Journal of Biomechanical Engineering-Transactions of the Asme最新文献

Patients with acute respiratory failure often require supportive mechanical ventilation to maintain adequate gas exchange. Recent studies have shown that multifrequency ventilation (MFV), the technique of presenting multiple simultaneous frequencies in flow or pressure at the airway opening, may provide more uniform ventilation distribution and parenchymal strain throughout the mechanically heterogeneous lung. In this study, we simulated gas flow within a porcine central airway tree, from the trachea to the fifth generation, with dynamic boundary conditions (BCs) during volume-controlled conventional mechanical ventilation (CMV) cycled at 0.27 Hz (16.2 min-1), as well as MFV waveforms comprised of two fast sinusoidal components (i.e., 3.5 Hz and 7.0 Hz) superimposed on the 0.27 Hz CMV waveform. By using forced gas flows at the airway opening of the computational lung model, dynamic pressures at various airway segments were predicted, based on the interactions of internal flow with the downstream elastances and peripheral resistances. Internal airflows were simulated and analyzed in both time- and frequency-domains. The results indicate that MFV resulted in stronger asymmetric flow (i.e., "pendelluft") at end-inspiration and end-expiration. MFV also appeared to augment inlet-outlet phase differences for both pressure and flow compared with CMV, suggesting that MFV may enhance gas mixing, thus facilitating more efficient ventilation.

This study presents a full three-dimensional multiscale computational model of lung parenchyma to investigate how heterogeneous alveolar ventilation generates regions of high stress. The model integrates elastin and collagen fiber mechanics at the alveolar level to capture microstructural interactions. Simulations of nonuniform alveolar pressure, particularly in the presence of atelectasis (collapsed lung regions), reveal significant localized distortions in adjacent normal parenchyma, especially along the atelectatic boundary. Results demonstrate that heterogeneous ventilation induces substantial stress concentrations in surrounding healthy tissue, which may contribute to lung injury and disease progression in acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). A reduced-dimension periacinar pressure model is introduced to provide a simplified yet effective framework for analyzing these mechanical interactions. Notably, the model shows that even under seemingly normal transmural pressures, alveolar collagen fibers near atelectatic regions experience extreme tensile stresses, which could be misinterpreted as microvolutrauma despite originating from atelectasis. These findings underscore the critical role of heterogeneous ventilation in driving injurious mechanical forces within the lung, highlighting the need for ventilation strategies that minimize airway closure or alveolar derecruitment.

Atherosclerotic plaque rupture is the precipitating event in most acute coronary syndromes. As rupture results from the material failure of arterial tissue under mechanical loading, in vivo image-based techniques that can accurately characterize arterial material stiffness offer potential in risk-stratifying lesions. This study developed and validated a novel magnetic resonance (MR) image-based computational framework to evaluate the material stiffness of vascular tissue. Porcine carotid arteries (n = 4) were subjected to biaxial mechanical testing, followed by MR image acquisition under controlled loading. Best-fit material parameters for an anisotropic material model were estimated via regression analysis on the biaxial data. A deformable image registration technique, termed hyperelastic warping, was utilized to derive strain fields from the MR images and integrated with an inverse parameter estimation algorithm to identify the parameters for the same constitutive model. Experimentally and warping-estimated material stiffness values (tangent moduli) were not significantly different at physiologic lumen pressures of 80 (0.36 ± 0.15 and 0.48 ± 0.20 MPa; p = 0.14) and 120 mmHg (0.64 ± 0.27 and 0.73 ± 0.36 MPa; p = 0.60). The warping-directed inverse modeling framework identified subtle, but observable variations in material stiffness within a sample and accurately illustrated the physical influence of loading conditions on those properties. Collectively, these results demonstrated the robustness of an innovative approach to characterize nonlinear, hyperelastic behaviors of arterial tissue and quantify material stiffness directly from image data.

