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

Ascending thoracic aortic aneurysms (aTAAs) can lead to life-threatening dissection and rupture. Recent studies have highlighted aTAA mechanical properties as relevant factors associated with progression. The aim of this study was to quantify in vivo aortic wall stretch in healthy participants and aTAA patients using displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging. Moreover, aTAA wall stretch between surgical and nonsurgical patients was investigated. Finally, DENSE measurements were compared to reference-standard mechanical testing on aTAA specimens from surgical repairs. In total, 18 subjects were recruited, six healthy participants and 12 aTAA patients, for this prospective study. Electrocardiogram-gated DENSE imaging was performed to measure systole-diastole wall stretch, as well as the ratio of aTAA stretch to unaffected descending thoracic aorta stretch. Free-breathing and breath-hold DENSE protocols were used. Uniaxial tensile testing-measured indices were correlated to DENSE measurements in five harvested specimens. in vivo aortic wall stretch was significantly lower in aTAA compared to healthy subjects (1.75±1.44% versus 5.28±1.92%, respectively, P = 0.0004). There was no correlation between stretch and maximum aTAA diameter (P = 0.56). The ratio of aTAA to unaffected thoracic aorta wall stretch was significantly lower in surgical candidates compared to nonsurgical candidates (0.993±0.011 versus 1.017±0.016, respectively, P = 0.0442). Finally, in vivo aTAA wall stretch correlated to wall failure stress and peak modulus of the intima (P = 0.017 and P = 0.034, respectively), while the stretch ratio correlated to whole-wall thickness failure stretch and stress (P = 0.013 and P = 0.040, respectively). Aortic DENSE has the potential to assess differences in aTAA mechanical properties and progressions.

Soft biological tissues often function as highly deformable membranes in vivo and exhibit impressive mechanical behavior effectively characterized by planar biaxial testing. The Generalized Anisotropic Inverse Mechanics (GAIM) method links full-field deformations and boundary forces from mechanical testing to quantify material properties of soft, anisotropic, heterogeneous tissues. In this study, we introduced an orthotropic constraint to GAIM to improve the quality and physical significance of its mechanical characterizations. We evaluated the updated GAIM method using simulated and experimental biaxial testing datasets obtained from soft tissue analogs (PDMS and TissueMend) with well-defined mechanical properties. GAIM produced stiffnesses (first Kelvin moduli, K1) that agreed well with previously published Young's moduli of PDMS samples. It also matched the stiffness moduli determined via uniaxial testing for TissueMend, a collagen-rich patch intended for tendon repair. We then conducted the first biaxial testing of TissueMend and confirmed that the sample was mechanically anisotropic via a relative anisotropy metric produced by GAIM. Next, we demonstrated the benefits of full-field laser micrometry in distinguishing between spatial variations in thickness and stiffness. Finally, we conducted an analysis to verify that results were independent of partitioning scheme. The success of the newly implemented constraints on GAIM suggests notable potential for applying this tool to soft tissues, particularly following the onset of pathologies that induce mechanical and structural heterogeneities.

This study proposes a numerical approach for simulating bone remodeling in lumbar interbody fusion (LIF). It employs a topology optimization method to drive the remodeling process and uses a pixel function to describe the structural topology and bone density distribution. Unlike traditional approaches based on strain energy density or compliance, this study adopts von Mises stress to guide the remodeling of LIF. A novel pixel interpolation scheme associated with stress criteria is applied to the physical properties of the bone, directly addressing the stress shielding effect caused by the implanted cage, which significantly influences the bone remodeling outcome in LIF. Additionally, a boundary inverse approach is utilized to reconstruct a simplified analysis model. To reduce computational cost while maintaining high structural resolution and accuracy, the scaled boundary finite element method (SBFEM) is introduced. The proposed numerical approach successfully generates results that closely resemble human lumbar interbody fusion.

