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

The respiratory system depends on complex biomechanical processes to enable gas exchange. The mechanical properties of the lung parenchyma, airways, vasculature, and surrounding structures play an essential role in overall ventilation efficacy. These complex biomechanical processes, however, are significantly altered in chronic obstructive pulmonary disease (COPD) due to emphysematous destruction of the lung parenchyma, chronic airway inflammation, and small airway obstruction. Recent advancements in computed tomography (CT) and magnetic resonance imaging (MRI) acquisition techniques, combined with advanced image post-processing algorithms and deep neural networks, have enabled comprehensive quantitative assessment of lung structure, tissue deformation, and lung function at the voxel level. These methods have led to better phenotyping, therapeutic strategies, and refined our understanding of pathological processes that compromise pulmonary function in COPD. In this review, we discuss recent developments in imaging and image processing methods for studying pulmonary biomechanics with a specific focus on clinical applications for COPD, including the assessment of regional ventilation, planning of endobronchial valve treatment, prediction of disease onset and progression, sizing of lungs for transplantation, and guiding mechanical ventilation. These advanced image-based biomechanical measurements, when combined with clinical expertise, play a critical role in disease management and personalized therapeutic interventions for patients with COPD.

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.

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.

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.

Blood pressure gradient (ΔP) across an aortic coarctation (CoA) is an important measurement to diagnose CoA severity and guide treatment. While invasive cardiac catheterization is the clinical gold-standard for measuring ΔP, it requires anesthesia and does not capture the effects of daily activity or exercise, potentially underestimating the disease's functional burden. This study aimed to identify patients with functionally significant CoA by evaluating exercise-induced ΔP using a hybrid mock circulatory loop (HMCL). Patient-specific aorta geometries (N = 5) of patients with CoA were generated from 4D-Flow magnetic resonance imaging (MRI) scans, then three dimensional (3D)-printed to create compliant aortic phantoms. The phantoms were incorporated into an HMCL with flow and pressure waveforms tuned to patient-specific rest and exercise states. Matched fluid-structure interaction (FSI) simulations were performed using simvascular for comparison. Results showed that mean ΔP increased nonlinearly with cardiac output (CO), with trends differing between patients. HMCL and FSI simulations exhibited excellent agreement in trends of ΔP change with CO, with minimal error of 1.6±1.1 mmHg. This study emphasizes the need for assessing exercise CoA hemodynamics beyond resting ΔP measurements. Overall, HMCLs and FSI simulations enable assessment of patient-specific hemodynamic response to exercise unattainable in clinical practice, thereby facilitating a comprehensive noninvasive assessment of CoA severity. Further, the excellent agreement between HMCL and FSI results indicates that our validated FSI approach can be used independently to assess exercise CoA hemodynamics hereafter, eliminating the need for repeated complex HMCL experiments.