arXiv subjects

Miho Yanagisawa

Publications and source records attributed to Miho Yanagisawa.

15 recordsLinked to original sources

arXiv2026

Interfacial Packing of DNA Nanostars Regulates Dynamics on Synthetic Cell Membranes

DNA nanostructures are emerging as programmable components for engineering synthetic cell membranes, yet how their collective packing and deformability regulate molecular dynamics at membrane interfaces remains poorly understood. Here, we investigate the packing and mobility of DNA nanostars with tunable stiffness on lipid-coated droplets. The negatively charged nanostars spontaneously adsorb onto cationic membranes, and their interfacial packing is changed by the bulk DNA concentration and droplet size, which together determine the number of encapsulated nanostars. Combining fluorescence recovery after photobleaching experiments with coarse-grained simulations, we reveal distinct packing-dynamics relationships for rigid and soft nanostars. For rigid nanostars, diffusion first decreases gradually and then drops sharply with increasing interfacial packing, approaching a dynamically arrested state consistent with jamming-like behavior. In contrast, at equivalent experimental conditions, soft nanostars systematically reach lower interfacial packing fractions and show a weaker decrease in apparent mobility. This behavior is consistent with their weaker membrane affinity, which facilitates adsorption-desorption with the bulk. When this exchange is suppressed in simulations, crowding reduces the lateral diffusion of both nanostar types, but produces distinct dense configurations: soft nanostars become strongly deformed, whereas rigid nanostars largely retain their shape and form interlocked, gear-like arrangements. Nanostar adsorption also impedes lipid diffusion, while differences in membrane affinity result in distinct lipid mobile fractions. These findings reveal how the interplay between nanostar packing and deformability regulates molecular transport at membrane interfaces, providing a physical design principle for tuning lateral fluidity and crowding in artificial cells.

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arXiv2026

Cooperative effects of membrane confinement and gelation on PEG crystallization pathway

Lipid-coated microscale hydrogels provide confined, hydrated environments in which polymer phase behavior can differ markedly from that in bulk. Here, we investigate the crystallization pathway of poly(ethylene glycol) (PEG) encapsulated in lipid-coated agarose microgels. Surprisingly, polarized-light microscopy reveals birefringence in the microgels under conditions where PEG remains non-crystalline in the corresponding bulk solution. The birefringence disappears upon heating and spontaneously reappears after further cooling or upon local mechanical stimulation. Infrared microspectroscopy demonstrates that the birefringent microgels contain crystalline PEG, whereas non-birefringent microgels contain PEG in an amorphous-like state, indicating the existence of a metastable precursor prior to crystallization. Furthermore, cooling below the phase-separation temperature produces PEG-rich domains preferentially near the membrane, suggesting that membrane wetting governs the spatial distribution of PEG before crystallization. Together, these results indicate that membrane confinement and agarose gelation cooperatively alter the local hydration environment of PEG, thereby stabilizing an amorphous-like precursor and redirecting the subsequent crystallization pathway. Our findings identify the coupling of membrane wetting and gelation as a key factor governing PEG crystallization in confined soft materials.

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arXiv2026

Tracer-free Contactless Acoustic Microrheometry Quantifies Viscoelastic Spectrum of Phase-separated Condensates

The rheology of phase-separated condensates plays a central role in applications spanning advanced materials design and cellular processes, yet quantitative characterization of their viscoelasticity remains challenging due to the limitations of existing microrheological methods that require tracer particles or mechanical contact. Here, we establish tracer-free and contactless acoustic microrheometry as a versatile platform for quantifying the frequency-dependent complex shear modulus of single microscale condensates over 0.01-10 Hz. Using spatiotemporally controlled acoustic radiation force generated within a micro-acoustic resonator, this method deforms condensates for creep-recovery and oscillatory viscoelastic measurements. Quantitative validation using dextran condensates in a polyethylene-glycol continuous phase successfully captures their size- and frequency-dependent mechanical responses, while application to nucleic-acid condensates reveals salt-dependent internal viscoelastic changes at single-condensate resolution. By enabling quantitative dissection of condensate mechanics without invasive probes, acoustic microrheometry provides a broadly applicable framework for investigating phase-separated condensates across materials science, soft matter physics, biology, and beyond.

