Acta Mechanica Sinica
The Journal covers all disciplines in the field of theoretical and applied mechanics, including solid mechanics, fluid mechanics, dynamics and control, and biomechanics. It explores analytical, computational and experimental progresses in all areas of mechanics. The Journal also encourages research in interdisciplinary subjects, and servess...
CN 11-2063/O3
ISSN 0567-7718(Print)
ISSN 1614-3116(Online)
Editors-in-Chief:
Professor Tian Jian Lu
Professor Wei Shyy
Professor Zhigang Suo
Impact Factor: 1.545
Citation: Acta Mech. Sin.
Frequency: Bimonthly
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Acta Mechanica Sinica--2019, 35 (2)   Published: 15 April 2019
THEMED ARTICLE ON MECHANICAL ENVIRONMENTS OF LIVING CELLS
Mechanical microenvironments of living cells: a critical frontier in mechanobiology
Guoyou Huang, Feng Xu, Guy M. Genin, Tian Jian Lu
Abstract

The fields of biomechanics and mechanobiology have long been predicated on the premise that mechanics governs cell behavior. However, over the past few years, a growing body of evidence has suggested that the mechanical environment very close to cells – the cell microenvironment – plays the most important role in determining what a cell feels and how it responds to tissue-level stimuli. To complicate matters further, cells can actively manipulate their microenvironments through pa...

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Tissue cell differentiation and multicellular evolution via cytoskeletal stiffening in mechanically stressed microenvironments
Junwei Chen, Ning Wang
Abstract

Evolution of eukaryotes from simple cells to complex multicellular organisms remains a mystery. Our postulate is that cytoskeletal stiffening is a necessary condition for evolution of complex multicellular organisms from early simple eukaryotes. Recent findings show that embryonic stem cells are as soft as primitive eukaryotes-amoebae and that differentiated tissue cells can be two orders of magnitude stiffer than embryonic stem cells. Soft embryonic stem cells become stiff as they differenti...

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Mechanical force drives the polarization and orientation of cells
Shijie He, Xiaomeng Li, Baohua Ji
Abstract

Collective cells are organized to form specific patterns which play important roles in various physiological and pathological processes, such as tissue morphogenesis, wound healing, and cancer invasion. Compared to single cell behaviors, which has been intensively studied from many aspects (cell migration, adhesion, polarization, proliferation, etc.) and at various scales (molecular, subcellular, and cellular), the multiple cell behaviors are relatively less understood, particularly in a quan...

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Mechanical microenvironments as key cellular regulator in the liver
Zhifeng You, Lyu Zhou, Wenjing Li, Chenyu Huang, Yanan Du
Abstract

Tissue stiffness, shear stress, and interstitial pressure make up major factors of liver mechanical microenvironment, which play the key regulatory role to control cell behaviors in the liver and progress of liver diseases. In this review, we focus on the characteristics of liver mechanical microenvironments and summarize cellular responses to mechanobiological changes during liver pathogenesis, especially in hepatic fibrosis and cirrhosis. A better understanding of the indispensable contribu...

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Nuclear mechanics during constricted migration
Yuntao Xia, Charlotte R. Pfeifer, Dennis E. Discher
Abstract

Cell migration through narrow interstitial space in tissues is commonly seen in both physiological and pathological conditions. For example, immune cells have to squeeze through vasculature and extracellular matrix to reach the wound or diseased sites, and similarly cancer cells need to crawl through porous space in tissues to invade surrounding tumor-free regions. Therefore, the bulky stiff nucleus in the cell becomes a barrier during constricted migration making such process pore-size depen...

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Effects of hypoxia on the biological behavior of MSCs seeded in demineralized bone scaffolds with different stiffness
Yuanyuan Sun,Guobao Chen,Yonggang Lv
Abstract

Matrix stiffness has been demonstrated in many studies to adjust the biological behaviors of mesenchymal stem cells (MSCs). However, in the initial phase of bone restore, MSCs will encounter a hypoxic microenvironment. Studying the connection existing between the matrix stiffness and biological behavior of MSCs under hypoxic condition can better simulate the microenvironment at the prime period of bone repairment. In this work, three-dimensional (3D) decalcified bone scaffolds with diverse st...

