Changes In Stiffness Research Articles

Micro-Scale Topography Triggers Dynamic 3D Nuclear Deformations.

Navigating complex extracellular environments requires extensive deformation of cells and their nuclei. Most in vitro systems used to study nuclear deformations impose whole-cell confinement that mimics the physical crowding experienced by cells during 3D migration through tissues. Such systems, however, do not reproduce the types of nuclear deformations expected to occur in cells that line tissues such as endothelial or epithelial cells whose physical confinement stems principally from the topography of their underlying basement membrane. Here, it is shown that endothelial cells and myoblasts cultured on microgroove substrates that mimic the anisotropic topography of the basement membrane exhibit large-scale 3D nuclear deformations, with partial to complete nuclear penetration into the microgrooves. These deformations do not lead to significant DNA damage and are dynamic with nuclei cyclically entering and exiting the microgrooves. Atomic force microscopy measurements show that these deformation cycles are accompanied by transient changes in perinuclear stiffness. Interestingly, nuclear penetration into the grooves is driven principally by cell-substrate adhesion stresses, with a limited need for cytoskeleton-associated forces. Finally, it is demonstrated that myoblasts from laminopathy patients exhibit abnormal nuclear deformations on microgrooves, raising the possibility of using microgroove substrates as a novel functional diagnostic platform for pathologies that involve abnormal nuclear mechanics.

Influence of matrix stiffness on microstructure evolution and magnetization of magneto-active elastomers.

Field-induced microstructure evolution can play an important role in defining the coupled magneto-mechanical response of Magneto-Active Elastomers (MAEs). The behavior of these materials is classically modeled using mechanical, magnetic and coupled magneto-mechanical contributions to their free energy function. If the MAE sample is fully clamped so it cannot deform, the mechanical coupling is reduced to the internal microscopic deformations caused by the particles moving and deforming the elastic medium that surrounds them. In the present study, we build on a unified mean-field theoretical approach which takes the microscopic elastic energy into account. Combined with experiment, this approach reveals how microstructure evolution affects the magnetization behavior of isotropic MAEs. MAE disks with various matrix stiffness and volume fraction of particles were fabricated and the magnetization curves were measured by vibrating sample magnetometry. We demonstrate that the idea of columnar structures forming from randomly distributed particles upon the application of an external magnetic field provides an effective approach in modeling microstructure evolution in these materials. Our unified mean-field model, using few and physically meaningful parameters, shows good quantitative agreement with the experimental data on magnetization and magnetic differential susceptibility of MAE samples. More importantly, our model can estimate microstructure evolution in highly filled samples, for which measurements are very challenging. Since changes in magnetization and stiffness are both driven by microstructural evolution, a quantitative relationship can be established between the two effects, as they represent different macroscopic manifestations of the same microscopic process. Therefore, our model can be used in conjunction with magnetization measurements to predict the mechanical modulus of MAEs without the need for elastic testing.

Age-related Arterial Stiffening is Associated with A Body Shape Index (ABSI) and Lean Body Mass Index -A Retrospective Cohort Study in Healthy Japanese Population.

Several anthropometric indices reflecting cardiometabolic risks have been developed, but the relationship of body composition with arterial stiffness remains unclear. We aimed to determine the interaction between age-related anthropometric changes and progression of arterial stiffness. This research analyzed cross-sectional data (N=13,672) and 4-year longitudinal data (N=5,118) obtained from a healthy Japanese population without metabolic disorders. The relationship of age with anthropometric indices comprising estimated lean body mass index (eLBMI), body mass index (BMI), waist circumference (WC) and a body shape index (ABSI) was examined. The mediating effects of the indices on the association between age and arterial stiffness assessed by cardio-ankle vascular index (CAVI) was analyzed. Unlike BMI and WC, ABSI (Rs=0.284) and CAVI (Rs=0.733) showed a positive linear relationship with aging in stratified analyses. Especially in the middle-older age groups, eLBMI showed a declining trend with aging. An increase in ABSI was associated with a decrease in eLBMI, whereas increase in BMI or WC was related to increased eLBMI. In cross-sectional analyses, age was associated with CAVI, partially mediated by ABSI or eLBMI after adjusting confounders. Baseline CAVI correlated negatively with 4-year change in (Δ)eLBMI (Rs=-0.120 in men, -0.161 in women). ΔCAVI correlated negatively with ΔeLBMI (Rs=-0.031). ABSI is a modifiable index that well reflects age-related changes in arterial stiffness and body composition including lean body mass. Since arterial stiffening may cause skeletal muscle loss, potentially creating a vicious cycle, prioritizing CAVI and anthropometric indices in clinical practice may be a useful strategy.