Mechanical stress is an important feature of brain tissue, which may play key roles in brain development and brain injury. Here, we characterize residual stresses in gray matter and white matter in the mouse brain, which has a smooth (lissencephalic) cortical surface, and the brain of the Yucatan minipig which has a folded (gyrencephalic) cortex. Stresses are estimated from the deformed shape of tissue cylinders extracted from the brain using a biopsy needle and imaged with high-resolution magnetic resonance imaging (MRI). We use finite element (FE) simulations to reconstruct the stress state of tissue sections in the intact brain from images of corresponding sections of the deformed excised tissue. In both adult mouse and minipig brains, cortical gray matter exhibited predominantly compressive stresses, while white matter exhibited strongly anisotropic tensile stresses. The direction of maximum tension in white matter generally aligns with axon orientation as observed with diffusion MRI in the minipig. These stress patterns (compressive in cortical gray matter, tensile along axons) are consistent with hypotheses of constrained cortical expansion and tension-induced axonal growth during brain development. These findings offer new insights into the biomechanical factors underlying brain morphogenesis, with implications for understanding neurodevelopmental disorders, predicting brain injuries, and planning neurosurgical interventions.

The present work characterized mechanical properties of human and porcine cornea along nasal-temporal (NT) and superior-inferior (SI) directions. Because of easy accessibility and comparable dimensions, porcine cornea has been widely used for investigating human corneal properties. Here, similarities and differences between human and porcine corneal biomechanics were characterized using a biaxial testing machine (ElectroForce Planar Biaxial TestBench, TA Instruments, New Castle, DE) and a uniaxial testing device (RSA-G2 Solids Analyzer, TA Instruments, New Castle, DE). Furthermore, transmission electron microscopy (TEM) was done to characterize the microstructure of samples. The biaxial and uniaxial experiments showed that neither human nor porcine cornea had anisotropic tensile properties along SI and NT directions. The tensile properties obtained from uniaxial tests were significantly lower than biaxial measurements (P < 0.05). Both testing methods gave significantly larger peak stress and tangent modulus for human cornea (p < 0.05). In comparison with those of porcine cornea, the human corneal collagen fibril diameter (FD), interfibrillar spacing (IFS), and lamellar projected thickness were significantly smaller (P < 0.05). The lamellar projected thickness of each species along SI and NT directions was significantly different (P < 0.05). The differences and similarities between mechanical response of porcine and human cornea were discussed in terms of microstructure of their extracellular matrices. It was concluded that improving awareness among researchers about mechanical differences between human and porcine cornea is essential.

Insufficient oxygenation in the lamina cribrosa (LC) may contribute to axonal damage and glaucomatous vision loss. To understand the range of susceptibilities to glaucoma, we aimed to identify key factors influencing LC oxygenation and examine if these factors vary with anatomical differences between eyes. We reconstructed three-dimensional, eye-specific LC vessel networks from histological sections of four healthy monkey eyes. For each network, we generated 125 models varying vessel radius, oxygen consumption rate, and arteriole perfusion pressure. Using hemodynamic and oxygen supply modeling, we predicted blood flow distribution and tissue oxygenation in the LC. ANOVA assessed the significance of each parameter. Our results showed that vessel radius had the greatest influence on LC oxygenation, followed by anatomical variations. Arteriole perfusion pressure and oxygen consumption rate were the third and fourth most influential factors, respectively. The LC regions are well perfused under baseline conditions. These findings highlight the importance of vessel radius and anatomical variation in LC oxygenation, providing insights into LC physiology and pathology. Pathologies affecting vessel radius may increase the risk of LC hypoxia, and anatomical variations could influence susceptibility. Conversely, increased oxygen consumption rates had minimal effects, suggesting that higher metabolic demands, such as those needed to maintain intracellular transport despite elevated intra-ocular pressure (IOP), have limited impact on LC oxygenation.

