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Making tiny complex controlled shapes

The active growth sides on the structures can be used to control the nucleation of a new structure on an already existing one to form hierarchically complex architectures. Here we nucleated a red coral on top of a green spiral.
[Image courtesy of Wim Noorduin]

A new study in the May 17 issue of Science reveals how to make minerals assemble themselves into complex but controlled architectures.

The findings pave the way toward developing complex architectures that are useful in optical materials and catalyst applications. Coral reefs are remarkably diverse complex architectures that can be seen by the eye, while invisible microorganisms like acantharea build intricate mineral skeletons.

Wim Noorduin at Harvard University and colleagues were interested in getting to the root of what kind of physical and chemical principles allow for such precise control.

For example, shells on the beach that have a spotted pattern may abruptly switch to wavy lines. This switch can result from changes in ocean temperature, pH, or carbon dioxide levels that alter the growth process.

Similarly, Noorduin and colleagues found that self-assembling structures in the lab are very sensitive to environmental changes like temperature, carbon dioxide concentration and acidity. The authors performed a reaction by dissolving two chemical compounds in water in a simple glass beaker.

By manipulating the conditions of the reaction mixture, one of two competing reactions would dominate, leading to a large diversity of shapes ranging from vases and stems to coral-like shapes and spirals.

The results show that it's possible to design and build all kinds of extremely complex structures with intricate patterns controlled all the way down to the molecular level.