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The selective calculation method has been successfully applied for several centuries due to its profitability. However, when calculating the failure-freeness in the case of fatigue fractures (often sudden), when there is a significant power relationship m = 10-15 for the super-cycle loading region between the strength (hardness, endurance limit) and the effective voltage, the reduction of the minimum component life will be 10-100 or more times. This is due to the unaccounted main part of the population. In our example, there are 104 50 = 9950 units of such parts, i.e., their potential failures. Therefore, for this case, the selective method is an intermediate stage of calculations.

Reduction of vibration in the cabin can be achieved by increasing the area of vibration absorption by placing on the ceiling and floor vibro-absorbing facings. The process of absorption of vibration occurs due to the transition of the energy of oscillating particles to heat due to frictional losses in the pores of the material; therefore, for effective vibration absorption, the material must have a porous structure, the pores must be open from the side of the vibration and join together (unclosed pores) so as not to prevent the penetration of the vibration wave into the thickness of the material. As a vibration-absorbing cladding, we use a construction in the form of a layer of a homogeneous porous material of a certain thickness, reinforced directly on the surface of the fence.

The paper proposes to consider the reliability of machines in terms of mass and individual production. The proposed approach makes it possible to assess the impact of various failures of machine parts on the reliability of single-purpose vehicles. Failures occurring as a result of fatigue wear are considered, but they are of a sudden nature of failure. A condition is defined to prevent such failures, from which the assigned resource to the limit state of the part must be less than the resource of each particular part that may be susceptible to sudden failure. This condition can be applied both for serial production machines and for single-source machines. An algorithm for determining sample and aggregate parameters and an algorithm for resource testing for reliability for single-source machines are proposed. The key stage for the development of the algorithm is the resource testing of machines, the carrying out of which makes it possible to objectively assess the reliability of the loaded parts. To reduce the period for obtaining test results, it is necessary to carry out accelerated resource tests of machines, which can be achieved by intensive operation of machines with short stops for inspection and maintenance. Failures resulting from tests constitute a sample that, after being processed by theoretical laws, allows the determination of the smallest values. Studies have shown that even with the estimation of sample values, the possibility of premature failure continues. In this regard, the paper proposes to use the aggregate parameters to estimate the minimum values. The use of such an algorithm will make it possible to exclude the possibility of the onset of premature failures by determining the period of operation of vehicles during which the failure-free operation of cars is guaranteed.

Reduction of vibration in the cabin can be achieved by increasing the area of vibration absorption by placing on the ceiling and floor vibro-absorbing facings. The process of absorption of vibration occurs due to the transition of the energy of oscillating particles to heat due to frictional losses in the pores of the material; therefore, for effective vibration absorption, the material must have a porous structure, the pores must be open from the side of the vibration and join together (unclosed pores) so as not to prevent the penetration of the vibration wave into the thickness of the material. As a vibration-absorbing cladding, we use a construction in the form of a layer of a homogeneous porous material of a certain thickness, reinforced directly on the surface of the fence.

The paper considers the development of methods for managing the reliability of single-production machines (lunar rover, rover, rolling mill, president’s car of the country, etc.). Many years of experience in the field of machine reliability allowed the leading specialists of the department of AS and DS to develop a method for managing reliability for serial and mass machines. in the case of evaluating the reliability of single-production machines, development of algorithms based on sample data and data obtained during the transition from the sample to the set of values was carried out. The resource of the parts is defined as the main parameter, which, irrespective of their purpose, form the sampled samples of units of finite volume. Given that the main parameter of the details the resource depends on the strength and loading parameters, the correlation between the strength parameters and the acting stresses (endurance limit, active stress in the dangerous section, strength increase coefficients and the coefficient of increasing the acting voltage) is used in the studies. In such conditions, the estimated resource should relate to each entity of the population or a sample from it. During the research, a parameter is defined as the minimum resource that will determine the homogeneity of the sample (the aggregate), while the main condition for ensuring the same main parameters of parts with sudden failures is the Veler-Sørensen-Kogayev formula based on the experimental initial fatigue and loading statistics . Thus, a method has been developed to ensure the reliability of single-source machines, based on the synthesis of two methods and principles for serial and single-purpose machines.

