Abstracts

Irving Epstein
epstein.AT.brandeis.edu

Keynote Lecture: Nonlinear Chemical Dynamics: Where Have We Been and Where Are We Going?
I will present an autobiographically flavored historical overview of nonlinear chemical dynamics, touching on many of the key discoveries, looking at applications to other fields, and speculating on where the field might go in the future.

 

Kuan-Lin Chen
kchen89.AT.jhu.edu (Rebecca Schulman Group)

Talk: Understanding chemical signal propagation in hydrogels containing synthetic genetic regulatory networks using reaction-diffusion models
Synthetic genetic regulatory networks (GRNs) are powerful tools with programmable dynamics, demonstrating different properties and functions by changing the interconnection of the circuit elements. We aim to design in vitro transcriptional networks of specialized spatiotemporal programs and integrate with designated materials to make robots capable of sensing and processing the change in environmental information with autonomous decision making. These networks would be composed of genelet nodes, which are short transcriptional templates that regulate the activity of one and another through transcriptional RNA products. With readily available acrydite groups, hydrogel is a perfect platform for housing these circuits and also provides a smooth interface to direct downstream control with the high DNA circuit compatibility. Here, we seek to build a spatiotemporal program patterned in hydrogel patches that can identify biochemical gradient signals to build target-following hydrogel robots. We first construct an assay with simplified conditions, assuming all components homogeneous in a well-mixed batch, to screen through multiple potential circuit topologies determining promising candidates to undergo second stage complex spatiotemporal simulation. Next, we arrange genelet nodes of potential circuits into different hydrogel patches to study the circuit behavior with spatial separation and diffusion of the RNA signals in reaction-diffusion models. We first find that size scale is important in reliable signal propagation; With rapid diffusion of RNA molecules in solutions, RNA signals created from one patch are often degraded or quickly diffused away before binding to the target site to effectively turn off designated nodes. Furthermore, we learn that degradation rate of RNA is also critical, as too high a degradation rate lowers the effective radius of RNA signals and increases the difficulty of signal propagation, while too low inhibits the reactivation of repressed nodes and disfavours signal turnovers. With multiple parameters interconnected in a nonlinear complex matter, more study is needed before we may unravel a robust circuit topology and nodal arrangement for a gradient sensing genetic regulatory network.

 

Max Cui-Stein
maccstein.AT.brandeis.edu (Seth Fraden Group)

Poster: Understanding Light Sensitivity of Oscillatory Belousov-Zhabotinsky Microreactors
Spatiotemporal patterns of oscillation are ubiquitous in biological systems and have the potential for engineering applications, such as the control of soft robots. As a model system, our lab studies networks of coupled microfluidic reactors manufactured from he elastomer PDMS that contain the oscillatory Belousov-Zhabotinsky (BZ) reaction. This platform allows the study of large oscillator networks and the selective spatiotemporal perturbation of reactors with light. However, the BZ microreactors light response is reagent concentration dependent and known to change in time. We firstly present how in simulations applied light reduces the frequency of BZ oscillations as a function of reagent concentrations. Secondly, since the batch microreactors age causing their frequencies to drift in a potential light exposure sensitive manner, we present preliminary results on the frequency stability of BZ mixtures to aging.

 

Noah DeTal
detaln.AT.gatech.edu (Flavio Fenton Group)

Talk: Low-energy antifibrillation pacing in a cellular automaton model
The heart is a classic example of an excitable medium; moderate electrical stimulation of a cardiac cell elicits a propagating wave across the whole myocardium which allows for coherent muscle contraction. Disruption of the healthy rhythm, known as cardiac fibrillation, is understood to be the result of reentrant spiral waves--a generic phenomenon exhibited by both oscillatory and excitable systems. Traditional defibrillation succeeds by applying a strong enough electric field to excite the entire heart, thereby eliminating any spiral activity. However, recent simulation and experiment has shown that a series of weaker shocks, which eliminate a few spiral waves at a time, can also lead to complete defibrillation. In order to understand the mechanism of this progressive defibrillation, we investigated the effects of shock strength and timing in the Greenberg-Hastings cellular automaton. Despite the extreme simplicity of this model, we find it reproduces key features of detailed cardiac bidomain simulations. By analyzing the model’s behavior in terms of its topological properties, we have been able to explain the presence of an optimal pacing frequency as well as motivate a novel feedback-based pacing protocol directly applicable to experiment.

