Due to the limited availability of donor hearts, left ventricular assist device (LVAD) therapy provides another alternative life-saving solution to many end-stage heart failure patients who would not otherwise survive while on the heart transplant waiting list (Molina et al., 2021). Third generation LVADs, comprising of contact-free magnetic or hydrodynamic bearings, have nearly superseded first generation volume displacement and second generation contact bearing devices due to enhanced durability and haemocompatibility (Kirklin et al., 2015, Mehra et al., 2018, Mehra et al., 2017, Rogers et al., 2017). Magnetic bearings allow for wide blood-flow gaps and lower shear stress, thus enhancing haemocompatibility (Bourque et al., 2016, Krabatsch et al., 2017, Uriel et al., 2017). Nonetheless, an active magnetic bearing needs additional sensors, power input, and a highly sophisticated control mechanism for stable suspension, which increases the system’s complexity and power consumption. Hydrodynamic bearing may offer an alternative solution to these problems (Fu et al., 2019). To develop a miniature LVAD, a hydrodynamic bearing has the advantage of maximum load capacity with minimum space requirements compared to active magnetic bearing because they are passive and do not require additional space for electrical control elements (Kink and Reul, 2004). However, narrow bearing gap in hydrodynamic bearings are required for dynamic pressure buildup to support bearing load, which leads to high mechanical shear stress that may initiate blood damage (Blackshear et al., 1966, Leverett et al., 1972).

The spiral groove bearing (SGB) is a unique hydrodynamic bearing, which features an excellent load capacity. Cell exclusion occurrence in SGB has been long discussed and investigated, which can potentially minimise blood cell exposure to high mechanical shear stress that may initiate blood damage. Kink et al. (Kink and Reul, 2004) first assumed that no blood cells enter the bearing gap once the SGB is spinning in an axial blood pump due to cell exclusion, with supporting results of flow visualisation experiments on a 10: 1 scale-up model. Later on, Leslie et al. observed that cell exclusion occurs in a SGB incorporated into a custom-built rig, leading to lower haematocrit and blood viscosity at the high shear ridge surface in a gap of 25 μm using ultra-low blood haematocrit of less than 1 % (Leslie et al., 2013). Further on, Murashige showed that cell exclusion occurs in the SGB of hydrodynamic bearing blood pumps, with less than 30 μm bearing gap using blood haematocrit of 1 % (Murashige et al., 2016). To prove the existence of cell exclusion in a SGB while maintaining a clinically-relevant haematocrit, we previously demonstrated that the cell exclusion occurs in SGB, which incorporated in the current custom-built Couette test rig with the same operating conditions using 35 % blood haematocrit of fluorescently-tagged erythrocyte ghost cells and visualised by a particle image velocimetry (Bieritz, 2020). However, the ability of mitigation effect of cell exclusion on blood damage in SGB remains questionable. Therefore, the aim of this study was to investigate whether cell exclusion in a SGB using clinically-relevant blood haematocrit of 35 %, can reduce blood damage such as haemolysis and high molecular weight von Willebrand factor (HMW vWF) multimer degradation using the same developed test rig.