Viscoelastic Changes Research Articles

Assessment of Physicochemical and Rheological Properties of Xylo-Oligosaccharides and Glucose-Enriched Doughs Fermented with BB-12.

Simple SummaryXylo-oligosaccharides (XOS) are considered indigestible fibers that could support the growth of potentially beneficial gut microbes, thus classified as “prebiotics”. Prebiotics are “a substrate that is selectively utilized by host microorganisms conferring a health benefit” as defined by the International Scientific Association for Probiotics and Prebiotics. The current work aimed to study the effect of XOS and glucose addition on wheat flour sourdough fermented with Bifidobacterium animalis subsp. lactis (BB-12) strain in terms of organic acid production and on the rheological properties of the doughs. The effect of XOS addition increased the production of organic acids, and positively influenced the rheological properties of the dough. Additionally, after frozen storage, there were no significant viscoelastic changes in the dough structure, which indicates that xylo-oligosaccharides improved the water retention capability of the dough. Through fermentation carbohydrates like, glucose, xylose, maltose, and XOS were consumed, and a high quantity of lactic and acetic acid were produced, organic acids with roles in the flavor generation and sensorial properties of the final product. This study showed the potential use of XOS as food ingredient in sourdoughs for bakery products manufacturing with improved quality and rheological properties.Xylo-oligosaccharides (XOS) are considered non-digestible fibers produced mainly from agricultural biomass and are classified as “emerging prebiotic” compounds. Since XOS were shown to promote the growth of bifidobacteria in the gut with potential effects on one’s health, scientists used them as food ingredients. For example, the addition of XOS in bakery products could improve their physicochemical characteristics. The current work aimed to investigate the effect of XOS and glucose addition on wheat flour sourdough fermented with Bifidobacterium animalis subsp. lactis (BB-12) strain in terms of organic acid production. The effect on viscoelastic changes during frozen storage and after the thawing process was also studied. The results showed that the viability of BB-12 increased slightly with the increase in XOS and glucose concentrations, which determined dough acidification due to accumulation of organic acids, that positively influenced the dough’s rheological properties such as a higher elasticity before and after frozen storage. With 10% XOS-addition, the acetic acid quantity reached 0.87 ± 0.03 mg/L, and the highest lactic acid concentration was found in the 10% XOS-enriched doughs, the glucose-enriched doughs and in the control sample (100% wheat dough). The quantity of glucose, maltose, XOS, and xylose decreased until the end of fermentation.

Characterizing the Mechanical and Viscoelastic Response of the Porcine Facet Joint Capsule Ligament in Response to a Simulated Impact.

The facet capsule ligament (FCL) is a structure in the lumbar spine that constrains motions of the vertebrae. Subfailure loads can produce microdamage resulting in increased laxity, decreased stiffness, and altered viscoelastic responses. Therefore, the purpose of this investigation was to determine the mechanical and viscoelastic properties of the FCL under various magnitudes of strain from control samples and samples that had been through an impact protocol. Two hundred FCL tissue samples were tested (20 control and 180 impacted). Impacted FCL tissue samples were obtained from functional spinal units that had been exposed to one of nine subfailure impact conditions. All specimens underwent the following loading protocol: preconditioning with five cycles of 5% strain, followed by a 30 s rest period, five cycles of 10% strain, and 1 cycle of 10% strain with a hold duration at 10% strain for 240 s (4 min). The same protocol was followed for 30% and 50% strain. Measures of stiffness, hysteresis, and force-relaxation were computed. No significant differences in stiffness were observed for impacted specimens in comparison to control. Impacted specimens from the 8 g flexed and 11 g flexed and neutral conditions exhibited greater hysteresis during the cyclic-30% and cyclic-50% portion of the protocol in comparison to controls. In addition, specimens from the 8 g and 11 g flexed conditions resulted in greater stress decay for the 50%-hold conditions. Results from this study demonstrate viscoelastic changes in FCL samples exposed to moderate and highspeed single impacts in a flexed posture.

Changes of network structure and water distribution in sludge with the stratified extraction of extracellular polymeric substances.

