Mechanics of elliptical interlocking sutures in biological interfaces.

Biological materials, such as beetle elytra and bird beaks, exhibit complex interfaces with diverse morphologies that have evolved to enhance their mechanical properties. However, the relationships between their geometric forms and mechanical properties remain inadequately understood. Here, we develop a theoretical model, supported by finite element simulations and experiments, to explore the strengthening and toughening mechanisms of biological interfaces characterized by elliptical interlocking sutures.

Applying Spatiotemporal Modeling of Cell Dynamics to Accelerate Drug Development.

Cells act as physical computational programs that utilize input signals to orchestrate molecule-level protein-protein interactions (PPIs), generating and responding to forces, ultimately shaping all of the physiological and pathophysiological behaviors. Genome editing and molecule drugs targeting PPIs hold great promise for the treatments of diseases. Linking genes and molecular drugs with protein-performed cellular behaviors is a key yet challenging issue due to the wide range of spatial and temporal scales involved.

Mechanochemical dynamics of collective cells and hierarchical topological defects in multicellular lumens.

Collective cell dynamics is essential for tissue morphogenesis and various biological functions. However, it remains incompletely understood how mechanical forces and chemical signaling are integrated to direct collective cell behaviors underlying tissue morphogenesis. Here, we propose a three-dimensional (3D) mechanochemical theory accounting for biochemical reaction-diffusion and cellular mechanotransduction to investigate the dynamics of multicellular lumens.

Basal actomyosin pulses expand epithelium coordinating cell flattening and tissue elongation.

Actomyosin networks constrict cell area and junctions to alter cell and tissue shape. However, during cell expansion under mechanical stress, actomyosin networks are strengthened and polarized to relax stress. Thus, cells face a conflicting situation between the enhanced actomyosin contractile properties and the expansion behaviour of the cell or tissue.

Interfacial Organization and Forces Arising from Epithelial-Cancerous Monolayer Interactions.

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 tissue level. We show that the monolayer interaction leads to competitive interfacial morphodynamics and drives an intricate spatial organization of MCF10A cells into multicellular finger-like structures, which further branch into multiple subfinger-like structures.

Mechanically sensitive HSF1 is a key regulator of left-right symmetry breaking in zebrafish embryos.

The left-right symmetry breaking of vertebrate embryos requires nodal flow. However, the molecular mechanisms that mediate the asymmetric gene expression regulation under nodal flow remain elusive. Here, we report that heat shock factor 1 (HSF1) is asymmetrically activated in the Kupffer's vesicle of zebrafish embryos in the presence of nodal flow.

Substrate nesting guides cyst morphogenesis of human pluripotent stem cells without 3D extracellular matrix overlay.

Understanding the principles underlying the self-organization of stem cells into tissues is fundamental for deciphering human embryo development. Here, we report that, without three-dimensional (3D) extracellular matrix (ECM) overlay, human pluripotent stem cells (hPSCs) cultured on two-dimensional soft elastic substrates can self-organize into 3D cysts resembling the human epiblast sac in a stiffness-dependent manner. Our theoretical modeling predicts that this cyst organization is facilitated and guided by the spontaneous nesting of the soft substrate, which results from the adhesion-dependent mechanical interaction between cells and substrate.

Polymerization force-regulated actin filament-Arp2/3 complex interaction dominates self-adaptive cell migrations.

Cells migrate by adapting their leading-edge behaviors to heterogeneous extracellular microenvironments (ECMs) during cancer invasions and immune responses. Yet it remains poorly understood how such complicated dynamic behaviors emerge from millisecond-scale assembling activities of protein molecules, which are hard to probe experimentally. To address this gap, we establish a spatiotemporal "resistance-adaptive propulsion" theory based on the interactions between Arp2/3 complexes and polymerizing actin filaments and a multiscale dynamic modeling system spanning from molecular proteins to the cell.

Curvature-dependent adhesion of vesicles.

The morphology and motion behavior of a cell are highly influenced by its external biological, chemical, and physical stimuli, and geometric confinement. In this paper, it is revealed that the mean curvature of the substrate significantly influences the adhesion of vesicles. By employing the variational method and investigating the Helfrich free energy, the configuration of axisymmetric vesicles adhered to curved spherical substrates is obtained theoretically.

Deciphering the adaption of bacterial cell wall mechanical integrity and turgor to different chemical or mechanical environments.

Bacteria adapt the mechanical properties of their cell envelope, including cell wall stiffness, turgor, and cell wall tension and deformation, to grow and survive in harsh environments. However, it remains a technical challenge to simultaneously determine these mechanical properties at a single cell level. Here we combined theoretical modelling with an experimental approach to quantify the mechanical properties and turgor of Staphylococcus epidermidis.

Assessment of vibration modulated regional cerebral blood flow with MRI.

Human brain experiences vibration of certain magnitude and frequency during various physical activities such as vehicle transportation and machine operation, which may cause traumatic brain injury or other brain diseases. However, the mechanisms of brain pathogenesis due to vibration are not fully elucidated due to the lack of techniques to study brain functions while applying vibration to the brain at a specific magnitude and frequency. Here, this study reported a custom-built head-worn electromagnetic actuator that applied vibration to the brain in vivo at an accurate frequency inside a magnetic resonance imaging scanner while cerebral blood flow (CBF) was acquired.

