Assessing the mechanical properties of the airway, such as compliance and viscoelasticity, is essential for diagnosing respiratory conditions particularly given the significant demand for evaluating the respiratory system since the onset of COVID-19. Traditional methods such as spirometry and plethysmography have limitations including patient discomfort and the need for active effort. We present a novel, noninvasive method using air pressure applied via a mouthpiece connected to a linear actuator. Experiments with subjects exhibiting normal respiratory function demonstrated the feasibility and accuracy of this method, minimizing patient discomfort. Pressure changes in response to rapid volume reduction within the mouthpiece induced by the actuator were analyzed using a viscoelastic Maxwell model. This approach allowed for the extraction of both compliance and viscoelastic properties with high reproducibility. The results showed that airway compliance, a measure of elasticity, varied with different breathing states, while fluidity, reflecting viscoelastic properties, remained consistent. While further research and clinical validation are needed, these findings indicate that this method has the potential to become a promising tool for respiratory diagnostics.

Abnormal blood jet flow impinging on the aortic wall has been implicated in the pathogenesis of aortic diseases. We have previously reported damage to the integrity of cultured vascular endothelial cells (ECs) exposed to a vertical impinging flow condition where both wall shear stress (WSS) and normal flow velocity immediately above the wall were high. However, it remains unclear whether the changes in ECs were caused by one factor or a combination of both. In this study, we newly designed an “inclined” impinging flow chamber to generate high WSS and high normal flow velocity conditions in different regions and examined the changes in EC morphology and actin cytoskeletal structure to the flow condition. Our findings revealed that high WSS or high normal velocity alone did not cause noticeable morphological and actin cytoskeletal changes in human aortic ECs. On the other hand, ECs exposed to the combination of both factors under a vertical impinging flow condition exhibited orientated morphology and developed actin filaments perpendicular to the direction of flow. The results suggest that high WSS or high normal velocity alone did not, but the combination of both factors led to distinct cell morphological responses in ECs.

Aortic aneurysms, characterized by local dilation of the aorta, often lead to catastrophic ruptures. Although aneurysm size is a well-established risk factor, smaller aneurysms can also rupture, indicating unclear rupture mechanisms. This study aims to elucidate the role of elastin-collagen fiber connections in failure positions within the aortic wall. Using porcine thoracic aorta samples, uniaxial tensile tests under a multiphoton microscope were conducted to capture images of elastin and collagen fibers. Potential connection points were identified by tracking fiber displacements. Simulation models—unconnected, connected, and partially connected fibers—were developed to analyze the impact of these connections on stress and failure positions. Results showed that up to 10% of crossing points were possibly connected; however, these connections had minimal effects on deformation, stress, and failure positions in collagen fibers, although they influenced stress in elastin fibers. This study confirms that elastin and collagen fiber connections do not significantly affect the initiation sites of aortic rupture. This work advances the understanding of aortic rupture mechanisms, highlighting the complexity of fiber interactions within the arterial wall.

The metabolism of bone tissue is regulated by mechanical stimuli. It has been reported that low-intensity, high-frequency vibratory stimuli can activate bone tissue metabolism. Identifying effective vibration conditions that enhance bone formation could potentially be exploited to prevent the onset and progression of osteoporosis, thereby improving quality of life in an aging society. Experiments using model animals have investigated the effects of various frequencies of vibratory stimuli, but there remains no consensus on the most effective frequency. In this study, we used a simple cell culture system to evaluate the calcium signaling response of osteoblasts subjected to micro-vibratory stimuli at different frequencies. Using a custom-developed vibration device, we applied vibratory stimuli to osteoblasts under microscopic observation and evaluated the calcium signaling response using a fluorescent calcium indicator. The vibratory stimuli were applied from 45 to 120 Hz in 15 Hz increments and from 120 to 45 Hz in 15 Hz decrements. The results of the experiment showed that the highest response rate was obtained at 60 Hz in the 45 to 120 Hz group, and at 105 Hz in the 120 to 45 Hz group. These results suggest that in an experimental system where the frequency is swept, the cells respond at the beginning of stimulation, and that habituation may contribute significantly thereafter.

