<p>Stretchable conductors are essential building blocks for next-generation wearable electronics and soft robotics. Among them, liquid metal-based conductors offer exceptional deformability but suffer from poor interfacial adhesion to substrates, often resulting in leakage under mechanical stress that compromises electromechanical stability and device durability. Here we report a universal interface-fusion printing strategy for fabricating metal-particle semi-embedded hydrogels, in which interconnected liquid metal and silver particles are firmly anchored at the hydrogel surface. The resulting liquid metal-based composite layer achieves a high interfacial adhesion strength of 234.4 kPa to the hydrogel substrate and a conductivity of 1.18 × 10⁶ S m⁻¹. This robust interface prevents liquid metal leakage and ensures stable electrical connection under extreme conditions, including prolonged ultrasonication, 300 MPa impacts, and thousands of stretching cycles. The strategy forms an interpenetrating cross‑linked polymer network through cross-interfacial assembly, fusing the circuit and substrate into an integrated structure. This simple and scalable method enables the fabrication of high‑resolution circuits for a wide range of electronic devices. We demonstrate its performance in applications including stretchable circuits, on-skin biosensors, and underwater soft robots.</p>