Vindokurov, Ilia Vladimirovich

Elenskaya N., Vindokurov I., Sadyrin E., Nikolaev A., Tashkinov M.

Bone transplantation ranks second worldwide among tissue prosthesis surgeries. Currently, one of the most promising approaches is regenerative medicine, which involves tissue engineering based on polymer scaffolds with biodegradable properties. Once implanted, scaffolds interact directly with the surrounding tissues and in a fairly aggressive environment, which causes biodegradation of the scaffold material. The aim of this work is to experimentally investigate the changes in the effective mechanical properties of polylactide scaffolds manufactured using additive technologies. The mechanism and the rate of the degradation process depend on the chosen material, contact area, microstructural features, and overall architecture of sample. To assess the influence of each of these factors, solid samples with different dimensions and layers orientation as well as prototypes of functionally graded scaffolds were studied. The research methodology includes the assessment of changes in the mechanical properties of the samples, as well as their structural characteristics. Changes in the mechanical properties were measured in compression tests. Microcomputed tomography (micro-CT) studies were conducted to evaluate changes in the microstructure of scaffold prototypes. Changes caused by surface erosion and their impact on degradation were assessed using morphometric analysis. Nonlinear changes in mechanical properties were observed for both solid samples and lattice graded scaffold prototypes depending on the duration of immersion in NaCl solution and exposure to different temperatures. At the temperature of 37 °C, the decrease in the elastic modulus of solid specimens was no more than 16%, while for the lattice scaffolds, it was only 4%. For expedited degradation during a higher temperature of 45 °C, these ratios were 47% and 16%, respectively. The decrease in compressive strength was no more than 32% for solid specimens and 17% for scaffolds. The results of this study may be useful for the development of optimal scaffolds considering the impact of the degradation process on their structural integrity.

Ershov P., Omelyanchik A., Vorontsov P., Amirov A.A., Zhansitov A.A., Musov I., Musov K., Khashirova S., Vindokurov I., Tashkinov M., Panina L., Rodionova V.

Vindokurov I., Tashkinov M., Silberschmidt V.V.

Materials for additive manufacturing (AM), such as PLA and PEEK, are often used in biomedical applications, which involve interaction with liquid media. Consequently, the degradation process is a part of the service life of such polymers that can alter their mechanical response due to gradual changes in materials’ properties. Studying the behaviour of polymers in such environments is thus important for the prediction of the mechanical performance of biomedical devices. This paper examines the process of accelerated degradation of AM PLA and PEEK samples in saline solution and distilled water at elevated temperatures. An analysis of changes in mechanical properties, such as tensile strength and density, of PLA and PEEK with the immersion time was performed. The influence of heat treatment on the degradation process was investigated. It was found that the degradation rate of PLA in distilled water was higher than in NaCl. The trends in density changes measured with hydrostatic weighing correspond to those in the strength properties of the studied samples.

Shalimov A., Tashkinov M., Terekhina K., Elenskaya N., Vindokurov I., Silbersсhmidt V.V.

Ivanov D., Vindokurov I., Dol A., Bessonov L., Parshina I., Tashkinov M.

Pepeliaev A., Lobov E., Vindokurov I., Tashkinov M.

Pirogova Y., Tashkinov M., Vindokurov I., Silberschmidt V.V.

This paper studies the effect of different combinations of morphological parameters of porous closed-cell materials on their elastic properties and mechanical behaviour. Three-dimensional representative volumes of porous media with different polyhedral void shapes are investigated, considering variation of statistical realisations of morphological features, such as shape, size and distribution of pores. Description of morphology of each investigated representative volume is formalized using second- and fourth-order correlation functions. The effective properties of representative volumes are calculated with finite-element analysis. Additionally, samples of the studied models were additively manufactured with polystyrene, using fused filament fabrication (FFF/FDM) 3D-printing technique, and subjected to compression. Experimental results for elastic mechanical properties and distributions of strain fields on the surface of the samples, obtained with micro-DIC (digital image correlation), are compared with results of numerical finite-element computations. This is accompanied by analysis of internal-stress distributions to assess the mechanical state of the structures. Patterns and trends observed in mechanical responses of porous materials depending on their different morphological parameters are outlined and discussed.

Lobov E., Vindokurov I., Tashkinov M.

This paper presents the results of experimental investigation of the mechanical characteristics of 3D-printed acrylonitrile butadiene styrene (ABS) and its modifications reinforced with different types of short-fiber fillers: carbon, glass, and basalt. Elastic modulus, tensile and bending strength, as well as fracture toughness were determined in series of mechanical tests for samples produced with different manufacturing parameters, such as nozzle diameter and infill angle. It was found that the use of ABS filament reinforced with the short fibers can significantly improve the mechanical properties of 3D-printed devices when the infill angle is oriented along the vector of the applied load. In such a case, the elastic modulus and tensile strength can be increased by more than 1.7 and 1.5 times, respectively. The use of a larger nozzle diameter led to the growth of tensile strength by an average of 12.5%. When the macroscopic load is applied along the normal to the printed layers, the addition of short fibers does not give much gain in mechanical properties compared to pure ABS, which was confirmed by both standard tensile and fracture toughness tests. The surface of the fractured samples was examined using scanning electronic microscopy, which allowed us to make conclusions on the type of defects as well as on the level of adhesion between the polymeric matrix and different types of short fibers.

Vindokurov I., Pirogova Y., Tashkinov M., Silberschmidt V.V.

Understanding the mechanical behaviour of additively manufactured (AM) biomedical polymeric devices under various loading regimes is important for tailoring their design to specific applications. This paper presents the results of an experimental study of compressive mechanical properties of AM cubic samples of biocompatible polylactic acid (PLA) manufactured with fused filament fabrication. The measured elastic modulus and ultimate compression strength were compared and analysed for varying testing parameters, such as strain rate and contact friction, for samples with different characteristic sizes. The changes in density of the samples were also assessed for evaluation of the extent of material compaction after deformation. Surface morphology of specimens was examined before and after compression tests using scanning electron and optical microscopy. Different types of defects induced by the manufacturing process and caused by the subsequent compressive deformation were studied and compared. The obtained results are useful for design and optimization of small-size biomedical devices, which require precise control of their structural morphology and mechanical behaviour.

