Here’s an interesting approach to volumetric 3D printing: instead of focusing light into a tiny point, stretch it into a thin sheet and sweep that sheet across the print.
That’s the basic idea behind a recent patent application from Miltenyi Biotec B.V. & Co. KG, WO2025088201A1, titled “Methods to Improve 3D Printing Using Two-Color Polymerization.”
The process uses two different colors of light.
One wavelength puts the photoinitiator into a temporary state where it is ready to react. A second wavelength then triggers polymerization.
Material hardens only where those two optical regions meet.
If that sounds familiar, it’s because this is closely related to Xolography and other dual-color volumetric printing processes.
Miltenyi’s twist is mostly about how those two light fields are shaped and moved.
Stretch The Focus Into A Light Sheet
Instead of using a conventional focal spot, Miltenyi proposes illuminating the resin with a long, narrow sheet of light.
A second structured beam — potentially from a projector — moves along with it.
You can think of the first beam as defining a thin zone where printing is possible, while the second beam decides exactly which portions of that zone actually solidify.
The interesting optical trick is something Miltenyi calls “tilted waist illumination,” or TWI.
Rather than producing a symmetrical point of focus, the beam is stretched into an elongated waist. That waist can even be tilted relative to the optical axis.
It sounds rather exotic, but there’s a good reason for doing this.
With two-color polymerization, the first wavelength puts the photoinitiator into an intermediate state, and that state only lasts for a certain amount of time.
If it lasts too long, material outside the intended intersection could potentially cure as the beams move. That would blur the print.
Miltenyi proposes scanning the two light fields together so that this intermediate state only needs to survive for the short duration of the scan.
In one example, the patent uses 405nm light and models very fine optical sections, including about 1.41 microns full width at half maximum in one larger-scale configuration.
Those are modeled numbers rather than demonstrated printer performance, but they show what Miltenyi is trying to achieve: keep the narrow dimension very small for resolution while making the illuminated region much longer for coverage.
In other words, print finely without being limited to a tiny work area.
Printing Straight Onto Electronics
This is where the patent gets more interesting.
Miltenyi describes using the process to print structures directly onto flat substrates.
Those could include silicon wafers containing electronics, transparent films and disposable microfluidic devices.
A prism arrangement could send both light beams through the same transparent surface, allowing structures to be printed directly on that substrate.
That opens up some interesting possibilities.
For example, microfluidic channels or connectors could be printed directly over existing electronics rather than being fabricated separately and assembled afterwards.
The patent also describes printing onto sample holders used with cells, organoids and embryos, including gel-based vascular structures.
Another possibility is printing through a moving transparent foil. Sections could be produced sequentially as the foil advances, potentially extending the printable area far beyond a fixed vat.
Then there’s an even stranger variation.
Miltenyi describes printing a disposable mold, filling it with another material — potentially metal, glass, ceramic or polymer — and later removing the printed mold.
That starts to push the process beyond photopolymer printing and into something closer to micro-scale investment casting.
There are, of course, plenty of things that would have to work perfectly.
The two optical systems would need very precise alignment and synchronization. The printer would have to compensate for distortion caused by the tilted illumination plane, and the resin chemistry would need to behave very predictably.
Producing the unusual light sheet could also require some fairly sophisticated optics.
Instead of increasing print size by simply making every optical component larger, Miltenyi proposes stretching one dimension of the exposure and scanning it across the job.
If that works, two-color volumetric printing might eventually move from producing tiny high-resolution structures to printing fine features across much larger surfaces.
And printing those structures directly onto electronics, wafers or fluidic devices could be considerably more useful than printing them separately and gluing everything together afterwards.
Via Espacenet
