Artificial Bone That's Almost Real

Scientists are unraveling the secrets of the sea to build a better artificial bone.

By grasping the way saltwater freezes, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory have developed a material that is four times stronger than the material currently used for synthetic bones.

The new composite mirrors the intricate structure of nacre, a finely layered substance found in oysters and abalone. Scientists have long sought to duplicate nacre's strength and lightness in ceramic materials, but nacre's architecture varies at several length scales, from micrometers to nanometers, and replicating these differences with synthetic materials proved extremely difficult. So researchers took a more natural approach.

"We allow nature to guide the process. Seawater can freeze like a layered material, so why not use this property to cast ceramics that mimic nacre," says Antoni Tomsia of Berkeley Lab.

When seawater freezes, crystals of pure ice form layers, while impurities such as salt and microorganisms are removing from the forming ice and entrapped in channels between the ice crystals. The result is a layered structure that roughly resembles nacre's wafer-like construction.

Tomsia's team mimicked this process with a watery suspension of hydroxyapatite, the mineral component of bone. Then, they froze it. Just like the impurities in sea ice, the hydroxyapatite concentrates in the space between the ice crystals, creating layers and layers of nacre-like material.

The result is a porous scaffolding composed of hydroxyapatite (top image) that exhibits striking similarities to nacre's multilayered structure (bottom image) across a wide range of length scales. Like nacre, the surface of each layer is rough; helping the layers lock in place with whatever substance fills the space between them. And some bridges form between the layers, which are believed to increase fracture resistance.

"We are half a micron away from mimicking nature," Tomsia said. 

This research is detailed in the Jan. 27 issue of the journal Science.