Tech Briefs

Welded nanoscale sheets form tough, porous material.

Flakes of graphene welded together into solid materials may be suitable for bone implants, according to a study led by Rice University scientists. The Rice lab of materials scientist Pulickel Ajayan and colleagues in Texas, Brazil, and India used spark plasma sintering to weld flakes of graphene oxide into porous solids that compare favorably with the mechanical properties and biocompatibility of titanium, a standard bone-replacement material.

A focused ion beam microscope image shows 3D graphene layers welded together in a block. The material is biocompatible and its material properties meet the standards necessary for consideration as a bone implant, according to researchers at Rice University. (Credit: Ajayan Group)

The discovery is the subject of a paper in Advanced Materials. The researchers believe their technique will give them the ability to create highly complex shapes out of graphene in minutes using graphite molds, which they believe would be easier to process than specialty metals.

“We started thinking about this for bone implants because graphene is one of the most intriguing materials with many possibilities and it’s generally biocompatible,” said Rice postdoctoral research associate Chandra Sekhar Tiwary, co-lead author of the paper with Dibyendu Chakravarty of the Inter national Advanced Research Center for Powder Metallurgy and New Materials in Hyderabad, India. “Four things are important: its mechanical properties, density, porosity, and biocompatibility.”

Tiwary said spark plasma sintering is being used in industry to make complex parts, generally with ceramics. “The technique uses a high pulse current that welds the flakes together instantly. You only need high voltage, not high pressure or temperatures,” he said. The material they made is nearly 50 percent porous, with a density half that of graphite and a quarter of titanium metal. But it has enough compressive strength — 40 MPa — to qualify it for bone implants, he said. The strength of the bonds between sheets keeps it from disintegrating in water.

To see how graphene oxide layers stack when welded by spark plasma sintering, watch a molecular dynamics simulation at https://www.youtube.com/watch?v=9itxVFu_p5U.

For more information, visit http://news.rice.edu.