Stiffness Levels Research Articles

Serum Malondialdehyde-Modified Low-Density Lipoprotein Level May Be a Biomarker Associated with Aortic Stiffness Among Patients Undergoing Peritoneal Dialysis

Background: Serum malondialdehyde-oxidized low-density lipoprotein (MDA-oxLDL) is associated with atherosclerosis and increased risk of cardiovascular disease (CVD). Vascular calcification frequently occurs with arterial stiffness in patients on peritoneal dialysis (PD). This cross-sectional study aimed to elucidate the correlation between aortic stiffness and MDA-oxLDL levels in patients on PD. Methods: Overall, 92 patients on PD were included. The carotid–femoral pulse wave velocity (cfPWV) was evaluated using cuff-based volumetric displacement, and blood samples were obtained from all patients. Aortic stiffness was classified based on cfPWV values (>10 m/s indicating aortic stiffness). Serum MDA-ox-LDL levels were quantified using commercial enzyme-linked immunosorbent assay kits. Results: In total, 33 (35.9%) patients were classified into the aortic stiffness group. Factors, including systolic blood pressure (SBP), serum triglyceride levels, C-reactive protein levels, age, weight, body mass index (BMI), waist circumference, MDA-oxLDL levels, and diabetes mellitus (DM) prevalence, were significantly higher in the aortic stiffness group. Multivariable logistic regression analysis revealed significant associations between aortic stiffness and MDA-oxLDL levels, BMI, and SBP. Furthermore, multivariable forward stepwise linear regression analysis revealed serum MDA-oxLDL levels as a significant independent predictor of cfPWV values. Conclusions: Serum MDA-oxLDL levels correlate positively with cfPWV values and may predict aortic stiffness among PD patients, highlighting its potential role in assessing CVD risk in this population.

Association between pulse wave velocity and cerebral microbleeds: a systematic review and meta-analysis.

Cerebral microbleeds are associated with events that are among the highest mortality and disability events combined worldwide, as well as with hypertensive vasculopathy. The aim of the present study was to investigate the relationship between a marker of hypertensive vasculopathy, arterial stiffness assessed by pulse wave velocity, and cerebral microbleeds. A systematic review and meta-analysis was performed using PubMed, Scopus, and Web of Science, according to the Meta-analysis of Observational Studies in Epidemiology (MOOSE) and Cochrane Collaboration Handbook statements. Data extraction, quality assessment and statistical analyses were performed following pre-established criteria. Twenty-one studies involving 18,436 participants were included. Higher levels of pulse wave velocity were associated with a higher presence of cerebral microbleeds p-OR = 1.26 (95% CI; 1.09-1.45), with considerable heterogeneity; even adjusting for potential confounding variables p-OR = 1.12 (95% CI, 1.05-1.20), with substantial heterogeneity. Only the percentage of women was related to p-OR in the adjusted model. Sensitivity analyses confirmed the robustness of our results. Adjusted models showed publication bias. Higher levels of arterial stiffness are associated with greater presence of cerebral microbleeds. This phenomenon may be caused by damage to the brain under higher blood flow loads, in turn due to age-induced reversal of the stiffness gradient between large and small vessels. As the world's population is undergoing demographic ageing, our results underline the importance of establishing pulse wave velocity as a cardiovascular marker for early screening and delaying the onset of the characteristic signs of both diseases.

Stretchable printed circuit boards using a silicone substrate of variable stiffness and conventional PCB fabrication methods

