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Regional stretch method to measure the elastic and hyperelastic properties of soft materials

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Science China(Physics,Mechanics & Astronomy) 2018年第2期61卷 56-64页

作者： JunYuan Sheng HaoYuan Guo YanPing Cao XiQiao Feng institute of biomechanics and Medical Engineering AML Department of Engineering Mechanics Tsinghua University

Characterizing the mechanical properties of soft materials and biological tissues is of great significance for understanding their deformation behaviors. In this paper, a regional stretching method is proposed to measure the elastic and hyperelastic properties of a soft material with an adhesive surface or with the aid of glue. Theoretical and dimensional analyses are performed to investigate the regional stretch problem for soft materials that obey the neo-Hookean model, the Mooney-Rivlin model, or the Arruda-Boyce model. Finite element simulations are made to determine the expressions of the dimensionless functions that correlate the stretch response with the constitutive parameters. Thereby, an inverse approach is established to determine the elastic and hyperelastic properties of the tested materials. The regional stretch method is also compared to the indentation technique. Finally, experiments are performed to demonstrate the effectiveness of the proposed method.

关键词： soft materials hyperelasticity adhesion dimensional analysis inverse problem

A cell-based model for analyzing growth and invasion of tumor spheroids

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Science China(Technological Sciences) 2019年第8期62卷 1341-1348页

作者： CHEN PengCheng LI Bo FENG XiQiao institute of biomechanics and Medical Engineering AMLDepartment of Engineering MechanicsTsinghua University

Both chemical and mechanical determinants adapt and react throughout the process of tumor invasion. In this study, a cell-based model is used to uncover the growth and invasion of a three-dimensional solid tumor confined within normal cells. Each cell is treated as a spheroid that can deform, migrate, and proliferate. Some fundamental aspects of tumor development are considered,including normal tissue constraints, active cellular motility, homotypic and heterotypic intercellular interactions, and pressureregulated cell division as well. It is found that differential motility between cancerous and normal cells tends to break the spheroidal symmetry, leading to a finger instability at the tumor rim, while stiff normal cells inhibit tumor branching and favor uniform tumor expansion. The heterotypic cell-cell adhesion is revealed to affect the branching geometry. Our results explain many experimental observations, such as fingering invasion during tumor growth, stiffness inhibition of tumor invasion, and facilitation of tumor invasion through cancerous-normal cell adhesion. This study helps understand how cellular events are coordinated in tumor morphogenesis at the tissue level.

关键词： tumor growth collective invasion cell-based modeling

Regulating wrinkling patterns by periodic surface stiffness in film-substrate structures

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Science China(Technological Sciences) 2019年第5期62卷 747-754页

作者： LI Bo ZENG ChongQing YIN SiFan FENG XiQiao institute of biomechanics and Medical Engineering AML Department of Engineering Mechanics Tsinghua University

Surface wrinkling of materials holds promise for important applications in diverse fields such as multifunctional surfaces and biomedical engineering. For these applications, it is of interest to attain various surface wrinkles with tunable wavelengths and amplitudes. Through a combination of experiments and numerical simulations, we here propose a method to regulate the wrinkling patterns in a film-substrate system by introducing periodic surface stiffness, which is generated through sequential specified ultraviolet-ozone(UVO) treatments. Both experiments and numerical simulations demonstrate that the proposed technique can produce various patterns with wide, tunable geometrical features and anisotropy. The effects of surface stiffness distribution, the exposure durations of UVO-treatments, and the loading biaxiality are examined on the generated surface patterns.

关键词： film-substrate system wrinkling surface patterns stiffness modification

Targets capture by distributed active swarms via bio-inspired reinforcement learning

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 210-221页

作者： Kun Xu Yue Li Jun Sun Shuyuan Du Xinpeng Di Yuguang Yang Bo Li institute of biomechanics and Medical Engineering Applied Mechanics Laboratory Department of Engineering MechanicsTsinghua University institute of Nuclear and New Energy Technology Tsinghua University Shanghai Aerospace Control Technology institute Shanghai Key Laboratory of Aerospace Intelligent Control Technology College of Automation Engineering Nanjing University of Aeronautics and Astronautics

Natural swarms arranged from cells to herds are usually decentralized but display intriguing collective intelligence in coordinating individuals across large scales to efficiently achieve their common goals. Learning from nature may provide new strategies for controlling collective dynamics of synthetic swarms to accomplish specific functions. Here, we present a bioinspired computational framework that steers distributed active swarms to collectively capture and merge targets via reinforcement learning. We exploit collective milling structures of natural herds to cage the targets, and adopt a switching control policy inspired by sperms' chiral dynamics to optimize the trajectories of individuals, through which the active swarms can selforganize to enclose single or multiple distant targets in a dynamical, adaptive and scalable manner. There exists a critical swarm size, beyond which the excessive competition between agents would generate large mechanical forces, leading to capture instability but enabling the transition from short-distance to long-distance merging capture of multiple targets. This work provides physical insights into distributed active swarms and could offer a multilevel, decentralized strategy toward controlling swarm robotics in wide applications such as bio-medical devices, machine immunity, and target clearance.

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Surface effects on cylindrical indentation of a soft layer on a rigid substrate

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Acta Mechanica Sinica 2020年第2期36卷 422-429页

作者： Min Li Huan-Xin Zhang Zi-Long Zhao Xi-Qiao Feng institute of biomechanics and Medical Engineering AMLDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China

In this paper,theoretical and numerical methods are combined to investigate the two-dimensional,cylindrical indentation of an elastic soft layer bonded on a rigid *** incorporating the Gurtin-Murdoch’s theory of surface elasticity into the Kerr model,we account for surface effects on the indentation behavior of a soft *** governing differential relation between the surface pressure and displacement of the film-substrate system is *** an incompressible thin layer,the explicit solutions are derived,which are simple and *** element simulations are performed using an explicit restart algorithm to study the indentation properties of the layer-substrate system and to examine the validity and accuracy of the theoretical *** work holds promise for applications in mechanical characterization of soft materials,such as biological tissues and cells.

