Monitoring the structural health of composite materials such as fibre-laminates is essential for the safe use of these materials e.g. in the aviation or building sector. Thin and flexible sensors as well as signal processing circuits based on organic-electrochemical transistors (OECTs) can be embedded between the different layers of the laminate providing a possibility to detect changes in the material early on without weakening the mechanical integrity of the material. OECTs are electrical devices consisting of a mixed organic conductor, whose conductivity can be controlled by the injection of ions from an electrolyte into the OECT channel. OECTs are currently tested for their use in the field of bio-electronics, making use of their bio-compatibility. However, due to their flexibility and thin structure, OECTs can potentially be integrated into composite materials as well, providing a means of sensing and data processing inside the material that can be used to monitor for potential damage. This is especially interesting for plate like structures built of composite prepreg, since an integration between the prepreg layers would be possible.