Xolography

Creating three-dimensional shapes from basic elements or even cells is an important research topic, with potentially many applications in the fields of medicine and general research. Although physical molds and scaffolding can be used, the use of ultrasonic holographs is in many ways preferable. Using ultrasonic sound waves into a liquid from two or more transducers shaped to interact in a predetermined manner, any particulates suspended in this liquid will be pushed into and remain in a specific location. Recent research by [Kai Melde] and colleagues has produced some fascinating results here, achieving recognizable 3D shapes in a liquid medium.

These are some of the most concrete results produced, following years of research. What distinguishes ultrasonic holography from light-based xolography is that the latter uses photon interference between two light sources in order to rapidly 3D print an object within the print medium, whereas ultrasonic holography acts more as a ultrasonic pressure-based mold. Here xolography is also more limited in its applications, whereas ultrasonic holography can be used with for example biological tissue engineering, due to the gentle pressure exerted on the suspended matter.

For ongoing medical research such as the growing of organs (e.g. for transplantation purposes), scaffolding is required, which could be assembled using such a technique, as well as the manipulation and assembly of biological tissues directly.

Over the past years, additive manufacturing (AM) has become a common tool for hackers and makers, with first FDM and now SLA 3D printers becoming affordable for the masses. While these machines are incredibly useful, they utilize a slow layer-by-layer approach to produce objects. A relatively new technology called Volumetric Additive Manufacturing (VAM) promises to change all that by printing the entire object in one go, and according to a recent article in Nature, it just got a big resolution boost.

The concept is similar to SLA printing, but instead of curing the resin by projecting a 2D image of the current layer into the container, VAM uses multiple lasers to create intersecting points within the liquid. After exposing the resin to this projection for several seconds, the 3D model is built all at once. Not only is this far faster, but it removes the need for support materials and even a traditional build plate is unnecessary.

Visualization of the dual-color printing process as used by Regehly et al. (Credit: Nature)

Up till now the resolution and maximum object size of VAM has left a lot to be desired, but in this new research by Regehly et al. claim to have accomplished a feature resolution of ‘up to 25 micrometers’ and a solidification rate of ‘up to 55 cm³/s’. They used two crossing laser beams of different wavelengths, one to form the ‘light sheet’ (blue in the graphic) and a second beam (in red) to project the slide onto this light sheet. They refer to this technique as ‘xolography’, as a mesh-up of ‘holo’ (Greek for ‘whole’) and the ‘X’ shape formed by the crossing laser beams.

Key to making this work is the chemistry of the resin: the first wavelength excites the molecules called DCPI (Dual-Color Photo Initiators) that are dissolved in the resin. The second wavelength when hitting the same molecules initiates the resin polymerization process. The object pictured at the top of the page was a test print; producing such a design on a traditional 3D printer would have required a considerable amount of difficult to remove support material.

While this is obviously not a technology hobbyists will be using to replace their FDM and SLA printers with any time soon, there are still many companies and institutes working on various VAM technologies and approaches. As more and more of the complexities and challenges are dealt with, who knows when VAM may become a viable replacement for at least some SLA applications?

Thanks to [Qes] for the tip.