3D printing of electrically conductive soft multi-material composites for strain and pressure sensors

Abstract

3D printing on flexible microelectronics design and manufacturing is an emerging and burgeoning field. However, the existing platforms cannot meet the requirements for processing complex 3D flexible electronic circuit models. This project aims to establish a full-scale framework for 3D printing and its applications. The combination of stretchable polymers with conductive carbon-based fillers has attracted attention in the multifunctional sensing materials field. Upon dynamic loading, these polymer composites exhibit piezoresistive behaviour that can be utilised for strain and tactile pressuresensing applications. This project investigates the piezoresistive behaviour of stretchable thermoplastic conductive polymers and their strain and pressure-sensing capabilities. Modification of the conductive composites has led to the development of fully 3D printed strain sensors. A 3D printer with a dual material extrusion system was employed to fabricate the conductive composites embedded in a stretchable elastomer substrate to create highly sensitive and linear strain sensors. Pre-straining of the 3D printed strain sensors caused crack formations; higher pre-straining values resulted in higher sensitivity. The sensors’ sensitivity reached a gauge factor (GF) value of 163. Highly sensitive and tuneable pressure sensors were also realised by utilising multi-material 3D printing techniques. Combining conductive flexible polymers and scaffold materials allowed the fabrication of novel pressure sensors with enhanced compressibility and a wide sensing range. The physical properties of the materials were tested, and the electromechanical properties of the 3D printed sensors were investigated. Characterisation through scanning electron microscopy (SEM) and optical microscopic imaging was conducted throughout this research. The 3D printed strain and pressure sensors demonstrated cyclic behaviour with linear, repeatable, and reproducible responses suggesting great potential for many applications.