Tomography reveals all

Credit: © 2009 AAAS

Biominerals, such as sea urchin spines or mollusc shells, are sources of inspiration and envy to materials researchers. These inorganic–organic hybrids have exceptional mechanical properties, such as strength, thanks to the intricate way the two components are arranged. Although methods of investigating how the biopolymers are distributed through the inorganic crystal lattice have been developed, none is completely satisfactory and they yield little information about the interface between polymer and crystal.

Now, Lara Estroff and colleagues from Cornell University have used electron tomography to image, in three dimensions, the internal structure of calcite single crystals that incorporate agarose polymers (pictured; Science 326, 1244–1247; 2009). Despite the fact that the inorganic phase contained this organic network, it was still single-crystalline in nature. Estroff and co-workers found that the internal surfaces that formed the inorganic–organic interface were a mixture of high- and low-energy facets.

The polymer network could be removed after heating the crystals to 400 °C for an hour, which left discrete cavities, but still a single crystal.