Bo Li

Tsinghua University | TH · Department of Engineering Mechanics

Cell migration towards stiff substrates has been coined as durotaxis and implicated in development, wound healing and cancer, where complex interplays between immune and non-immune cells are present. Compared to the emerging mechanisms underlying the strongly adhesive mesenchymal durotaxis, little is known about whether immune cells - migrating in...

Cell migration towards stiff substrates has been coined as durotaxis and implicated in development, wound healing and cancer, where complex interplays between immune and non-immune cells are present. Compared to the emerging mechanisms underlying the strongly adhesive mesenchymal durotaxis, little is known about whether immune cells - migrating in...

The interfacial interactions between epithelia and cancer cells have profound relevance for tumor development and metastasis. Through monolayer confrontation of MCF10A (nontumorigenic human breast epithelial cells) and MDA-MB-231 (human epithelial breast cancer cells) cells, we investigate the epithelial−cancerous interfacial interactions at the ti...

The actin-rich cortex plays a fundamental role in many cellular processes. Its architecture and molecular composition vary across cell types and physiological states. The full complement of actin assembly factors driving cortex formation and how their activities are spatiotemporally regulated remain to be fully elucidated. Using Dictyostelium as a...

Active topological phase transitions widely occur in active matters and biological systems, such as developing embryos. Since the discovery of the intriguing bulk-boundary effects of topological insulators in Hermitian and non-Hermitian systems, various electric, optical, acoustic, and mechanical topological metamaterials with efficient energy tran...

The growth of biological tissues, which is regulated by a variety of factors, can induce stresses that may, in turn, destabilize the tissues into diverse patterns. In most previous studies, however, tissue growth was usually assumed as a prescribed parameter independent of stresses, limiting our understanding of the mechanobiological morphogenesis...

Active topological phase transitions widely occur in active matters and biological systems, such as developing embryos. Since the discovery of the intriguing bulk–boundary effects of topological insulators in Hermitian and non-Hermitian systems, various electric, optical, acoustic, and mechanical topological metamaterials with efficient energy tran...

Physical interfaces widely exist in nature and engineering. Although the formation of passive interfaces is well elucidated, the physical principles governing active interfaces remain largely unknown. Here, we combine simulation, theory, and cell-based experiment to investigate the evolution of an active–active interface. We adopt a biphasic framew...

Morphogenesis of active shells such as cells is a fundamental chemomechanical process that often exhibits three-dimensional (3D) large deformations and chemical pattern dynamics simultaneously. Here, we establish a chemomechanical active shell theory accounting for mechanical feedback and biochemical regulation to investigate the symmetry-breaking...

Mechanical nociception is an evolutionarily conserved sensory process required for the survival of living organisms. Previous studies have revealed much about the neural circuits and sensory molecules in mechanical nociception, but the cellular mechanisms adopted by nociceptors in force detection remain elusive. To address this issue, we study the...

Designing intelligent microrobots that can autonomously navigate and perform instructed routines in blood vessels, a crowded environment with complexities including Brownian disturbance, concentrated cells, confinement, different flow patterns, and diverse vascular geometries, can offer enormous opportunities and challenges in biomedical applicatio...

Skyrmions are topologically protected vortex-like excitations that hold promise for applications such as information processing and electron manipulation. Here we combine theoretical analysis and numerical simulations to show that skyrmions can spontaneously emerge in chiral active matter without external confinements or regulation. Strikingly, the...

Physiological and pathological processes of living soft tissues always involve complicated interplays of biological, chemical, mechanical, and physical cues. Understanding the coupling mechanisms of these factors and their biological implications has attracted extensive interest from the fields of biomechanics, biophysics, biomaterials, and medical...

Rigidity of extracellular matrix markedly regulates many cellular processes. However, how cells detect and respond to matrix rigidity remains incompletely understood. Here, we propose a unified two-dimensional multiscale framework accounting for the chemomechanical feedback to explore the interrelated cellular mechanosensing, polarization, and migr...

