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

Blood pumps have become popular whether for use as an implantable ventricular assist device or as extracorporeal membrane oxygenation. The quality of these pumps is assessed according to their ability to reduce the risk of blood damage thanks to an optimal choice of their geometric and operating properties. Lack of the research focused on the geometrical optimization of impellers has prompted this study. This study evaluated a computational and experimental analysis comparing the hemolytic performance of three centrifugal pumps. For this purpose, methods of Eulerian and Lagrangian are respectively used for hemodynamic and hemocompatibility investigations. Referring to the pediatric demands, these pumps function under clinically applicable pressure-flow conditions: 1 l/min of blood flow and a pressure differential of 60 mm Hg. These three pumps all use the same volute, but their impellers differ in terms of blade thickness. The objective is to examine how surface area affects the generation of hemolysis. In silico simulations were employed for both of the following tasks: first, identifying the distributions of velocities, pressures, and shear stresses; second, applying the Lagrangian approach to estimate the hemolysis index. Results showed the importance of the flow passage and the surface of the clearance on the hemocompatibility of the pumps. However, it was observed that there is not a linear effect of the blade thickness on the shear stress or index of hemolysis. Additionally, this work can provide information to develop an optimal design of a more hemocompatible blood pump.

Micromotion exceeding 150μm at the implant-bone interface may prevent bone formation and limit fixation after cementless knee arthroplasty. Understanding the critical parameters impacting micromotion is required for optimal implant design and clinical performance. However, few studies have focused on UKA. This study assessed the impacts of alignment, surgical, and design factors on implant-bone micromotions for a novel cementless UKA design during a series of simulated daily activities. Three validated finite element knee models for predicting cementless micromotions were loaded with design-specific kinematics/loading to simulate gait, deep knee bending, and stair descent. The implant-bone micromotion and the porous surface area ideal for bone ingrowth were estimated and compared. Overall, the peak tray-bone micromotions were consistently found at the lateral aspect of the tibial baseplate and were consistently higher than the femoral micromotions. The femoral micromotion was insensitive to almost all the factors studied, and the porous area favorable for bone ingrowth was no less than 93%. For a medial uni, implanting the tray 1mm medially or the femoral component 1mm laterally reduced the tibial micromotion by 19.3% and 26.3% respectively. A 5 mm more posterior femoral translation increased the tibial micromotion by 35.8%. The presence of the tray keel prevented the spread of the micromotion and increased the overall porous surface area. In conclusion, centralizing the load transfer to minimize tibial tray applied moment and optimizing the fixation features to minimize micromotion are consistent themes for improving cementless fixation in UKA.

Quantitative magnetic resonance imaging (qMRI), in combination with mechanical testing, offers potential to investigate how loading is related to joint and tissue function. However, current testing devices compatible with MRI are often limited to uniaxial compression, often applying low loads, or loading individual tissues (instead of multiple), while more complex simulators do not facilitate MRI. Hence, in this work, we designed, built and tested (N=1) an MRI-compatible multiaxial load-control system which enables scanning cadaveric joints (healthy or pathologic) loaded to physiologically-relevant levels. Testing involved estimating and validating physiologic loading conditions before implementing them experimentally on cadaver knees to simulate and image gait loading (stance and swing). The resulting design consisted of a portable loading device featuring pneumatic actuators to reach a combined loading scenario, including axial compression (=2.5 kN), shear (=1 kN), bending (=30 N·m) and muscle tension. Initial laboratory testing was carried out; specifically, the device was instrumented with force and pressure sensors to evaluate loading and contact response repeatability in one cadaver knee specimen. This loading system was able to simulate healthy or pathologic gait with reasonable repeatability (e.g., 1.23 to 2.91 % coefficient of variation for axial compression), comparable to current state-of-the-art simulators, leading to generally consistent contact responses. Contact measurements demonstrated a tibiofemoral to patellofemoral load transfer with knee flexion and large contact pressures concentrated over small sites between the femoral cartilage and menisci, agreeing with experimental studies and numerical simulations in the literature.