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arXiv2026

Programming Nonlinear Interfacial Mechanics of Synthetic Cells: Lipid Geometry and DNA Nanostructures

Soft interfaces formed by lipid membranes are fundamental to living cells, synthetic cells, and membrane-based soft materials. However, a quantitative framework linking molecular organization with nonlinear interfacial mechanics remains elusive. Here, we establish an analytical framework that captures the nonlinear elastic response of lipid-membrane-coated synthetic cells under micropipette aspiration. Incorporating both area stretching and curvature bending enables the model to quantitatively reproduce the complete pressure-displacement response within the small-deformation regime. This approach reduces interfacial mechanics to two parameters: the in-plane area-stretching modulus and an out-of-plane bending-related term. Using this unified framework, we experimentally demonstrate that nonlinear interfacial mechanics can be programmed by altering the molecular geometry and effective dimensionality of adsorbed elements. The lipid molecular shape and curvature-dependent packing regulate in-plane stiffness, while DNA nanostructures, the other adsorbed element, introduce an orthogonal control axis via dimensionality: isolated motifs primarily enhance area stretching, whereas three-dimensional network architectures markedly reinforce bending resistance. Together, these results establish a general molecular design principle for programming interfacial mechanics and provide a quantitative foundation for engineering mechanically tunable synthetic cells and soft interfaces.

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arXiv2026

Power-law molecular-weight distributions dictate universal behaviors in highly polydisperse polymer solutions

Polydispersity is a universal feature of synthetic polymers and biological molecules in the cytoplasm. However, its quantitative impact on collective behavior remains poorly understood because conventional metrics, such as the polydispersity index, fail to capture broad, non-Gaussian size distributions. Here, we develop an experimental platform in which polyethylene glycol (PEG) solutions are engineered to follow tunable power-law molecular-weight distributions spanning an extensive range, from $M = 1$ kg/mol to $10^{4}$ kg/mol. By systematically varying the $M$ distribution exponent $a$, we identify a robust regime ($1 < a \lesssim 2.5$) in which the viscosity scaling exponent in the entangled regime, the overlap concentration $c^{\ast}$, and the entanglement concentration ${c_{\mathrm{e}}}$ all exhibit pronounced maxima that exceed monodisperse limits. This amplification minimizes as the upper cutoff $M_{\max}$ is reduced, with the system approaching monodisperse behavior. The enhanced rheology arises from a competition between long-chain-dominated entanglement and short-chain-mediated void filling, demonstrating that the whole shape of the molecular-weight distribution plays a decisive role. Consequently, these collective behaviors cannot be reproduced by simply tuning the average molecular weight. Together, our results establish the power-law exponent $a$ as a quantitative control parameter that links polymer entanglement, soft packing, and molecular crowding in highly polydisperse systems.

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arXiv2025

Cation accumulation drives the preferential partitioning of DNA in an aqueous two-phase system

Mixtures of polyethylene glycol (PEG) and dextran (Dex) represent a widely used class of aqueous two-phase systems (ATPS), with applications ranging from the purification of various biomolecules such as nucleic acids to the synthesis of protocells. A key feature underlying these applications is the selective accumulation of biomolecules within Dex-rich droplets in an aqueous PEG phase, but the physical origin of this partitioning remains unclear. Entropic interactions were long assumed to be the primary driving force; however, our systematic experiments using DNA of different lengths indicate that entropy alone cannot fully explain the observed behavior. We identify an additional and previously underappreciated contribution from electrostatic interactions: Dex carries a slightly more negative charge than PEG, which drives preferential cation accumulation in the Dex-rich phase. These counterions facilitate the selective partitioning of DNA inside the Dex-rich droplets. This mechanism explains the dependency of DNA uptake in Dex-rich droplets on polymer length and salt concentration. Our findings establish that Donnan-type ion partitioning plays a crucial role in the localization of long nucleic acids in Dex-rich droplets, offering a unified explanation for this long-standing phenomenon. They lay the foundation for designing ATPS-based systems and help elucidate the physicochemical principles of biomolecular partition upon phase separation in cells.

