3D printed embedded flexible circuits enabled by hydrogel-liquid metal filling synergy

The manufacturing of integrated liquid metal flexible electronics remains a major challenge because of its high surface tension and the surface oxide layer. Here, the liquid crystal display (LCD) vat photopolymerization 3D printing technology combined with the liquid metal filling method is used to fabricate liquid metal flexible electronics. These electronics are featured with embedded and integrated characteristics. Large-scale packing and bonding are avoided, and liquid metal leakage as well as external impact on the liquid metal structures can be effectively prevented. Also, the advantages of simple process flow and low cost are possessed. The principle of hydrogel photocuring printing was analyzed, the influence of material and process parameters on the mechanical performance and printing accuracy of hydrogel substrates was studied, and then summarized the principle of size compensation for embedded liquid metal functional structures. To demonstrate the effectiveness and robustness of the proposed method, we designed and optimized a piezoresistive flexible pressure sensor based on liquid metal deformation, and conducted the applications in tactile sensing and stroke recognition. The research in this paper lays a foundation for the structure innovation, function innovation and application innovation of liquid metal-based flexible electronics.