Biomechanics and Modeling in Mechanobiology最新文献

After total hip replacement, the primary and secondary implant stability is critical to ensure long-term success. Excessive migration of the femoral stem can cause implant loosening. In this work, a novel approach for the simulation of the femoral stem migration using the finite element method is presented. Currently, only a few mostly contact-based models exist for this purpose. Instead, a bio-active interface model is used for the bone-stem interface which transforms from the Drucker–Prager to the von Mises plasticity criterion during the osseointegration process. As the position of the implant generally stabilises within one week after the implantation, the migration and osseointegration simulations are decoupled. To understand the effects on the migration, various parameter combinations are examined and a sensitivity analysis is performed. The results indicate that the joint force and the adhesion parameter have the most substantial influence on the migration. Furthermore, the influence of the migration on the subsequent osseointegration process is explored for a numerical example. The proposed model is able to depict the femoral stem migration with values up to 0.27 mm, which are in the order of magnitude of clinically observed values. Further, the model is provided as an open-source Abaqus user material subroutine. Numerical simulation of the stem migration could assist in clinical decision-making by identifying optimal parameter combinations to improve implant stability.

This study explored the biomechanical behavior of co-polymeric swelling bone anchors and their bone remodeling induction using finite element analysis of a model with heterogeneous properties. First, a hygro-elastic finite element framework was developed to capture the swelling of the bone anchors over time by moisture gain, validated against the data from free swelling experiments. Afterward, finite element models were developed using micro-CT data to capture heterogeneous material properties, and finally, bone remodeling induced by the swelling, acting as a mechanical stimulus, was investigated. The study examined three co-polymeric ratios of methyl methacrylate and acrylic acid (MMA/AA)—80/20, 85/15, and 90/10—and assessed the impact of their associated swelling ratios on bone remodeling and fixation strength. Moreover, in parallel with the numerical investigations, an in vivo study using a sheep model was conducted to evaluate the biocompatibility of these anchors and bone remodeling response to the swelling. The numerical findings highlighted the importance of optimizing swelling ratios to enhance mechanical engagement without causing adverse resorption. More specifically, the results demonstrated that bone regeneration in the region of interest is highly sensitive to the swelling ratio. When the swelling is maintained within an optimal range—such as in the 85/15 composition—favorable densification occurs at the bone–implant interface, enhancing osteointegration. In contrast, excessive swelling (e.g., the 80/20 composition) induces localized overload resorption due to elevated stress concentrations at the interface, which may compromise implant success. Additionally, correlations found between the numerical and in vivo study outcomes supported the notion of an optimal swelling threshold and confirmed the predictive capabilities of the developed hygro-elastic finite element framework. To underscore the importance of favorable bone remodeling in the interface, a push-out study was performed to analyze the fixation strength prior and subsequent to bone remodeling. The significant difference in push-out forces before and after remodeling demonstrates that bone densification at the interface can substantially enhance fixation strength.

Acute ischemic stroke (AIS) is a leading cause of death worldwide. In recent years, several studies have characterized the material properties of clot types that were removed from stroke patients, showing a highly nonlinear, asymmetric behavior in compression and tension. However, little is still known about the clot phenotype underlying complications in endovascular thrombectomy (EVT). In this study, we propose a spectrum of clot surrogates for highly stiff, red blood cell-rich, aged, calcified clots that may underpin the outcomes of AIS procedures, often called ‘hyperdense middle cerebral artery signs’ by clinicians. This study aims to characterize the high-strain, rate-dependent mechanical properties of a broad range of aged and calcified clot analogs. Blood from healthy donors was used to form aged and calcified clots, which were subjected to rate-dependent uniaxial testing and structural analyses. A method for curve fitting standard linear solids with multiple hyperelastic elements is considered, and a subsequent procedure is outlined for fitting rate-dependent data. High-strain clot analog peak stresses and moduli are on the same order of magnitude as previous studies, with the hypercalcified clots nearly an order of magnitude stiffer than previously recorded. The calcification was shown to be time dependent, as the longer the clots incubated in the calcium solutions, the stiffer they became. SEM images show drastic changes in clot morphology, with mineral nucleation evident around all components of the clot. The curve fitting produced parameters for a host of models that can be used in numerical implementation. The authors note that when curve fitting, energy state of the system should be taken into consideration, in addition to the minimization of the relative error. We demonstrate a wide spectrum of clot properties that are captured well by rate-dependent models for the full dataset, the compressive data, and the tensile data. In this study, we provide a method for creating and characterizing hypercalcified clot analogs as surrogates for the clot phenotype underlying EVT complications. The library of clot properties reported here can be used in numerical simulations, with careful considerations of the curve fitting methods that are employed. These data highlight the need for further investigation into this clot phenotype, which may be related to the subset of AIS patients where clots are unable to be removed.

