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

Localized muscle fatigue arises from interacting central and peripheral mechanisms whose contributions vary with contraction intensity and joint velocity. The four-compartment controller with enhanced recovery (4CCr) model captures these processes but its practical use is limited by parameter identifiability and sensitivity to optimization settings. This study systematically evaluates the robustness of 4CCr parameters across joints, velocities, optimization algorithms, and sample-size subsets. Residual capacity (RC) is extracted from peak isometric torque across five isometric-isokinetic cycles in 32 participants, and the three unknown 4CCr parameters-baseline peripheral fatigue, baseline peripheral recovery, and velocity coefficient-are estimated using genetic algorithm (GA) and particle swarm optimization (PSO). Comprehensive GA hyperparameter sweeps and PSO validation reveal strong equifinality in recovery and velocity coefficient and unexpectedly high stability in fatigue across subjects, velocities, and solvers. Sample-size analyses (N = 10, 14, 18) further confirm that the fatigue parameter converges rapidly with increasing dataset, whereas other two parameters fluctuate substantially across datasets and therefore do not yield consistent physiological interpretations. The recovery analysis indicates that the 4CCr model reflects realistic two-phase recovery, unlike the 3CCr model which recovers rapidly. These findings demonstrate that peripheral fatigue rate is the only well-constrained parameter in the 4CCr muscle fatigue model, and that fixing fatigue parameter enables more reliable optimization of the remaining parameters. This work clarifies parameter identifiability within the 4CCr model and supports the development of a more stable, generalizable fatigue model for digital human simulations and velocity-dependent strength prediction.

Purpose: Cell therapies and 3D bioprinting often require suspended cells to be delivered through needles of 20-gauge and smaller. This often damages cells, affecting their short and long-term viability. Most researchers have attributed this to excessive viscous stresses encountered entering or within the needle, but the experimental evidence contradicts that, as higher viscosity suspension fluids generally yield higher cell viabilities when injected at the same flow rate. We therefore sought to determine the most relevant fluid flow parameter influencing cell mechanical damage.

Methods: A combination of reprocessing published results and cell injection experiments were conducted. Human umbilical vein endothelial cells were suspended in Newtonian fluids of varying viscosities and injected through 30-gauge syringe needles in experiments that controlled for either shear stress or shear rate.

Results: Based on evidence from injection experiments using a variety of fluids, it is shown that shear rate (a kinematic quantity) correlates better with cell viability than shear stress.

Conclusion: Knowledge that shear rate is the influential fluid mechanical parameter governing mechanical damage provides a rational basis for designing injection protocols (injectors and suspension fluid rheological properties) to maximize cell viability.

Prosthetic ankle-foot devices provide valuable assistance for individuals with a unilateral transtibial amputation (TTA) to effectively engage in daily living activities, although users often experience diminished walking performance such as increased metabolic cost, knee joint loading, and dynamic balance asymmetry due to the lack of torque control from commonly prescribed passive devices. Consequently, active powered prosthetic devices have been developed; however, it is unclear how to optimally tune them. The purpose of this study was to identify the optimal ankle torque profile of a powered ankle-foot prosthesis that improves walking performance for individuals with TTA. Specifically, we used a musculoskeletal simulation-based optimization framework to optimize a powered prosthesis torque profile while emulating group averaged kinematics and ground reaction forces. We compared the metabolic cost, knee joint loading, sagittal plane dynamic balance symmetry and torque profiles across the following simulated conditions: a passive prosthesis tracking individuals with TTA walking data, a powered prosthesis tracking able-bodied walking data and a powered prosthesis that separately minimized metabolic cost, knee joint loading, and dynamic balance asymmetry. Distinct torque profiles emerged for each measure, but there was no clear trend in the positive prosthetic work performed, which suggests increased prosthetic work alone is insufficient to improve walking performance. Further analysis showed the prosthetic torque must be properly timed over the gait cycle to improve each measure. This work provides a framework for future work developing customized controllers for powered prostheses to improve various aspects of walking performance of individuals with TTA.