 

Denvert Dsilva
dsd18b.AT.my.fsu.edu (Oliver Steinbock Group)

Poster: Life-like micro-structures in chemical precipitation reactions: The effect of spatial confinement on biomorphs
Certain precipitation reactions create complex microstructures with intricate internal architectures as well as surprising life-like shapes. An important example is the biomorph system which displays morphologies ranging from three-dimensional helices, worms, and coral-like patterns to pseudo-two-dimensional leaf-shaped sheets. All of them consist of crystalline nanorods and form in alkaline solutions containing barium or strontium, silicate, and carbonate ions. Here, we present preliminary results on the effects of spatial confinement on biomorph structures. For solution layers with heights of about 10-50 µm, we observed the formation of novel structure types such as single filaments and spiraling coils. The effects of different substrate materials as well as the internal crystalline organization of these new morphologies will be discussed.

 

Brigitta Dúzs
duzsbrigitta.AT.gmail.com (István Szalai Group)

Poster: Hydrogel device with flow-through channels to maintain dissipative non-equilibrium phenomena
The development of autonomous chemical systems that could imitate the properties of living matter, is a challenging problem at the meeting point of materials science and non-equilibrium chemistry. A straightforward and biologically relevant way to provide non-equilibrium conditions is the separation of the initial reactants, which results in the formation of a localized reaction zone at the meeting of the counter-diffusing species. Classical experimental setups, where sustained chemical reaction-diffusion patterns have been studied, typically contain a tiny piece of hydrogel which is fed from one or two liquid reservoirs. This design may cause some limitations in the potential practical applications, so we propose to turn this configuration inside out. Our device is a rectangular hydrogel with two or more embedded channels for the flows of separated reactants, which diffuse into the gel to react. The relative position of the channels acts as geometric control parameters, while the concentrations of the chemicals in the channels and the variable composition of the hydrogel, which affects the diffusivity of the chemicals, can be used as chemical control parameters. This flexibility allows finding easily the optimal conditions for the development of non-equilibrium phenomena. We demonstrate this straightforward operation by generating diverse spatiotemporal patterns, e.g., pH waves and Turing structures using well-known chemical oscillators. One of the most exciting achievements of this new design are the long-lasting dynamic precipitate patterns in the aluminum hydroxide precipitation-redissolution system. As a unique feature, our device can be extended with additional channels. In two different three channel arrangements we show the evidence of interaction of diffusively coupled reaction-diffusion zones by generating two parallel arrays of pH waves.

 

Brecklyn Groce
bgroce2.AT.lsu.edu (John Pojman Group)

Poster: Radical- induced cationic frontal polymerization systems containing vinyl ethers to increase reactivity
Frontal polymerization (FP) is a phenomenon in polymer science where an input of energy initiates a reaction zone that propagates through a material, converting monomer to polymer as it travels. Thermal FP is initiated by thermal energy and relies on the kinetics of an exothermic reaction coupled with heat diffusion. Formulations containing vinyl ethers and an epoxy were successfully frontally polymerized through a radical-induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and silica as a filler, to eliminate front-quenching buoyancy-driven convection. Once a propagating front reaches a steady state, the speed at which a front travels can be observed (front velocity), which is a result of the system’s reactivity. It was found that an increase of vinyl ether content resulted in higher front velocities for some vinyl ethers in formulations with an epoxy. The kinetic effects of the acid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the vinyl ether system exhibiting higher sensitivity to the acid generator concentration.