The water in sludge is trapped within the extracellular polymeric substance (EPS) with gelatinous structure, greatly challenging the sludge deep dewatering. In this paper, the effect of the EPS viscoelasticity and the structural characteristics of sludge flocs on water distribution was revealed to provide a highly efficient approach in research on sludge dewatering. After biological, and physical method conditioning, the change of viscoelasticity and sludge network structure before/after EPS extraction was comprehensively explored, together with the sludge dewaterability and water distribution. The results suggested the proportion of capillary water and adsorption water carried in soluble EPS (S-EPS) was 59.17% and 40.83%, and that in tightly bound EPS (TB-EPS) was 54.77% and 45.23%, respectively. By contrast, the capillary water in loosely bound EPS (LB-EPS) accounted for as high as 99.99%. In comparison with raw sludge, adsorption water proportion in TB-EPS and S-EPS was reduced after lysozyme (LZM) or freezing-thaw conditioning, which was ascribed to reduction of EPS viscosity and the weakness of water adsorption capacity. Additionally, the sludge yield stress (τy) value first reduced and then increased with the extraction of EPS. Meanwhile, the consistency coefficient (k) also decreased from 4.23Pa·sn to 0.006Pa·sn and then slightly increased after LZM conditioning. This observation indicated the sludge system became sensitive to shearing, and its network structural strength as well as colloid elasticity first weakened and then slightly strengthened. In addition, after LZM or freezing-thaw conditioning, the sludge particle size significantly increased after TB-EPS extraction, while the sludge particle more easily absorbed water molecules, thereby increasing adsorption water and capillary water within the sludge flocs. This phenomenon also resulted in an increasing trend of capillary suction time (CST) after TB-EPS extraction, indicating the deterioration of sludge filtration performance.

Preparation of poly(acrylamide‐co‐acrylonitrile) grafted glass and thermal stimulated detachment of surface‐attached human immortalized mesenchymal stem cells

AbstractNovel cell culture substrates for non‐invasive‐targeted cell recovery were developed by grafting an upper‐critical‐solution‐temperature (UCST)‐type poly(acrylamide‐co‐acrylonitrile) (PAA) onto a glass substrate as a cell attachment scaffold by surface‐initiated reversible addition‐fragmentation chain‐transfer (Si‐RAFT) polymerization. To optimize the UCST of PAA, the cloud point of the free polymer was first determined. Varying the chain lengths of PAA with an optimized AN‐compositions of 31 mol% followed by Si‐RAFT produced immobilized glass substrate (PAA‐g). The PAA‐g surface became hydrophilic, and the polymer brushes swelled as the temperature increased from 30 to 38°C. In addition, the viscoelasticity of PAA‐g was increased by the polymer brushes swelled. Thermal detachment of PAA‐g attached human immortalized mesenchymal stem cells (hiMSC) was observed by raising the temperature from 30 to 38°C. The polymer brushes length of PAA‐g affects the degree of hiMSC detachment, likely due to the change in viscoelasticity with the polymer brushes length.

Effect and Mechanism of Acid-Induced Soy Protein Isolate Gels as Influenced by Cellulose Nanocrystals and Microcrystalline Cellulose.

The effects of cellulose nanocrystals (CNC) and microcrystalline cellulose (MCC) on the gel properties and microstructure of glucono-δ-lactone-induced soy protein isolate (SPI) gels were investigated. The water-holding capacity, gel strength, and viscoelastic modulus of CNC–SPI gels were positively associated with CNC concentration from 0 to 0.75% (w/v). In contrast, MCC–SPI gels exhibited decreased water-holding capacity, gel strength, and viscoelastic modulus. All composite gels displayed high frequency dependence and the typical type I (strain thinning) network behavior. Changes in viscoelasticity under large strain were correlated with differences in the microstructure of SPI composite gels. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) showed that CNC were more evenly and steadily distributed in the protein matrix and formed a compact network structure. In contrast, MCC–SPI gels exhibited a discontinued and rough gel network with some large aggregates and pores, in which MCC was randomly entrapped. Fourier transform infrared spectroscopy (FTIR) and molecular forces results revealed that no new chemical bonds were formed in the gelation process and that the disulfide bond was of crucial importance in the gel system. With the addition of CNC, electrostatic interactions, hydrophobic interactions, and hydrogen bonds in the SPI gel network were significantly strengthened. However, the incorporation of MCC might obstruct the connection of the protein network. It is concluded that both cellulose type and concentration affect gelling properties.