In situ bioprinting is one of the most clinically relevant techniques in the emerging bioprinting technology because it could be performed directly on the human body in the operating room and it does not require bioreactors for post-printing tissue maturation. However, commercial in situ bioprinters are still not available on the market. In this study, we demonstrated the benefit of the originally developed first commercial articulated collaborative in situ bioprinter for the treatment of full-thickness wounds in rat and porcine models. We used an articulated and collaborative robotic arm from company KUKA and developed original printhead and correspondence software enabling in situ bioprinting on curve and moving surfaces. The results of in vitro and in vivo experiments show that in situ bioprinting of bioink induces a strong hydrogel adhesion and enables printing on curved surfaces of wet tissues with a high level of fidelity. The in situ bioprinter was convenient to use in the operating room. Additional in vitro experiments ( in vitro collagen contraction assay and in vitro 3D angiogenesis assay) and histological analyses demonstrated that in situ bioprinting improves the quality of wound healing in rat and porcine skin wounds. The absence of interference with the normal process of wound healing and even certain improvement in the dynamics of this process strongly suggests that in situ bioprinting could be used as a novel therapeutic modality in wound healing., Competing Interests: The authors declare no conflicts of interest., (Copyright: © 2023 Author(s).)

In situ 3D bioprinting is a new emerging therapeutic modality for treating human skin diseases. The tissue spheroids have been previously suggested as a powerful tool in rapidly expanding bioprinting technology. It has been demonstrated that the regenerative potential of human dermal fibroblasts could be quantitatively evaluated in 2D cell culture and confirmed after implantation in vivo. However, the development of unbiassed quantitative criteria of the regenerative potential of 3D tissue spheroids in vitro before their in situ bioprinting remains to be investigated. Here it has been demonstrated for the first time that specific correlations exist between the regenerative potential of human dermal fibroblasts cultured in vitro as 2D cell monolayer with biological properties of 3D tissue spheroids fabricated from these fibroblasts. In vitro assessment of biological properties included diameter, spreading and fusion kinetics, and biomechanical properties of 3D tissue spheroids. This comprehensive characterization could be used to predict tissue spheroids' regenerative potential in vivo., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The concept of "lockyballs" or interlockable mini-scaffolds fabricated by two-photon polymerization from biodegradable polymers for the encagement of tissue spheroids and their delivery into the desired location in the human body has been recently introduced. In order to improve control of delivery, positioning, and assembly of mini-scaffolds with tissue spheroids inside, they must be functionalized. This review describes the design, fabrication, and functionalization of mini-scaffolds as well as perspectives on their application in tissue engineering for precisely controlled cell and mini-tissue delivery and patterning. The development of functionalized mini-scaffolds advances the original concept of "lockyballs" and opens exciting new prospectives for mini-scaffolds' applications in tissue engineering and regenerative medicine and their eventual clinical translation.

Magnetic tissue engineering is one of the rapidly emerging and promising directions of tissue engineering and biofabrication where the magnetic field is employed as temporal removal support or scaffold. Iron oxide nanoparticles are used to label living cells and provide the desired magnetic properties. Recently, polymer microcapsules loaded with iron oxide nanoparticles have been proposed as a novel approach to designing magnetic materials with high local concentrations. These microcapsules can be readily internalized and retained intracellularly for a long time in various types of cells. The low cytotoxicity of these microcapsules was previously shown in 2D cell culture. This paper has demonstrated that cells containing these nontoxic nanomaterials can form viable 3D tissue spheroids for the first time. The spheroids retained labeled fluorescent microcapsules with magnetic nanoparticles without a detectable cytotoxic effect. The high concentration of packed nanoparticles inside the microcapsules enables the evident magnetic properties of the labeled spheroids to be maintained. Finally, magnetic spheroids can be effectively used for magnetic patterning and biofabrication of tissue-engineering constructs.

