Optimised hyperbolic microchannels for the mechanical characterisation of bio-particles

TL;DR

This paper introduces an innovative microfluidic device with optimised converging-diverging channels and a microscopy tracking system to study the mechanical behaviour of bio-particles under controlled homogeneous straining flows, enabling detailed analysis of diverse biological particles.

Contribution

The work presents a novel microfluidic design and tracking method for characterising bio-particles' dynamics in homogeneous straining flows, addressing previous challenges in flow control.

Findings

Successfully generated linear velocity gradients in microchannels

Demonstrated tracking of bio-particles over long distances with high-quality imaging

Validated the approach with DNA, actin filaments, and protein aggregates

Abstract

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 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 the dynamics of objects with a wide range of sizes, characteristics and behaviours of relevance in the biological world.