 

Ian Hunter
ihunte01.AT.brandeis.edu (Seth Fraden Group)

Talk: Testing equivariant dynamics in a network of reaction-diffusion oscillators
Does form follow function in reaction-diffusion networks? Symmetry controls both the steady-state and the transient spatiotemporal patterns that form in mathematically ideal networks to a remarkable degree. But what happens in the real-world networks, with imperfections in their nodes and connections? To address these questions, we developed a model experimental reaction-diffusion network formed by the oscillatory Belousov-Zhabotinsky reaction confined to a square symmetric ring of 4 diffusively coupled microfluidic reactors. We compared experimental dynamics to theory assuming perfect symmetry and theory incorporating slight heterogeneity. We observed that even slight heterogeneity selectively modifies and eliminates some patterns, while preserving others. This work demonstrates that a surprising degree of the natural network’s dynamics are constrained by symmetry, in spite of the breakdown of the assumptions of perfect symmetry, and raises the question of why heterogeneity destabilizes some symmetry predicted states, but not others.

 

Syed Jazli Syed Jamaluddin
ssyedjam.AT.mix.wvu.edu (Ken Showalter Group)

Poster: Motion control of Belousov-Zhabotinsky droplets using feedback light intensity gradients
A Belousov-Zhabotinsky (BZ) droplet that is immersed in an oil-phase can self-propel due to a surface tension gradient that occurs on the droplet surface. The surface tension gradient is created as a result of the reactions that occur within and on the surface of the BZ droplet. By influencing the rates of these reactions, the directionality of the BZ droplet motion can be controlled. In our experiment, we tune the reactions that occur within and on the BZ droplet surface by imposing a light intensity gradient on the droplet. We have analyzed the BZ droplet motion and demonstrated that we can control the droplet directionality via the light intensity gradient. We also demonstrated that the shape of the light intensity gradient imposed on the BZ droplet can help us fine-tune our ability to control the directionality of the BZ droplet motion.

 

Pawan Kumar
pawandahiya4.AT.gmail.com (Agota Toth and Dezso Horvath Group)

Poster: Bio-inspired flow-driven chitosan pattern formations
Organic chemical gardens of chitosan hydrogel develop upon injecting an acidic chitosan solution into an alkaline solution. Besides complex and budding structures, tubular hydrogel formations develop that exhibit periodic surface patterns. The underlying wrinkling and folding instability are identified by its characteristic wavelength dependence on the depth of the tubular elastic material formed. The flow-driven conditions allow precise control over the structure that can help the design of soft bio-inspired materials.

 

Christopher Konow
ckonow.AT.brandeis.edu (Irv Epstein Group)

Talk: Growth of Chemical Turing Patterns
Turing patterns, spatially periodic and temporally stable structures that form in reaction-diffusion systems, have been implicated as examples of morphogenesis in a wide variety of systems. While Turing patterns are predominately a biological phenomenon, any have used chemical systems such as the chlorine dioxide-iodine-malonic acid (CDIMA) reaction to study the behavior of Turing patterns under a variety of conditions. Growth, which is ubiquitous in biological systems, can significantly impact both the formation and morphology of Turing patterns. In this talk, I will share recent insights into how growth can affect chemical Turing patterns. Specifically, the domain growth velocity controls both the final pattern morphology and the growth mode of the pattern. these results are reproduced both experimentally and in simulations of the Lengyel-Epstein model. In addition, I will discuss ongoing efforts to determine the impact obstacles on the domain have on growing Turing patterns.

 

Evan M. Lloyd
elloyd3.AT.illinois.edu (Jeffrey Moore Group)

Talk: Frontal polymerization: A molecular toolkit for developmental manufacturing
Multiscale patterns and structures in natural systems emerge spontaneously through a series of symmetry breaking events. Impressively, both the form and function of biological materials are replicated with unprecedented fidelity, despite the non-deterministic nature of growth and development. Synthetic polymer manufacturing, in great contrast, is highly deterministic, requiring teams of engineers, precision machined molds, and carefully controlled ovens and autoclaves. Subsequently, we are limited in the attainable complexity of structures and functions in synthetic systems. In this work, we propose frontal polymerization as a non-deterministic approach to polymer manufacturing. The coupled reaction-thermal transport processes of frontal polymerization are leveraged to synthesize high-performance thermosets and composites with orders of magnitude savings in manufacturing time and energy. Further, thermal instabilities which develop under conditions of competing reaction and thermal transport are harnessed to spontaneously pattern morphological, optical, chemical, and mechanical properties on multiple length scales. Finally, frontal copolymerization is explored to impart synthetic materials with functional attributes, including triggered degradation and upcycling.

