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Design and fabrication of 3D-printed stretchable tactile sensors

(Nanowerk News) Researchers at the University of Minnesota, led by Professor Michael C. McAlpine, have developed a series of novel inks, which can be cured at room temperature with tunable printability, high flexibility, electrical conductivity, and sensitivity.
As the team reports in Advanced Materials ("3D Printed Stretchable Tactile Sensors"), the inks were used to manufacture 3D tactile sensors under mild conditions on a free-form surface using multimaterial 3D printing and inverse engineering techniques.
Tactile sensor design principle and 3D printing procedure
Tactile sensor design principle and 3D printing procedure. a) Schematic of the tactile sensor consisting of a base layer, top and bottom electrodes, an isolating layer, a sensor layer, and a supporting layer. b) Side and c) top view of the tactile sensor. d) 3D printing process of the sensor on a glass substrate in eight sequential steps. In step I, a 4 × 4 mm2 silicone base layer is printed. In step II, a 3 × 3 mm2 bottom electrode layer is printed using the 75 wt% Ag/silicone ink. In step III, a 1 mm tall, 150 µm thick cylinder wall with a radius of 350 µm is printed using the 68 wt% Ag/silicone ink as the sensor layer. In step IV, a 3 × 3 mm2 isolating layer is printed using the silicone ink. In step V, a 3 × 3 mm2 supporting layer with a thickness of 0.8 mm is printed using the 40 wt% Pluronic ink. In step VI, a 2 × 2 mm2 top electrode layer is printed using the 75 wt% Ag/silicone ink. In step VII, the supporting layer is removed by immersing the sensor in water for 3 hours. Finally, in step VIII, the sensor is dried for completion. (© Wiley-VCH Verlag) (click on image to enlarge)
The printed flexible, stretchable, and sensitive sensors were found proven to be capable of detecting and differentiating human movements, including radial pulse, and finger pressing and bending.
The researchers point out that their work represents a proof-of-concept illustration that image-coupled 3D multimaterial printing approaches can facilitate customized wearable devices in previously inaccessible ways.
Development of a custom-built multifunctional 3D printing process, combined with functional inks, is at the core of this approach and determines the features of the final devices.
3D scanning and reverse engineering allowed the team to design the specific geometry to fit the curved surface. Mechanical and computational tools enabled them to design, analyze, and optimize the integrity of the devices.
A one-pot multimaterial 3D printing process provided the researchers with the ability to integrate various functional inks into a 3D sensor with a conformal design and high performance.
This combination of complex geometries and sophisticated functions offers a proof-of-concept approach for the next generation of wearable devices.
Future studies will focus on several directions including: 1) further optimization of the inks, including incorporation of semiconducting materials and devices; 2) development of other critical devices such as temperature sensors to monitor tissue; and 3) development of new 3D printing platforms with closed-loop feedback control for real-time printing of objects on arbitrary and moving substrates.
"Overall, we expect that our methodologies will open new routes to fabricating various sensors with the potential for advancing prosthetic skins, bionic organs, and human–machine interfaces," conclude the authors.
Source: Wiley
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