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3D printing, otherwise known as additive manufacturing, has become a very useful technique for fabricating very small and complex structures. Its initial inception facilitated the creation of individual and interesting objects that were printed at home by people interested in the technology.
However, as the years have gone on, more manufacturers have started to turn to 3D printing methods as a way of producing complex and bespoke parts at a much lower cost than other methods. It is a field of science, engineering and manufacturing that is continuously growing and it is likely to continue along this path for many years to come.
Unlike 3D printing, which is a relatively new technology, gold nanoparticles have been used for many years - even before we knew what nanoparticles were. This is apparent in the Lycurgus Cup, a 4th-century artifact, where gold nanoparticles have been shown to be responsible for the dichroic color observed.
In modern-day science, gold nanoparticles have been trialed for a number of applications, from anti-cancer agents, to surface plasmon imaging enhancers, to conductive conduits in electronics, catalysts, active sensor materials, and many more.
Compared to more complex nanoparticles, they are relatively simple to synthesize, and their wide usage has meant that researchers are now turning to other ways of manufacturing, using and incorporating them.
In recent years, researchers have developed the use of 3D printing methods to incorporate gold nanoparticles directly into polymers and other mediums during the printing process to generate a 3D-printed composite material containing gold nanoparticles.
This crossover area has greatly advanced in recent years and shows a lot of promise for the optical and pharmaceutical industries. Below, we look at how this field has developed.
Embedding Gold Nanoparticles in Polymers via 3D Printing
One of the more established, common, and easier ways to leverage these technologies is to use polymers as a composite medium for embedding multiple types of nanoparticles, including gold nanoparticles.
There are a number of polymer-nanoparticle composites out there, but a recent piece of research involves using polymers and gold nanoparticles to create 3D printed composites that are dichroic in nature (much like the Lycurgus Cup), for use as optical filters.
These nanocomposites have been created with fused deposition modeling (FDM) methods using poly(vinyl)acetate (PVA) as the carrier for the gold nanoparticles. When the nanoparticle-PVA nanocomposite dried, it showed a dichroic effect that manifested as a brown reflection and a purple transmission, but similar nanocomposites formed by more traditional methods do not exhibit the same effects.
The researchers also used this dichroic material to make a vase and a drinking cup, although to be usable, they need to be coated with a layer of polydimethylsiloxane (PDMS) to prevent water from penetrating into the nanocomposite.
This area is not as well-developed, but interesting nonetheless, and relies on creating polymeric devices that can then be used to synthesize gold nanoparticles, rather than using them in the 3D printing process.
Researchers created a poly(lactic) acid (PLA) microfluidic device using FDM and placed it on top of a poly(methyl methacrylate) (PMMA) slide, to create microfluidic channels. These microfluidic channels were then used as reaction chambers to create gold (and silver) nanoparticles through a continuous-flow synthetic route, as this prevented the polymer channels from becoming fouled.
The microfluidic synthesis parameters (concentrations, temperature, flow rate, etc.) could be changed to yield gold nanoparticles of different sizes.
Creating Gold Nanoparticle Inks
The most recent piece of research involved the use of comb-like polymer architectures to develop gold nanoparticle inks. The team used various step-growth polymerization and click chemistry methods to develop different polymer architectures (based around polyurethane) that could wrap around and encapsulate gold nanoparticles.
This was followed by a (3D printed) inkjet printing of the encapsulated gold nanoparticle inks. In many cases, gold nanoparticle inks are unstable when being inkjet-printed as the nanoparticles tend to agglomerate, but when encapsulated, the polymers stabilized the gold nanoparticles, meaning that they could be printed on a surface without agglomeration occurring.
The polymer-nanoparticle inks were found to be stable for long time periods (over six months). Gold nanoparticles have a lot of potential in the pharmaceutical industry and this polymer-stabilized printing method could be used to create stable and tailored gold nanoparticle-based biosensors.
It’s thought that this approach could also be adapted for stabilizing and embedding other metal nanoparticles within the polymers, opening the potential for more applications.
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Scientists are finding more innovative ways of combining polymers and gold nanoparticles using 3D printing methods, and because they show a lot of potential for different industries, it is an area that is likely to continue in the future. While a lot of applications have centered around the optics and pharmaceutical industries, the versatile nature of polymers and 3D printing methods, alongside the established applications of gold nanoparticles, could mean that these methods will start to be trialed in other industries and application areas.
References and Further Reading