 

Anthony Q. Mai
amai3.AT.lsu.edu (John Pojman Group)

Talk: Watermelon seed Urease: utilization of the clock reaction with applications in polymerization
We present a novel and stable source of urease enzyme, extracted from watermelon seeds. The resulting powder is rich in enzyme and can be used in reactions that gel in high pH. With the small (~10 micron) size of the powder, dispersions are possible in both aqueous and organic systems. To make the powder more user friendly, we immobilize them in various substrates from agar to porous acrylates. These polymeric carriers then can be used in a similar fashion to the watermelon seed powder with reusability in subsequent reactions. These enzyme carriers also exhibit quorum sensing behavior where their proximity, size, or number determine whether a clock reaction occurs or not. In addition, they can be paired with a system that reacts to increases in pH, i.e. thiol-acrylate polymerization. Reaction diffusion hydrogel growth with agar and watermelon seed powder particles in a flow cell are presented.

 

Dave Mersing
damersing.AT.mix.wvu.edu (Ken Showalter Group)

Talk: Relay synchronization in coupled chemical oscillators
We study phase synchronization of peripheral nodes in a star network, which are connected to a hub oscillator but not to each other, using photosensitive Belousov-Zhabotinsky (BZ) micro-oscillators. Experimental and computational investigations include either excitatory or inhibitory coupling. In both cases, phase synchronized clusters are observed along with the phase divergence of the hub oscillator from the cluster(s). We show that the mechanism for phase synchronization of the peripheral nodes involves an inhibitory signal from the hub leading to a phase alignment. The phase alignment of the peripheral nodes can be explained using the phase responsive curve (PRC), which gives the response of an oscillator due to a perturbation. The PRC can also be used to demonstrate a limit of the heterogeneity in the peripheral oscillators for observing the cluster behavior.

 

Maria Eleni Moustaka
mmoustak.AT.brandeis.edu (Seth Fraden Group)

Poster: Partition, reaction and diffusion coefficients of bromine in elastomeric poly(dimethylsiloxane) PDMS
Combined experiments and models were used to determine the extent to which aqueous bromine permeated into, and reacted with, the elastomer poly(dimethylsiloxane) (PDMS). The experiments consisted of immersing bromine-passivated and unpassivated PDMS films in brominated water and measuring the absorbance of bromine in solution as a function of time, mass and thickness of the PDMS. The decrease of bromine in solution was modeled as arising from permeation into the PDMS followed by a combination of diffusion and both reversible binding to, and irreversible reaction with, the PDMS. Fits of the models to a variety of experiments yielded the bromine partition coefficient between the water and PDMS phases, the diffusion constant of bromine in PDMS, the irreversible reaction constant between bromine and PDMS, the molar concentration of the bromine reactants within the PDMS, and the on- and off-rates of reversible binding of bromine to PDMS. Determination of these constants is necessary for the quantitative modeling of experiments to study non-linear dynamics that employ PDMS as a material to fabricate reaction-diffusion networks containing Belousov-Zhabotinsky chemical oscillators.

