Nonetheless, good hydraulic and blood compatibility designs are still very important for maglev pumps. Therefore, maglev blood pump is the trend of blood pumps ( Fraser et al., 2011). The clearance of Maglev bearing is can be wide, resulting in low stress, reduced blood damage and good biocompatibility. Maglev bearings avoid mechanical contact, friction and dynamic sealing thus, it can avoid blood damage and flow dead zone. Moreover, mechanical bearings result in friction and heating, bringing secondary damage to blood the flow dead zone around mechanical bearing increases thrombosis risk. Turbulence and secondary flow will further increase the blood damage ( Wu et al., 2020). The main cause of blood mechanical damage is the complex geometric structure and mechanical movement in blood pumps, which makes blood cells experience non-physiological stress which is much higher than normal physiological stress ( Li et al., 2013). Blood damage and its complications have become the pain point in the clinical application of VADs and mechanical circulatory support devices, as well as other blood contacting medical devices ( Bluestein et al., 2002 Ge et al., 2008 Polaschegg, 2009 Faghih and Sharp, 2019). However, after the implantation of these VADs, adverse effects related to blood mechanical damage, such as bleeding and stroke and thromboembolic events, were often reported ( Birschmann et al., 2014 Maltais et al., 2016 Netuka et al., 2016 Mehra et al., 2017 Shah et al., 2017).

In recent years, ventricular assist devices (VAD, also called blood pumps) have gradually replaced heart transplantation as an effective treatment for heart failure ( Bellumkonda and Bonde, 2012 Molina and Boyce, 2013 Magruder et al., 2016 Cui et al., 2018 Gaffey et al., 2018 Kawabori et al., 2018 Shahreyar et al., 2018). Collectively, these results shed light on the impact of major design variables on the performance of modern centrifugal blood pumps with a secondary flow path. A hydraulic test was conducted to validate the CFD regarding the hydraulic performance. Computational fluid dynamics (CFD) combined with hemolysis models were mainly used for the evaluation of pump performance. Turbulent intensities have been greatly reduced, the hydraulic and hemolytic performance of the pump model was considerably improved. Starting from a baseline design, through changing design variables such as blade angles, blade thickness, and position of splitter blades. The purpose of this study is to optimize the hydraulic and hemolytic performance of an inhouse centrifugal maglev blood pump with a secondary flow path through variation of major design variables, with a focus on bringing down intensity of turbulence and secondary flows. Moreover, current hemolysis models are inadequate in an accurate prediction of hemolysis in turbulence. To date, little scientific study has been published concerning optimization and experimental validation of centrifugal blood pumps with secondary flow paths. Empirical relationships between design variables and performance metrics generally do not exist for this type of blood pump. Conventional design theory is no longer applicable to centrifugal blood pumps with a secondary flow path. Due to the secondary flow path, the intensity of secondary flows and turbulence in centrifugal blood pumps is generally very high. 3Institute for Medical Device Control, National Institutes for Food and Drug Control, Beijing, ChinaД¬entrifugal blood pumps are usually designed with secondary flow paths to avoid flow dead zones and reduce the risk of thrombosis.2School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing, China.1Artificial Organ Technology Laboratory, School of Mechanical and Electric Engineering, Soochow University, Suzhou, China.Peng Wu 1*, Jiadong Huo 1, Weifeng Dai 1, Wei-Tao Wu 2, Chengke Yin 1* and Shu Li 3*

Blade of blood 3.5