotoxicity towards endothelial cells was noted. We suggest that SIBS&ndash, CNT may become a promising material for the manufacture of implantable devices, such as cardiovascular patches or cusps of the polymer heart valve.

Superior polymers represent a promising alternative to mechanical and biological materials commonly used for manufacturing artificial heart valves. The study is aimed at assessing poly(styrene-block-isobutylene-block-styrene) (SIBS) properties and comparing them with polytetrafluoroethylene (Gore-texTM, a reference sample). Surface topography of both materials was evaluated with scanning electron microscopy and atomic force microscopy. The mechanical properties were measured under uniaxial tension. The water contact angle was estimated to evaluate hydrophilicity/hydrophobicity of the study samples. Materials&rsquo, hemocompatibility was evaluated using cell lines (Ea.hy 926), donor blood, and in vivo. SIBS possess a regular surface relief. It is hydrophobic and has lower strength as compared to Gore-texTM (3.51 MPa vs. 13.2/23.8 MPa). SIBS and Gore-texTM have similar hemocompatibility (hemolysis, adhesion, and platelet aggregation). The subcutaneous rat implantation reports that SIBS has a lower tendency towards calcification (0.39 mg/g) compared with Gore-texTM (1.29 mg/g). SIBS is a highly hemocompatible material with a promising potential for manufacturing heart valve leaflets, but its mechanical properties require further improvements. The possible options include the reinforcement with nanofillers and introductions of new chains in its structure.

The study analysed the mechanical properties by uniaxial test of porcine and bovine pericardial specimens, stabilised with the glutaraldehyde or with the ethylene glycol diglycidyl ether. Also the paper describes, the ability of these samples compressed to 18 Fr with via the finite element method. Analysis of the properties of the biomaterial demonstrated a low strength for all types of porcine pericardium with the lowest value for the EGDE-treated pericardium (2.75 N). The lowest stress-strain state during the simulation of the leaflet crimping was observed in experimental porcine pericardial patch with the minimum principal logarithmic strain of 0.32 m/m. The results of this study allow us to make conclusions about the desirability of the use of porcine pericardium treated with glutaraldehyde for transcatheter aortic valve prostheses.