Small calibre (〈6mm) polytetrafluoroethylene (PTFE) bypass grafts have poor medium and long term patency due to the development of neointimal hyperplasia at the distal anastomosis. The inelasticity of PTFE is implicated in this mechanism of failure. We have developed a novel polyhedral oligomeric silsesquioxane (POSS) nanocage incorporated into a poly(carbonate)urethane (PCU) biomaterial with enhanced biostability and improved antithrombogenicity making it ideal for cardiovascular applications. In this study the compliance and viscous component of a POSS-PCU small calibre graft was measured using a biomimetic pulsatile flow circuit and wall tracking ultrasound. A POSS-PCU graft displays elastic and viscous behaviour similar to the native artery. Furthermore, platelet adhesion and activation studies suggest POSS-PCU is a more biocompatible material than current industry favourite ePTFE. Alleviating the thrombogenicity of grafts and the mechanical mismatch between artery and graft is encouraging for the short and long term patency of the POSS-PCU graft.