Abstract Stretchable printed circuit boards (S-PCBs) offer unique advantages over rigid PCBs such as enabling conformability to changing environments and ergonomic designs with increased lifetime under dynamic loads. This study introduces an innovative fabrication method and a cost-effective solution for rapid prototyping S-PCBs using commercially available materials. By utilizing silicone substrates with different levels of stiffness and structured copper sheets for electrical connections, the S-PCBs feature ‘stiff islands’ embedded in a flexible base material. This fabrication method helps alleviate mechanical strain on strain-sensitive components while allowing local deformation of the S-PCB. The proposed fabrication method does therefore enable to integrate surface mount device components into S-PCBs and facilitates complex circuit designs while maintaining stretchability and fatigue resistance. Through material characterization, video strain analysis, as well as quasi-static and cyclic loading tests, this article demonstrates the efficacy of our approach. Based on the experimental results, we provide insights into failure modes and suggest design principles to further enhance the durability of S-PCBs fabricated with our method. We then conclude by presenting a soft wearable S-PCB demonstrator. The S-PCBs fabricated with this method withstood mechanical strains up to 100% and cyclic loads with 30% strain up to 625 cycles. The results are very promising for applications in soft robotics, wearable devices, and soft sensors and actuators. Overall, our study offers a comprehensive toolkit for fast S-PCB prototyping, paving the way for advancements in stretchable electronics with a high degree of complexity and stretchability.

A Study of Sliding Base Isolation System: A Review

Seismic isolation systems are crucial for protecting structures by minimizing the transmission of acceleration during seismic events, and among the various types, the resilient sliding system, which combines restoring springs and sliders, is highly effective in mitigating seismic impacts. This system controls structural responses by balancing stiffness and friction, ensuring safety while maintaining the functionality of buildings. However, optimizing the design of this system requires carefully selecting combinations of stiffness and the coefficient of friction to achieve low acceleration levels, while simultaneously managing the relative displacement within the isolation system to protect both the structure and its occupants. Excessive displacement may compromise the integrity of the isolation system or cause damage to the structure it is meant to protect. The challenge lies in finding the optimal friction and stiffness levels that provide sufficient energy dissipation and restore forces without allowing displacement to exceed acceptable thresholds. Studies show that restoring forces generated by springs help limit excessive displacements, while sliders dissipate seismic energy, and adjustments in these parameters must account for variations in ground motion intensity and frequency. Thus, a balance between flexibility and resistance is essential in sliding systems to ensure maximum structural safety and occupant protection during earthquakes. This paper reviews different sliding isolation systems which fulfils the requirements of controlling the earthquake and functioning accordingly. It include systems such as PF, FPS, VFPI , CFPI,VFPS,PFPE, VCFPS,VFFPI etc.

Improved Pain, Morning Stiffness, and Fatigue With Bimekizumab in Axial Spondyloarthritis: Results From the Phase III BE MOBILE Studies.

To assess the effect of bimekizumab on pain, morning stiffness, and fatigue in patients with nonradiographic and radiographic axial spondyloarthritis (axSpA) in the phase III BE MOBILE studies (ClinicalTrials.gov: NCT03928704 and NCT03928743). Patients were randomized to bimekizumab 160 mg or placebo every 4 weeks; and all patients received bimekizumab from week 16. Patients reported spinal pain, peripheral pain, morning stiffness, and fatigue to week 52. Total and nocturnal spinal pain were each assessed on a 0-10 numerical rating scale (NRS). Individual Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) items (0-10-point NRS) assessed peripheral arthritis pain (question [Q] 3), enthesitis pain/discomfort (Q4), morning stiffness (mean of Q5 and Q6), and fatigue (Q1). Functional Assessment of Chronic Illness Therapy Fatigue subscale score (FACIT-Fatigue) is also reported. At week 16, bimekizumab-treated patients reported lower mean nocturnal spinal pain, total spinal pain, and BASDAI scores (nominal except for nocturnal spinal pain; all P ≤ 0.001), as well as higher FACIT-Fatigue scores (nominal P < 0.05) vs placebo, indicating improved symptom levels. Improvements continued to week 52 in continuous bimekizumab-treated patients and in placebo-bimekizumab switchers. A higher proportion of bimekizumab- vs placebo-randomized patients achieved increasingly stringent thresholds for low spinal and peripheral pain at week 16; this was sustained or improved at week 52. Results were similar for morning stiffness and fatigue. At week 52, over half of patients were considered FACIT-Fatigue responders (≥ 8-point increase in score). Bimekizumab treatment led to rapid improvements in levels of pain and morning stiffness. Substantial improvements were seen in all domains across the full disease spectrum of axSpA and continued to week 52.