 

František Muzika
Frantisek.Muzika.AT.vscht.cz (Jerzy Gorecki Group)

Poster: Dynamic regimes and discrete spatiotemporal patterns of yeast extract glycolytic reaction in coupled CSTRs
The main part of our work is focused on experimental parameter analysis of glycolytic reaction of solution of Select yeast extract with addition of NaHCO3 and solution of D-glucose in the system of coupled and heated continuous stirred tank reactors. Following yeast extract oscillations quenching and various dynamic regimes in one cell by Nielsen et al. [1], our system was built to provide experimental evidence of transitions between discrete nonuniform spatiotemporal patterns and uniform oscillations under condition of equal transport rate coefficients of all transported species using perturbations by selected species [2].
The experimental system was composed of quartz cuvettes coupled by peristaltic reciprocal pumping. Reaction solution in each cuvette was measured by UV-Vis spectrophotometer at 340nm (absorbance of NADH). The varied parameters were flow rate, coupling strength, temperature of reaction solution in cuvettes, concentration of D-glucose stock solution, concentration of Select yeast extract stock solution and addition of NaHCO3 in Select yeast extract stock solution.
We report in-phase irregular oscillations, out of phase irregular oscillations, phase shifted irregular oscillations and switching between oscillatory regimes and nonuniform stationary states using perturbation by ATP and Na2SO3 solutions. We show comparison of bifurcation diagrams of Morán and Goldbeter model [3] with original parameters with bifurcation diagram of Morán and Goldbeter model with enhanced kinetic rate coefficients necessary for coexistence of nonuniform spatiotemporal patterns with uniform oscillations under condition of equal transport rate coefficients for both activator and inhibitor species.
References:
[1] Nielsen K, Sørensen PG, Hynne F, Busse HG (1998) Biophysical Chemistry 72:49–62; [2] Muzika F, Schreiberová L, Schreiber I (2014) RSC Adv 4:56165–56173; [3] Goldbeter A and Morán F (1984) Biophys. Chem. 20: 149-156.

 

Jorge Luis Ocampo-Espindola
jorgeluis.ocampoespindola.AT.slu.edu (István Kiss Group)

Talk: Synchronization engineering of oscillatory chemical reactions in the presence of a low-pass filter
Synchronization of chemical oscillators can be tuned by a linear feedback mechanism in which the average concentration (or rate of reaction) is fed back to a system parameter with a given strength [1]. In such practical applications, the measured signals are often filtered to remove experimental noise. In this contribution, we study the synchronization patterns of electrochemical oscillators induced by feedback in the presence of a low-pass filter (LPF). Close to a Hopf bifurcation, without the filter, as expected [2], the synchronization transition took place above a critical coupling strength following a second-order phase (Kuramoto) transition. With LPF, the transition occurred through explosive synchronization, which corresponds to a first-order phase transition and multistability between synchronized and desynchronized states. These experimental results confirm recent theoretical development on the impact of LPF on the synchronization of Stuart-Landau oscillators [3]. Further away from Hopf bifurcation, the LPF can generate patterns with one- and two-cluster states from a desynchronized state. The cluster formation and stability can be understood using a theory that estimates the LPF induced amplitude attenuation and phase shift of the coupling functionsin the phase model of the oscillatory process. Our study points to the importance of using filtering in engineering synchronization states of oscillatory chemical reactions.
1. Kiss, I. Z., et al., Science, 2007. 316(5833): p. 1886. 2. Kiss, I. Z., Y. Zhai, and J. L. Hudson, Science, 2002. 296(5573): p. 1676. 3. Zou, W., M. Zhan, and J. Kurths, Physical Review E, 2019. 100(1): p. 012209.

 

Vaibhav Palker
vpalkar.AT.g.clemson.edu (Olga Kuksenok Group)

Talk: Nonlinear dynamics of erosion and reverse gelation in degrading polymer networks
Controlled degradation in hydrogel materials finds numerous applications from controlled drug release to sequential release of encapsulated cells for tissue engineering. While several chemical pathways can be used to introduce controlled degradation in hydrogels, the physical processes that occur during degradation are not well understood. Better understanding of the physics behind the polymer degradation process is essential to further develop applications. Herein, we present a Dissipative Particle Dynamics (DPD) based simulation approach for modeling controlled degradation and erosion in hydrogel films. Our recently developed framework allows us to model controlled degradation in films with first order kinetics for the degradation reaction. We track the evolution of the weight average degree of polymerization and occurrence of network disintegration (reverse gelation) in our simulations. We focus on the crossover between the surface and bulk erosion in hydrogel films. Our simulations help us to analyze impact of parameters such as crosslink density, system size and stoichiometric ratio of degradable bonds.

