Constructing precise metal patterns on complex three-dimensional
(3D) plastic parts allows the fabrication of functional devices for
advanced applications. However, it is currently expensive and requires
complex processes. This study demonstrates a process for the fabrication
of 3D metal–plastic composite structures with arbitrarily complex
shapes. A light-cured resin is modified to prepare the active precursor
allowing subsequent electroless plating (ELP). A multimaterial digital
light processing 3D printer was newly developed to fabricate the parts
containing regions made of either standard resin or active precursor
nested within each other. Selective 3D ELP processing of such parts
provided various metal–plastic composite parts having complicated
hollow structures with specific topological relationships with the
resolution of 40 μm. Using this technique, 3D devices that cannot
be manufactured by traditional methods are possible, and metal patterns
can be produced inside plastic parts as a means of further miniaturizing
electronics. The proposed method can also generate metal coatings
exhibiting improved adhesion of metal to substrate. Finally, several
sensors composed of different functional materials and specific metal
patterns were designed and fabricated. The present results demonstrate
the viability of the proposed method and suggest potential applications
in the fields of 3D electronics, wearable devices, and sensors.