Speaker
Description
Microfluidics has emerged as a powerful tool for the manipulation of bioparticles, enabling operations such as sorting, immobilization and encapsulation. While these approaches are predominantly applied in biomedical and environmental diagnostics, their extension to industrial processes remains limited. One such application is the production of microalgae-based biofuels, for which the dewatering step constitutes a major technological bottleneck. Currently relying on centrifugation or filtration techniques, this step is energy-intensive and economically costly.
Inertial microfluidics offers a passive alternative to address this limitation by exploiting hydrodynamic lift forces arising from particle–flow interactions in laminar Poiseuille flow. These forces induce the lateral migration and focusing of suspended particles at well-defined equilibrium positions within microchannels. By coupling inertial focusing with flow separation, the fluid phase can be efficiently removed, enabling concentration of microalgal suspensions without external fields. Hill and co-authors (Hill C., 2022 doi:10.1016/j.biteb.2022.101014) developed a spiral device that achieves a concentration factor of 130 starting from a suspension of Chlorella vulgaris of about 0.5% v/v initial volume fraction. Based on in situ visualization of microalgal migration, we subsequently demonstrated that an optimized spiral microsystem could be designed to enable more energy-efficient microalgae concentration. However, these visualizations also revealed distinct migratory behaviours depending on microalgal cultures and growth ages. In the present work, we investigate the flow behaviour of Chlorella vulgaris suspensions of different cultures and growth ages with the aim of improving the understanding of how microalgal physical properties influence the inertial focusing phenomenon.
Our experiments are conducted in a spiral microchannel with a rectangular cross-section of 170 × 30 µm², six loops, a single central inlet and four outlets. Various C.Vulgaris cultures and growth ages are investigated. A direct optical method using a high-speed camera is used to assess 2D statistical distributions of particles at multiple locations within the microchannels. In parallel, the size (imaging) and deformability (force spectroscopy) of microalgae before and after passing through the spiral microchannel are characterized using atomic force microscopy (AFM). The microalgae density and aspect are also determined using Lumisizer measurements and transmission electron microscopy (TEM) observations.
Our results show that C.vulgaris microalgae purchased from Greensea (France) cultivated in MC102 medium focus efficiently near the inner wall, with up to 99% of the cells confined within less than one-fifth of the channel width. In contrast, C.vulgaris (CCAP 211/11B) cultivated in Wright’s Cryptophyte (WC) medium exhibit a different migration behavior: while a fraction of the cells migrates toward the conventional equilibrium position near the inner wall, others align with the flow direction to form evenly spaced trains located in the central region of the channel. The exact location of this region depends on the Reynolds number in a non-trivial manner. Differences in microalgal size, density, deformability, and morphology are examined to elucidate the origins of these distinct behaviors.
These results provide insight into interparticle interactions within confined flows, revealing how they influence particle dynamics.