Horizontal Cyclic Bearing Characteristics of Bucket Foundation in Sand for Offshore Wind Turbines

During the service period, the offshore wind turbine foundation mainly bears the wind load from the upper structure and the periodic loads such as wave load and sea currents from the lower structure. Long-term cyclic loads have an important impact on the cumulative deformation, foundation stiffness changes, and horizontal ultimate bearing capacity of the offshore wind turbine bucket foundation. This paper conducts cyclic loading tests on mono-bucket foundations under unidirectional and multidirectional cyclic loading conditions based on the multidirectional intelligent cyclic loading system of offshore wind turbine foundations and analyzes the cumulative effects of the loading direction, vertical load, and drainage status on the mono-bucket foundation during the cyclic loading process, effects of rotation angle, cyclic stiffness, and monotonic bearing capacity of foundation after cycles. The research results show that multidirectional cyclic loading significantly reduces the cyclic cumulative rotation angle of the mono-bucket foundation, and the maximum reduction rate can reach more than 50%. After unidirectional and multidirectional cyclic loading, the bearing capacity of the bucket foundation can be increased by up to 30% and 20%, respectively. At the same time, this paper proposes calculation formulas for vertical load, number of cyclic loading, and normalized cumulative rotation and establishes a calculation method for vertical load and bearing capacity of the foundation after cycles.

A multifunctional sensor for cell traction force, matrix remodeling and biomechanical assays in self-assembled 3D tissues in vitro.

Cell-matrix interactions, mediated by cellular force and matrix remodeling, result in dynamic reciprocity that drives numerous biological processes and disease progression. Currently, there is no available method for directly quantifying cell traction force and matrix remodeling in three-dimensional matrices as a function of time. To address this long-standing need, we developed a high-resolution microfabricated device that enables longitudinal measurement of cell force, matrix stiffness and the application of mechanical stimulation (tension or compression) to cells. Here a specimen comprising of cells and matrix self-assembles and self-integrates with the sensor. With primary fibroblasts, cancer cells and neurons we have demonstrated the feasibility of the sensor by measuring single or multiple cell force with a resolution of 1 nN and changes in tissue stiffness due to matrix remodeling by the cells. The sensor can also potentially be translated into a high-throughput system for clinical assays such as patient-specific drug and phenotypic screening. We present the detailed protocol for manufacturing the sensors, preparing experimental setup, developing assays with different tissues and for imaging and analyzing the data. Apart from microfabrication of the molds in a cleanroom (one time operation), this protocol does not require any specialized skillset and can be completed within 4-5 h.

The magneto-mechanical coupling of multiphase magnetorheological elastomers.

Magnetorheological elastomers (MREs) are soft magnetic composites that achieve tunable changes in stiffness and energy response in the presence of a magnetic field. Rigid particle composite (RC) MREs have been studied for decades for their potential applications to automotive dampers and robotic systems. Recently, magnetic fluid composite (FC) MREs have been developed which utilize magnetic fluids as inclusions to elastomers. An investigation into how inclusion phase affects magneto-mechanical performance may greatly improve MRE design capabilities. Here we experimentally evaluate the impact of solid and liquid magnetic inclusions on MRE properties, construct a simple model that captures the performance of diverse MRE material architectures, and demonstrate the use of the model to create material design maps relating the material structure, zero-field properties, and applied field to the elastic modulus and specific loss. The magneto-mechanical response is evaluated for three material architectures: RC, FC, and hybrid composite (HC) MREs that use solid particles, magnetic fluids, and a combination of the two as inclusions respectively. The model is developed through magnetic and mechanical energy principles, which suggests that the phase of the magnetic inclusions impacts the change in energy density during deformation. We show that the magneto-mechanical coupling factor is dependent on the zero-field properties of the composites, which allows for the development of material design maps to inform the fabrication of MREs based on desired properties.

