arXiv subjects

Hanumantha Rao Vutukuri

Publications and source records attributed to Hanumantha Rao Vutukuri.

14 recordsLinked to original sources

arXiv2026

Active spinners drive passive matter into chiral rotors

Active spinners inject angular momentum into their surroundings without persistent translation, providing a route to chiral active matter distinct from self-propelled particles moving along curved trajectories. Recent studies have shown that spinner fluids can self-organize into rotating clusters with circulating edge currents characteristic of odd-viscous fluids. Whether angular-momentum injection alone can transmit chirality and edge-current dynamics to ordinary passive matter - and thus serve as a generic mechanism for imparting chiral functionality to undriven material components - remains an open question. Here, we show experimentally and numerically that purely rotational magnetic spinners can transfer chirality and edge-current dynamics to passive colloidal matter. At high passive-particle fraction, active spinners assemble into rotating clusters surrounded by passive matter. Remarkably, upon changing composition and spinner attraction, this organization turns inside out: passive colloids form rotating clusters surrounded by a chiral spinner fluid. These passive rotors exhibit edge currents and the same angular-velocity scaling, $|Ω|\sim R^{-2}$, as their active counterparts. A minimal model shows that spinner-mediated transverse and non-reciprocal interactions are sufficient to reproduce these complementary chiral states and their boundary-driven dynamics. Our results establish angular-momentum injection by active spinners as a route to endow otherwise passive matter with chirality, collective rotation and boundary transport.

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arXiv2026

Dynamic bidirectional coupling of membrane morphology and rod organization in flexible vesicles

The ordering of rod-like particles in soft, deformable containers emerges from the interplay of anisotropic interactions, geometric confinement, and boundary compliance. This competition couples internal particle organization to container morphology, producing behavior distinct from both rigid confinement and bulk systems. Such coupling is also relevant to biological contexts in which filamentous structures are confined by deformable membranes. Using a minimal model combining experiments and simulations of colloidal rods encapsulated in lipid vesicles, we show that soft confinement drives a bidirectional coupling between internal order and vesicle shape. This interplay gives rise to a phase diagram in which elongated vesicles promote nematic alignment at lower packing fractions, whereas higher packing fractions induce smectic-like ordering that reshapes vesicles into plate-like morphologies with increased bending energy. Furthermore, by controlling vesicle volume and membrane area, we demonstrate that boundary conditions enable reversible tuning of both vesicle shape and internal rod organization. These results establish a framework for dynamically controlling colloidal self-assembly in soft containers and provide insight into the organization of anisotropic building blocks in deformable, cell-like, confinements.

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arXiv2026

Shape anisotropy governs organization of active rods: Swarming, turbulence, flocking, and jamming

Shape anisotropy of individual building blocks plays a crucial role in creating exotic structures and controlling phase behavior in equilibrium systems. We present a combined experimental and simulation study in which we used light-driven self-propelled rods to investigate when and how shape-induced alignment and steric and hydrodynamic interactions govern self-organization. Varying rod aspect ratio and area fraction causes the system to evolve from active Brownian motion to swarming, active turbulence, flocking, large clusters, and jamming. A state diagram summarizes emergent behaviors, and spatiotemporal analyses reveal distinct giant-number fluctuations across states. This minimal model offers insight into the self-organization of biological rodlike microswimmers, enabling the decoupling of physical from biological mechanisms. Our results provide design rules for programmable synthetic active materials and highlight parallels with bacterial swarms and other biological assemblies.

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arXiv2026

Programmable Persistent Random Walks in Active Brownian Particles Govern Emergent Dynamics

Self-propelled particles serve as minimal models for emulating the dynamic self-organization of microorganisms, yet most synthetic systems remain limited to a single mode of motion, namely active Brownian particles (ABPs). Here, we present an experimental strategy to encode various persistent random walks in ABPs by combining light-modulated propulsion strength with magnetic control of propulsion direction. Our system enables programmable Levy walks with tunable step-length distributions, run-and-tumble dynamics, self-avoiding random walks, and Gaussian walks, with on-demand switching between motion modes within a single experiment. In addition, particles are steered along complex trajectories such as Fibonacci spirals and nested polygons. Beyond single-particle behavior, we show that propulsion modes influence clustering dynamics by comparing ABPs with chiral active particles undergoing circular motion. These results establish a versatile platform for investigating how encoded motion at the level of individual particles governs transport, search strategies, and emergent organization in active matter systems.

