Ramon Sanchez1
Boston University1
Current manufacturing methods for prototyping soft tactile displays rely on complex techniques with limited scalability that are incompatible with stretchable electronics. This work presents a stretchable wearable tactile display with sensing and feedback capabilities manufactured by hybrid multi-material 3D printing in a single fabrication process. The electrical wiring and sensing elements of the display are 3D printed using a strain-induced electrically conductive liquid metal emulsion, which exhibits the shear yielding and shear thinning behavior necessary for direct ink writing (DIW). The actuators and off-the-shelf electronics are combined with the LM emulsion through automated pick-and-place. Once the LM emulsion and the electronics are integrated on a 3D printed polymer base with walls, they are packaged with liquid elastomer and cured. Upon mechanical activation of the LM emulsion composite through axial and lateral strains of 200% each, they reached a conductivity that is within an order of magnitude of the bulk LM. The sensing elements are force sensing resistors (FSR) composed of printed filaments on a spiral architecture. Electro-mechanical characterization of the sensors indicated that their sensitivity and response time were directly related to their conductivity. Upon further activation of the FSR at compressive strains of 60%, their conductivity increased to the same order of magnitude as the bulk LM, and a sensitivity of 0.05 kPa<sup>-1</sup>, which is an order of magnitude higher than that of the electrical wiring. To show the capabilities of the tactile display, we fabricated two self-contained devices, one with an embedded array of FSR, and one with an embedded array of actuators. The device with the array of FSR collects data in the form of tactile patterns, collecting both the location and magnitude of the signal, and transmitting this data wirelessly in real time. The device with the array of actuators receives this signal and reproduces the tactile pattern for an immersive and synchronized tactile experience between two individuals.