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by Keyword: shear


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Tejo-Otero A, Fenollosa-Artés F, Achaerandio I, Rey-Vinolas S, Buj-Corral I, Mateos-Timoneda MÁ, Engel E, (2022). Soft-Tissue-Mimicking Using Hydrogels for the Development of Phantoms Gels 8, 40

With the currently available materials and technologies it is difficult to mimic the mechanical properties of soft living tissues. Additionally, another significant problem is the lack of information about the mechanical properties of these tissues. Alternatively, the use of phantoms offers a promising solution to simulate biological bodies. For this reason, to advance in the state-of-the-art a wide range of organs (e.g., liver, heart, kidney as well as brain) and hydrogels (e.g., agarose, polyvinyl alcohol –PVA–, Phytagel –PHY– and methacrylate gelatine –GelMA–) were tested regarding their mechanical properties. For that, viscoelastic behavior, hardness, as well as a non-linear elastic mechanical response were measured. It was seen that there was a significant difference among the results for the different mentioned soft tissues. Some of them appear to be more elastic than viscous as well as being softer or harder. With all this information in mind, a correlation between the mechanical properties of the organs and the different materials was performed. The next conclusions were drawn: (1) to mimic the liver, the best material is 1% wt agarose; (2) to mimic the heart, the best material is 2% wt agarose; (3) to mimic the kidney, the best material is 4% wt GelMA; and (4) to mimic the brain, the best materials are 4% wt GelMA and 1% wt agarose. Neither PVA nor PHY was selected to mimic any of the studied tissues. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords: brain, composite hydrogel, elastography, hardness, hydrogels, in-vitro, liver, materials, mechanical-properties, mimicking, soft tissues, tissue scaffolding, viscoelasticity, warner-braztler shear test, Dynamic mechanical analysis, Hardness, Hydrogels, Materials, Mimicking, Soft tissues, Tissue scaffolding, Viscoelastic characterization, Viscoelasticity, Warner–braztler shear test


Nashimoto Y, Abe M, Fujii R, Taira N, Ida H, Takahashi Y, Ino K, Ramon-Azcon J, Shiku H, (2021). Topography and Permeability Analyses of Vasculature-on-a-Chip Using Scanning Probe Microscopies Advanced Healthcare Materials 10

Microphysiological systems (MPS) or organs-on-chips (OoC) can emulate the physiological functions of organs in vitro and are effective tools for determining human drug responses in preclinical studies. However, the analysis of MPS has relied heavily on optical tools, resulting in difficulties in real-time and high spatial resolution imaging of the target cell functions. In this study, the role of scanning probe microscopy (SPM) as an analytical tool for MPS is evaluated. An access hole is made in a typical MPS system with stacked microchannels to insert SPM probes into the system. For the first study, a simple vascular model composed of only endothelial cells is prepared for SPM analysis. Changes in permeability and local chemical flux are quantitatively evaluated during the construction of the vascular system. The morphological changes in the endothelial cells after flow stimulation are imaged at the single-cell level for topographical analysis. Finally, the possibility of adapting the permeability and topographical analysis using SPM for the intestinal vascular system is further evaluated. It is believed that this study will pave the way for an in situ permeability assay and structural analysis of MPS using SPM.

Keywords: cell, electrochemical microscopy, membrane-permeability, microphysiological systems, organs-chips, platform, scanning electrochemical microscopy, scanning ion conductance microscopy, scanning probe microscopy, shear-stress, surface-topography, Ion conductance microscopy, Microphysiological systems, Organs-chips, Scanning electrochemical microscopy, Scanning ion conductance microscopy, Scanning probe microscopy


Blanco-Cabra N, López-Martínez MJ, Arévalo-Jaimes BV, Martin-Gómez MT, Samitier J, Torrents E, (2021). A new BiofilmChip device for testing biofilm formation and antibiotic susceptibility Npj Biofilms And Microbiomes 7,

