Viscoelastic Changes Research Articles

The impact of ice on the tensile strength of unconsolidated sand - A model for gas hydrate-bearing sands?

Tensile strength is an important parameter when it comes to predictions of potential fracturing of sediments by natural processes such as the emplacement of ice or gas hydrate lenses, as well as anthropogenic fracturing or else the stability of engineering constructions such as boreholes. Yet, tensile strength (στ) measurements of unconsolidated ice-bearing or gas hydrate-bearing sands are scarce and affected by a large variability.In the course of the SUGAR project we successfully used ice as a model for pore-filling and “load-bearing” gas hydrate in sand to determine compressional wave velocity. We were thus able to verify comparable formation characteristics and morphologies of ice and gas hydrate within the pore space. As these are important values for the tensile strength of ice/hydrate-bearing sands, ice was also used as a model for hydrate-bearing sands, despite differences in the mechanical behavior and strength of pure ice and gas hydrate. Water-saturated sand cores with ice saturations (Sice) between 0 and 100% were tested at −6.8 °C. The varying Sice were a result of the freezing point depression caused by saline solutions of different concentrations. The στ was directly determined using a sleeve-fracturing test with an internal pressure that was created within the frozen samples. The setup was also adapted to fit a pressure vessel for tests using confining pressure.The correlation of Sice – στ shows an exponential increase of στ with Sice. Whereas at Sice < 60% the increase is small, it is large at Sice > 80%. In conjunction with the change in strength, the viscoelastic behavior changes. A clear peak strength occurs at Sice > 80%. We conclude that given 60% < Sice < 80% the pore-filling morphology of the ice converts into a frame-building habitus and at Sice > 80% the frame gains strength while the amount of residual water decreases. Tensile failure and cracking now exceed grain boundary sliding as the prevailing failure mode. The ice morphology in the sand is non-cementing and comparable to a gas hydrate-sand mixture.

A constitutive framework for finite viscoelasticity and damage based on the Gram–Schmidt decomposition

A novel thermodynamic framework for the continuum mechanical response of nonlinear solids is described. Large deformations, nonlinear hyperelasticity, viscoelasticity, and property changes due to evolution of damage in the material are all encompassed by the general theory. The deformation gradient is decomposed in Gram–Schmidt fashion into the product of an orthogonal matrix and an upper triangular matrix, where the latter can be populated by six independent strain attributes. Strain attributes, in turn, are used as fundamental independent variables in the thermodynamic potentials, rather than the usual scalar invariants of deformation tensors as invoked in more conventional approaches. A complementary set of internal variables also enters the thermodynamic potentials to enable history and rate dependence, i.e., viscoelasticity, and irreversible stiffness degradation, i.e., damage. Governing equations and thermodynamic restrictions imposed by the entropy production inequality are derived. Mechanical, thermodynamic, and kinetic relations are presented for material symmetries that reduce to cubic or isotropic thermoelasticity in the small strain limit, restricted to isotropic damage. Representative models and example problems demonstrate utility and flexibility of this theory for depicting nonlinear hyperelasticity, viscoelasticity, and/or damage from cracks or voids, with physically measurable parameters.

Effect of cell geometry in the evaluation of erythrocyte viscoelastic properties.

The red blood cell membrane-cytoskeleton is a complex structure mainly responsible for giving the cell rigidity and shape. It also provides the erythrocyte with the ability to pass through narrow capillaries of the vertebrate blood circulatory system. Although the red blood cell viscoelastic properties have been extensively studied, reported experimental data differ by up to three orders of magnitude. This could be attributed to the natural cell variability, to the different techniques employed, and also to the models used for the cell response, which are highly dependent on cell geometry. Here, we use two methodologies based on optical tweezers to investigate the viscoelastic behavior of healthy human red blood cells, one applying small cell deformations (microrheology) and another imposing large deformations (tether extraction). We also establish a defocusing microscopy-based method to characterize the cell geometry and thus the erythrocyte form factor, an essential parameter that allows comparisons among the viscoelastic properties at different conditions. Moreover, for small deformations, a soft glassy rheology model is used to discuss the results, while for large deformations two surface shear moduli and one surface viscosity are determined, together with the surface tension and bending modulus of the erythrocyte membrane lipid component. We also show that F-actin is not detected in tethers, although the erythrocyte membrane has physical properties like those of other adherent cells, known to have tethers containing F-actin inside. Altogether, our results show good agreement with the reported literature and we argue that, to properly compare the viscoelastic properties of red blood cells in different situations, the task of cell geometry characterization must be accomplished. This may be especially important when the influence of agents, like the malaria parasite, induces changes in both the geometry and chemical constituents of the erythrocyte membrane. Together, the new methodologies and procedures used in this study would allow the erythrocyte community to better explore the mechanical behavior of red blood cells and may be useful to characterize erythrocyte viscoelasticity changes in several blood diseases.

