The current results point to potential applications in autonomous mass transport systems carrying minuscule substances in which the newly developed surface and interface act as material mimicking functions in living organisms and can be used for new nanomachines.
Conceptual rendering of interface grafted with self-oscillating polymer incorporating gradient structure. The red region represents the metal catalyst Ru(bpy)3 in a reduced state, repelling water (hydrophobic/reduced membrane thickness), which enhances the BZ reaction, while the green region shows the oxidized state, mixing well with water (hydrophilic/increased membrane thickness). Regions in the interface undergo changes in their physical properties, structure, and form as the chemical reaction travels along the surface. In the current study, researchers observed unidirectional motion along the interface with the gradient structure. (Image: Ryo Yoshida)
In recent years, so-called soft interfaces, the surface and interface composed of soft materials such as polymers, have attracted a great amount of attention as functional materials exhibiting specific functions derived from their chemical and physical characteristics.
In particular, designing dynamic interfaces that respond to temperature, pH, light, and other stimuli and change their structure, form, and physical properties has become possible by introducing what are called stimuli-responsive polymers to the interface.
For the interfaces to demonstrate their function, the presence of external stimuli is a necessary condition. But, if scientists are able to design soft interfaces that are capable of autonomous function in the absence of external systems, like motor proteins in living systems, it would open the door to new applications such as nanomachines.
The research group led by Professor Ryo Yoshida at the Graduate School of Engineering, the University of Tokyo, developed a “self-oscillating” polymer that under certain conditions exhibits autonomous periodic motion (like a heartbeat) when inducing the Belousov-Zhabotinsky (BZ) reaction, which serves as an artificial model of metabolic circuits in living systems, in polymer materials.
The researchers developed a novel soft interface exhibiting autonomous motion by grafting the self-oscillating polymer onto the nanoscale surface of a substrate.
The group also succeeded in controlling the direction of the propagating chemical wave of the BZ reaction, which induces the mechanical motion of the grafted polymer chain, by introducing a nanoscale gradient structure in the thickness of the grafted polymer.
“Our study of polymer materials that repeatedly swell and collapse without any external stimuli is pioneering, innovative research,” says Yoshida. He continues, “The nonlinear dynamics of the polymer chain that generates particular cooperative phenomena with the oscillation is important. This is the attraction of the system we developed, which shares features with life phenomena.”
“The functional surface in this research exhibits unique functions, namely the expression of autonomous function under certain conditions, localized physical property changes, and their propagation, which are uncommon in other surfaces.” says graduate student Tsukuru Masuda. He continues, “We succeeded in controlling mobility by introducing a nanoscale gradient structure.”