Analysis of stiffness changes and factors induced by smart suit with trunk kinetic chain SLIP model

We are currently developing a suit that assists human running motion based on the Smart Suit (SS). The SS is a wearable assistive device that intervenes in trunk kinetic chain movements by linking trunk rotation to hip flexion and extension through elastic belts. By intervening in the trunk kinetic chain, our goal is to enhance stiffness, thereby improving running economy and speed. The purpose of this study is to acquire fundamental insights into the changes in leg and trunk rotational stiffness induced by the SS, as well as the underlying mechanisms. We defined the SS torque intervention rate pss, which focuses on the magnitude of force, and the peak time difference index, elag, between SS and humans, which focuses on the timing of force, and analyzed the relationship between the stiffness change rate due to SS wearing. The results of the analysis suggest that SS affects human running sensitively rather than mechanically. We also confirmed that the degree of adaptation to SS, assessed by the timing gap between SS exertion and human exertion, contributes significantly to changes in trunk rotation stiffness.

The (un)known crosstalk between metabolism and mechanotransduction: Implications for metabolic syndrome (MetS)-associated neurological complications.

Metabolic syndrome (MetS) has been associated with disruptions in tissue mechanical homeostasis and inflammatory and metabolic derangements. However, the direct correlation between metabolic alterations and changes in tissue stiffness, and whether they could play a role as upstream initiators of disease pathology remains to be investigated. This emerging concept has yet to be put into clinical practice as many questions concerning the interplay between extracellular matrix mechanical properties and regulation of metabolic pathways remain unsolved. This review will highlight key foundational studies examining mutual regulation of cell metabolism and mechanotransduction, and opening questions lying ahead for better understanding MetS pathophysiology.

Associations of Short-Term Ozone Exposure With Hypoxia and ArterialStiffness.

Epidemiological studies reported associations between ozone (O3) exposure and cardiovascular diseases, yet the biological mechanisms remain underexplored. Hypoxia is a shared pathogenesis of O3-associated diseases; therefore, we hypothesized that O3 exposure may induce changes in hypoxia-related markers, leading to adverse cardiovascular effects. This study aimed to investigate associations of short-term O3 exposure with hypoxic biomarkers and arterial stiffness. We conducted a panel study involving 210 young healthy residents in 2 cities at different altitudes on the Qinghai-Tibetan Plateau in China, where O3 concentrations are high and particulate pollution is low. Participants underwent 4 repeated visits to assess ambient O3 exposure levels, hypoxic biomarkers, and arterial stiffness. We applied linear mixed-effects models to assess the associations of O3 exposure (lag1 to lag1-7 days) with hypoxic biomarkers and arterial stiffness, adjusted for confounders. Mediation analyses explored the hypoxia's role in O3-related arterial stiffness changes. We further examined effect modification by residence altitude and the robustness of results by including PM2.5 (particulate matter≤2.5μm in aerodynamic diameter) or NO2 in 2-pollutant models. O3 exposure 1 to 7days before visits was significantly associated with changes in multiple hypoxic biomarkers. A 10-ppb increase in O3 exposure was linked to significant decreases in oxygen saturation (SpO2) and increases in red blood cell count (RBC), hemoglobin concentration, and hematocrit, with maximum changes by-0.42%, 0.92%, 0.97%, and 1.92%, respectively. Laboratory analysis of mRNA and protein markers consistently indicated that O3 exposure activated the hypoxia-inducible factor 1 (HIF-1) signaling pathway. Additionally, a 10-ppb increase in O3 corresponded to a 1.04% to 1.33% increase in carotid-femoral pulse wave velocity (cfPWV), indicating increased arterial stiffness. RBC, hemoglobin concentration, and hematocrit increases significantly mediated the O3-cfPWV association, whereas the SpO2 reduction had an insignificant mediating effect. Associations of O3 with hypoxic biomarkers varied by altitude. The higher altitude group showed delayed associations with SpO₂ and HIF-1 expression but stronger associations with RBC indices. These associations remained robust after adjusting for copollutants. O3 exposure may reduce oxygen availability, prompting compensatory increases in red blood cells and hemoglobin, which exacerbate arterial stiffening. These findings provide new insights into the mechanisms underlying O3-induced cardiovascular injury.