Microcellular PETs with High Expansion Ratio Produced by Supercritical CO2 Molding Compression Foaming Process and Their Mechanical Properties

Supercritical CO2 molding compression foaming is an emerging technology for preparing thick microcellular polymer sheets. In a temperature range of 245–255 °C and CO2 foaming pressure range of 5–20 MPa, the molding compression foaming behavior of polyethylene terephthalate (PET) is systematically studied. The maximum expansion ratio of the prepared PET foams is above 30, while the bubble size is only ≈20 μm. It is observed that during the foaming process, the temperature drop caused by rapid depressurization reaches up to 57 °C, which greatly changes the viscoelasticity of PET and limits its foaming behavior. The nucleation and bubble growth behavior of PET is simulated and analyzed based on this change in viscoelasticity. Microcellular PET foams have excellent compression performance due to their smaller cell size and thinner cell wall, and the compression elastic modulus of the prepared microcellular PET sample is twice that of the extrusion foaming PET sample with a similar expansion ratio.

Fertile window and biophysical biomarkers of cervical secretion in subfertile cycles: a look at biotechnology applied to NaProTechnology

Background: The principal objective of this study was to correlate biophysical properties of vaginal discharge present in the cervical mucus with the timing of the fertile window. In particular, we produce measures of the viscoelasticity of the cervical secretion using two methods. The first uses only the elasticity extracted from the Creighton Model Fertility Care System (CrMs) scale, calculated P-6 ovulation estimated day (OED) with respect to the peak day of the CrMs. The second uses a numerical method that takes into account the changes in viscoelasticity, but without reference to the peak day calculated using the CrMs model. Using both methods, twelve records were obtained from a single female subject. Methods: The methodology used to evaluate the viscoelasticity factor was by measuring the approximate length in centimeters (cm) of the vaginal discharge of cervical discharge. For this, the scale of the stretching graph established by observing the stretching of CrMS was used, taking into account the previous 6 days at peak day P-6. The first method, which we termed CFW (Clinical Fertile Window), uses a measure based on the approximate length (cm) of the maximal stretchiness of the vaginal discharge. The second method we termed SFW (Software-CrMS/strectching) (Software-based Fertile Window). Results: The fertile window was detected correctly in 100% of the cases using either method, and a correlation value of 0.71 was observed between the two methods. Conclusions: We conclude that the assessment of viscoelasticity using SFW algorithm allowed in this pilot study to detect the fertile window and to describe the evolution pattern of cervical discharge throughout the fertile window. Our study provides support for the use of computational methods in detecting the fertile window, taking only into account the time evolution of the cervical discharge throughout the menstrual cycle.

Intratree Variation in Viscoelastic Properties of Cell Walls of Masson Pine (Pinus Massoniana Lamb)

In this study, Pinus massoniana Lamb at different heights, across the annual rings, and between earlywood and latewood was measured by X-ray diffraction and the chemical composition was analyzed by chemical treatment. Results indicated that the microfibril angle (MFA) decreased and the chemical composition changed little with the increase in height from 1 m to 9 m. In the radial direction, the MFA decreased and the chemical composition changed little with an increase in annual rings. The cellulose content of latewood was higher than that of earlywood. The viscoelastic changes of wood cell walls at different heights, across the annual rings by the method of quasi-static nanoindentation and dynamic modulus mapping techniques. Results indicated that the wood cell walls’ elastic modulus increased, and the creep rate and creep compliance decreased with the increase in height; The elastic modulus and hardness increased with the annual rings. The cell walls’ storage modulus increased and the loss modulus gradually decreased with an increase in height; the storage modulus gradually increased and the loss modulus decreased with the annual rings.

