Printing Micron-Scale Benchies With Resin and Turmeric

Resin 3D printing has opened up a whole new scale of resolution for hackers, but the technology can go still finer; commercial micro-SLA and two-photon polymerization printers can print items with sub-micron feature sizes, but the machines are well out of reach for hackers. There’s more than one way to get such high resolution, though, as [Diffraction Limited] demonstrated with his micron-scale resin printer.

The printer builds on [Diffraction Limited]’s previous micro-manipulator and fiber-coupled laser. The micro-manipulator holds the end of the optical fiber just in front of the build plate, which is coated with resin. A 405-nm laser shines through the fiber, curing the resin in a narrow cone in front of the fiber’s core, which the micro-manipulator can trace in a pattern to build up objects, much like an FDM printer. Since the fiber’s inner core is only three microns across, the cured resin shears cleanly away from it when the fiber moves. Since the principle is so similar to an FDM printer, a standard slicer could be used to generate the tool paths.

Early testing proved that the principle worked, but the resin wasn’t absorbent enough for very high resolutions; UV light passed through previously cured resin too easily, limiting the minimum layer height. A UV-absorbent dye dissolved in the resin solves this by limiting the light’s penetration depth. [Diffraction Limited] found that curcumin, the natural dye responsible for turmeric’s bright yellow colour, worked well for this; as an added bonus, alcohol easily extracts it from turmeric powder. This solved the resolution issues well enough for [Diffraction Limited] to print a series of Benchies 150 µm long, a Stanford bunny dwarfed by a human hair, and a few other microscopic pieces. Conveniently, the curcumin dye leaves the printed objects slightly fluorescent under UV light, making them easier to pick up under a microscope.

For a slightly different approach to FDM-inspired microscopic 3D printing, check out necroprinting. For the absolute limits of 3D printing, check out the world’s smallest Benchy.