Replication through cell division is one of the fundamental processes of life and a major driver of dynamics in systems ranging from bacterial colonies to embryogenesis, tissues and tumors. While regulation also shapes self-organization, many biologically relevant behaviors arise from a limited number of physical ingredients, and particle-based models have become a popular platform to investigate these emergent dynamics. However, incorporating division into such models often produces aberrant mechanical fluctuations that hinder meaningful analysis. Here, we introduce a minimal model ensuring mechanical consistency during cell division. Cells consist of two nodes, overlapping disks which separate during division, forming transient dumbbell shapes. Internal degrees of freedom, cell-cell interactions and equations of motion guarantee force continuity at all times, including during division, both for the dividing cell and its interaction partners, while allowing arbitrary anisotropic mobilities. As a benchmark, we also translate an established model of proliferating spherocylinders with similar dynamics into our theoretical framework. Numerical simulations demonstrate force continuity of the new disk cell model, quantify the improvements, and show agreement in terms of collective behaviors such as alignment and orientational order. We also demonstrate force extraction and a Voronoi-based interpretation in a confluent-tissue context-with a three-dimensional generalization in embryonic-like confinement. A reference implementation of the model in two and three dimensions is freely available as a Julia package based on InPartS.jl. Our model provides a framework for analyzing mechanical observables such as velocities and stresses, and can be readily extended with additional biological features.

To investigate the mechanical correlations between intraocular pressure (IOP) variations and glaucoma, this study presents a linear transversely isotropic poroelastic model of the lamina cribrosa (LC) based on Reissner-Mindlin plate theory. A key feature of the proposed framework is its analytical tractability, which allows the governing poroelastic equations to be solved in closed form under appropriate mechanical and hydraulic boundary conditions. Within this setting, linearity is used to capture the reversible component of the tissue response, providing a baseline description of the coupled solid-fluid feedback on which more complex time-dependent phenomena, such as viscoelastic effects and remodelling, may build. The results indicate that both strain and stress measures (in the form of shear strain and deviatoric stress measures) peak in the peripheral region of the LC, which is currently suspected to be the initial site of glaucomatous damage. These quantities increase with IOP, suggesting a pressure-dependent mechanical insult to the retinal ganglion cell (RGC) axons. In parallel, the model predicts a monotonic reduction in fluid content as IOP rises, which may contribute to ischemic phenomena and disc haemorrhages. The influence of material anisotropy was also examined, revealing that isotropic assumptions tend to overestimate the fluid content while underestimating shear strain. Given the current experimental challenges in measuring blood flow within the LC, the proposed model provides a valuable framework for exploring the coupled mechanical-hemodynamic behavior of the tissue and for inverse estimation of its mechanical parameters, such as the stiffness of the opening for the central retinal vessels.

Rod and cone photoreceptors are sensory neurons required for the first steps of image-forming vision. Mutations in PRPH2 damage photoreceptor viability and produce a broad range of inherited retinal degenerations (IRDs) for which no treatments are available. The gene product, PRPH2 (peripherin-2), is an integral membrane tetraspanin that is required for the biogenesis and normal structure of photoreceptor outer segment (OS) disks. Peripherin-2 and its homologous partner Rom1 (rom1) self-assemble into non-covalent dimers that organize into three parallel belts that encircle each disk, forming a supramolecular scaffold that imposes extreme curvature on the disk rim. The mechanism by which curvature is generated and maintained is not yet understood. Here, we report the development of blue native (BN)-PAGE and molecular dynamics (MD) simulation approaches that suggest these proteins form an interaction web characterized by multiple interaction modes. BN-PAGE reveals that disk rim belts consist of a mixture of free peripherin-2 dimers and variously-sized chains of disulfide-linked dimers. MD simulations find that although free dimers can generate spontaneous curvature in a model membrane, dimers that are disulfide-linked into linear chains generate highly anisotropic curvature - a key hallmark of normal disk rims. The MD findings further suggest that although individual belts likely provide sufficient thermodynamic driving force to generate extreme curvature, non-covalent inter-belt interactions may also constrain rim diameter. The new findings advance understanding of peripherin-2 and rom1 structure and function in health and disease, and simultaneously provide promising new strategies for molecular phenotyping these clinically important proteins.