The effect of tongue-to-palate on deep neck flexor activity

Deep neck flexor (DNF) muscles contribute to cervical stability and proprioception. Reduced muscle strength and endurance lead to faulty movement patterns, muscle imbalances, and dysfunction. Potentially, the orofacial muscles contribute to cervical strength by providing stability through muscular connections. This study examined effects of tongue muscle activity on cervical spine muscular stiffness. Twenty-three healthy subjects assumed three supine positions [at rest (AR), chin tuck (CT), and head lift (HL)] with and without tongue-to-palate pressure. The DNF stiffness was measured using shear wave elastography. Without tongue-to-palate, stiffness increased with CT and HL compared to AR (p <0.001) but not between CT and HL (p = 0.22). Tongue-to-palate increased stiffness AR (p <0.001) but not during CT (p = 0.95) or HL (p = 0.67). Stiffness levels between the AR and HL conditions during tongue-to-palate performance did not differ (p = 0.734), but CT stiffness was significantly greater than AR (p = 0.029) with tongue-to-palate. Tongue-to-palate AR increases DNF stiffness to a similar level as HL with or without tongue-to-palate, while CT with or without tongue-to-palate resulted in the highest stiffness levels. Tongue-to-palate pressure AR or with CT performance may be alternatives to HL strengthening in healthy necks. This may be a useful strategy to increase cervical stability during loads on the cervical spine.

Novel approaches to assessing brake squeal propensity: comparative evaluation of two index formulations

The persistence of brake squeal as a significant NVH issue within automotive brake systems necessitates the development of robust methods for assessing squeal propensity. This study introduces two novel squeal index formulations for assessment purposes and evaluates their performance against the formulation defined by the SAE J2521 standard. Experimental data essential for formulating the squeal index are collected on a controlled mass-sliding belt experiment. Experiments are performed at three different spring stiffness levels, and squeal index formulations are derived based on time and frequency domain data. The first formulation places particular emphasis on the time domain, explicitly considering the duration of individual squeal events. Conversely, the second formulation is based on the frequency response characteristics of the system, which considers the number of super-harmonic peaks in frequency spectra. To evaluate the performance and discriminatory capabilities of the newly developed squeal index formulations, extensive comparisons are made against the Squeal Index based on the test procedure described in SAE J2521. In conclusion, through meticulous analysis and interpretation of the experimental results, it is discerned that the squeal index formulation defined by time domain exhibits superior efficacy in discerning the nuanced effects of varying design parameters on the occurrence of squeal-like behavior.

Detailed Investigation of Mechanical and Radiation Shielding Efficacy of TeO2-ZnO-Bi2O3-Nb2O5Glasses

This study presents a comprehensive examination of the glass systems consisting of TeO2, ZnO, Bi2O3, and Nb2O5. The objective is to assess their suitability as radiation shielding materials and analyze their mechanical characteristics. Analysis of TZBN1's mass attenuation coefficients (MAC) was conducted using FLUKA modeling and XCOM. The findings indicated that TZBN1 had the highest Mean Absolute Change (MAC) at low energy levels (0.02 MeV), measured 38.547 cm2/g. These findings suggest that TZBN1 has a more favorable photoelectric effect interaction. Over energies beyond 20 MeV, TZBN4 has exceptional performance in comparison to other samples, with a mass attenuation coefficient (MAC) of 0.043996 cm2/g. These findings suggest an improved capacity to provide protection against high-energy photons. The density of the glass substrates is an essential factor, and TZBN4 exhibits a peak density of 6.15 g/cm³. Consequently, it exhibits a reduced gamma-ray transmission factor (TF), thereby underscoring its efficacy in mitigating gamma radiation. Based on the Makishima and Mackenzie model, TZBN1 exhibits the greatest Young's Modulus, measured at around 814.67 kJ/mol per PD. These findings suggest that TZBN1 exhibits the highest level of mechanical strength and stiffness among the glasses examined. In contrast, TZBN4 exhibits the lowest Young's Modulus of 453.47 kJ/mol per PD, making it potentially appropriate for certain applications that need flexibility. The results underscore the importance of glass chemical composition in tailoring materials for radiation protection and mechanical robustness. The glasses composed of TeO2, ZnO, Bi2O3, and Nb2O5, namely TZBN4, are regarded as very promising for applications that need efficient shielding against high-energy photons, while also providing material flexibility and strength. This paper presents a substantial framework for selecting and creating glass materials for the goal of providing safe shielding in the domains of medicine, industry, and nuclear facilities.

