Deformable particles have many uses. A study unlocks their secrets

A precise understanding of how deformable particles flow through various arrangements of obstacles and constrictions could greatly benefit the development of pharmaceuticals, wastewater treatment, and other applications. But when it comes to how particles that change their shapes significantly flow, crucial details are still unknown. For example, how much deformation can soft particles undergo before breaking?

Using a combination of laboratory experiments and computer simulations, a team of researchers has set out to uncover the secrets of highly deformable particles. Led by Corey O’Hern, professor of mechanical engineering & materials science, the team has received a grant of $680,000 from the National Science Foundation.  

For the study, the researchers will develop an improved understanding of how deformable particles move through narrow channels and obstacle arrays. Doing so, they say, will likely lead to the improved operation of microfluidic and lab-on-a-chip devices. The researchers bring complementary skills to the study. Eric Weeks of Emory University will conduct the laboratory experiments of flows of oil-in-water droplets. O'Hern and Mark Shattuck of the City College of New York will develop novel computational models of capillary droplets, which can then be compared to Weeks’ experiments and used to make predictions about deformable particle flows. 

Deformable particles can move through obstacle arrays and flow constrictions in multiple ways. O’Hern uses the example of a particle passing through a narrow channel.  

“Suppose you have a droplet flowing through a channel, and then suddenly the width changes,” he said. “The constriction can either slow down the droplet or it can cause the droplet to break apart. In the first case, the droplet slows down because it is too small to fit through the opening. The droplet needs to wait until it can deform to pass through the opening.  We have shown that we can model this deformation process exactly and recapitulate the experimental results. However, the droplet can also break if the forces on the droplet from the channel boundaries are sufficiently large. Modeling the droplet break-up process is relatively unexplored in flows through confined geometries.”

Knowledge of how droplets break up, as well as how they coalesce, can benefit numerous fields. One example O’Hern points to is developing more accurate dosages for pharmaceuticals and lap-on-a-chip applications. 

“For instance, you can take two droplets each containing particular doses, have them collide and merge, effectively adding the two doses," he said. "If you do this successively, you can create any dosage you want. Then once you create the correct dosage, you can have the dose incorporated into a capsule or pill.”

Another application involves cell sorting. “You insert droplets with different properties into flows through obstacle arrays,” O’Hern said. “Droplets with different stiffnesses will exit the obstacle array at different locations. Thus, one exciting application is to use knowledge from our studies to develop methods to sort healthy and cancerous cells since cancer cells are stiffer than normal cells.”