Scientists have uncovered how heavy, motorized objects climb steep slopes — a newly discovered mechanism that also mimics how rock climbers navigate inclines. The finding stems from a series of experiments in which motorized objects were placed in liquid and then moved up tilted surfaces. These “micro-swimmers” are about 20 times heavier than the fluid they swim in but they were able to climb almost vertical steep slopes.
Gravitaxis — directional movement in response to gravity — is a vital phenomenon not only in engineering but also in medicine and pharmaceutical development. It explains, in part, how bacteria move through the body and provides insights into ways to create more effective drug-delivery mechanisms.
The motorized swimmers, or nanorods, are roughly 1/40th the width of a strand of human hair and were tasked with moving up an inclined surface while immersed in a liquid solution within a walled container. The swimmers were composed of two types of metal: gold and rhodium as well as gold and platinum — a make-up that gave them unbalanced densities given the varying weights of these metals. The swimmers’ composition, liquid environment, and juxtaposition of surfaces enabled them to move upward, despite their significant weight.
The motors reorient themselves upward against gravity thanks to their density imbalance, much like a seesaw reorients itself in response to the movement and weight of its riders. A hydrodynamic effect amplifies this movement — swimming next to a wall yields a bigger torque in repositioning the motors’ bodies upwards. Future motors will be designed to reach targeted locations and to perform designated functions.