 

Fahima Shaon
fshaon2.AT.lsu.edu (John Pojman Group)

Poster: Effect of thermally conductive metals on front temperature and front velocity of frontal polymerization
Frontal Polymerization (FP) is a self-propagating localized reaction the propagates through the coupling of thermal transport and the Arrhenius dependence of an exothermic polymerization. Frontal polymerization can be used for the cure-on-demand preparation of polymers and polymer-based composites. We explored the effects of conductive metal elements using aluminum and copper strips that increased the transport of heat. Out study showed that, there was no significant change in temperature profile in comparison between system with and without conductive metal. We found that the velocity could be doubled by a 0.5 mm strip and that thicker meal strips were less effective. Not surprisingly, copper was more effective than aluminum.

 

James Sheehy
javinshee.AT.brandeis.edu (Seth Fraden Group)

Poster: Impact of PDMS-based microfluidics on Belousov – Zhabotinsky chemical oscillators
Chemical oscillators are rich model systems which prove ideal for studying extended networks of interacting oscillators. One example of a chemical oscillator is the Beluosov-Zhabotinksy (BZ) reaction, which cycles between two visually distinct states. This reaction can be combined with polydimethylsiloxane (PDMS) microfluidics to create networks, which are coupled via excitatory and inhibitory connections. This network has been used to create a dynamic pattern which mimics neural circuits, but to create more complex networks, it is necessary to better understand the underlying interactions affecting the oscillators. The inhibitor found in BZ is known to permeate and react with PDMS. To understand the effects of this interaction, we can isolate a single oscillator and vary the amount of PDMS surrounding it. By examining the change in period as a function of PDMS volume and comparing the result with a theoretical model, we find that the bromine reaction with the PDMS plays a significant role in the chemical oscillation dynamics. This interaction can be partially canceled by adding a constant chemical boundary, allowing us to reduce the effects of the reaction on the chemical dynamics. Using the knowledge gleaned from these insights, we are able to control the phase and period of the BZ oscillators.

 

Keren Sneh
ksneh.AT.terpmail.umd.edu (Rebecca Schulman Group)

Poster: Using reaction-diffusion models to understand information propagation within spatial networks of synthetic genetic regulatory networks
Cells are constantly taking in environmental inputs and adapting their behavior to respond appropriately. Their complex sensory and signal processing networks allow them to precisely coordinate sophisticated responses to multiple stimuli. Creating “programmable materials” that emulate the cell’s ability to take in and respond to environmental inputs presents powerful possibilities for biological nanotechnology. Cells adapt to their environment using genetic regulatory networks (GRNs), which are networks of interconnected genes that regulate one another to coordinate gene expression. In vitro transcriptional circuits have emerged as a way to synthetically emulate GRNs. These circuits are made up of short transcriptional templates called genelets. The RNA transcribed from a genelet can be designed to basepair to a target genelet and act as a repressor. Additionally, the RNA signals are degraded by RNase A and RNase H, which allows for a signal turnover at a rate that is comparable to cellular GRNs. By connecting together multiple genelets, the complex circuits found in cellular GRNs can be emulated in vitro using short DNA sequences and a few well-characterized enzymes. Previous genelet circuits have been designed to work in well mixed solutions. As a next step, we would like to place genelet circuits into materials in order to build programmable materials. Hydrogels, in particular, are of interest because of their ability to easily integrate DNA and because they allow us to control the spatial patterns of our genelets. We would like to design a genelet circuit housed in a hydrogel that can detect a concentration gradient of a target molecule, which in turn will trigger specific shape change in the hydrogel that will allow it to move towards the source of the target molecule. Placing a genelet circuit in a hydrogel presents new challenges, as we must now consider how a signal will translate to different locations in the gel. In order to understand how the RNA transcripts move through the hydrogel and their ability to reach their targets, we are modeling our systems using COMSOL Multiphysics. Using these models, we are able to investigate both what parameters are necessary for a reliable genelet circuit that can communicate in space and how to connect the genelet circuit so that a concentration gradient can be detected.