The impact of vildagliptin as an add-on therapy on matrix metalloproteinase-14 levels, liver stiffness and subclinical atherosclerosis in adolescents with type 1 diabetes and non-alcoholic steatohepatitis: A randomized controlled trial.

Many patients with type 1 diabetes mellitus (T1DM) met the histological criteria for non-alcoholic steatohepatitis (NASH), which leads to cardiovascular disease morbidity and mortality. Matrix metalloproteinase-14 (MMP-14) is involved in cardiovascular disease and atherosclerosis. To assess the impact of oral dipeptidyl peptidase-4 inhibitor, vildagliptin, as adjunctive therapy on NASH in adolescents with T1DM and its effect on glycaemic control, MMP-14 levels and carotid intima media thickness (CIMT). Sixty adolescents with T1DM and NASH were randomly assigned to receive oral vildagliptin (50 mg once daily) for 6 months or not. Glycated haemoglobin, lipid profile, hepatic steatosis index, triglyceride glucose (TyG) index and MMP-14 levels were assessed. Transient elastography with controlled attenuation parameter (CAP) was performed together with measuring CIMT. By transient elastography, 12 (20%) patients with T1DM with NASH had elevated liver stiffness ≥7 kPa (F2 stage or higher). Baseline MMP-14 was positively correlated to insulin dose (p = 0.016), triglycerides and TyG index, CIMT, liver stiffness and CAP levels among the studied patients (p < 0.001 for all). After 6 months, patients with T1DM on vildagliptin therapy had significantly lower glycated haemoglobin, lipid profile, hepatic steatosis index and TyG index, as well as MMP-14 (p < 0.001). CIMT, liver stiffness and CAP were significantly decreased post-therapy compared with baseline levels and compared with the control group (p < 0.001). Vildagliptin was safe and well-tolerated. Administration of vildagliptin for adolescents with T1DM and NASH improved glycaemic control, dyslipidaemia and MMP-14 levels and decreased liver stiffness and CIMT; hence, reducing subclinical atherosclerosis and disease progression.

Cyclic stretch enhances neutrophil extracellular trap formation

BackgroundNeutrophils, the most abundant leukocytes circulating in blood, contribute to host defense and play a significant role in chronic inflammatory disorders. They can release their DNA in the form of extracellular traps (NETs), which serve as scaffolds for capturing bacteria and various blood cells. However, uncontrolled formation of NETs (NETosis) can lead to excessive activation of coagulation pathways and thrombosis. Once neutrophils are migrated to infected or injured tissues, they become exposed to mechanical forces from their surrounding environment. However, the impact of transient changes in tissue mechanics due to the natural process of aging, infection, tissue injury, and cancer on neutrophils remains unknown. To address this gap, we explored the interactive effects of changes in substrate stiffness and cyclic stretch on NETosis. Primary neutrophils were cultured on a silicon-based substrate with stiffness levels of 30 and 300 kPa for at least 3 h under static conditions or cyclic stretch levels of 5% and 10%, mirroring the biomechanics of aged and young arteries.ResultsUsing this approach, we found that neutrophils are sensitive to cyclic stretch and that increases in stretch intensity and substrate stiffness enhance nuclei decondensation and histone H3 citrullination (CitH3). In addition, stretch intensity and substrate stiffness promote the response of neutrophils to the NET-inducing agents phorbol 12-myristate 13-acetate (PMA), adenosine triphosphate (ATP), and lipopolysaccharides (LPS). Stretch-induced activation of neutrophils was dependent on calpain activity, the phosphatidylinositol 3-kinase (PI3K)/focal adhesion kinase (FAK) signalling and actin polymerization.ConclusionsIn summary, these results demonstrate that the mechanical forces originating from the surrounding tissue influence NETosis, an important neutrophil function, and thus identify a potential novel therapeutic target.

