Taking advantage of molecules that switch states when exposed to particular wavelengths of light, researchers have developed a 3-D printing method that can make precise objects in a matter of minutes. The technique, developed by Stefan Hecht of RWTH Aachen University, Martin Regehly of Brandenburg University of Applied Sciences, and colleagues at the Berlin-based start-up xolo, is called xolography because it uses the crossing of light beams to create whole objects (holo is the prefix for whole and x signifies criss-crossing). The technique offers a way to make multicomponent objects with fine details, such as flow cells with blades that spin on an axle for transporting and mixing reagents. Xolo plans to commercialize the xolographic printer.

Xolography is a variant of volumetric 3-D printing. Instead of laying material down layer-by-layer with nozzles, like most 3-D printing, volumetric methods use light to selectively polymerize portions of a container of viscous liquid and wash away the rest, resulting in a solid object. Interest is growing in volumetric 3-D printing to make objects with fine features. In contrast to other volumetric approaches, Hecht and Regehly’s xolography technique is both fast and doesn’t require the expensive equipment that some other volumetric techniques do.

The new method relies on a photoswitchable molecule, which changes its structure when exposed to light. The researchers mix a photoswitchable spiropyran into the monomer-containing viscous liquid in their setup. When the researchers shine UV light on the material, the spiropyran molecules in the beam’s path switch to a merocyanine state. If the researchers then expose the molecules in the merocyanine state to visible light, the compounds initiate a polymerization reaction, hardening the viscous liquid. If merocyanine molecules don’t encounter visible light, they quickly switch back to the spiropyran state and no polymerization occurs. By shining the visible light from the perpendicular direction to the UV beam, the researchers can harden the liquid just at the point of intersection, giving precise control


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