Ashok Kumar Dasmahapatra

Coarse-grain molecular dynamics study of fullerene transport across a cell membrane.

The study of the ability of drug molecules to enter cells through the membrane is of vital importance in the field of drug delivery. In cases where the transport of the drug molecules through the membrane is not easily accomplishable, other carrier molecules are used. Spherical fullerene molecules have been postulated as potential carriers of highly hydrophilic drugs across the plasma membrane. Here, we report the coarse-grain molecular dynamics study of the translocation of C60 fullerene and its derivatives across a cell membrane modeled as a 1,2-distearoyl-sn-glycero-3-phosphocholine bilayer. Simulation results indicate that pristine fullerene molecules enter the bilayer quickly and reside within it. The addition of polar functionalized groups makes the fullerenes less likely to reside within the bilayer but increases their residence time in bulk water. Addition of polar functional groups to one half of the fullerene surface, in effect creating a Janus particle, offers the most promise in developing fullerene models that can achieve complete translocation through the membrane bilayer.

Magnetic field induced push–pull motility of liquibots

Liquid droplets loaded with paramagnetic or diamagnetic salts, namely liquibots, showed controlled migration inside a fluid medium and on slippery solid surfaces under remote magnetic guidance. The water or oilbots of size ranging from a millimetre to a few microns showed facile attraction, repulsion, division, and coalescence when guided by a magnetic field. The speed of the liquibots could be tuned by varying the size, salt-loading, and magnetic field strength. While the paramagnetic liquibot migrated towards a magnet with a velocity as high as ∼8 body length per s, the diamagnetic one migrated away from the field with a maximum velocity of ∼1 body length per s. The liquibots transported and delivered commercially available drugs to targeted locations showing their potential as drug-delivery vehicles. Remarkably, the experiments showed the utility of the liquibots in digital microfluidics because they moved easily on slippery solid surfaces. For example, a waterbot was split into many droplets on an oil coated solid surface before forming the patterns resembling polygons under magnetic guidance. Further, the liquibot based Packman™ game could also be played with the help of magnetic guidance. The extent of control demonstrated on the motions of the remotely guided liquibots could be useful in diverse futuristic applications including drug-transport, digital-microfluidics, and droplet-electronics.

Multi-scale molecular dynamics study of cholera pentamer binding to a GM1-phospholipid membrane.

The AB5 type toxin produced by the Vibrio cholerae bacterium is the causative agent of the cholera disease. The cholera toxin (CT) has been shown to bind specifically to GM1 glycolipids on the membrane surface. This binding of CT to the membrane is the initial step in its endocytosis and has been postulated to cause significant disruption to the membrane structure. In this work, we have carried out a combination of coarse-grain and atomistic simulations to study the binding of CT to a membrane modelled as an asymmetrical GM1-DPPC bilayer. Simulation results indicate that the toxin binds to the membrane through only three of its five B subunits, in effect resulting in a tilted bound configuration. Additionally, the binding of the CT can increase the area per lipid of GM1 leaflet, which in turn can cause the membrane regions interacting with the bound subunits to experience significant bilayer thinning and lipid tail disorder across both the leaflets.

Prediction of oil-water flow patterns, radial distribution of volume fraction, pressure and velocity during separated flows in horizontal pipe

Flow of two immiscible fluids gives rise to variety of flow patterns, which influence transportation process. In this work, we present detailed analysis on the prediction of flow pattern maps and radial distribution of volume fraction, pressure and velocity of a pair of immiscible liquids through a horizontal pipeline by computational fluid dynamics (CFD) simulation using ANSYS FLUENT 6.3. Moderately viscous oil and water have been taken as the fluid pair for study. Volume of fluid (VOF) method has been employed to predict various flow patterns by assuming unsteady flow, immiscible liquid pair, constant liquid properties, and co-axial flow. From the grid independent study, we have selected 47 037 number of quadrilateral mesh elements for the entire geometry. Simulation successfully predicts almost all the flow patterns (viz., plug, slug, stratified wavy, stratified mixed and annular), except dispersion of oil in water and dispersion of water in oil. The simulated results are validated with experimental results of oil volume fraction and flow pattern map. Radial distribution of volume fraction, pressure and velocity profiles describe the nature of the stratified wavy, stratified mixed and annular flow pattern. These profiles help to developing the phenomenological correlations of interfacial characteristics in two-phase flow.

Phase separation and crystallization in double crystalline symmetric binary polymer blends

Blending of two or more pure polymers is an effective way to produce composites with tunable properties. In this paper, we report dynamic Monte Carlo simulation results on the crystallization of crystalline/crystalline (A/B) symmetric binary polymer blend, wherein the melting temperature of A-polymer is higher than B-polymer. We study the effect of segregation strength (arises from the immiscibility between A- and B-polymers) on crystallization and morphological development. Crystallization of A-polymer precedes the crystallization of B-polymer upon cooling from a homogeneous melt. Simulation results reveal that the morphological development is controlled by the interplay between crystallization driving force (viz., attractive interaction) and de-mixing energy (viz., repulsive interaction between two polymers). With increasing segregation strength, the interface becomes more rigid and restricts the development of crystalline structures. Mean square radius of gyration shows a decreasing trend with increasing segregation strength, reflecting the increased repulsive interaction between A- and B-polymers. As a consequence, a large number of smaller size crystals form with lesser crystallinity. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. We also observe a path-dependent crystallization behavior in isothermal crystallization: two-step (sequential) isothermal crystallization yields superior crystalline structure in both A- and B-polymers than one-step (coincident) crystallization.