Cell viscoelasticity is linked to fluctuations in cell biomass distributions

The viscoelastic properties of mammalian cells can vary with biological state, such as during the epithelial-to-mesenchymal (EMT) transition in cancer, and therefore may serve as a useful physical biomarker. To characterize stiffness, conventional techniques use cell contact or invasive probes and as a result are low throughput, labor intensive, and limited by probe placement. Here, we show that measurements of biomass fluctuations in cells using quantitative phase imaging (QPI) provides a probe-free, contact-free method for quantifying changes in cell viscoelasticity. In particular, QPI measurements reveal a characteristic underdamped response of changes in cell biomass distributions versus time. The effective stiffness and viscosity values extracted from these oscillations in cell biomass distributions correlate with effective cell stiffness and viscosity measured by atomic force microscopy (AFM). This result is consistent for multiple cell lines with varying degrees of cytoskeleton disruption and during the EMT. Overall, our study demonstrates that QPI can reproducibly quantify cell viscoelasticity.

Recovery dynamics of acrylic coating surfaces under elevated relative humidity monitored by atomic force microscopy

Surface recovery of acrylic coatings under elevated relative humidity (RH) is observed in real-time using atomic force microscopy. It is found that the extent and rate of recovery are closely related to the glass transition temperature (Tg) of the polymer and RH. The phenomenon is explained by viscoelastic mechanics theory, in which mechanical characteristics such as elastic modulus and viscosity of the polymer have influence over the dynamics as well as the extent of recovery. The experimental data suggests that the polymer undergoes change in viscoelasticity at elevated RH due to water uptake. It is believed that this behavior may provide new insights in research areas such as controlled repair of coatings, and this experimental approach will help us better understand the mechanical performance of coatings under deviated environmental conditions.

Ultrasound response of viscoelastic changes of cellulose hydrogels triggered with Sono-deviced rheometer.

Sono-deviced rheometer,which enabled viscoelastic properties under ultrasound operation, was used to investigate for cellulosic hydrogels. The viscoelastic behavior was compared in cellulosic hydrogels prepared at 0.5, 1 and 2wt% concentration in the DMAc/LiCl solution. The sono-deviced equipment could measure the effect of changes in storage modulus G' and loss modulus G" under 43kHz ultrasound exposure. It was noted that the 43kHz ultrasound significantly changed the values of the G', meaning that the hydrogel was soften under the exposure within few seconds. When the ultrasound exposed 50W of the out-put power at 1% strain, the G' value of 4.2x104 Pa was reduced to 4.0x103 Pa during 5min of the US interval. The declined lowering value of G' then returned to the original moduli value when ultrasound was stopped. The values of both G' and G" values were measured at applied strain % during viscoelastic measurements of the cellulosic hydrogels without and with ultrasound exposure. The comparison indicated that the ultrasoundhas reinforced the effect of the mechanical deformationof the hydrogel structureat the smaller mechanical strain values appliedduring the ultrasound operation. The ultrasound soften effect onthe viscoelastic change efficiently occurred in the 0.5wt% sample and easily induced the structural deformation probably due to the breakage of hydrogen bonds in the cellulose hydrogels.

Nasal Mucociliary Clearance in Smokers: A Systematic Review.

