Better artificial limbs thanks to a breakthrough self-stiffening material from biomedical researchers at University of Bridgeport and Rice University


Anyone who has spent time at the gym knows that working out improves one’s strength. That’s not the case, however, with artificial tissue and cartilage, which break down over time.

Until now, that is.

A team of researchers, including a professor of biomedical and mechanical engineering from the University of Bridgeport, have developed a unique nanocomposite material that can, for the first time ever, self-stiffen under repeated use and loading. Their findings could pave the way for a new generation of biomimetic materials, and appear in the recently published scientific journal ACS Nano.

Their material consists of a carbon nanotube forest filled with polydimethyl siloxane rubber. The interface between these two materials, they say, evolves when repeatedly stressed and improves the overall composite.

That’s a big breakthrough for biomedical engineers, who have long desired to develop materials that are as adaptive as our body’s natural tissues.

“This is fascinating in the sense that if we can precisely control the nanocomposite interface, we can engineer exciting materials that will adapt to the loads that they are subjected to,” said Prabir K. Patra, assistant professor of biomedical engineering and mechanical engineering at UB. “We believe that this discovery will not only lead to interesting artificial biological structures, but its implications likely extend beyond such applications.”

Patra worked with Brent Carey, a graduate student at Rice University and first author of the paper, and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Engineering, Mechanical Engineering and Materials Science and of Chemistry at Rice University, whose lab carried out the experiments.

Offering an analogy between their material and bones, Carey said, “As long as you’re regularly stressing a bone in the body, it will remain strong. For example, the bones in the racket arm of a tennis player are denser than those of limbs that aren’t used as frequently. Essentially, this is an adaptive effect our body uses to withstand the loads applied to it.

“Our material is similar in the sense that a static load on our composite doesn’t cause a change. You have to dynamically stress it in order to improve it. We can envision this response being attractive for developing artificial cartilage that can respond to the forces being applied to it but remains pliable in areas that are not being stressed.”

“People have been trying to address the question of how polymer layer around a nanoparticle behaves” says Professor Ajayan. “It’s a very complicated problem. But fundamentally, it is important if you’re an engineer of nanocomposites. From that perspective, I think this is a beautiful result. It tells us that it’s feasible to engineer interfaces that make the material do unconventional things.”

Other coauthors of the paper are former Rice postdoctoral researcher Lijie Ci; and Glaura Goulart Silva, associate professor at the Federal University of Minas Gerais, Brazil.
Media contact: Leslie Geary, (203) 576-4625,