A General Ink Formulation Strategy for Transforming Recycled Metals into Printed Electronics

One key challenge preventing commercially viable domestic recycling lies in the gap between the high costs of the recycling process and the limited value of recycled raw materials. While additive manufacturing (AM) has the potential to narrow such a gap by converting waste materials into value‐added products through the remanufacturing process, the ink formulation for waste materials remains a formidable task due to poor processability. In contrast to high‐temperature metallurgy (1000–2000 K), a facile approach is developed to convert waste metals (e.g., stainless steel machining chips) into printable and stable inks for 3D‐printed electronics at near room temperature. Moreover, the binder chemistry and percolation mechanism are studied, enabling sustainable ink formulation with non‐toxic solvents and environmentally benign polymers (i.e., no fluorinated polymer). The ink formulation is generalizable for various functional materials, including other metals, carbons, and clays. As a proof of concept, a 3D‐printed strain sensor from recycled stainless steel (SS) chips is demonstrated, which is shown to effectively identify even minor strains from the human body, highlighting potential wearable applications.