Jean-Pierre Sauvage, at the University of Strasbourg, succeeds in 1983 in synthesizing for the first time a "catenane" — two ring-shaped molecules interlocked with each other, like the links of a chain, but joined only by their mechanically interlocked topology, with no covalent chemical bond between them — demonstrating that it is possible to build molecular structures whose parts can move relative to one another in a controlled way, like mechanical parts at molecular scale. Fraser Stoddart develops in 1991 a "rotaxane", a structure in which a ring-shaped molecule can slide freely along a linear molecular axle, and designs methods to control the movement of that ring from one end of the axle to the other by applying external chemical or electrical stimuli, laying the groundwork for building functional molecular switches and motors. Bernard Feringa, at the University of Groningen, builds in 1999 the first true rotary molecular motor: a molecule designed to rotate continuously in a single, controlled direction when illuminated with light, rather than moving randomly through thermal agitation as most molecules do. Feringa would go on to build a four-wheeled "nanocar" capable of moving across a surface powered by these molecular motors. Together, these developments found the field of molecular machines, with potential applications in controlled drug release, smart materials, and nanotechnology.