Nondestructive Mechanical Characterization of Bioengineered Tissues by Digital Holography.

Mechanical properties of engineered connective tissues are critical for their success, yet modern sensors that measure physical qualities of tissues for quality control are invasive and destructive. The goal of this work was to develop a noncontact, nondestructive method to measure mechanical attributes of engineered skin substitutes during production without disturbing the sterile culture packaging. We optimized a digital holographic vibrometry (DHV) system to measure the mechanical behavior of Apligraf living cellular skin substitute through the clear packaging in multiple conditions: resting on solid agar as when the tissue is shipped, on liquid media in which it is grown, and freely suspended in air as occurs when the media is removed for feeding. We utilized full-field measurement to assess the complete surface deformation pattern to compare with vibration theory and found the patterns observed in air showed the closest behavior to theory. To simulate the effects of the actual culture dish geometry and the trilayer composition of the tissue on the porous membrane support, we employed finite element (FE) analysis. To simulate changes in thickness and stiffness that may occur with manufacturing process variations, we dried samples over time and observed measurable increases in the fundamental mode frequency which could be predicted by altering the thickness of the tissue layers in the FE model. However, quantitative estimates of the engineered tissue stiffness based on vibration theory are unrealistically high due to the signal being dominated by the stiff underlying membrane on which the tissue is cultured. Thus, although DHV is not able to specifically quantify the thickness or modulus or identify small spot defects, it has the potential to be used assess the overall properties of a tissue in-line and noninvasively for quality control.

Interlaminar Fracture Toughness Analysis for Reliability Improvement of Wind Turbine Blade Spar Elements Based on Pultruded Carbon Fiber-Reinforced Polymer Plate Manufacturing Method.

The key structural components of a wind turbine blade, such as the skin, spar cap, and shear web, are fabricated from fiber-reinforced composite materials. The spar, predominantly manufactured via resin infusion-a process of resin injection and curing in carbon fibers-is prone to initial defects, such as pores, wrinkles, and delamination. This study suggests employing the pultrusion technique for spar production to consistently obtain a uniform cross-section and augment the reliability of both the manufacturing process and the design. In this context, this study introduces carbon fiber-reinforced polymer (CFRP/CFRP) and glass fiber-reinforced polymer (GFRP/CFRP) test specimens, which mimic the bonding structure of the spar cap, utilizing pultruded CFRP in accordance with ASTM standards to analyze the delamination traits of the spar. Delamination tests-covering Mode I (double cantilever beam), Mode II (end-notched flexure), and mixed mode (mixed-mode bending)-were performed to gauge displacement, load, and crack growth length. Through this crack growth mechanism, the interlaminar fracture toughness derived was examined, and the stiffness and strength changes compared to CFRP based on the existing prepreg manufacturing method were analyzed. In addition, the interlaminar fracture toughness for GFRP, which is a material in contact with the spar structure, was analyzed, and through this, it was confirmed that the crack behavior has less deviation compared to a single CFRP material depending on the stiffness difference between the materials when joining dissimilar materials. This means that the higher the elasticity of the high-stiffness material, the higher the initial crack resistance, but the crack growth behavior shows non-uniform characteristics thereafter. This comparison provides information for predicting interlaminar delamination damage within the interior and bonding area of the spar and skin and provides insight for securing the reliability of the design life.

High matrix stiffness accelerates migration of hepatocellular carcinoma cells through the integrin β1-Plectin-F-actin axis

BackgroundAbundant research indicates that increased extracellular matrix (ECM) stiffness significantly enhances the malignant characteristics of hepatocellular carcinoma (HCC) cells. Plectin, an essential cytoskeletal linker protein, has recently emerged as a promoter of cancer progression, particularly in the context of cancer cell invasion and metastasis. However, the responsiveness of plectin to changes in ECM stiffness and its impact on HCC progression remain unclear. In this study, we aimed to investigate whether plectin responds to variations in ECM stiffness and to explore its involved molecular mechanisms in regulating HCC cell migration.ResultsOur results showed that, when compared with control group (7 kPa), high ECM stiffness (53 kPa) boosts HCC cell migration by upregulating plectin and integrin β1 expression and increasing F-actin polymerization. Knockdown of integrin β1 negated the high stiffness-upregulated plectin expression. Furthermore, reducing either plectin or integrin β1 levels, or using latrunculin A, effectively prevented the high ECM stiffness-induced F-actin polymerization and HCC cell migration.ConclusionsThese findings demonstrate that integrin β1-plectin-F-actin axis is necessary for high matrix stiffness-driven migration of HCC cells, and provide evidence for the critical role of plectin in mechanotransduction in HCC cells.

