Beachcombers who gather seashells and corals know just how good nature is at building intricate structures. Chemists have rarely achieved similar prowess. But by mimicking how the environment shapes biological materials, a team at Harvard University has sculpted tiny, beautiful flowerlike structures (Science 2013, DOI: 10.1126/science.1234621). In the future, the work might be adapted to craft patterned surfaces for catalysis and other applications.
In nature, developing shells can change patterns abruptly—from dots to wavy lines, for instance. Changes in temperature, pH, or other factors affect patterns while the shell grows, says postdoc Wim L. Noorduin, first author of the new study. So Noorduin, Alison Grinthal, Lakshminarayanan Mahadevan, and Joanna Aizenberg set out to apply this concept in the lab.
Their setup was deceptively simple: a glass microscope slide, a solution of barium chloride and sodium silicate in water, and a beaker covered with a petri dish. The two compounds aren’t used by living things, but others have shown they can generate lifelike shapes. Two different minerals—SiO2 and BaCO3—precipitate from that solution onto the slide. By moving slides from one pH or temperature condition to another as the minerals grew on them, the team sculpted the substances into flowers. Some conditions led to stemlike spirals, others to flowerlike bulbs.
Pupa Gilbert, who studies biominerals at the University of Wisconsin, Madison, marvels at their results. “They just open and close the beaker,” adding pulses of CO2 from air, she says. “Yet the structures produced are stupendously complex.”
The method doesn’t make structures uniform enough to use as catalytic materials, Noorduin says. The team is exploring microfluidics to attain that reproducibility. For now, Noorduin enjoys gazing at his handiwork under an electron microscope. “It’s amazing—like diving in the ocean,” he says. “You can really get lost.”