In recent years, organic electrochemical transistors (OECTs) have attracted interest in the field of organic bioelectronics thanks to their distinctive properties. In these devices, the channel consists of an organic semiconducting polymer which is in contact with an electrolyte. The gate electrode, immersed in the electrolyte, regulates the conductivity of the channel. Biocompatibility, ease of fabrication, low cost, high ionic sensitivity and low-voltage operation are among the properties that make this class of devices suitable for a wide range of applications, such as biosensing, in-vitro monitoring, and wearable and implantable devices. The purpose of this thesis, which is part of the Cobalt project, is the fabrication of an OECT-based device capable of continuously monitoring the behaviour of the endothelial barrier.