This supporting information includes supplemental figures, movies, additional results, and the key steps in the neural network training algorithm. Corresponding author Email: yyang60@jhu.edu (Y.Y.) libome@tsinghua.edu (B.L.)

Chirality can endow nonequilibrium active matter with unique features and functions. Here, we explore the chiral dynamics in biphasic active nematics composed of self-rotating units that continuously inject energy and angular momentum at the microscale. We show that the self-rotation of units can regularize the boundaries between two phases, render...

The folded mitochondria inner membrane-cristae is the structural foundation for oxidative phosphorylation (OXPHOS) and energy production. By mechanically simulating mitochondria morphogenesis, we speculate that efficient sculpting of the cristae is organelle non-autonomous. It has long been inferred that folding requires buckling in living systems....

Nano/micromotors (NMMs) are tiny objects capable of converting energy into mechanical motion. Recently, a wealth of active matter including synthetic colloids, cytoskeletons, bacteria, and cells have been used to construct NMMs. The self-sustained motion of active matter drives NMMs out of equilibrium, giving rise to rich dynamics and patterns. Alo...

Mechanical nociception is an evolutionarily conserved sensory process required for the survival of living organisms. Previous studies have revealed much about the neural circuits and key sensory molecules in mechanical nociception, but the cellular mechanisms adopted by nociceptors in force detection remain elusive. To address this issue, we study...

The roughness or microstructures of natural and artificial materials significantly affect their surface properties. The performance of micro-sized materials and devices often exhibit a strong dependence on their surface elasticity, but it remains unclear how the surface elastic parameters can be theoretically predicted for rough solid surfaces. In...

Intelligent microrobot systems at the microscopic scale provide enormous opportunities for emerging biomedical and environmental applications. Herein, a multiagent stochastic feedback control framework to control colloidal microrobot swarms for capturing Brownian cargo particles in complex environments such as mazes is proposed. The decision‐making...

This supporting information includes supplemental figures, movies, additional results, and the pseudocode of breadth-first-search target generation algorithm. Corresponding author Email: yyang60@jhu.edu (Y.Y.) libome@tsinghua.edu (B.L.)

Understanding the emergent nonequilibrium dynamics of collective units is crucial for steering and engineering active many-body systems. Here, we explore flow transitions and topological defect dynamics of channel-confined active nematics under chiral boundary anchoring. We discover that the anchoring chirality can engender unanticipated solitonlik...

Collective cell migration is extensively observed in embryo development and cancer invasion. During these processes, the interactions between cells with distinct identities and fates are of importance for boundary formation and host defense against cancer. In this paper, we explore the collective dynamics of a two-dimensional cell mixing monolayer...

Living thin structures such as cell cortex layers and multicellular sheets often exhibit intricate morphologies and dynamic behaviors, including Turing’s pattern, periodic oscillation, and wave propagation. In this paper, we present a bio-chemo-mechanical theoretical framework to model these morphogenetic processes and to unveil the underlying mech...

Designing intelligent microrobots that can autonomously navigate and perform instructed routines in blood vessels, a complex and crowded environment with obstacles including dense cells, different flow patterns and diverse vascular geometries, can offer enormous possibilities in biomedical applications. Here we report a hierarchical control scheme...

Cell dynamics is of crucial significance for the morphogenesis, self-repair, and other physiological and pathological processes of tissues. Collective cells exhibit greatly different dynamic behaviors from isolated cells. In this lecture, some recent advances in experimental and theoretical researches on collective cell dynamics will be presented,...

Investigation of energy mechanisms at the collective cell scale is a challenge for understanding various biological processes, such as embryonic development and tumor metastasis. Here we investigate the energetics of self-sustained mesoscale turbulence in confluent two-dimensional (2D) cell monolayers. We find that the kinetic energy and enstrophy...

