Some of the smallest, most useful machines known to science are the biological molecules that keep living things living. The protein myosin drives the contraction and relaxation of muscle. Kinesin drags cellular cargo around the cell. Motor enzymes unwind, rewind, and maintain DNA, and bacteria use a molecular motor to rotate their whip-like flagella up to 100,000 times per minute, propelling them forward. These machines turn chemical energy into motion. They’re very efficient at their jobs.
The idea of using molecules to build minuscule machines that perform useful tasks dates back at least to a lecture given in 1959 by physicist Richard Feynman titled “There’s Plenty of Room at the Bottom.”* More recently, demonstrations of artificial molecular machines offer good reasons to think that such devices are feasible. Researchers have forged motors, shuttles, elevators, walkers, and pumps out of molecules, and powered them with electrical energy, chemical reactions, or light. Tiny motor by tiny motor, these demonstrations are inching toward future applications that could range from molecular electronics to artificial muscles.
...molecular machines are by nature floppy, like the soft matter that makes up the human body, whereas macroscopic machines are typically made from rigid materials such as metal. But it’s also a consequence of scale. Although the laws of physics don’t change in the nanoworld, their relative influences do. Concepts such as inertia and momentum—critical to the design of machines like cars and planes—become irrelevant. So does gravity, because molecules have such a small mass. Movement at the nanoscale is dominated instead by viscosity and Brownian motion, the random bumbling of individual molecules caused by thermal fluctuations...Katsonis calls this molecular environment a “Brownian storm.” In a 2007 article on the physics of nanoscale machines, physicist R. Dean Astumian at the University of Maine in Orono, ME, likened the challenges to swimming in molasses and walking in a hurricane.The article gives numerous examples of efforts to develop nanoscale motors driven by electrical energy, chemical energy, or light.