Journal of biomechanics最新文献

Damage-accumulation failure models are broadly used to examine tissue property changes caused by mechanical loading. However, damage accumulation models are purely phenomenological. The underlying justification in using this type of model is often that damage occurs to the extracellular fibers and/or cells which changes the fundamental mechanical behavior of the system. In this work, we seek to align damage accumulation models with microstructural models to predict alterations in the mechanical behavior of biological materials that arise from structural heterogeneity associated with nonuniform remodeling of tissues. Further, we seek to extend this multiscale model toward assessing catastrophic failure events such as cerebral aneurysm rupture. First, we demonstrate that a model made up of linear elastin and actin and nonlinear collagen fibers can replicate bot the pre-failure and failure tissue-scale mechanics of uniaxially-stretched cerebral aneurysms. Next, we investigate how mechanical heterogeneities, like those observed in cerebral aneurysms, influence fiber and tissue failure. Notably, we find that failure occurs and the interface between regions of high and low material stiffness, suggesting that spatial mechanical heterogeneity influences aneurysm failure behavior. This model system is a step toward linking structural changes in growth and remodeling to failure properties.

Storage solutions have a significant impact on the physiological properties of saphenous veins (SV), yet their effects on the biomechanics remained unclear. This study investigated how different storage solutions affect the biomechanical properties of SV. The goal was to find a solution that minimally impacts SV biomechanics, providing an effective method for SV preservation. A total of 108 SV samples (54 axial, 54 circumferential) were randomly divided into four groups: Baseline (tested within 24 h after surgical removal), and three stored for 72 h-sodium lactated ringer's solution (SLR), physiological saline (PS), and Air. Uniaxial tensile experiments were performed, and differences in elastic modulus, maximum stress, and average stress-strain curves were evaluated. In the axial direction, the elastic modulus of SVs stored in SLR was significantly higher than in PS (7.21 ± 2.78 MPa vs. 3.90 ± 1.54 MPa, p = 0.009) and similar to Baseline (vs. 8.52 ± 3.43 MPa), while the PS group did not differ significantly from the Air group (3.90 ± 1.54 MPa vs. 2.50 ± 1.34 MPa, p > 0.99). The maximum stress in SLR was similar to Baseline (1.92 ± 0.82 MPa vs. 1.91 ± 0.58 MPa) and significantly higher than in PS (vs. 1.05 ± 0.56 MPa, p = 0.002). Similar trends could also be observed in the circumferential direction. PS significantly impairs the mechanical performance of SVs, while short-term storage in SLR can effectively preserve the biomechanical characteristics of SVs. SLR may be considered as an effective short-term storage solution for SV.

Selective antegrade cerebral perfusion (SACP) is a protective procedure to ascertain adequate brain perfusion during aortic arch surgeries requiring moderate hypothermic circulatory arrest. SACP entails catheterization of arteries feeding the brain, which can be done bilaterally (bSACP) or unilaterally (uSACP), but there is no consensus on when to use each approach. bSACP may increase the risk of embolization, while uSACP risks hypoperfusion due to insufficient perfusion pressure in the contralateral hemisphere, since a single catheter must perfuse both hemispheres. We developed and tested the feasibility of a new method for predicting cerebral perfusion pressures (CPP) during SACP, which could potentially aid clinicians in preoperatively identifying which SACP approach to use. Feasibility of the method was evaluated in five patients eligible for aortic arch surgery (65 ± 7 years, 3 men). Patients were investigated preoperatively with computed tomography angiography (CTA) and 4D flow magnetic resonance imaging (MRI) to assess patient-specific arterial anatomy and blood flows. From the imaging, computational fluid dynamics (CFD) simulations estimated the patients' vascular resistances. Applying these resistances and intraoperative SACP pressure/flow settings to the model's boundary conditions allowed for predictions of contralateral CPP during SACP. Predicted pressures were compared to corresponding intraoperative pressure measurements. The method showed promise for predicting contralateral CPP during both uSACP (median error (range): 2.4 (-0.2-18.0) mmHg) and bSACP (0.8 (-3.3-5.4) mmHg). Predictions were most sensitive to collateral artery size. This study showed the feasibility of CPP predictions of SACP, and presents key features needed for accurate modelling.

Although there is currently sufficient information on various parameters of capillary blood flow, including the average values of blood velocity, there is no data on the dynamics of velocity and the mechanisms of its modulation in various parts of the capillary. The main idea of this work is to develop a tool and image data processing to study the characteristics of the capillary blood flow dynamics. In this study, using the developed method of high-speed videocapillaroscopy, the red blood cells (RBC) velocities in the arterial and venous parts of the nailfold capillaries were compared and a time-frequency analysis of the dynamics of the velocity signals with the calculation of phase coherence was performed. We indicated that the velocity in the arterial part is twice as high and that the ratio of velocities in the arterial and venous parts is stable regardless of the local velocity. This study also empirically confirms the similarity between the oscillations of blood flow in different parts of the capillary and the synchronization of the velocity phases. We believe that the determination of the absolute velocity characteristics of blood flow, together with the mechanisms of its regulation and the ratio of velocities in the arterial and venous parts, can act as a diagnostic approach.

