  We experimentally study the mechanical pressure exerted by a set of
respectively passive isotropic and self-propelled polar disks onto two
different flexible unidimensional membranes. In the case of the isotropic
disks, the mechanical pressure, inferred from the shape of the membrane, is
identical for both membranes and follows the equilibrium equation of state for
hard disks. On the contrary, for the self-propelled disks, the mechanical
pressure strongly depends on the membrane in use, and is thus not a state
variable. When self propelled disks are present on both sides of the membrane,
we observe an instability of the membrane akin to the one predicted
theoretically for Active Brownian Particles against a soft wall. In that case,
the integrated mechanical pressure difference across the membrane can not be
computed from the sole knowledge of the packing fractions on both sides; a
further evidence of the absence of equation of state.