关键词： Soft materials Indentation Surface effect Contact Kerr model

Regulation of substrate surface topography on differentiation of mesenchymal stem cells

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Acta Mechanica Sinica 2020年第5期36卷 1158-1169,I0004页

作者： Bo Huo Yang Zhao Xue Bai Qing Sun Fei Jiao biomechanics Lab Department of MechanicsSchool of Aerospace EngineeringBeijing Institute of TechnologyBeijing 100081China

Mesenchymal stem pells(MSCs)have been extensively used in the field of tissue engineering and regenerative *** effect of surface properties on the differentiation of MSCs is a very important issue for the design and fabrication of scaffolds or *** review is mainly focused on the morphological or topographic characteristics of cell adhesion substrate,*** area and shape for individual cell,cell density and cell-cell contact for multiple cells,substrate roughnessridge width,micropillar height,nanoparticle diameter and aspect ratio of *** results from different studies were quantitativcly analyzed using comparable or unified parameters and definitions under the specific experimental conditions such as cell source,culture time,induction medium,matrix material and differentiation *** interesting phenomena and properties were discovered by this integrated and systematic analysis,which might give insights into the regulatory mechanism of surface morphology or topography on MSCs differentiation.

关键词： Mesenchymal stem cell Adhesion morphology Surface topography Differentiation Biomaterial

A dynamic cellular vertex model of growing epithelial tissues

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Acta Mechanica Sinica 2017年第2期33卷 250-259页

作者： Shao-Zhen Lin Bo Li Xi-Qiao Feng institute of biomechanics and Medical Engineering AMLDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China

Intercellular interactions play a significant role in a wide range of biological functions and processes at both the cellular and tissue scales, for example, embryogenesis, organogenesis, and cancer invasion. In this paper, a dynamic cellular vertex model is presented to study the morphomechanics of a growing epithelial monolayer. The regulating role of stresses in soft tissue growth is revealed. It is found that the cells originating from the same parent cell in the monolayer can orchestrate into clustering patterns as the tissue grows. Collective cell migration exhibits a feature of spatial correlation across multiple cells. Dynamic intercellular interactions can engender a variety of distinct tissue behaviors in a social context. Uniform cell proliferation may render high and heterogeneous residual compressive stresses, while stress-regulated proliferation can effectively release the stresses, reducing the stress heterogeneity in the tissue. The results highlight the critical role of mechanical factors in the growth and morphogenesis of epithelial tissues and help understand the development and invasion of epithelial tumors.

关键词： Soft tissue Cellular vertex model Cell Morphogenesis

Torsion Instability of Anisotropic Cylindrical Tissues with Growth

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Acta Mechanica Solida Sinica 2019年第5期32卷 621-632页

作者： Sang Ye Si-Fan Yin Bo Li Xi-Qiao Feng institute of biomechanics and Medical Engineering AMLDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China

Growth shapes soft tissues not only through mass addition or volume expansion but also through deformation instabilities and consequent morphological *** this paper,we probe the torsion instability of an anisotropically growing tube with fiber reinforcement,which mimics many tubular organs in animals or *** derive the Stroh formulation for the incremental boundary value problem and numerically solve it using the surface impedance method.A linear st ability analysis is conducted to investigate the critical condition for the onset of *** thresholds of helical wrinkling are calculated in terms of growth ratio and external *** effect of fibers on the critical state under axial stretching is *** is found that the tangential growth tends to enhance the critical torsion angle but has a weak influence on the critical longitudinal mode of wrinkling,which,however,can be remarkably affected by the axial *** study can help understand the formation of helical morphologies in biological mat erials and provide cues for engineering desired st ruc tu res or devices.

关键词： Biological material Tube Growth Instability Stroh formulation

The impact of N-terminal phosphorylation on LHCII conformation in state transition

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Acta Mechanica Sinica 2014年第3期30卷 447-456页

作者： Jin-Hong Ding Ning Li Man-Liu Wang Yan Zhang Shou-Qin Lü Mian Long Key Laboratory of Microgravity(National Microgravity Laboratory)and Center of biomechanics and Bioengineering Institute of MechanicsChinese Academy of Sciences

State transition is an important protection mechanism of plants for maintaining optimal efficiency through redistributing unbalanced excitation energy between photosystem II （PSII） and photosystem I （PSI）. This process depends on the reversible phosphorylation/dephosphorylation of the major light-harvesting complex II （LHCII） and its bi-directional migration between PSII and PSI. But it remains unclear how phosphorylation/dephosphorylation modulates the LHCII conformation and further regulates its reversible migration. Here molecular dynamics simulations （MDS） were employed to elucidate the impact of phosphorylation on LHCII conformation. The results indicated that N-terminal phosphorylation loosened LHCII trimer with decreased hydrogen bond （H-bond） interactions and extended the distances between neighboring monomers, which stemmed from the conformational ad- justment of each monomer itself. Global conformational change of LHCII monomer started from its stromal N- terminal （including the phosphorylation sites） by enhancing its interaction to lipid membrane and by adjusting the interaction network with surrounded inter-monomer andintra-monomer transmembrane helixes of B, C, and A, and finally triggered the reorientation of transmembrane helixes and transferred the conformational change to luminal side helixes and loops. These results further our understanding in molecular mechanism of LHCII migration during state transition from the phosphorylation-induced microstructural feature of LHCII.

关键词： State transition LHCII Phosphorylation Conformation