Rapid 3D printing in water using semiconductor-metal hybrid nanoparticles as photo-initiators

Additive manufacturing processes enable fabrication of complex and functional 3D objects ranging from engine parts to artificial organs.
Photo-polymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes organic photo-initiators to form reactive species.
However, this process, although commonly used in non-aqueous systems, is limited in water-based printing due to poor water solubility and low efficiency of the photoinitiators and restricted suitability to the emerging LED technology.

We report on a new family of water soluble photo-initiators based on hybrid semiconductor-metal nanoparticles.
Unlike conventional photo-initiators which are consumed upon irradiation, these nanoparticles 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 reactive species in aerobic conditions.
In particular, we demonstrate their use in 3D printing in water, where they simultaneously form hydroxyl radicals for the polymerization and consume dissolved oxygen which is a known retarder.
We also demonstrate their potential for two-photon polymerization due to their giant two-photon absorption cross section.

The advantages of the quantum photoinitiators, will open the path for efficient photo-polymerization in water.
This will hopefully lead to the introduction of new environmentally friendly approaches for photo-curing in general, and for additive manufacturing in particular, replacing current technology of printing in organic based solvents.
Furthermore, it opens exciting opportunities in the biomedical arena for the tailored fabrication of important medical devices and for printing of scaffolds for tissue engineering.