The McAlpine Research Group at the University of Minnesota’s Department of Mechanical Engineering have released an article demonstrating a method for 3D printing tiny, multimaterial sensors.

The electronics used in the devices are stretchable, a fraction of the size of a human fingertip, and capable of differentiating movements, marking them as an introductory channel for future wearable electronics and bionic skin.

3D printing the silicone base layer of a sensor. Clip via Inside Science on YouTube

Inks and the process

The sensors developed by the McAlpine Research Group are 3D printed in 6 layers using 4 different inks. This can broken down as follows:

  • Layer 1 – Pure silicone support
  • Layer 2 – Bottom electrode 3D printed in a silicone composite containing 75% silver
  • Layer 3 – A conductive corkscrew sensor printed in the middle in a silicone composite ink containing 68% silver
  • Layer 4 – Pure silicone ink to isolate the bottom electrode from a subsequent top electrode
  • Layer 5 – Sacrificial ink to provide support for the top electrode
  • Layer 6 – Top electrode in 75% silver/silicone composite

Each layer is directly written using a custom-made 3D printer with four moving nozzles based on the AGS 1000 gantry system from Aerotech. The sacrificial ink is removed in water, and the other materials are left to cure at room temperature.

The result is an electrically conductive material with high levels of stretchability.

Mechanical test of the sensor material’s stretchability. Clip via supplementary materials for 3D Printed Stretchable Tactile Sensors

Performance under pressure

To test the material’s functionality as a sensor, devices are 3D printed onto a human wrist and finger tip. At the wrist, the sensor is used to take pulse readings, and various fingertip tests demonstrate the device’s ability to read pressure, i.e when pressing buttons or bending the finger.

Real time data feedback from eh sensor 3D printed on a dummy hand and pressed by another hand. Screenshot via supplementary materials S6, McAlpine Research Group

Real time data feedback from eh sensor 3D printed on a dummy hand and pressed by another hand. Screenshot via supplementary materials S6, McAlpine Research Group

Further study of the inks and this method include further optomization of the materials; developing devices that can to read temperature; and “3D printing platforms with closed-loop feedback control for real-time printing of objects on arbitrary and moving substrates.” 

The ultimate achievement would be an ability to integrate such sensors into human skin giving people the ability to read real time conditions in the body.

3D printed glass and other research from Minnesota

In collaboration with Oklahoma State University and the Lawrence Livermore National Laboratory, the University of Minnesota is contributing research into 3D printed glass lenses. Other 3D printing projects at the university, as reported by 3D Printing Industry, includes research that has produced a digital patch for treating heart diseases.

A full article on 3D Printed Stretchable Tactile Sensors is published online in the journal Advanced Materials. It is co-authored by Shuang-Zhuang Guo, Kaiyan Qiu, Fanben Meng, Sung Hyun Park, and Michael C. McAlpine.

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Featured image: A 3D printed sensor with cent for scale. Screenshot via supplementary materials, McAlpine Research Group

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