Bone implants are typically made of solid metal – usually titanium. Though well tolerated by the body, such implants are significantly stiffer than bone.
This means that an implant may end up carrying a far higher load than the bone it is placed next to, according to Peter Quadbeck of the Fraunhofer Institute for Manufacturing Technology and Advanced Materials Research in Dresden, Germany. In a worst-case scenario, the decrease in stress placed on the bone means it will deteriorate, while the implant loosens and needs to be replaced.
Now Quadbeck and colleagues have created a titanium implant with a foam-like structure, inspired by the spongy nature of bone. The titanium foam does a better job than solid metal when it comes to matching the mechanical properties of bone, such as flexibility, and this encourages more effective bone regrowth.
What's more, the foam is porous, so the bone can grow around and within it, truly integrating the implant with the skeleton.
The titanium foam is made by saturating polyurethane foam with a solution of titanium powder and binding agents. The titanium clings to the polyurethane matrix, which is then vaporised away along with the binding agents. This results in a titanium lattice which is finally heat-treated to harden it.
Though the foam has yet to be approved for use in humans, Quadbeck and colleagues are now working with physicians to explore its suitability for treating certain injuries.
Peter Lee of the Department of Materials at Imperial College London is impressed. He says there are applications where inserting one of these titanium foams "looks like the most promising solution", such as bridging long gaps between broken bones.
Yuyuan Zhao, a materials engineer at the University of Liverpool, UK, adds that "if human bone isn't good enough, an implant could give your body better performance" than leaving bone to heal naturally or using other types of implant.