Steven Wrenn
Thursday, November 17th
2:00 – 3:00pm
Location: Lehman Auditorium
Abstract
This talk will describe interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. Microbubble physics, including inertial cavitation and the influence of membrane properties - surface tension, surface dilatational viscosity, and area expansion modulus – thereon will be reviewed, and a comparison between model predictions and experimental measurements will be made concerning the inertial cavitation threshold or the peak negative pressure at which a microbubble implodes. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on area expansion modulus through the variation of PEG molecular weight and mole fraction in the microbubble monolayer coating. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. The talk will also involve a discussion of nesting microbubbles inside the aqueous core of vesicles and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and also offers the ability to achieve ultrasound-triggered release of vesicle contents. Moreover, nesting enables one to tune ultrasound-triggered release kinetics by taking advantage of different material properties associated with different bilayer phases. Nesting thus constitutes a truly “theranostic” vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery.
Biography
Steven Wrenn earned his B.S. in chemical engineering from Virginia Tech in 1991. While an undergraduate, he worked as a co-op for G.E. Plastics (formerly Borg Warner) in Parkersburg, WV. After graduating he worked for three years as a process engineer for Zeneca, Inc. (formerly ICI Americas, Inc.) in New Castle, DE. He then returned to school, earning his Ph.D. in chemical engineering from the University of Delaware in 1999. His doctoral thesis involved development of a new fluorescence assay to detect nucleation of cholesterol crystals from synthetic biliary vesicles in the context of gallstone disease. After graduating from Delaware, he joined the chemical engineering faculty at Drexel University in Philadelphia. In 2006 he became an Alexander von Humboldt research fellow and spent a year at Ruhr University in Bochum, Germany. His research involves the study of colloids in the context of human disease, interactions of phospholipid bilayers with ultrasound, and theranostic applications of microbubbles.
Contact
The George Washington University, Mechanical and Aerospace Engineering
800 22nd St NW, suite 3000
Washington, DC 20052
[email protected]