University researchers develop hybrid nanoparticles for rapid 3D printing in water

Semiconductor metal hybrid nanoparticles (HNPs) as photoinitiators. a. An electron microscope image of hybrid nanocrystal. The inset shows a schematic of semiconductor nanorod with a metal tip. b. a bucky ball structure produced by rapid 3D printing in water using HNPs as photoinitiators. c. A spiral printed with HNPs on a two photon printer providing high resolution features. Adapted with permission from Pawar et al., Nano Lett. DOI: 10.1021/acs.nanolett.7b01870. Copyright (2017) American Chemical Society.

A team of eight university researchers from the Hebrew University of Jerusalem, in Israel, and the University of Maryland, in the USA, has developed semiconductor metal hybrid nanoparticles (HNPs), described as ‘a new type of photoinitiator (PI)’, for rapid photopolymerization-based 3D printing in water. It is believed that these HNPs could pave the way for a bio-friendly approach to the creation of hydrogels, bioscaffolds and artificial organs.

PIs are the molecules responsible for inducing the radical photopolymerization process, namely the chemical reactions necessary to form solid 3D printed material using light. The ability to print structures in water has so far proved challenging, mainly due to an absence of efficient water-soluble PIs and the dissolved oxygen in water inhibiting the photopolymerization process.

The current method of 3D printing traditional, organic PI-based inks often depends on a dangerous UV light excitation range of between 200 and 350 nm and/or the use of organic solutions and solvents that raise health and environmental concerns. 3D printing in water is generally regarded as a safer and more environmentally friendly approach to creating the same or similar products. The researchers’ development of HNPs is considered a milestone achievement since it potentially allows for further realization of this capability.

HNPs are said to afford a number of advantages over traditional, organic PIs, namely:

  • they are not consumed during light irradiation;
  • their function is based on a photocatalytic mechanism that gives rise to the formation of hydroxyl radicals for polymerization as well as consumption of the known inhibitor dissolved oxygen, enabling their use in 3D printing at ambient conditions;
  • they exhibit high absorption cross sections at the operating wavelengths of commercially available digital light processing (DLP) printers, resulting in fast polymerization and printing;
  • their giant, two-photon absorption cross sections enable them to be used for high-resolution printing of sub-micron objects;  
  • they offer wide near-ultra violet (UV) and -visible (VIS) light excitation ranges;
  • they are highly sensitive to light; and
  • they possess tunable properties.

The researchers believe 3D printing in water could present opportunities for the fabrication of implantable medical devices and bioscaffolds for tissue engineering. In particular, they envision it being used for bespoke bone plates and joint replacements as well as heart valves, ligaments and tendons.

Bioscaffolds are already being 3D printed out of water, but this is mainly because printing them in water is not yet viable. The holy grail is to have biodegradable scaffolds that incorporate stem cells as well as other supportive cells and proteins that assist in the regeneration of the tissue. Since cells cannot survive without water and proteins deform in organic solutions and solvents, methods for 3D printing out of water limit the potential to optimize these scaffolds. 

ACS (American Chemical Society) Publications has published the researchers’ paper—titled Rapid Three-Dimensional Printing in Water Using Semiconductor–Metal Hybrid Nanoparticles as Photoinitiators—in its journal Nano Letters.

The researchers are affiliated to the Center for Nanoscience & Technology and Institute of Chemistry at the Hebrew University of Jerusalem and the Department of Mechanical Engineering and Institute of Systems Research at the University of Maryland.

The research has been financially supported in part by the Israel Science Foundation as well as the National Research Foundation of Singapore under the CREATE program.

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