Research Highlights 2014

1. Morphogenesis in Coupled Brusselators
D. Goldstein, M. Giver, B. Chakraborty


Theoretical analysis of emergence of patterns in an initially homogenous ring of chemical oscillators exhibits a multitude of patterns. The chemical reactions are modeled by the Brusselator, which is one of the simplest autocatalytic reactions, in the regime of high nonlinearity. They are coupled diffusively. The emergent heterogeneity is characterized by the oscillator phase (color in diagrams). A black circle denotes an oscillator that has stopped oscillating.

2. Defect Dynamics in 2D Active Nematic Liquid Crystals
S. DeCamp, G. Redner, M. Hagan, and Z. Dogic

2      2b

While conventional materials are assembled from inanimate building blocks, we are exploring the behavior of soft materials in which the constituent components consume energy and spontaneously coordinate their microscopic behavior and form novel materials such as active gels, crawling emulsion droplets, and living liquid crystals.
In active liquid crystals, defects proliferate to a dynamical steady state through unconventional creation and annihilation processes. Pairs of defects stream across the nematic liquid crystal exhibiting tunable dynamics not readily observed in equilibrium liquid crystals.

3. Imprintable membranes from incomplete chiral coalescence
M. J. Zakhary, T. Gibaud, C. N. Kaplan, E. Barry, R. Oldenbourg, R. B. Meyer and Z. Dogic

3   3b

We have discovered two novel frustrated coalescence pathways in colloidal membranes that result in the formation of stable liquid crystalline defects. This frustration propagates up several hierarchical levels, beginning with the molecular chirality inherent to the constituent virus particles. We observe the structure of these defects using optical microscopy, measure the energetic cost of their formation, and imprint arbitrary arrays of these defects through optical tweezer-driven membrane self-coalescence.

4. Photophobic and phototropic movement of a selfoscillating gel
I.R. Epstein and Q. Gao


Gels containing the components of the photosensitive oscillatory Belousov-Zhabotinsky reaction have been predicted to move toward darker regions when illuminated by a patterned light source. We have demonstrated experimentally that, with appropriately chosen patterns of light intensity, these gels can move either toward or away from brighter regions, mimicking the behavior of phototropic and photophobic organisms.

5. Continuum theory of an overdamped Active Nematics
E. F. Putzig, A. Baskaran, M. F. Hagan

5   5b

We are developing a dynamical theory of an overdamped active nematic. This will enable us to identify universal mechanisms for dynamical phenomena in diverse active nematic systems. The image on the right shows three sequential images from experimental system in which +½ and -½ defects are created through a bending stability and subsequently separate. The image on the left shows similar defect behaviors observed in the numerical solution of the non-equilibrium dynamical theory.

6. A New Mechanism for Flagella-Like Beating
R. Chelakkot, A. Gopinath, L. Mahadevan, M. F. Hagan

6   6b 6c

The planar dynamics of a semi-flexible filament anchored at one end and comprised of connected, self-propelled, spheres were predicted using Brownian dynamics simulations and continuum elastic theory theory. For certain parameter ranges the filament undergoes periodic motion. With a clamped anchor, the filament undergoes flagella-like beating (top right), while a pivoting end leads to a steadily rotating coiled conformation (bottom right).
Designing simple, experimentally feasible systems that mimic the periodic beating of eukaryotic cilia and flagella has important implications for controlling fluid flow at the microscale, as well as for understanding biological cilia and flagella.

7. Simulations of Active Nematics
G. Redner, A. Baskaran, M. F. Hagan

7   7b

Simulations of a model for microtubule(MT)-based active nematics capture experimentally observed defect dynamics. The image on the right shows three sequential images from experimental system in which +½ and -½ defects are created through a bending stability and subsequently separate. The image on the left shows similar defect behaviors observed in dynamical simulations of a coarse grain model for the MTbased active nematics.

8. Development of a novel reagent to aid study of macromolecular 
K.C. Anthony, C. You, J. Piehler, D.A. Pomeranz Krummel

8        8b

Novel reagent consisting of a gold cluster or nanoparticle conjugated 
to a tris-­NTA scaffold (called AuNPtris-NTA, see figure).
This reagent has been employed to localize protein(s) of interest in
large multi-­‐protein assemblies as shown in the negative-­‐stain 
electron microscopic image where the gold nanoparticles site-­‐ specifically aGached to the protein appear as dense black spots due to
their significant scattering of electrons as a consequence of the gold’s 
electron dense structure.