Pulmonary valves do not display a fibrous annulus as do other valves in the heart; thus, pulmonary valves can be implanted at multiple orientations and locations within the right ventricular outflow tract (RVOT). This gives surgeons more freedom when implanting the valve but it also results in uncertainties regarding placement, particularly with respect to valve orientation. We investigate the pulmonary artery hemodynamics and valve leaflet dynamics of pulmonary valve replacements (PVRs) with various orientations via fluid-structure interaction (FSI) models. A canonical model of the branching pulmonary artery is coupled with a dynamic model of a pulmonary valve, and from this we quantify the effect of valve implant orientation on the postvalvular hemodynamics and leaflet dynamics. Metrics such as turbulent kinetic energy (TKE), branch pulmonary artery flow distributions, projected valve opening area (PVOA), and pressure differentials across the valve leaflets are analyzed. Our results indicate that off-axis orientation results in higher pressure forces and flow and energy asymmetry, which potentially have implications for long-term durability of implanted bioprosthetic valves.

Fatigue failure in biological soft tissues plays a critical role in the etiology of chronic soft tissue injuries and diseases such as osteoarthritis (OA). Understanding failure mechanisms is hindered by the decades-long timescales over which damage takes place. Analyzing the factors contributing to fatigue failure requires the help of validated computational models developed for soft tissues. This study presents a framework for fatigue failure of fibrous biological tissues based on reaction kinetics, where the composition of intact and fatigued material regions can evolve via degradation and breakage over time, in response to energy-based fatigue and damage criteria. Using reactive constrained mixture theory, material region mass fractions are governed by the axiom of mass balance. Progression of fatigue is controlled by an energy-based reaction rate, with user-selected probability functions defining the damage propensity of intact and fatigued material regions. Verification of this reactive theory, which is implemented in the open-source FEBio finite element software, is provided in this study. Validation is also demonstrated against experimental data, showing that predicted damage can be linked to results from biochemical assays. The framework is also applied to study fatigue failure during frictional contact of cartilage. Simulating previous experiments suggests that frictional effects slightly increase fatigue progression, but the main driver is cyclic compressive contact loading. This study demonstrated the ability of theoretical models to complement and extend experimental findings, advancing our understanding of the time progression of fatigue in biological tissues.

Alzheimer's disease is a progressive degenerative condition that has various levels of effect on one's memory. It is thought to be caused by a buildup of protein in small fluid-filled spaces in the brain called perivascular spaces (PVS). The PVS often takes on the form of an annular region around arteries and is used as a protein-clearing system for the brain. To analyze the modes of mass transfer in the PVS, a digitized scan of a mouse brain PVS segment was meshed and used for computational fluid dynamics (CFD) studies. Tandem analyses were then carried out and compared between the mouse PVS section and a cylinder with commensurate dimensionless parameters and hydraulic resistance. The geometry pair was used to first validate the CFD model and then assess mass transfer in various advection states: no-flow, constant flow, sinusoidal flow, sinusoidal flow with zero net solvent flux, and an anatomically correct asymmetrical periodic flow. Two mass transfer situations were considered, one being a protein build-up and the other being a protein blend-down using a multitude of metrics. Bulk arterial solute transport was found to be advection-controlled. The consideration of temporal evolution and trajectories of contiguous protein bolus volumes revealed that flow pulsation was beneficial at bolus break-up and that additional local wall curvature-based geometry irregularities also were. Using certain measures, local solute peak concentration blend-down appeared to be diffusion-dominated even for high Peclet numbers; however, bolus size evolution analyses showed definite advection support.

