Polyether ether ketone (PEEK) is a plastic widely used in the aerospace, automotive and oil and gas sectors because of its mechanical properties and resistance to high temperatures and chemicals. Now the usually non-conductive material has been infused with microscale carbon fibers that impart the ability to carry an electric charge. This renders PEEK a lightweight, self-sensing material of value in designing medical implants and prosthetics.

Researchers from University of Glasgow, Khalifa University (United Arab Emirates) and University of Cambridge (U.K.) used 3D printing to produce three different honeycomb configurations — a hexagonal structure, a cross-shaped chiral structure and a six-sided re-entrant design using both the carbon fiber-filled and conventional PEEK. During crush tests, each carbon fiber-PEEK structure was outperformed by its conventional PEEK counterpart, which were able to withstand higher pressures.

During impact tests, where a weight is dropped from a height onto the structures, the three carbon-fiber-PEEK structures demonstrated greater resistance to damage. The hexagonal honeycomb configuration demonstrated the best response, withstanding greater impacts than any of the others. Change in resistance to applied strain declined as the compressive strain increased, leading to a near complete loss of electrical resistance when the structures were completely crushed. The results indicate that the piezoresistivity of carbon fiber-PEEK could be of benefit in engineering a new generation of smart lightweight multifunctional structures, such as medical implants capable of in situ sensing of strain or damage.

“3D printing gives us a remarkable amount of control over the design and density of the cellular structure. That could allow us to build materials which more closely resemble the physiology of the native bone than the solid metal alloys traditionally used in medical implants like hip or knee replacements, potentially making them more comfortable and effective,” said University of Glasgow researcher Dr. Shanmugam Kumar.

The research is published in Materials & Design.