Laser-assisted direct ink writing allowed this delicate 3D butterfly to be printed without any auxiliary support structure. (Credit: Lewis Lab/Wyss Institute at Harvard University)

A team of engineers at Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS) say that a new form of 3D printing and laser annealing of conductive metallic inks without supports could lead to customized electronic and biomedical devices.

No longer stiff and flat, flexible, wearable electronics, sensors, antennas, and biomedical devices have led the researchers to innovate a new way of printing complex metallic architectures which appear to be suspended in midair. Their laser-assisted direct ink writing method allows microscopic metallic, free-standing 3D structures to be printed in one step without additional support material.

The team used an ink composed of silver nanoparticles, sending it through a printing nozzle and then annealing it using a precisely programmed laser that applies just the right amount of energy to drive the ink’s solidification. The printing nozzle moves along the x, y, and z axes and is combined with a rotary print stage to enable freeform curvature.

In this way, they say, they were able to create tiny hemispherical shapes, spiral motifs, even a butterfly made of silver wires less than the width of a hair within seconds. The printed wires exhibit excellent electrical conductivity, almost matching that of bulk silver.

When compared to conventional 3D printing techniques used to fabricate conductive metallic features, laser-assisted direct ink writing is not only superior in its ability to produce curvilinear, complex wire patterns in one step, but also in the sense that localized laser heating enables electrically conductive silver wires to be printed directly on low-cost plastic substrates.