Current understandings on cell motility and directionality rely heavily on accumulated investigations of the adhesion-actin cytoskeleton-actomyosin contractility cycles, while microtubules have been understudied in this context. Durotaxis, the ability of cells to migrate up gradients of substrate stiffness, plays a critical part in development and...

Cell polarization, a process depending on both intracellular and intercellular interactions, is crucial for collective cell migration that commonly emerges in embryonic development, tissue morphogenesis, wound healing and cancer metastasis. Although invasive cancer cells display weak cell–cell interactions, they can invade host tissues through a co...

Many biological materials contain nanofibers of helical shape to achieve multiple biological functions and superior mechanical properties. In this paper, we establish a microstructure-based crack-bridging model to investigate how the chiral morphologies of nanofibers contribute to the fracture properties of these natural nanocomposites. By using a...

Ventral bending of the embryonic tail within the chorion is an evolutionarily conserved morphogenetic event in both invertebrates and vertebrates. However, the complexity of the anatomical structure of vertebrate embryos makes it difficult to experimentally identify the mechanisms underlying embryonic folding. This study investigated the mechanisms...

Bacteria usually grow in populations to survive in various environments. A yet unsolved issue is how mechanical forces at the cellular level regulate the morphogenesis of bacterial population. In this paper, we combine experiments and theoretical analysis to investigate the growth of bacterial chains constituted by rod-shaped Bacillus subtilis. Our...

Cell migration and invasion are two essential processes during cancer metastasis. Increasing evidence has shown that the Piezo1 channel is involved in mediating cell migration and invasion in some types of cancers. However, the role of Piezo1 in the breast cancer and its underlying mechanisms have not been clarified yet. Here, we show that Piezo1 i...

Collective cell dynamics plays significant roles in various physiological or pathological processes including embryo development, wound healing, and cancer invasion. It involves the self-organization of cytoskeleton and biochemical signaling transduction, as well as complex cell-cell interactions and cell-environment interactions. Therefore, collec...

The mechanical properties of soft tissues are strongly dependent on their microstructures which evolve with aging and diseases. In this paper, a micromechanical model is presented to investigate the mechanical properties of tendons and ligaments, which are treated as planar crimped fiber-reinforced composites. The interaction among the constituents...

Many biological systems display intriguing chiral patterns and dynamics. Here, we present an active nematic theory accounting for individual spin to explore the collective handedness in chiral rod-shaped aggregations. We show that coordinated individual spin and motility can engender a vortex-array pattern with chirality and drive ordering of topol...

Migratory dynamics of collective cells is central to the morphogenesis of biological tissues. The statistical distribution of cell velocities in 2D confluent monolayers is measured through large‐scale and long‐term experiments of various cell types lying on different substrates. A linear relation is discovered between the variability and the mean o...

Cell division is central for embryonic development, tissue morphogenesis, and tumor growth. Experiments have evidenced that mitotic cell division is manipulated by the intercellular cues such as cell-cell junctions. However, it still remains unclear how these cortical-associated cues mechanically affect the mitotic spindle machinery, which determin...

Fascin1 is known to participate in the migration of cancer cells by binding to actin filaments. Recent studies evidenced that fascin1 also modulates processes, such as the tumorigenesis and maintenance of pluripotency genes, in cancer stem cells. However, the function of fascin1 in embryonic stem cells remains unclear. In this paper, we report that...

Efficient navigation and precise localization of Brownian micro/nano self‐propelled motor particles within complex landscapes could enable future high‐tech applications involving for example drug delivery, precision surgery, oil recovery, and environmental remediation. Here, a model‐free deep reinforcement learning algorithm based on bio‐inspired n...

Mechanical adaptions of cells, including stiffness variation, cytoskeleton remodeling, motion coordination, and shape changing, are essential for tissue morphogenesis, wound healing, and malignant progression. In this paper, we take confluent monolayers of Madin-Darby canine kidney (MDCK) and mouse myoblast (C2C12) cells as model systems to probe h...

