Periodic Reporting for period 1 - COATING (COATING - slippery wires: revolutionizing COronAry sTentING) Reporting period: 2019-07-01 to 2021-06-30 Summary of the context and overall objectives of the project 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. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far Three different experimental activities have been performed. The first one was dedicated to the investigation of the ferrofluid rheology, aiming at the understanding of the so called magnetoviscous effect. In particular, changes in viscosity of the ferrofluid induced by external magnetic field and by shear stresses have been investigated using microfluidics. The observations provided evidence on the ferrofluid structure re-organization and mechanics related to the formation/disruption of magnetic particle chains. Results provide a mechanistic explanation of earlier macroscopic observations on ferrofluid rheology in the literature and they further provide the basis for upscaling approaches, which require small scale information to devise macroscopic models for effective parameters, such as the effective viscosity of the suspension.The second experimental activity was aimed at the development of a drag reduction technique based on the adoption of a ferrofluid coating. The performance of the technique was evaluated in a square duct (section 1cm x 1cm) by adopting optical velocimetry techniques (PIV, PTV) for the reconstruction of the flow field. The dynamics of the interface between the coating layer and the outer fluid have been evaluated. The main result is that a slip velocity characterized with a slip length of order of a millimetre has been observed achieving remarkable results in terms of drag reduction in the laminar regime up to 90%.The third experimental activity was aimed at the evaluation of the feasibility of the drag reduction technique in a complex geometry as the one of the stent application. Experiments mimicking this complex geometry have been reconstructed inside a rectangular duct (5cm wide and 1cm high) installing different protruding obstacles at the wall. The adherence of the ferrofluid layer to the obstacles was tested for the laminar regime. The results obtained were qualitative and showed the feasibility of the proposed technique for stent application.The results of COATING were disseminated to the scientific community and to the wide public. The findings of research have been submitted to conference. We expect to submit two Journal publications (one on the micro- and one on the macroscale experiments) in 2021. The project and the developed research activity has been presented in scientific events organized in the host research community, the ETH Domain. Moreover, a webpage in scientific social media has been created to advertise the project to the scientific community. Dissemination was carried out also using social media as Twitter, in order to show the ongoing experiments to the research community and to the wider public. The project was also presented during the European Researchers’ Night 2019. Finally, an illustrative video has been created for the wider community, with the aim of increasing awareness of the frontiers of fluid based nanotechnologies. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The results achieved by the COATING project are beyond the state of art for the understanding of ferrofluids rheology and for the development of drag reduction technique. For the first time the magnetoviscous effect of ferrofluids was investigated at the microscope during flow regime. This allows to link the macroscopic effect of change of viscosity with the direct re-organisation of chains in flow. Then the drag reduction technique using ferrofluid coating shows remarkable results in the laminar regime; well established technique so far has achieved results up to 25%, while this technique shows performance up to 90%. Moreover, the qualitative results achieved in terms of the feasibility of the drag reduction technique for stent application are promising in looking for the opening to new strategy for healing cardiovascular diseases as post-stent restenosis.The potential impacts of the research are direct and indirect. The direct impact consists of the development of a technique for the reduction of shear stresses at the stent wall, which is responsible for life-threatening complications. Considering that millions of patients worldwide undergo coronary stenting each year, there is enormous potential in terms of the number of beneficiaries. The research results are also expected to foster other applications of ferrofluids in the bio-engineering medical field. An important indirect impact is related to the development of a new drag reduction technology applicable in other research fields (e.g. naval sector and oil pipe industries) that strive for reduced energy consumption. COATING Project: a novel drag reduction technique based on ferrofluid coating