Introduction Smoking is one of the most important causes of mortality and morbidity in the world, as it is related to the risk factor and etiology of respiratory-tract diseases. Long-term smoking causes both structural and functional damage in the respiratory airways, leading to changes in nasal mucociliary clearance (NMC). Objectives The aim of the present study was to look systematically into the current literature and carefully collect and analyze results to explore NMC in smokers. Data Synthesis Two independent reviewers conducted a literature search on some Electronic database: Pubmed, Medline, Ebsco, Springer Link, Science Direct, Scopus, and Proquest searching for articles fulfilling the inclusion and exclusion criteria. The lead author independently assessed the risk of bias of each of the included studies and discussed their assessments with the other two authors to achieve consensus. Of the 1,654 articles identified in the database search, 16 met the criteria for this review. Most of the articles (15 out of 16) showed the impairment of NMC in smokers. Conclusion The present systematic review suggests that there is an impairment of NMC in smokers. The impairment is not only observed in cigarette smoking, but also in passive smoking, bidi smoking, electronic smoking, and hookah smoking. The impairment of NMC in chronic exposure to smoking is caused by the ciliotoxic effect, hypersecretion and viscoelastic change of mucous, airway surface liquid depletion, increased oxidative stress, and deteriorations in the inflammatory and immune systems.

Comparative analysis of the viscoelastic properties of collagen-like proteins by virtual creep test

Viscoelasticity of collagen is essential for the integrity of connective tissue and its aberrancy may result in collagen dysfunction and the emergence of connective tissue diseases. Precise identification of viscoelastic properties of collagens, and affecting factors are necessary to understand collagen behavior in the extracellular matrix as well as the mechanism of collagen-related diseases. The aim of this study is to investigate the mechanical and viscoelastic properties and time-lapse changes of protein-protein and protein-solvent hydrogen bonds of proline-rich and hydroxyproline-rich collagens by molecular dynamics simulation applying a virtual creep test. To this end, ten different collagen-like protein structures including [(Gly-Pro-Ala)7]3, [(Gly-Pro-Arg)7]3, [(Gly-Pro-Asp)7]3, [(Gly-Pro-Lys)7]3, [(Gly-Pro-Ser)7]3, [(Gly-Pro-Hyp)7]3, [(Gly-Ala-Hyp)7]3, [(Gly-Glu-Hyp)7]3, [(Gly-Leu-Hyp)7]3 and [(Gly-Val-Hyp)7]3 were virtually built and the viscoelastic properties of the structures were determined by virtual creep test according to Kelvin–Voigt model with various constant pulling forces. Different pulling forces ranged from 500 piconewton (pN) to 5000 pN were applied. As a result, Young’s modulus of the collagens was found positively correlated with the pulling force. The viscosity values and relaxation times were negatively correlated. Results also revealed a decreased number of intramolecular hydrogen bonds in hydroxyproline-rich collagens (but not in proline-rich collagens) and an increased number of protein-solvent hydrogen bonds in response to the increasing pulling force. Our results also confirmed that proline and hydroxyproline are the most critical amino acids in determining the collagen viscoelasticity. We suggest that collagen length and mechanical force may be additional important factors for biomechanical properties and behavior of collagen in the extracellular matrix. Communicated by Ramaswamy H. Sarma

Estimation of viscoelasticity of radial artery via simultaneous measurement of changes in pressure and diameter using a single ultrasound probe

To establish an evaluation index for vascular endothelial function, we developed an ultrasonic probe that can measure changes in blood pressure and blood vessel diameter at the same position in the radial artery. Based on phantom experiments, the pressure waveforms measured using the piezoelectric effect of the ultrasonic probe element and those using a pressure sensor exhibited a high correlation (correlation coefficient: r = 0.979 – 0.999). We confirmed the continuous measurement of the relationship between changes in blood pressure and the diameter from the in vivo experiments. We could then estimate the changes in viscoelasticity by calibrating the output from the probe element to the absolute blood pressure values in advance. The average coefficients of variations were 0.02 and 0.24 for elasticity and viscosity, respectively. This study demonstrated the possibility of measuring changes in the viscoelastic moduli of the radial arterial wall due to flow-mediated dilation using the developed ultrasonic probe.