Electromagnetism, Blood Flow and Coagulation

There is a lot of uncertainty in the theory of hemodynamics. The amount of work need to displace the blood in the systemic circulation, exceeds the work done by the left ventricle. With this, blood recovers increased flow resistance between the heartbeats with the Womersley number alterations in the rhythm of the accompanying electrocardiogram (ECG). Viscoelastic transformation is heavily expressed in coagulation. There must be a relationship between the ECG and blood transient flow resistance. The influence of the electromagnetic field on blood coagulation was studied. Venous blood was affected by the oscillated electromagnetic field (500 - 5000 Hz), with the square wave input signal in 25 healthy individuals (15 males, 10 females in the age 18 - 57 years). Electromagnetic irradiation (EMI) time of the sample 3 - 10 min. Hypocoagulation in normal blood samples was revealed (decreased quantity of Platelets up to 10 - 23 × 109/L, Prothrombin index up to 9% - 10%, Fibrinogen concentration up to 0.20 - 0.21 g/L) and thrombolysis after the blood stasis. Ac electric field from the myocardial depolarization initiates electroacoustic phenomena. An emerging repulsing electromagnetic force acts on the red blood cells (RBC) and in addition to the pulse pressure from the heart, promotes blood motion and viscoelastic changes. The alterations of the blood inertial and elasticity, in addition to hemodynamics, are facilitated by the magnetic features of the hemoglobin. The external electromagnetic signal can manage the blood coagulation process, including thrombolysis.

3Pa5-10 Examination of change in arterial wall viscoelasticity by internal pressure in ultrasonic measurement

3Pa5-10 Examination of change in arterial wall viscoelasticity by internal pressure in ultrasonic measurement

Intranuclear mesoscale viscoelastic changes during osteoblastic differentiation of human mesenchymal stem cells

Cell nuclei behave as viscoelastic materials. Dynamic regulation of the viscoelastic properties of nuclei in living cells is crucial for diverse biological and biophysical processes, specifically for intranuclear mesoscale viscoelasticity, through modulation of the efficiency of force propagation to the nucleoplasm and gene expression patterns. However, how the intranuclear mesoscale viscoelasticity of stem cells changes with differentiation is unclear and so is its biological significance. Here, we quantified the changes in intranuclear mesoscale viscoelasticity during osteoblastic differentiation of human mesenchymal stem cells. This analysis revealed that the intranuclear region is a viscoelastic solid, probably with a higher efficiency of force transmission that results in high sensitivity to mechanical signals in the early stages of osteoblastic differentiation. The intranuclear region was noted to alter to a viscoelastic liquid with a lower efficiency, which is responsible for the robustness of gene expression toward terminal differentiation. Additionally, evaluation of changes in the mesoscale viscoelasticity due to chromatin decondensation and correlation between the mesoscale viscoelasticity and local DNA density suggested that size of gap and flexibility of chromatin meshwork structures, which are modulated depending on chromatin condensation state, determine mesoscale viscoelasticity, with various rates of contribution in different differentiation stages. Given that chromatin within the nucleus condenses into heterochromatin as stem cells adopt a specific lineage by restricting transcription, viscoelasticity is perhaps a key factor in cooperative regulation of the nuclear mechanosensitivity and gene expression pattern for stem cell differentiation.

Possible influence of static and viscoelastic stress perturbations in Musgrave block (Central Australia) earthquake sequence

The spatial and temporal distribution of earthquakes inside continental interiors, where tectonic loading rate is negligible, is much more complicated than plate boundary regions. On 30 March 1986, the moment magnitude (Mw) 5.7 Marryat Creek earthquake occurred in the Musgrave Block of central Australia. Subsequent earthquakes include the1989 Ml 5.6 Uluru, 2012 Mw 5.2 Pukatja, 2013 Mw 5.6 Mulga Park, and 2016 Mw 6.0 Petermann earthquakes. In this study, I explore whether coseismic and viscoelastic Coulomb stress changes following the 1986 Marryat Creek earthquake could have played a role in influencing the basic spatiotemporal characteristics of this earthquake sequence. I find that coseismic stress change does not successfully explain earthquake triggering in the area. I then explore this issue using a viscoelastic stress change model with a range of rheology parameters. In some models, the magnitude of viscoelastic stress change is higher than coseismic stress changes and may be of sufficient magnitude to be considered within an earthquake triggering context. Moreover, I also hypothesize that these earthquakes may have occurred due to dynamic stress triggering or other processes such as fluid migration, nonlinear friction, and/or aseismic deformation, which due to the small distribution of seismic networks across the area I have not been able to investigate in detail. However, I cannot dismiss the possibility that these earthquakes occurred randomly, with no identifiable stress triggering relationships among them.