Vertebrate heart evolution has undergone substantial morphological and functional adaptations in response to diverse environments. Our previous study comparing ventricular stiffness in anurans from different habitats suggested that terrestrial anurans possess stiffer ventricles than aquatic counterparts. However, as this hypothesis was tested on only one species per habitat, the generality of this trend remained uncertain. This study aimed to expand upon these findings by examining two representative species: aquatic Xenopus borealis (X. bor) and terrestrial Buergeria buergeri (B. bue). Pressure loading tests were conducted to measure ventricular stiffness, while histological analyses examined structural differences. Pressure-loading tests revealed that the ventricles of B. bue were significantly stiffer than those of aquatic X. bor, which was consistent with previous findings. Histological analysis revealed that the increased stiffness correlated with a thick and compact myocardium layer and elevated collagen content in terrestrial species. These findings indicate that the ventricles of anurans stiffen during terrestrial adaptation, providing insights into the evolutionary changes in heart structure and mechanical properties in response to environmental shifts.

Actin stress fibers are crucial determinants of cellular adhesion morphology, and their structural formation depends on the mechanical properties of the extracellular microenvironment. This study aims to expand on the established understanding of two-dimensional actin arcs by uncovering the mechanisms driving the formation of three-dimensional actin arcs on deformable substrates. Specifically, we evaluated how the viscoelasticity of the extracellular matrix influences the three-dimensional dynamics of actin stress fibers. Using PNIPAAm-grafted substrates with varying polymer chain lengths, we observed that longer chains with higher deformability and energy dissipation promoted the formation of three-dimensional actin arcs. Furthermore, we examined the impact of substrate energy dissipation on the central angle of actin arcs, revealing that matrix viscoelasticity plays a significant role in regulating the three-dimensional behavior of actin stress fibers. These findings highlight the critical role of matrix viscoelasticity in modulating the three-dimensional dynamics of actin stress fibers.

Mechanical forces transmitted to the nucleus that affect nuclear organization, such as nuclear shape and intranuclear DNA distribution, are crucial regulators of key transcriptional activities directing the differentiation of mesenchymal stem cells (MSCs). Several studies have reported that the actin cytoskeleton plays an important role in force transmission to the nucleus, thereby defining nuclear organization. However, the effects of structural changes in the actin cytoskeleton on nuclear organization during osteogenic differentiation remain unclear. Here, we investigated the relationship between the perinuclear actin cytoskeleton and nuclear organization at each stage of osteogenic differentiation of MSCs, based on fluorescence images. The results demonstrated that actin fibers on top of the nucleus transiently developed in the early stage of osteogenic differentiation, which was correlated with a decrease in nuclear height. In addition, we revealed that the development of the actin fibers on top of the nucleus contributed to DNA condensation with histone modification (H3k9me3) in the nuclear peripheral area. These findings suggest that, from MSCs to the early stage of osteogenic differentiation, the compressive forces exerted on the nucleus by the actin cytoskeleton induce a decrease in nuclear height and promote DNA condensation in the nuclear peripheral area.

The fluidity of endothelial cell (EC) membranes, consisting of a lipid bilayer and heterogeneous multicomponent, undergoes alterations in response to shear stress. Although localized variations in membrane fluidity are assumed to induce region-specific signal transduction by modulating membrane protein dynamics on almost planar bilayers, membrane protein diffusion under shear stress remains uncertain. Hence, this study aimed to quantify membrane protein diffusion on ECs under fluid shear stress. We used the photochromic fluorescent protein Dronpa to tag a glycosylphosphatidylinositol-anchored protein (GPI-AP), which diffuses across the outer membranes, and quantified its surface diffusion based on the spatiotemporal distribution of Dronpa-Green-labeled GPI-AP (DGGPI-AP) on EC membranes. We developed an experimental platform to measure the GPI-AP surface diffusion under fluid shear stress and quantified the diffusion coefficient of GPI-AP in two distinct membrane regions: upstream and downstream relative to the direction of fluid flow. Our experimental results showed that there were not statistically significant differences in GPI-AP diffusion on EC membranes between the time points or between the upstream and downstream regions of ECs for at least 15 minutes under shear stress. Our developed methodology and experimental results will be useful to understand a relationship between the membrane protein diffusion and shear-induced cellular processes.