Currently, three major circumstances threaten the management of bacterial infections: increasing antimicrobial resistance, expansion of chronic biofilm-associated infections, and lack of an appropriate approach to treat them. To date, the development of accelerated drug susceptibility testing of biofilms and of new antibiofouling systems has not been achieved despite the availability of different methodologies. There is a need for easy-to-use methods of testing the antibiotic susceptibility of bacteria that form biofilms and for screening new possible antibiofilm strategies. Herein, we present a microfluidic platform with an integrated interdigitated sensor (BiofilmChip). This new device allows an irreversible and homogeneous attachment of bacterial cells of clinical origin, even directly from clinical specimens, and the biofilms grown can be monitored by confocal microscopy or electrical impedance spectroscopy. The device proved to be suitable to study polymicrobial communities, as well as to measure the effect of antimicrobials on biofilms without introducing disturbances due to manipulation, thus better mimicking real-life clinical situations. Our results demonstrate that BiofilmChip is a straightforward tool for antimicrobial biofilm susceptibility testing that could be easily implemented in routine clinical laboratories.

Keywords: cells, model, resistance, shear, technology, In-vitro


López-Canosa A, Perez-Amodio S, Yanac-Huertas E, Ordoño J, Rodriguez-Trujillo R, Samitier J, Castaño O, Engel E, (2021). A microphysiological system combining electrospun fibers and electrical stimulation for the maturation of highly anisotropic cardiac tissue Biofabrication 13,

The creation of cardiac tissue models for preclinical testing is still a non-solved problem in drug discovery, due to the limitations related to thein vitroreplication of cardiac tissue complexity. Among these limitations, the difficulty of mimicking the functional properties of the myocardium due to the immaturity of the used cells hampers the obtention of reliable results that could be translated into human patients.In vivomodels are the current gold standard to test new treatments, although it is widely acknowledged that the used animals are unable to fully recapitulate human physiology, which often leads to failures during clinical trials. In the present work, we present a microfluidic platform that aims to provide a range of signaling cues to immature cardiac cells to drive them towards an adult phenotype. The device combines topographical electrospun nanofibers with electrical stimulation in a microfabricated system. We validated our platform using a co-culture of neonatal mouse cardiomyocytes and cardiac fibroblasts, showing that it allows us to control the degree of anisotropy of the cardiac tissue inside the microdevice in a cost-effective way. Moreover, a 3D computational model of the electrical field was created and validated to demonstrate that our platform is able to closely match the distribution obtained with the gold standard (planar electrode technology) using inexpensive rod-shaped biocompatible stainless-steel electrodes. The functionality of the electrical stimulation was shown to induce a higher expression of the tight junction protein Cx-43, as well as the upregulation of several key genes involved in conductive and structural cardiac properties. These results validate our platform as a powerful tool for the tissue engineering community due to its low cost, high imaging compatibility, versatility, and high-throughput configuration capabilities.

Keywords: bioreactor, cardiac tissue engineering, cardiomyocytes, electrospinning, fabrication, fibroblasts, heart-on-a-chip, heart-tissue, in vitro models, myocardium, orientation, platform, scaffolds, Cardiac tissue engineering, Electrospinning, Field stimulation, Heart-on-a-chip, In vitro models, Microphysiological system


Pieper CC, Feißt A, Meyer C, Luetkens J, Praktiknjo M, Trebicka J, Attenberger U, Jansen C, (2021). Impact of transjugular intrahepatic portosystemic shunt creation on the central lymphatic system in liver cirrhosis Scientific Reports 11, 7065