 

Dimitra Spanoudaki
dimitra.spanoudaki.AT.ulb.ac.be (Anne De Wit Group)

Poster: The growth of an electrochemical garden on a zinc electrode
The far-from equilibrium precipitation reaction of chemical gardens can lead to the formation of biomimetic and complex structures providing a new route for the rational architectural design of functional materials. Inspired by recent developments in the field of chemical gardens1 , we put forward a new scientific question: "Is it possible to create an electrochemical garden?" By implementing state-of-the-art electrochemical techniques and using the phenomenon of metal corrosion2 , we sculpture self-organized micro-structures on a zinc disc-electrode surface by a mechanism similar to that of chemical gardens. A deeper search in the formation mechanism reveals that ion-selective membranes are the driving force for the growth of an electrochemical garden3 . At last, electrochemical instabilities, introduced under proper conditions, result in the emergence of current oscillations2 in the region where electrochemical gardens were discovered. Current oscillations sculpture the electrode surface with a variety of self-organized precipitation structures.
1. Barge, L, et al. (2015). From Chemical Gardens to Chemobrionics, Chem. Rev., 115, 8652. 2. Spanoudaki, D. et al. (2018). Analysis of the temporal self-organizational phenomena observed during the electrodissolution of Zn in sulphuric acid solutions. Mater. Today, 5, 27626. 3. Sato, N. (1996). Interfacial ion-selective diffusion layer and passivation of metal anodes. Electrochim. Acta, 41, 1525.

 

John A. Tetteh
john.tetteh.AT.slu.edu (István Kiss Group)

Poster: Synchronization patterns of two coupled electrochemical oscillators in a closed bipolar cell
We investigate the dynamical behavior of the oscillatory electrodissolution of nickel and hydrogen reduction reaction in a closed electrochemical bipolar cell with two embedded wires. In the bipolar setup, two half U cells are separated by an epoxy plate with the two nickel electrodes; the oxidation and reduction reactions take place at the two ends of the same wire. By tuning the concentration of electrolyte in the anode and cathode compartments, the current level and the dynamics of the oscillatory range can be varied without any external resistance. Phase analysis of the chronopotentiometric measurements showed that the potential oscillations of the two nickel anodes are in-phase synchronized, and thus strongly coupled, when 1.00 mm diameter electrodes were employed. The in-phase synchronization and the strong coupling effect was lost as the electrode diameter was decreased from 1.00 mm to 0.25 mm. The synchronization effects could be attributed to the enhanced coupling that occurs concurrently on both the cathode and anode sides. The experiments demonstrate the use of bipolar electrochemical cells for the investigation of coupling and synchronization in chemical oscillatory processes.

 

Jan Totz
jantotz.AT.mit.edu

Talk: Topological braiding of vortices in the membrane of a living cell
Braiding of topological structures in complex matter fields provides a robust framework for encoding and processing information, and has been extensively studied in the context of topological quantum computation. In contrast, braiding of topological defects in macroscopic living systems remains to be explored thoroughly. To this end, we investigate spiral wave turbulence of self-organized Rho-GTP protein waves on the membrane of starfish egg cells. The worldlines of the spiral wave defects undergo rich spontaneous braiding dynamics, and are also capable of forming intricate loop structures. The worldline creation and annihilation events, topological entropy and braiding exponents, as well as loop statistics correlate with cellular activity and exhibit universal scaling behaviors, in agreement with predictions from a generic complex Ginzburg-Landau continuum theory.

