arXiv subjects

Vahid Nasirimarekani

Publications and source records attributed to Vahid Nasirimarekani.

5 recordsLinked to original sources

arXiv2026

Evaporation-Induced Pattern Formation and Wetting in Active Microtubule-Kinesin Droplets

Active networks composed of biopolymers and motor proteins provide versatile biomimetic systems that have advanced active matter physics and deepened our understanding of cytoskeletal dynamics and self-organization under diverse stimuli. In these systems, activity arises in aqueous solutions where motor proteins cross-link biopolymers and generate active stress driving the emergent network behavior. Here, we establish the active network in the form of a sessile, multi-component droplet on a substrate and investigate how evaporation influences its dynamics. We focus on how mass loss and compositional changes in the droplet reshape the behavior of the active suspension. We show that capillary and Marangoni flows drive the self-organization of microtubules into a distinctive radial arrangement within the droplet. The cross-linking ability of motor proteins gives rise to a striking non-monotonic wetting behavior, where the extensile stresses generated by the motor proteins strongly affect the characteristic timescale of the contact-line retracting and subsequent expansion. Using a combined experimental and theoretical approach, we demonstrate the crucial role of crosslinking in evaporating microtubule networks, and explain how active stresses together with evaporation-induced flows govern the dynamics of reconstituted microtubule systems and their wetting behavior. Evaporating droplets have recently attracted significant attention in the scientific community, and the findings of the setup presented in this study can have broad implications, ranging from self-organization and mechanical pattern formation in biological systems to questions about the origin of life.

cond-mat.soft↗

arXiv2024

Flat Cell Imaging

Recent advances in optical technology have significantly enhanced the resolution of imaging of living cells, achieving nanometer-scale precision. However, the crowded three-dimensional environment within cells presents a challenge for measuring the spatio-temporal dynamics of cellular components. One solution to this issue is expansion microscopy, which cannot be used for living cells. Here, we present a method for flattening live cells to a thickness of down to 200 nanometers by confining them between two surface-treated transparent plates. The anti-fouling coating on the surfaces restricts the cells to a quasi-two-dimensional space by exerting osmotic control and preventing surface adhesion. This technique increases the distance between cellular components, thereby enabling high-resolution imaging of their spatio-temporal dynamics. The viability and phenotype of various cell types are demonstrated to be unaltered upon release from flat-cell confinement. The flat cell imaging method is a robust and straightforward technique, making it a practical choice for optical microscopy.

physics.optics↗

arXiv2024

Phase separation bursting and symmetry breaking inside an evaporating droplet; formation of a flower-like pattern

Pattern formation inside a liquid phase is a phenomenon involved in many different aspects of life on our planet. The droplet form of a liquid that evaporates can reveal patterns that depend on the chemistry of the droplet and the physical parameters involved. We observed a flower-like deposition pattern of micrometer-sized particles as a result of the evaporation of a droplet containing salt and a non-ionic polymer. We show experimentally that the phase separation of the polymer due to the salting-out effect causes a strong entropic flow, which manifests as vortices. The flow is called phase separation bursting flow, which leads to the axial symmetry breaking and the formation of a radially aligned flower-like pattern. We foresee that understanding the observed flow can provide insights into the fluid physics aspects of phase separation and may have implications for technical applications.

cond-mat.soft↗

arXiv2024

Liquid-liquid phase separation at the interface of an evaporating droplet; formation of a regular lattice pattern

Evaporation alters the molecular interactions and leads to phase separation within the evaporating liquid. The question of whether evaporation could lead to specific phase separation at the liquid interface and eventually to the formation of patterns in small liquid volumes remains unaddressed. In this study, we investigated the liquid-liquid phase separation (LLPS) of an organic polymeric monomer in a salt-containing buffer within an evaporating sessile droplet. We observed that LLPS occurs at the dynamic interface of the droplet and leads to the formation of polymeric coacervates or regular lattice patterns depending on the initial concentration of the polymer. Our results show that the interaction of salt with the polymeric monomers at the droplet interface can lead to LLPS and the formation of regular patterns. This study suggests that the sessile droplet setup can be utilized to achieve very regular patterns as a result of LLPS.

cond-mat.soft↗

arXiv2023

Pattern formation under mechanical stress in active biological networks confined inside evaporating droplets

Active networks made of biopolymers and motor proteins are valuable bioinspired systems that have been used in the last decades to study the cytoskeleton and its self-organization under mechanical stimulation. Different techniques are available to apply external mechanical cues to such structures. However, they often require setups that hardly mimic the biological environment. In our study we use an evaporating sessile multi-component droplet to confine and mechanically stimulate our active network made of microtubules and kinesin motor proteins. Due to the well-characterized flow field inside an evaporating droplet, we can fathom the coupling of the intrinsic activity of the biological material with the shear stress generated by the flow inside the droplet. We observe the emergence of a dynamic pattern due to this combination of forces that vary during the evaporation period. We delineate the role that the composition of the aqueous environment and the nature of the substrate play in pattern formation. We demonstrate that evaporating droplets may serve as bioreactors that supports cellular processes and allows investigation on the dynamics of membraneless compartments. Such a setup is an original tool for biological structures to understand the mechanisms underlying the activity of the cytoskeleton under stress and, on the other hand, to investigate the potential of such adaptive materials compared to conventional materials.

cond-mat.soft↗