Mubassarova V.A., Panteleev I.A., Plekhov O.A., Iziumova A.Y., Vshivkov A.N., Vindokurov I.V., Tashkinov M.A.

The paper deals with X-ray computed tomography results of a polyetheretherketone (PEEK) and a short carbon fibre reinforced by acrylonitrile butadiene styrene (ABS+CF). Individual carbon fibres and 3D printing defects (consolidated structures of interconnected fibres and densified resin clumps) are detected on an initial microstructure of the ABS+CF composite. The carbon fibres and the consolidated structures are densely packed with uniform sub-horizontal locations throughout in a sample volume. In the PEEK samples, the process-induced defects during the composite manufacturing process are visualised as tubular structures of a densified resin with internal voids. Significant changes in the structure of both composites are observed after five times pulsed laser shock peening. In case of a single pulse exposure and a surface treatment, no microstructural changes occur. In a test mode without a protective layer, a material evaporation to a depth of 0.3 mm and a structural degradation of the PEEK samples takes place, while the process-induced interlayer voids do not close. A single consolidated area with a porous spongy structure occurs due to melting of the carbon fibres in the ABS+CF composite. The results show that the laser shock peening has a significant effect on the surface microstructure. It is therefore necessary to carry out further experiments to select the optimum laser shock peening parameters and a protective layer material to eliminate the process-induced defects and improve the strength properties of the composites.

Shur P.Z., Lir D.N., Alekseev V.B., Barg A.O., Vindokurov I.V., Khrushcheva E.V.

Introduction. Assessment of work intensity (WI) is challenged by several methodical complications. It may involve certain underestimation of an actual hazard category of working conditions and fails to consider work modification. Materials and methods. The study relies on using analytical, sociological, and statistical methods. To test the selected approach, a sample was created from workers with mostly mental work (n=137, 77% females). Their average age was 43.9±8.0 years; average work experience was 14.5±3.7 years. Results. In this article, we suggest certain approaches to assessing WI. They include self-assessment of a factor using a specifically designed questionnaire; they clarify indicators that describe WI; when assessing working conditions, they rely on matrices of interrelated indicators. This procedure makes it possible to estimate levels of individual components and create an integral WI profile as well as identify contributions made by various intensity types to its overall structure. When testing the procedure, we established workers with mostly mental work to tend to have harmful working conditions as per WI factor (the hazard category 3.1 in 24.8% of the cases; 3.2, 56.9% of the cases; and the hazard category 3.3 in 17.5% of the cases). Mental (28.6±6.1%) and sensory (24.0±7.0%) loads are limiting components. Amid implementation of anti-epidemic activities, work regime was established as the most sensitive WI component (its contribution grew from 11.1±6.0 to 16.0±5.7%, p<0.05). Working conditions moved to a higher hazard category for 35.8% workers. Limitations. Assessment of working conditions uses threshold values introduced more than 30 years ago and can be adjusted for the existing employment conditions. The testing was accomplished on a rather small sample, which was biased as per gender and included workers with different occupations and positions. Conclusion. The suggested approaches offer wider opportunities to assess working conditions as per WI with respect to some occupations. This may substantiate a list of indicators that should be regulated by the existing sanitary legislation. Investigation of possible modification of factors during the pandemic makes it possible to describe eligibility of anti-epidemic activities without any deterioration of working conditions.

Elenskaya N., Tashkinov M., Vindokurov I., Pirogova Y., Silberschmidt V.V.

Applications of additive manufacturing (AM) in tissue engineering develop rapidly. AM offers layer-by-layer creation of complex objects, developed to restore functionality of, or replace, damaged tissues. Porous 3D-printed functional gradient structures are of particular interest: their special architecture makes it possible to simulate the heterogeneity of the replaced tissue and, by continuously changing the mechanical properties, to avoid the concentration of stresses that can be caused by abrupt geometric changes. Such structures also allow combinations of different types of unit cells and a smooth transition between them, making design of personalised scaffolds with optimal parameters for the replacement of damaged host tissue at the interface between tissues possible. This paper presents the results of development of scaffold structures with gradients of porosity and multi-morphology using unit cells based on triply periodic minimal surfaces (TPMS). The mechanical behaviour of additively manufactured scaffold prototypes made of polylactide acid (PLA) was studied under compressive loading. Strain fields on their surface were captured using the Vic-3d Micro-DIC digital image correlation system and compared with those obtained with detailed numerical simulations, employing elastic-plastic properties of PLA, obtained in experiments. The effect of gradient parameters and unit-cell morphology on the stress distribution in scaffolds was analysed. A smooth gradient transition between cells with different morphologies was found to reduce the probability of structural failure under intense compressive loading. A good agreement between numerical results and experimental data was achieved, which justifies application of the developed approach to design of personalised bone scaffolds.

Tashkinov M., Tarasova A., Vindokurov I., Silberschmidt V.V.

This study is focused on the deformation behaviour of composites formed by auxetic lattice structures acting as a matrix based on the re-entrant unit-cell geometry with a soft filler, motivated by biomedical applications. Three-dimensional models of two types of the auxetic-lattice structures were manufactured using filament deposition modelling. Numerical finite-element models were developed for computational analysis of the effect of the filler with different mechanical properties on the effective Poisson’s ratio and mechanical behaviour of such composites. Tensile tests of 3D-printed auxetic samples were performed with strain measurements using digital image correlation. The use of the filler phase with various elastic moduli resulted in positive, negative, and close-to-zero effective Poisson’s ratios. Two approaches for numerical measurement of the Poisson’s ratio were used. The failure probability of the two-phase composites with auxetic structure depending on the filler stiffness was investigated by assessing statistical distributions of stresses in the finite-elements models.

