Jun 30, 2015 | By Alec

A few months ago, we reported on the amazing work being done by a team of scientists from Northwestern University, who have made a great breakthrough in the possibilities of 3D printing graphene structures. This material, as you might now, could be called the holy grail of 3D manufacturing. We’ve already learned that the team from Northwestern University have developed a solution-based 3D printable graphene ink that can be used to make objects multiple centimeters in length. But through a publication, the team led by Ramille Shah has just unveiled a lot more about the potential and limitations of their graphene ink, which amazingly consists of 60 percent graphene (in terms of volume), making up 75 percent of its weight.

To explain, graphene is essentially a form of carbon, just like diamonds or the lead in pencils. But unlike most forms of carbon, graphene is a 2D material that consists of a hexagonal sheet only a single atom thick. This means it can be made into shapes of literally any size, but its properties are especially interesting. Not only is it very light, flexible, and extremely durable (about a hundred times stronger than steel), it is also a very efficient conductor of heat and electricity and is compatible with human cell tissue. In short, it could be the perfect filament for various technological and medical applications.

And while some graphene successes have been previously achieved, this specific ink contains more graphene than any previously developed 3D printable materials (the previous record was around the 20 percent). This means that the electrical and mechanical properties of graphene can soon be taken into use.  What's more, the rest of the ink consists of a biocompatible biodegradable polyester (PLG) that, the scientists explain, also makes the ink flexible and safe to use in medical situations.

Led by Ramille Shah, who is the assistant professor of materials science and engineering at the McCormick School of Engineering, and her postdoc Adam Jakus, the team are thus really onto something. ‘People have tried to print graphene before. But it’s been a mostly polymer composite with graphene making up less than 20 percent of the volume,’ Shah explains on her university’s website. This means these materials don’t copy graphene’s properties and remain to brittle and fragile to use. And while you might think that a 60-70 percent graphene content isn’t the real deal either, this does in fact copy all the properties you need, while the remaining materials ensure flexibility and robustness.

‘It’s a liquid ink,’ Shah explains. ‘After the ink is extruded, one of the solvents in the system evaporates right away, causing the structure to solidify nearly instantly. The presence of the other solvents and the interaction with the specific polymer binder chosen also has a significant contribution to its resulting flexibility and properties. Because it holds its shape, we are able to build larger, well-defined objects.’ This ink has described in a recent paper in ACS Nano, entitled ‘Three-dimensional printing of high-content graphene scaffolds for electronic and biomedical applications.’ 3D printed graphene appeared on the cover.

And so far, biomedical experiments have been quite successful. As a test, her team populated a graphene scaffold with stem cells, with the results being excellent. The cells survived, first of all, but even went on to divide, proliferate and transform into neuron-like cells. ‘That’s without any additional growth factors or signaling that people usually have to use to induce differentiation into neuron-like cells,’ Shah says. ‘If we could just use a material without needing to incorporate other more expensive or complex agents, that would be ideal.’

They are also already envisioning sensors, implants and other structures. ‘Cells conduct electricity inherently — especially neurons. So if they’re on a substrate that can help conduct that signal, they’re able to communicate over wider distances,’ Shah added. The secret to this graphene ink is that the graphene is embedded into microscopic flakes. This makes the ink highly viscous, but extrusion realigns all the flakes to create a single filament with all the characteristics of graphene. Printing takes place as small as 100 micrometers (speed of 40 mm/s).

What’s more, the elasticity of the material can be tuned by changing the portions of graphene and polymers. The standard formula can be stretched up to 81 percent, but that increases when the amount of graphene is decreased (though eventually this means losing some graphene properties). This means that this ink could be used for a wide range of applications requiring slightly different properties. In short, while 3D printing itself is revolutionary, throwing graphene into that mix really changes the playing field.

 

 

Posted in 3D Printing Applications

 

 

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