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arXiv2025

Real-space observation of salt-dependent aging in Laponite gels

Colloidal gels gradually evolve as their structures reorganize, a process known as aging. Understanding this behavior is essential for fundamental science and practical applications such as drug delivery and tissue engineering. This study examines the aging of low-concentration Laponite suspensions with varying salt concentrations using fluorescence microscopy, scattering imaging, and particle tracking microrheology. Structural heterogeneity appeared earlier at higher salt concentrations, and the average size of aggregates decreased as the salt concentration increased further. Fourier transform analysis corroborated these trends, and scattering images showed similar results. Microrheology revealed distinct dynamics in Laponite-rich and Laponite-poor regions: the poor phase exhibited liquid-like behavior, while the rich phase exhibited gel-like properties. Further analysis suggested the presence of submicron or nanoscale structural heterogeneities within the rich phase. These findings provide insight into how aging and salt concentration shape the structure and dynamics of colloidal gels.

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arXiv2025

Analytical model and experimental validation for nonlinear mechanical response of aspirated elastic shells

We developed a physics-based analytical model to describe the nonlinear mechanical response of aspirated elastic shells. By representing the elastic energy through a stretching modulus, $K$, and a dimensionless ratio, $δ$, capturing the balance between stretching and bending energies, the model reveals mechanical behaviors extending beyond conventional approaches. Validated across microscale droplets and macroscale silicone sheets by fitting experimental force-displacement curves, this approach provides accurate, scalable characterization of deformed elastic shells. This framework advances our understanding of soft thin-shell mechanics, with broad applications in probing living cells and designing soft materials.

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arXiv2024

Compression Causes Expansion and Compaction of the Jammed Polydisperse Particles

This study focused on the expansion in polydisperse granular materials owing to mechanical annealing, which involved compression and decompression. Following minor annealing, the polydisperse systems exhibited compaction as well as the systems having uniform-sized particles. However, following extensive annealing, only the polydisperse systems were observed to expand. Pressure history and structure analysis indicated that this expansion results from the size segregation of the particles. We attribute this segregation to particle-size-dependent effective attraction. The results of this study highlight the strong history dependence of the packing fraction and structure in polydisperse particles and reveal a potential-energy-driven segregation mechanism.

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arXiv2024

Marangoni droplets of dextran in PEG solution and its motile change due to coil-globule transition of coexisting DNA

Motile droplets using Marangoni convection are attracting attention for their potential as cell-mimicking small robots. However, the motion of droplets relative to the internal and external environments that generate Marangoni convection has not been quantitatively described. This study used an aqueous two-phase system (polyethylene glycol (PEG) and dextran) in an elongated chamber to generate motile dextran droplets in a constant PEG concentration gradient. We demonstrated that dextran droplets move by Marangoni convection, resulting from the PEG concentration gradient and the active transport of PEG and dextran into and out of the droplet. Furthermore, by spontaneously incorporating long DNA into the dextran droplets, we achieved cell-like motility changes controlled by coexisting environment-sensing molecules. The DNA changes its position within the droplet and motile speed in response to external conditions. In the presence of Mg2+, the coil-globule transition of DNA inside the droplet accelerates the motile speed due to the decrease in the droplet's dynamic viscosity. Globule DNA condenses at the rear part of the droplet along the convection, while coil DNA moves away from the droplet's central axis, separating the dipole convections. These results provide a blueprint for designing autonomous small robots using phase-separated droplets, which change the mobility and molecular distribution within the droplet in reaction to the environment. It will also open unexplored areas of self-assembly mechanisms through phase separation under convections, such as intracellular phase separation.

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arXiv2024

Preparation and observation of jammed particles with power size distribution

Several materials, such as rocks, powders and molecules, are multi-component systems. However, compared to single-component systems, it is difficult to understand the physical component. In this study, as a coarse-grained model for powders with extremely large size variations, we experimentally and numerically filled circular particles with a power size distribution and investigated their structure at the jamming transition point. In the experiment, oil in water droplets following a power size distribution were created, and then we constructed a model with steady injection and fracture to explain the size distribution. In numerical calculations, the dependence of the packing structure on the exponent of the particle size distribution was investigated. The existence of fractal structure with cutoffs was experimentally and numerically found from the structure factor. Numerical calculations show that the area fraction of rattlers is almost independent of exponent, but the number fraction is significantly dependent.

