Shrinking bubbles and dancing cells: combining microfluidics and ultrasound for medical diagnostics and therapy

ROOM 125

Microbubbles are clinically used to enhance the contrast of ultrasound images, for the diagnosis of several heart diseases and cancers. Recently, nanobubbles–bubbles that are orders-of-magnitude smaller than microbubbles–have emerged as even more promising contrast agents for diagnostics applications due to their ability to extravasate from vessels into organ tissue. However, current state-of-the-art techniques to generate nanobubbles are unable to create uniform size nanobubbles, which limits the clinical efficacy of the nanobubbles. In this talk, I describe a microfluidic approach to produce monodisperse–uniform size–nanobubbles. We exploit the differential solubility of gases in aqueous solution to shrink microbubbles into nanobubbles. Namely, we use a two-component gas mixture of water-soluble nitrogen and water-insoluble octafluoropropane as the gas phase. We first generate microbubbles microfluidically, then allow the microbubbles to shrink, due to the dissolution of the water-soluble gas component, to achieve nanobubbles. We find that these nanobubbles show better homogeneity and brightness in both in vitro and in vivo ultrasound imaging experiments, in phantoms and in live mice, respectively, when compared with state-of-the-art bulk-made nanobubbles. These results suggest that the monodisperse nanobubbles may be suitable as ultrasound contrast agents for detecting nanoscale physiological leakages. The second half of this talk focuses on a newly discovered biophysical phenomenon, whereby adherent cells under the perturbation of an acoustic field self-generates microstreaming flows in a microfluidic channel. We find that the velocity of the microstreaming flow is a strong proxy for cellular mechanical properties, and that large molecule drugs can be selectively delivered into the cells via such microstreaming.

Dr. Scott Tsai is an Associate Professor in the Department of Mechanical and Industrial Engineering at Ryerson University, and an Affiliate Scientist at the Li Ka Shing Knowledge Institute of St. Michael’s Hospital. He obtained his BASc degree (2007) in Mechanical Engineering from the University of Toronto, and his SM (2009) and PhD (2012) degrees in Engineering Sciences from Harvard University. Dr. Tsai is the theme lead for Biomedical Delivery Systems at the Institute for Biomedical Engineering, Science, and Technology (iBEST), and he directs the Laboratory of Fields, Flows, and Interfaces (LoFFI). At Ryerson, Dr. Tsai is the interim director of the Biomedical Engineering Graduate Program. Dr. Tsai is a recipient of the United States’ Fulbright Visiting Research Chair Award (2018), Ontario’s Early Career Researcher Award (2016), Canadian Society for Mechanical Engineering’s I. W. Smith Award (2015), and Ryerson University’s Deans’ Teaching Award (2015). 

Holiday Closure

The Department of Mechanical Engineering will be closed from 3:00 pm on Friday, December 20th, 2019 and will re-open at 8:30 am on Monday, January 6th, 2020.

We would like to wish everyone a Safe and Happy Holiday!

See you in 2020!

2020 Educational Summer Camp, York University, Toronto, Canada



Solomon Boakye-Yiadom
Assistant Professor, Mechanical Engineering Department
437 Bergeron Center for Engineering Excellence
Lassonde School of Engineering, York University
Toronto, Canada

NOV 19 – Paula Meyer – MECH Research Seminar Series

Paula Meyer, P.Eng., holds her Bachelor, Master’s and Ph.D. degrees in Mechanical Engineering from McMaster University.  Dr. Meyer’s Ph.D. research was in vibrations and ultra precision machining.  Dr. Meyer worked in the automotive, nuclear and construction industries.  She was a senior contact engineer for General Motors of Canada Ltd., a senior engineer for AMEC NSS Ltd., and a project manager for RWDI.  Dr. Meyer is now a professor in Conestoga College’s Bachelor of Mechanical Systems Engineering Program, an accredited engineering degree program.

A Career in Industry and Academia

Dr. Paula Meyer will discuss her research in academia, and her career in industry.   Dr. Meyer will also describe Conestoga College’s current bachelor of Mechanical Systems Engineering program, where she is a professor.

See poster here


NOV 12 – Caroline Wagner – MECH Research Seminar Series

Caroline Wagner is a postdoctoral researcher in the Ecology and Evolutionary Biology department at Princeton University. She completed her PhD in Mechanical Engineering at the Massachusetts Institute of Technology (MIT), combining experimentation and mathematical modeling to study how the fluid mechanical properties of biological gels could be interpreted as indicators of the underlying biopolymer microstructure. Dr. Wagner’s current work focuses on modeling the nonlinear dynamics of infectious diseases, both at the population level and at the level of the in-host dynamics and biological processes regulating parasite transmission and suppression by natural immunity or vaccines. Dr. Wagner completed her B. Eng. at McGill University and her MS at MIT, both in Mechanical Engineering.

Mathematical disease models: from mucus rheology to infectious disease dynamics and control

The cross-linked polymeric microstructures of biological hydrogels give rise to their mechanical properties, which in turn contribute to their proper biological function. Quantification and modeling of the mechanical properties of these materials can provide insight into their microstructures, which is particularly important when structural changes are associated with impaired biological function. In the first part of this presentation, we will discuss this relationship between microstructure and mechanical properties in the context of the biological hydrogel mucus. To do so, we explore the network structure and association dynamics of reconstituted mucin gels using micro- and macrorheology in order to gain insight into how environmental factors, including pathogens and therapeutic agents, alter the mechanical properties of fully-constituted mucus. We then apply these findings to interpret changes in the mechanical properties of cervical mucus and saliva as biomarkers for disease. In the second part of this presentation, I will present plans for my current and future research directions, which include leveraging data sets in order to explore the complex forcing functions of nonlinear epidemic dynamics across the molecular-to-individual and the individual-to-global length-scales.

See poster here