Cytoskeleton systems, actin microfilaments, microtubules (MTs) and intermediate filaments (IFs) provide the biomechanical stability and spatial organization in cells. To understand the specific contributions of each cytoskeleton systems to intrinsic properties of spheroids, we've scrutinized the effects of the cytoskeleton perturbants, cytochalasin D (Cyto D), nocodazole (Noc) and withaferin A (WFA) on fusion, spreading on adhesive surface, morphology and biomechanics of chondrospheres (CSs). We confirmed that treatment with Cyto D but not with Noc or WFA severely affected CSs fusion and spreading dynamics and significantly reduced biomechanical properties of cell aggregates. Noc treatment affected spheroids spreading but not the fusion and surprisingly enhanced their stiffness. Vimentin intermediate filaments (VIFs) reorganization affected CSs spreading only. The analysis of all three cytoskeleton systems contribution to spheroids intrinsic properties was performed for the first time., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)

Objective: Chondrospheres represent a variant of tissue spheroids biofabricated from chondrocytes. They are already being used in clinical trials for cartilage repair; however, their biomechanical properties have not been systematically investigated yet. The aim of our study was to characterize chondrospheres in long-term in vitro culture conditions for morphometric changes, biomechanical integrity, and their fusion and spreading kinetics., Results: It has been demonstrated that the increase in chondrospheres secant modulus of elasticity is strongly associated with the synthesis and accumulation of extracellular matrix. Additionally, significant interplay has been found between biomechanical properties of tissue spheroids and their fusion kinetics in contrast to their spreading kinetics., Conclusions: Extracellular matrix is one of the main structural determinants of chondrospheres biomechanical properties during chondrogenic maturation in vitro . The estimation of tissue spheroids' physical behavior in vitro prior to operative treatment can be used to predict and potentially control fusogenic self-assembly process after implantation in vivo .

Tissue spheroids have been proposed as building blocks in 3D biofabrication. Conventional magnetic force-driven 2D patterning of tissue spheroids requires prior cell labeling by magnetic nanoparticles, meanwhile a label-free approach for 3D magnetic levitational assembly has been introduced. Here we present first time report on rapid assembly of 3D tissue construct using scaffold-free, nozzle-free and label-free magnetic levitation of tissue spheroids. Chondrospheres of standard size, shape and capable to fusion have been biofabricated from primary sheep chondrocytes using non-adhesive technology. Label-free magnetic levitation was performed using a prototype device equipped with permanent magnets in presence of gadolinium (Gd 3+ ) in culture media, which enables magnetic levitation. Mathematical modeling and computer simulations were used for prediction of magnetic field and kinetics of tissue spheroids assembly into 3D tissue constructs. First, we used polystyrene beads to simulate the assembly of tissue spheroids and to determine the optimal settings for magnetic levitation in presence of Gd 3+ . Second, we proved the ability of chondrospheres to assemble rapidly into 3D tissue construct in the permanent magnetic field in the presence of Gd 3+ . Thus, scaffold- and label-free magnetic levitation of tissue spheroids is a promising approach for rapid 3D biofabrication and attractive alternative to label-based magnetic force-driven tissue engineering.

Tissue spheroids biofabricated from primary human fibroblasts using non-adhesive agarose forms, were placed by 3D bioprinter on the surface of microfibrous electrospun matrix. It was demonstrated that tissue spheroids attached to the surface of matrix during several hours and then gradually spread for several days which indicates high level of biocompatibiity of electrospun microfibrous polyurethane matrix. During this activity, human fibroblasts used processes of leading cell borders for initial step of attachment to matrix filaments. Tissue constructions formed during spreading of tissue spheroids on the surface of electrospun microfibrous polyurethane matrix seem to be a perspective technology platform for development of new methods of biofabrication and 3D bioprinting.

