A phenomenon that interested Charles Darwin has led to bioengineers and chemists working together.

Mingjun Zhang, a professor of bioengineering and robotics at the University of Tennessee, was playing with his son one afternoon when he noticed some ivy climbing over the fence in his backyard. Curious about the climbing mechanism, and the yellowish material secreted by the ivy, Zhang pored through the literature and found just one publication on the subject — a book by none other than Charles Darwin in 1876. He then got three former colleagues from Agilent Technologies interested in the problem and they decided to look at ivy in more detail.

The team started by allowing ivy branches to climb up silicon and mica wafers in their lab for a week. Harry Prest and Steve Fisher, who are chemists at Agilent Labs in California, then isolated and analysed the yellow secretion using chromatography, while Maozi Liu imaged it with an atomic force microscope. To their surprise, they found that the ivy secreted a large number of nanoparticles with diameters of about 70 nm. Chemical analysis revealed the presence of a large number of different compounds, but Zhang and co-workers were able to show that oxygen, nitrogen and sulphur — elements widely known for their ability to form hydrogen bonds — featured strongly (Nano Lett. doi:10.1021/nl0725704; 2008). The team concluded that hydrogen bonding and weak adhesion (due to the presence of tiny 'fingers' in the rootlets of the ivy) made it possible for the ivy to climb. Besides providing inspiration for Zhang in his work as an engineer, the work might also lead to new ways of making eco-friendly nanoparticles.

“It is not difficult to start an interdisciplinary collaboration because most people will be interested,” says Zhang. “The problem is that most of the preliminary work is not funded, so we must work around our main research schedule and consider it an investment.”