Melatonin mitigates matrix stiffness-induced intervertebral disk degeneration by inhibiting reactive oxygen species and melatonin receptors mediated PI3K/AKT/NF-κB pathway.

Intervertebral disk degeneration (IVDD) may lead to an increase in extracellular matrix (ECM) stiffness, potentially contributing to the progression of the disease. Melatonin reportedly mitigates IVDD; however, its potential to attenuate elevated matrix stiffness-induced IVDD remains unexplored. Therefore, we aimed to investigate whether melatonin can alleviate the progression of IVDD triggered by increased matrix stiffness and elucidate its underlying mechanisms. Nucleus pulposus (NP) tissues were collected from patients, and ECM stiffness, reactive oxygen species (ROS) levels, apoptosis rates, and P65 expression in these tissues with varying Pfirrmann scores were determined. In vitro experiments were conducted to investigate the effects of melatonin on various pathophysiological mechanisms within the NP cells cultured on soft substrates with differing stiffness levels. Our findings revealed a positive correlation between ECM stiffness in human NP tissue and degree of IVDD. In addition, phosphorylation of P65 exhibited a strong association with matrix stiffness. Enhanced levels of ROS and cellular apoptosis were observed within degenerated intervertebral disks. In vitro experiments demonstrated that melatonin significantly inhibited catabolism and apoptosis induced by stiff matrices, along with elevated ROS levels. Furthermore, we observed that melatonin inhibited NP cell catabolism and apoptosis by reducing the melatonin receptors mediated activation of the PI3K/AKT and nuclear factor-kappa B (NF-κB) pathways. Also, we found that the reduction of ROS by melatonin can assist in inhibiting the activation of the NF-κB pathway. The outcomes of the in vivo experiments corroborated the results of the in vitro experiments, illustrating that melatonin treatment could alleviate the compression-induced upregulation of matrix stiffness in NP and IVDD. Collectively, melatonin can potentially alleviate high matrix stiffness-induced IVDD by reducing intracellular ROS levels and inhibiting the PI3K/AKT/NF-κB pathway.NEW & NOTEWORTHY Melatonin mitigates intervertebral disk degeneration (IVDD) induced by matrix stiffness through reactive oxygen species (ROS) reduction. Matrix stiffness is related to increased nucleus pulposus cell ROS, apoptosis, and degeneration. Melatonin inhibits PI3K/AKT/NF-κB pathways via melatonin receptors in a stiff matrix environment. In vivo, melatonin restores disk height and alleviates IVDD progression.

The Impact of DAZZEON αSleep® Far-Infrared Blanket on Sleep, Blood Pressure, Vascular Health, Muscle Function, Inflammation, and Fatigue.

The application of far-infrared blankets has shown certain benefits in health promotion and therapy, such as improving blood circulation and alleviating muscle pain. However, the effects of such blankets on increasing deep sleep, reducing blood pressure, enhancing memory, dilating microvessels for blood flow, reducing chronic inflammation, and decreasing fatigue remain to be studied. We aim to investigate the effects of the DAZZEON αSleep® far-infrared blanket on these indicators. This study adopted a double-blind design, recruiting 24 male participants aged over 45 years, divided into two groups of 12 each: (A) a placebo group and (B) a DAZZEON αSleep® group. The participants used the blanket every night for two weeks, with sleep records taken using a wearable device and blood pressure, blood oxygen levels, arterial stiffness, and surface temperature measured before and after the intervention. Blood samples were collected for an analysis of inflammation and sleep-related blood indicators (serotonin and melatonin), and exercise tests were conducted to assess fatigue improvement. Compared with before the intervention, the blanket significantly increased changes in grip strength and reaction time. Additionally, it significantly increased blood serotonin, melatonin, and nitric oxide concentrations (p < 0.05), thus significantly increasing deep sleep and REM sleep durations (p < 0.05) and improving subjective sleep quality (p < 0.05). This study confirmed that using the DAZZEON αSleep® far-infrared blanket for 14 consecutive days helps to improve blood circulation, reduce vascular age and arterial stiffness, increase serotonin and melatonin levels, and improve sleep quality, as well as enhances muscle strength and reaction time.