Myotonometric comparison of sternocleidomastoideus and masseter muscles in multiple sclerosis patients with swallowing problem and healthy individuals

BackgroundDysphagia occurring in the oral and pharyngeal phases of swallowing in MS patients may be caused by changes in muscles' viscoelasticity. The aim of this study was to compare the muscles' (sternocloideomastoideus and masseter) viscoelasticity properties by myotonometer between MS patients and healthy individuals. MethodsThis study design was a cross-sectional, non-interventional study. Ten healthy individuals were allocated to the control group, eleven MS patients without swallowing problems were allocated to the without swallowing group, ten MS patients with swallowing problems were allocated to the swallowing group. Disability was evaluated using the Expanded Disability Status Scale (EDSS), swallowing problem was assessed with Dysphagia in Multiple Sclerosis (DYMUS) scale, and to measure the viscoelastic parameters (tone, stiffness, elasticity) of sternocloideomastoideus (SCM) and masseter muscles bilaterally, MyotonPro® was used. The comparison between the groups was performed using the Kruskal-Wallis H test. ResultsIt was observed that there was no difference in terms of viscoelastic properties of the masseter muscle in groups (p > 0.05). There was no difference between the groups in terms of the elasticity of the SCM muscle (p > 0.05). However, the tonus and stiffness of the SCM on the left side of the MS patients were higher than in other groups (p = 0.050, p = 0.005). ConclusionThe increment level of tone and stiffness of SCM muscle is related to swallowing problems in patients with MS. Due to swallowing problems in MS, the orofacial and neck region's muscles' viscoelastic properties may change in time and may be affected by phases of swallowing problems.

Fuzzy analysis of a viscoelastic damper in seismic retrofit of structures

Due to the dependency of viscoelastic materials on the input frequency, amplitude, and temperature, the effectiveness of a viscoelastic damper changes depending on loading and environmental conditions. Generally, this is neglected in the seismic design of structures with viscoelastic dampers due to the complexity in mathematical modeling and nonlinear analysis. This study developed a kriging model for predicting mechanical properties of a viscoelastic damper based on experimental data, and applies it to fragility analysis of a case study structure retrofitted with viscoelastic dampers. Fuzzy analysis was carried out to investigate the effectiveness of the damper in uncertain conditions, including both stochastic and informal uncertainties. The results showed that the proposed analytical scheme can adequately simulate the seismic performance of the viscoelastic damper with uncertain parameters, and that even under the worst combination of the VED mechanical properties, the probability of reaching all limit states was greatly reduced after installation of the VEDs.

Real-Time Monitoring of HL-1 Cell Viscoelasticity for Drug Cardiotoxicity Assessment using a Love Wave Biosensor

Recently, there is increasing interest in measuring the mechanical properties of cardiomyocytes for drug screening and drug evaluation, such as their contraction force and viscoelasticity. Conventional cardiac physiology experiments usually investigate cardiac function based on imaging and electrophysiology techniques. But it is difficult to quantitatively detect viscoelasticity of cell population. Therefore, an in vitro method for viscoelasticity detection of cardiomyocyte population is urgently needed. In this study, we used Love Wave biosensors to study the viscoelasticity of HL-1 cardiomyocyte population treated with doxorubicin hydrochloride (ADM). First, we optimized the cell density to maximize the cell viscoelastic changes and signal differences between different ADM doses. Then we monitored the viscoelasticity change of cardiomyocytes after ADM treatment. For the ADM dose of 0.1 μM, 1 μM, and 10 μM, we observed that the viscoelasticity of cells decreased with increasing ADM dose. Although HL-1 cardiomyocytes do not have the beating function, our results showed that they can still react to drug such as abnormal reproduction, shape adjustment, membrane properties change, and even detaching from the sensor surface. In addition, we demonstrated that the Love Wave biosensor is a potentially useful tool for early assessment of drug cardiotoxicity.