 

Mikael Toye
mtoye.AT.gatech.edu

Poster: Quantifying Chaos in Cardiac Tissue Under Fast Periodic Stimuli: Leading Lyapunov Exponent and Unstable Periodic Orbits
Cardiac tissue has long been modeled as a nonlinear system that can exhibit chaotic dynamics. However, little concrete evidence has been derived from cardiac tissue itself supporting its description as a chaotic system. In this study, we aim to quantify the chaotic nature of a cardiac system by calculating the leading Lyapunov exponent of action potential duration (APD) sequences generated by the system’s response. This was accomplished by recording APD time series complexity observed in cardiac tissue during fast pacing from the experimental data of a restitution curve map and direct measurements from a frog ventricle stimulated with a range of constant periodic forcing signals. We calculated the leading Lyapunov exponents from the resulting APD sequences with the time series analysis tools of Tisean. Initial results have shown to produce negative Lyapunov exponents for forcing frequencies near the bifurcation points and positive during the complex response. In addition, we find several unstable periodic orbits during the complex response further showing that the response is not random but in fact chaotic.

 

Qingpu Wang
qwang9.AT.fsu.edu (Oliver Steinbock Group)

Poster: Flow-assisted self-organization of hybrid membranes in microfluidic devices
Microfluidic flows are a powerful tool to drive reactions far from equilibrium and, thus, induce chemical self-organization. We produce complex membranes in microfluidic devices at the reactive interface between laminar streams of reactant solutions. For a purely inorganic reaction of CoCl2 and NaOH, the resulting linear membranes show striking color bands that, over time, expand exclusively in the direction of the Co2+ solution. The effective diffusion coefficients are proportional to the hydroxide concentration, but the membrane growth slows down with increasing concentrations of Co2+. For a redox reaction of AgNO3 and TMB, a hybrid membrane is formed which thickens in both directions and reveals oscillatory dynamics. The hybrid membrane mainly consists of hair-like Ag microstructures, Ag nanowires, and unbranched TMB–TMB2+ microfibers. Branched dendrite-like fibers form on the TMB side when the flow is stopped. Our study provides direct insights into the growth dynamics of precipitate structures in chemobrionics and offers an alternative route for materials synthesis.

 

Yao Xiong
xiong3.AT.g.clemson.edu (Olga Kuksenok Group)

Poster: Modeling pattern formation and restructuring in hydrogel membranes
Pattern formation and dynamic restructuring plays a critical role in a plethora of natural processes. Controlling pattern formation dynamically in soft synthetic materials would allow one to control an entire range of surface functionalities. Herein, we focus on the dynamic restructuring between different patterns in thermoresponsive poly(N-isopropylacrylamide) membranes constrained between two rigid surfaces. We use three-dimensional gel Lattice Spring Model to simulate the dynamics of constrained hydrogels. Mechanical instability due to the constrained swelling of a polymer network undergoing extensive volume changes in response to external stimuli results in pattern formation in these systems. We show that the wavelength, the amplitude, and the mode of patterns formed could be controlled dynamically by varying the rates of stretching and compression the sample along its width. Furthermore, the sample exhibits bistability, which in turn is controlled by the rates of the stretching and compression. In effect, our results indicate that the sample has an effective memory of previous state. Our results point out that the functionality of soft structured interfaces can be controlled dynamically via mechanical forcing.

 

Franco Zanotto
fzanotto.AT.fsu.edu (Oliver Steinbock Group)

Talk: Hyper-scroll dynamics: Vortices in four-dimensional networks
Spaces beyond our three-dimensional world have stimulated human fascination for generations. Higher-dimensional spaces are a common feature in networks of coupled oscillators such as electronic circuits or neuronal cells. In such networks, information can be relayed over long distances, circulate along closed paths, or form complex patterns. We investigate a network of excitable nodes diffusively coupled to their neighbors along four orthogonal directions. This regular network effectively forms a four-dimensional reaction-diffusion system and has rotating wave solutions. We analyze some of the general features of these hyper-scroll waves, which evolve around surfaces such as planes, spheres, or tori. We also discuss the robustness of these network states against the removal of random node connections and report an example of hyper-scroll turbulence.