The puropse of this study was to evaluate associations of cisterna chyli (CCh) diameter with portal hemodynamics and the influence of TIPS-creation in cirrhotic patients. 93 cirrhotic patients (57 male, mean age 59 years) received CT prior to TIPS-creation. 38/93 additionally underwent post-interventional CT. CCh-diameter was measured. After categorization into patients with and without large venous collaterals (i.e. > 6 mm), data were analyzed regarding associations between CCh-diameter, clinical and portal-hemodynamic parameters and diameter-changes after TIPS-creation. Patient survival post-TIPS was analyzed. Median portosystemic pressure-gradient decreased from 20 to 9 mmHg after TIPS-creation. Large venous collaterals were observed in 59 patients. In 69/93 patients (74.2%) the CCh was detectable. Mean pre-interventional diameter was 9.4 ± 2.7 mm (large collaterals: 8.7 ± 2.0 mm, no large collaterals: 10.7 ± 3.2 mm, p = 0.003). CCh-diameter correlated strongly with pre-TIPS portal-pressure (Rs = 0.685, p = 0.0001), moderately with portosystemic-gradient (Rs = 0.524, p = 0.006), liver shear-wave-elastography (Rs = 0.597, p = 0.004) and spleen size (Rs = 0.501, p = 0.01) in patients without large collaterals, but not in patients with large collaterals. Post-TIPS CCh-diameter decreased significantly from 10.2 ± 2.8 mm to 8.3 ± 3.0 mm (p < 0.001). Patients without a detectable CCh on CT survived significantly shorter. The diameter of the CCh is associated with portal-pressure and decreases after TIPS-creation in cirrhotic patients, reflecting a portal decompression mechanism via the lymphatic system. Lack of larger central lymphatics detectable on CT may be associated with shorter survival.

Keywords: circulation, cisterna chyli, fluid, hepatic cirrhosis, shear-wave elastography, thoracic-duct, vessels, Significant portal-hypertension


Feiner-Gracia N, Glinkowska Mares A, Buzhor M, Rodriguez-Trujillo R, Samitier Marti J, Amir RJ, Pujals S, Albertazzi L, (2021). Real-Time Ratiometric Imaging of Micelles Assembly State in a Microfluidic Cancer-on-a-Chip Acs Applied Bio Materials 4, 669-681

© 2020 American Chemical Society. The performance of supramolecular nanocarriers as drug delivery systems depends on their stability in the complex and dynamic biological media. After administration, nanocarriers are challenged by physiological barriers such as shear stress and proteins present in blood, endothelial wall, extracellular matrix, and eventually cancer cell membrane. While early disassembly will result in a premature drug release, extreme stability of the nanocarriers can lead to poor drug release and low efficiency. Therefore, comprehensive understanding of the stability and assembly state of supramolecular carriers in each stage of delivery is the key factor for the rational design of these systems. One of the main challenges is that current 2D in vitro models do not provide exhaustive information, as they fail to recapitulate the 3D tumor microenvironment. This deficiency in the 2D model complexity is the main reason for the differences observed in vivo when testing the performance of supramolecular nanocarriers. Herein, we present a real-time monitoring study of self-assembled micelles stability and extravasation, combining spectral confocal microscopy and a microfluidic cancer-on-a-chip. The combination of advanced imaging and a reliable 3D model allows tracking of micelle disassembly by following the spectral properties of the amphiphiles in space and time during the crucial steps of drug delivery. The spectrally active micelles were introduced under flow and their position and conformation continuously followed by spectral imaging during the crossing of barriers, revealing the interplay between carrier structure, micellar stability, and extravasation. Integrating the ability of the micelles to change their fluorescent properties when disassembled, spectral confocal imaging and 3D microfluidic tumor blood vessel-on-a-chip resulted in the establishment of a robust testing platform suitable for real-time imaging and evaluation of supramolecular drug delivery carrier's stability.