Best1 mitigates ER stress induced by the increased cellular microenvironment stiffness in epilepsy.

Changes in brain tissue stiffness are closely linked to the development and diseases of the nervous system. Endoplasmic reticulum (ER) stress plays a role in various pathological processes related to epilepsy. However, the relationship between stiffness changes, ER stress, and epilepsy remains unclear. This study aimed to investigate the impact of Best1 upregulation on alleviating ER stress and the underlying mechanism. Additionally, we proposed a protective strategy to prevent cell death resulting from ER stress in epilepsy. This study investigated the expression levels of ER stress-related proteins in epileptic tissues of varying stiffness. Atomic force microscopy revealed differences in stiffness across various lesion regions in patients with epilepsy. The expression levels of ECM and ER stress-related proteins were elevated in tissues with higher stiffness. Polypropionamide hydrogels were used to simulate extracellular matrix (ECM) with varying stiffness levels. Basal ER stress increased in the stiffer hydrogel substrates. Furthermore, the calcium-activated anion channel Bestrophin 1 (Best1) mitigated ER stress induced by both the stiffer substrate and thapsigargin. The loss-of-function mutations in Best1 inhibited this activity. The underlying mechanism involves the upregulation of the endosomal sorting complex required for the transport (ESCRT) components by Best1, which helps mitigate ER stress. These findings suggest that increased stiffness of the cellular microenvironment may contribute to neuronal death during epileptogenesis. Additionally, Best1 upregulation may serve as a protective strategy against excessive ER stress-induced neuronal damage in epilepsy.

Dynamic Hydrogel-Based Strategy for Traumatic Brain Injury Modeling and Therapy.

Traumatic brain injury (TBI) is one of the most traumatizing and poses serious health risks to people's bodies due to its unique pathophysiological characteristics. The investigations on the pathological mechanism and valid interventions of TBI have attracted widespread attention worldwide. With bio-mimic mechanic cues, the dynamic hydrogels with dynamic stiffness changes or reversible crosslinking have been suggested to construct the invitro disease models or novel therapeutic agents for TBI. However, there is a lack of clarification on the dynamic hydrogels currently reported and their biomedical applications on TBI. Our review starts with introducing the native mechanical characters and changes in TBI and then summarizes the common chemical strategies of the dynamic hydrogels with dynamically tunable stiffness and reversible networks for invitro modeling and therapy. Finally, we prospect the future development of dynamic hydrogels in the mechanical modeling of TBI, providing new mechanical insights for TBI and guidance for tailored brain-targeted biomaterials.

Experimental Studies on Freeplay Induced Limit Cycle Oscillations and Their Major Drivers

A new experimental wind tunnel test-bed has been developed for the study of limit cycle oscillations induced by control surface freeplay. A thorough examination of several factors affecting the limit cycle is presented—starting from a reference configuration, the effect of changes in inertia and stiffness, a time-varying gap size, gravitational loading, and aerodynamic preload due to an angle of attack. Both time-marching simulations and describing functions analytical methods have been used to understand the experimental measurements and study the capability of the methods to capture the physical behavior. Good agreement was found in all cases, and physical insights are gained from the mathematical models. Limitations of the analytical tools are also addressed, focusing on the important difference between the self-excited dynamics of the nonlinear system and its forced response to external excitation.

Biomechanical assessment of ligament maturation after arthroscopic ligament reconstruction of the anterior talofibular ligament.