Biological and Pharmacological Profiling of Pentosan Polysulfate (PPS) in Comparison to Heparin and its Relative Neutralization by Protamine Sulfate

BackgroundPentosan Polysulfate has traditionally been used to treat patients with Interstitial Cystitis and more recently osteoarthritis, cancer, HIV and prion disease. Such widespread clinical application of PPS and the active search for new effective alternatives to traditional heparin compels a comprehensive investigation of the effect of PPS batches on anticoagulation in comparison to Heparin. The purpose of this study is to create a comprehensive profile and comparison of new PPS batches (L‐15, L‐19, L20 and Ba), old PPS batch (PPS Ba), and Heparin. Furthermore, the feasibility of protamine sulfate as a neutralizing agent to reverse the anticoagulant effects of PPS is investigated.Materials and MethodsVarious batches of PPS at 1 mg/ml were prepared in saline. For whole blood clotting profile, thromboelastography (TEG) was carried from 2.5 – 5.0 ug/ml and activated clotting time (ACT) at 25ug/mL. Clotting profile in whole blood, retrieved plasma and supplementation in normal human pooled plasma (NHP) were carried out at 100 – 0.0 ug/ml by using anticoagulant assays. Amydolytic methods were used to measure anti‐Xa/ IIa effects. Thrombin generation inhibition studies (TGA) were carried out in NHP from 100 ‐ 0.0 ug/ml. Heparin supplementation and protamine sulfate neutralization in NHP from 10 ‐0 ug/mL were compared to PPS batches in a logarithmic scale.ResultsAll drugs produced a concentration dependent effect. Similar effects in anticoagulation assays were noted except anti‐Xa assay. In TEG, significant viscoelastic changes were observed at 5ug/mL. Prolongation of ACT was observed at 25ug/mL. No significant differences were noted in between batches of PPS in TEG and ACT studies. In TGA, concentration dependent but no significant difference in between the batches were noted. Neutralization of protamine sulfate was observed up to 12.5 ug/mL in anticoagulant assays and marginal effect on anti‐protease assays. Lastly, logarithmic comparison of the protamine sulfate neutralization indicated that protamine sulfate is a weaker neutralizing agent of PPS compared to heparin.ConclusionThese studies suggest that multiple batches of PPS have a similar anticoagulant profile. In comparison to heparin, PPS presents itself as a 10‐fold weaker anticoagulant alternative for use in a variety of clinical applications. Neutralization of PPS at low concentrations by protamine sulfate in anticoagulant assays warrants further investigation on an effective neutralizing concentration for clinical use.

Storability of porcine blood in forensics: How far should we go?

Previous studies on the storability of porcine blood for bloodstain pattern analysis (BPA) focused on abattoir blood only and did not include measurements of viscoelasticity. Although known to provoke echinocyte formation, EDTA is widely used for BPA issues. We compared ageing samples taken from live pigs with abattoir blood and detected considerable differences in hematocrit (HCT), total protein and shear viscosity that even worsened with time. Upon storage, high shear viscosity continuously increased, resulting in a partial loss of the typical shear thinning property of blood. Furthermore, we explored CPDA-1, the gold standard in preserving red blood cells (RBCs), for storage of forensic samples. We found it to be a superior choice for anticoagulation, as the rise of high shear viscosity was attenuated compared to EDTA. When performing oscillation measurements, we found a sudden change of viscoelasticity of blood after 22 days, providing a cut-off for storage time. To highlight the importance of hematological and hemorheological changes upon cold storage, we performed simple drip pattern experiments. These tests revealed a tendency to smaller stain diameters and higher numbers of satellite spatter. While this contradicts expectations from elevated viscosity values, we associate this trend to microscopic inhomogeneities due to storage. We recommend CPDA-1 for prolonged storage of BPA samples and suggest the use of comprehensive test protocols including viscoelasticity for determination of the maximum shelf life of pig blood.

Mechanism of affinity-enhanced protein adsorption on bio-nanocapsules studied by viscoelasticity measurement with wireless QCM biosensor

Recent advances in functionalized bio-nanocapsules (BNCs) have allowed a significant sensitivity enhancement in label-free biosensors. It is suggested that sensitivity amplification is caused by the higher binding affinity of BNCs to target antibodies. We here study the high-affinity interaction mechanism between BNCs and antibodies with wireless high-frequency QCM biosensors. We first confirmed the higher affinity between BNCs and human immunoglobulin G. We then found that the number of binding sites for the target antibody significantly increases by immobilizing BNC molecules on the sensor surface. We finally studied changes in viscoelasticity near the sensor surface using a MEMS wireless QCM biosensor using up to the ninth overtone (522 MHz). The inversely determined effective shear modulus on BNCs was found to be significantly lower than that on a standard surface on which the receptor molecules were immobilized. We have thus clarified that this surface flexibility achieves high affinity with target antibodies.