Assessing Placental Shear Wave Elastography as a Tool for Evaluating Preeclampsia.

Background Hypertensive disorders of pregnancy, especially its dreaded complication preeclampsia, remain a major cause of morbidity and mortality for both the mother and the fetus. Existing tools for the prediction of preeclampsia remain inadequate in their sensitivity and specificity. Hence, there is an urgent need for a reliable, economically feasible, and objective marker for its diagnosis/early prediction. In this regard, shear wave elastography has shown great promise. Shear wave elastography is a novel method to quantify tissue stiffness, which is objective and has significantly lower inter-observer variability. Objectives We aim to quantify the tissue elasticity using point shear wave elastography (pSWE) in the placentas of diagnosed cases of preeclampsia and to compare them with the placentas of healthy controls in order to evaluate if there is a significant statistical difference between the two. Materials and methods This comparative study was conducted at the Department of Radiodiagnosis, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Pune, India, from August 2022 to July 2024. The study included 60 participants, divided into two groups: 30 patients with preeclampsia and 30 healthy pregnancies. Placental stiffness was measured using a Samsung HS70A ultrasound machine (Samsung Electronics Pvt. Ltd., Seoul, South Korea), and pSWE was performed with a curvilinear probe. Data was analyzed using IBM SPSS Statistics for Windows, Version 21 (Released 2012; IBM Corp., Armonk, New York, United States), and the significance of differences between the two groups was assessed using an independent t-test with a p-value of <0.05, considered statistically significant. Results The mean placental stiffness, measured in kilopascals (kPa), was significantly higher in the preeclampsia group (11.71 ± 1.52 kPa) in comparison to the healthy group (3.36 ± 0.66 kPa) (p = 0.001). Patients suffering from preeclampsia were found to have significantly higher levels of placental stiffness. Conclusion Early diagnosis remains key to managing preeclampsia so that adequate monitoring and treatment could be provided to the patients. Our study showed that there is a significant statistical difference in the placental stiffness in patients with preeclampsia in comparison to a healthy placenta. Hence, shear wave elastography can be used as a supplementary tool to aid in the diagnosis/prediction of preeclampsia.

The impact of various curing methods on the curing process of polymer-fiber composites analyzed using analytical approach

Ti/Gf/Cf represents a novel form of hybrid fiber metal laminates (HFMLs) that successfully blend the benefits of titanium alloy, glass fiber reinforced plastic (GFRP), and carbon fiber reinforced plastic (CFRP). These materials have garnered attention in the field of engineering due to their exceptional levels of stiffness, strength, and shear resistance. The quality of HFMLs during the curing process was significantly impacted by the chosen curing method. Moreover, the use of multiple types of fibers complicated the optimization of curing parameters in HFMLs. A comprehensive study was conducted using a multi-physics field coupling finite element method to investigate the impact of various curing methods on the development of temperature distribution, curing degree, and curing stress in HFMLs during the curing process. By integrating thermal transmission equations, curing kinetics, and viscoelastic mechanical models, a detailed curing simulation model was established. Increasing the cooling rate from 1 °C to 5 °C was shown to raise the maximum curing stress by 4.7 MPa. Additionally, higher curing temperatures were found to induce internal curing stress due to variations in thermal properties. Insufficient insulation times were observed to exacerbate non-uniform temperature distribution and curing degree fields in HFMLs, potentially leading to increased internal stress. To mitigate the generation of large residual stress, it is recommended to lower the heating and cooling rates, reduce curing temperatures, and extend the insulation time appropriately during the curing process of HFMLs. The primary goal of this research was to accurately predict the evolution of curing parameters in HFMLs under different curing regimes, which were impacted by the chosen curing method. The results of the study demonstrated that rapid changes in temperature during heating and cooling stages can lead to uneven curing, resulting in the accumulation of residual stress within the laminates.

