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

Patients with ascending thoracic aortic aneurysms (ATAA) only have a 10-20% chance of survival upon aneurysm rupture. If aneurysm growth is detected, however, surgical repair can mitigate the rupture risk. Current CT- and MRI-based surveillance methods require frequent hospital visits, increasing healthcare costs and reducing patient adherence. Pulse-based measurements, which could eventually be performed at home, are an attractive but poorly explored alternative. In this study, we investigated the feasibility of using frequency analysis of the pulse waveform to determine whether the ATAA radius or wall stiffness has changed. We first determined a correction to the standard 0D model for blood flow through curved vessels, using fluid-structure-interaction (FSI) modeling as ground truth. We then studied idealized ATAA geometries and found that changes in the size of an aneurysm led to consistent changes in the Fast Fourier Transform of the outlet pressure waveform. Furthermore, when the vessel stiffened and grew, these changes were detectable by comparing the low versus high frequency response of the outlet pressure. Similar trends were observed for FSI simulations based on retrospective study of longitudinal scans of a patient over 5 years. This study showed that analyzing the pulse waveform, as clinically measurable by surface tonometry, has potential to form the basis for an at-home method for detecting ATAA growth.

Meniscus tears compromise its mechanical function, leading to impaired joint loading and, if left untreated, increase risk of further joint degeneration. Surgical repair can be successful for certain tear patterns. Establishing new methods quantifying in vivo meniscus mechanics under weight-bearing facilitates improvements in surgical techniques and postoperative care. The goal of this study was to establish a method for quantifying meniscus mechanics under loading in vivo using magnetic resonance imaging (MRI). A custom MRI-compatible knee loading device was instrumented with the capability of applying loads up to 700N at variable flexion angles. To evaluate the device, the medial and lateral menisci of healthy young participants and participants with knee pathologies were evaluated. MRI was acquired when the knees were loaded under 10% and 50% bodyweight at 0° extension and 30° flexion. Displacements were quantified in both menisci and articular cartilage. All participants completed the knee loading protocol without issue or discomfort. The participants with knee pathologies exhibited greater amounts of displacement compared to the healthy participants. Cartilage strain was consistent and within expected physiological range amongst all participant groups. This study demonstrated the safety and effectiveness of using an in vivo MRI-compatible knee loading device that can apply physiological compressive loads at varying knee flexion angles. Our results provide proof-of-concept of this technique to quantify altered joint kinematics in surgical patients with meniscus or cartilage pathologies. The novel methodology substantiates further study on patients who receive meniscus surgical procedures.

Clinically relevant performance metrics for shape memory polymer (SMP) scaffolds intended for the endovascular treatment of intracranial aneurysms were evaluated in various in-vitro experiments. Multiple SMP formulations were first evaluated for glass transition properties, with saturated scaffolds demonstrating Tg midpoints of 39 °C, 35 °C, and 32 °C, respectively. Then, scaffold?s porosity (85?95%) and infill pattern (rectilinear, honeycomb, gyroid) were systematically varied, and designs were compared by compressibility, shape recovery, and pulsatile compaction resistance. The compressibility of ideal and wide-necked aneurysm geometries, each in 6 mm and 8 mm diameter sizes, indicated an upper limit of ~9 mm in treatable aneurysm diameter for a 5 French microcatheter. Under physiologically relevant pulsatile loading, all scaffold designs resisted notable compaction, with maximum deformation values not exceeding 55 µm. The shape recovery forces were primarily governed by the porosity level, with low- and medium-porosity scaffolds showing complete and reliable shape recovery, and high-porosity scaffolds exhibiting reduced completeness of shape recovery. Shape recovery rates varied both within and across infill pattern and porosity groups. Together, these findings provide quantitative benchmarks for the performance of our SMP scaffold in different key stages of device deployment and establish design guidelines for further optimization of patient-specific endovascular devices.

