Graphene Ink 3-D Printed Medical Implant Grows Nerve Cells

There is no shortage of excitement for the possibilities of 3-D printing. The manufacturing technique uses a machine that squirts layer upon layer of material to build three-dimensional objects. The prevailing vision for 3-D printing is that one day we’ll be able to make smartphones, sensors, drones or other complex machines right in our homes.

But if we’re ever to have desktop devices that can output things like consumer electronics or novel biomedical devices, there are a number of obstacles that need to be overcome. Today’s consumer units most commonly use hot plastic that quickly solidifies to build shapes. This material is neither particularly strong nor is it electrically conductive, a characteristic necessary to build electronic components into devices.

Researchers all around the world are looking for materials that can unlock some of 3-D printing’s bigger promises. Now Northwestern University researchers say they have created a 3-D printing ink that is stronger, electrically conductive and biocompatible using another material that has been generating much excitement over the last decade–graphene. See more gifs and learn more below.

(Real time video showing 3-D printable graphene (3DG) 1 cm-diameter cylinder 3D printing in process using liquid 3DG ink. Specific attention should be given to the speed at which the construct is being printed, as well as the rapid, seamless merging of each successive layer with the previous. Note that contrast and brightness have been enhanced to make the normally very dark 3DG more visible. Gif created from video courtesy of Jakus et al./ACS Nano.)

They made their ink by mixing nanoscopic flakes of graphene, which are atom-thick sheets of linked carbon atoms, with a bit of biocompatible polymer and solvents that quickly evaporate. Unlike previous attempts to make graphene ink, this one imparts in the final object all of the valued properties of graphene including conductivity, flexibility, strength and the ability to be placed within the human body without harming it or triggering an immune response.

The difference, says biomaterials scientist Ramille Shah, is an ink engineered with a higher proportion of graphene in the mix than previous attempts. Her team’s design brings graphene nanoflakes up to 70 percent of the ink’s total volume. Previous work saw such high proportions create a finished object that was brittle.

“It’s a liquid ink,” Shah said. “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.”

(Fabrication multi-hundred layer 3DG object. 64x speed video of 3DG 5 mm-diameter hollow cylindrical nerve conduit being 3D printed with a 250 µm diameter tip. High aspect ratio structures such as this can be fabricated with ease using 3DG inks. Gif created from video courtesy of Jakus et al./ACS Nano.)

Shah is particularly interested in using 3-D printed graphene scaffolds as biodegradable sensors and medical implants inside patients. To test out whether the graphene-based objects could be used in biomedical applications, her team seeded a printed scaffold with stem cells. These survived on the structure, divided into new cells and evolved 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 said. “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.”



Their work was published last month in the journal ACS Nano. Compare Northwestern’s achievement to similar work underway in the European Nanomaster project, which is successfully 3-D printing weakly conductive sensors using graphene and plastic.

Top Image: Animation illustrating the layer-by-layer build process. This particular cylinder is 5 mm-diameter and 3D printed using a 100 µm diameter tip with an advancing 120˚ angle. Photographs were taken automatically each layer by the 3D-Bioplotter. Note that brightness and contrast have been significantly enhanced to make the layers and features easily visible. Gif created from video courtesy of Jakus et al./ACS Nano.