Athlete Performance can be enhanced thanks to 3D Printed Insoles with Integrated Sensors

In elite sports, fractions of a second sometimes make the difference between victory and defeat. To optimize their performance, athletes use custom-​made insoles. But people with musculoskeletal pain also turn to insoles to combat their discomfort.

Researchers at ETH Zurich, Empa and EPFL are developing a 3D-​printed insole with integrated sensors that allows the pressure of the sole to be measured in the shoe and thus during any activity. This helps athletes or patients to determine performance and therapy progress.

One device, multiple inks

These insoles aren’t just easy to use, they’re also easy to make. They are produced in just one step – including the integrated sensors and conductors – using a single 3D printer, called an extruder.

For printing, the researchers use various inks developed specifically for this application. As the basis for the insole, the materials scientists use a mixture of silicone and cellulose nanoparticles.

Next, they print the conductors on this first layer using a conductive ink containing silver. They then print the sensors on the conductors in individual places using ink that contains carbon black. The sensors aren’t distributed at random: they are placed exactly where the foot sole pressure is greatest. To protect the sensors and conductors, the researchers coat them with another layer of silicone.

An initial difficulty was to achieve good adhesion between the different material layers. The researchers resolved this by treating the surface of the silicone layers with hot plasma.

As sensors for measuring normal and shear forces, they use piezo components, which convert mechanical pressure into electrical signals. In addition, the researchers have built an interface into the sole for reading out the generated data.

Running data soon to be read out wirelessly

Tests showed the researchers that the additively manufactured insole works well. “So with data analysis, we can actually identify different activities based on which sensors responded and how strong that response was,” co-​project leader Gilberto Siqueira, Senior Assistant at Empa and at ETH Complex Materials Laboratory, says.

At the moment, Siqueira and his colleagues still need a cable connection to read out the data; to this end, they have installed a contact on the side of the insole. One of the next development steps, he says, will be to create a wireless connection. “However, reading out the data hasn’t been the main focus of our work so far.”

In the future, 3D-​printed insoles with integrated sensors could be used by athletes or in physiotherapy, for example to measure training or therapy progress. Based on such measurement data, training plans can then be adjusted and permanent shoe insoles with different hard and soft zones can be produced using 3D printing.

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