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Since 3D printing began to diversify, allowing for the printing of materials beyond just metal and plastic, scientists have been experimenting with the 3D printing of magnets. 3D printed magnets can be made more quickly and less expensively than more conventional methods of production, and they can be easily made into complex geometries if so desired. While many researchers have 3D printed magnets, however, few actual use cases exist, but a new study entitled “3D Printing of Functional Assemblies with Integrated Polymer-Bonded Magnets Demonstrated with a Prototype of a Rotary Blood Pump,” applies 3D printed magnets to a rotary blood pump. Successfully 3D printing magnets embedded in 3D prints could open up the world to a whole host of new 3D printing applications. Tiny machines, medical devices, motors are just some of the things that could be possible. By letting a housing or another part of a device function as the case but also as a magnet the form factor and functionality of many devices could change radically.

To 3D print the pump, the ETH Zurich researchers created a filament made from thermoplastic combined with isotropic NdFeB powder. The material was used to 3D print a prototype of a turbodynamic pump with integrated magnets in the impeller and housing. The pump was 3D printed in one piece on a low-cost, consumer-level 3D printer (a Prusa i3 MK2 with a multi-material upgrade, to be exact), then the magnetic components were fully magnetized in a pulsed Bitter coil.

Besides heart transplantation, rotary blood pumps are the only option for patients suffering from end-stage heart failure. The pumps use magnets as critical components in the driving and bearing systems of the impeller. Unfortunately, currently available pumps have the side effects of hemolysis and thrombus formation, which manufacturers are attempting to address in the development of next-generation pumps. Regular 3D printing is being applied in the development of rotary blood pumps, but according to the researchers, to their knowledge, 3D printed magnets are not being used for testing new designs of medical devices.

“The basic design of the pump prototype is similar to that of conventional RBP designs—however, complicated geometries with inside twists and undercut elements would not allow for conventional manufacturing,” the researchers explain. “The bearing concept for the impeller consisted of two passive magnetic bearings for radial forces and a pivot tip for axial forces. For the radial magnetic bearings, hollow cylinder magnets were integrated into the impeller and housing. The impeller comprises of four blades with twisted internal blade channels in a helical shape around the inflow axis. In each of the blades, a driving magnet was embedded just above the bottom surface. The shape of the magnet was matched to the blade geometry, thereby maximizing the magnet volume. The impeller was actuated by magnetic coupling to a set of matching non-printed permanent magnets spinning on a servo motor just below the housing.

The pump was 3D printed on the first try, in a print that took about 15 hours. Arbitrarily-shaped magnets were integrated into the pump, and the magnetic filament, which the researchers called MagFil, was able to be printed from a standard spool without breaking. The hydraulic performance of the pump was then tested with water using an ultrasonic flow probe and pressure sensors at the pump inlet and outlet.

“An operation of the pump prototype at a maximum rotational speed of 1000 rpm, with a flow rate of 3 L/min against a pressure head of 6 mmHg was achieved,” the researchers state. “At higher rotational speeds, the magnetic coupling broke off and the delivered flow rate decreased concomitantly. The pump prototype could therefore not deliver a sufficient flow rate at head pressures that are realistic for clinically used RBPs.”

The researchers attributed this failure to inferior print quality caused by some difficulties with multi-material printing, but they still concluded that 3D printing is a promising method for speeding up the development process for medical devices and for creating devices with integrated magnets with geometrical complexity.

Authors of the paper include Kai von Petersdorff-Campen, Yannick Hausworth, Julia Carpenter, Andreas Hagmann, Stefan Boës, Marianne Schmid Daners, Dirk Penner and Mirko Meboldt.

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