Materials in contact with tissue and biological fluids affect cell reaction that could eventually lead to clinical complications (i.e. thrombosis, restenosis). Improving the biological performances of the materials used for biomedical applications is the main goal of this study. In particular, cardiovascular devices require excellent haemo- and biocompatibility properties. PTFE is currently the main material used for vascular prostheses. After long contact periods with blood, clinical complications leading to thrombosis and restenosis are often reported. Improving the haematological performances of PTFE could significantly increase its life-time and decrease long-term complications. However, inadequately engineered surfaces could trigger the coagulation cascade with the formation of a clot, the first step towards a thrombosis. Plasma carbon-based coatings with varying nitrogen contents deposited on PTFE have been studied as promising coating to improve the haematological performances of PTFE implants. In this work, several techniques were applied to study the viscoelastic properties of blood after contact with virgin and treated PTFE as well as the presence and the clot morphology eventually formed onto the surfaces. The chemical composition of the surfaces was analysed with XPS and FTIR.