Ventricular assist devices (VADs), among which the HeartMate 3 (HM3) is the latest clinically approved representative, are often the therapy of choice for patients with end-stage heart failure. Despite advances in the prevention of pump thrombosis, rates of stroke and bleeding remain high. These complications are attributed to the flow field within the VAD, among other factors. One of the HM3's characteristic features is an artificial pulse that changes the rotor speed periodically by 4000 rpm, which is meant to reduce zones of recirculation and stasis. In this study, we investigated the effect of this speed modulation on the flow fields and stresses using high-resolution computational fluid dynamics. To this end, we compared Eulerian and Lagrangian features of the flow fields during constant pump operation, during operation with the artificial pulse feature, and with the effect of the residual native cardiac cycle. We observed good washout in all investigated situations, which may explain the low incidence rates of pump thrombosis. The artificial pulse had no additional benefit on scalar washout performance, but it induced rapid variations in the flow velocity and its gradients. This may be relevant for the removal of deposits in the pump. Overall, we found that viscous stresses in the HM3 were lower than in other current VADs. However, the artificial pulse substantially increased turbulence, and thereby also total stresses, which may contribute to clinically observed issues related to hemocompatibility.

Patients with ventricular assist devices still suffer from high rates of adverse events. Since many of these complications are linked to the flow field within the pump, optimization of the device geometry is essential. To investigate design aspects that influence the flow field, we developed a centrifugal blood pump using industrial guidelines. We then systematically varied selected design parameters and investigated their effects on hemodynamics and hydraulic performance using computational fluid dynamics. We analysed the flow fields based on Eulerian and Lagrangian features, shear stress histograms and six indicators of hemocompatibility. Within the investigated range of clearance gaps (50-500 µm), number of impeller blades (4-7), and semi-open versus closed shroud design, we found association of potentially damaging shear stress conditions with larger gap size and more blades. The extent of stagnation and recirculation zones was reduced with lower numbers of blades and a semi-open impeller, but it was increased with smaller clearance. The Lagrangian hemolysis index, a metric commonly applied to estimate blood damage, showed a negative correlation with hydraulic efficiency and no correlation with the Eulerian threshold-based metric.

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Conventional magnet manufacturing is a significant bottleneck in the development processes of products that use magnets, because every design adaption requires production steps with long lead times. Additive manufacturing of magnetic components delivers the opportunity to shift to agile and test-driven development in early prototyping stages, as well as new possibilities for complex designs. In an effort to simplify integration of magnetic components, the current work presents a method to directly print polymer-bonded hard magnets of arbitrary shape into thermoplastic parts by fused deposition modeling. This method was applied to an early prototype design of a rotary blood pump with magnetic bearing and magnetic drive coupling. Thermoplastics were compounded with 56 vol.% isotropic NdFeB powder to manufacture printable filament. With a powder loading of 56 vol.%, remanences of 350 mT and adequate mechanical flexibility for robust processability were achieved. This compound allowed us to print a prototype of a turbodynamic pump with integrated magnets in the impeller and housing in one piece on a low-cost, end-user 3D printer. Then, the magnetic components in the printed pump were fully magnetized in a pulsed Bitter coil. The pump impeller is driven by magnetic coupling to non-printed permanent magnets rotated by a brushless DC motor, resulting in a flow rate of 3 L/min at 1000 rpm. For the first time, an application of combined multi-material and magnet printing by fused deposition modeling was shown. The presented process significantly simplifies the prototyping of products that use magnets, such as rotary blood pumps, and opens the door for more complex and innovative designs. It will also help postpone the shift to conventional manufacturing methods to later phases of the development process.

A mock circulation allows the in vitro investigation, development, and testing of ventricular assist devices. An aqueous-glycerol solution is commonly used to mimic the viscosity of blood. Due to evaporation and temperature changes, the viscosity of the solution drifts from its initial value and therefore, deviates substantially from the targeted viscosity of blood. Additionally, the solution needs to be exchanged to account for changing viscosities when mimicking different hematocrits. This article presents a method to control the viscosity in a mock circulation. This method makes use of the relationship between temperature and viscosity of aqueous-glycerol solutions and employs the automatic control of the viscosity of the fluid. To that end, an existing mock circulation was extended with an industrial viscometer, temperature probes, and a heating nozzle band. The results obtained with different fluid viscosities show that a viscosity controller is vital for repeatable experimental conditions on mock circulations. With a mixture ratio of 49 mass percent of aqueousglycerol solution, the controller can mimic a viscosity range corresponding to a hematocrit between 29 and 42% in a temperature range of 30-428C. The control response has no overshoot and the settling time is 8.4 min for a viscosity step of 0.3 cP, equivalent to a hematocrit step of 3.6%. Two rotary blood pumps that are in clinical use are tested at different viscosities. At a flow rate of 5 L/min, both show a deviation of roughly 15 and 10% in motor current for high rotor speeds. The influence of different viscosities on the measured head pressure is negligible. Viscosity control for a mock circulation thus plays an important role for assessing the required motor current of ventricular assist devices. For the investigation of the power consumption of rotary blood pumps and the development of flow estimators where the motor current is a model input, an integrated viscosity controller is a valuable contribution to an accurate testing environment. Key Words: Ventricular assist device-Blood pump-Viscosity controller-Flow estimator-Flow probe calibration.Despite significant clinical and technical developments, heart failure remains one of the major health challenges in developed countries (1). For end-stage heart failure, the only option next to heart transplantation is the implantation of a ventricular assist device (VAD). A so-called mock circulation (MC) allows the in vitro investigation, development, and testing of VADs. Instead of blood, the majority of mock circulations (2-11) use an aqueous-glycerol solution to mimic the viscosity of blood in the human body.The viscosity of human blood mainly depends on the hematocrit (12), whereas the viscosity of an aqueous-glycerol solution depends on its mixture ratio and temperature. In this study, viscosity is defined as the dynamic viscosity that yields a measure of internal resistance to flow. Viscosity has the unit centipoise (cP) which is equal to millipascalsecond (mPaÁs). The viscosity of bloo...