Mechanobiological tissue instability induced by stress-modulated growth.

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 of real tissues. In this paper, we propose a theoretical model to investigate the mechanobiological response of soft tissues undergoing stress-modulated growth.

Three-dimensional chiral morphodynamics of chemomechanical active shells.

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 and 3D chiral morphodynamics emerging in the cell cortex. The active bending and stretching of the elastic shells are regulated by biochemical signals like actomyosin and RhoA, which, in turn, exert mechanical feedback on the biochemical events via deformation-dependent diffusion and inhibition.

'Phase transitions' in bacteria - From structural transitions in free living bacteria to phenotypic transitions in bacteria within biofilms.

Phase transitions are common in inanimate systems and have been studied extensively in natural sciences. Less explored are the rich transitions that take place at the micro- and nano-scales in biological systems. In conventional phase transitions, large-scale properties of the media change discontinuously in response to continuous changes in external conditions.

mechanical nociceptors preferentially sense localized poking.

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 mechanosensation of a fly larval nociceptor (class IV da neurons, c4da) using a customized mechanical device.

Chiral topographic instability in shrinking spheres.

Many biological structures exhibit intriguing morphological patterns adapted to environmental cues, which contribute to their important biological functions and also inspire material designs. Here, we report a chiral wrinkling topography in shrinking core-shell spheres, as observed in excessively dehydrated passion fruit and experimentally demonstrated in silicon core-shells under air extraction. Upon shrinkage deformation, the surface initially buckles into a buckyball pattern (periodic hexagons and pentagons) and then transforms into a chiral mode.

Force-Regulated State Transitions of Growing Axons.

Growing axons are one-dimensional active structures that are important for wiring the brain and repairing nerves. However, the biophysical mechanisms underlying the complex kinetics of growing axons remain elusive. Here, we develop a theoretical framework to recapitulate force-regulated states and their transitions in growing axons.

Impact Forces of Water Drops Falling on Superhydrophobic Surfaces.

A falling liquid drop, after impact on a rigid substrate, deforms and spreads, owing to the normal reaction force. Subsequently, if the substrate is nonwetting, the drop retracts and then jumps off. As we show here, not only is the impact itself associated with a distinct peak in the temporal evolution of the normal force, but also the jump-off, which was hitherto unknown.

Unified multiscale theory of cellular mechanical adaptations to substrate stiffness.

Rigidity of the 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 migration, which constitute the dynamic cascade in cellular response to matrix stiffness but are often modeled separately in previous theories.

Dual-Scale Stick-Slip Friction on Graphene/h-BN Moiré Superlattice Structure.

Using atomic force microscopy, we have shown that friction on graphene/h-BN superlattice structures may exhibit unusual moiré-scale stick slip in addition to the regular ones observed at the atomic scale. Such dual-scale slip instability will lead to unique length-scale dependent energy dissipation when the different slip mechanisms are sequentially activated. Assisted by an improved theoretical model and comparative experiments, we find that accumulation and unstable release of the in-plane strain of the graphene layer is the key mechanism underlying the moiré-scale behavior.

Multi-functional topology optimization of veins.

The growth and development of biological tissues and organs strongly depend on the requirements of their multiple functions. Plant veins yield efficient nutrient transport and withstand various external loads. , a tropical species of the Nymphaeaceae family of water lilies, has evolved a network of three-dimensional and rugged veins, which yields a superior load-bearing capacity.

Experimental and theoretical studies on the dynamic landing of water striders on water.

As a species of insects living on water, water striders jump from the water surface to avoid predation and then steadily land without piercing the surface. This spectacular property has attracted extensive interests since it provides bio-inspirations for designing functional microrobots moving on water. In this work, we investigate the landing dynamics of water striders by using artificial striders with different masses and leg lengths.

Domino-like stacking order switching in twisted monolayer-multilayer graphene.

Atomic reconstruction has been widely observed in two-dimensional van der Waals structures with small twist angles. This unusual behaviour leads to many novel phenomena, including strong electronic correlation, spontaneous ferromagnetism and topologically protected states. Nevertheless, atomic reconstruction typically occurs spontaneously, exhibiting only one single stable state.

Evaporation of liquid nanofilms: A minireview.

Evaporation of virus-loaded droplets and liquid nanofilms plays a significant role in the pandemic of COVID-19. The evaporation mechanism of liquid nanofilms has attracted much attention in recent decades. In this minireview, we first introduce the relationship between the evaporation process of liquid nanofilms and the pandemic of COVID-19.

Regulation of cell attachment, spreading, and migration by hydrogel substrates with independently tunable mesh size.

Hydrogels are widely used as substrates to investigate interactions between cells and their microenvironment as they mimic many attributes of the extracellular matrix. The stiffness of hydrogels is an important property that is known to regulate cell behavior. Beside stiffness, cells also respond to structural cues such as mesh size.