Synergistic combination of 4D printing and conventional metal plating for the fabrication of highly-conductive electrical devices

Abstract Four-dimensional (4D) printing of stimuli-responsive materials with the ability to change their shapes or functions when subjected to external stimuli has garnered much interest due to their tremendous potential applications in various biomedical and engineering devices. Recently, 4D printing of electrically-conductive shape memory polymers (SMPs) have become increasingly attractive due to its prospects in the fields of biomedicine, soft robotics, flexible electronics etc. However, the translation of these research into practical applications is often hindered by low electrical conductivity, as well as complicated programming and design. In this work, we report a facile approach to achieve highly conductive SMP-based 4D-printed devices. The SMP-based devices can be printed on typical 3D digital light projection (DLP) or mask stereolithography (MSLA) printers from photopolymer resins with the ability to tune the shape memory transition temperatures ranging from 20 °C to 50 °C. High electrical conductivity of up to 2 × 104 S cm-1 was achieved through electroless deposition of copper with high adhesion strength of up to 1.5 MPa. The application of the technique to fabricate smart switches – with the ability to monitor temperature changes – for electrical safety devices was successfully demonstrated. The approach presented herein may be further explored and developed to capitalise on the stimuli-responsiveness and electrical conductivity of 4D-printed SMPs to find value in various engineering applications.