Researchers Develop New Water-Soluble Photoinitiators for 3D Printing

Medical 3D printing has made great strides, but there’s still a very long way to go before we reach the day when we can actually 3D print working organs and transplant them into humans. One issue that’s been holding research back, according to a team of researchers at the Hebrew University of Jerusalem, is that there’s a lack of satisfactory photoinitiators that are soluble in water and suitable for biocompatible materials.

Professor Shlomo Magdassi has been responsible for several 3D printing-related breakthroughs at the Hebrew University. The director of the university’s 3D and Functional Printing Center, opened in 2015, is famous for helping to develop the conductive inks used by Nano Dimension for its Dragonfly 2020 3D printer, and has led numerous studies related to advanced 3D printing materials, such as UV curable elastomers, shape memory polymers and much more. Magdassi, along with colleague Uri Banin, was also the leader of a recent study entitled “Rapid Three-Dimensional Printing in Water Using Semiconductor-Metal Hybrid Nanoparticles as Photoinitiators,” which you can access here.

The study discusses the use of semiconductor-metal hybrid nanoparticles as photoinitiators for 3D printing processes.

“Photopolymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes photoinitiators that break into radicals upon light absorption,” the researchers explain. “We report on a new family of photoinitiators for 3D printing based on hybrid semiconductor−metal nanoparticles. Unlike conventional photoinitiators that are consumed upon irradiation, these particles form radicals through a photocatalytic process. Light absorption by the semiconductor nanorod is followed by charge separation and electron transfer to the metal tip, enabling redox reactions to form radicals in aerobic conditions.”

The particles, immersed in water, create free radicals within the water upon being exposed to light radiation. Those free radicals create 3D structures through DLP technology. Unlike regular photoinitiators, according to the researchers, these particular photoinitiators are non-consumable and can therefore be reused. In addition, the particles consume oxygen within the water, preventing it from inhibiting the polymerization.

“Moreover, due to their giant two-photon absorption cross section they can be used in high-resolution 3D printing of submicron objects,” the researchers add.

Two photon polymerization 3D printers can produce objects with higher resolution than any other 3D printing technology; as an example, Nanoscribe’s 3D printers can produce objects with feature sizes of 1 µm or less. Incidentally, a Nanoscribe 3D printer was used by the researchers in their work with the semiconductor-metal hybrid nanoparticles.

“The semiconductor and metal segments can be tuned in terms of their composition, size, shape, and relative location toward optimal performance in photopolymerization and in particular in 3D printing,” the researchers continue.

Tunable characteristics include:

• The semiconductor band gap and its one- and two-photon characteristics to match printing characteristics such as wavelength of irradiation
• The relative energetics of the semiconductor and metal components to optimize the charge separation characteristics
• Selective efficient radical formation for best performance
• The nanoparticule surface coating, allowing for dispersability in various solvents

“Therefore, we envision high potential for further realization of HNPs as PIs UV curable inks and in 3D printing applications,” the researchers conclude.

Authors of the paper include Amol Ashok Pawar, Shira Halivni, Nir Waiskopf, Yuval Ben-Shahar, Michal Soreni-Harari, Sarah Bergbreiter, Uri Banin, and Shlomo Magdassi. Discuss in the Water Soluble Photo-initiators forum at 3DPB.com.