Many techniques have been described for lateral ankle ligament reconstruction. Although the biomechanical properties of gracilis tendons are different from those of ligaments, the use of a gracilis tendon autograft is a popular option for anatomical reconstruction. Graft maturation and the biomechanical processes over time remain unclear. This study describes changes in graft stiffness following anterior talofibular ligament (ATFL) reconstruction and graft reaction to varus stress. The reconstruction would be stiffer than the native ATFL, but would decrease during follow-up. Twenty patients were prospectively included after arthroscopic reconstruction of the ATFL and calcaneofibular ligament for ankle stabilization. All patients were followed up 3, 6, and 12 months after surgery to assess graft stiffness by shear wave elastography (SWE) at different angles of varus in the ankle. At one year the EFAS and AOFAS functional scores were obtained. A control group of twenty healthy subjects were included to compare graft stiffness to that of a native ATFL. The stiffness of the native ATFL in the control group was 12.8 +/- 2.4 kPa in neutral position, 18.4 +/- 4.8 kPa at 15 ° of varus, 31.9 +/- 6.6 kPa at 30 ° of varus. One year after surgery, graft stiffness was statistically higher and averaged 56 +/- 9 kPa, 70.2 +/- 11.6 kPa and 84.9 +/- 10.5 kPa, respectively. Postoperative graft stiffness at three, six, and twelve months was not correlated with any of these scores, reflecting patient satisfaction and good function at one year. Graft stiffness decreases over time but remains four times stiffer than that of a native ATFL at one year in the neutral position. ATFL graft stiffness at one year during varus stress appears to be different from that of a native ATFL. III.

Point shear wave elastography application in assessment pancreas tissue stiffness: A pilot study.

Recent advancements in medical imaging, such as point shear wave elastography (pSWE), offer non-invasive methods to assess tissue stiffness and structural changes. This study explores the use of pSWE to evaluate pancreatic stiffness and dimensions in three different pancreas parts. This study was conducted at diagnostic radiology department, King Abdulaziz University Hospital, Jeddah, between June 2022 and November,2022. Thirty-one diabetic patients and thirty-one healthy controls were included. Ultrasound pSWE examination was performed using a ultrasound system (Philips Elite Epic 7) to measure stiffness across different pancreatic parts. Pancreatic stiffness was quantified in meters per second (m/s), and the dimensions of each pancreatic part were recorded. Different parameters, including age, sex, height, weight, body mass index (BMI), and comorbidities, were collected and analyzed. Diabetic patients exhibited significantly higher shear wave velocities (SWVs) compared to healthy controls, indicating increased pancreatic stiffness. The mean shear wave velocity was 1.7m/s in diabetic versus 0.6m/s in controls (p<0.001). Additionally, the pancreatic head dimensions were significantly large in diabetic patients (2.1cm vs. 1.8cm; p=0.003), while the body and tail part showed no significant differences. A positive correlation was found between SWVs and BMI. The findings underscore the potential of pSWE as a non-invasive diagnostic tool for early detection and monitoring of diabetes-related pancreatic alterations. Assessing pancreatic stiffness and dimensions through pSWE can help in identify patients at risk for pancreatic complications and optimize management strategies. Point shear wave elastography (pSWE) could be a useful, non-invasive tool for early detection of pancreatic changes in diabetic patients, identifying those at risk for complications. Integrating pSWE into routine diabetes check may enhance early interventions and improve outcomes.

Loading Speed and Intensity in Eccentric Calf Training Impact Acute Changes in Achilles Tendon Thickness and Stiffness: A Randomized Crossover Trial.