Cellular dynamic behaviors in organ morphogenesis and embryogenesis are affected by geometrical constraints. In this paper, we investigate how the surface topology and curvature of the underlying substrate tailor collective cell migration, which are crucial in many important aspects of development and disease. An active vertex model is developed to...

Efficient navigation and precise localization of Brownian micro/nano self-propelled motor particles within complex landscapes could enable future high-tech applications involving for example drug delivery, precision surgery, oil recovery, and environmental remediation. Here we employ a model-free deep reinforcement learning algorithm based on bio-i...

Progression of cancers involves complicated and coupled interactions among mechanical, physical, chemical, and biological factors. Given the broad implications of tumor morphogenesis in clinics, we review the state-of-the-art morphomechanics of solid tumors, with an aim to highlight mechanistic factors that might potentially collude with oncology t...

Epithelial tumor cells may display different collective invasion behaviors, forming an unjammed flow like a fluid or a jammed deformation like a solid depending on such factors as cell–cell adhesion, cell–substrate adhesion, or the density and shapes of the cells. We investigate the relation between the collective motility and the shapes of human c...

Solitary, persistent wave packets called solitons hold potential to transfer information and energy across a wide range of spatial and temporal scales in physical, chemical, and biological systems. Mechanical solitons characteristically emerge either as a single wave packet or uncorrelated propagating topological entities through space and/or time,...

Equipping micro‐/nanoscale colloidal robots with artificial intelligence such that they can efficiently navigate in unknown complex environments could dramatically impact their use in emerging applications like precision surgery and targeted nano‐drug delivery. Here we develop a model‐free deep reinforcement learning algorithm that can train colloi...

Brownian dynamics of colloidal particles on complex curved surfaces has found important applications in diverse physical, chemical, and biological processes. However, most Brownian dynamics simulation algorithms focus on relatively simple curved surfaces that can be analytically parameterized. In this work, we develop an algorithm to enable Brownia...

Determining the macroscopic mechanical properties of composites with complex microstructures is a key issue in many of their applications. In this Letter, a machine learning-based approach is proposed to predict the effective elastic properties of composites with arbitrary shapes and distributions of inclusions. Using several data sets generated fr...

Facile methods toward strain-tolerant graphene-based electronic components remain scarce. Although being frequently used to disperse low-dimensional carbonaceous materials, ultrasonication (US) has never been reliable to fabricate stretchable carbonaceous nanocomposite (SCNC). Inspired by the unusual sonochemical assembly between graphene oxide (GO...

Brownian dynamics of colloidal particles on complex surfaces has found important applications in diverse physical, chemical and biological processes. However, current Brownian dynamics simulation algorithms mostly work for relatively simple surfaces that can be analytically parameterized. In this work, we develop an algorithm to enable Brownian dyn...

Multipolar divisions of heated cells has long been thought to stem from centrosome aberrations of cells directly caused by heat stress. In this paper, through long-term live-cell imaging, we provide direct cellular evidences to demonstrate that heat stress can promote multiple multipolar divisions of MGC-803 and MCF-7 cells. Our results show that,...

Migrating cells constantly experience geometrical confinements in vivo, as exemplified by cancer invasion and embryo development. In this paper, we investigate how intrinsic cellular properties and extrinsic channel confinements jointly regulate the two-dimensional migratory dynamics of collective cells. We find that besides external confinement, a...

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 tu...

Functional fluorescent silkworm silk holds promise for many important applications in biomedical engineering, optics, and photonics. However, it remains a challenge to obtain fluorescent silk in scale-up with both good mechanical properties and highly stable fluorescence simultaneously. In this work, we report a highly efficient strategy to produce...

Equipping active particles with intelligence such that they can efficiently navigate in an unknown complex environment is essential for emerging applications like precision surgery and targeted drug delivery. Here we develop a deep reinforcement learning algorithm that can train active particles to navigate in environments with random obstacles. Th...

