Graphene, the sheet-form carbon allotrope, long heralded as a wonder material since its unambiguous discovery in 2004, is characterized by its high strength to weight ratio, corrosion resistance, excellent conductivity, and scratch-resistant qualities. As such, the material is perfect for applications in various electronic devices, including energy storage cells and sensors.
This begs the question: is it possible to 3D print with graphene? Yes, but not in its pure form. Since graphene comprises a single layer of carbon atoms bonded together in a honeycomb-like structure, it is often regarded as the only truly 2D material in existence. This means that its atomic bonds only occur laterally - in one plane.
Once you stack multiple layers of graphene together, what you get is graphite, but this takes its toll on the material’s properties. Ultimately, 3D printing the pure 2D form of the material is impossible, so a 3D structure is only possible when it is mixed with other materials in a matrix.
With that out the way, let’s have a look at some of the production methods and applications of 3D printable graphene.
Fused deposition modeling
The first method of 3D printing graphene is fused deposition modeling, or FDM, which is the most widely used additive manufacturing process today. It involves heating and extruding polymer and composite material filaments through a small nozzle. Researchers from the Department of Materials at the Imperial College in London have previously developed composite FDM filaments composed of graphene additives in polymer matrices.
Here, the graphene flakes allow for the utilization of the material’s desirable properties while the polymer matrix acts as an adhesive, keeping the 3D printed part together. In this case, the team determined that for the final part to display the full suite of graphene’s qualities, the 3D printed object must be exposed to high temperatures post-printing, setting the material composition in place.
As far as applications go, the Imperial researchers have been working on finding partners to commercialize their material, claiming use cases in the creation of novel pressure sensors. In robotics, this may be great for super sensitive "skin" for robots, whereby logistics rovers would be able to navigate a busy warehouse or production line. In the medical field, it may enable new skin-contacting health monitoring devices that operate on electrical signals (owing to graphene’s excellent electrical conductivity).
Another method of printing with graphene is stereolithography, more commonly known as SLA. With SLA, resins are cured and hardened under UV light and stacked in layers to form complex 3D shapes. Research teams from Virginia Tech and Lawrence Livermore National Laboratory have previously developed a high-resolution method of 3D printing graphene based on this SLA process.
The scientists started by making a graphene oxide hydrogel. For reference, graphene oxide is a compound similar to graphene, but with oxide integrated with the carbon atoms. The hydrogel is a 3D structure made from polymer chains with cross-links holding the polymer chains together. After breaking the graphene oxide down with ultrasound, they added a UV-curable resin to act as the polymer matrix, meaning it could be 3D printed.
While this technique did preserve graphene’s conductivity properties, it was limited to printing very small structures in the region of several microns across. Further work needs to be done here, but if it can be scaled up, the scientists cite major applications in conductive energy storage devices, whereby the printed graphene structures would compose a portion of the cell’s electrodes.
Aerosol jet 3D printing
The third and final promising method of printing with graphene is aerosol jet additive manufacturing. Researchers from the USA recently used AJP technology from New Mexico-based 3D printer manufacturer Optomec to develop a graphene-based electrochemical sensor for detecting toxins in food. The technology is commonly used to manufacture electronics on both 2D and 3D substrates and works by forming structures using small ink-like droplets of metals that can adhere to readymade surfaces.
In this case, the design freedom granted by 3D printing came in very useful, as the material was only deposited where it was needed, resulting in a very low-cost portable sensor. Again leveraging graphene's excellent conductivity, the scientists believe their approach could enable applications where continuous on-site monitoring of food samples is needed to determine and maintain the quality of products.
The future of graphene 3D printing
As is clear, graphene 3D printing is very much an experimental venture and has yet to be commercialized. It has been limited to laboratories in recent years, but the undeniably fantastic strength and conductivity properties make it worth researching and developing, with promising applications in sensors that detect electrical signals.
Impressively, it has its uses in the medical sector, energy storage cells, and even food processing - it just needs a little more time to be scaled up and refined. Nevertheless, it’s exciting to see where additive manufacturing with the wonder material will end up in the coming years.