Microfluidic Brillouin platform for frequency-resolved mechanics of complex fluids

We introduce an integrated microfluidic platform that combines pressure-flow rheology with depth-resolved Brillouin microspectroscopy to investigate complex fluids in extensive frequency ranges. Apparent viscosity is measured via calibrated pressure-flow in a rectangular polydimethylsiloxane microchannel, while GHz-frequency Brillouin spectroscopy probes longitudinal mechanics under identical steady-flow conditions. Using semi-dilute methylcellulose solutions in a cell-culture medium as a model, we reveal mild shear-thinning behavior, whereas the Brillouin frequency shift and linewidth values remain constant throughout the flow rate range, mainly influenced by polymer concentration. This confirms the decoupling between steady-shear and GHz-frequency acoustic responses observed previously. The platform offers a compact, calibrated approach for frequency-resolved mechanical analysis of flowing soft materials and perfused media.