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19 results on '"Dingari, Naga Neehar"'

14. Nonlinear electrokinetics of the bacterial cell envelope for applications in biomicrofluidics

Author

Cullen R. Buie., Massachusetts Institute of Technology. Department of Mechanical Engineering., Dingari, Naga Neehar, Cullen R. Buie., Massachusetts Institute of Technology. Department of Mechanical Engineering., and Dingari, Naga Neehar

Abstract

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 211-227)., Mathematical modeling is a powerful tool to improve the fundamental understanding in life sciences and to guide experiments. In this thesis, we primarily focus on developing a modeling platform for the electrokinetic ion transport around bacterial cell envelope under the influence of externally applied electric fields. The ability to understand the physics of this ion transport has experimental applications in cell envelope phenotyping of bacteria, cell sorting, intracellular delivery of nucleic acids for genetic engineering, and cell-cycle arrest for controlling antibiotic resistant bacteria. In the first part of my thesis we model the direct current (DC) electric field polarizability of two strains of Streptococcus Salivarius bacteria - fibrillated and unfibrillated, which differ in their cell envelope appendage (soft layer) properties. Using the Poisson-Nernst-Planck equations for ion transport and Stokes equation for fluid flow, we model the electric double layer polarization within and outside the soft layers to calculate the polarizability for these two strains. Firstly, we demonstrate that soft layers have significant influence on the polarizability of bacteria, especially when the soft layer conductivity is much higher than the buffer conductivity (high soft layer Dukhin number). Secondly, we demonstrate a significant difference in the polarizability of these two strains in the high soft layer Dukhin number regime, highlighting the potential use of polarizability based separation (using dielectrophoresis) of two very similar strains of bacteria. We have extended our model to alternating current (AC) fields and demonstrated a transition from cell envelope dominated polarizability at low frequencies (-kHz) to intracellular polarizability at high frequencies (-MHz). The model agrees qualitatively with the experimental literature on AC field polarizability. In the second part of my thesis, we perform finite-element simulations to model the influence of soft laye, by Naga Neehar Dingari., Ph. D.

Published
2017

18. Theoretical Investigation of Bacteria Polarizabilityunder Direct Current Electric Fields.

Author

Dingari, Naga Neehar and Buie, Cullen R.

Subjects
*POLARIZABILITY (Electricity), *DIRECT currents, *ELECTRIC fields, *POLYELECTROLYTES, *CHEMICAL kinetics, *PERMEABILITY
Abstract

We present a theoretical model toinvestigate the influence ofsoft polyelectrolyte layers on bacteria polarizability. We resolvesoft-layer electrokinetics by considering the pH-dependent dissociationof ionogenic groups and specific interactions of ionogenic groupswith the bulk electrolyte to go beyond approximating soft-layer electrokineticsas surface conduction. We model the electrokinetics around a softparticle by modified Poisson–Nernst–Planck equations(PNP) to account for the effects of ion transport in the soft layerand electric double layer. Fluid flow is modeled by modified Stokesequations accounting for soft-layer permeability. Two test cases arepresented to demonstrate our model: fibrillated and unfibrillated Streptococcus salivariusbacteria. We show that electrolyticand pH conditions significantly influence the extent of soft-particlepolarizability in dc fields. Comparison with an approximate analyticalmodel based on Dukhin–Shilov theory for soft particles showsthe importance of resolving soft-layer electrokinetics. Insights fromthis study can be useful in understanding the parameters that influencesoft-particle dielectrophoresis in lab-on-a-chip devices. [ABSTRACT FROM AUTHOR]

Published
2014
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19. Combined Effects of Surface Roughness and WettingCharacteristics on the Moving Contact Line in Microchannel Flows.

Author

Chakraborty, Debapriya, Dingari, Naga Neehar, and Chakraborty, Suman

Subjects
*SURFACE roughness, *WETTING, *MICROREACTORS, *CONTACT angle, *MENISCUS (Liquids), *MICROFLUIDICS, *ASYMPTOTIC expansions
Abstract

The present study investigates movingcontact lines in microfluidicconfinements with rough topographies modeled with random generatingfunctions. Using matched asymptotic expansion, the description ofthe whole contact line is obtained and the dynamic contact angle isextracted by extrapolating the bulk meniscus to the channel wall.Significant variations are observed in the contact angle because ofthe heterogeneities of the confining walls of the microfluidic channel.The effects of the surface wetting condition also play a crucial rolein altering the description of the contact line bearing particularnontrivial interactions with the topological features of the solidboundaries. In an effort to assess the underlying consequences, twodifferent surface wetting conditions are studied; namely, completewetting substrate and partial wetting substrate. Our studies revealthat the consequent wetting characteristics are strongly influencedby action of intermolecular forces in presence of surface roughness.The effect of slip, correlation length, and roughness parameters onthe dynamic contact angle have been also investigated. [ABSTRACT FROM AUTHOR]

Published
2012
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