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Graphene Extended for 3-D Printing, Medical Devices

Graphene piece inside a flower

3-D printed graphene matrix balanced inside a strawberry blossom (Virginia Tech)

24 August 2018. Two recent studies describe methods for fabricating the material graphene into complex shapes with 3-D printing, as well as showing graphene can likely degrade inside the human body. These findings were published recently by researchers from Virginia Tech and Lawrence Livermore National Lab, and a European consortium sponsored by the Graphene Flagship project.

Graphene is a material closely related to graphite like that used in pencils, one atom in thickness and arrayed in an hexagonal atomic pattern. The material is very light, chemically stable, strong — from 100 to 300 times stronger than steel — and can conduct both heat and electricity, with applications in electronics, energy, manufacturing, and health care. And compared to other materials, graphene is inexpensive to produce.

But graphene also has drawbacks. One of those issues is its stiffness that prevents graphene from being 3-D printed in fine, complex, high-resolution free-form matrices. A team from the Advanced Manufacturing and Metamaterials Lab at Virginia Tech in Blacksburg led by Xiaoyu “Rayne” Zheng, and materials scientist Marcus Worsley at Lawrence Livermore National Lab in Livermore, California developed a process for creating these hierarchical structures in graphene with 3-D printing, which they describe in the 13 August issue of the journal Materials Horizons.

Most 3-D devices today use an extrusion process to print their materials, which is too crude and imprecise for the complex matrix graphene structures envisioned by the authors. Zheng, Worsley, and colleagues devised a process where they mixed graphene oxide, a precursor of graphene, in a hydrogel foam, and then in light-sensitive acrylate polymer resins. The 3-D printing is done with a laser process called stereolithography, which hardens the graphene and acrylate polymer into the desired shape and hierarchical structure, followed by a heating process to burn off the acrylate, leaving the pure graphene.

“We’ve been able to show you can make a complex, three-dimensional architecture of graphene,” says Zheng in a university statement, “while still preserving some of its intrinsic prime properties.” The complex pieces produced by the Virginia Tech/Livermore Lab researchers achieved resolutions of 10 microns, or millions of a meter, yet were light enough to be balanced inside a strawberry blossom flower.

A separate team from the Universities of Strasbourg and Bordeaux in France, Karolinska Institute in Sweden, and University of Castilla–La Mancha in Spain tested a key property of graphene needed for some implanted medical devices: the ability to degrade inside the body. Results of the study, funded by the EU’s Graphene Flagship project, appear in the 13 July issue of the journal Angewandte Chemie, International Edition (paid subscription required).

Researchers led by materials scientist Alberto Bianco at University of Strasbourg tested single and multi-layered graphene sheets in the lab for their ability to degrade when exposed to conditions similar to inside the human body. As Bianco notes in a Graphene Flagship statement, “We used two forms of graphene, single- and few-layer, prepared by two different methods in water. They were then taken and put in contact with myeloperoxidase in the presence of hydrogen peroxide. This peroxidase was able to degrade and oxidize them.”

Myeloperoxidase is an enzyme released by neutrophils, white blood cells in the immune system that are among the first to react to infections. The researchers say they did not expect graphene to respond in this way, which opens up the possibility that graphene could be used in medical devices implanted for brief periods that could then degrade inside the body, rather than be removed surgically. Co-author Bengt Fadeel of the Karolinska Institute adds, “The fact that cells of the immune system are capable of handling graphene is very promising.” Tests with animals are expected to be the next stage in the project.

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