Direct Printing of Liquid Metal Matrix Composites for Flexible Embedded Circuits

Flexible circuits are crucial for applications such as wearable electronics, soft robotics, and human–machine interaction. However, achieving high conductivity and stable electrical performance under large deformations remains a challenge. Here, we propose an embedded composite conductive material circuit manufactured through direct printing. Firstly, we modified conductive material by adding Cu particles to liquid metal (LM), resulting in a new composite conductive material with higher viscosity and adhesion. Subsequently, the composite conductive material is directly scraped and printed onto a substrate with micro-pillar structures, forming a high-stability embedded patterned flexible circuits with controllable depth and width. The conductivity of the proposed embedded circuits remains stable under cyclic tensile strains of 50% and large cyclic pressures. Compared to conventional planar circuits, the embedded circuits exhibit over a threefold increase in compressive strength under a pressure of 2 MPa. Even under cyclic pressures of 3 MPa, the conductivity of the embedded circuits remains stable while the conventional planar circuits suffer damage. The composite conductive material is compatible with the printing method, providing a new approach and technique for the mass production of large-area flexible electronic devices.