Zaitseva N.V., Shur P.Z., Lir D.N., Alekseev V.B., Barg А.О., Vindokurov I.V., Khrushcheva Е.V.

High work intensity (HWI) can occur in various occupational groups and induce health disorders, which means occu-pational health risk (OHR) assessment is necessary. This article describes methodical approaches to assessing OHR caused by HWI with a possibility to examine contributions made by its specific components and transition to personified risk assessment. The suggested approaches to assessing OHR caused by HWI include subjective assessment of the factor and health self-assessment. They allow identifying additional likelihood of health disorders and performing further risk assessment when exposure to HWI grows by one unit as per separate HWI indicators describing its specific components. Personified risk assessment involves using a template created for specific HWI components (intellectual, sensory, or emotional loads; work monotony; work regime). The approaches were tested on workers with mostly mental work (n = 137, respondents’ mean age was 43.9 ± 8.01 years; mean work records were 14.5 ± 3.7 years). Calculated data of personified levels of the integral health risk were used to rank likely health outcomes as per their priority. Mental disorders and diseases involving elevated blood pressure were established to correspond to ‘high’ health risk. Myopia, strained headache, atherosclerosis of peripheral vessels, and chronic laryngitis corresponded to ‘medium’ risk. Certain disorders involving the immune mechanism, tinnitus, ischemic heart disease, and atherosclerosis of coronary vessels as well as stomach and duodenum ulcer corresponded to ‘moderate’ risk. Detailed HWI assessment made it possible to identify its leading components; the shares of sensory and emotional loads in the integral health risk reached 29.0 ± 2.4 and 25.9 ± 3.9 % accordingly (р = 0.37). It is advisable to use these findings for creating personified activities aimed at OHR mitigation.

Lobov E., Dobrydneva A., Vindokurov I., Tashkinov M.

The effect of short carbon fiber (SCF) filler on the mechanical properties of 3D-printed acrylonitrile butadiene styrene (ABS) was investigated. The fused filament fabrication (FFF) method was used for the manufacturing of samples. Elastic properties and strength characteristics of samples made of conventional ABS and SCF-reinforced ABS were compared in tensile and bending tests. Fracture toughness and critical strain energy release rate were also determined. In addition, 3D-printed monofilament SCF-reinforced samples were fabricated, the internal structure of which was analyzed using microcomputed tomography (micro-CT). Based on the tomography data, finite-element (FE) models of representative volume elements (RVEs) of the reinforced material were created and used for the numerical calculation of effective characteristics. Numerical and experimental results for the effective elastic properties were compared with the Mori-Tanaka homogenization technique. The ABS samples filled with SCF showed considerably higher mechanical characteristics than those of the conventional ABS. Finally, the dependence between the strength characteristics and elastic properties of the samples on the diameter of the nozzle used for 3D printing was established. 3D-printed ABS reinforced with SCF demonstrated a gain in tensile strength and fracture toughness by 30% and 20%, respectively. Interlayer adhesion strength in flexure tests showed an increase of 28% compared to pure ABS samples.

Yeetsorn R., Chitvuttichot S., Tuantranont A., Treeratanaphitak T., Gostick J.

R N.J., Aravind Raj S.

Abstract Additive manufacturing has transformed the production of complex and tailored components in multiple industries, including aerospace, automotive, biomedical, and consumer products. Nonetheless, maintaining the quality and reliability of these components presents a significant challenge. This review paper examines the progress made in quality control methodologies specifically designed for additive manufacturing processes. Conventional quality assurance techniques, including dimensional measurement, visual assessment, and mechanical evaluations (such as tensile, compression, and impact testing), are essential for determining the quality of the final component. Nonetheless, these techniques might not adequately identify internal flaws. This review analyzes the increasing importance of non-destructive testing (NDT) methods, including ultrasonic testing, computed tomography (CT), and infrared thermography, in detecting internal defects such as porosity, cracks, and lack of fusion. The document examines the foundational principles of these NDT techniques, evaluates their benefits and drawbacks within the framework of additive manufacturing, and underscores the latest developments in their utilization. Additionally, the analysis highlights the critical role of in-process monitoring and real-time quality assurance techniques. These methods focus on identifying and rectifying flaws during the printing process, thereby reducing the likelihood of generating defective components. This detailed analysis offers an in-depth examination of the present advancements in additive manufacturing quality control, emphasizing the essential contributions of both conventional and innovative methods. By analyzing the strengths and limitations of these methods, researchers and industry professionals can create more robust and effective quality control strategies, ultimately resulting in the production of high-quality and reliable AM components.

Mulge P.K., Kalashetty S.S.

This study explored the effects of glass fiber and granite powder reinforcements on the mechanical properties of Acrylonitrile Butadiene Styrene (ABS) polymer composites produced via injection molding. Four formulations were tested: pure ABS (Batch A), ABS with 10% glass fiber (Batch B), ABS with 10% granite powder (Batch C), and a hybrid of 10% glass fiber and 10% granite powder (Batch D). Mechanical testing included tensile, flexural, compressive, impact strength, and hardness tests. Batch B showed the highest tensile strength (45.76 MPa), outperforming pure ABS (41.6 MPa), whereas the granite powder in Batch C reduced the tensile strength (36.9 MPa). Hybrid Batch D moderately improved the tensile strength (42.54 MPa) but was less effective than glass fiber alone. Batch B exhibited the highest flexural strength, whereas Batch D exhibited the highest compressive strength. The impact resistance decreased for all filled composites, particularly Batch D. Hardness was the highest in Batch D, reflecting greater material rigidity. Morphological analysis confirmed the good filler dispersion, which influenced the observed mechanical properties. Glass fiber proved to be highly effective for tensile, flexural, and hardness improvements, whereas the combination of fillers enhanced the compressive strength and hardness, offering tailored property enhancements for specific applications.

