Proceedings Article | 5 April 2007
Proc. SPIE. 6524, Electroactive Polymer Actuators and Devices (EAPAD) 2007
KEYWORDS: Actuators, Gold, Molecules, Biomimetics, Integration, Nanoelectromechanical systems, Molecular machines, Molecular self-assembly, Molecular assembly, Oxidation
Artificial molecular motors have recently attracted considerable interest from the nanoscience and nanoengineering
community. These molecular-scale systems utilize a 'bottom-up' technology centered around the design and
manipulation of molecular assemblies, and are potentially capable of delivering efficient actuations at dramatically
reduced length scales when compared to traditional microscale actuators. When stimulated by light, electricity, or
chemical reagents, a group of artificial molecular motors called bistable rotaxanes - which are composed of mutually recognizable
and intercommunicating ring and dumbbell-shaped components - experience relative internal motions of
their components just like the moving parts of macroscopic machines.
Bistable rotaxanes' ability to precisely and cooperatively control mechanical motions at the molecular level reveals the
potential of engineering systems that operate with the same elegance, efficiency, and complexity as biological motors
function within the human body. We are in a process of developing a new class of bistable rotaxane-based
electroactive/photoactive biomimetic muscles with unprecedented performance (strain: 40-60%, operating frequency: up
to 1 MHz, energy density: ~50 J/cm<sup>3</sup>, multi-stimuli: chemical, electricity, light). As a substantial step towards this longterm
objective, we have proven, for the first time, that rotaxanes are mechanically switchable in condensed phases on
solid substrates. We have further developed a rotaxane-powered microcantilever actuator utilizing an integrated
approach that combines "bottom-up" assembly of molecular functionality with "top-down" micro/nano fabrication. By
harnessing the nanoscale mechanical motion from artificial molecular machines and eliciting a nanomechanical response
in a microscale device, this system mimics natural skeletal muscle and provides a key component for the development of
nanoelectromechanical system (NEMS).
