Artificial muscle-like function from hierarchical supramolecular assembly of photoresponsive molecular motors

Abstract

A striking feature of living systems is their ability to produce motility by amplification of collective molecular motion from the nanoscale up to macroscopic dimensions. Some of nature's protein motors, such as myosin in muscle tissue, consist of a hierarchical supramolecular assembly of very large proteins, in which mechanical stress induces a coordinated movement. However, artificial molecular muscles have often relied on covalent polymer-based actuators. Here, we describe the macroscopic contractile muscle-like motion of a supramolecular system (comprising 95% water) formed by the hierarchical self-assembly of a photoresponsive amphiphilic molecular motor. The molecular motor first assembles into nanofibres, which further assemble into aligned bundles that make up centimetre-long strings. Irradiation induces rotary motion of the molecular motors, and propagation and accumulation of this motion lead to contraction of the fibres towards the light source. This system supports large-amplitude motion, fast response, precise control over shape, as well as weight-lifting experiments in water and air. A centimetre-long string formed by the hierarchical self-assembly of a photoresponsive amphiphilic molecular motor — composed of 95 wt% of water — undergoes muscle-like contraction. Under irradiation, rotary motion at the molecular level is amplified through non-covalent interactions to sustain a fast macroscopic mechanical motion of large amplitude.