Chatzigeorgiou C., Piotrowski B., Meraghni F., Chemisky Y.

Turker B.

Fused Deposition Modeling (FDM) is a prominent additive manufacturing technique known for its ability to provide cost-effective and fast printing solutions. FDM enables the production of computer-aided 3D designs as solid objects at macro scales with high-precision alignment while sacrificing excellent surface smoothness compared to other 3D printing techniques such as SLA (Stereolithography) and SLS (Selective Laser Sintering). Electro-Spinning (ES) is another technique for producing soft-structured nonwoven micro-scale materials, such as nanofibers. However, compared to the FDM technique, it has limited accuracy and sensitivity regarding high-precision alignment. The need for high-precision alignment of micro-scaled soft structures during the printing process raises the question of whether FDM and ES techniques can be combined. Today, the printing technique with such capability is called Melt Electro Writing (MEW), and in practice, it refers to the basic working principle on which bio-printers are based. This paper aims to examine how these two techniques can be combined affordably. Comparatively, it presents output production processes, design components, parameters, and materials used in output production. It discusses the limitations and advantages of such a hybrid platform, specifically from the perspective of engineering design and its biomedical applications.

Li Y., Wang P., Zhai Y., Lv J., Sun Y.

Nanocrystalline FeCoNi medium‐entropy alloys (MEAs), characterized by their unique internal microstructure and substantial industrial application potential, often exhibit superior performance compared to conventional alloys and high‐entropy alloys. Herein, nanocrystalline FeCoNi MEAs are fabricated using an alternating current pulse electrodeposition method. The microstructure, crystallographic characteristics, and mechanical properties of the electrodeposited layers are systematically investigated. A MEA foil with a nanoscale grain thickness of 45 μm is successfully prepared. Furthermore, the foil is subjected to microbulging tests using a gas‐pressure microforming setup. The morphology and stress distribution of the deformed alloy are analyzed in detail.

Kohutiar M., Kakošová L., Krbata M., Janík R., Fekiač J.J., Breznická A., Eckert M., Mikuš P., Timárová Ľ.

This article presents a comprehensive analysis of polyamide 6 (PA6) and polyamide 12 (PA12) composites fabricated using additive manufacturing technologies such as Selective Laser Sintering (SLS) and Multi Jet Fusion (MJF). It focuses on the mechanical properties, preparation processes, and the influence of technological parameters on the final material characteristics. PA6 is characterized by a higher degree of crystallinity, contributing to its strength and resistance to high temperatures, whereas PA12 exhibits a more amorphous structure, offering better dimensional stability and lower moisture absorption. The article examines these properties and their implications for the use of composites in various applications. Applications of PA6 and PA12 composites span a wide range of industries, including automotive, aerospace, and electronics, where they provide a combination of high strength, wear resistance, and chemical stability. Mechanical properties, such as tensile strength and toughness, are analyzed within the context of modern manufacturing processes, with MJF technology delivering more homogeneous properties compared to traditional methods. The preparation process of these composites involves optimizing temperature, cooling rates, and material layering, which significantly impact the final properties and the applicability of the composites.

Nicolau K., Yang R., Gupta V., Maya F., Breadmore M.

Azizian-Farsani E., Rouhi Moghanlou M., Mahmoudi A., Wilson P.J., Khonsari M.M.

Abstract This study uses the Taguchi optimization methodology to optimize the fatigue performance of short carbon fiber-reinforced polyamide samples printed via fused deposition modeling (FDM). The optimal printing properties that maximize the fatigue limit were determined to be 0.075 mm layer thickness, 0.4 mm infill line distance, 50 mm/s printing speed, and 55 °C chamber temperature with layer thickness being the most critical parameter. To qualify fatigue endurance limit, the energy dissipation in uniaxial fatigue was quantified by using hysteresis energy and temperature rise at steady state. From these results, the fatigue limit for a specimen printed with optimized printing parameters was predicted to be 69 and 70 MPa from hysteresis energy and temperature rise at steady state methods, consecutively, and it was experimentally determined to be 67 MPa. This work demonstrates the effectiveness of the Taguchi optimization method when applied to additive manufacturing and the swift ability to predict the fatigue limit of a material with only one specimen to produce optimal additively manufactured components for industrial applications, as validated by experimental fatigue testing.

Yang Y., Yu T., Tao M., Wang Y., Yao X., Zhu C., Xin F., Jiang M.

Skin tissue engineering scaffolds should possess key properties such as porosity, degradability, durability, and biocompatibility to effectively facilitate skin cell adhesion and growth. In this study, recombinant human collagen (RHC) was used to fabricate porous scaffolds via freeze-drying, offering an alternative to animal-derived collagen where bovine collagen (BC)-based scaffolds were also prepared for comparison. The internal morphology of the RHC scaffolds were characterized by scanning electron microscopy (SEM) and the pore size ranged from 68.39 to 117.52 µm. The results from compression and fatigue tests showed that the mechanical strength and durability of RHC scaffolds could be tailored by adjusting the RHC concentration, and the maximum compressive modulus reached to 0.003 MPa, which is comparable to that of BC scaffolds. The degradation test illustrated that the RHC scaffolds had a slower degradation rate compared to BC scaffolds. Finally, the biocompatibilities of the porous scaffolds were studied by seeding and culturing the human foreskin fibroblasts (HFFs) and human umbilical vein endothelial cells (HUVECs) in samples. The fluorescent images and Cell Counting Kit-8 (CCK-8) assay revealed RHC porous scaffolds were non-cytotoxic and supported the attachment as well as the proliferation of the seeded cells. Overall, the results demonstrated that RHC-based scaffolds exhibited adequate mechanical strength, ideal biodegradability, and exceptional biocompatibility, making them highly suitable for skin-tissue-engineering applications.