Dynamical and noninvasive monitoring of curcumin effect on the changes in the viscoelasticity of human breast cancer cells: A novel model to assess cell apoptosis

A real-time quartz crystal microbalance (QCM) cytosensor was first developed for dynamical and noninvasive monitoring of cell viscoelasticity for evaluation of apoptosis degree. In this work, human breast cancer cells MCF-7 and MDA-MB-231 were employed as cell model and respectively captured on the surface of QCM electrode modified with mercaptosuccinic acid and poly-l-lysine. Cell viscoelasticity was measured dynamically by real-time monitoring energy dissipation with QCM, and the dynamic diagram of the energy dissipation of MDA-MB-231 cells treated with curcumin was first obtained. The results displayed that the changes of energy dissipation in MDA-MB-231 cells and MCF-7 cells were 8.81 × 10−6 and 5.29 × 10−6, particularly due to the difference in cell viscoelasticity. Furthermore, curcumin was used to induce cell apoptosis and suppress energy dissipation of MDA-MB-231 cells. Combining apoptosis assay with QCM measurement, the results revealed good linear relationship between cell viscoelasticity inhibition and apoptosis rate with correlation coefficient R = 0.9908. The QCM cytosensor could rapidly, accurately, dynamically, and noninvasively monitor the changes of cell viscoelasticity for evaluation of apoptosis degree in MDA-MB-231 cells. The study established a new model for cell apoptosis assessment, facilitating understanding of the mechanisms of cell apoptosis on the aspect of mechanical properties.

Adipose Tissue-Derived Stromal Cells Alter the Mechanical Stability and Viscoelastic Properties of Gelatine Methacryloyl Hydrogels.

The extracellular matrix provides mechanical cues to cells within it, not just in terms of stiffness (elasticity) but also time-dependent responses to deformation (viscoelasticity). In this work, we determined the viscoelastic transformation of gelatine methacryloyl (GelMA) hydrogels caused by adipose tissue-derived stromal cells (ASCs) through mathematical modelling. GelMA-ASCs combination is of interest to model stem cell-driven repair and to understand cell-biomaterial interactions in 3D environments. Immortalised human ASCs were embedded in 5%, 10%, and 15% (w/v) GelMA hydrogels and evaluated for 14 d. GelMA had a concentration-dependent increase in stiffness, but cells decreased this stiffness over time, across concentrations. Viscoelastic changes in terms of stress relaxation increased progressively in 5% GelMA, while mathematical Maxwell analysis showed that the relative importance (Ri) of the fastest Maxwell elements increased proportionally. The 10% GelMA only showed differences at 7 d. In contrast, ASCs in 15% GelMA caused slower stress relaxation, increasing the Ri of the slowest Maxwell element. We conclude that GelMA concentration influenced the stiffness and number of Maxwell elements. ASCs changed the percentage stress relaxation and Ri of Maxwell elements transforming hydrogel viscoelasticity into a more fluid environment over time. Overall, 5% GelMA induced the most favourable ASC response.

Different Passive Viscoelastic Properties Between the Left and Right Ventricles in Healthy Adult Ovine.

Ventricle dysfunction is the most common cause of heart failure, which leads to high mortality and morbidity. The mechanical behavior of the ventricle is critical to its physiological function. It is known that the ventricle is anisotropic and viscoelastic. However, the understanding of ventricular viscoelasticity is much less than that of its elasticity. Moreover, the left and right ventricles (LV&RV) are different in embryologic origin, anatomy, and function, but whether they distinguish in viscoelastic properties is unclear. We hypothesized that passive viscoelasticity is different between healthy LVs and RVs. Ex vivo cyclic biaxial tensile mechanical tests (1, 0.1, 0.01 Hz) and stress relaxation (strain of 3, 6, 9, 12, 15%) were performed for ventricles from healthy adult sheep. Outflow track direction was defined as the longitudinal direction. Hysteresis stress-strain loops and stress relaxation curves were obtained to quantify the viscoelastic properties. We found that the RV had more pronounced frequency-dependent viscoelastic changes than the LV. Under the physiological frequency (1 Hz), the LV was more anisotropic in the elasticity and stiffer than the RV in both directions, whereas the RV was more anisotropic in the viscosity and more viscous than the LV in the longitudinal direction. The LV was quasi-linear viscoelastic in the longitudinal but not circumferential direction, and the RV was nonlinear viscoelastic in both directions. This study is the first to investigate passive viscoelastic differences in healthy LVs and RVs, and the findings will deepen the understanding of biomechanical mechanisms of ventricular function.

