As a permanent solution for patients who cannot contract their urinary bladder, an artificial detrusor muscle appears a higher outcome approach compared to current sacral neurostimulators featured by severe long-term side effects. In this paper, a novel soft robotic detrusor is presented to overcome the limitations of the state-of-the-art solutions. It is based on two identical origami-based hydraulic actuators, which completely surround the bladder and contract upon water aspiration. Design, manufacturing, and experimental characterization both in terms of contraction capabilities and voiding efficiency on ex vivo swine bladders are reported for two different origami geometries, as well as a proof-of-concept implementation of an autonomous driving circuit as control unit. Results from assisted urination tests outlined very good performances proving an active voiding efficiency of the hydraulic soft robotic detrusor equal to 84.8%$\pm 7.4\%$in simulated environment.