Post-traumatic joint contracture (PTJC) frequently occurs in elbows after injury, decreasing range of motion (ROM) and causing dysfunction. Physical therapy improves ROM but does not address underlying inflammation and fibrosis. Combining physical exercise with biological treatment has shown positive results in other physiological systems. Objective: evaluate whether active physical therapy and anti-inflammatory drug treatment, alone or in combination, could preserve mechanics and function in a rat model of PTJC. Elbow PTJC was surgically induced in rats followed by joint immobilization. Animals received either anti-inflammatory drug (celecoxib or CEL) treatment, active physical therapy (wheel activity or WA), or both (CELWA). An untreated cage activity group (CA) served as control. Functional evaluation, joint mechanical testing, and histological analysis were used to compare groups. All treatments improved gait parameters compared to CA, with WA showing the most improvements. Joint mechanics were most improved in CELWA compared to CA. Histological analysis showed that all treatments improved fibrosis, adhesions, vascularity, and thickness of capsule tissue to varying degrees. Cartilage surfaces showed improved structure and cellularity for all treatments. Physical therapy resulted in the most improvement in functional parameters, but active joint use in combination with anti-inflammatory drug treatment showed the most improvement in joint mechanics and histological properties. PTJC involves multiple tissues and cell types, and thus a multi-treatment approach will likely be needed to address all underlying causes: biological modulation of the inflammatory response combined with physical disruption of fibrotic tissue may show more efficacy than either treatment alone.

The occurrence of blunt abdominal injuries resulting from thoracic high-rate non-penetrating impacts (NPBIs) are often missed and associated with increased mortality and morbidity. Diagnosis of penetrating gunshot wounds successfully predicts injury locations using bullet trajectory, but no similar correlation has been applied for blunt impacts. Historically, thoracic NPBIs have been studied on ovine subjects and have reported thoracic only and thoracoabdominal injuries for impacts at the same location. The purpose of this study is to investigate if the finite element ovine thorax model (FE-OTM) can indicate changes in multi-compartment injury risk based on impact angle and determine a method for measuring this change. Twelve thoracic NPBIs were run over six impact angles (0 - 25°). Tissue directly under the impactor and along the path of impact, was analyzed for changes in composition and strain. Tissue composition analysis identified abdominal, lung, and liver as key tissue types. Cumulative volume analysis was used to determine a combine strain - volume metric for regions of interest. Within each region, Spearman's rank correlation was used to determine the strength of the relationship between this metric and impact angle. The key tissues experienced very strong correlations with impact angles and directionalities that corresponded to their change in volume. In conclusion, the FE-OTM can be used to indicate changes to multi-compartment injury risk based on impact angle. A 1st principal strain-volume based metric in the key tissue types is recommended.

Pulmonary hypertension (PH) is a serious condition affecting patients with end-stage renal disease (ESRD), yet the hemodynamic mechanisms underlying development remain poorly understood. Novel alternative methods (NAMs), such as computational fluid dynamics (CFD), provide a powerful and ethical approach to investigate vascular physiology using patient-specific data. We developed a CFD model of the pulmonary artery (PA) informed by noninvasive magnetic resonance imaging (MRI) from an ESRD patient to characterize flow dynamics and wall shear metrics relevant to PH. Simulations were performed using image-based geometry, and velocity fields, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were quantified. Results demonstrated physiologically consistent flow distributions, with higher velocities localized near outlet regions and lower velocities in branches. Spatially averaged TAWSS was approximately 9 dyn/cm2, in agreement with previously reported ranges. OSI values were low across the pulmonary vasculature, suggesting limited flow reversal. Together, these results highlight the feasibility of using patient-specific CFD to capture PA hemodynamics in ESRD and demonstrate consistency with published physiological values. This framework demonstrates the utility of NAMs to provide insight into complex biomechanical systems and a foundation for future studies seeking to clarify mechanistic links between ESRD development, arteriovenous fistula (AVF) creation, and eventual PH development, ultimately informing development of patient-specific diagnostic and therapeutic strategies. As NAMs gain regulatory and scientific traction, approaches like this will play an important role in reducing reliance on animal models while enabling ethically responsible, patient-specific discovery in cardiovascular research.