Aortic dissection Stanford type B cases often see false lumen enlargement, leading to severe complications. This study hypothesizes that in chronic aortic dissection, upon exposure to blood flow, vascular smooth muscle cells (VSMCs) switch their phenotype to be synthetic, increasing the production of matrix metalloproteinases (MMPs) that degrade the extracellular matrix (ECM) and weaken the false lumen wall, leading to the false lumen enlargement. Male Sprague-Dawley rats’ aortas, with endothelial cells removed, were incubated under flow-loading conditions in a specialized ex vivo system for 48 hours to test this hypothesis. Viability assays confirmed that VSMCs remained largely viable post-incubation. Gene expression analysis revealed a decrease in the contractile phenotype but no change in the synthetic phenotype, with no differences due to the wall shear stress (WSS) value. MMP-2 and MMP-9 expression changed after the incubation, but no remarkable difference was detected for the WSS value. Elastin structure remained unchanged, indicating no ECM degradation during the incubation period. These results suggest that ex vivo incubation does induce phenotype change in VSMCs, but direct flow on VSMCs might not lead to further phenotype changes or MMP production within 48 hours. Potential reasons include the presence of the internal elastic lamina preventing direct WSS on VSMCs or the short incubation duration. This study underscores the complexity of VSMC phenotype switching and its role in vascular diseases, advocating for more nuanced analysis and advanced techniques to unravel the mechanisms of false lumen enlargement in aortic dissection.

Lateral stiffness and topography of culture substrate are critical parameters for controlling stem cell differentiation. However, controlling the lateral stiffness of the VACNT bundle tip, that is included in pillar category, is remained to be solved in a range of cell culture. In this study, we transferred the 18 μm VACNT length into PDMS matrix to control VACNT lateral stiffness with a partial immersion method. VACNT/PDMS composite was synthesized in which 5–10 μm of VACNT length at top surface was maintained free to move. The Lateral force measurement (LFM) demonstrated that VACNT/PDMS composite bundle tip with 6 μm PDMS was the stiffest, followed by raw VACNT and VACNT with 8.6 μm PDMS. The lateral stiffness values of the three VACNT condition were 1.037 N/m, 0.914 N/m, and 0.535 N/m, respectively. These values at certain thickness of PDMS could take a role as reinforcement or declination for VACNTs tips stiffness. We suggest that the VACNT have potential to control stem cell differentiation due to their sophisticate change of lateral stiffness.

Understanding the mechanical properties of cells is essential for elucidating their biological functions, such as migration, differentiation, and maintenance of tissue integrity. Scanning acoustic microscopy (SAM) is a noninvasive and rapid method for exploring mechanical properties while preserving physiological conditions. In this study, we used SAM to investigate the effects of actin filaments (AFs) and microtubules (MTs) disruption on the acoustic impedance of cultured smooth muscle cells (SMCs). The results showed that the disruption of AFs significantly reduced the acoustic impedance, suggesting a decrease in cell stiffness. In contrast, MT disruption had a minor effect. These results are consistent with previously reported mechanical tests of cells with disrupted AFs and MTs, suggesting that SAM could be a powerful tool for the noninvasive exploration of cell mechanics and highlighting the need for further research to enable broader application of this technique in cell mechanics research.

Directional migration of eukaryotic cells results from an interplay between cell motility and environmental cues such as stiffness, roughness, and microtopological features of substrates. While the effects of aligned grooves on the substrate lithographically designed on active cell migration are well documented, the impact of unorganized and wrinkled substrates remains poorly understood. We investigated how microscale wrinkles on gelatin substrates regulate two-dimensional (2D) migration of immortalized human mesenchymal stem cells (iMSCs). We showed that there exists an optimal wrinkle size to enhance iMSC migration, where the iMSCs exhibited larger travel distance with moderate wrinkle size (30 μm) than shorter or larger wrinkle sizes (10 μm and 50 μm). These findings reveal a size-dependent effect of wrinkles on iMSC migration and provide insights into designing biomaterials to control stem cell behavior in regenerative medicine applications.