Tensiometrical and Rheological Parameters of The Blood Serum of Patients Operated on The Heart

The aim of this study was to establish patterns of changes in surface tension and dilatational viscoelasticity of serum of patients operated on for the heart under cardiopulmonary bypass during intra- and intraoperative periods.

In vitro effects of lactated Ringer's solution, hypertonic saline, hydroxyethyl starch, hypertonic saline/hydroxyethyl starch, and mannitol on thromboelastographic variables of canine whole blood.

To assess the in vitro effects of crystalloid and colloid IV fluids on the thromboelastographic (TEG) variables of canine whole blood. In vitro experimental study. Veterinary teaching hospital. Twenty-two healthy dogs. Citrated whole blood samples collected from healthy dogs were diluted with 3.4% hypertonic saline (HTS 3.4), 7% hypertonic saline (HTS 7), and 20% mannitol at 8% and 16% dilutions; hydroxyethyl starch 130/0.4 (HES 130/0.4) at 16% dilution; lactated Ringer's solution (LRS) at 16%, 33%, and 66% dilutions; and HTS 7-HES 130/0.4 at 25% and 50% dilutions. Kaolin-activated TEG analysis was concurrently performed on diluted and control (undiluted) samples. Dilution of canine whole blood with LRS compared to control reduced α angle and MA at both 33% (P = 0.009 and P = 0.011, respectively) and 66% dilution (P<0.001 and P<0.001, respectively), and prolonged K time at 66% dilution (P = 0.003). At 16% dilution, HTS 3.4, prolonged R time (P = 0.007), while mannitol, a fluid iso osmolar to HTS 3.4, prolonged K time (P = 0.006), reduced α angle (P<0.001), MA (P = 0.046), and LY60 (P = 0.015). At 8% dilution, HTS 7, a fluid of high osmolarity and tonicity, prolonged R time (P = 0.009) and reduced MA (P = 0.015), while all measured TEG variables were altered at the 16% dilution (P<0.01 for all variables). HES 130/0.4 reduced α angle (P = 0.031) and MA (P = 0.001) and increased LY60 (P<0.001) at 16% dilution. Comparing different fluid types, HES 130/0.4 and HTS 3.4 had no to minor, mannitol intermediate, and HTS 7 profound effects on TEG variables (P<0.05) when compared to LRS at the same dilution. In vitro dilution of canine whole blood with commonly used IV fluids leads to thromboelastographic changes consistent with hypocoagulability in a dose dependent manner for all fluid types tested. Viscoelastic changes are also influenced by fluid characteristics, specifically tonicity and osmolarity.

Ultrasound Shear Wave Elastography and Doppler Sonography to Assess the Effect of Hydration on Human Kidneys: A Preliminary Observation

To assess the feasibility of ultrasound imaging in depicting the changes in kidney size, hemodynamics and cortex viscoelasticity after hydration, we prospectively performed 2-D ultrasound shear wave elastography (SWE) and Doppler sonography of bilateral kidneys in 30 volunteers. Kidney length, cortex shear wave velocity (SWV), shear wave dispersion (SWD), interlobar artery peak systolic velocity (PSV), end-diastolic velocity (EDV) and resistive index (RI) were measured before and 60 min after with and without drinking water (1 L). The differences in kidney length, SWV, PSV, EDV and color pixel intensity before and after hydration were significant (p < 0.001), whereas these differences were not significant without hydration (p > 0.05). SWD and RI did not significantly differ with or without hydration. Inter- and intra-observer reliability in performing SWE and Doppler sonography was good. The use of Doppler sonography and ultrasound SWE to evaluate the effect of hydration on kidney size, hemodynamics and viscoelasticity seem to be feasible.

Identification of Normal Pressure Hydrocephalus by Disease-Specific Patterns of Brain Stiffness and Damping Ratio.