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arXiv2025

From shallow to full wrapping: geometry and deformability dictate lipid vesicle internalization

The deformability of vesicles critically influences their engulfment by lipid membranes, a process central to endocytosis, viral entry, drug delivery, and intercellular transport. While theoretical models have long predicted this influence, direct experimental validation has remained elusive. Here, we combine experiments with continuum simulations to quantify how vesicle deformability affects the engulfment of small giant unilamellar vesicles (GUVs) by larger GUVs under depletion-induced adhesion. Using 3D confocal reconstructions, we extract vesicle shape, curvature, wrapping fraction, and the bendo-capillary length, a characteristic length scale that balances membrane bending and adhesion forces. We find that when vesicle size exceeds this length scale, engulfment is primarily governed by geometry. In contrast, when vesicle size is comparable to this scale, deformability strongly affects the transition between shallow, deep, and fully wrapped states, leading to suppression of full engulfment of vesicles. These findings connect theoretical predictions with direct measurements and offer a unified framework for understanding vesicle-mediated uptake across both synthetic and biological systems, including viral entry, synthetic cell design, drug delivery, and nanoparticle internalization.

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arXiv2024

Unifying atoms and colloids near the glass transition through bond-order topology

In this combined experimental and simulation study, we utilize bond-order topology to quantitatively match particle volume fraction in mechanically uniformly compressed colloidal suspensions with temperature in atomistic simulations. The obtained mapping temperature is above the dynamical glass transition temperature, indicating that the colloidal systems examined are structurally most like simulated undercooled liquids. Furthermore, the structural mapping procedure offers a unifying framework for quantifying relaxation in arrested colloidal systems.

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arXiv2023

Role of shape in particle-lipid membrane interactions: from surfing to full engulfment

Understanding and manipulating the interactions between foreign bodies and cell membranes during endo- and phagocytosis is of paramount importance, not only for the fate of living cells but also for numerous biomedical applications. This study aims to elucidate the role of variables such as anisotropic particle shape, curvature, orientation, membrane tension, and adhesive strength in this essential process, using a minimal experimental biomimetic system comprising giant unilamellar vesicles and rod-like particles with different curvatures and aspect ratios. We find that the particle wrapping process is dictated by the balance between the elastic energy penalty and adhesion energy gain, leading to two distinct engulfment pathways, tip-first and side-first, emphasizing the significance of the particle orientation in determining the pathway. Moreover, our experimental results are consistent with theoretical predictions in a state diagram, showcasing how to control the wrapping pathway from surfing to partial to complete wrapping by the interplay between membrane tension and adhesive strength. At moderate particle concentrations, we observed the formation of rod clusters, which exhibited cooperative and sequential wrapping. Our study not only contributes to a comprehensive understanding of the mechanistic intricacies of endocytosis by highlighting how the interplay between the anisotropic particle shape, curvature, orientation, membrane tension, and adhesive strength can influence the engulfment pathway but also provides a foundational base for future research in the field.

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arXiv2023

A colloidal viewpoint on the finite sphere packing problem: the sausage catastrophe

It is commonly believed that the most efficient way to pack a finite number of equal-sized spheres is by arranging them tightly in a cluster. However, mathematicians have conjectured that a linear arrangement may actually result in the densest packing. Here, our combined experimental and simulation study provides a realization of the finite sphere packing problem by studying non-close-packed arrangements of colloids in a flaccid lipid vesicle. We map out a state diagram displaying linear, planar and cluster conformations of spheres, as well as bistable states which alternate between cluster-plate and plate-linear conformations due to membrane fluctuations. Finally, by systematically analyzing truncated polyhedral packings, we identify clusters of $56\leq N \leq 70$ spheres, excluding $N=57$ and 63, that pack more efficiently than linear arrangements.

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arXiv2020

Light-switchable propulsion of active particles with reversible interactions

Active systems such as microorganisms and self-propelled particles show a plethora of collective phenomena, including swarming, clustering, and phase separation. Control over the propulsion direction and switchability of the interactions between the individual self-propelled units may open new avenues in designing of materials from within. Here, we present a self-propelled particle system, consisting of half-gold coated titania ($\mathrm{TiO}_2$) particles, in which we can fast and on-demand reverse the propulsion direction, by exploiting the different photocatalytic activities on both sides. We demonstrate that the reversal in propulsion direction changes the nature of the hydrodynamic interaction from attractive to repulsive and can drive the particle assemblies to undergo both fusion and fission transitions. Moreover, we show these active colloids can act as nucleation sites, and switch rapidly the interactions between active and passive particles, leading to reconfigurable assembly and disassembly. Our experiments are qualitatively described by a minimal hydrodynamic model.