Role of inertial nonlinearity and coupling stiffness on a series of coupled harvesters

This study investigates the effect of coupling configuration on a state-of-the-art harvesting system consisting of a series of spring-coupled piezoelectric nonlinear monostable tip-loaded cantilever-based vibration energy harvesters (VEHs). The investigation finds favorable coupling configurations that exploit complex nonlinear interaction for improving system performance. The system model incorporates the beam's geometric nonlinearities in the governing equation using inertial and stiffness nonlinear terms. The study first analytically investigates the effect of grounding stiffness on a single harvester's performance. Then, it numerically investigates the effect of increasing array size and changing stiffness distribution. The study discovers a novel hardening/softening transition phenomenon at a critical grounding stiffness value induced by the inertial nonlinear effect. This critical event also maximizes peak output power near the largest eigenfrequency at an optimum grounding stiffness value. At larger arrays, the peak power shows a complex bifurcation behavior, hinting at the presence of multiple attractors. The numerical study of different stiffness configurations and linearized eigenanalysis reveals the necessity of a multilevel optimization strategy focused on both the stiffness ratio between the coupling springs' and their overall stiffness level. This study bridges the gap between previous studies on spring-coupled linear and bistable arrays, offering new insights into coupled nonlinear interactions and proposing novel optimization strategies.

Comparative Study of Methods for Robot Control with Flexible Joints

Robots with flexible joints are gaining importance in areas such as collaborative robots (cobots), exoskeletons, and prostheses. They are meant to directly interact with humans, and the emphasis in their construction is not on precision but rather on weight reduction and soft interaction with humans. Well-known rigid robot control strategies are not valid in this area, so new control methods have been proposed to deal with the complexity introduced by elasticity. Some of these methods are seldom used and are unknown to most of the academic community. After selecting the methods, we carried out a comprehensive comparative study of algorithms: simple gravity compensation (Sgc), the singular perturbation method (Spm), the passivity-based approach (Pba), backstepping control design (Bcd), and exact gravity cancellation (Egc). We modeled these algorithms using MATLAB and simulated them for different stiffness levels. Furthermore, their practical implementation was analyzed from the perspective of the magnitudes to be measured and the computational costs of their implementation. In conclusion, the Sgc method is a fast and affordable solution if joint stiffness is relatively high. If good performance is necessary, the Pba is the best option.

Biomechanical comparison of two fixation methods for pediatric femoral neck fractures: an in vitro study using ovis aries lambs.

In pediatric patients, femoral neck fracture is a relatively rare injury with a high complication rate despite proper diagnosis and treatment. Fixation of femoral neck fractures is usually performed with screws placed along the neck axis. In this study, we aim to compare two different implants and methods in terms of biomechanics. Twenty-eight right-left fresh femur bones of 6-month-old male Ovis aries lambs grown on the same farm were used. Bones were randomly divided into 4 groups (n=7). In group 1, the Delbet type III femoral neck fracture model was fixed with two 4.5 mm cannulated screws, one screw crossing the physis. In group 2, two 4.5 mm cannulated screws, which did not cross the physis, were used. In group 3, Delbet type III femoral neck fracture model was fixed with a 3.5 mm proximal femoral anatomical plate and five screws, one screw crossing the physis. Finally, in group 4, Delbet type III femoral neck fracture model was fixed with one 3.5 mm proximal femoral anatomical plate and five screws that did not exceed the physis. Biomechanical tests were performed using a Zwick/Roell AllroundLine 100 kN device. While axial failure burden (F = 6.819, p<.05, d = .46) and axial stiffness (F = 3.576, p<.05, d = .30) have been found to be significantly different between the independent treatment groups, axial failure displacement (F = .622, p>.05) and axial failure energy (F = .727, p>.05) have been found not to be significant between the independent groups. The effect sizes of the axial failure load and axial stiffness variables were 0.46 and 0.30, respectively, suggesting a moderate clinical effect. The highest axial failure load was recorded in group 3, while the smallest load was recorded in group 2. Similarly, the axial stiffness level in group 3 was statistically higher than the axial stiffness measurement recorded in group 2, p<.05. Consequently, we found that the biomechanical fixation success was the highest with a 3.5 mm proximal femoral anatomical plate, a 3.5 mm locking screw crossing the physis, and five 3.5 mm screws.

In Vitro Model Integrating Substrate Stiffness and Flow to Study Endothelial Cell Responses.

