Polymer Blood Pump Housing Design Under Cyclic Mechanical Load

Created by Leon Robers | | Technical Article

Hemovent GmbH optimizes its unique blood pump, which works without motors or electronics, in cooperation with Tribecraft AG, using simulation results and PART software solutions to ensure higher performance and durability.

Introduction

Hemovent GmbH from Aachen, Germany is an innovative medical technology company that specializes in applications in the field of extracorporeal membrane oxygenation (ECMO). With its unique approach, the company is developing a portable heart-lung machine that does not require motors, batteries or complex electronics (Fig. 1). This makes the system particularly robust and ideal for mobile applications such as use in rescue helicopters. Hemovent has set itself the goal of continuously improving its products to meet the growing demands in the medical field.

Optimization of a plastic blood pump

The centerpiece of the system is the blood pump, which is operated exclusively by the gas pressure from an oxygen cylinder. An elastic membrane inside the pump is moved by the pressure to suck in the blood on one side and eject it on the other. A bistable switching mechanism ensures that the suction and pump sides are constantly alternating (Fig. 2). The gas flow is controlled by a simple controller, which regulates the volume of blood pumped. The blood is enriched with oxygen in the so-called oxygenator (artificial lung) to ensure that the patient is supplied with oxygen.

To optimize the pump, Hemovent worked together with Tribecraft AG from Zurich, Switzerland, which provides innovation services at the highest level in the areas of design, engineering and systems technology.  The aim was to increase the pump's flow rate and improve its resistance to higher gas pressures. To accomplish this, extensive simulations were carried out (Fig. 3) to analyze the loads under different pressure conditions. Pressure sensors on the gas and blood side made it possible to precisely determine the loads in pumping and suction conditions.

Using the available, non-linear and temperature-dependent material properties in MatScape, material cards were generated and S-N curves were estimated automatically (Fig. 4). This was used to calculate stresses and identify weak spots. S-Life Plastics was used to determine the utilization ratio for the required durability (Fig. 5). Practical tests under extreme conditions verified these results by operating the system under cyclic load until cracks formed. These tests made it possible to calibrate the simulation results with real behavior.

The stress level was significantly reduced by specific reinforcements in the critical areas (Fig. 6). The durability tests were successfully passed after one design iteration. This showed that it is not only the level of stress that is decisive, but also the size of the stressed area and the stress gradient inside the component. As a result, in this case the most critical location was not the one with the highest stress. The knowledge gained was directly integrated into the development of the next generation of pumps.

Conclusion

The collaboration between Hemovent GmbH, Tribecraft AG and PART Engineering was a complete success. Thanks to accurate simulations, material analyses and targeted optimizations, the pump was significantly improved in terms of both performance and durability. The innovative use of software and the focused exchange between the partners accelerated the development and enabled an efficient solution. The optimized pump generation sets new standards for mobile ECMO systems.

Author: Leon Robers, Development Engineer, Tribecraft AG, Zurich, Switzerland

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