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

The aim of this work is to improve musculoskeletal-based models of the upper-limb wrench feasible set (WFS), i.e., the set of achievable maximal wrenches at the hand for applications in collaborative robotics and computer aided ergonomics. In particular, a recent method performing wrench capacity evaluation called the iterative convex hull method (ICHM) is upgraded in order to integrate nondislocation and compression limitation constraints at the glenohumeral (GH) joint not taken into account in the available models. Their effects on the amplitude of the force capacities at the hand, glenohumeral joint reaction forces and upper-limb muscles coordination in comparison to the original iterative convex hull method are investigated in silico. The results highlight the glenohumeral potential dislocation for the majority of elements of the wrench feasible set with the original iterative convex hull method and the fact that the modifications satisfy correctly stability constraints at the glenohumeral joint. Also, the induced muscles coordination pattern favors the action of stabilizing muscles, in particular the rotator-cuff muscles, and lowers that of known potential destabilizing ones according to the literature.

This study investigated the effect of collagen fiber tortuosity distribution on the biomechanical failure and prefailure properties of arterial wall tissue. An in-silico model of the arterial wall was developed using data obtained from combined multiphoton microscopy imaging and uni-axial tensile testing. Layer-dependent properties were prescribed for collagen, elastin, and ground substance. Collagen fibers were modeled as discrete anisotropic elements, while elastin and ground substance were modeled as homogeneous isotropic components. Our parametric analysis, using a finite element approach, revealed that different parameters of collagen fibers tortuosity distribution significantly influence both prefailure and failure biomechanical properties. Increased fiber tortuosity improved the tissue strength whereas the dispersion in the tortuosity distribution reduced it. This study provides novel insights into the structural-mechanical interdependencies in arterial walls, offering potential targets for clinical assessments and therapeutic interventions aimed at mitigating rupture risks.

Capillary refill time (CRT) is a widely used noninvasive measure of cardiovascular health. Despite its widespread diagnostic utility, it has several limitations, particularly its low sensitivity for certain conditions, because factors such as the contraction and relaxation of distal blood vessels can influence CRT readings. This study was performed to explore the relationships between CRT and distal blood flow. The right hand of each of ten healthy adult volunteers was cooled to induce blood vessel contraction. CRT, fingertip temperature, and blood flowrate were measured using a custom device, a thermometer, and a laser Doppler blood flowmeter, respectively, before and after cooling. Hand cooling significantly decreased blood flowrate and increased CRT. A robust inverse correlation was observed between blood flowrate and CRT, supporting a model where CRT is the time required for blood to flow through a cylindrical pipe. Furthermore, CRT showed a significant negative correlation with fingertip temperature. Most participants had high correlation coefficients, although two showed lower values. However, all data points exhibited a linear relationship, with the slopes of the regression lines between CRT and temperature varying among participants. These results suggested that the slope between CRT and fingertip temperature indicates individual differences in arterial contractility. These findings could improve the diagnostic utility of CRT in assessing vascular health, including arterial age and Raynaud's phenomenon, based on the contractility of peripheral arteries.

The interlamellar matrix (ILM), located between the annular layers of the intervertebral disc (IVD), is an adhesive component which acts to resist delamination. Investigating the mechanical properties of the ILM can provide us with valuable information regarding risk of disc injury; however given its viscoelastic nature, it may be necessary to conduct preconditioning on tissue samples before measuring these ILM properties. Therefore, the aim of this study was to optimize mechanical testing protocols of the ILM by examining the effect of preconditioning on stiffness and strength of this adhesive matrix. Eighty-eight annular samples were dissected from 22 porcine cervical discs and randomized into one of four testing conditions consisting of ten cycles of 15% strain followed by a 180 deg adhesive peel test. The four testing groups employed a different strain rate for the ten cycles of preconditioning: 0.01 mm/s (n = 23); 0.1 mm/s (n = 26); 1 mm/s (n = 23); and no preconditioning employed (n = 16). Samples preconditioned at 0.01 mm/s were significantly less stiff than those that had not received preconditioning (p = 0.014). No other results were found to be statistically significant. Given the lack of differences observed in this study, preconditioning is likely not necessary prior to conducting a 180 deg peel test. However, if preconditioning is employed, the findings from this study suggest avoiding preconditioning conducted at very slow rates (i.e., 0.01 mm/s) as the long testing time may negatively affect the tissue.

The objective of this research is to analyze the hemodynamic differences in five configurations of left subclavian artery (LSA) stent grafts after LSA endovascular reconstruction in thoracic endovascular aortic repair (TEVAR). For numerical simulation, one three-dimensional thoracic aortic geometry model with an LSA stent graft retrograde curved orientation was reconstructed from post-TEVAR computed tomography angiography (CTA) images, and four potential LSA graft configurations were modified and reconstructed: three straight (0, 2, and 10 mm aortic extension) and one anterograde configuration. The blood perfusion of the LSA, flow field, and hemodynamic wall parameters were analyzed. The vortex evolution process was visualized by the Liutex method which enables accurate extraction of the pure rigid rotational motion of fluid and is highly suitable for identifying the vortex structure of blood flow near the vessel wall. The average flow in the retrograde configuration decreased by 11.2% compared to that in the basic configuration. When the LSA stent graft extends in the aortic lumen, flow separation is observed, and vortex structures begin to form at the proximal inferior arterial geometry and the wall of the extension in late systole. A greater extension length and inflow angle upstream resulted in a greater oscillatory shear index (OSI) and relative residence time (RRT) on the nearby wall of the posterior flow field of the extension. Shorter intra-aortic extension length (<10 mm) and smaller LSA stent graft inflow angle (<120 deg) may be recommended in TEVAR, considering LSA perfusion and minimized flow field disturbance.

