Inside Blood Pump Engineering: CFD in Medicine

Alvaro Filho
11 hours ago
4 min read

Heart failure has been the leading cause of death globally for the past 15 years, with 23.6 million deaths expected each year by 2030, according to the WHO. Heart transplantation is one solution, but it faces limitations due to a shortage of compatible donors, leading patients to wait months, often without success.

To assist in these cases, devices such as Ventricular Assist Devices (VADs) and Extracorporeal Membrane Oxygenation (ECMO) are used. Both, as well as hemodialysis, depend on blood pumps, which are essential for mechanical support of the heart and lungs, especially during surgery. These pumps, in addition to being disposable and easy to manufacture, must be carefully designed to minimize damage to the blood. This includes avoiding areas of turbulence, stagnation and high levels of shear stress, factors that can lead to the degradation of red blood cells, leukocytes and other essential biological components.

Challenges and solutions

Centrifugal blood pumps are designed to reduce the risk of thrombosis by avoiding stagnation of flow. However, over-prioritizing efficiency can generate regions of high shear stress (>10 Pa) due to high rotational speeds, which can damage blood cells and cause complications such as bleeding, stroke, and clot formation.

Previously, the evaluation of problems such as thrombosis depended on physical experiments. Today, the use of computational fluid dynamics (CFD) allows predicting critical areas, such as high-shear regions, and adjusting designs more quickly and efficiently. Simulations also demonstrate that keeping the shear rate below certain limits reduces the risk of thrombi.

The performance evaluation of these pumps uses metrics such as the size of high-stress regions and the rate of red blood cell damage (hemolysis). Experimental and computational studies help optimize designs, minimizing blood damage, especially in long-term applications.

Blood Pump Simulation

The simulation study, using STAR-CCM+, in question focuses on the detailed analysis of the blood pump, with the aim of investigating key variables such as efficiency, pressure drop, system torque and operational stability of the equipment. The numerical results were compared with experimental data available in the literature to validate the model.

The modeling considered a single-phase and steady-state flow regime, adopting the Moving Reference Frame (MRF) approach to simulate the rotor rotation. For turbulence modeling, the k-Omega SST model, widely recommended in the literature for flows with strong rotor-stator interaction, was used. The computational mesh was refined in the critical regions, especially in the vicinity of the rotor, where high velocity gradients and significant shear effects occur.

Figure 1. Geometry and computational mesh

Figure 2 (a) and (b) show the velocity magnitude and absolute pressure profiles for an operating condition of 3.5 L/min and 3500 RPM. The presence of zones of maximum velocities in the thrust and external regions of the rotor (leakage region) can be observed, as well as zones of low velocity and stagnant flow in the center of the pump. These regions are critical, as they can be optimized to reduce the risk of damage to blood cells.

Figure 2. Variable profile: (a) velocity; (b) absolute pressure

Figure 3 shows the shear stress profile on the rotating walls of the pump under the same operating conditions. Areas with high shear stress are particularly relevant, as they are associated with the potential for hemolysis, i.e., the rupture of red blood cells, and are therefore essential in assessing the biocompatibility of the equipment.

Figure 3. Wall shear stress profile

Finally, Figure 4 shows the simulation results for different inlet flow conditions, ranging from 2.5 L/min to 6 L/min. The pump efficiency and pressure values were obtained for each condition and compared with the experimental data available in the work of Malinauskas et al. (2017), demonstrating good agreement between the numerical and experimental results.

Figure 4. Graph of Gauge Pressure and Efficiency by Flow Rates

Numerical simulation is a powerful tool that accelerates the development of medical technologies and expands our understanding of complex challenges. Fifteen years ago, Takehisa Mori began using CFD in the development of cardiovascular devices at his company, revolutionizing the design process and bringing significant advances to the field. About this journey, Mori reflects:

"When I started with CFD, I realized how much better I was able to understand designs. One caveat is that some people think too lightly of simulation, assuming that anything can be simulated or imagined. In reality, it is important to consider what the problem means and what the physical implications are... By using CFD, we can build a foundation for prototyping to some extent."

Takehisa Mori, Principal R&D Research Manager, Terumo Corporation

The computer simulation of the blood pump made it possible to identify critical regions of speed, pressure and shear stress, which are key factors for optimizing hydraulic performance and mitigating blood risks. The use of computer-aided engineering (CAE) tools has proven essential for reducing development time and cost, while increasing design reliability. By combining technical rigor with clinical requirements, computer engineering directly contributes to the development of safer, more efficient medical devices that are suitable for prolonged use in patients.

References

MALINAUSKAS, Richard A. et al. FDA benchmark medical device flow models for CFD validation. Asaio Journal, v. 63, n. 2, p. 150-160, 2017.

SIEMENS. Applying simulation and CFD for better medical device designs with Terumo Corporation. Siemens Blog, 18 march. 2022. Available at: https://blogs.sw.siemens.com/medical-devices-pharmaceuticals/2022/03/18/applying-simulation-and-cfd-for-better-medical-device-designs-with-terumo-corporation/. Accessed on: June 5, 2025.

SARIZEYBEK, Ceren. DESIGN OF CENTRIFUGAL BLOOD PUMP. 2020. Doctoral Thesis. İzmir Institute of Technology.

HAN, Dong et al. Computational fluid dynamics analysis and experimental hemolytic performance of three clinical centrifugal blood pumps: Revolution, Rotaflow and CentriMag. Medicine in novel technology and devices, v. 15, p. 100153, 2022.

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