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

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.

The optic nerve head (ONH) is subjected to both intra-ocular pressure (IOP) and intracranial pressure (ICP). The translaminar pressure difference (TLPD) is defined as the difference between IOP and ICP. A change in TLPD, whether from changes in IOP or ICP, could subject the lamina cribrosa (LC) to altered deformation, potentially damaging the axons, activating the mechanosensitive glial cells, and promoting remodeling of the connective tissue structures in the ONH. In this study, we applied spectral domain optical coherence tomography (SD-OCT) and digital volume correlation (DVC) to calculate the deformation response of the LC in 7 eyes of 7 patients with normal pressure hydrocephalus (NPH). Radial SD-OCT scans centered on the ONH were acquired prior to and after therapeutic extended cerebrospinal fluid (CSF) drainage. IOP was measured immediately before imaging, and ICP was measured at the beginning and end of the drainage procedure. The procedure led to a mean ICP decrease of 11.24±1.84 mmHg and a small, nonsignificant mean IOP increase of 0.67±2.56 mmHg. ICP lowering produced a significant Ezz=-0.50%±0.47%, Err=0.53%±0.48%, and Eθz=0.35%±0.21% (p≤0.031). A larger compressive Ezz was associated with a larger ICP decrease (p=0.007). Larger Err, Erθ, maximum principal strain, Emax and maximum shear strain, Smax in the plane of the radial scans were associated with a larger increase in a calculated TLPD change (p≤0.035).

Interlobar sliding has long been suspected to help the lungs adapt to changes in thoracic cavity shape by reducing parenchymal distortion. Our previous controlled computational experiment tested the hypothesis that lung lobar sliding reduces parenchymal distortion during breathing, but only the left lung was studied. The goal of this study was to extend this analysis to the right lung which has three lobes and two fissures compared to the left lung's two lobes and single fissure. Finite elastic contact mechanics models of the right lung were used to perform paired subject-specific simulations of lung deformation with and without lobar sliding from end inhale to end exhale at both tidal breathing volumes (n = 8) and breath hold volumes near total lung capacity and functional residual capacity (n = 6). Consistent with the hypothesis, we found that parenchymal distortion, quantified with the spatial mean of the anisotropic deformation index (ADI) throughout each lung model, was lesser in the models with lobar sliding than their nonsliding counterparts (p = 0.008, 13% median difference for tidal breathing and p = 0.03, 19.6% median difference for breath holds). This effect was several times larger than was previously observed in the left lung (p = 0.008, 5.3% median difference for tidal breathing and p = 0.03, 3.2% median difference for breath holds), likely due to the greater number of sliding interfaces in the right lung than the left which better allow the right lung to adapt to the thoracic cavity.

Robot-assisted gait rehabilitation is an increasingly common therapeutic intervention for enhancing locomotion and improving quality of life for children with lower-limb mobility impairments. However, there are few systems specifically designed for pediatric use, and those that do exist are largely cumbersome, bulky, and noncustom devices that ultimately reduce therapy effectiveness. This paper introduces the Cable-Driven Joint System (CDJS), a novel approach for pediatric gait rehabilitation that addresses these shortcomings in a lightweight and compact robotic device using the patient's professionally fitted orthosis. The CDJS consists of a 2.1 kg actuation unit that is held by a clinician which delivers assistive torques through a Bowden cable transmission to a 0.3 kg joint mounted to user-custom bracing. This work details an actuator benchtop evaluation, demonstrating a peak torque of 20 N·m, peak velocity of 7.2 rad/s, bandwidth of 9.7 Hz, and a mass moment of inertia of 58.38 kg cm2. An actuator model was developed and evaluated in simulation, showing a strong correlation with the experimental torque data (R-squared = 0.95) and indicating a transmission efficiency of 72%. In-air gait tracking experiments on an emulated subject showed that the CDJS assisted the subject to track a nominal knee trajectory with an average root-mean-squared error of 2.56 deg at a continuous torque of 1.37 N·m. These results suggest that the cable-driven actuator meets the design requirements for use in pediatric gait rehabilitation and is ready for implementation in clinical device trials.