In the last decade, the use of flexible biosensors for neuroprosthetic and translational applications has widely increased. Among them, the polyimide (PI)-based thin-film electrodes got a large popularity. However, the usability of these devices is still hampered by a non-optimal tissue-device interface that usually compromises the long-term quality of neural signals. Advanced strategies able to improve the surface properties of these devices have been developed in the recent past. Unfortunately, most of them are not easy to be developed and combined with micro-fabrication processes, and require long-term efforts to be testable with human subjects. Here we show the results of the design and in vitro testing of an easy-to-implement and potentially interesting coating approach for thin-film electrodes. In particular, two biocompatible coatings were obtained via covalent conjugation of a laminin-derived peptide, CAS-IKVAV-S (IKV), with polyimide sheets that we previously functionalized with vinyl- and amino- groups (PI_v and PI_a respectively). Both the engineered coatings (PI_v+IKV and PI_a+IKV) showed morphological and chemical properties able to support neuronal adhesion, neurite sprouting, and peripheral glial cell viability while reducing the fibroblasts contamination of the substrate. In particular, PI_v+IKV showed promising results that encourage further in vivo investigation and pave the way for a new generation of peptide-coated thin-film electrodes.