Subjects with unilateral transtibial amputation exhibit altered minimum toe clearance (MTC) depending on the ankle prosthesis used, possibly due to a limited prosthetic ankle angle. The aim of this study was to investigate the alterations in joints kinematics responsible for the changes in MTC when using an Articulating Hydraulic Ankle (AHA) compared to a Non Articulating Ankle (NAA) prosthesis. Twelve participants with unilateral transtibial amputation walked at self-selected speed on a 10 meter pathway. They used the same AHA and NAA prosthetic models and the prosthetic characteristics were unchanged except for the ankle mechanisms and, consequently, its mass. Data from MTC and hip, knee and ankle angles in the sagittal, frontal and transversal plane at the time of MTC were statistically analyzed with a paired sample t-test. The AHA prosthesis showed significantly higher MTC mean (AHA = 24.7 ± 9.6 mm vs. NAA = 17.4 ± 5.2 mm, P < 0.01) and variability (13.4 ± 9.6 mm vs. 6.7 ± 4.2 mm, P = 0.03) on the prosthetic limb than the NAA. A higher mean MTC could be explained by an increase in ankle angle dorsiflexion (AHA = -1.2 ± 2.6° vs. NAA = -2.9 ± 1.5°, P = 0.01) while the variability of the prosthetic MTC appears to be influenced by changes in prosthetic mass. The results of this study suggests that ankle dorsiflexion during swing and the mass of the prosthesis have a direct influence in mean MTC and its variability, respectively.

Continuum Mechanics is the discipline that studies the motion and deformation of material bodies, and is at the basis of both Solid Mechanics and Fluid Mechanics. This works aims at highlighting how a basic education in modern Continuum Mechanics can be of fundamental importance not only in the Biomechanics of Tissue, but also in the Biomechanics of Movement. The latter is largely based on Rigid Body Mechanics, which can be considered as a simple particular case of the general theory of Continuum Mechanics. As an example, a straightforward methodology for the extraction of the angular velocity from motion analysis data is illustrated. The method is based on a quantity that is more primitive than the angular velocity: the spin tensor.

Background: Cigarette smoking affects fracture repair, leading to delayed healing or nonunion.

Purpose: We sought to investigate if cigarette smoke differentially affects intramembranous and endochondral ossification in healing fractures, focusing on whether endochondral ossification is particularly impaired.

Methods: This study utilized a bilateral femur fracture model in Sprague Dawley rats to examine the impact of cigarette smoke exposure on healing of femur fractures, treated with either a custom-locked intramedullary nail or compression plating to induce endochondral and membranous ossification, respectively. Animals were exposed to tobacco smoke 30 days before and after surgery, with evaluations including radiographs, histomorphometry, and microCT at 10 days, 1, 3, and 6-months post-operation, and biomechanical testing at 3, 6 months.

Results: Sixty-eight animals were randomized to control or exposure groups (two died perioperatively), and 89% of the femora achieved union when harvested at 3 and 6 months. Smoke exposure delayed cartilaginous callus formation and bone maturation in nailed fractures compared to plated fractures and controls in same animals. Plated fractures in exposed animals exhibited little cartilage callus and healed like control animals. At 3 months, plated fractures were stiffer and stronger than nailed fractures in both groups, but these differences vanished by 6 months.

Conclusions: Plated fractures healed more rapidly and more completely than nailed fractures under both control and smoke-exposed conditions.

Clinical relevance: Using compression plating instead of IM nailing for closed long bone fractures may lead to better outcomes in patients who smoke compared to current results with nailing.

Tendinopathy is a leading cause of mobility issues. Currently, the cell-matrix interactions involved in the development of tendinopathy are not fully understood. In vitro tendon models provide a unique tool for addressing this knowledge gap as they permit fine control over biochemical, micromechanical, and structural aspects of the local environment to explore cell-matrix interactions. In this study, direct-write, near-field electrospinning of gelatin solution was implemented to fabricate micron-scale fibrous scaffolds that mimic native collagen fiber size and orientation. The stiffness of these fibrous scaffolds was found to be controllable between 1 MPa and 8 MPa using different crosslinking methods (EDC, DHT, DHT+EDC) or through altering the duration of crosslinking with EDC (1 h to 24 h). EDC crosslinking provided the greatest fiber stability, surviving up to 3 weeks in vitro. Differences in stiffness resulted in phenotypic changes for equine tenocytes with low stiffness fibers (∼1 MPa) promoting an elongated nuclear aspect ratio while those on high stiffness fibers (∼8 MPa) were rounded. High stiffness fibers resulted in the upregulation of matrix metalloproteinase (MMPs) and proteoglycans (possible indicators for tendinopathy) relative to low stiffness fibers. These results demonstrate the feasibility of direct-written gelatin scaffolds as tendon in vitro models and provide evidence that matrix mechanical properties may be crucial factors in cell-matrix interactions during tendinopathy formation.