Keywords: cancer-on-a-chip, complex, delivery, endothelial-cells, in-vitro, microfluidic, model, nanoparticle, penetration, shear-stress, stability, supramolecular, Cancer-on-a-chip, Cell-culture, Micelle, Microfluidic, Nanoparticle, Stability, Supramolecular


Solà-Soler, J., Giraldo, B. F., (2020). Comparison of ECG-eerived respiration estimation methods on healthy subjects in function of recording site and subject position and gender Engineering in Medicine & Biology Society (EMBC) 42nd Annual International Conference of the IEEE , IEEE (Montreal, Canada) , 2650-2653

Respiration rate can be assessed by analyzing respiratory changes of the electrocardiogram (ECG). Several methods can be applied to derive the respiratory signal from the ECG (EDR signal). In this study, four EDR estimation methods based on QRS features were analyzed. A database with 44 healthy subjects (16 females) in supine and sitting positions was analyzed. Respiratory flow and ECG recordings on leads I, II, III and a Chest lead was studied. A QR slope-based method, an RS slope-based method, an QRS angle-based method and an QRS area-based method were applied. Their performance was evaluated by the correlation coefficient with the reference respiratory volume signal. Significantly higher correlation coefficients in the range r = 0.77 – 0.86 were obtained with the Chest lead for all methods. The EDR estimation method based on the QRS angle provided the highest similarity with the volume signal for all recording leads and subject positions. We found no statistically significant differences according to gender or subject position.Clinical Relevance— This work analyzes the EDR signal from four electrocardiographic leads to obtain the respiratory signal and contributes to a simplified analysis of respiratory activity.

Keywords: Electrocardiography, Lead, Estimation, Correlation coefficient, Databases, Heart, Correlation


Romero, D., Jané, R., (2020). Hypoxia-induced effects on ECG depolarization by time warping analysis during recurrent obstructive apnea Engineering in Medicine & Biology Society (EMBC) 42nd Annual International Conference of the IEEE , IEEE (Montreal, Canada) , 2626-2629

In this work, we evaluated a non-linear approach to estimate morphological variations in ECG depolarization, in the context of intermittent hypoxia (IH). Obstructive apnea sequences were provoked for 15 minutes in anesthetized Sprague-Dawley rats, alternating with equal periods of normal breathing, in a recurrent obstructive sleep apnea (OSA) model. Each apnea episode lasted 15 s, while the frequency used for each sequence was randomly selected. Average heartbeats obtained before the start and at the end of each episode, were delineated to extract only the QRS wave. Then, the segmented QRS waves were non-linearly aligned using the dynamic time warping (DWT) algorithm. Morphological QRS changes in both the amplitude and temporal domains were estimated from this alignment procedure. The hypoxic and basal segments were analyzed using ECG (lead I) recordings acquired during the experiment. To assess the effects of IH over time, the changes relative to the basal QRS wave were determined, in the intervals prior to each successive events until the end of the experiment. The results showed a progressive increase in the amplitude and time-domain morphological markers of the QRS wave along the experiment, which were strongly correlated with the changes in traditional QRS markers (r ≈ 0.9). Significant changes were found between pre-apnea and hypoxic measures only for the time-domain analysis (p<0.001), probably due to the short duration of the simulated apnea episodes.Clinical relevance Increased variability in ECG depolarization morphology during recurrent hypoxic episodes would be closely related to the expression of cardiovascular dysfunction in OSA patients.

Keywords: Electrocardiography, Rats, Heart rate variability, Sleep apnea, Protocols, Heuristic algorithms


Romero, D., Jané, R., (2019). Non-linear HRV analysis to quantify the effects of intermittent hypoxia using an OSA rat model Engineering in Medicine and Biology Society (EMBC) 41st Annual International Conference of the IEEE , IEEE (Berlín, Germany) , 4994-4997

