arXiv subjects

Karthik Nayani

Publications and source records attributed to Karthik Nayani.

4 recordsLinked to original sources

arXiv2026

Depletant-DNA Induces Chirality in the Condensed Domains of Lyotropic Liquid Crystals

We report on the phase behavior of solutions of a chromonic liquid crystal, disodium cromoglycate (DSCG) resulting from the presence of DNA that acts as a depletant. We show that DNA (both single and double stranded) can induce phase condensation of DSCG at volume fractions a thousand-fold lower than a commonly studied depletant of similar size, namely polyethylene glycol. Twist angle characterization via polarized optical microscopy reveals DNA introduces macroscopic chirality within the condensed phase, despite being present only in the continuous phase- as confirmed by imaging of fluorescently tagged DNA. UV-vis absorption spectroscopy reveals that the introduction of chirality reduces the absorption coefficient strongly, indicating that induced chirality leads to considerable increase in the average lengths of DSCG aggregates. We also show that DNA at concentrations (~nmol/L) typical for a post amplification event (such as PCR) can induce an isotropic-biphasic phase transition of DSCG enabling a fast optical method to report the presence of DNA. Overall, these findings establish DNA as exceptionally efficient depletants that regulate both phase condensation and chirality transfer in lyotropic liquid crystals and thereby providing a simple optical platform for detection of amplified DNA.

cond-mat.soft↗

arXiv2026

An Active Matter Pathway for Non-Equilibrium Liquid-Liquid Extractions

We report on a Marangoni flow-driven pathway for non-equilibrium transport of metal ions across an oil-water interface. Under specific conditions, we show that the adsorption of a metallic species onto the extractant-decorated oil-water interface creates interfacial tension gradients that give rise to Marangoni flows. Strikingly, we observe that these flows are accompanied by removal of metal from the aqueous phase and that the extraction kinetics follow a non-diffusive behavior. The extraction rates are significantly higher - at least a threefold increase - when Marangoni flows are present. We show that the strength of the interfacial instability is coupled to the lowering of the interfacial tension- which is metal-dependent and therefore can lead to rate-mediated selective extractions. Overall, our study shows a fundamentally different paradigm for liquid-liquid extractions opening up a range of new directions of inquiry and future technologies.

cond-mat.soft↗

arXiv2024

Rapid Sensing of Heat Stress using Machine Learning of Micrographs of Red Blood Cells Dispersed in Liquid Crystals

An imbalance between bodily heat production and heat dissipation leads to heat stress in organisms. In addition to diminished animal well-being, heat stress is detrimental to the poultry industry as poultry entails fast growth and high yield, resulting in greater metabolic activity and higher body heat production. When stressed, cells overexpress heat shock proteins (such as HSP70, a well-established intracellular stress indicator) and may undergo changes in their mechanical properties. Liquid crystals (LCs, fluids with orientational order) have been recently employed to rapidly characterize changes in mechanical properties of cells enabling a means of optically reporting the presence of disease in organisms. In this work, we explore the difference in the expression of HSP70 to a change in the LC response pattern via the use of convolutional neural networks (CNNs). The machine-learning (ML) models were trained on hundreds of such LC-response micrographs of chicken red blood cells with and without heat stress. Trained models exhibited remarkable accuracy of up to 99% on detecting the presence of heat stress in unseen microscope samples. We also show that crosslinking the chicken and human RBCs using glutaraldehyde in order to simulate a diseased cell was an efficient strategy for planning, building, training, and evaluating ML models. Overall, our efforts build towards the rapid detection of disease in organisms, which is accompanied by a distinct change in the mechanical properties of cells. We aim to eventuate CNN-enabled LC-sensors can rapidly report the presence of disease in scenarios where human judgment could be prohibitively difficult or slow.

physics.bio-ph↗

arXiv2024

Liquid Crystalline Assembly of Collagen for Deterministic Alignment and Spread of Human Schwann Cells

Collagen is a key component of the extracellular matrix and well-oriented domains of collagen are relevant for mimicking the local cell environment in vitro. While there has been significant attention directed towards the alignment of collagen, formation of large-scale oriented domains remains a key challenge. Type I collagen self-assembles to form liquid crystalline (LC) mesophases in acidic conditions at concentrations above 100 mg/ml. The LC mesophase provides an efficient platform for large-scale alignment and patterning of collagen coated substrates. However, there exist challenges related to solubilizing and processing of collagen at such high concentrations in order to replicate the native extra cellular matrix (ECM). In this contribution, we report on centimeter-scale alignment in collagen-coated glass substrates using solutions that are well below the LC-forming concentrations. Importantly, we are also able to extend this method to create a mimic of the native ECM via macroscopic 3-D collagen hydrogels with programmed anisotropy within them. We explain the formation of these uniform domains via shear-induced and magnetically-induced liquid crystallinity of the collagen solutions. We show that the orientation, spreading and aspect ratio of Human Schwann Cells (HSCs) all are strongly coupled with the alignment of the collagen substrate/hydrogel. We use a simple Metroplis-based model to reveal that a critical magnetic field strength exists for a given concentration of collagen, exceeding which, macroscopic alignment is permissible- enabling guidance for future studies on alignment of collagen at high concentrations.

cond-mat.soft↗