Sadaghian H., Khalilzadehtabrizi S., Khodadoost S., Yeon J.H.

Abstract Background A myriad of materials, ranging from soft sensors to bone substitutes, undergo torsional loading throughout their operational lifespan. Many of these materials are produced using additive manufacturing (AM) technology due to its broad applicability. Understanding the torsional behavior of these AM components is crucial prior to their utilization. However, research on the torsional behavior of solid additively-manufactured resin polymers remains very limited. Objective To address the gap in understanding the torsional behavior of additively-manufactured resin polymers, this study aimed to investigate the effect of varying gage lengths and UV post-curing durations on the torsional capacity, shear modulus, and energy absorption characteristics of these materials. Methods Torsion specimens were fabricated using vat photopolymerization (VPP) with AnyCubic UV Tough Resin. The specimens were prepared with different gage lengths (20, 40, 60, and 80 mm) and were subjected to five UV post-curing durations (0, 15, 30, 60, 90, and 120 min). Monotonic torsion was applied to the specimens until failure at a rate of 0.1 revolutions per minute. Results The tests revealed ductile failure patterns across all specimens. Longer post-curing times were found to correlate with increased torsional capacities and shear moduli. However, conclusions regarding energy absorption per unit volume remained inconclusive. The results showed that UV exposure had a significantly greater impact on the mechanical properties of the specimens compared to the gage length. Additionally, a normalized trilinear model was proposed to characterize the behavior of additively-manufactured resin polymers under monotonic torsion, which facilitates numerical simulation of material responses in finite element software.

Houriet C., Ulyanov B., Pascoe J., Masania K.

Tashkinov M., Pirogova Y., Kononov E., Shalimov A., Silberschmidt V.V.

Generative adversarial neural networks with a variational autoencoder (VAE-GANs) are actively used in the field of materials design. The synthesis of random structures with nonrepeated geometry and predetermined mechanical properties is important for solving various practical problems. Geometric parameters of such artificially generated random structures can vary within certain limits compared to the training dataset, causing unpredicted fluctuations in their resulting mechanical response. This study investigates the statistical variability of mechanical and morphological characteristics of random 3D models reconstructed from 2D images using a VAE-GAN neural network. A combined multitool method employing different mathematical and statistical instruments for comparison of the reconstructed models with their corresponding originals is proposed. It includes the analysis of statistical distributions of elastic properties, morphometric parameters, and stress values. The neural network was trained on two datasets, containing models created based on Gaussian random fields. Statistical fluctuations of the mechanical and morphological parameters of the reconstructed models are analyzed. The deviation of the effective elastic modulus of the reconstructed models from that of the original ones was less than 5.7% on average. The difference between the median values of ligament thickness and distance between ligaments ranged from 3.6 to 6.5% and 2.6 to 5.2%, respectively. The median value of the surface area of the reconstructed geometries was 4.6–8.1% higher compared to the original models. It is thus shown that mechanical properties of the NN-generated structures retain the statistical variability of the corresponding originals, while the variability of the morphology is highly affected by the training set and does not depend on the configuration of the input 2D image.

Elenskaya N., Vindokurov I., Sadyrin E., Nikolaev A., Tashkinov M.

Bone transplantation ranks second worldwide among tissue prosthesis surgeries. Currently, one of the most promising approaches is regenerative medicine, which involves tissue engineering based on polymer scaffolds with biodegradable properties. Once implanted, scaffolds interact directly with the surrounding tissues and in a fairly aggressive environment, which causes biodegradation of the scaffold material. The aim of this work is to experimentally investigate the changes in the effective mechanical properties of polylactide scaffolds manufactured using additive technologies. The mechanism and the rate of the degradation process depend on the chosen material, contact area, microstructural features, and overall architecture of sample. To assess the influence of each of these factors, solid samples with different dimensions and layers orientation as well as prototypes of functionally graded scaffolds were studied. The research methodology includes the assessment of changes in the mechanical properties of the samples, as well as their structural characteristics. Changes in the mechanical properties were measured in compression tests. Microcomputed tomography (micro-CT) studies were conducted to evaluate changes in the microstructure of scaffold prototypes. Changes caused by surface erosion and their impact on degradation were assessed using morphometric analysis. Nonlinear changes in mechanical properties were observed for both solid samples and lattice graded scaffold prototypes depending on the duration of immersion in NaCl solution and exposure to different temperatures. At the temperature of 37 °C, the decrease in the elastic modulus of solid specimens was no more than 16%, while for the lattice scaffolds, it was only 4%. For expedited degradation during a higher temperature of 45 °C, these ratios were 47% and 16%, respectively. The decrease in compressive strength was no more than 32% for solid specimens and 17% for scaffolds. The results of this study may be useful for the development of optimal scaffolds considering the impact of the degradation process on their structural integrity.

Zou J., Deng Q., Song X., Cui L., Li X.

Senaysoy S., Ilhan R., Lekesiz H.

Large or carcinogenic bone defects may require a challenging bone tissue scaffold design ensuring a proper mechanobiological setting. Porosity and biodegradation rate are the key parameters controlling the bone-remodeling process. PLA presents a great potential for geometrically flexible 3-D scaffold design. This study aims to investigate the mechanical variation throughout the biodegradation process for lattice-type PLA scaffolds using both experimental observations and simulations. Three different unit-cell geometries are used for creating the scaffolds: basic cube (BC), body-centered structure (BCS), and body-centered cube (BCC). Three different porosity ratios, 50 %, 62.5 %, and 75 %, are assigned to all three structures by altering their strut dimensions. 3-D printed scaffolds are soaked in PBS solution at 37 °C for 15, 30, 60, 90, and 120 days both unloaded and under dead load. Water absorption, weight loss, and compression stiffness are measured to characterize the first-stage degradation and investigate the possible influences of these parameters on the whole biodegradation process. The strength reduction stage of biodegradation is simulated by solving pseudo-first-order kinetics-based molecular weight change equation using FEA with equisized cubic (voxel-like) elements. For the first stage, mechanical load does not have a statistically significant effect on biodegradation. BCC with 62.5 % porosity shows a maximum water absorption rate of around 25 % by the 60th day which brings an advantage in creating an aquatic environment for cell growth. Results indicate a significant water deposition inside almost all scaffolds and water content is determined to be the main reason for the retained or increased compression stiffness. A distinguishable stiffness increase in the initial degradation process occurs for 75 % porous BC and 50 % porous BCC scaffolds. Following the quasi-stable stage of biodegradation, almost all scaffolds lost their rigidity by around 44-48 % within 120 days based on numerical results. Therefore, initial stiffness increase in the quasi-stable stage of biodegradation can be advantageous and BCC geometry with a porosity between 50% and 62 % is the optimum solution for the whole biodegradation process.

