Stretchable Capacitive and Resistive Strain Sensors: Accessible Manufacturing Using Direct Ink Writing

TL;DR

This paper introduces an accessible, scalable 3D printing method for creating customizable, highly stretchable capacitive and resistive strain sensors using direct ink writing on silicone substrates, enabling flexible design and high performance.

Contribution

The authors develop a novel fabrication technique combining a custom printhead with commercial 3D printers for direct ink writing of stretchable sensors, offering high design flexibility and performance.

Findings

Capacitive sensor shows high linearity (R^2=0.99)

Sensor achieves large stretchability (550%)

Method enables fabrication of both capacitive and resistive sensors

Abstract

As robotics advances toward integrating soft structures, anthropomorphic shapes, and complex tasks, soft and highly stretchable mechanotransducers are becoming essential. To reliably measure tactile and proprioceptive data while ensuring shape conformability, stretchability, and adaptability, researchers have explored diverse transduction principles alongside scalable and versatile manufacturing techniques. Nonetheless, many current methods for stretchable sensors are designed to produce a single sensor configuration, thereby limiting design flexibility. Here, we present an accessible, flexible, printing-based fabrication approach for customizable, stretchable sensors. Our method employs a custom-built printhead integrated with a commercial 3D printer to enable direct ink writing (DIW) of conductive ink onto cured silicone substrates. A layer-wise fabrication process, facilitated by stackable trays, allows for the deposition of multiple liquid conductive ink layers within a silicone matrix. To demonstrate the method's capacity for high design flexibility, we fabricate and evaluate both capacitive and resistive strain sensor morphologies. Experimental characterization showed that the capacitive strain sensor possesses high linearity (R^2 = 0.99), high sensitivity near the 1.0 theoretical limit (GF = 0.95), minimal hysteresis (DH = 1.36%), and large stretchability (550%), comparable to state-of-the-art stretchable strain sensors reported in the literature.