Rheology of active fluids

This chapter on the rheology of active fluids is an attempt to correlate theoretical and experimental work. A considerable amount of theoretical work and most of the experimental data focus on the rheology of active fluids in a Newtonian matrix, which displays uncommon macroscopic rheological behaviors, such as the apparent superfluid-like state of the pusher suspensions. The failure of the "scallop theorem" for reciprocal swimmers in a non-Newtonian matrix is highlighted. Finally, recent findings concerning the turbulent-like behaviour in concentrated systems are described in detail.