Full Abstracts

January 23, 2012

Biological Physics Seminar

Restitution curves and their role in determining the stability of cardiac rhythms

Every year, thousands of people die from ventricular fibrillation. Fibrillation occurs when the normal sinus rhythm of the heart becomes dynamically unstable, leading to spatiotemporally chaotic electrical waves propagating through the heart. These arrhythmic waves prevent the heart from pumping blood effectively, leading to death of the afflicted individual. It has been suggested that the loss of stability of normal sinus rhythm can be predicted through the use of restitution curves.

Restitution curves relate the duration of the electrochemical pulse, called the action potential duration (APD), to the previous diastolic interval (DI), the rest period between pulses. This talk will discuss the experimental measurement of restitution curves and how our view of their role in the stability of cardiac rhythms has evolved over time.

January 25, 2012

Special Biological Physics Seminar

From individuals to colonies, the emergent behaviors of cellular systems

Cells are intrinsically stochastic creatures. Not only individual cells behave randomly during growth, migration and chemo response, but also they differ from each other even if the cells are derived from the same source. Despite this variability, multicellular organisms are capable of performing highly regulated, coordinated activities which are crucial to maintain the normal functionality of complex life systems. A crucial step to understand these two apparently conflicting facts is the emergent behavior coming out of cell-cell interactions.

In this talk, I will present two salient examples of such collective behaviors observed with mammalian cells. In the first example, we studied the spatial-temporal dynamics of fibroblast cells collectively responding to ATP molecules. By using single cell calcium imaging in microfluidic devices, we characterized the correlations within the cell populations and identified the importance of pacemaker cells. We also found two channels of cell-cell signaling: gap junctions and diffusing molecules induced different collective responses. Unifying these observations yields a novel picture of collective chemo sensing and also points to interesting theoretical questions in network theory. In the second example, we studied in vitro models of cancer invasion. Two driving forces of cancer invasion were tested. First in a micro fabricated landscape of micro pillars, cell migrate to the top of the pillars because of the need for more spaces. On the other hand, due to cell-cell interactions, invasion can be suppressed. These two competing factors resulted in distinct invasion profiles for metastatic and non-metastatic prostate cancer cells and interesting social behaviors between the two cell species. In another model, we studied breast cancer cell invasion into extracellular matrix (ECM) driven by nutrition gradient, as a mimic to physiological conditions.

This ongoing project focuses on the single cell movements and the elastic stresses built up in the ECM. We would like to understand how long range mechanical interactions affects the observed rich dynamics during the three-dimensional invasion.

January 30, 2012

Biological Physics Seminar

Using functional magnetic resonance imaging to study human spatial and temporal brain dynamics

Human functional magnetic resonance imaging (fMRI) is an experimental discipline that establishes structure-function correspondences in the brain through the interdisciplinary application of principles from physics, engineering, statistics, biology, medicine, and psychology. In the last two decades, research in fMRI has resulted in an enormous amount of data intended to spatially localize the neural regions that perform specific mental operations (e.g., perception, action, cognition, emotion and autonomic functions). I will describe the fMR imaging modality and present prior work developing novel data analysis methods for investigating the spatial topography of distinct brain regions, as well as various new techniques for assessing the functional and effective connectivity of these regions. Recent results demonstrating the use of data mining algorithms to provide functional explication of intrinsic connectivity networks will also be presented.

February 1, 2012

Biological Physics Seminar

Observing nanoscale structure and dynamics on biological membranes

The plasma membrane of living cells is responsible for sensing and transmitting information of the extracellular environment into the cell. Membranes undergo nanoscale lateral reorganization of membrane-bound molecules to initiate signaling cascades and specific cellular responses. However, these processes often occur at nanometer sizes with millisecond dynamics that are inaccessible by most experimental methods. First, we will discuss how a diverse collection of methods from materials science, physical chemistry, and biophysics have combined to probe the initial biological response of membranes to anthropogenic nanomaterials, namely poly(amidoamine) dendrimers. These studies have guided the development of multifunctional chemotherapeutics with targeted membrane binding by revealing the supramolecular structure of dendrimers binding with phospholipids. Secondly, we will discuss the creation of a novel sub-diffraction-limited optical method for 60 nanometer and 1 microsecond resolution of membrane organization and dynamics via planarized apertures for near-field fluorescence cross-correlation spectroscopy. In particular, this optical method is being used to probe the FcεRI receptor cross-linking and recruitment of downstream signaling molecules on the plasma membrane of mast cells. These studies are providing key insights into the underlying nanoscale principles which govern membrane functionality in both the response to anthropogenic nanoparticles as well as the natural signaling cascades within the immune system.

February 8, 2012

Ron Stites, Pennsylvania State University

A Narrow Feshbach Resonance in Fermionic Lithium Atoms

Feshbach resonances have proven to be an invaluable tool in the atomic physics community. By turning one "knob" the s-wave scattering length of two interacting particles can be tuned to any arbitrary value from negative to positive infinity. We have measured the interaction energy and three-body recombination rate for a two-component Fermi gas near a narrow Feshbach resonance and found both to be strongly energy dependent. The behavior of the interaction energy as a function of temperature cannot be simply described by atoms interacting via a contact potential. Rather, energy-dependent corrections beyond the scattering length approximation are required, indicating a resonance with an anomalously large effective range. This narrow resonance can be used to study strongly correlated Fermi gases that simultaneously have a sizable effective range and a large scattering length.
 

April 4, 2012
J. Zach Hilt, University of Kentucky
Hydrogel Nanocomposites:  Controlled Synthesis and Application as Biomedical Devices  
In my laboratory, we apply chemical engineering fundamentals to the rational design, synthesis, and application of novel nanoparticle systems and macromolecular materials.  We are particularly interested in designing and applying advanced materials based on nanocomposite hydrogels.  Although the majority of hydrogel applications have been in biology and medicine, there is great promise for these materials to impact other areas, especially as nanocomposites.

Nanocomposite hydrogels are a new class of advanced materials, which have recently attracted interest as biomaterials and intelligent materials.  The incorporation of nanoparticles into a hydrogel matrix can provide enhancement to properties (e.g., mechanical, electrical, etc.) or introduce new and unique properties such as remote actuation.  These resultant properties of the nanocomposites can be easily tailored by manipulating the composition of the hydrogel and the nanoparticulate material.  Here, our broad activities in the development and application of hydrogel nanocomposites will be presented.  In particular, hydrogel nanocomposites with magnetic particles will be highlighted, which have been demonstrated as potential candidates in combination cancer therapies, pulsatile drug delivery, and soft actuator applications. In addition, our recently developed methodology for synthesizing stable functionalized nanoparticles with improved properties, where nanoparticles are isolated, functionalized, and then released (ISOFURE platform), will be presented.