Vindokurov I., Tashkinov M., Silberschmidt V.V.

Materials for additive manufacturing (AM), such as PLA and PEEK, are often used in biomedical applications, which involve interaction with liquid media. Consequently, the degradation process is a part of the service life of such polymers that can alter their mechanical response due to gradual changes in materials’ properties. Studying the behaviour of polymers in such environments is thus important for the prediction of the mechanical performance of biomedical devices. This paper examines the process of accelerated degradation of AM PLA and PEEK samples in saline solution and distilled water at elevated temperatures. An analysis of changes in mechanical properties, such as tensile strength and density, of PLA and PEEK with the immersion time was performed. The influence of heat treatment on the degradation process was investigated. It was found that the degradation rate of PLA in distilled water was higher than in NaCl. The trends in density changes measured with hydrostatic weighing correspond to those in the strength properties of the studied samples.

Elenskaya N., Koryagina P., Tashkinov M., Silberschmidt V.V.

Porous polymeric scaffolds are used in tissue engineering to maintain or replace damaged biological tissues. Once embedded in body, they are involved into different physical and biological processes, among which their degradation and dissolution of their material can be singled out as one of the most important ones. Degradation parameters depend mostly on the properties of both the material and surrounding native tissues, which can substantially alter the original mechanical parameters of the scaffolds. The aim of this study is to examine the change in the effective mechanical properties of functionally graded additively manufactured polylactide scaffolds with a linear porosity gradient and morphology based on triply periodic minimal surfaces during simultaneous degradation and compressive loading. Two main types of scaffold-degradation processes, bulk and surface erosions are simulated with two suggested modelling methods. The fundamental differences in the proposed approaches are identified and the influence of different types of scaffold morphology on the change in effective elastic properties is evaluated. The results of this study can be useful for design of optimal scaffolds taking into account the effect of the degradation process on their structural integrity.

Shalimov A., Tashkinov M., Silberschmidt V.V.

Trabecular bone plays an important role in structural integrity of bone tissues. Its complex microstructure characterised by high porosity and intricate composition with multiple trabeculae is a challenge for analysis of fracture initiation and propagation in it. This work investigates mechanical behaviour and failure of representative volume elements (RVEs) of porous structure of trabecular bone using numerical simulations. The extended finite-element method (XFEM) is used together with an original algorithm for the growth of multiple cracks in individual trabeculae of the structure. The obtained results are presented in comparison with the model of degradation of elastic properties. The effect of morphology on accumulation of damage and crack growth - both on the scale of a RVE and in individual ligaments - was investigated using the developed approach for estimation of a relative crack-surface area. The results are presented for five RVEs, obtained with high-resolution computed tomography of human trabecular bone, subjected to applied tensile and compressive loads.

Vindokurov I., Pirogova Y., Tashkinov M., Silberschmidt V.V.

Understanding the mechanical behaviour of additively manufactured (AM) biomedical polymeric devices under various loading regimes is important for tailoring their design to specific applications. This paper presents the results of an experimental study of compressive mechanical properties of AM cubic samples of biocompatible polylactic acid (PLA) manufactured with fused filament fabrication. The measured elastic modulus and ultimate compression strength were compared and analysed for varying testing parameters, such as strain rate and contact friction, for samples with different characteristic sizes. The changes in density of the samples were also assessed for evaluation of the extent of material compaction after deformation. Surface morphology of specimens was examined before and after compression tests using scanning electron and optical microscopy. Different types of defects induced by the manufacturing process and caused by the subsequent compressive deformation were studied and compared. The obtained results are useful for design and optimization of small-size biomedical devices, which require precise control of their structural morphology and mechanical behaviour.

Bakhtiari H., Nouri A., Khakbiz M., Tolouei-Rad M.

Bone scaffolds play a crucial role in bone tissue engineering by providing mechanical support for the growth of new tissue while enduring static and fatigue loads. Although polymers possess favourable characteristics such as adjustable degradation rate, tissue-compatible stiffness, ease of fabrication, and low toxicity, their relatively low mechanical strength has limited their use in load-bearing applications. While numerous studies have focused on assessing the static strength of polymeric scaffolds, little research has been conducted on their fatigue properties. The current review presents a comprehensive study on the fatigue behaviour of polymeric bone scaffolds. The fatigue failure in polymeric scaffolds is discussed and the impact of material properties, topological features, loading conditions, and environmental factors are also examined. The present review also provides insight into the fatigue damage evolution within polymeric scaffolds, drawing comparisons to the behaviour observed in natural bone. Additionally, the effect of polymer microstructure, incorporating reinforcing materials, the introduction of topological features, and hydrodynamic/corrosive impact of body fluids in the fatigue life of scaffolds are discussed. Understanding these parameters is crucial for enhancing the fatigue resistance of polymeric scaffolds and holds promise for expanding their application in clinical settings as structural biomaterials. STATEMENT OF SIGNIFICANCE: Polymers have promising advantages for bone tissue engineering, including adjustable degradation rates, compatibility with native bone stiffness, ease of fabrication, and low toxicity. However, their limited mechanical strength has hindered their use in load-bearing scaffolds for clinical applications. While prior studies have addressed static behaviour of polymeric scaffolds, a comprehensive review of their fatigue performance is lacking. This review explores this gap, addressing fatigue characteristics, failure mechanisms, and the influence of parameters like material properties, topological features, loading conditions, and environmental factors. It also examines microstructure, reinforcement materials, pore architectures, body fluids, and tissue ingrowth effects on fatigue behaviour. A significant emphasis is placed on understanding fatigue damage progression in polymeric scaffolds, comparing it to natural bone behaviour.