Rod and cone photoreceptors are sensory neurons required for the first steps of image-forming vision. Mutations in peripherin-2 damage photoreceptor viability and produce a broad range of inherited retinal degenerations for which no treatments are available. The gene product, peripherin-2, is an integral membrane tetraspanin that is required for the biogenesis and normal structure of photoreceptor outer segment disks. Peripherin-2 and its homologous partner rom1 self-assemble into non-covalent dimers that organize into three parallel belts that encircle each disk, forming a supramolecular scaffold that imposes extreme curvature on the disk rim. The mechanism by which curvature is generated and maintained is not yet understood. Here, we report the development of blue native-PAGE and molecular dynamics (MD) simulation approaches that suggest these proteins form an interaction web characterized by multiple interaction modes. Blue native -PAGE reveals that disk rim belts consist of a mixture of free peripherin-2 dimers and variously-sized chains of disulfide-linked dimers. MD simulations find that although free dimers can generate spontaneous curvature in a model membrane, dimers that are disulfide-linked into linear chains generate highly anisotropic curvature - a key hallmark of normal disk rims. The MD findings further suggest that although individual belts likely provide sufficient thermodynamic driving force to generate extreme curvature, non-covalent inter-belt interactions may also constrain rim diameter. The new findings advance understanding of peripherin-2 and rom1 structure and function in health and disease, and simultaneously provide promising new strategies for molecular phenotyping these clinically important proteins.

The transition from lipid flat disks to vesicles under shock waves is essential for producing nanosized vesicles during sonication. We perform non-equilibrium molecular dynamics simulations to examine how shock waves interact with a lipid flat disk. The lipid disk consists of coarse-grained saturated phospholipid models and is approximately 30 nm in diameter in the gel phase. Shock waves are simulated using a piston-driven method, with piston speeds limited to 1.0 km s[-1] or less. When a planar shock wave strikes, the disk's structural changes depend on the impact angle and the shock intensity. A disk with its rotation axis parallel to the shock direction decreases in thickness while maintaining its circular shape. In contrast, a disk with its rotation axis perpendicular to the shock wave direction undergoes radial compression in the shock propagation direction, causing a temporary increase in ellipticity. Behind the shock front, lipid molecules become disordered, as indicated by a reduction in the average P2 order parameter of lipid chains and the gel fraction in the disk. This suggests that shock waves can trigger the phase transition of lipid disks from the gel to the liquid phase. The shock's intensity and the resulting structural changes influence subsequent vesicle formation. During recovery, vesicles often form from the disk after exposure to higher-intensity shock waves or after a temporary anisotropic disk induced by a side impact. This highlights the importance of impact angle. These structural changes in lipid flat disks caused by shock waves may help in understanding and controlling vesicle sizes through sonication.

Molecular recognition in drug design relies on accurate characterization of ligand-binding pockets on macromolecular targets such as proteins and RNA. While protein binding sites have been extensively described, the geometric organization of RNA pockets remains comparatively underexplored. Here, we introduce a unified and size-independent geometric framework to describe and compare RNA and protein binding pocket shapes. Pocket geometry is captured using size-independent and residue-agnostic measures of global anisotropy, enabling direct comparison across RNA and protein binding pockets without introducing macromolecule-specific assumptions. This approach defines 4 interpretable pocket shape archetypes: sphere-like, rod-like, disk-like, and strongly anisotropic. Application to balanced datasets of 300 RNA and 300 protein binding pockets reveals a largely shared geometric landscape, with substantially overlapping shape descriptors within each archetype. However, archetype frequencies differ: Sphere-like pockets are more frequent in proteins, whereas disk-like and strongly anisotropic pockets are enriched in RNA, while rod-like pockets occur at comparable frequencies. Notably, strongly anisotropic pockets lacking a dominant symmetry axis represent a substantial fraction of pockets in both datasets. By organizing diverse binding sites into a small number of reproducible geometric regimes, this framework reduces structural heterogeneity and provides a transferable geometrical reference for comparative analysis of RNA and protein pocket architectures, thereby supporting the exploration of RNA pocket accessibility in structure-based studies.

The hard sphere model is widely used in the description of fluids and solid media as a zero approximation to real systems. Despite the uniqueness of the model, few analytical results are known for it, both for the 2D and 3D cases. In the present research, we have investigated the melting of the hard disk system by considering the accumulation of extended defects of a certain type in the crystalline phase, and jamming of the disk packing. This results in the formulation of melting criteria with lower and upper bounds on the volume ratio at the melting transition: 25/21 ≤ Vm/V0 ≤ 5/4. It was found that, in full agreement with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young theory, the 2D crystal melts into an anisotropic liquid. The second transition, which is the transition between an anisotropic and isotropic liquid, has a volume ratio of 5/4 ≤ Vi/V0 ≤ 13/9.