Contribution of Tissue Inflammation and Blood-Brain Barrier Disruption to Brain Softening in a Mouse Model of Multiple Sclerosis.

Neuroinflammatory processes occurring during multiple sclerosis cause disseminated softening of brain tissue, as quantified by in vivo magnetic resonance elastography (MRE). However, inflammation-mediated tissue alterations underlying the mechanical integrity of the brain remain unclear. We previously showed that blood-brain barrier (BBB) disruption visualized by MRI using gadolinium-based contrast agent (GBCA) does not correlate with tissue softening in active experimental autoimmune encephalomyelitis (EAE). However, it is unknown how confined BBB changes and other inflammatory processes may determine local elasticity changes. Therefore, we aim to elucidate which inflammatory hallmarks are determinant for local viscoelastic changes observed in EAE brains. Hence, novel multifrequency MRE was applied in combination with GBCA-based MRI or very small superparamagnetic iron oxide particles (VSOPs) in female SJL mice with induced adoptive transfer EAE (n = 21). VSOPs were doped with europium (Eu-VSOPs) to facilitate the post-mortem analysis. Accumulation of Eu-VSOPs, which was previously demonstrated to be sensitive to immune cell infiltration and ECM remodeling, was also found to be independent of GBCA enhancement. Following registration to a reference brain atlas, viscoelastic properties of the whole brain and areas visualized by either Gd or VSOP were quantified. MRE revealed marked disseminated softening across the whole brain in mice with established EAE (baseline: 3.1 ± 0.1 m/s vs. EAE: 2.9 ± 0.2 m/s, p < 0.0001). A similar degree of softening was observed in sites of GBCA enhancement i.e., mainly within cerebral cortex and brain stem (baseline: 3.3 ± 0.4 m/s vs. EAE: 3.0 ± 0.5 m/s, p = 0.018). However, locations in which only Eu-VSOP accumulated, mainly in fiber tracts (baseline: 3.0 ± 0.4 m/s vs. EAE: 2.6 ± 0.5 m/s, p = 0.023), softening was more pronounced when compared to non-hypointense areas (percent change of stiffness for Eu-VSOP accumulation: −16.81 ± 16.49% vs. for non-hypointense regions: −5.85 ± 3.81%, p = 0.048). Our findings suggest that multifrequency MRE is sensitive to differentiate between local inflammatory processes with a strong immune cell infiltrate that lead to VSOP accumulation, from disseminated inflammation and BBB leakage visualized by GBCA. These pathological events visualized by Eu-VSOP MRI and MRE may include gliosis, macrophage infiltration, alterations of endothelial matrix components, and/or extracellular matrix remodeling. MRE may therefore represent a promising imaging tool for non-invasive clinical assessment of different pathological aspects of neuroinflammation.

Photocleavable Regenerative Network Materials with Exceptional and Repeatable Viscoelastic Manipulability.

The development of solventless system for modulating properties of network materials is imperative for the next generation sustainable technology. Utilization of photostimulation is important owing to its spatial and temporal locality, yet designing photoresponsive network materials exhibiting repeatable and dramatic change in their properties remains a challenge. Here, the authors report a photocleavable regenerative network (PRN) linked with photoresponsive hexaarylbiimidazoles (HABIs) synthesized from narrow dispersity star‐shaped poly(dimethylsiloxane)s (PDMSs) having 2,4,5‐triphenylimidazole end groups. The use of urea anion as a catalyst for ring opening polymerization (ROP) of cyclic siloxane initiated from silanols enables control of molecular weight and dispersity. The rheological measurements for the synthesized PRNs exhibit drastic changes in storage and loss moduli (G′ and G″) upon photoirradiation in the solid state (G′ > G″). This photocontrolled change in viscoelasticity with retaining solidity enables application of PRNs as a remotely‐controlled photo‐melt adhesive and photo‐scissible string. The developed PRNs will enable a wide variety of applications such as industrially important next‐generation sustainable adhesive, sealant, and reversibly‐deformable 3D printing materials with their spatially and temporally local manipulability, solventless handleability, and excellent reversibility.