26 research outputs found
Predictive assembling model reveals the self-adaptive elastic properties of lamellipodial actin networks for cell migration
Branched actin network supports cell migration through extracellular microenvironments. However, it is unknown how intracellular proteins adapt the elastic properties of the network to the highly varying extracellular resistance. Here we develop a three-dimensional assembling model to simulate the realistic self-assembling process of the network by encompassing intracellular proteins and their dynamic interactions. Combining this multiscale model with finite element method, we reveal that the network can not only sense the variation of extracellular resistance but also self-adapt its elastic properties through remodeling with intracellular proteins. Such resistance-adaptive elastic behaviours are versatile and essential in supporting cell migration through varying extracellular microenvironments. The bending deformation mechanism and anisotropic Poissonâs ratios determine why lamellipodia persistently evolve into sheet-like structures. Our predictions are confirmed by published experiments. The revealed self-adaptive elastic properties of the networks are also applicable to the endocytosis, phagocytosis, vesicle trafficking, intracellular pathogen transport and dendritic spine formation
Micro/Nanostructures and Mechanical Properties of Trabecular Bone in Ovariectomized Rats
Bone mechanical properties encompass both geometric and material factors, while the effects of estrogen deficiency on the material and structural characteristics of bone at micro- to nanoscales are still obscure. We performed a series of combined methodological experiments, including nanoindentation assessment of intrinsic material properties, atomic force microscopy (AFM) characterization of trabecular (Tb) nanostructure, and Tb microarchitecture and 2D BMD. At 15 weeks after surgery, we found significantly less Tb bone mineral density (BMD) at organ (â27%) and at tissue level (â12%), Tb bone volume fraction (â29%), Tb thickness (â14%), and Tb number (â17%) in ovariectomy (OVX) rats than in sham operated (SHAM) rats, while the structure model index (+91%) and Tb separation (+19%) became significantly greater. AFM images showed lower roughness Tb surfaces with loosely packed large nodular structures and less compacted interfibrillar space in OVX than in SHAM. However, no statistically significant changes were in the Tb intrinsic material propertiesânanoindentation hardness, elastic modulus, and plastic deformationânanoindentation depths, and residual areas. Therefore, estrogen deprivation results in a dramatic deterioration in Tb micro/nanoarchitectures, 3D volumetric BMD at both organ and tissue levels, and 2D BMD, but not in the nanomechanical properties of the trabeculae per se
Influence of Variable Blocking Ratio on DDT Process
The influence of a variable blocking ratio on the DDT process is investigated through numerical simulation and experiment. Two dimensionless parameters, the average blocking ratio (BRÂŻ) and the blocking ratio change rate (α), are specified to characterize the blocking ratio of obstacles. Four arrangements are utilized to describe the variation trend of the blocking ratio in a combustor. The main results are as follows: The obstacles can stretch the flame surface and facilitate reflection and diffraction of shock waves, which causes the acceleration of the flame front. The âhot spotâ plays a vital role in the formation process of detonation waves. The overdriven detonation waves generated from âhot spotsâ promote the energy in the primary reaction zone, stimulating the formation of self-sustaining detonation. Compared with the fixed blocking ratio arrangement, the variable blocking ratio of obstacles can shorten the DDT distance. When BRÂŻ=0.43, |α| = 0.03, and the variation trend (0.52â0.34â0.49) is adopted, the minimum DDT distance is obtained in numerical and experimental results. This paper can help with the design of detonation combustors in the future
Influence of Variable Blocking Ratio on DDT Process
The influence of a variable blocking ratio on the DDT process is investigated through numerical simulation and experiment. Two dimensionless parameters, the average blocking ratio (BR¯) and the blocking ratio change rate (α), are specified to characterize the blocking ratio of obstacles. Four arrangements are utilized to describe the variation trend of the blocking ratio in a combustor. The main results are as follows: The obstacles can stretch the flame surface and facilitate reflection and diffraction of shock waves, which causes the acceleration of the flame front. The “hot spot” plays a vital role in the formation process of detonation waves. The overdriven detonation waves generated from “hot spots” promote the energy in the primary reaction zone, stimulating the formation of self-sustaining detonation. Compared with the fixed blocking ratio arrangement, the variable blocking ratio of obstacles can shorten the DDT distance. When BR¯=0.43, |α| = 0.03, and the variation trend (0.52–0.34–0.49) is adopted, the minimum DDT distance is obtained in numerical and experimental results. This paper can help with the design of detonation combustors in the future
Morphological stability analysis of vesicleswith mechanical-electrical coupling effects
Using a recently established liquid crystal model for vesicles, we present a theoretical method to analyze the morphological stability of liquid crystal vesicles in an electric field. The coupled mechanical-electrical effects associated with elastic bending, osmotic pressure, surface tension, Maxwell pressure, as well as flexoelectric and dielectric properties of the membrane are taken into account. The first and second variations of the free energy are derived in a compact form by virtue of the surface variational principle. The former leads to the shape equation of a vesicle embedded in an electric field, and the latter allows us to examine the stability of a given vesicle morphology. As an illustrative example, we analyze the stability of a spherical vesicle under a uniform electric field. This study is helpful for understanding and revealing the morphological evolution mechanisms of vesicles in electric fields and some associated phenomena of cells
Surface effects on the persistence length of nanowires and nanotubes
Surface effects on the persistence length of quasi-one-dimensional nanomaterials are investigated by using the theory of surface elasticity and the coreâshell model of nanobeams. A simple and unified expression is provided to determine the persistence length of nanowires and nanotubes with any regular polygonal cross-sections. It is demonstrated that surface effects have a distinct influence on the persistence length when the characteristic sizes of materials shrink to nanometers. This work is helpful not only for understanding the size-dependent behavior of nanomaterials but also for the design of devices based on nanotubes or nanowires
Mechanosensing model of fibroblast cells adhered on a substrate with varying stiffness and thickness
Semi-Analytic Solution of Multiple Inhomogeneous Inclusions and Cracks in an Infinite Space
This work develops a semi-analytic solution for multiple inhomogeneous inclusions of arbitrary shape and cracks in an isotropic infinite space. The solution is capable of fully taking into account the interactions among any number of inhomogeneous inclusions and cracks which no reported analytic or semi-analytic solution can handle. In the solution development, a novel method combining the equivalent inclusion method (EIM) and the distributed dislocation technique (DDT) is proposed. Each inhomogeneous inclusion is modeled as a homogenous inclusion with initial eigenstrain plus unknown equivalent eigenstrain using the EIM, and each crack of mixed modes I and II is modeled as a distribution of edge climb and glide dislocations with unknown densities. All the unknown equivalent eigenstrains and dislocation densities are solved simultaneously by means of iteration using the conjugate gradient method (CGM). The fast Fourier transform algorithm is also employed to greatly improve computational efficiency. The solution is verified by the finite element method (FEM) and its capability and generality are demonstrated through the study of a few sample cases. This work has potential applications in reliability analysis of heterogeneous materials.ASTAR (Agency for Sci., Tech. and Research, Sâpore