The rising use of biologic drugs has increased the demand for alternative gastric administration methods. Inception of devices engineered to insert medication into the mucosal lining overcomes limitations of traditional administration methods. Mechanical forces from such microneedle insertions can affect tissue and cellular behavior, particularly mechanotransduction markers. This study investigates the effects of needle insertion in gastric tissue to inform the design of alternative drug delivery devices. Experimental and computational approaches were utilized, using tension and radial compression tests on porcine gastric tissue to inform a finite element analysis (FEA) model. This model was validated with atomic force microscopy (AFM)-based micro-indentation to examine stiffness variations near the insertion site, and yes-associated-protein-1 (YAP-1) expression was analyzed to assess cellular mechanotransduction. AFM results revealed a distance-dependent decrease in tissue stiffness from the insertion site (p < 0.05), with significant differences in needle geometry (p < 0.05). The FEA model correlated well with AFM findings, confirming its validity for further cellular simulations. Mechanical stresses from needle insertion were shown to propagate through the tissue, affecting both cytoplasmic and nuclear stress distributions and altering nuclear morphology near the insertion site. The blunt needle produced a higher localized stress field compared to the sharp needle. Additionally, YAP-1 expression was lower in the injected samples than in control samples showing distance-dependent responses observed. This study demonstrates a validated model linking tissue mechanics and cellular responses, highlighting how needle geometry impacts gastric tissue mechanics and mechanotransduction, providing insights essential for designing gastric drug delivery devices.

Transcatheter aortic valve replacement (TAVR) has revolutionized the treatment of severe aortic stenosis, yet paravalvular leakage (PVL) remains a significant complication, associated with increased mortality. Clinical studies have identified correlations between PVL and both anatomical features and calcification patterns. Numerical simulations, particularly patient-specific models, offer valuable insights into PVL, but the limited scale of these studies hinders robust statistical analysis. This study introduces a novel in silico clinical trial (ISCT) framework to investigate the correlation between calcification severity, localization and PVL. For this purpose, a synthetic cohort of calcified aortic roots was generated. A conditional convolutional variational autoencoder was used to create calcification patterns for an existing virtual cohort of the aortic root. The workflow includes finite element analyses for pre-dilation and deployment simulations as well as computational fluid dynamic simulations for PVL calculations of 243 virtual TAVR patients. The results show that the absolute amount of calcification in the device landing zone has no significant influence, but its regional distribution does, especially in the combined leaflet regions. In addition, sinotubular junction diameter, annular eccentricity index, oversizing as well as the combination of aortic angle and calcification in the combined non and left coronary leaflet region influence the occurrence of PVL. This framework not only advances our understanding of PVL mechanisms but also demonstrates the potential of ISCT to complement traditional clinical studies, enabling systematic exploration of complex factors influencing TAVR outcomes.

A nonlinear continuum theory is advanced for high-rate mechanics and thermodynamics of liver parenchyma. The homogenized continuum is idealized as a solid–fluid mixture of dense viscoelastic tissue and liquid blood. The solid consists of a matrix material comprising the liver lobules and a collagenous fiber network. Under high loading rates pertinent to impact and blast, the velocity difference between solid and fluid is assumed negligible, leading to a constrained mixture theory. The model captures nonlinear isotropic elasticity, viscoelasticity, temperature changes from thermoelasticity and dissipation, and tissue damage, the latter via a scale-free phase-field representation. Effects of blood volume and initial constituent pressures are included. The model is implemented in 3-D finite element software. Analytical and numerical solutions for planar shock loading are compared with observations of liver trauma from shock-tube experiments. Finite-element simulations of dynamic impact are compared with cylinder drop-weight experiments. Model results, including matrix damage exceeding fiber damage at high rates and reduced mechanical stiffness with higher perfused blood volume, agree with experimental trends. Viscoelasticity is important at modest impact speeds.

