My research explores the mechanics of soft and biological materials: from self-assembled bilayer membranes to structured fluids such as emulsions and blood. I am a theorist interested in the analytical modeling of the interrelation between the microscale physics, microstructure and macroscopic behavior of these so called complex fluids under non-equilibrium conditions. I also have a Lab, which has been an amazing source of discoveries and inspiration for new theories!
My current research focuses on:
1) Deformation of soft particles (drops, vesicles, capsules) in flow and electric fields
Project: “Electrohydrodynamics of particle-covered drops” funded by NSF CBET –Particulate and Multiphase Processes program
This project studies the behavior of liquid drops that have small particles adsorbed on their interfaces. When the drops are placed in an electric field, the particles on the interface can assemble into a variety of interesting structures, including particle belts that rotate and undulate around the drop. These structures can become unstable in some conditions, leading to bucking or wrinkling. We will experimentally map out the structures that form as a function of fluid, particle, and electric field properties. Then, we will use the experimental results to develop a model to predict the observed instabilities. When the particles completely cover the interface of the drop, the interface resembles an elastic solid. The way the drop shape deforms in flow will be used to deduce the mechanical characteristics of the interface. The information from this project will be useful to scientists and engineers to design and process novel colloidal products such as drops with interfaces that can respond to their local environment.
Project: “CAREER: Dynamics of cells and celullar mimetics in flow and electric fields: An integrated biophysical and engineering approach” funded by NSF CBET –Particulate and Multiphase Processes and Fluid Dynamics programs
The interplay between deformable microstructure and macroscale flow dynamics is a long-standing problem in particulate and multiphase fluid dynamics. The major challenge stems from the free-boundary nature of the particle interface. Lipid bilayer membranes that envelop cells are particularly complex interfaces because of their unique mechanics: the molecularly thin membrane is a highly-flexible incompressible fluid sheet. As a result, particles made of closed lipid bilayers (cells and vesicles) exhibit richer dynamics than would capsules and drops. The objective of this project is to understand the fluid-bilayer membrane coupling, with the long-term goal of explaining the non-equilibrium dynamics of suspensions of soft particles, such as biological cells. To achieve these goals, I integrate ideas from fluid dynamics and biophysics to build a unified theoretical framework that elucidates the interrelation between membrane deformation and composition, fluid motion, and external fields. This approach encompasses three fundamental non-equilibrium problems: flows, electric fields, and multicomponent membranes. The combination of theoretical, numerical, and experimental work will quantify vesicle deformation, orientation, and motion in external fields.
The proposed research will advance our understanding of the interplay of physical processes at the nano-scale (e.g., membrane thermal undulations, poration), micro-scale (e.g., single vesicle deformation), and macro-scale (e.g., rheology of vesicle suspensions). Moreover, it will shed light on several controversial topics, e.g., the diversity of vesicle behaviors in linear and complex flows, the unusual shapes of vesicles in electric fields, and the viscosity of vesicle suspensions.
2) Nonlinear physics, active suspensions
Project: “Nonlinear droplet electrohydrodynamics in Stokes flow regime” funded by NSF CBET-Fluid dynamics program
Electric fields provide a versatile means to control small-scale fluid and particle motion. Experiments in our group have discovered unusual droplet behavior such as tumbling, oscillations and chaotic dynamics in response to uniform DC electric fields. The project is motivated by (1) the scientific intrigue of these new nonlinear phenomena occurring under creeping flow conditions and (2) applied interest to exploit them in technologies related to microfluidics and electrorheological materials. The objective of this research is to uncover the mechanisms by which interface deformation and charging give rise to nonlinear droplet electrohydrodynamics. To this end, I integrate (1) dynamical systems theory to analyze drop behavior in the small-deformation regime and the transition to chaos; (2) numerical simulations based on the Boundary Integral Method to explore large drop deformations and the collective dynamics of drops; and (3) experiments to guide and test the theoretical analyses and computations.
The combination of theory, computation and experiment provides a comprehensive understanding of droplet electrodeformation and electrorheology of emulsions. These are challenging and unexplored problems at the intersection of fluid mechanics, dynamical systems, and soft condensed matter. The potential novelty of our work lies in identifying yet unexplained physics that could yield new applications related to microscale flows and complex fluids. The work could become a prototypical physical example of chaotic nonlinear dynamics.
3) Interfacial stability, dynamics of multicomponent bilayer membranes
Project: “Tension Effects on Phase Transitions in Biomimetic Bilayer Membranes “ funded by NSF CMMI-Biomechanics and Mechanobiology program
The research objective of this project is to determine the phase diagram of biomimetic membranes under tension. Membranes in eukaryotic cells are mixtures of hundreds of lipid species. The lipid diversity enables membranes to phase separate and form domains, called rafts, which play a critical role in cell functions such as signaling and trafficking. The phase transitions underlying raft formation have been extensively studied as a function of temperature and composition. However, the third dimension of the phase diagram, i.e., the tension, is still unexplored because membrane tension is difficult to control and quantify. To overcome this challenge, we are developing two novel approaches, capillary micromechanics and electrodeformation, in which the tension is regulated by the area dilation accompanying deformation of a vesicle (a closed membrane). These experimental tools will be applied to study the tension-induced domain formation and evolution.
If successful, the new tension-control techniques would allow to determine the complete phase-diagram of ternary biomimetic lipid bilayers. The knowledge gained from this work could lead to potentially transformative insights into the biomechanical signal transduction mechanisms that couple changes in membrane tension to changes in cell shape and motility. This will benefit the development of bioengineering applications that exploit the cell signaling and trafficking machinery, e.g., targeted drug delivery.