We present an innovative in vitro model aimed at investigating the combined effects of tissue rigidity and shear stress on endothelial cell (EC) function, which are crucial for understanding vascular health and the onset of diseases such as atherosclerosis. Traditionally, studies have explored the impacts of shear stress and substrate stiffness on ECs, independently. However, this integrated system combines these factors to provide a more precise simulation of the mechanical environment of the vasculature. The objective is to examine EC mechanotransduction across various tissue stiffness levels and flow conditions using human ECs. We detail the protocol for synthesizing gelatin methacrylate (GelMA) hydrogels with tunable stiffness and seeding them with ECs to achieve confluency. Additionally, we describe the design and assembly of a cost-effective flow chamber, supplemented by computational fluid dynamics simulations, to generate physiological flow conditions characterized by laminar flow and appropriate shear stress levels. The protocol also incorporates fluorescence labeling for confocal microscopy, enabling the assessment of EC responses to both tissue compliance and flow conditions. By subjecting cultured ECs to multiple integrated mechanical stimuli, this model enables comprehensive investigations into how factors such as hypertension and aging may affect EC function and EC-mediated vascular diseases. The insights gained from these investigations will be instrumental in elucidating the mechanisms underlying vascular diseases and in developing effective treatment strategies.

Biomechanical effects of hemin and sildenafil treatments on the aortic wall of chronic-hypoxic lambs.

Introduction: Gestation under chronic hypoxia causes pulmonary hypertension, cardiovascular remodeling, and increased aortic stiffness in the offspring. To mitigate the neonatal cardiovascular risk, pharmacological treatments (such as hemin and sildenafil) have been proposed to improve pulmonary vasodilation. However, little is known about the effects of these treatments on the aorta. Therefore, we studied the effect of hemin and sildenafil treatments in the aorta of lambs gestated and raised at highlands, thereby subjected to chronic hypoxia. Methods: Several biomechanical tests were conducted in the descending thoracic aorta (DTA) and the distal abdominal aorta (DAA), assessing 3 groups of study of hypoxic animals: non-treated (Control) and treated either with hemin or sildenafil. Based on them, the stiffness level has been quantified in both zones, along with the physiological strain in the unloaded aortic duct. Furthermore, a morphological study by histology was conducted in the DTA. Results: Biomechanical results indicate that treatments trigger an increment of axial pre-stress and circumferential residual stress levels in DTA and DAA of lambs exposed to high-altitude chronic hypoxia, which reveals a vasodilatation improvement along with an anti-hypertensive response under this characteristic environmental condition. In addition, histological findings do not reveal significant differences in either structure or microstructural content. Discussion: The biomechanics approach emerges as a valuable study perspective, providing insights to explain the physiological mechanisms of vascular function. According to established results, alterations in the function of the aortic wall may not necessarily be explained by morphostructural changes, but rather by the characteristic mechanical state of the microstructural components that are part of the studied tissue. In this sense, the reported biomechanical changes are beneficial in mitigating the adverse effects of hypobaric hypoxia exposure during gestation and early postnatal life.

Effect of inter-module connection properties on structural sway of high-rise modular buildings

The modular steel building is a rapidly evolving prefabricated structural system, consisting of discrete volumetric modules assembled with inter-module connections. Despite numerous studies on the design optimization of inter-module connections, research on the development of realistic connection models and the correlation between connection properties and the overall structural behavior is relatively scarce. This paper introduces a multiple-spring inter-module connection model and supplies detailed property calculations of different load transfer components. The model can effectively simulate different stiffness and strength levels at inter-module connections and predict relative dislocations between assembled modules. The model is then applied to analyze the structural sway of modular buildings under seismic loads. Influences of connection modelling methods and the real connecting abilities on structural sway responses are investigated through comparative analysis of connection and module drift deformations when using conventional pin or rigid constraint connection models and the proposed realistic multiple spring model. Results indicate that simplified pin or rigid constraints cannot accurately represent the actual load transfer mechanisms at inter-module connections. The horizontal link determines the composition extent of horizontally assembled columns and modules. The horizontal shear resistance is closely related to column loads and follows the downwardly increased mode, which induces different structural sway and module drift levels in modular buildings.