The uncontrolled tipping in the treatment of incisor retraction with clear aligners is still compromising orthodontic treatment. Different countermeasures have been proposed to improve the predictability of aligners.This work inspected the biomechanics of the overcorrection in reducing the tipping angle and moment during incisor retraction with a clear aligner, with in-vitro experiments and finite element analysis. Specifically, the influence of angle, retraction distance, and the combination of both were assessed through in vitro experiments and the simulation. Further computational simulations were conducted to inspect the mechanical performance of clear aligners with different overcorrection angles for a fixed retraction distance of 0.15 mm. As the overcorrection angle increased from 0deg; to 1deg; and 2deg; for the clear aligner with a retraction of 0.15 mm, the tipping angle of the incisor decreased from 0.29deg; to 0.25deg; and 0.21deg;, and the tipping moment in the tooth root decreased from 13.60 N∙mm to 9.38 N∙mm and 6.27 N∙mm. However, the retraction force also decreased from 0.84 N to 0.73 N and 0.47 N, which leads to a trade-off and may result from the increased counteractive moment and decreased force exerted onto the tooth crown by the aligner. In conclusion, this study presents both the benefits and limitations of overcorrection strategies in reducing the tipping angle and moment during incisor retraction using clear aligners, providing biomechanical insight for the optimal design of clear aligners for improving treatment outcomes.

Adolescent females are at a higher risk of anterior cruciate ligament (ACL) injury than males. While prior studies have associated injury timing and menstrual cycle phase, these data are limited by indirect cycle tracking and lack of analysis on ACL structure, mechanics, or composition. Additionally, little is known about how female sex hormones influence the distinct ACL bundles. This exploratory study investigated associations between serum sex hormone concentrations and size, mechanics, and composition of the ACL and its bundles in a female adolescent pig model. Serum from nine adolescent female Yorkshire crossbreed pigs was collected pre-euthanasia and analyzed for levels of estradiol, progesterone, and testosterone. The ACL and its bundles were assessed for size via MRI, mechanics via robotic testing, and composition via biochemical and histological analyses. While individual hormone levels and the estradiol-to-progesterone (E/P) ratio had no association with most metrics, the E/P ratio was significantly associated with ACL size and T2* relaxation time. Higher E/P ratios were negatively associated with AM bundle cross-sectional area (CSA) (R2=0.44) and overall ACL volume (R2=0.49) and positively associated with PL bundle T2* relaxation time (R2=0.69, p < 0.05). Serum E/P ratio was also positively associated with normalized ACL stiffness, but there were no associations observed for tissue composition. The results of this exploratory study indicate that the ACL may be responsive to exposure to the relative concentration of female sex hormone in a bundle-specific manner.

The mechanical response of biological soft tissues is influenced by wall heterogeneity, including spatial variations in wall thickness. Traditional models for homogeneous soft tissues under uniaxial loading predict higher stretch and stress in thinner regions. In prior studies, the role of collagen fibers in regions of thickness transition has been largely neglected or only considered in terms of their effect on anisotropy. Here, we explore the role of collagen fibers as primary load-bearing components across regions of varying wall thickness, using a three-dimensional meso-scale model (MSM) incorporating explicit collagen fiber architecture and a gradual thickness gradient. We examined two distinct collagen fiber configurations across the thickness transition: one featuring abrupt fiber termination and another with fiber continuity. Finite element analysis (FEA) under uniaxial tension revealed that load transfer by the continuous fibers markedly reduced the importance of the change in wall thickness, with stretch differentials dropping from 20.97% (fiber-termination network) to 0.68% (continuous fibers) and stress differentials dropping from ~65% (fiber-termination network) to 2.3% (continuous fibers). Fiber tortuosity delayed the point at which mechanical response was governed by fiber structure. These findings demonstrate the critical role of fiber continuity in reducing stretch and stress gradients across regions of varying wall thickness and clarify the importance of accurately representing fiber architecture when modeling soft tissues with heterogeneous wall thickness.

In light of the recent reprioritization of federal funding, the Journal of Biomechanical Engineering (JBME) reaffirms its commitment to reporting scientific excellence, advancements in knowledge, and technical innovations that benefit healthcare for everyone. Furthermore, we recognize that this commitment to excellent and rigorous science and engineering is supported by promoting diversity, equity, and inclusion, which ensures that advances in biomedical engineering address the distinct health needs of the broadest possible population. In this editorial, we highlight the recent actions that the journal has taken to support diversity and inclusion, including the appointment of Diversity Advocate positions, implementation of a double-blind review process, and publication of special issues on inclusive science and engineering. Finally, we present research and publication recommendations to the broader biomechanical engineering community that collectively embody the core principles of our field and that will lead to more equity and impact in biomechanical engineering.