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Imaging oxygen microenvironment in hydrogel microwell array
Meng Wang, Shaobao Liu, Fei Li
Abstract

Hydrogel microwell arrays (HMAs) have been wildly used for engineering cell microenvironment by providing well-controlled biophysical and biochemical cues (e.g., three dimensional (3D) physical boundary, biomolecule coating) for cells. Among these cues, the oxygen microenvironment has shown great effect on the cellular physiological processes. However, it is currently technically challenging to characterize the local oxygen microenvironment within HMAs. Here, we prepared HMAs with different c...

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Fabrication of three-dimensional islet models by geometry-controlled hanging drop method
Bin Gao, Ce Jing, Kelvin Ng, Belinda Pingguan-Murphy, Qingzhen Yang
Abstract

Hanging-drop method has been widely used to fabricate three-dimensional (3D) in vitro tissue models due to its advantages such as being easy to perform, inexpensive, and permitting precise control of cell spheroid formation. The geometry of hanging drop may play a critical role on the formation of cell spheroids, which, however, has not been explored. In this study, we developed a modified hanging-drop platform that enables the production of cell spheroids in a high-throughput manner...

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Volumetric response of an ellipsoidal liquid inclusion: implications for cell mechanobiology
Xin Chen, Wei He, Shaobao Liu, Moxiao Li, Guy M. Genin, Feng Xu, Tian Jian Lu
Abstract

Elastic composites containing liquid inclusions exist widely in nature and engineering fields. The volumetric response of liquid inclusions is important in many cases, such as an isolated cell embedded in an extracellular matrix and an oil pocket embedded within shale. In this study, we developed a model for describing the volumetric response of an ellipsoidal liquid inclusion. Specifically, we investigated the volumetric response of an ellipsoidal liquid inclusion embedded in a three-dimensi...

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Diffusive-stochastic-viscoelastic model on specific adhesion of viscoelastic solids via molecular bonds
Kuncheng He, Long Li, Jizeng Wang
Abstract

A diffusive-stochastic-viscoelastic model is proposed for the specific adhesion of viscoelastic solids via stochastically formed molecular bonds. In this model, we assumed that molecular level behaviours, including the diffusion of mobile adhesion molecules and stochastic reaction between adhesion molecules and binding sites, obey the Markovian stochastic processes, while mesoscopic deformations of the viscoelastic media are governed by continuum mechanics. Through Monte Carlo simulations of ...

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Harnessing structural instability for cell durotaxis
Jie Wei, Xiaofeng Chen, Bin Chen
Abstract

Cells were suggested to sense matrix rigidity by applying fluctuating forces, but the underlying mechanism remains elusive. Here with a generic filament-crosslinker modeling system for stress fibers, we demonstrate that high mechanical forces can be induced by specific protein-protein interactions with biased kinetics. Strikingly, we further find that there exist two patterns of force generation, a stable pattern and a fluctuated pattern, in agreement with previous experimental observations. ...

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Buckling of filamentous actin bundles in filopodial protrusion
Yanzhong Wang, Jin Qian
Abstract

The mechanical behaviors of filamentous actin (F-actin) bundles play an essential role in filopodial protrusions at the leading edge of crawling cells. These bundles consist of parallel actin filaments that are hexagonally packed and interconnected via cross-linking proteins including α-actinin, filamin, and fascin. As pushing against the plasma membrane and/or external barriers, the actin bundles in filopodial protrusion inevitably encounter a compressive load. The bending stiffness an...

