Ústav mechaniky těles, mechatroniky a biomechaniky
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- ItemLayer-specific residual strains in human carotid arteries revealed under layer separation(PLOS, 2025-04-07) Hrubanová, Anna; Lisický, Ondřej; Sochor, Ondřej; Bednařík, Zdeněk; Joukal, Marek; Burša, JiříResidual stresses are considered as a significant factor influencing the stress-states in arteries. These stresses are typically observed through opening angle of a radially cut artery segment, often regarded as a primary descriptor of their stress-free state. However, the experimental evidence regarding the stress-free states of different artery layers is scarce. In this study, two experimental protocols, each employing different layer-separating sequences, were performed on 17 human common carotid arteries; the differences between both protocols were found statistically insignificant. While the media exhibited opening behaviour (reduced curvature), a contrasting trend was observed for the adventitia curvature, indicating its closing behaviour. In addition to the different bending effect, length changes of both layers after separation were observed, namely shortening of the adventitia and elongation of the media. The results point out that not all the residual stresses are released after a radial cut but a significant portion of them is released only after the layer separation. Considering the different mechanical properties of layers, this may significantly change the stress distribution in arterial wall and should be considered in its biomechanical models.
- ItemModeling Mechanical Properties of Titanium Scaffolds with Variable Microporosity(WILEY-V C H VERLAG GMBH, 2024-10-01) Slámečka, Karel; Skalka, Petr; Pokluda, JaroslavThe article introduces a two-level finite element model for metallic scaffolds with porosity at both design and material levels. Despite several additive manufacturing methods producing structures with controlled hierarchical porosity, their functional properties remain largely unknown, hindering industrial utilization. This article examines how material microporosity affects the mechanical properties of a scaffold prepared by direct ink writing from pure titanium with dimensions typical for orthopedic implants. The study focuses on the compressive response of scaffolds with microporosity ranging from 0.05 to 0.65. The article demonstrates the practical application of the model by estimating the effective Young's modulus and the relative length of the fatigue crack initiation stage. Tensile plastic strains at critical sites exhibit a delocalization from around micropores followed by relocalization into thinning interpore walls with increasing microporosity, resulting in the highest fracture strain predicted for microporosities between 0.2 and 0.3. These strains enable the estimation of the length of the fatigue crack initiation stage, which proves to be very short for all microporosities. This emphasizes the crucial role of the crack growth stage in scaffold fatigue life and confirms the potential for additional experiments on scaffolds with microporosities exceeding 0.15 to enhance their fatigue resistance. The article presents a finite element model for metallic scaffolds, investigating the impact of material microporosity on mechanical behavior. Specifically, the study investigates regular microporous titanium scaffolds prepared by direct ink writing, highlighting the effects of strain delocalization and relocalization on fracture strain. Moreover, the model estimates the relative length of the fatigue crack initiation stage in these materials.image (c) 2024 WILEY-VCH GmbH
- ItemLong-term zinc treatment alters the mechanical properties and metabolism of prostate cancer cells(BMC, 2024-10-11) Navrátil, Jiří; Kratochvílová, Monika; Raudenská, Martina; Balvan, Jan; Vičar, Tomáš; Petrláková, Kateřina; Suzuki, Kanako; Jadrná, Lucie; Burša, Jiří; Kräter, Martin; Kyoohyun, Kim; Masařík, Michal; Gumulec, JaromírThe failure of intracellular zinc accumulation is a key process in prostate carcinogenesis. Although prostate cancer cells can accumulate zinc after long-term exposure, chronic zinc oversupply may accelerate prostate carcinogenesis or chemoresistance. Because cancer progression is associated with energetically demanding cytoskeletal rearrangements, we investigated the effect of long-term zinc presence on biophysical parameters, ATP production, and EMT characteristics of two prostate cancer cell lines (PC-3, 22Rv1). Prolonged exposure to zinc increased ATP production, spare respiratory capacity, and induced a response in PC-3 cells, characterized by remodeling of vimentin and a shift of cell dry mass density and caveolin-1 to the perinuclear region. This zinc-induced remodeling correlated with a greater tendency to maintain actin architecture despite inhibition of actin polymerization by cytochalasin. Zinc partially restored epithelial characteristics in PC-3 cells by decreasing vimentin expression and increasing E-cadherin. Nevertheless, the expression of E-cadherin remained lower than that observed in predominantly oxidative, low-invasive 22Rv1 cells. Following long-term zinc exposure, we observed an increase in cell stiffness associated with an increased refractive index in the perinuclear region and an increased mitochondrial content. The findings of the computational simulations indicate that the mechanical response cannot be attributed exclusively to alterations in cytoskeletal composition. This observation suggests the potential involvement of an additional, as yet unidentified, mechanical contributor. These findings indicate that long-term zinc exposure alters a group of cellular parameters towards an invasive phenotype, including an increase in mitochondrial number, ATP production, and cytochalasin resistance. Ultimately, these alterations are manifested in the biomechanical properties of the cells.
