Inspired by the Mimosa plant’s folding response to touch, researchers have engineered a material that folds when in contact with water.
Many of us have fond childhood memories of poking the ubiquitous Mimosa pudica plant’s leaflets, then exclaiming in delight when they fold up at even the slightest touch. This spontaneous, protective motion, which is more complicated than it looks, is triggered by a cascade of reactions and pressure waves. Now, researchers from Hong Kong and Australia have drawn inspiration from the ever-so-sensitive plant to develop self-organizing soft materials that fold themselves into predetermined shapes when wet.
The study is published in the journal Science Advances.
The Mimosa plant responds to touch by undergoing self assembly, which is how many organisms in nature adapt to their environments. One such example is the crystallization-driven formation of seashells. “This is a bit like your skin reacting automatically to cold temperatures,” corresponding author Associate Professor Antonio Tricoli from Australian National University told Asian Scientist Magazine. “Imagine a material that becomes waterproof if it gets even slightly wet.”
Led by Tricoli and Associate Professor Wang Zuankai from the City University of Hong Kong, the research team engineered a unique material made out of a stack of multi-functional layers, some hydrophilic and some hydrophobic. The material incorporates Janus nanoparticles, named after the two-faced god Janus, as they have two distinct types of chemistry on the same particle. In response to contact with a water droplet, the engineered material efficiently transforms surface energy into directional kinetic and elastic energies that propel its self-assembly into a quasi-cylindrical ‘straw’ shape.