Researchers Develop Unique 3D Manufacturing Method to Create and Control Material Architecture on the Nanoscale

Back in 2014, the National Institute of Health awarded Washington State University (WSU) researchers a five-year grant of $1.8 million, in order to improve the coating used for 3D printed titanium knee and hip replacement parts. While that team is in the middle of their work, another team of WSU researchers are looking at 3D printing on a much smaller scale: they have developed a unique, patent-pending 3D manufacturing method to create and control the architecture of a material from the nanoscale to centimeters. The resulting complex, bio-like materials mimic the architecture of natural materials such as bone and wood.

Microstructures could be used in batteries, lightweight ultrastrong materials, catalytic converters, supercapacitors and biological scaffolds.

This is the first time that 3D manufacturing has been able to precisely control, as well as quickly create, a material’s architecture. The research team’s work, recently published in a paper titled “Three-dimensional microarchitected materials and devices using nanoparticle assembly by pointwise spatial printing,” for Science Advances journal, has many applications for cutting edge engineering. Rahul Panat, associate professor in the School of Mechanical and Materials Engineering since 2014, led the research and co-authored the paper; graduate students Mohammad Sadeq Saleh and Chunshan Hu are the other co-authors.

Rahul Panat

Panat said, “This is groundbreaking advance in the 3D architecturing of materials at nano- to macroscales with applications in batteries, lightweight ultrastrong materials, catalytic converters, supercapacitors and biological scaffolds. This technique can fill a lot of critical gaps for the realization of these technologies.”

Manufactured 3-D electronic interconnects light an LED.

The researchers used a 3D printing method in order to make microdroplets, similar to fog, that contain silver nanoparticles, and then deposit the microdroplets at specific locations. The nanoparticles stayed put, and as the liquid evaporated, porous, strong, but delicate structures were created; the tiny structures actually have a large surface area, and resemble an object one might construct using Tinkertoys. Silver is easy to use, which is why it was the preferred testing material, but Panat explained that their method can be used with any material that can be crushed into nanoparticles – which is true of nearly all materials.

According to the paper’s abstract, “Three-dimensional (3D) hierarchical materials are important to a wide range of emerging technological applications. We report a method to synthesize complex 3D microengineered materials, such as microlattices, with nearly fully dense truss elements with a minimum diameter of approximately 20 μm and having high aspect ratios (up to 20:1) without using any templating or supporting materials. By varying the postprocessing conditions, we have also introduced an additional control over the internal porosity of the truss elements to demonstrate a hierarchical porous structure with an overall void size and feature size control of over five orders of magnitudes in length scale. The method uses direct printing of nanoparticle dispersions using the Aerosol Jet technology in 3D space without templating or supporting materials followed by binder removal and sintering. In addition to 3D microlattices, we have also demonstrated directly printed stretchable interconnects, spirals, and pillars. This assembly method could be implemented by a variety of microdroplet generation methods for fast and large-scale fabrication of the hierarchical materials for applications in tissue engineering, ultralight or multifunctional materials, microfluidics, and micro-optoelectronics.”

Fig. 1 Analogy of the natural growth of Desert Rose and the 3D buildup of nanoparticles by pointwise printing to realize microarchitectures.
(A) An illustration of the Desert Rose formation process by condensation of sulfur-containing fog along with the elevated temperature of the desert climate. Desert Rose photo courtesy of O. Apostolidou (reprinted with permission). (B) In a process inspired by that shown in (A), we used successive condensation of droplets of nanoparticle ink in the spatial dimension followed by solvent evaporation and sintering to create controlled 3D microarchitectures with hierarchical porosity. The scanning electron microscopy (SEM) image resembles a petal-shaped structure (right). The truss element diameter is about 40 μm.

Using their new manufacturing method, the researchers created multiple intricate structures, including microscaffolds which contain “solid truss members” like spirals, bridges, and electronic connections, which look like doughnut-shaped pillars or the bellows of an accordion. Their method actually resembles the rare process of creating crystalline, flower-like structures that are called desert roses. Tiny fog droplets containing dissolved sulfur compounds naturally evaporate in the hot atmosphere of an African desert, and this process results in the 3D desert rose structures.

According to the paper, this type of free-form fabrication that results from first 3D printing nanoparticle solutions and inks and then sintering them is a fairly new area of research. Two of the main parameters that can inhibit 3D microscaffold geometry are the stability of the growing elements, and the determination of the critical growth angle. But the researchers were ultimately able to demonstrate a “3D microscale assembly method for nanoparticles to form self-supported complex architectures.”

This new manufacturing method creates little waste, allows for quick, large-scale manufacturing, and is very efficient, thanks to 3D printing technology. These hierarchical 3D structures have applications in areas such as microfluidic devices, energy storage, tissue engineering, and strain-tolerant ultralight materials. The research team isn’t done yet, and wants to utilize nanoscale and porous metal structures for industrial purposes. As an example, they are currently developing detailed, porous cathodes and anodes for batteries, which could greatly increase battery capacity and speed, and allow the industry to use new, higher energy materials.

This research is right in line with the university’s Grand Challenges initiative, which brings research priorities into focus and partners WSU researchers with other scholars, along with national laboratories, federal and state agencies, and philanthropists, to address complex issues around the world. Discuss in the 3D Micro-Architectures forum at 3DPB.com.