Sickle cell disease (SCD) is a genetic condition characterized by an abundance of sickle hemoglobin in red blood cells. SCD patients are more prone to intracranial aneurysms (ICA) compared to the general population, with distinctive features such as multiple intracranial aneurysms: 66% of SCD patients with ICAs have multiples ICAs, compared to 20% in nonsickle patients. The exact mechanism behind these associations is not fully understood, but there is a hypothesized link between hypoxic conditions in blood vessels and impaired synthesis of extracellular matrix, which may weaken the vessel walls, favoring aneurysm formation and rupture. SCD patients experience reduced oxygen levels in their blood, potentially exacerbating hypoxia in intracranial aneurysms, and potentially creating a feedback loop that could contribute to aneurysm development and early onset in these patients. In this work, we performed a series of computational studies (Fluent) using idealized geometries to investigate the key differences in the oxygen transport and blood flow dynamics inside an aneurysm formation for sickle and nonsickle cases. We found that using sickle cell disease parameters resulted in a 14% to 68% reduction in blood flow and a 37% to 70% reduction in oxygen availability within the aneurysm, depending on the vessel curvature and the aneurysm throat diameter, due to factors including oxygen-dependent viscosity and alteration in the oxygen transport. The results indicate that depending on geometry and flow characteristics, some degree of hypoxia maybe present in aneurysm bulb and would be more severe in sickle-cell disease patients. This study hopes to bring into attention the potential presence of hypoxic environment in the aneurysm bulb.

Elevation in left ventricular (LV) myocardial stiffness is a key remodeling-mediated change that underlies the development and progression of heart failure (HF). Despite the potential diagnostic value of quantifying this deterministic change, there is a lack of enabling techniques that can be readily incorporated into current clinical practice. To address this unmet clinical need, we propose a simple protocol for processing routine echocardiographic imaging data to provide an index of left ventricular myocardial stiffness, with protocol specification for patients at risk for heart failure with preserved ejection fraction. We demonstrate our protocol in both a preclinical and clinical setting, with representative findings that suggest sensitivity and translational feasibility of obtained estimates.

Collagen XI is ubiquitous in tissues such as joint cartilage, cancellous bone, muscles, and tendons and is an important contributor during a crucial part in fibrillogenesis. The COL11A1 gene encodes one of three alpha chains of collagen XI. The present study elucidates the role of collagen XI in the establishment of mechanical properties of tendons and ligaments. We investigated the mechanical response of three tendons and one ligament tissues from wild type and a targeted mouse model null for collagen XI: Achilles tendon (ACH), the flexor digitorum longus tendon (FDL), the supraspinatus tendon (SST), and the anterior cruciate ligament (ACL). Area was substantially lower in Col11a1ΔTen/ΔTen ACH, FDL, and SST. Maximum load and maximum stress were significantly lower in Col11a1ΔTen/ΔTen ACH and FDL. Stiffness was lower in Col11a1ΔTen/ΔTen ACH, FDL, and SST. Modulus was reduced in Col11a1ΔTen/ΔTen FDL and SST (both insertion site and midsubstance). Collagen fiber distributions were more aligned under load in both wild type group and Col11a1ΔTen/ΔTen groups. Results also revealed that the effect of collagen XI knockout on collagen fiber realignment is tendon-dependent and location-dependent (insertion versus midsubstance). In summary, this study clearly shows that the regulatory role of collagen XI on tendon and ligament is tissue specific and that joint hypermobility in type II Stickler's Syndrome may in part be due to suboptimal mechanical response of the soft tissues surrounding joints.

Background: Cigarette smoking adversely affects fracture repair, causing delayed healing or nonunion rates twice those seen in nonsmokers.

Purpose: We sought to investigate if cigarette smoke differentially affects intramembranous and endochondral healing of fractures. We hypothesize that healing via endochondral ossification will be preferentially impaired compared to intramembranous ossification.

Methods: We utilized a bilateral femur fracture model in Sprague Dawley rats to examine effects of cigarette smoke exposure on healing of femur fractures, treated with either 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; evaluations included radiographs, histomorphometry, and micro-CT at 10 days, 1, 3, and 6 months postoperation, and biomechanical testing at 3 and 6 months.

Results: Sixty-eight animals were randomized to control or exposure (two died perioperatively); 89% of femora achieved union when harvested at 3 or 6 months. Smoke exposure delayed cartilaginous callus formation and bone maturation in nailed fractures compared to plated fractures and controls in the 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. These differences vanished by 6 months.

Conclusions: Plated fractures healed more rapidly and 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.

Design and analysis are presented for a new device to test the response of endothelial cells to the simultaneous action of cyclic shear stresses and pressure fluctuations. The design consists of four pulsatile-flow chambers connected in series, where shear stress is identical in all four chambers and pressure amplitude decreases in successive chambers. Each flow chamber is bounded above and below by two parallel plates separated by a small gap. The design of the chamber planform must ensure that cells within the testing region experience spatially uniform time-periodic shear stress. For conditions typically encountered in applications, the viscous unsteady flow exhibits order-unity values of the associated Womersley number. The corresponding solution to the unsteady lubrication problem, with general nonsinusoidal flowrate, is formulated in terms of a stream function satisfying Laplace's equation, which can be integrated numerically to determine the spatial distribution of shear stresses for chambers of general planform. The results are used to optimize the design of a device with a hexagonal planform. Accompanying experiments using particle tracking velocimetry (PTV) in a fabricated chamber were conducted to validate theoretical predictions. Pressure readings indicate that intrachamber pressure variations associated with viscous pressure losses and acoustic fluctuations are relatively small, so that all cells in a given testing region experience nearly equal pressure forces.