Atypical femoral fracture (AFF) is a rare fracture associated with prolonged bisphosphonate (BP) treatment that occurs in the subtrochanter and midshaft of the femur. The association of AFF with BP treatment suggests alterations in femoral material properties with treatment. Femoral geometry has also been identified as a potential contributor to AFF. This study aims to demonstrate the novel integration of high-resolution magnetic resonance imaging (MRI) with cohesive extended finite element method (XFEM) to assess AFF. Using this approach, we quantified the independent contributions of femoral geometry and material property distribution to fracture resistance at the AFF site. MRI-based finite element models of female donor femurs incorporating homogeneous and specimen-specific heterogeneous material properties derived from MRI-based bone volume fraction (BVF) were evaluated. To assess the predictive capability of the models, experimental testing of the femur under stance loading was performed. Simulation results showed that when only geometrical properties of the femur were considered anterior bowing angle and neck shaft angle showed negative and positive correlations with fracture load, respectively. Fracture load increased with increasing specimen-specific means BVF. Simulation femoral stiffness and lateral strains where AFF occurs correlated significantly with experimental values. Our findings demonstrate that MRI-based cohesive XFEM can assess crack formation in AFF and highlight the need for considering both geometrical and material properties when assessing AFF risk. This study lays the foundation for MRI-based AFF assessment, which can be extended to MRI-specific measurements that cannot be quantified by other imaging modalities.

Anterior cruciate ligament (ACL) reconstruction in pediatric patients has a higher graft failure rate compared to adults. Restoring joint stability and reducing graft failure is essential. However, how graft biomechanical properties change with age and affect reconstruction outcomes remains unclear. This study investigated the biomechanical development of porcine flexor tendons across skeletal growth and evaluated how graft size and stiffness influence knee biomechanics in a pediatric porcine model. Flexor tendons (n = 57) were harvested from pigs at 0.5, 1.5, 5, and 9 months of age to measure cross-sectional area (CSA), stiffness, and failure load. ACLs in nine early adolescent porcine knees were reconstructed using both 1.5- and 5-month-old (1.5 mo and 5 mo) grafts and tested under anterior-posterior, compressive, and varus-valgus (VV) loading at 40 deg of flexion using a robotic testing system. ACL and graft forces were calculated, and in situ properties were derived from force-displacement curves. Tendon CSA, stiffness, and failure load increased with age, and stiffness associated with CSA. The CSA of 5 mo tendons was 57% greater than that of 1.5 mo tendons, but stiffness increased only 20%. ACL reconstruction with 5 mo grafts resulted in 29% less anterior-posterior tibial translation and 44% higher graft force compared to 1.5 mo grafts. In situ stiffness of 5 mo grafts was 51% higher than 1.5 mo grafts. These findings highlight the differences between tendon size and biomechanical development, which together contribute to the improvements in joint function following ACL reconstruction.

Accurate in vivo characterization of skin mechanical properties is essential for diagnostics and treatment planning across dermatological and surgical applications. Existing noninvasive techniques are limited in capturing the nonlinear and anisotropic behavior of skin. In this work, we propose a Bayesian inference framework that leverages active membranes to induce desired deformations and infer patient-specific skin properties from a measured strain field. A finite element model of skin-membrane interaction, parameterized using the Holzapfel-Gasser-Ogden model, is used to generate strain field data under various membrane actuation conditions. To overcome the computational cost of repeated simulations required for Bayesian sampling, we construct a data-driven surrogate using principal component analysis for dimensionality reduction and Gaussian process regression for rapid evaluation. Our approach enables probabilistic inference of key skin parameters, including shear modulus, fiber stiffness, dispersion, and orientation. An advatange of the proposed method is that inference of skin biomechanics does not require direct force measurements. Rather, the method relies on known properties of active membranes (which can be tested ahead of time). The method does require strain field measurements. Through synthetic studies, we demonstrate that our method accurately recovers most model parameters even under moderate levels of spatially correlated noise, and that multi-frame or multi-membrane observations significantly enhance identifiability. These results establish the potential of active membranes as a viable platform for noninvasive, in vivo skin biomechanics assessment.