Rational Design of Conductive Pathways in Flexible Tactile Sensors via Indirect 3D-Printing of Liquid Metal for High-Precision Monitoring and Recognition

Abstract

Highly sensitive and conformal sensors are essential for the implementation of human−machine interfaces, health monitoring, and rehabilitation prostheses. The proper adjustment of conductive pathways in the sensing materials is essential for their sensitive transduction of mechanical stimuli into electrical signals. However, the rational, precise, and wide-range control of electrical networks within traditional conductive composites is difficult due to the randomly distributed fillers. Herein, we adopt an indirect 3D-printing method to fabricate pressure sensors with various microchannels for liquid metal (LM) to form consistent and tunable conductive pathways. LM is highly conductive, fluidic, and incompressible at ambient conditions, which guarantees the reliable regulation and function of our pressure sensor. Additive manufacturing provides a facile way to construct complicated microchannels with different lengths, different orientations, crosssectional sizes, depth-width ratios, and shapes, which can effectively modulate the sensitivity and the sensing range. Under the optimized structural configurations, our sensor achieves a high sensitivity of 1.139 kPa −1 , a detection range of 0−68 kPa (loading process), and stability of over 5000 cycles, whose sensing performance is better than most microchannel-filled LM sensors. It can achieve high-accuracy monitoring of pulse, speaking and gestures, and exhibit a full recognition of objects under the assistance of machine learning. This work can provide new ideas on the design of conductive pathways in flexible electronics and expand the application of recyclable LM in human−machine interfaces.

Liquid Metal–Polymer Conductor-Based Conformal Cyborg Devices

“…In the experiment, the resistance of Ag interconnections significantly changes during bending, resulting in wrong recordings and overcompression of the raspberry; while interconnections made of bilayer liquid–solid conductors always maintain stable resistance, and the raspberry remains undamaged. Furthermore, advancements in the field include the successful implementation of LM pressure sensors with various applications, such as high-accuracy monitoring of pulse, speech, and gestures . These sensors are fabricated using an indirect 3D-printing method, marking a significant stride in the realm of flexible electronics.…”

Recent developments in stretchable and flexible tactile sensors towards piezoresistive systems: A review

“…In both these figures, materials are categorized in the order of the discussion in the material selection section. On the x axis, four sections are shown for metallic materials, 63,64,196,210,211,215,250–252 carbon allotrope, 26,66,149,152,221,222,252–258 conductive polymer and hydrogel, 153,237,240,259–261 and composite of materials 178,224,239,262–264 . The discussed articles are arranged in ascending order of the GF/sensitivity, whereas the y‐axis shows the actual value.…”

“…The pressure sensors performance analysis graph has been plotted for LOD and sensitivity and Pressure range and sensitivity, shown in Figure 16. Microchannel based pressure sensors are plotted first and shown in Figure 16A, where the EGaIn/Ecoflex 251 sensor has the highest sensitivity of 1.139 kPa −1 , and LOD of 1 kPa with up to 68 kPa range. There are other sensors with very low LOD, such as 15 Pa 48 and ~16 Pa, 211 and with a high‐pressure range of up to 100 kPa 51 as well, but possess low values of sensitivities.…”