Welcome to the Biological Colloids Laboratory at Drexel University. Our research applies principles of colloid science to the study of human diseases. Examples include enzyme-driven aggregation, and subsequent retention within the arterial wall, of low density lipoproteins (or LDL, the so-called bad cholesterol) as a contributing factor (if not the root cause) of atherosclerosis and nucleation of cholesterol crystals in the context (again) of atherosclerosis, where crystals arising from LDL influence plaque vulnerability to rupture, and in the context of gallstone pathogenesis, where crystals arising from hepatic vesicles, or liposomes, are precursors to gallstones.

A primary research thrust involves "theranostic" applications of ultrasound in combination with microbubble-containing formulations. The term theranostic stems from therapy and diagnostics; we are developing a triggered-release drug delivery vehicle (therapy) for which ultrasound serves as a remote, mechanical trigger and are developing novel enhanced ultrasound contrast agents (diagnostics) for multiple cardiac imaging applications. In addition to the practical, clinical aspects of microbubbles, we are studying the fundamentals of ultrasound-microbubble interactions. A primary goal is to map cavitation phenomena in pressure and frequency space for a variety of complex fluids and to identify the corresponding mechanisms by which cavitation events produce changes over colloidal length scales.

Below are some specific examples of our ongoing research projects involving ultrasound:

Sonoporation Kinetics and Mechanism: Sonoporation is a process whereby ultrasound opens a cell bilayer for cargo transport across an otherwise impermeable membrane. We study sonoporation across liposomal bilayers. On one hand, the liposome serves as a controllable cell mimic, allowing us to study cargo transport systematically as a function of bilayer composition and phase. On the other hand, the liposome serves a drug delivery vehicle. We intend to apply what we learn about cell sonoporation (ultrasound-mediated delivery of cargo into a cell) to design formulations for ultrasound-triggered release of cargo from liposomes.

Acoustic Activity of Nested Microbubbles: We invented (in a literal sense; a U.S. patent is pending) nesting a microbubble inside the aqueous core of vesicles and microcapsules. We are interested in nesting from both a practical and a fundamental perspective. Some of the practical aspects are safe, long-lasting ultrasound contrast of ventricles, perfusion imaging with ultrasound, and ultrasound-triggered drug release. There are also interesting fundamental questions relating to the nest architecture. For example, how does the nest change in response to applied ultrasound to permit water transport so as to allow microbubble expansion and what acoustic phenomena induce such changes in the nest (e.g., does stable cavitation of a microbubble induce microstreaming which then tears a hole within a phospholipid bilayer?) We are actively attacking such questions and using what we learn to improve and develop real-world theranostic applications.

Improving Food Quality and Safety: We employ microbubbles to eliminate spoilage bacteria from produce. Specifically, the use of microbubbles in combination with high frequency, focused ultrasound allows to control inertial cavitation with the goal of selectively destroying harmful bacteria without damaging the food. We are presently investigating proximity effects and the role of agents which can decrease the inertial cavitation threshold in a known way.

Single-Fluid Epoxies: We are applying the nest architecture to the study of epoxies, with a long-term goal of developing a single fluid, ultrasound-cured, epoxy with an infinite pot life. Traditional epoxies involve two fluids, one with the curing agent and a second containing the resin. We are investigating the feasibility of nesting the curing agent - together with microbubbles - within a microcapsule, and suspending a population of microcapsules within the resin. No curing would take place within this single fluid, as the curing agent is separated from the resin by the microcapsule shell; the fluid could thus be applied to a surface without concern for hardening during the process of coating (that is, the formulation would have an effectively infinite pot life). Curing would proceed via the application of ultrasound - after the surface has been coated.

Video: "Introducing our CBE Faculty: Prof. Steven Wrenn"