The assessment of smoothness, range of motion (ROM), and head repositioning accuracy (HRA) has gained attention in identifying sensorimotor impairments. Uncertainty persists on the approach for acquiring reliable measures, including choice of smoothness metric, normalization factors, and the required number of measurements for reliable results. This study aimed to address this uncertainty. Thirty healthy participants were included in this single-session randomized cross-over study. The experiment consisted of two parts. One focused on the test-retest assessment of head ROM into right rotation to the end of range from a neutral position using a self-selected movement speed and the HRA when returning to the start-position. In the other part, participants repeated the previous tasks and performed head rotations at slower and faster speeds than their self-selected pace and to the beat of a metronome. All tasks were repeated ten times. For the test-retest, the inter-class-correlation (ICC) values for ROM were between 0.84-0.91, 0.20-0.31 for HRA, and 0.65-0.90 for jerk for 1-10 repetitions. Normalizing jerk through v_mean and v_peak had similar variability and appeared equally valid for our data. However, normalizing by v_max ensures desirable properties in the smoothness metric. Lower variability was observed when standardizing movements using a metronome. Based on test-retest findings, three repetitions are recommended, as ICC values show marginal improvement beyond 2-3 repetitions, providing limited additional value.

This study proposes a novel method for evaluating the risk of adverse events (AE) in patients with coronary stenosis based on the morphology and hemodynamics along a whole coronary artery. Twenty-eight specific coronary artery tree models with different stenotic degrees are established from the CCTA images and divided into AE group and Non-AE group. Pressures are obtained by computational fluid dynamics method. The left anterior descending branches are divided equidistantly along the centerline. The characteristic diameters of each segment are measured and normalized to standard the patient-specific coronary arteries as characteristic straight pipes with variable cross-sections. Based on the energy loss theory, the normalized characteristic diameters ( [Formula: see text] ) and pressure drops (Δp_i) of each segment are fitted to a binomial equation. The differences of binomial coefficients between the two groups are compared. The results show that: [Formula: see text] changes suddenly in the lesions part and Δp_i fluctuates in the posterior half of lesions part and its upstream and downstream. There is a significant difference in the ratio of two binomial equation coefficients, which represents the combination of local resistance coefficient, length, flow rate and maximum characteristic diameter of the standard pipe (0.93 ± 0.16 vs. 1.42 ± 0.58, p = 0.0003). This method emphasizes the influences of stenosis on the whole coronary artery, and reflects the cardiac function requirements of the stenotic coronary artery from the patient itself. The ratio of two binomial equation coefficients can supplement the information obtained by existing detection methods and may help evaluate the risk of AEs.

In-stent restenosis represents a major cause of failure of percutaneous coronary intervention with drug-eluting stent implantation. Computational multiscale models have recently emerged as powerful tools for investigating the mechanobiological mechanisms underlying vascular adaptation processes during in-stent restenosis. However, to date, the interplay between intervention-induced inflammation, drug delivery and drug retention has been under-investigated. Here, an original patient-specific multiscale agent-based modelling framework was developed to investigate the interplay between drug release, plaque composition and intervention-induced inflammation on in-stent restenosis following drug-eluting stent implantation. The framework integrated a finite element simulation of stent expansion, with a drug transport simulation and an agent-based model of cellular dynamics. A patient-specific coronary cross-section with heterogeneous diseased tissue was considered and rigorously analyzed through a variety of scenarios, including different plaque compositions and different inflammatory responses. The analysis revealed three significant findings: (i) calcifications substantially impeded drug transport, resulting in drug-depleted regions and reduced stent efficacy; (ii) by impacting drug transport, variations in plaque composition influenced arterial wall response, with the fully-calcific scenario showing the greatest lumen area reduction; (iii) the impact of different drug receptor saturation conditions (obtained with different plaque compositions) was particularly evident under conditions of persistent inflammatory state. This study represents a significant advancement in multiscale modelling of in-stent restenosis following drug-eluting stent implantation. The results obtained provided deeper insights into the complex interactions among patient-specific plaque composition, inflammation and drug retention, suggesting a patient-specific management of the intervention, particularly in cases of complex disease.

Identifying measures which accurately quantify reactive balance adaptation during walking is essential to understand how emerging perturbation-based gait paradigms impact stability over the course of an intervention. These perturbation paradigms have shown promise in reducing falls for numerous clinical populations, however tracking progress in objective terms throughout an intervention remains challenging. Whole body angular momentum (H) may be particularly suited to detect subtle adaptations in the reactive balance response and is applicable within numerous perturbation environments. We assessed the ability of young healthy adults to adapt to varying intensities of discrete, unexpected, treadmill-based perturbations directed mediolaterally, anteriorly, and posteriorly during a single session while ambulating at their comfortable walking speed. We assessed corrective step length and width, trunk deviation and flexion, peak H over a stride, peak-to-peak differences in whole-body angular momentum over a stride (H_R), and the participants ability to maintain their H trajectory within two standard deviations of their normal (PNT). Measures derived from H, particularly H_R and PNT, demonstrated significant changes with increasing intensity and repetition. Corrective step length and width, trunk deviation and flexion, and peak H also demonstrated significant, but weaker, differences with increasing intensity and repetition. Derivatives of H are sensitive to changes in intensity and repetition, particularly when assessed as peak-to-peak differences and ability to maintain a normal trajectory over a stride. These measures may be utilized to detect changes in reactive balance during perturbation-based gait paradigms.