Cardiac fibrosis is a pathological condition involving remodeling that impairs cardiac function. Common forms include replacement fibrosis, where damaged myocytes are substituted by collagenous tissue, and interstitial fibrosis, involving matrix expansion between the myocytes. These occur alongside other remodeling processes, including myocardial stiffening and collagen alignment. The mechanical impact of each process remains an active area of investigation. In this work, we used a computational model with explicit myocyte and collagen geometries to study the microscale mechanical effects of fibrotic remodeling. Replacement fibrosis was simulated by substituting myocytes with extracellular matrix, while interstitial fibrosis was modeled by increasing transverse spacing between the cells. These geometric changes were combined with increased matrix and myocyte stiffness and collagen alignment to assess individual and combined effects during contraction and stretch. Structural changes alone led to substantially higher myocyte stresses during contraction (53.9 kPa for increased interstitial space and 35.4 kPa for myocyte replacement, versus 30.9 kPa at baseline). Collagen alignment and myocyte stiffening mitigated increased stress levels. Stretch experiments showed less structural differences in resulting tissue-level load values, which combined with stiffening were slightly higher for increased interstitial space. Individual and combined analyzes attributed total tissue stiffening more to myocyte than matrix stiffening. Our findings suggest that fibrotic remodeling leads to elevated stress in surviving myocytes. Myocyte stiffening and collagen alignment may serve compensatory roles, while also increasing tissue-level stiffness. Integrating microscale modeling with experimental data in future studies may offer deeper insights into the mechanical consequences of fibrotic remodeling.

Operative repair of the rotator cuff (RC) of the shoulder can return a patient to normal function but is not without complications. An understanding of the tissue strains in the RC of the shoulder under normal and pathological conditions can inform surgeons about the conditions needed for restoration of function and the state of the tissue under repair. The current work applied digital image correlation (DIC) to quantify rotator cuff strains with the goals of (1) determining whether the tension created by the supraspinatus (SS) muscle is transmitted without diversion by the structure of the cuff from the supraspinatus to the cuff insertion; and (2) whether releases of the SS tendons at their insertions alter the strain field in the region away from the cuff insertion. DIC methods recorded the bursal-side cuff strains created using a shoulder simulator, which could apply physiologic loads to the cuff muscles. The SS and infraspinatus (IS) insertions of the humerus were sequentially released while muscle loads were applied. The first principal strains and their directions showed changes after releases of both the anterior and posterior SS insertions and after the IS release. The results demonstrated (1) that the RC transmits SS muscle forces without diversion and (2) that RC releases do affect the strain field. Release of both heads of the SS led to statistically significant changes in strain magnitude and direction.

This study validates a finite deformation, nonlinear viscoelastic constitutive model for the collagen matrix of immature bovine articular cartilage, using reactive viscoelasticity. Tissue samples underwent proteoglycan (PG) digestion, losing more than 98% of their initial PG content to increase their hydraulic permeability. To verify that PG-digestion eliminated flow-dependent viscoelasticity, samples were subjected to a gravitational permeation experiment, demonstrating that their hydraulic permeability, k=268±152 mm4/N⋅s (n=8), was five orders of magnitude greater than reported for untreated cartilage. Digested cartilage plugs were subjected to unconfined compression stress relaxation (four consecutive 10% strain ramp-hold profiles) to fit the load response and extract material properties (RMSE_fit=1.86±0.61 kPa, n=8). Successful curve-fitting served as a necessary condition for validating the model. Then, a separate unconfined compression stress-relaxation test was performed on the same samples, to 40% compressive strain at the same ramp rate. The model was able to faithfully predict this experimental response using fitted material properties (RMSE_pred=3.95±1.33 kPa, with 0=stresses=155±37 kPa), providing a sufficient condition for validation in unconfined compression stress-relaxation. A computational model showed that flow-independent viscoelasticity of cartilage collagen can enhance the stress response by ~15% at fast strain rates, over flow-dependent effects. However, we estimate from prior studies that flow-independent viscoelasticity may enhance the stress response of cartilage by up to 200%, implying that PGs probably contribute significantly to the tissue?s flow-independent viscoelasticity.