3D printing allows rapid fabrication of complex objects from digital designs. One 3D-printing process, direct laser writing, polymerises a lightsensitive material by steering a focused laser beam through the shape of the object to be created. The highest-resolution direct laser writing systems use a femtosecond laser to effect two-photon polymerisation. The focal (polymerisation) point is steered over the shape of the desired object with mechanised stages or galvanometer-controlled mirrors. Here we report a new high-resolution direct laser writing system that employs a resonant mirror scanner to achieve a significant increase in printing speed over galvanometer-or piezo-based methods while maintaining resolution on the order of a micron. This printer is based on a software modification to a commerically available resonant-scanning two-photon microscope. We demonstrate the complete process chain from hardware configuration and control software to the printing of objects of approximately 400 × 400 × 350 µm, and validate performance with objective benchmarks.Released under an open-source license, this work makes micro-scale 3D printing available the large community of two-photon microscope users, and paves the way toward widespread availability of precision-printed devices.Comments: Corresponding author: BWP (bwpearre@bu.edu). TJG and TMO contributed equally to this work.Conflict-of-Interest statement: TJG is an employee of Neuralink Inc.

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