Eccentric calf training for Achilles tendinopathy shows variable success in athletes. Recent insights suggest a role for tendon fluid flow (exudation or redistribution) during exercise, which explains post-exercise reductions in thickness and increases in stiffness of the tendon. This fluid flow is thought to be beneficial as it may promote tendon remodeling, reduce intratendinous pressure, and alleviate pain. In this perspective, slow, high-load exercises are promoted as they theoretically facilitate tendon fluid flow. However, evidence supporting this assumption is lacking. Therefore, this study aimed to investigate whether loading speed and intensity during eccentric calf training impact acute changes in midportion Achilles tendon thickness and stiffness, reflecting alterations in local tendon fluid content. A randomized, assessor-blinded, crossover trial was conducted with 34 healthy athletes (17 men, 17 women, age: 23.7 ± 6 years). Participants underwent 3 single-leg eccentric heel-drop interventions with 20% additional bodyweight, varying in loading speed (fast: 1 s, slow: 3 s) and loading intensity (low: to plantigrade, high: to maximal dorsiflexion). Achilles tendon anteroposterior diameter (APD), cross-sectional area (CSA), and shear-wave velocity (SWV) were assessed in the midportion region using ultrasonography and shear-wave elastography pre-and immediately post-intervention. The slow, high-load intervention produced greater immediate reductions in tendon APD and CSA (8.7% and 10.1%), compared to the slow, low-load (4.0% and 4.7%) and fast, high-load (2.9% and 3.4%) interventions (p < 0.001). Moreover, only the slow, high-load intervention increased tendon SWV (52.4%, p < 0.001). These findings provide the first evidence that both loading speed and intensity during eccentric calf training impact acute changes in Achilles tendon thickness and stiffness, likely mediated by changes in fluid flow, which could be relevant for tendinopathy rehabilitation.

Design and vibration damping study of a novel variable stiffness composite based on electrorheological fluid

We propose a novel variable stiffness composite (VSERF) made of soft materials, featuring a three-layer fluid-membrane composite structure with electrorheological fluid encapsulated in a thin film. The overall shear storage modulus of this composite can be described using a viscoelastic model. Under a 3 kV/mm electric field, the electrorheological fluid transitions from a liquid to a quasi-solid state, resulting in a 25-fold increase in the overall shear storage modulus of the VSERF, allowing for controllable changes in stiffness. We used VSERF as a variable stiffness element in a vibration absorber. When the electric field strength was increased from 0 to 3 kV/mm, the natural frequency of the absorber shifted from 13 to 21 Hz, indicating that vibrations within this range of excitation frequencies could be effectively controlled. The damping ratio of the VSERF absorber is below 0.189, and its transmissibility peak exceeds 2.9, ensuring that the absorber can effectively transmit vibrations from the excitation source to the mass, enhancing vibration damping. Consequently, VSERF shows promising potential for energy absorption and vibration damping applications.

Role of multi-parametric ultrasonography for the assessment and monitoring of functional status of renal allografts with histopathological correlation.

The study focuses on the use of multi-parametric ultrasound [gray scale, color Doppler and shear wave elastography (SWE)] to differentiate stable renal allografts from acute graft dysfunction and to assess time-dependent changes in parenchymal stiffness, thereby assessing its use as an efficient monitoring tool for ongoing graft dysfunction. To date, biopsy is the gold standard for evaluation of acute graft dysfunction. However, because it is invasive, it carries certain risks and cannot be used for follow-up monitoring. SWE is a non-invasive imaging modality that identifies higher parenchymal stiffness values in cases of acute graft dysfunction compared to stable grafts. To assess renal allograft parenchymal stiffness by SWE and to correlate its findings with functional status of the graft kidney. This prospective observational study included 71 renal allograft recipients. Multi-parametric ultrasound was performed on all patients, and biopsies were performed in cases of acute graft dysfunction. The study was performed for a period of 2 years at Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, a tertiary care center in north India. Independent samples t-test was used to compare the means between two independent groups. Paired-samples t-test was used to test the change in mean value between baseline and follow-up observations. Thirty-one patients had experienced acute graft dysfunction at least once, followed by recovery, but none of them had a history of chronic renal allograft injury. Mean baseline parenchymal stiffness in stable grafts and acute graft dysfunction were 30.21 + 2.03 kPa (3.17 + 0.11 m/s) and 31.07 + 2.88 kPa (3.22 + 0.15 m/s), respectively; however, these differences were not statistically significant (P = 0.305 and 0.252, respectively). There was a gradual decrease in SWE values during the first 3 postoperative months, followed by an increase in SWE values up to one-year post-transplantation. Patients with biopsy-confirmed graft dysfunction showed higher SWE values compared to those with a negative biopsy. However, receiver operating characteristic analysis failed to show statistically significant cut-off values to differentiate between the stable graft and acute graft dysfunction. Acute graft dysfunction displays higher parenchymal stiffness values compared to stable grafts. Therefore, SWE may be useful in monitoring the functional status of allografts to predict any ongoing dysfunction.