Assessing movement biomechanics is important for understanding healthy locomotion, injury or disease progression, and recovery. However, laboratory- or clinic-based studies fail to capture the ecological factors of real-world activity. Advancements in wearable sensors provide an opportunity to capture movement biomechanics in these settings. This study demonstrates the capacity of a wearable system to measure patellar and Achilles tendon kinetics via tensiometry as well as knee and ankle kinematics via inertial measurement units (IMUs) while walking across varied terrains, including level ground, sloped pavement, and stairs. The wearable system successfully captured time-varying tendon loading over the walking gait cycle. Both patellar and Achilles tendon loading showed distinct sensitivities to changes in slope and stairs. Importantly, these tendon loading patterns correspond well with prior measurements of knee extension and ankle plantarflexion moment profiles obtained via traditional motion analysis. This represents a significant advancement over studies that relied on traditional complex, immobile equipment to obtain comparable results. The portability of the wearable system may allow for objective assessments of human performance, injury risk, functional adaptation due to injury, and treatment response in real-world environments.

In 1926, Cecil D. Murray published a fundamental law of physiology relating the form and function of branched vessels. Murray's Law predicts that the diameter of a parent vessel branching into two child branches is mathematically related by a cube law based on parabolic flow and power minimization with vascular volume. This law is foundational for computational analyses of branching vascular structures. However, pulmonary arteries exhibit morphometric and hemodynamic characteristics that may deviate from classical predictions. This study investigates the morphometry of pulmonary arterial networks, examining relationships between parent and child vessel diameters across species. We analyzed three-dimensional segmentations of pulmonary arterial geometries from healthy subjects across four species: human (n = 7), canine (n = 5), swine (n = 4), and murine (n = 3). Our findings reveal an average exponent value of 2.31(±0.60) in human, 2.13(±0.54) in canine, 2.10(±0.49) in swine, and 2.59(±0.58) in murine, all lower than the predicted value of 3.0 from Murray's Law. Extending Murray's Law to fully developed pulsatile flow based on minimal impedance, we show that mean flow is proportional to radius raised to a power between 2.1 and 3, depending on the Womersley number. Our findings suggest that while Murray's Law provides a useful baseline, pulmonary artery (PA) branching follows a different optimization principle depending on Womersley number. This study contributes to a deeper understanding of pulmonary arterial structure-function relationships and implications for vascular disease modeling.

Breast reconstruction using tissue expanders is the primary treatment option following mastectomy. Although skin growth in response to chronic supra-physiological stretch is well-established, individual patient factors such as breast shape, volume, skin prestrain, and mechanical properties, create unique deformation and growth patterns. The inability to predict skin growth and deformation prior to treatment often leads to complications and suboptimal esthetic outcomes. Personalized predictive simulations offer a promising solution to these challenges. We present a pipeline for predictive computational models of skin growth in tissue expansion. At the start of treatment, we collect three-dimensional (3D) photos and create an initial finite element model. Our framework accounts for uncertainties in treatment protocols, mechanical properties, and biological parameters. These uncertainties are informed by surgeon input, existing literature on mechanical properties, and prior research on porcine models for biological parameters. By collecting 3D photos longitudinally during treatment, and integrating the data through a Bayesian framework, we can systematically reduce uncertainty in the predictions. Calibrated personalized models are sampled using Monte Carlo methods, which require thousands of model evaluations. To overcome the computational limitations of directly evaluating the finite element model, we use Gaussian process surrogate models. We anticipate that this pipeline can be used to guide patient treatment in the near future.

Endovascular procedures require sheaths with contradictory mechanical properties: flexibility for navigation through tortuous vessels, yet rigidity for device delivery. Current approaches rely on multiple device exchanges, increasing procedural time, and complication risks. Here we present a novel endovascular sheath design scheme with dynamically controllable flexural rigidity along its entire length. The device incorporates axially aligned metal string arrays between inner and outer lumens, enabling transition between flexible and rigid states through suction actuation. Three-point bend testing demonstrated that actuation increases flexural rigidity from the range associated with diagnostic catheters to that associated with support sheaths. In simulated contralateral access procedures, the device reduced access time to 1/3 of the time required when using conventional approaches. in vivo porcine studies validated the sheath's ability to navigate tortuous anatomy in its flexible state and successfully support advancement of increasingly rigid therapeutic devices when actuated. Technology enables single-sheath delivery of treatment, potentially reducing procedural complexity, decreasing complication rates, and improving patient outcomes across various endovascular interventions. This design represents a promising approach to combining catheter and sheath design that benefits both peripheral and neurovascular procedures.