Building sub-wavelength structures using photons, and using 3D printers to create scaffolds for human cells.
One of the interesting features of Photonics West is that it covers the full spectrum, from academic research to industrial research to new products in the commercial exhibits. This range of interrelated ideas was on show in 3D fabrication.
At one extreme, the latest research in scanning multi-spot three-photon patterning showed 3D structures 100μm thick with 50nm features. Researchers also showed 3D printed bio-sourced material. And new commercial 3D printers capable of creating meter sized objects were on display.
Scanned three-photon patterning is a way to create 3D sub-wavelength structures. It starts with two photons. A material that requires a 360nm photon, is exposed using two longer wavelength photons. These two photons have to arrive at the same time, which only occurs at the focus of a microscope lens, so a 3D spherical spot is exposed. Scan the focus around in X, Y and Z and a 3D structure is created with a minimum feature size around the original exposure wavelength.
The addition of a third photon at an intermediate wavelength “stimulates” the decay of the excited state, blocking the exposure photochemistry. When an image using the blocking wavelength forms a spherical shell around the exposing spot, then the exposed spot becomes much smaller. Features as small as 50nm have been created.
Julian Hering, a researcher at Kaiserlautern University of Technology in Germany, discussed a three-photon system that used spatial light modulators to control the alignment and shape of these two images, so the setup went from hours to minutes. In addition, he showed that five spots in a line could be created. He noted that “the SLM would allow independent switching of the beams, and that 100 unswitched beams had also been demonstrated.” This suggests that there are ways to significantly speed up the serial scanning process.
Fiorenzo Omenetto from Tufts University used a 3D printer to create bio-compatible scaffolds from reconstituted silk. Thanks to compliant insects, silk is a naturally occurring protein with excellent mechanical properties. It can be dissolved and reformed into a 3D printed object in a similar way to cellulose being reformed as fibers in Rayon. He showed inserts for blood vessels that were 3D printed, and that human cells had been found to happily grow and reproduce on these scaffolds.
There were also new 3D printers on show in the exhibit section. TI had a space where it brought together new Digital Mirror Devices (DMD), the implementers who developed turnkey image processing modules, and the systems integrators who designed the final products. Prodways showed a UV cure 3D printer that scanned a high resolution 2560 pixel-wide DMD image to build parts up to meters on a side. This is obviously an industrial scale printer, which can support multiple heads to increase throughput. The system used an image processing and DMD package made by Vialux. The systems’ complexity and design challenges were clearly illustrated.