One Size Fits All: A Novel Varying Cross-Section Microfluidic Device for Wide-Range Cell Harvesting

Microalgae are promising feedstocks for high-value compounds and biomass production, but harvesting remains a major challenge due to the high capital and energy costs, contamination risk, and low efficiency of conventional methods. In this study, we developed a novel spiral inertial microfluidic device with varying cross-sections to enable efficient concentration of microalgae across a broad size range. The device was designed to combine variable cross-sections with an expanded channel area to improve particle focusing and separation. Its performance was first evaluated using particles spanning a wide size range (3–20 μm) and then demonstrated using two representative microalgae species with distinct morphologies: Haematococcus pluvialis (spherical, ~ 20 μm) and Phaeodactylum tricornutum (non-spherical, ~ 3 μm in width). The device achieved excellent focusing performance for model particles, while recovery efficiencies for microalgae reached > 95% for H. pluvialis and up to 85% for P. tricornutum . These findings demonstrate that the proposed device can effectively concentrate microalgae with different sizes and shapes, highlighting its potential as a versatile platform for microalgae harvesting and other bioprocessing applications.