In this paper, a non-linear HRV analysis was performed to assess fragmentation signatures observed in heartbeat time series after intermittent hypoxia (IH). Three markers quantifying short-term fragmentation levels, PIP, IALS and PSS, were evaluated on R-R interval series obtained in a rat model of recurrent apnea. Through airway obstructions, apnea episodes were periodically simulated in six anesthetized Sprague-Dawley rats. The number of apnea events per hour (AHI index) was varied during the first half of the experiment while apnea episodes lasted 15 s. For the second part, apnea episodes lasted 5, 10 or 15 s, but the AHI index was fixed. Recurrent apnea was repeated for 15-min time intervals in all cases, alternating with basal periods of the same duration. The fragmentation markers were evaluated in segments of 5 minutes, selected at the beginning and end of the experiment. The impact of the heart and breathing rates (HR and BR, respectively) on the parameter estimates was also investigated. The results obtained show a significant increase (from 5 to 10%, p <; 0.05) in fragmentation measures of heartbeat time series after IH, indicating a clear deterioration of the initial conditions. Moreover, there was a strong linear relationship (r > 0.9) between these markers and BR, as well as with the ratio given by HR/BR. Although fragmentation may be impacted by IH, we found that it is highly dependent on HR and BR values and thus, they should be considered during its calculation or used to normalize the fragmentation estimates.

Keywords: Rats, Time series analysis, Radio access technologies, Protocols, Heart beat


Farré, N., Jorba, I., Torres, M., Falcones, B., Martí-Almor, J., Farré, R., Almendros, I., Navajas, D., (2018). Passive stiffness of left ventricular myocardial tissue is reduced by ovariectomy in a post-menopause mouse model Frontiers in Physiology 9, Article 1545

Background: Heart failure (HF) – a very prevalent disease with high morbidity and mortality – usually presents with diastolic dysfunction. Although post-menopause women are at increased risk of HF and diastolic dysfunction, poor attention has been paid to clinically and experimentally investigate this group of patients. Specifically, whether myocardial stiffness is affected by menopause is unknown. Aim: To investigate whether loss of female sexual hormones modifies the Young’s modulus (E) of left ventricular (LV) myocardial tissue in a mouse model of menopause induced by ovariectomy (OVX). Methods: After 6 months of bilateral OVX, eight mice were sacrificed, fresh LV myocardial strips were prepared (∼8 × 1 × 1 mm), and their passive stress–stretch relationship was measured. E was computed by exponential fitting of the stress–stretch relationship. Subsequently, to assess the relative role of cellular and extracellular matrix components in determining OVX-induced changes in E, the tissues strips were decellularized and subjected to the same stretching protocol to measure E. A control group of eight sham-OVX mice was simultaneously studied. Results: E (kPa; m ± SE) in OVX mice was ∼twofold lower than in controls (11.7 ± 1.8 and 22.1 ± 4.4, respectively; p < 0.05). No significant difference between groups was found in E of the decellularized tissue (31.4 ± 12.05 and 40.9 ± 11.5, respectively; p = 0.58). Conclusion: Loss of female sexual hormones in an OVX model induces a reduction in the passive stiffness of myocardial tissue, suggesting that active relaxation should play a counterbalancing role in diastolic dysfunction in post-menopausal women with HF.

Keywords: Decellularized tissue, Female hormones, Heart tissue, Ovariectomy, Stress-strain


Giraldo, B. F., Tellez, J. P., Herrera, S., Benito, S., (2013). Analysis of heart rate variability in elderly patients with chronic heart failure during periodic breathing CinC 2013 Computing in Cardiology Conference (CinC) , IEEE (Zaragoza, Spain) , 991-994

Assessment of the dynamic interactions between cardiovascular signals can provide valuable information that improves the understanding of cardiovascular control. Heart rate variability (HRV) analysis is known to provide information about the autonomic heart rate modulation mechanism. Using the HRV signal, we aimed to obtain parameters for classifying patients with and without chronic heart failure (CHF), and with periodic breathing (PB), non-periodic breathing (nPB), and Cheyne-Stokes respiration (CSR) patterns. An electrocardiogram (ECG) and a respiratory flow signal were recorded in 36 elderly patients: 18 patients with CHF and 18 patients without CHF. According to the clinical criteria, the patients were classified into the follow groups: 19 patients with nPB pattern, 7 with PB pattern, 4 with Cheyne-Stokes respiration (CSR), and 6 non-classified patients (problems with respiratory signal). From the HRV signal, parameters in the time and frequency domain were calculated. Frequency domain parameters were the most discriminant in comparisons of patients with and without CHF: PTot (p = 0.02), PLF (p = 0.022) and fpHF (p = 0.021). For the comparison of the nPB vs. CSR patients groups, the best parameters were RMSSD (p = 0.028) and SDSD (p = 0.028). Therefore, the parameters appear to be suitable for enhanced diagnosis of decompensated CHF patients and the possibility of developed periodic breathing and a CSR pattern.

