The present research aims to provide the foundation for the development of an alternative strategy for the inhibition of stent thrombosis and restenosis. Instead of modifying blood rheology (i.e. acting on the fluid side), it is hypothesized that a substantial reduction of the shear stress in the vessel can be achieved by modifying the properties of the vessel wall, with the aim of lubricating the stent struts, wires composing the stent structures. Specifically, the project intends to explore the potential of magnetorheological fluids (also called ferrofluids FFs), by investigating their capability in terms of drag reduction and evaluating their possible use in coronary stents. The proposed technology strives to complement or even replace adjunctive pharmacological treatments (dual antiplatelet therapy) usually adopted after stent implantation, which often have significant harmful side effects. This new technology thus has the potential to improve the quality of life of patients with stent applications, and to provide a new solution for patients in which the dual antiplatelet drug treatment cannot be prescribed. The overall objectives of the COATING projects are the following:
• To evaluate the performance in terms of magnetoviscous effects of various biocompatible FFs under different shear flows and different magnetic fields. This data will be used to select the optimal FFs for drag reduction in relation to different flow regimes.
• To evaluate the performance of the novel drag reduction technique based on a layer of FFs at the wall of a pipe. Results will be obtained under both laminar and turbulent flows and using different fluids, spanning the parameter range of physiological flows and beyond (e.g. Newtonian fluids with different viscosity; non Newtonian fluids with shear dependent viscosity, characteristic Re of small and large arteries, turbulent flow etc.).
• To evaluate the efficiency of the FF drag reduction technique in stents in vitro. Measurements will be carried out using a blood-mimicking fluid under pulsatile flow regimes. The experimental analysis will provide an important test of the feasibility of the technique for the targeted application (stent), in view of future clinical implementation (for example, on the FF diffusion).
The COATING research activities showed for the first time the relation of the magnetoviscous effect in relation to the microscopic reorganization (chain formation and disruption in flow). Moreover, it has been demonstrated that a drag reduction technique based on the adoption of ferrofluids is feasible in different flow regimes (laminar, transitional and turbulent). Experimental evidences provide results in terms of drag reduction up to 90% for flow in laminar regime. Finally, qualitative results showed the feasibility of the technique for complex geometry configuration as the one of the targeted stent application.
