A therapeutic product delivery device is described, which comprises a circuit layer, an actuator layer carrying an actuator, an occlusion detection layer (118), and a valve layer, through which a therapeutic product is conveyed by the action of the actuator. A plurality of conductive pins (155) extend from the circuit layer through or to each of the actuator layer, the occlusion detection layer and the valve layer, the conductive pins aligning the layers with each other. The occlusion detection layer comprises a plurality of contacts, each electrically connected to a respective one of the conductive pins, the contacts being provided at a detection region at which the therapeutic product is deposited in the event of a blockage. A blockage inhibiting the therapeutic product from being conveyed to the patient is detected when therapeutic product deposited in the detection region provides an electrical connection between the contacts. The conductive pins therefore provide at least two functions; firstly they align the layers of the cartridge (at assembly and during use), and a secondly they provide a conductive route between the circuit layer and the occlusion layer, permitting therapeutic product deposited at the occlusion layer to be able to complete an electric circuit with the circuit layer to enable occlusion detection.