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Molecular simulation of diffusion of rigidity-tuned nanoparticles in biological hydrogels
Falin Tian, Hui Wang, Huawei Li, Ping Cheng, Xinghua Shi
Abstract

The penetration capability of the drug nano-carriers (NCs) in biological hydrogels, such as mucus and tumor interstitial matrix, would typically influence the efficiency of drug delivery. Understanding the effect of the physicochemical property of the drug carriers on their diffusion capability in biological hydrogel becomes important for designing and optimizing the nano-carriers. Here, using a coarse-grained molecular dynamics model, we studied how the rigidity of NCs affected their diffusi...

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FLUID MECHANICS
Direct numerical simulation of turbulent boundary layer over an anisotropic compliant wall
Qian-Jin Xia, Wei-Xi Huang, Chun-Xiao Xu
Abstract

Direct numerical simulation of a spatially developing turbulent boundary layer over a compliant wall with anisotropic wall material properties is performed. The Reynolds number varies from 300 to approximately 860 along the streamwise direction, based on the external flow velocity and the momentum thickness. Eight typical cases are selected for numerical investigation under the guidance of the monoharmonic analysis. The instantaneous flow fields exhibit the traveling wavy motion of the compli...

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Numerical solutions of 2-D steady compressible natural convection using high-order flux reconstruction
Yaojie Yu,Feng Liu,Tingbo Zhou,Chao Gao,Ya Liu
Abstract

Low Mach number flows are common and typical in industrial applications. When simulating these flows, performance of traditional compressible flow solvers can deteriorate in terms of both efficiency and accuracy. In this paper, a new high-order numerical method for two-dimensional (2-D) state low Mach number flows is proposed by combining flux reconstruction (FR) and preconditioning. Firstly, a Couette flow problem is used to assess the efficiency and accuracy of preconditioned FR. It is foun...

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Physical mechanism for origin of streamwise vortices in mode A of a square-section cylinder
L. M. Lin,S. Y. Shi,Y. X. Wu
Abstract

In the present paper, physical mechanism responsible for origin of streamwise vortices in mode A appeared in the threedimensional (3-D) wake transition of a square-section cylinder is investigated. Direct numerical simulations at a Reynolds number of 180 firstly show that such streamwise vorticity is not originated from lateral surfaces. Then through the analysis of local flow field in the immediate neighborhood of rear surface, based on the theory of vortex-induced vortex, a new physical mec...

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SOLID MECHANICS
Influence of stress and high temperature treatment on the permeability evolution behavior of sandstone
Peng Xu, Sheng-Qi Yang
Abstract

Permeability is an important property of rock in gas and oil exploration engineering, environment temperature and geo-stress have great influence on it. This paper aims to analyze the influence of thermal treatment on the permeability of sandstone under triaxial compression. Based on the gas seepage tests on a sandstone specimen after different thermal treatment temperatures with different gas pressures, hydrostatic stresses and deviatoric stresses, the thermal effect on physical property of ...

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Topology optimization of continuum structures considering damage based on independent continuous mapping method
Jiazheng Du,Yunhang Guo,Zuming Chen,Yunkang Sui
Abstract

A continuum topology optimization usually produces results similar to a skeleton structure. In addition, the material utilization in the optimized structure is greatly improved compared with the original structure. On the other hand, the redundancy of the structure is greatly reduced due to the removed material. A partial local failure in the optimized structure makes it more difficult for the entire structure to meet the strength/stiffness requirements. By using the independent continuous ma...

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Surface evolution caused by curvature driven forces based on natural exponential pair potential
Dan Wang, Yajun Yin, Zheng Zhong, Zhu Su, Zhili Hu
Abstract

Based on the natural exponential pair potential, the interaction potential between curved surface body and on surface particle is studied. Firstly, the interaction potential is written as a function of curvatures through the differential geometry. Secondly, idealized numerical experiments are designed to test the accuracy of curvature-based potential. Then, the driving forces induced by curvatures are analyzed, which confirms that micro/nano curved surface body can induce driving forces, curv...

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