Biomineralization: Micelles in a crystal.

to fit the nucleus of the cubic polymorph (Fig. 2b). Conversely, the nucleus of a triclinic crystal would be a poor fit to pores with right-angled corners because the crystal would need to incorporate either strain or defects. As a consequence, right-angled pores should selectively favour nucleation of the cubic polymorph. Another application of nanopatterned surfaces may be found in surface-induced ice nucleation. On the basis of work on rough surfaces, such as those of typical atmospheric microparticles, it has been assumed that water droplets in contact with a surface start to freeze from the edge of the droplet — that is, along the contact line. However, recent experiments on very smooth surfaces have indicated that nucleation occurs away from the edge of the droplet 7. Lithography-produced surfaces such as those of Diao and colleagues 1 may offer a way to resolve this apparent contradiction. S ynthetic efforts have identified a growing number of classes of organic (macro)molecular impurities — 1-nm dye molecules 1 , 10–20-nm polymeric gel fibres 2 and even 200-nm colloidal particles 3,4 — that can be trapped within inorganic crystalline hosts such as calcite single crystals without significantly disrupting their crystalline lattices. Inclusion of an organic phase is believed to play a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals 5–7 and to have both increased hardness and fracture toughness relative to their pure, geological counterparts. However, the growth mechanisms of the single-crystal composites, the distribution of the organic phase and its effect on the resulting improved mechanical properties are poorly understood. Writing in Nature Materials 8 , Kim et al. now report the synthesis of single crystals of calcite containing a considerable 13 wt% (approximately 30 vol%) of 20-nm anionic diblock copolymer micelles that have structural and mechanical properties analogous to those of natural biominerals (Fig. 1). The system should be an excellent model for further property characterization and for the study of growth mechanisms in biogenic minerals. Using a variety of techniques, including X-ray diffraction and infrared spectroscopy, the researchers demonstrated that the incorporated micelles lead to an increase in the level of atomic disorder at the inorganic–organic interface and to a compressive-strain gradient in the calcite lattice. High-resolution transmission electron microscopy imaging of thin slices of the crystals revealed further details about their internal structure, in particular a preferred orientation of …