Credit: © 2009 Wiley

Many chemists are aware of the 'chemical garden' demonstration, in which structures that look similar to plants grow from solution. The growths are millimetre-scale hollow tubes that form through a precipitation reaction, which occurs on the addition of crystals of soluble metal salts to solutions of anions such as silicates, borates or carbonates. Now, Oliver Steinbock and colleagues at Florida State University have modified1 this approach to gain greater control and understanding of the tubular growths, which could eventually lead to applications in microfluidic devices.

They use agarose beads that are loaded with copper sulfate solution as reactant vessels that seed the precipitation growth of micrometre-scale tubules (orange in the picture). The beads are exposed to a sodium silicate solution and microtubules grow out from a bubble on their surface. The bubble is attached to the end of the growing microtubule and moves away from the bead as the tube grows. Nodular objects (shown in pink) that have a completely different morphology to the tubules are also seen to grow from the beads.

During microtubule growth, the team also saw examples of the bead moving rather than the bubble, showing that the system could be exploited to harness chemical energy to perform motion.