Stefano Aime – Rheofluidics: single-drop oscillatory rheology with microfluidics

The measurement of frequency-dependent viscoelastic moduli is of paramount importance in many fields, from material science to biology, and is typically accomplished in bulk materials using commercial rheometers. The trend towards miniaturization in the biotechnology, manufacturing and chemical processing industries has motivated the extension of viscoelastic measurements to microscopic objects with well-defined shape and size such as droplets, vesicles, microcapsules, or even single cells. Due to the reduced size of the samples, this extension requires novel mechanical techniques to control stress and strain, and novel strategies to disentangle bulk rheology from the contribution of interfaces. In addition, it faces the challenge of sampling highly heterogeneous populations such as those typical of biological samples.

To this end, we developed a microfluidic technique to measure the rheology of cells and droplets flowing through narrow channels. Named Rheofluidics, this technique combines the high throughput of microfluidics with the versatility of traditional rheological probes. Like a stress-controlled rheometer, Rheofluidics measures the time-dependent deformation of droplets subject to a well-defined hydrodynamic stress, controlled by the shape of the microfluidic channel in which the droplets are flowing. To validate this approach and to demonstrate the power of Rheofluidics, we use it to study the linear and nonlinear rheology of oil droplets, hydrogel beads and lipid vesicles, extracting their viscoelastic properties with a throughput more than 1000 times higher than that of standard rheology.