Clogging of microfluidic constrictions by monoclonal antibody aggregates: role of aggregate shape and deformability.

The formation of aggregates in solutions of monoclonal antibodies is difficult to prevent. Even if the occurrence of large aggregates is rare, their existence can lead to partial or total clogging of constrictions in injection devices, with drastic effects on drug delivery. Little is known on the origin and characteristics of such clogging events. Here we investigate a microfluidic model system to gain fundamental understanding of the clogging of constrictions by monoclonal antibody aggregates. Highly concentrated solutions of monoclonal antibodies were used to create protein aggregates (larger than 50 microns) using mechanical or heat stress. We show that clogging occurs when aggregates reach the size of the constriction and that clogs can in some cases be released by increasing the applied pressure. This indicates the important role of protein aggregate deformability. We perform systematic experiments for different relative aggregate sizes and applied pressures, and measure the resulting flow-rate. This allows us to present first in situ estimates of an effective Young's modulus. Despite their different shapes and densities, we can predict the number of clogging events for a given constriction size from the aggregate size distribution measured by Flow Imaging Microscopy (MFI). In addition our device can detect the occurrence of very rare big aggregates often overlooked by other detection methods.

Optimised hyperbolic microchannels for the mechanical characterisation of bio-particles.

The transport of bio-particles in viscous flows exhibits a rich variety of dynamical behaviour, such as morphological transitions, complex orientation dynamics or deformations. Characterising such complex behaviour under well controlled flows is key to understanding the microscopic mechanical properties of biological particles as well as the rheological properties of their suspensions. While generating regions of simple shear flow in microfluidic devices is relatively straightforward, generating straining flows in which the strain rate is maintained constant for a sufficiently long time to observe the objects' morphologic evolution is far from trivial. In this work, we propose an innovative approach based on optimised design of microfluidic converging-diverging channels coupled with a microscope-based tracking method to characterise the dynamic behaviour of individual bio-particles under homogeneous straining flow. The tracking algorithm, combining a motorised stage and a microscopy imaging system controlled by external signals, allows us to follow individual bio-particles transported over long-distances with high-quality images. We demonstrate experimentally the ability of the numerically optimised microchannels to provide linear velocity streamwise gradients along the centreline of the device, allowing for extended consecutive regions of homogeneous elongation and compression. We selected three test cases (DNA, actin filaments and protein aggregates) to highlight the ability of our approach for investigating dynamics of objects with a wide range of sizes, characteristics and behaviours of relevance in the biological world.