Keywords: cardiovascular system, diseases, electrocardiography, frequency-domain analysis, geriatrics, medical signal processing, patient diagnosis, pneumodynamics, signal classification, Cheyne-Stokes respiration patterns, ECG, autonomic heart rate modulation mechanism, cardiovascular control, cardiovascular signals, chronic heart failure, decompensated CHF patients, dynamic interaction assessment, elderly patients, electrocardiogram, enhanced diagnosis, frequency domain parameters, heart rate variability analysis, patient classification, periodic breathing, respiratory flow signal recording, Electrocardiography, Frequency modulation, Frequency-domain analysis, Heart rate variability, Senior citizens, Standards


van Zanten, T. S., Garcia-Parajo, M. F., (2012). Super-resolution near-field optical microscopy Comprehensive Biophysics (ed. Egelman, E. H.), Elsevier (Desdren, Germany) Volume 2: Biophysical Techniques for Characterization of Cells, 144-164

Near-field optical microscopy is a technique not limited by the laws of diffraction that enables simultaneous high-resolution fluorescence and topographic measurements at the nanometer scale. This chapter highlights the intrinsic advantages of near-field optics in the study of cellular structures. The first part of the chapter lays the foundations of the near-field concept and technical implementation of near-field scanning optical microscopy (NSOM), whereas the second part of the chapter focuses on applications of NSOM to the study of model membranes and cellular structures on the plasma membrane. The last part of the chapter discusses further directions of near-field optics, including optical antennas and fluorescence correlation spectroscopy approaches in the near-field regime.

Keywords: Biological membranes, Cell membrane nanoscale compartmentalization, Cellular nanodomains, Fluorescence correlation spectroscopy in reduced volumes, Immunoreceptor imaging, Lipid rafts, Near-field scanning optical microscopy, Optical nano-antennas, Shear force imaging, Single molecule detection, Super-resolution microscopy


Hofer, M., Adamsmaier, S., van Zanten, T. S., Chtcheglova, L. A., Manzo, C., Duman, M., Mayer, B., Ebner, A., Moertelmaier, M., Kada, G., Garcia-Parajo, M. F., Hinterdorfer, P., Kienberger, F., (2010). Molecular recognition imaging using tuning fork-based transverse dynamic force microscopy Ultramicroscopy , 110, (6), 605-611

We demonstrate simultaneous transverse dynamic force microscopy and molecular recognition imaging using tuning forks as piezoelectric sensors. Tapered aluminum-coated glass fibers were chemically functionalized with biotin and anti-lysozyme molecules and attached to one of the prongs of a 32 kHz tuning fork. The lateral oscillation amplitude of the tuning fork was used as feedback signal for topographical imaging of avidin aggregates and lysozyme molecules on mica substrate. The phase difference between the excitation and detection signals of the tuning fork provided molecular recognition between avidin/biotin or lysozyme/anti-lysozyme. Aggregates of avidin and lysozyme molecules appeared as features with heights of 1-4 nm in the topographic images, consistent with single molecule atomic force microscopy imaging. Recognition events between avidin/biotin or lysozyme/anti-lysozyme were detected in the phase image at high signal-to-noise ratio with phase shifts of 1-2 degrees. Because tapered glass fibers and shear-force microscopy based on tuning forks are commonly used for near-field scanning optical microscopy (NSOM), these results open the door to the exciting possibility of combining optical, topographic and biochemical recognition at the nanometer scale in a single measurement and in liquid conditions.

Keywords: Tuning fork, Atomic force microscopy, Shear-force microscopy, Molecular recognition, Avidin-biotin