The stress of dilute active suspensions in non-Newtonian linear flow

Active suspensions, containing self-propelling particles, exhibit unique collective behaviours and rheological properties that differ significantly from those found in passive particle suspensions. Given that most biological fluids are non-Newtonian, understanding the rheology of these active systems in complex fluids is crucial. This study theoretically investigates the rheology of dilute microswimmer suspensions in weakly viscoelastic linear flows. We specifically calculate the average extra stress for active spherical particles suspended in a second-order viscoelastic fluid under both shear and extensional flow conditions. Our findings quantify the contribution of surface actuation to normal stress differences and the effective viscosity, providing insights into predicting and controlling the dynamics and mechanics of active fluids.