Intervertebral disk pathology, including disk herniation and degeneration, is a major contributor to chronic low back pain, and when conservative treatment fails, surgical management often involves discectomy-based procedures that leave residual annulus fibrosus (AF) defects associated with reherniation and progressive degeneration. These limitations have motivated interest in regenerative strategies using biomaterial scaffolds; however, reproducing the hierarchical, angle-ply architecture of the AF remains challenging. Here, we present a single-step extrusion-based 3D-printing approach to fabricate polycaprolactone (PCL) scaffolds with aligned microscale surface grooves that promote AF-like organization. Patterned nozzles with circumferential peaks generated uniaxial concave microgrooves (10-17 µm wide) directly during printing, enabling formation of multilamellar angle-ply constructs. Human bone marrow-derived mesenchymal stem cells cultured on patterned scaffolds aligned longitudinally within concave grooves, forming end-to-end arrays that guided extracellular matrix deposition. Gene expression analysis showed that topographical cues governed cellular organization without significantly altering gene expression profiles, while TGF-β3 supplementation upregulated outer AF-associated markers, including COL1, COL12, SFRP2, MKX, MCAM, and SCX. TAGLN expression increased specifically on patterned scaffolds in the absence of TGF-β3, indicating an association between microgroove-guided cellular organization and TAGLN expression, warranting further investigation into potential tension-related mechanisms. This novel single-step extrusion-printing approach leverages custom nozzle geometry to impart concave microgrooves, facilitating scalable fabrication of multilamellar angle-ply scaffolds that induce aligned cellular organization and support potential applications in annulus fibrosus repair, as well as mechanobiological studies of anisotropic musculoskeletal tissues.

Small inspection robots are highly desirable for inspecting complex machinery and detecting damage in confined spaces. However, common climbing robots that rely on vacuum suction or bioinspired dry adhesion often suffer from bulky sizes or slow locomotion speeds. Developing compact yet intelligent wall-climbing robots that mimic the agility and payload capacity of geckos remains an important challenge. In this work, we design a 20-g, 10-cm artificial intelligence (AI)-integrated robot capable of carrying a 70-g payload while climbing on vertical and inverted surfaces at a speed of 70 mm/s. Acoustic adhesion is generated by vibrating a flexible annular disk on smooth surfaces, where air is periodically absorbed and expelled, resulting in negative pressure. The thin air layer with negative pressure indicates anisotropic performance, characterized by strong normal adhesion and negligible tangential resistance, making it highly suitable for designing small, yet strong, climbing robots. The theoretical model and laser surface morphology measurements reveal the thickness-dependent adhesion of a thin air layer beneath the disk. A servo-spring system is designed to meet the stringent requirements of a thin air layer thickness, yielding robust normal adhesion. Resonance analysis and the use of proper spring material stiffness further enhance adhesion performance. Therefore, combining this innovative acoustic adhesion with optimized structural design, our robot achieves gecko-like mobility and payload capacity. Additionally, integrated AI techniques simplify robot control, allowing voice-commanded operation and autonomous task execution. We demonstrate the functions of these climbing robots through agile inspections in a 3-dimensional maze and retired aircraft engines. This work presents the design of small, strong, and agile climbing robots that utilize anisotropic acoustic adhesions, demonstrating agile mobility across gaps, right corners, and discontinuous curved surfaces. It offers potential solutions for in situ damage detection in aero-engines and other complex equipment cavities.