Individuals with transtibial amputation (TTA) experience asymmetric lower-limb loading which can lead to joint pain and injuries. However, it is unclear how walking over unexpected uneven terrain affects their loading patterns. This study sought to use modeling and simulation to determine how peak joint contact forces and impulses change for individuals with unilateral TTA during an uneven step and subsequent recovery step and how those patterns compare to able-bodied individuals. We expected residual limb loading during the uneven step and intact limb loading during the recovery step would increase relative to flush walking. Further, individuals with TTA would experience larger loading increases compared to able-bodied individuals. Simulations of individuals with TTA showed during the uneven step, changes in joint loading occurred at all joints except the prosthetic ankle relative to flush walking. During the recovery step, intact limb joint loading increased in early stance relative to flush walking. Simulations of able-bodied individuals showed large increases in ankle joint loading for both surface conditions. Overall, increases in early stance knee joint loading were larger for those with TTA compared to able-bodied individuals during both steps. These results suggest that individuals with TTA experience altered joint loading patterns when stepping on uneven terrain. Future work should investigate whether an adapting ankle-foot prosthesis can mitigate these changes to reduce injury risk.

Cervical remodeling is critical for a healthy pregnancy. Premature tissue changes can lead to preterm birth (PTB), and the absence of remodeling can lead to post-term birth, causing significant morbidity. Comprehensive characterization of cervical material properties is necessary to uncover the mechanisms behind abnormal cervical softening. Quantifying cervical material properties during gestation is challenging in humans. Thus, a nonhuman primate (NHP) model is employed for this study. In this study, cervical tissue samples were collected from Rhesus macaques before pregnancy and at three gestational time points. Indentation and tension mechanical tests were conducted, coupled with digital image correlation (DIC), constitutive material modeling, and inverse finite element analysis (IFEA) to characterize the equilibrium material response of the macaque cervix during pregnancy. Results show, as gestation progresses: (1) the cervical fiber network becomes more extensible (nonpregnant versus pregnant locking stretch: 2.03 ± 1.09 versus 2.99 ± 1.39) and less stiff (nonpregnant versus pregnant initial stiffness: 272 ± 252 kPa versus 43 ± 43 kPa); (2) the ground substance compressibility does not change much (nonpregnant versus pregnant bulk modulus: 1.37 ± 0.82 kPa versus 2.81 ± 2.81 kPa); (3) fiber network dispersion increases, moving from aligned to randomly oriented (nonpregnant versus pregnant concentration coefficient: 1.03 ± 0.46 versus 0.50 ± 0.20); and (4) the largest change in fiber stiffness and dispersion happen during the second trimester. These results, for the first time, reveal the remodeling process of a nonhuman primate cervix and its distinct regimes throughout the entire pregnancy.

Skin undergoes mechanical alterations due to changes in the composition and structure of the collagenous dermis with aging. Previous studies have conflicting findings, with both increased and decreased stiffness reported for aging skin. The underlying structure-function relationships that drive age-related changes are complex and difficult to study individually. One potential contributor to these variations is the accumulation of nonenzymatic crosslinks within collagen fibers, which affect dermal collagen remodeling and mechanical properties. Specifically, these crosslinks make individual fibers stiffer in their plastic loading region and lead to increased fragmentation of the collagenous network. To better understand the influence of these changes, we investigated the impact of nonenzymatic crosslink changes on the dermal microstructure using discrete fiber networks representative of the dermal microstructure. Our findings suggest that stiffening the plastic region of collagen's mechanical response has minimal effects on network-level stiffness and failure stresses. Conversely, simulating fragmentation through a loss of connectivity substantially reduces network stiffness and failure stress, while increasing stretch ratios at failure.