Kazantseva N., Il’inikh M., Kuznetsov V., Koemets Y., Bakhrunov K., Karabanalov M.

The influence of implant design and structural factors on fatigue life under cyclic loading was investigated. The implants were manufactured from 316L steel powder using 3D printing for medical use. A simulation model of implant deformation was built using ANSYS software. The obtained data showed that the geometry of the implant had the necessary margin of safety for osseointegration time. It was found that the stress concentration factor, which is associated with fatigue life, for an implant with a hexagon head and internal thread depends on the mechanical properties of the metal, design, and load conditions. The presence of internal threads and holes in the implant increases the stress concentration factor by more than 10 times. The number of load cycles for the failure of the implant, which was calculated by taking into account a coefficient for reducing the endurance limit, was found to be sufficient for implant osseointegration.

Kiselevskiy M.V., Anisimova N.Y., Kapustin A.V., Ryzhkin A.A., Kuznetsova D.N., Polyakova V.V., Enikeev N.A.

We overview recent findings achieved in the field of model-driven development of additively manufactured porous materials for the development of a new generation of bioactive implants for orthopedic applications. Porous structures produced from biocompatible titanium alloys using selective laser melting can present a promising material to design scaffolds with regulated mechanical properties and with the capacity to be loaded with pharmaceutical products. Adjusting pore geometry, one could control elastic modulus and strength/fatigue properties of the engineered structures to be compatible with bone tissues, thus preventing the stress shield effect when replacing a diseased bone fragment. Adsorption of medicals by internal spaces would make it possible to emit the antibiotic and anti-tumor agents into surrounding tissues. The developed internal porosity and surface roughness can provide the desired vascularization and osteointegration. We critically analyze the recent advances in the field featuring model design approaches, virtual testing of the designed structures, capabilities of additive printing of porous structures, biomedical issues of the engineered scaffolds, and so on. Special attention is paid to highlighting the actual problems in the field and the ways of their solutions.

Elenskaya N., Tashkinov M., Vindokurov I., Pirogova Y., Silberschmidt V.V.

Applications of additive manufacturing (AM) in tissue engineering develop rapidly. AM offers layer-by-layer creation of complex objects, developed to restore functionality of, or replace, damaged tissues. Porous 3D-printed functional gradient structures are of particular interest: their special architecture makes it possible to simulate the heterogeneity of the replaced tissue and, by continuously changing the mechanical properties, to avoid the concentration of stresses that can be caused by abrupt geometric changes. Such structures also allow combinations of different types of unit cells and a smooth transition between them, making design of personalised scaffolds with optimal parameters for the replacement of damaged host tissue at the interface between tissues possible. This paper presents the results of development of scaffold structures with gradients of porosity and multi-morphology using unit cells based on triply periodic minimal surfaces (TPMS). The mechanical behaviour of additively manufactured scaffold prototypes made of polylactide acid (PLA) was studied under compressive loading. Strain fields on their surface were captured using the Vic-3d Micro-DIC digital image correlation system and compared with those obtained with detailed numerical simulations, employing elastic-plastic properties of PLA, obtained in experiments. The effect of gradient parameters and unit-cell morphology on the stress distribution in scaffolds was analysed. A smooth gradient transition between cells with different morphologies was found to reduce the probability of structural failure under intense compressive loading. A good agreement between numerical results and experimental data was achieved, which justifies application of the developed approach to design of personalised bone scaffolds.

Elenskaya N., Koryagina P., Tashkinov M., Silberschmidt V.V.

Artificial porous scaffolds are used in biomedical applications to sustain or replace damaged biological tissues. Embedded into a body, such scaffolds become involved in many physical and biological processes, with degradation and dissolution of the scaffold material being among the most important. Parameters of degradation depends, first of all, on material properties as well as on the properties of the surrounding tissues. It can drastically change the initial mechanical properties of scaffolds. The aim of this work is to investigate the change in effective mechanical properties of polylactide (PLA) porous scaffolds, with morphology based on triply periodic minimum surfaces (TPMS) during degradation and simultaneous compressive loading. Two strategies for modelling of scaffold degradation processes - volumetric and surface degradation - are proposed. Fundamental differences in the proposed approaches are identified and the effects of different types of scaffold morphology on changes in effective elastic properties evaluated. The present study may be useful for design of optimal TPMS scaffold structures taking into account the effect of degradation process on their structural integrity.

Asbai-Ghoudan R., Nasello G., Pérez M.Á., Verbruggen S.W., Ruiz de Galarreta S., Rodriguez-Florez N.