The aim of this study was to perform a whole-brain analysis of alterations in brain mechanical properties due to normal pressure hydrocephalus (NPH). Magnetic resonance elastography (MRE) examinations were performed on 85 participants, including 44 cognitively unimpaired controls, 33 with NPH, and 8 who were amyloid-positive with Alzheimer clinical syndrome. A custom neural network inversion was used to estimate stiffness and damping ratio from patches of displacement data, accounting for edges by training the network to estimate the mechanical properties in the presence of missing data. This learned inversion was first compared with a standard analytical approach in simulation experiments and then applied to the in vivo MRE measurements. The effect of NPH on the mechanical properties was then assessed by voxel-wise modeling of the stiffness and damping ratio maps. Finally, a pattern analysis was performed on each individual's mechanical property maps by computing the correlation between each person's maps with the expected NPH effect. These features were used to fit a classifier and assess diagnostic accuracy. The voxel-wise analysis of the in vivo mechanical property maps revealed a unique pattern in participants with NPH, including a concentric pattern of stiffening near the dural surface and softening near the ventricles, as well as decreased damping ratio predominantly in superior regions of the white matter (family-wise error corrected P < 0.05 at cluster level). The pattern of viscoelastic changes in each participant predicted NPH status in this cohort, separating participants with NPH from the control and the amyloid-positive with Alzheimer clinical syndrome groups, with areas under the receiver operating characteristic curve of 0.999 and 1, respectively. This study provides motivation for further development of the neural network inversion framework and demonstrates the potential of MRE as a novel tool to diagnose NPH and provide a window into its pathogenesis.

Sulfone derivatives enter the cytoplasm of Candida albicans sessile cells

Since our study showed that sulfone derivatives’ action mode creates a lesser risk of inducing widespread resistance among Candida spp., we continued verifying sulfones’ antifungal activity using the following newly synthesized derivatives: bromodichloromethy-4-hydrazinyl-3-nitrophenyl sulfone (S1), difluoroiodomethyl-4-hydrazinyl-3-nitrophenyl sulfone (S2), and chlorodifluoromethyl-4-hydrazinyl-3-nitrophenyl sulfone (S3). As the mechanism by which sulfones gain access to the cytoplasm has not been elucidated yet, in order to track S1-3, we coupled their hydrazine group with BODIPY (final S1-3 BODIPY-labelled were named SB1-3). This approach allowed us to follow the vital internalization and endocytic routing of SB1-3, while BODIPY interacts primarily with fungal surfaces, thus confirming that S1-3 and their counterparts SB1-2 behaved as non-typical agents by damaging the cell membrane and wall after being endocytosed (SB1-3 fluorescence visible inside the unlysed sessile cells). Thus greatly decreasing the likelihood of the appearance of strains resistance. Core sulfones S1-3 are a promising alternative not only to treat planktonic C. albicans but also biofilm-embedded cells. In the flow cytometric analysis, the planktonic cell surface was digested by S1-3, which made the externalized PS accessible to AnnexinV binding and PI input (accidental cell death ACD). The occurrence of ACD as well as apoptosis (crescent-shaped nuclei) and anoikis of sessile cells (regulated cell death by 100%-reduction in attachment to epithelium) was assessed through monitoring the AO/PI/HO342 markers. CLSM revealed the invasion of S1-3 and SB1-3 in C. albicans without inducing cell lysis. This was a novel approach in which QCM-D was used for real-time in situ detection of viscoelastic changes in the C. albicans biofilm, and its interaction with S1 as a representative of the sulfones tested. S1 (not toxic in vivo) is a potent fungicidal agent against C. albicans and could be administered to treat invasive candidiasis as a monotherapy or in combination with antifungal agents of reference to treat C. albicans infections.

Imaging brain function with simultaneous BOLD and viscoelasticity contrast: fMRI/fMRE

