A microfluidic device comprising: a device body; a porous support extending across an internal volume in the device body to define a partition between an upper, apical compartment that is bounded on its lower side by the upper surface of the porous support and a lower, basolateral compartment that is bounded on its upper side by a lower surface of the porous support and on its lower side by an internal surface of the device body; an inlet and an outlet arranged in the device body that provide a path for fluid flow of a liquid medium through a flow channel that includes the basolateral compartment; a first electrode and a second electrode arranged on the internal surface of the device body on the lower side of the flow channel, the first and second electrodes being electrically connected to respective internal ends of respective electrically conductive paths, the electrically conductive paths having respective external ends that provide respective external contacts via which a bias voltage is applicable between the first and second electrodes to create an electric field to induce an electrical current to flow between the first and second electrodes at least in part via the cell layer when a liquid medium is present in the flow channel and when a cell layer has been grown on the porous support; and a septum arranged in the flow channel between the first electrode and the second electrode, the septum extending at least part way between the internal surface of the device body and the porous support, the septum being made of a material that acts as an electrical barrier to the electric field, so that the septum is configured to inhibit electrical current flowing directly from the first electrode to the second electrode through the liquid medium and to promote electrical current flowing from the first electrode to the second electrode via the cell layer. a device body; a porous support extending across an internal volume in the device body to define a partition between an upper, apical compartment that is bounded on its lower side by the upper surface of the porous support and a lower, basolateral compartment that is bounded on its upper side by a lower surface of the porous support and on its lower side by an internal surface of the device body; an inlet and an outlet arranged in the device body that provide a path for fluid flow of a liquid medium through a flow channel that includes the basolateral compartment; a first electrode and a second electrode arranged on the internal surface of the device body on the lower side of the flow channel, the first and second electrodes being electrically connected to respective internal ends of respective electrically conductive paths, the electrically conductive paths having respective external ends that provide respective external contacts via which a bias voltage is applicable between the first and second electrodes to create an electric field to induce an electrical current to flow between the first and second electrodes at least in part via the cell layer when a liquid medium is present in the flow channel and when a cell layer has been grown on the porous support; and a septum arranged in the flow channel between the first electrode and the second electrode, the septum extending at least part way between the internal surface of the device body and the porous support, the septum being made of a material that acts as an electrical barrier to the electric field, so that the septum is configured to inhibit electrical current flowing directly from the first electrode to the second electrode through the liquid medium and to promote electrical current flowing from the first electrode to the second electrode via the cell layer.