3D Printed Touch Sensors Yield Feeling Future for Cybernetics

Around the middle of the twentieth century, America’s electronic communications infrastructure started to centralize around two newly-forming sciences — cybernetics and information theory —  that are still fundamental to everything we now find commonplace in our daily lives. ‘Cybernetics’ is a term typically most closely associated with MIT professor Norbert Wiener (1894-1964), “one of the first to theorize that intelligent behavior is the result of feedback mechanisms”. 

Now, the latest MIT project to follow in Wiener’s footsteps may have its greatest long-term implications for a field that was also amongst the first to captivate the minds of the earliest cyberneticians (including Wiener): human prostheses. Combining 3D printing with metamaterials — plastic and/or metal composites that are modified to “possess properties that don’t naturally occur…[enabling] them to have high specificity for a particular function” — a team of researchers at MIT has developed a software program called MetaSense, designed to use additive manufacturing specifically for the production of devices that employ embedded electrodes in their functioning.

A 3D printed sensor made up of cells of conductive and non-conductive plastic. Image courtesy of MIT.

In this case, the metamaterials are made from a grid of repeating cells designed within MetaSense. These flexible cells are then 3D printed with conductive and non-conductive filament, with the former material acting as the electrode. Then, when compressed, the cells can act as capacitive sensors for a number of applications.

“What I find most exciting about the project is the capability to integrate sensing directly into the material structure of objects. This will enable new intelligent environments in which our objects can sense each interaction with them,” said senior author Stefanie Mueller, associate professor in the MIT Department of Electrical Engineering and Computer Science and a member of the Computer Science and Artificial Intelligence Laboratory (CSAIL). “For instance, a chair or couch made from our smart material could detect the user’s body when the user sits on it and either use it to query particular functions (such as turning on the light or TV) or to collect data for later analysis (such as detecting and correcting body posture).”

So far, this technique has only been applied to objects like joysticks and door handles. But it’s the team’s hyperfocus on the concept of feedback that really gets one’s imagination going in the direction of this technology’s potential for redefining the industry of prosthetics. 

“Feedback” is a seemingly simple concept with disproportionately complex significance to basically everything in our surroundings at all times: essentially, feedback means using information about the effect something has on its environment to modify future output. For instance, when your car starts shifting to the left and you unconsciously move the steering wheel back to the right, that’s feedback.

A 3D printed capacitive sensor. Image courtesy of MIT.

Feedback is pivotal to the team’s project in multiple ways. For one thing, the team is ingeniously using conductive shear cells, “flexible cells that have two opposing walls made from conductive filament and two walls made from nonconductive filament”, in objects like joysticks, to test not only the destructive impact made by the user’s sheer force, but also taking rotation of movement and acceleration into account.

Even more interesting, however, is the relevance of feedback to the production process: the feedback loop between the nonconductive and conductive parts being manufactured. The team envisions that eventually, MetaSense software would be used to synchronize, in a single production process of objects using embedded electrodes, the use of separate 3D printers or separate nozzles for nonconductive and conductive components. The more information that can be gathered as to how these two very different production processes impact on one another — which combinations work and which don’t — the more you can actually envision the fully-integrated manufacture of embedded electrode 3D printed objects. 

And I would imagine big investors are envisioning the same thing! If 3D printed prosthetics are showing results when it comes to animals, we can assume the landscape will only continue to evolve regarding humans in years to come. A research team a couple of years ago at Virginia Tech showed that 3D printing has enormous promise for creating much more personalized prosthetics, and even installed electrodes into the products after printing. Always seemingly at the forefront of groundbreaking developments in 3D printing, the U.S. military’s interest in using AM for prosthetics has for years been one of its biggest dogs in the fight. Pairing this with the connection to MIT, an institution that historically has not been unfriendly to military research dollars, we can safely assume that venture capitalists both indirectly and directly related to the Pentagon are thinking more and more all the time about how embedded electrodes can be integrated into 3D printed prosthetics. 

The most optimistic angle to all this involves how it could impact the end-user: “Regardless of the possible improvement in performance, the subjective experience of embodiment tends to increase when feedback is added,” notes a 2020 study. In other words, the more the technology improves, the more the quality-of-life may also improve for people who need prosthetics.