Handling very soft, delicate items without damaging them is hard with human hands, let alone doing it at the microscopic scale with lab instruments. Three recent studies have honed a technique for handling tiny, soft particles using precisely controlled fluid flows that act as gentle microscopic hands to test the physical limits of these soft particles – ranging from biological tissues to fabric softeners.
The three studies, led by the University of Illinois' Charles Schroeder, the Ray and Beverly Mentzer Faculty Scholar of chemical and biomolecular engineering, detail the technology and application of the Stokes trap – a method for manipulating small particles using only fluid flow.
In the newest study, published in the journal Soft Matter, the team used the Stokes trap to study the dynamics of vesicles – squishy fluid-filled particles that are stripped-down versions of cells and have direct relevance to biological systems, the researchers said. This follows up on two recent studies in the journals Physical Review Fluids and Physical Review Applied that expanded the power of the trapping method.
Other techniques
"There are several other techniques available for manipulating small particles, such as the widely used and Nobel Prize-winning optical trap method that uses carefully aligned lasers to capture particles, " said Dinesh Kumar, a chemical and biomolecular engineering graduate student and lead author of two of the studies.
"The Stokes trap offers several advantages over other methods, including the ease of scaling up to study multiple particles and the ability to control the orientiation and trajectories of different shape particles such as rods or spheres." Armed with the improved Stokes trap technology, the team set out to understand the dynamics of lipid vesicles when they are far from their normal equilibrium state.
Phase diagram
With their new data, the team was able to produce a phase diagram that can be used by researchers to determine how certain types of fluid flow will influence deformation and, ultimately, the physical properties of soft particles when pulled on from different flow directions.
"Products like fabric softeners – which are composed of vesicle suspensions – do not work correctly when they clump together," Dinesh Kumar said. "Using the Stokes trap, we can figure out what types of particle interactions cause the vesicles to aggregate and then design a better-performing material."
The technique is currently limited by the size of particles that the Stokes trap can catch and handle, the researchers said. They are working with particles larger than 100 nanometers in diameter, but in order for this technology to apply more directly to biological systems, they will need to be able to grab particles that are 10 to 20 nanometers in diameter – or even down to a single protein.