Crouch gait is one of the most common compensatory walking patterns found in individuals with neurological disorders, often accompanied by their limited physical capacity. Notable kinematic characteristics of crouch gait are excessive knee flexion during stance and reduced range of motion during swing. Knee exoskeletons have the potential to improve crouch gait by providing precisely controlled torque assistance directly to the knee joint. In this study, we implemented a finite-state machine-based impedance controller for a powered knee exoskeleton to provide assistance during both stance and swing phases for five children and young adults who exhibit chronic crouch gait. The assistance provided a strong orthotic effect, increasing stance phase knee extension by an average of 12 deg. Additionally, the knee range of motion during swing was increased by an average of 15 deg. Changes to spatiotemporal outcomes, such as preferred walking speed and percent stance phase, were inconsistent across subjects and indicative of the underlying intricacies of user response to assistance. This study demonstrates the potential of knee exoskeletons operating in impedance control to mitigate the negative kinematic characteristics of crouch gait during both stance and swing phases of gait.

This study aims to explore the effects of helmet structure designs and wearing modes on the protective performance of safety helmets under the impact of falling objects. Four helmet types (no helmet, V-shaped, dome-shaped, and motorcycle helmets) and five wearing modes (left and right tilt by 5 deg, backward tilt by 15 deg, 0 deg without chin strap, 0 deg with chin strap) were included in this study. The axial impact of a concrete block under various impact velocities was simulated. The results indicate that the energy absorption and shock mitigation effects of the foam cushion are superior to those of the suspension system in traditional industrial safety helmets. The structure of the top of V-shaped helmets is designed to withstand greater impact. Regarding the wearing mode, the helmet strap's deflection angle increases stress in the brain tissue and skull, heightens intracranial pressure, and causes pressure diffusion toward the forehead.

The purpose of this study was to identify side-to-side and sex-based differences in hip kinematics during a unilateral step-up from deep flexion. Twelve (eight men, four women) asymptomatic young adults performed a step ascent motion while synchronized biplane radiographs of the hip were collected at 50 images per second. Femur and pelvis position were determined using a validated volumetric model-based tracking technique that matched digitally reconstructed radiographs created from subject-specific computed tomography (CT) bone models to each pair of synchronized radiographs. Hip kinematics and side-to-side differences were calculated and a linear mixed effects model evaluated sex-based differences. Women were on average 10.2 deg more abducted and 0.2 mm more medially translated than men across the step up motion (p < 0.001). Asymmetry between hips was up to 14.1 ± 12.1 deg in internal rotation and 1.3 ± 1.4 mm in translation. This dataset demonstrates the inherent asymmetry during movements involving unilateral hip extension from deep flexion and may be used provide context for observed kinematics differences following surgery or rehabilitation. Previously reported kinematic differences between total hip arthroplasty and contralateral hips may be well within the natural side-to-side differences that exist in asymptomatic native hips.

In designing femoral components, which restore native (i.e., healthy) knee kinematics, the flexion-extension (F-E) axis of the tibiofemoral joint should match that of the native knee. Because the F-E axis is governed by the curvature of the femoral condyles in the sagittal plane, the primary objective was to determine the variation in radii of curvature. Eleven high accuracy three-dimensional (3D) femur models were generated from ultrahigh resolution CT scans. The sagittal profile of each condyle was created. The radii of curvature at 15 deg increments of arc length were determined based on segment circles best-fit to ±15 deg of arc at each increment. Results were standardized to the radius of the best-fit overall circle to 15 deg-105 deg for the femoral condyle having a radius closest to the mean radius. Medial and lateral femoral condyles exhibited multiradius of curvature sagittal profiles where the radius decreased at 30 deg flexion by 10 mm and at 15 deg flexion by 8 mm, respectively. On either side of the decrease, radii of segment circles were relatively constant. Beyond the transition angles where the radii decreased, the anterior-posterior (A-P) positions of the centers of curvature varied 4.8 mm and 2.3 mm for the medial and lateral condyles, respectively. A two-radius of curvature profile approximates the radii of curvature of both native femoral condyles, but the transition angles differ with the transition angle of the medial femoral condyle occurring about 15 deg later in flexion. Owing to variation in A-P positions of centers of curvature, the F-E axis is not strictly fixed in the femur.