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arXiv2019

Sculpting vesicles with active particles: Less is more

Biological cells are able to generate intricate structures and respond to external stimuli, sculpting their membrane from within. Simplified biomimetic systems can aid in understanding the principles which govern these shape changes and elucidate the response of the cell membrane under strong deformations. Here, a combined experimental and simulation approach is used to identify the conditions under which different non-equilibrium shapes and distinct active shape fluctuations can be obtained by enclosing self-propelled particles in giant vesicles. Interestingly, the most pronounced shape changes are observed at relatively low particle loadings, starting with the formation of tether-like protrusions to highly branched, dendritic structures. At high volume fractions, globally deformed vesicle shapes are observed. The obtained state diagram of vesicles sculpted by active particles predicts the conditions under which local internal forces can generate dramatic cell shape changes, such as branched structures in neurons.

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arXiv2017

Rational design and dynamics of self-propelled colloidal bead chains: from rotators to flagella

The quest for designing new self-propelled colloids is fuelled by the demand for simple experimental models to study the collective behaviour of their more complex natural counterparts. Most synthetic self-propelled particles move by converting the input energy into translational motion. In this work we address the question if simple self-propelled spheres can assemble into more complex structures that exhibit rotational motion, possibly coupled with translational motion as in flagella. We exploit a combination of induced dipolar interactions and a bonding step to create permanent linear bead chains, composed of self-propelled Janus spheres, with a well-controlled internal structure. Next, we study how flexibility between individual swimmers in a chain can affect its swimming behaviour. Permanent rigid chains showed only active rotational or spinning motion, whereas longer semi-flexible chains showed both translational and rotational motion resembling flagella like-motion, in the presence of the fuel. Moreover, we are able to reproduce our experimental results using numerical calculations with a minimal model, which includes full hydrodynamic interactions with the fluid. Our method is general and opens a new way to design novel self-propelled colloids with complex swimming behaviours, using different complex starting building blocks in combination with the flexibility between them.

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arXiv2015

Fabrication of polyhedral particles from spherical colloids and their self-assembly into rotator phases

Particle shape is a critical parameter that plays an important role in self-assembly, for example, in designing targeted complex structures with desired properties. In the last decades an unprecedented range of monodisperse nanoparticle systems with control over the shape of the particles have become available. In contrast, the choice of micron-sized colloidal building blocks of particles with flat facets, i.e., particles with polygonal shapes, is significantly more limited. This can be attributed to the fact that, contrary to nanoparticles, the larger colloids are significantly harder to synthesize as single crystals. Herein, we demonstrate that the simplest building block, such as the micron-sized polymeric spherical colloidal particle, is already enough to fabricate particles with regularly placed flat facets, including completely polygonal shapes with sharp edges. As an illustration that the yields are high enough for further self-assembly studies we demonstrate the formation of 3D rotator phases of fluorescently labelled, micron-sized and charged rhombic dodecahedron particles. Our method for fabricating polyhedral particles opens a new avenue for designing new materials.

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arXiv2013

Colloidal analogues of charged and uncharged polymer chains with tunable stiffness

Herein, we describe new methods to produce colloidal particle chains of three stiffness regimes that can be observed on a single-particle level, that is, on the level of the monomers that make up the chain; the chains can even be observed in concentrated systems without using molecular tracers. These methods rely on the following: dipolar interactions induced by external electric fields in combination with long-range charge repulsion to assemble the particles into chains only, and a bonding step to ensure that the particles remain assembled as chains even after the external field is switched off. We can control the length and the flexibility of the chains. Additionally, we demonstrate that our method is generally applicable by using it to prepare several other colloidal polymers, such as block-copolymer chains, which are formed by combining rigid and flexible chains, spherocylinders, which are formed by heating rigid chains, and both atactic and isotactic chains, which are formed from heterodimericparticle monomer units. We demonstrate that the flexibility of the charged chains can be tuned from very rigid (rod-like) to semiflexible (as in the simplified polymer model of beads on a string) by changing the ionic strength. This method can, in principle, be used with any type of colloidal particle. Moreover, our systems can be matched in terms of refractive index and density, so that bulk measurements in real space are possible.

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arXiv2011

Rotational averaging-out gravitational sedimentation of colloidal dispersions and phenomena

We report on the differences between colloidal systems left to evolve in the earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsions above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in the structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsions, an unusual sequence of dilute-Fluid/dilute-Crystal/dense-Fluid/dense-Crystal phases was observed throughout the suspension under the effect of gravity, related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes.

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