Dorsal closure is an essential developmental process of Drosophila embryogenesis, during which the ectoderm fuses the two sides of a gap into a complete ectodermal epithelium. A defective closure may cause scar formation or even embryonic lethality. In this paper, a multiscale fracture mechanics model is established by treating the dorsal closure a...

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...

Mechanoreceptive organelles (MOs) are specialized subcellular entities in mechanoreceptors that transform extracellular mechanical stimuli into intracellular signals. Their ultrastructures are key to understanding the molecular nature and mechanics of mechanotransduction. Campaniform sensilla detect cuticular strain caused by muscular activities or...

Growth shapes soft tissues not only through mass addition or volume expansion but also through deformation instabilities and consequent morphological evolution. In this paper, we probe the torsion instability of an anisotropically growing tube with fiber reinforcement, which mimics many tubular organs in animals or plants. We derive the Stroh formu...

Active particles capable of self-propulsion commonly exhibit rich collective dynamics and have attracted increasing attention due to their applications in biology, robotics, social transport, and biomedicine. However, it remains unclear how the geometric features of active particles affect their collective behaviors. In this paper, we explore the c...

Deterministic design of surface patterns has seen a surge of interests due to their wide applications in flexible and stretchable electronics, microfluidics, and optical devices. Recently, instability of bi-layer systems has been extensively utilized by which micro/nano-patterns of a film can be easily achieved through macroscopically deforming the...

Deciphering the bio–chemo–mechanical mechanisms in tissue growth and deformation helps understand the morphogenesis of organs and organisms under physiological and pathological conditions. In this paper, we present a finite element method that can account for the interplay of volumetric growth, chemical transport, and mechanical deformation in soft...

Owing to their exquisite geometric structures and excellent mechanical properties, spider orb webs possess an outstanding ability to capture flying prey. In this work, we report a mechanism that enhances the energy absorption ability of spider webs. Through systematic measurements of the mechanical properties of both spiral and radial silks, we fin...

Collective cell migration occurs in a diversity of physiological processes such as wound healing, cancer metastasis, and embryonic morphogenesis. In the collective context, cohesive cells may move as a translational solid, swirl as a fluid, or even rotate like a disk, with scales ranging from several to dozens of cells. In this work, an active vert...

The collapse of blood vessels are widely observed in solid tumors, but the mechanisms underpinning this abnormal behavior remain unclear. In this paper, we investigate the stability of blood vessels embedded in a growing solid tumor by using a chemomechanical poroelastic theory. Linear stability analysis is first made to give the critical condition...

Swertia mussotii (Gentianaceae) is a traditional Chinese medicinal plant grown in the Qinghai-Tibet Plateau. Three fractions from S. mussotii extract, named SWF50, SWF 70 and SWF100, were screened for in vitro anti-proliferative activity on two gastric cancer cell lines, MGC-803 and BGC-823 cells using MTT assay. Our results demonstrated that SMF70...

Cellulose nanopaper exhibits superior mechanical properties with both high strength and toughness, and the crack bridging mechanism of nanofibers makes the most significant contribution to its fracture toughness. In this paper, we investigate the fracture toughness of a mode-I crack in cellulose nanopaper by using a modified crack-bridging model. D...

Material anisotropy regulates the instabilities of film-substrate systems at different length scale. In this paper, we investigate the surface wrinkling and morphological evolution of an orthotropic thin film resting on a compliant substrate. Under different loading conditions, the system may buckle into various surface patterns, e.g., stripe, chec...

Curvature plays an important role in the morphological evolution of soft shells under stretch. Here, through a combination of experiment, theory and simulation, we investigate the behavior of a hemispherical soft shell subject to an increasing outward point force at its pole. In contrast to an inward point force inducing a polygonal pattern of buck...

Soft membranous materials widely exist in engineering and nature, and the determination of their constitutive parameters is of both scientific and engineering significance. In this paper, the bulge test method is extended to determine the hyperelastic parameters of soft membranes with or without initial stresses. Two extensively applied models—neo-...