Recently, amorphous nanomaterials with unique structural features that crystalline materials may lack such as long-range atomic disorder have attracted great attention due to their outstanding surface-enhanced Raman scattering (SERS) properties. Herein, uniform hydrophobic gold nanoparticles (4.4 ± 0.95 nm) have been fabricated for realizing dodecylamine-assisted interfacial self-assembly at the air-water interface of Langmuir-Blodgett (LB) instruments for producing disordered amorphous disc superstructures, with their diameter ranging from ∼200 to ∼700 nm and height within 10-15 nm. When the surface tension of the air-water interface is increased from 0 to 10 and 20 mN/m, they can be linked together to form disc chains and networks, respectively. Interestingly, in the absence of free dodecylamine, these dodecylamine-stabilized hydrophobic gold nanoparticles will form highly ordered hexagonal close-packed monolayer films. Significantly, these amorphous disk superstructures possess better SERS performance than the ordered monolayer films. Further studies suggest that amorphous disc superstructures prepared for SERS sensors have advantages of low limit of detection (0.032 nM), excellent long-term stability, and a wide linear range (0.01-1000.0 nM) for detecting acetamiprid. Furthermore, they display splendid SERS performance for rapid determination of acetamiprid residues on the surface of apples, showing their ability for reliable and accurate detection of pesticide residues in real samples. Our research provides an effective approach for preparing amorphous structures via interfacial self-assembly, which reveals promising application prospects for detecting pesticide residues in real food samples.

Brownian motion plays a crucial role in determining the structural stability and transport properties of colloidal dispersions. Accurately capturing these dynamics requires consistent treatment of both hydrodynamic interactions (HI) and thermal fluctuations, which are not explicitly resolved in standard Brownian dynamics simulations. Direct numerical simulation (DNS), when coupled with fluctuating hydrodynamics (FHD), provides a rigorous framework to incorporate these effects. In this study, we develop a DNS approach that integrates the smoothed profile method with FHD to simulate the Brownian motion of arbitrarily shaped rigid particles. To validate our approach, we consider two standard non-spherical shapes, for which analytical results are available: rods and disks. For rod-like particles, the short-time diffusion is anisotropic, with preferential motion along the long axis because of the reduced hydrodynamic resistance. On the other hand, disk-like particles exhibit dominant in-plane diffusion in the short-time regime, with out-of-plane motion significantly suppressed. At long times, rotational motions lead to isotropic behavior in both cases. Our results demonstrate that this DNS framework can accurately reproduce Brownian motion while consistently accounting for both HI and thermal fluctuations. This study contributes to understanding and controlling dispersions of non-spherical particles.

We study the hydrodynamic drag force exerted on a sphere in a static anisotropic porous medium. This problem is analyzed using the Brinkman-Debye-Bueche equations with an axisymmetric shielding (or permeability) tensor. Using the exact Green's functions for this model fluid within a single-layer boundary element formulation, we numerically compute the friction tensor for a translating sphere subjected to stick boundary conditions. Furthermore, we derive approximate analytical expressions for small anisotropy using the Lorentz reciprocal theorem. By benchmarking this result against the numerical solutions, we find that a linear approximation is valid in a broad parameter regime. Our results are important for studying self-diffusion in general anisotropic porous media, but can also be applied to small tracers in nematic fluids composed of disk- or rodlike crowders.

The Yb:KREW (Yb:KRE(WO4)2, where RE = Y, Gd, Lu) crystal family is an excellent laser medium for ultrashort pulse lasers due to its broad bandwidth and high gain. However, it is a highly anisotropic and biaxial medium, making its use as a thin-disk laser challenging. In this study, to the best of our knowledge, we demonstrate the first Kerr-lens mode-locked thin-disk laser based on Yb:KLuW, utilizing a sufficiently thin gain medium and low thermal resistance bonding. This configuration achieved a pulse duration of 48.0 fs, a spectral width of 24.1 nm at center wavelength of 1026.0 nm, and an average output power of 0.425 W. Additionally, 3.3 W of output power with 59.8 fs pulses were obtained by adjusting the output coupling ratio. Furthermore, multimode CW operation yielded 138 W of output power with a 62% slope efficiency.

Mechanochemical patterns arising in the actomyosin cortex drive many cellular processes. Here we consider a hydrodynamic model for the actomyosin cortex of cells and study the sensitivity of the emergent patterns to both physical parameters and the geometry of the confining domain. We first establish a general framework for the Galerkin analysis of such patterns far from the linear stability regime on an arbitrary two-dimensional domain. In the case of a circular disk, our analytical results predict transitions from isotropic to anisotropic patterns upon changing the strength of the active stress and the turnover rate. We confirm the existence of this secondary bifurcation of the homogeneous state by an explicit numerical analysis of our model. Extending our numerical analysis to harmonic deformations of the circular disk, we show that the emergent patterns are also sensitive to the curvature of the domain. In particular, the actomyosin patterns resulting from our study closely resemble those seen in cells confined to micropatterned substrates. Our study demonstrates the role of geometry in controlling patterns within the context of a simple model for the actomyosin cortex.