Microscopic 3D Printing Could Build Structures Inside the Body

Researchers have used ultrathin optical fibers to create microscopic structures via laser-based 3D printing. The microstructures, which were created on a microscope slide, exhibited a 1.0-µm lateral and 21.5-µm axial printing resolution. The approach could one day be used to build tiny biocompatible structures inside the human body.

Current microfabrication techniques rely on two-photon photopolymerization (TPP), a selective curing process that requires complex, expensive lasers and bulky optical systems to deliver light to the photopolymer. The researchers’ use of an inexpensive and compact alternative to TPP could open up new possibilities for advanced and functional microfabrication through endoscopic probes using inexpensive laser sources.

Researchers used an optical fiber housed inside the needle pictured to deliver light for 3D printing microstructures. The light selectively hardens volumes inside the droplet of photopolymer on the glass slide. The new system could one day allow 3D printing inside the body. Courtesy of Damien Loterie and Paul Delrot, École Polytechnique Fédérale de Lausanne.

Researchers from École Polytechnique Fédérale de Lausanne (EPFL) took advantage of a chemical phenomenon in which curing only occurs above a certain threshold in light intensity. After studying the light scanning parameters and the photopolymer’s behavior, they determined the best parameters for using this phenomenon. By exploiting this nonlinearity with a specific overcuring method, the researchers were able to demonstrate single-photon 3D fabrication of solid and hollow microstructures through a multimode fiber using a low-power, inexpensive continuous wave (CW) laser rather than a pulsed laser.

Researchers used the optical fiber to deliver and digitally focus laser light point-by-point into the liquid to build their 3D microstructure. They used an organic polymer precursor doped with a photo-initiator made from off-the-shelf chemicals. They focused a CW laser emitting light at 488-nm wavelength through an optical fiber small enough to fit in a syringe. Using wavefront shaping, they were able to focus the light inside the photopolymer so that only a small 3D point was cured. Performing a calibration step prior to microfabrication allowed the researchers to digitally focus and scan laser light through the optical fiber without moving the fiber.

Using an inexpensive laser and an ultrathin optical fiber, the researchers created hollow microstructures such as the one shown here. They were able to create microstructures with a 1.0-micron lateral (side-to-side) and 21.5-micron axial (depth) printing resolution. Courtesy of Paul Delrot, École Polytechnique Fédérale de Lausanne.

“Our group has expertise in manipulating and shaping light through optical fibers, which led us to think that microstructures could be printed with a compact system. In addition, to make the system more affordable, we took advantage of a photopolymer with a nonlinear dose response. This can work with a simple continuous wave laser, so expensive pulsed lasers were not required,” said researcher Paul Delrot.

“Compared to two-photon photopolymerization state-of-the-art systems, our device has a coarser printing resolution, however, it is potentially sufficient to study cellular interactions and does not require bulky optical systems nor expensive pulsed lasers,” Delrot said. “Since our approach doesn't require complex optical components, it could be adapted to use with current endoscopic systems.”

The researchers are working to develop biocompatible photopolymers and a compact photopolymer delivery system, which are necessary before the technique can be used in people. A faster scanning speed is also needed, but in cases where the instrument size is not critical, this limitation could be overcome by using a commercial endoscope instead of the ultrathin fiber. A technique to finalize and post-process the printed structure inside the body is also needed to create microstructures with biomedical functions.

“Our work shows that 3D microfabrication can be achieved with techniques other than focusing a high-power femtosecond pulsed laser,” said Delrot. “Using less complex lasers or light sources will make additive manufacturing more accessible.”

The research was published in Optics Express, a publication of OSA, The Optical Society (doi: 10.1364/OE.26.001766).