Liquid transport is a fundamental process relevant to a wide range of applications, e.g. heat transfer, anti-icing, self-cleaning, drag reduction, and microfluidic systems. For these applications, a deeper understanding of the sliding behavior of water droplets on solid surfaces is of particular importance. In this study, the frictional behavior of...

The control of surface wrinkling patterns at the microscale is a concern in many applications. In this letter, we regulate surface wrinkling patterns on a film–substrate system by introducing microbeads atop the film. Both experiments and theoretical analysis reveal the changes in surface wrinkles induced by microbeads. Under equibiaxial compressio...

Biofilm morphogenesis not only reflects the physiological state of bacteria but also serves as a strategy to sustain bacterial survival. In this paper, we take the Bacillus subtilis colony as a model system to explore the morphomechanics of growing biofilms confined in a defined geometry. We find that the growth-induced stresses may drive the occur...

Periodic oscillations of collective cells occur in the morphogenesis and organogenesis of various tissues and organs. In this paper, an oscillating cytodynamic model is presented by integrating the chemomechanical interplay between the RhoA effector signaling pathway and cell deformation. We show that both an isolated cell and a cell aggregate can...

The superhydrophobicity and self-cleaning property of micro/nano-structured solid surfaces require a stable Cassie-Baxter (CB) wetting state at the liquid-solid interface. We present an energy method to investigate how the three-phase line tension affects the CB wetting state on nanostructured materials. For some nanostructures, the line tension ma...

Mechanics plays a crucial role in the growth, development, and therapeutics of tumors. In this paper, a nonlinear poroelastic theory is established to describe the mechanical behaviors of solid tumors. The free-swollen state of a tumor is chosen as the reference state, which enables us to avoid pursuing a dry and stress-free state that is hard to a...

Significance Oscillatory morphodynamics of collective cells is of fundamental importance for concerting cellular events and tissue-level developments in many living systems. We demonstrate that the collective cell oscillations in an epithelium-like monolayer are attributed to a chemomechanical Hopf bifurcation tailored by external forces and bounda...

We investigate the edge wrinkling of a soft ridge with gradient thickness under axial compression. Our experiments show that the wrinkling wavelength undergoes a considerable increase with increasing load. Simple scaling laws are derived based on an upper-bound analysis to predict the critical buckling conditions and the evolution of wrinkling wave...

The conflict between strength and toughness is a long-standing challenge in advanced materials design. Recently, a fundamental bottom-up material design strategy has been demonstrated using cellulose nanopaper to achieve significant simultaneous increase in both strength and toughness. Fertile opportunities of such a design strategy aside, mechanis...

Surface wrinkling of thin films on substrates offers an effective strategy to create controllable surface patterns of wide applications. In this paper, both theoretical analysis and numerical simulations are performed to study the surface wrinkling of thin films bonded on a microstructured soft substrate under compression. We consider two typical k...

The extracellular matrix (ECM) of a solid tumor not only affords scaffolding to support tumor architecture and integrity but also plays an essential role in tumor growth, invasion, metastasis, and therapeutics. In this paper, a non-equilibrium thermodynamic theory is established to study the chemo-mechanical behaviors of tumor ECM, which is modeled...

Substrate stiffness is crucial for diverse cell functions, but the mechanisms conferring cells with mechanosensitivity are still elusive. By tailoring substrate stiffness with 10-fold difference, we showed that L-type voltage-gated Ca²⁺ channel current density was greater in chick ventricular myocytes cultured on the stiff substrate than on the sof...

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 ro...

Instabilities in bilayered systems can generate a wide variety of patterns ranging from simple folds, wrinkles, and creases to complex checkerboards, hexagons, and herringbones. Physics-based theories traditionally model these systems as a thin film on a thick substrate under confined compression and assume that the film is orders of magnitude stif...