Mechanical environment plays a crucial role in regulating bone regeneration in bone defects. Assessing the mechanobiological behavior of patient-specific orthopedic scaffolds in-silico could help guide optimal scaffold designs, as well as intra- and post-operative strategies to enhance bone regeneration and improve implant longevity. Additively manufactured porous scaffolds, and specifically triply periodic minimal surfaces (TPMS), have shown promising structural properties to act as bone substitutes, yet their ability to induce mechanobiologially-driven bone regeneration has not been elucidated. The aim of this study is to i) explore the bone regeneration potential of TPMS scaffolds made of different stiffness biocompatible materials, to ii) analyze the influence of pre-seeding the scaffolds and increasing the post-operative resting period, and to iii) assess the influence of patient-specific parameters, such as age and mechanosensitivity, on outcomes. To perform this study, an in silico model of a goat tibia is used. The bone ingrowth within the scaffold pores was simulated with a mechano-driven model of bone regeneration. Results showed that the scaffold's architectural properties affect cellular diffusion and strain distribution, resulting in variations in the regenerated bone volume and distribution. The softer material improved the bone ingrowth. An initial resting period improved the bone ingrowth but not enough to reach the scaffold's core. However, this was achieved with the implantation of a pre-seeded scaffold. Physiological parameters like age and health of the patient also influence the bone regeneration outcome, though to a lesser extent than the scaffold design. This analysis demonstrates the importance of the scaffold's geometry and its material, and highlights the potential of using mechanobiological patient-specific models in the design process for bone substitutes.

Mohol S.S., Kumar M., Sharma V.

The implantation of bio-degradable scaffolds is considered as a promising approach to address the repair of bone defects. This article aims to develop a computational approach to study the mechanical behaviour, fluid dynamic, and degradation impact on polylactic acid scaffolds with nature-inspired design structures. Scaffold design is considered to be one of the main factors for the regulation of mechanical characteristics and fluid flow dynamics. In this article, five scaffolds with different nature-inspired architectures have been designed within a specific porosity range. Based on finite element analysis, their mechanical behaviour and computational fluid dynamic study are performed to evaluate the respective properties of different scaffolds. In addition, diffusion-governed degradation analysis of the scaffolds has been performed to compute the total time required for the scaffold to degrade within a given environment. Based on the mechanical behaviour, the Spider-web architecture scaffold was found to have the least deformation, and also the lowest value of equivalent stress and strain. The Nautilus Shell architecture scaffold had the highest value of equivalent stress and strain. The permeability of all the scaffolds was found to meet the requirement of the cancellous bone. All computational fluid dynamics (CFD) results of wall shear stress are in line with the requirement for cell differentiation. It was observed that the Spider-web architecture scaffold had undergone the slowest degradation, and the Giant Water Lily architecture scaffold experienced the fastest degradation.

Zohoor S., Abolfathi N., Solati-Hashjin M.

A correct understanding of the process of scaffold degradation can help a proper scaffold design of bone regeneration. Polylactide acid (PLA) scaffolds are a suitable alternative for bone regenerations due to their mechanical and biodegradable properties, but their degradation tests are time-consuming and costly. Using reliable accelerated methods for in vitro experiments to save time and cost and give valid test results for scaffold degradation can be critical. In this study, two kinds of scaffolds with 60% and 80% porosities have been fabricated using the fused deposition modeling (FDM) technique. The accelerated degradation method was investigated using an alkaline solution of 0.074 M NaOH at 37 °C with pH 12.5, and the results were analyzed. The degradation of PLA scaffolds subjected to hydrolysis was evaluated based on changes in weight loss, molecular weight distribution, mechanical properties, crystallinity, and morphological analyses, for a 50 day time interval. It was found that changes in the scaffolds’ porosity greatly influence weight loss, molecular weight loss, and decrease in mechanical properties. A 20% increase in porosity leads to 2.6% more weight loss and 2% greater average molecular weight loss. Rapid yield stress reduction was observed in both porosities. Elastic modulus had a 91% reduction in 80% and a 42% reduction in 60% porosity scaffolds. The morphological changes are more evident in porosity of 80% with surface erosion in both scaffolds. The 60% porosity scaffolds showed better mechanical properties and integrity until the end of the test.

Motiee E., Karbasi S., Bidram E., Sheikholeslam M.

Mechanical properties appropriate to native tissues, as an essential component in bone tissue engineering scaffolds, plays a significant role in tissue formation. In the current study, Poly-3 hydroxybutyrate-chitosan (PC) scaffolds reinforced with graphene oxide (GO) were made by the electrospinning method. The addition of GO led to a decrease in fibers diameter, an increase in thermal capacity and an improvement in the surface hydrophilicity of nanocomposite scaffolds. A significant increase in the mechanical properties of PC/GO (PCG) nanocomposite scaffolds was achieved due to the inherent strength of GO as well as its uniform dispersion throughout the polymeric matrix owing to hydrogen bonding and polar interactions. Also, lower biological degradation of the scaffolds (~30% in 100 days) due to the presence of GO provides essential mechanical support for bone regeneration. In addition, the bioactivity results showed that GO reinforcement significantly increases the biomineralization on the surface of the scaffolds. Evaluating cell adhesion and proliferation, as well as ALP activity of MG-63 cells on PC and PCG scaffolds indicated the positive effect of GO on scaffolds' biocompatibility. Overall, the improvement of physicochemical, mechanical, and biological properties of GO-reinforced scaffolds shows the potential of PCG nanocomposite scaffolds for bone tissue engineering.

Lo L., Lin H.

Three-dimensional (3D) imaging technologies are increasingly used in craniomaxillofacial (CMF) surgery, especially to enable clinicians to get an effective approach and obtain better treatment results during different preoperative and postoperative phases, namely during image acquisition and diagnosis, virtual surgical planning (VSP), actual surgery, and treatment outcome assessment. The article presents an overview of 3D imaging technologies used in the aforementioned phases of the most common CMF surgery. We searched for relevant studies on 3D imaging applications in CMF surgery published over the past 10 years in the PubMed, ProQuest (Medline), Web of Science, Science Direct, Clinical Key, and Embase databases. A total of 2094 articles were found, of which 712 were relevant. An additional 26 manually searched articles were included in the analysis. The findings of the review demonstrated that 3D imaging technology is becoming increasingly popular in clinical practice and an essential tool for plastic surgeons. This review provides information that will help for researchers and clinicians consider the use of 3D imaging techniques in CMF surgery to improve the quality of surgical procedures and achieve satisfactory treatment outcomes.