Magnetic resonance elastography (MRE) is emerging as a new tool for studying viscoelastic changes in the brain resulting from functional processes. Here, we demonstrate a novel time series method to generate robust functional magnetic resonance elastography (fMRE) activation maps in response to a visual task with a flashing checkerboard stimulus. Using a single-shot spin-echo (SS-SE) pulse sequence, the underlying raw images inherently contain blood-oxygen-level dependent (BOLD) contrast, allowing simultaneous generation of functional magnetic resonance imaging (fMRI) activation maps from the magnitude and functional magnetic resonance elastography (fMRE) maps from the phase. This allows an accurate comparison of the spatially localized stiffness (fMRE) and BOLD (fMRI) changes within a single scan, eliminating confounds inherent in separately acquired scans. Results indicate that tissue stiffness within the visual cortex increases 6–11% with visual stimuli, whereas the BOLD signal change was 1–2%. Furthermore, the fMRE and fMRI activation maps have strong spatial overlap within the visual cortex, providing convincing evidence that fMRE is possible in the brain. However, the fMRE temporal SNR (tSNRfMRE) maps are heterogeneous across the brain. Using a dictionary matching approach to characterize the time series, the viscoelastic changes are consistent with a viscoelastic response function (VRF) time constant of 12.1 ​s ± 3.0 ​s for a first-order exponential decay, or a shape parameter of 8.1 ​s ± 1.4 ​s for a gamma-variate.

Magnetic resonance elastography quantification of the solid-to-fluid transition of liver tissue due to decellularization

Maintenance of tissue extracellular matrix (ECM) and its biomechanical properties for tissue engineering is one of the substantial challenges in the field of decellularization and recellularization. Preservation of the organ-specific biomatrix is crucial for successful recellularization to support cell survival, proliferation, and functionality. However, understanding ECM properties with and without its inhabiting cells as well as the transition between the two states lacks appropriate test methods capable of quantifying bulk viscoelastic parameters in soft tissues.We used compact magnetic resonance elastography (MRE) with 400, 500, and 600 Hz driving frequency to investigate rat liver specimens for quantification of viscoelastic property changes resulting from decellularization. Tissue structures in native and decellularized livers were characterized by collagen and elastin quantification, histological analysis, and scanning electron microscopy.Decellularization did not affect the integrity of microanatomy and structural composition of liver ECM but was found to be associated with increases in the relative amounts of collagen by 83-fold (37.4 ± 17.5 vs. 0.5 ± 0.01 μg/mg, p = 0.0002) and elastin by approx. 3-fold (404.1 ± 139.6 vs. 151.0 ± 132.3 μg/mg, p = 0.0046). Decellularization reduced storage modulus by approx. 9-fold (from 4.9 ± 0.8 kPa to 0.5 ± 0.5 kPa, p < 0.0001) and loss modulus by approx. 7-fold (3.6 kPa to 0.5 kPa, p < 0.0001), indicating a marked loss of global tissue rigidity as well as a property shift from solid towards more fluid tissue behavior (p = 0.0097).Our results suggest that the rigidity of liver tissue is largely determined by cellular components, which are replaced by fluid-filled spaces when cells are removed. This leads to an overall increase in tissue fluidity and a viscous drag within the relatively sparse remaining ECM. Compact MRE is an excellent tool for quantifying the mechanical properties of decellularized biological tissue and a promising candidate for useful applications in tissue engineering.

Evidence of Fault Immaturity from Shallow Slip Deficit and Lack of Postseismic Deformation of the 2017 Mw 6.5 Jiuzhaigou Earthquake

ABSTRACTThe Mw 6.5 Jiuzhaigou earthquake occurred on 8 August 2017 36 km west-southwest of Yongle, Sichuan, China. We use both ascending and descending Interferometric Synthetic Aperture Radar (InSAR) data from Sentinel-1 and coseismic offsets of four Global Positioning System sites to obtain the coseismic surface deformation field and invert for the fault geometry and slip distribution. Most slip of the left-lateral strike-slip earthquake occurred in the 3–10 km depth interval with a maximum slip of about 1 m and a large shallow slip deficit (SSD). An eight-month InSAR time-series analysis documents a lack of resolvable postseismic deformation, and inversions for the distribution of postseismic slip demonstrate the lack of shallow afterslip. We argue that the observations of a pronounced SSD and no early afterslip of the Jiuzhaigou earthquake are indicative of an immature fault and that all incipient young strike-slip faults likely feature a SSD. We would expect a complex rupture geometry with distributed coseismic failure in the uppermost part of the brittle crust during the fault-zone development. As faults mature, they straighten out, develop a localized fault-zone core, and the SSD diminishes. By calculating the static Coulomb stress change and nine-year viscoelastic stress change caused by the Wenchuan earthquake, we also show that the 2008 Wenchuan earthquake did not significantly affect the time of occurrence of the 2017 Jiuzhaigou earthquake.