Artificial cilia as autonomous nanoactuators: Design of a gradient self-oscillating polymer brush with controlled unidirectional motion

摘要

A gradient self-oscillating polymer brush surface with ordered, autonomous, and unidirectional ciliary motion has been designed. The self-oscillating polymer is a random copolymer composed of N-isopropylacrylamide and ruthenium tris(2,2′-bipyridine) [Ru(bpy)₃], which acts as a catalyst for an oscillating chemical reaction, the Belousov-Zhabotinsky reaction. The target polymer brush surface was designed to have a thickness gradient by using sacrificial-anode atom transfer radical polymerization. The gradient structure of the polymer brush was confirmed by x-ray photoelectron spectroscopy, atomic force microscopy, and ultraviolet-visible spectroscopy. These analyses revealed that the thickness of the polymer brush was in the range of several tens of nanometers, and the amount of Ru(bpy)₃ increased as the thickness increased. The gradient polymer brush induced a unidirectional propagation of the chemical wave from the region with small Ru(bpy)₃ amounts to the region with large Ru(bpy)₃ amounts. This spatiotemporal control of the ciliary motion would be useful in potential applications to functional surface such as autonomous mass transport systems.