- ItemSize Effect on the Ductile Fracture of the Aluminium Alloy 2024-T351(Springer Nature, 2024-09-10) Šebek, František; Salvet, Patrik; Boháč, Petr; Adámek, Roman; Věchet, Stanislav; Návrat, Tomáš; Zapletal, Josef; Ganjiani, MehdiBackground Reliably calibrated criteria are needed for an accurate prediction of fracture of various components. However, there is not always a sufficient amount of material available. Therefore, miniature testing provides an alternative that is researched together with the following calibration of the ductile fracture criteria and investigating the size effect. Objective The aim is to design miniature testing equipment and specimens for tensile testing, which covers various stress states. This is supplemented by the small punch test, which has the same specimen thickness, taken from the literature to broaden the portfolio for calibration. The second part deals with conducting the finite element analysis, which provided a basis for the calibration of the phenomenological ductile fracture criterion applicable to crack-free bodies to indicate the crack initiation. Methods The steel frame to test thin specimens is designed with optical measurement of deformations. The finite element method is used, within Abaqus and user subroutines, to simulate the tests to obtain the variables needed for the calibration. In addition, the calibration of the criterion using machine learning is explored. Results The feasibility of the proposed experimental program is tested on the aluminium alloy 2024-T351. Moreover, the numerical simulations, which showed a good match with experiments in terms of force responses, adds to the knowledge of modelling in the scope of continuum damage mechanics. Conclusions The presented results provide a material basis for the aluminium alloy studied on a lower scale, while they broaden the testing possibilities and analyses the calibration strategies for the best failure predictability possible.
- ItemSmall-scale domain switching near sharp piezoelectric bi-material notches(Springer Nature, 2025-03-08) Hrstka, Miroslav; Kotoul, Michal; Profant, Tomáš; Kianicová, MartaAssuming a scenario of small-scale domain switching, the dimensions and configuration of the domain switching region preceding a clearly defined primarily monoclinic piezoelectric bi-material notch are determined by embracing the energetic switching principle and micromechanical domain switching framework proposed by Hwang et al. (Acta Metall Mater 43(5):2073-2084, 1995. https://doi.org/10.1016/0956-7151(94)00379-V) for a given set of materials, structure, and polarization alignment. The piezoelectric bi-material under consideration comprises piezoelectric ceramics PZT-5H and BaTiO3. The analysis of the asymptotic in-plane field around a bi-material sharp notch is conducted utilizing the extended Lekhnitskii-Eshelby-Stroh formalism (Ting in Anisotropic elasticity, Oxford University Press. 1996. https://doi.org/10.1093/oso/9780195074475.001.0001). Subsequently, the boundary value problem with the prescribed spontaneous strain and polarization within the switching domain is solved and their influence on the in-plane intensity of singularity at the tip of interface crack is computed. The effects of the initial poling direction on the resulting variation of the energy release rates are discussed.