Lymphedema is a chronic condition characterized by impaired lymphatic drainage, leading to fluid accumulation, swelling, and progressive tissue remodeling. Compression therapy is the primary treatment used to alleviate swelling and enhance fluid drainage, yet its precise impact on interstitial fluid dynamics remains to be understood. In this study, we developed a poroelastic computational model that simulates fluid flow and tissue deformation in the lower limb under different compression strategies and compression levels. A key feature of our work is the integration of patient-specific geometries, allowing for a more physiologically accurate representation of tissue mechanics and fluid redistribution. We simulated edema formation induced by venous insufficiency by increasing blood capillary pressure from a baseline of 10–80 mmHg, and we observed that interstitial fluid pressure (IFP) increased from a baseline value of 0 mmHg to 8 mmHg, highlighting the impact of vascular dysfunction on fluid accumulation. Simulating complete blockage of lymphatic capillaries resulted in even higher IFP values (40 mmHg) compared to models with functional lymphatics, where IFP remained around 8 mmHg for high capillary pressures, underscoring the critical role of lymphatic drainage. We further showed that an increase in tissue permeability increases gravity-driven fluid pooling, potentially exacerbating swelling in lymphedematous limbs. Additionally, we incorporated an interface pressure derived from Laplace’s law to offer a more realistic estimation of IFP and volume changes, emphasizing its importance for refining compression models and optimizing treatment strategies. These findings contribute to a deeper understanding of compression therapy’s role in interstitial fluid drainage and provide a foundation for improving patient-specific lymphedema management.

Aortic dissection is a life-threatening disease with high mortality rates. The degradation of the layers of the aorta wall causes tears, which then propagate further due to high-pressure blood penetrating the vessel wall, creating a false lumen. The intimal flap separating the true and false lumen can either bulge inwards constricting the true lumen’s blood flow or bulge outwards leading to catastrophic rupture and internal bleeding. Therefore, to understand the role of critical pressure on tear propagation, a computational study of the initiation and propagation of tears of various sizes and at multiple depths and locations in three-dimensional aortas was conducted. Tears were modelled using the extended finite element method, and the wall of the aortas is an anisotropic hyperelastic material. Blood-pressure-loaded aorta geometries were obtained from the corresponding unloaded geometries using an iterative procedure to match the in vivo geometries. Pressure-driven tear initiation and propagation were studied. Our results show that when the tear surface’s normal is perpendicular to the blood flow, the critical pressure required to cause further propagation is higher for the shorter and deeper tears and reduces when the initial tear size increases. When the normal is parallel to the blood flow, the difference in critical pressure with an increase in tear depth is small and is more likely to propagate transversely. Also, the critical pressure decreases with an increase in the diameter of the aorta for all the tear orientations. This study concludes that tear size, depth inside the medial layer and the diameter of the aorta near the tear location are critical parameters in assessing the risk of further propagation.

We present a 1D-0D model that couples a 0D description of lung mechanics to the closed-loop Anatomically-Detailed Arterial-Venous Network (ADAVN) model. We show that our model can satisfactorily reproduce a set of cardiovascular indices of interest observed in healthy young males at rest. Next, we assess the impact of respiration on cardiac performance and on the periodicity and average values of pressure and flow waveforms in different vascular districts. In particular, our results confirm that respiration has a fundamental pumping function, which aids venous return, and that its action affects mainly the average of haemodynamic variables on the arterial side, while on the venous side it has a significant effect on wave periodicity and triggers a complex interplay in terms of waveform conformation. Additionally, we assess the sensitivity of model predictions to variations in model parameters through a local sensitivity analysis, both in the presence and absence of respiration, highlighting a strong relationship between the arterial and venous side of the model.