Magnetic Building Blocks Show Promise in Medical and Soft Robotics Applications

If individuals have ever attempted to place several small but powerful cube magnets directly next to one another on a magnetic board, they would know that this is simply impossible.

What exactly occurs is that the magnets invariably organize themselves in a column that protrudes out in a vertical fashion from the magnetic board. Besides that, it is virtually impossible to connect many rows of these magnets together to create a flat surface. This is because magnets are naturally dipolar.

It is well known that like poles repel each other, with the south pole of one magnet invariably attaching itself to the north pole of another and the other way around. This phenomenon demonstrates why these poles create a column with all the magnets aligned in the same manner.

Now, for the first time, researchers at ETH Zurich have successfully developed cube-shaped magnetic building blocks that can be linked together to create two-dimensional (2D) shapes. The novel building blocks, which the researchers call modules, are quadrupolar and not dipolar. In other words, each building block has two south poles and two north poles.

Two small traditional dipole magnets, with their like poles facing one another, are present inside all quadrupole modules. These modules are 3D printed in plastic.

The magnetic building blocks can be organized just like tiny chess boards to create any 2D shapes. It operates like this: since the north and south poles of magnets attract each other, a single quadrupole building block with its two south poles facing right and left will attract a building block on each of its four sides. This block gets rotated by 90° so that its north poles face right and left.

Based on this principle, the researchers developed colored modules that had an edge length of just over 1 mm. They subsequently arranged the modules into pixel art emojis to show what exactly the colored modules can do. But potential application examples go much beyond these gimmicks.

We’re particularly interested in applications in the field of soft robotics.

Hongri Gu, Study Lead Author and Doctoral Student, ETH Zurich

Gu works in Professor Bradley Nelson’s group at ETH Zurich. The article was recently published in Science Robotics.

Quadrupole and Dipole in the Same Building Block

The magnetic properties of the modules are dominated by the quadrupole. But it is slightly more complicated than that, because apart from the powerful quadrupole, the researchers also integrated a weak dipole into the magnetic building blocks. They accomplished this feat by assembling the tiny magnets in the quadrupole module at a slight angle to one another rather than parallel.

This causes the modules to align themselves with an external magnetic field, like a compass needle does. With a variable magnetic field, we can then move the shapes we have built out of the modules. Add in some flexible connectors and it’s even possible to build robots that can be controlled by a magnetic field.

Hongri Gu, Study Lead Author and Doctoral Student, ETH Zurich

According to Gu, their work was originally focused on advancing the latest principle. He added that it is not dependent on size, which means relatively smaller quadrupole modules could indeed be developed.

Furthermore, the researchers are investigating how the quadrupole modules can be utilized to integrate a linear structure into a multidimensional object using a magnetic field. This is something that could prove useful in the medical field in the days to come: for example, objects like stents can possibly be developed from a thread containing such quadrupole modules.

Through a small opening, the thread can be inserted inside the body in a comparatively simple, minimally invasive procedure and a magnetic field can be subsequently applied to arrange it into the ultimate multidimensional structure within the body.