A new manufacturing technique for 3D printing objects thousands of times smaller


wenxin zhang
Mechanical engineering graduate student Wenxin Zhang works in the nano-fabrication lab. Credit: Caltech

Studies on mechanical size effects in nanosized metals often emphasize the strength of uniform microstructures, emphasizing the importance of internal microstructure and external dimensions to understand size-dependent characteristics.

In a new study, Caltech scientists developed a hydrogel infusion-based additive manufacturing (AM) technology to print objects a thousand times smaller: 150 nanometers, which is equivalent to the size of a flu virus. This technology is similar to previously developed manufacturing techniques for printing coarse and micro-sized metal parts. In this new technology each step has been re-imagined to work at the nanoscale.

Creating a light-sensitive “cocktail” is the first step in the process. This “cocktail” is composed primarily of hydrogel, a type of polymer that can absorb several times its own weight in water. Then, using a laser, this mixture is selectively hardened to create a 3D scaffold that has the same shape as the required metal products. The objects in this study were nanolattices and a collection of small pillars.

The hydrogel parts are then injected with a nickel-ion containing aqueous solution. The components are baked until the hydrogel completely burns off, leaving parts that are exactly the same size as the original but smaller and composed entirely of metal ions that have been oxidized. Has been (attached to oxygen atoms). In the final step the oxygen atoms are chemically removed from the components, returning the metal oxide to the metallic state.

Julia R. A nanoscale lattice prepared using a new technique developed by Greer’s laboratory. Credit: Caltech

In the final stage the parts develop their unexpected strengths.

Julia R. Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering. Greer said, “During this process all these thermal and kinetic processes occur simultaneously, and they lead to a very messy microstructure. You see defects like holes and irregularities in the atomic structure, which are generally considered power-depleting defects. If you were to make an engine block out of steel, you would not want to see this microstructure as it would significantly weaken the material.

“However, they found exactly the opposite. Many defects that would weaken large-scale metal parts instead strengthen nanoscale parts.

When a column is free of defects, failure occurs catastrophically at what is known as a grain boundary or the place where tiny crystals of the material rub against each other.

However, when the material is full of imperfections the failure cannot easily propagate from one grain boundary to the other. As a result, the deformation becomes more evenly distributed throughout the material, indicating that the material will not fail suddenly.

Irregular internal structure of a nanoscale nickel pillar. Credit: Caltech

Wenxin Zhang, lead author of the work and a graduate student in mechanical engineering, said, “Typically, the distortion carrier in a metal nanopillar – i.e., a dislocation or slip – diffuses until it can no longer escape to the outer surface. But in the presence of internal pores, diffusion will quickly terminate at the pore surface rather than continuing through the entire column. As a rule, it is harder to nucleate a distortion carrier than to allow it to diffuse, explaining why current columns can be stronger than their counterparts.

This is one of the first demonstrations of 3-D printing of metal structures at the nanoscale. This technology is expected to produce many useful components, such as catalysts for hydrogen, storage electrodes for carbon-free ammonia and other chemicals, and essential parts of devices such as sensors, microrobots and heat exchangers.

Journal Reference:

  1. Wenxin Zhang, Xie Li, Ruoqi Dong, et al. Manufacture of many useful components, such as catalysts for hydrogen, storage electrodes for carbon-free ammonia and other chemicals, and essential parts of devices such as sensors, microrobots and heat exchangers. Nano letter. DOI: 10.1021/acs.nanolet.3c02309


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