Centrifugal casting allows rapid biofabrication of tubular tissue constructs by suspending living cells in an in situ cross-linkable hydrogel. We hypothesize that introduction of laser-machined micropores into a decellularized natural scaffold will facilitate cell seeding by centrifugal casting and increase hydrogel retention, without compromising the biomechanical properties of the scaffold. Micropores with diameters of 50, 100, and 200 mum were machined at different linear densities in decellularized small intestine submucosa (SIS) planar sheets and tubular SIS scaffolds using an argon laser. The ultimate stress and ultimate strain values for SIS sheets with laser-machined micropores with diameter 50 mum and distance between holes as low as 714 mum were not significantly different from unmachined control SIS specimens. Centrifugal casting of GFP-labeled cells suspended in an in situ cross-linkable hyaluronan-based hydrogel resulted in scaffold recellularization with a high density of viable cells inside the laser-machined micropores. Perfusion tests demonstrated the retention of the cells encapsulated within the HA hydrogel in the microholes. Thus, an SIS scaffold with appropriately sized microholes can be loaded with hydrogel encapsulated cells by centrifugal casting to give a mechanically robust construct that retains the cell-seeded hydrogel, permitting rapid biofabrication of tubular tissue construct in a "bioreactor-free" fashion.

Tissue engineering is a fast-evolving field of biomedical science and technology with future promise to manufacture living tissues and organs for replacement, repair, and regeneration of diseased organs. Owing to the specific role of hemodynamics in the development, maintenance, and functioning of the cardiovascular system, bioreactors are a fundamental of cardiovascular tissue engineering. The development of perfusion bioreactor technology for cardiovascular tissue engineering is a direct sequence of previous historic successes in extracorporeal circulation techniques. Bioreactors provide a fluidic environment for tissue engineered tissue and organs, and guarantee their viability, maturation, biomonitoring, testing, storage, and transportation. There are different types of bioreactors and they vary greatly in their size, complexity, and functional capabilities. Although progress in design and functional properties of perfusion bioreactors for tissue engineered blood vessels, heart valves, and myocardial patches is obvious, there are some challenges and insufficiently addressed issues, and room for bioreactor design improvement and performance optimization. These challenges include creating a triple perfusion bioreactor for vascularized tubular tissue engineered cardiac construct; designing and manufacturing fluidics-based perfused minibioreactors; incorporation of systematic mathematical modeling and computer simulation based on computational fluid dynamics into the bioreactor designing process; and development of automatic systems of hydrodynamic regime control. Designing and engineering of built-in noninvasive biomonitoring systems is another important challenge. The optimal and most efficient perfusion and conditioning regime, which accelerates tissue maturation of tissue-engineered constructs also remains to be determined. This is a first article in a series of reviews on critical elements of cardiovascular tissue engineering technology describing the current status, unsolved problems, and challenges of bioreactor technology in cardiovascular tissue engineering and outlining future trends and developments.

The mechanical properties and structure of a human common carotid artery were studied in order to develop criteria for designing and manufacturing compliant textile vascular grafts. The arterial wall comprised a composite of elastin and collagen fibers with the collagen fibers crimped. This structure led to a unique pressure-circumferential stretch ratio curve, the slope of which increased with an increase in strain. The increase in slope was particularly rapid at a stretch ratio above 1.4 or pressure above 120 mmHg. Based on the knowledge gained, a criteria for the design of biomechanically compliant arterial grafts was developed. An elastomeric prestretched polyurethane monofilament yarn with a low modulus of elasticity and a bulked polyester multifilament yarn with a high modulus of elasticity were combined and used as threads in the manufacture of grafts. Tubular structures of diameters in the range 4-6 mm were made by weaving. Transverse compliance and morphological and permeability properties of these grafts were determined and compared with those of a currently available woven commercial grafts and human carotid arteries. Results indicated that the compliance values of the hybrid grafts were comparable with those of the human carotid artery. Preliminary in vivo studies in dogs showed promising results: a thin, stable neointima developed within 6 months of implantation on the flow surface.