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arXiv2023

Role of Motility and Nutrient Availability in Drying Patterns of Algal Droplets

Sessile drying droplets in various bio-relevant systems, encompassing passive bio-colloids like DNA, proteins, and blood to active microbes, gain considerable attention due to intricate interplay among different convective flows, droplet pinning, mechanical stress, wettability, and the emergence of distinctive patterns. Chlamydomonas reinhardtii, or chlamys, is a versatile algal model employed in molecular biology research and spanning diverse biotechnological realms. While chlamys are harnessed at single-cell and population levels, their exploration in the context of drying sessile droplets remains limited. This paper illuminates the multifaceted potential of chlamys, delving into motility-nutrient interactions and their role in emergent morphological patterns. The interplay of two competing stressors -- localized nutrient scarcity and mechanical stress during drying -- is investigated. Irrespective of these stressors, the global mechanical stress fails to induce any cracks during the drying process. Interestingly, the reverse ``coffee-ring effect" is predominantly observed in the non-motile chlamys in the presence of local nutrients whereas the nutrient depletion prompts local stress in motile chlamys, culminating in cooperative aggregation and cluster formation. Furthermore, the quantitative image processing technique leverages textural statistics to classify the patterns into four classes, motile+with nutrients, motile+without nutrients, non-motile+with nutrients, and non-motile+without nutrients, with five distinct drying stages -- Droplet Deposition, Capillary Flow, Dynamic Droplet Phase, Aggregation Phase, and Dried Morphology.

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arXiv2023

Cell-sized confinements alter molecular diffusion in concentrated polymer solutions due to length-dependent wetting of polymers

Living cells are characterized by the micrometric confinement of various macromolecules at high concentrations. Using droplets containing binary polymer blends as artificial cells, we previously showed that cell-sized confinement causes phase separation of the binary polymer solutions because of the length-dependent wetting of the polymers. Here we demonstrate that the wetting-induced heterogeneity of polymers also emerges in single-component polymer solutions. The resulting heterogeneity leads to a slower transport of small molecules at the center of cell-sized droplets than that in bulk solutions. This heterogeneous distribution is observed when longer polymers with lower wettability are localized at the droplet center. Molecular simulations support this wetting-induced heterogeneous distribution by polymer length. Our results suggest that cell-sized confinement functions as a structural regulator for polydisperse polymer solutions that specifically manipulate the diffusion of molecules, particularly those with sizes close to the correlation length of the polymer chains.

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arXiv2022

Confinement-induced fractionation and liquid-liquid phase separation of polymer mixtures

The formation of (bio)molecular condensates via liquid-liquid phase separation in cells has received increasing attention, as these coacervates play important functional and regulatory roles within biological systems. However, the majority of studies focused on the behavior of pure systems in bulk solutions, thus neglecting confinement effects and the interplay between the numerous molecules present in cells. To advance our knowledge, we perform simulations of binary polymer mixtures in droplets, considering both monodisperse and polydisperse molecular weight distributions for the longer polymer species. We find that confinement induces a spatial separation of the polymers by length, with the shorter ones moving to the droplet surface. This partitioning causes a distinct increase of the local polymer concentration in the droplet center, which is more pronounced in polydisperse systems. Consequently, the systems exhibit liquid-liquid phase separation at average polymer concentrations where bulk systems are still in the one-phase regime.

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arXiv2022

Common Packing Patterns for Jammed Particles of Different Power Size Distributions

We introduce a model for particles that are extremely polydisperse in size compared to monodisperse and bidisperse systems. In two dimensions (2D), size polydispersity inhibits crystallization and increases packing fraction at jamming points. However, no packing pattern common to diverse polydisperse particles has been reported. We focused on polydisperse particles with a power size distribution $r^{-a}$ as a ubiquitous system that can be expected to be scale-invariant. We experimentally and numerically constructed 2D random packing for various polydisperse particles with different size exponents, $a$. Analysis of the packing pattern revealed a common contact number distribution for $a<3$ and a higher jamming point in $2<a<3$ than monodisperse systems. These findings demonstrate that the ambiguity of the characteristic length provides the common properties that leads to a novel classification scheme for polydisperse particles.

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