Ants, though tiny, are known for their ability to lift things many times their own weight. Researchers have created a nano-sized device that acts similarly as a small muscle; while it weighs only 1.6 milligrams—or about the same as five poppy seeds—it can lift 265 milligrams, 165 times its own weight.
The strength of the device—called an “inverted-series-connected (ISC) biomorph actuation device” and built by researchers at Rutgers University-New Brunswick— comes from a process of inserting and removing ions between very thin sheets of the material molybdenum disulfide (MoS2), an inorganic crystalline mineral compound.
In this way, the device acts as a new type of actuator that can work in aqueous environments, converting electrical energy to mechanical energy, explained Manish Chhowalla, professor and associate chair of the Department of Materials Science and Engineering in the School of Engineering.
“Based on the principles of beam theory in mechanics of solids, we identified the back-to-back bimorph cantilever configuration as an effective configuration to amplify the strain generated by the electrochemical material into a large macroscopic mechanical displacement and force,” he told Design News.
By applying a small voltage, the team found that the device, although very small, could lift a weight much greater than itself, Chhowalla said.
“The actuation performance is attributed to the high electrical conductivity of the metallic 1T phase of MoS2 nanosheets, the elastic modulus of restacked MoS2 layers, and fast proton diffusion between the nanosheets--all of which are confined into a bimorph geometry promoting high generated displacement and force,” he said.
Shown are very thin sheets of molybdenum disulfide and a schematic and photos of working actuators developed using the material. Researchers at Rutgers University-New Brunswick developed the actuator—which is nanosized but can live 165 times its own weight. (Source: Muharrem Acerce, Rutgers University)
Molybdenum disulfide is a naturally occurring mineral commonly used as a solid-state lubricant in engines. Like graphite, it’s a layered material, with strong chemical bonding within thin layers but weak bonding in between the layers. Because of this composition, chemists can separate layers of the material into individual thin sheets—or nanosheets.
The nanosheets, which remain suspended in solvents such as water, can be assembled into stacks by putting the solution onto a flexible material and allowing the solvent to evaporate. Researchers can then use the restacked sheets as electrodes like the ones in typical batteries with high electrical conductivity to insert and remove ions, Chhowalla said. This, in turn, leads to the expansion and contraction of nanosheets, resulting in force on the surface and thus triggering the actuation of the flexible material.
The team—which also included Muharrem Acerce, a doctoral student in Chhowalla’s group who discovered the potential for actuation of the materials with the help of E. Koray Akdoğan, a teaching assistant professor in Department of Materials Science and Engineering--published a study on their work in the journal Nature. Acerce is the lead author on the paper.
Chhowalla said the device has a range of potential applications to provide actuation for robotics and devices that operate in aqueous environments, particularly in marine biology or medicine.
“As such, the device may find applications in catheter fabrication or marine robotics,” he said.
The team plans to continue its work to use the same principles to develop actuators that can move even bigger things, Chhowalla said. They also aim to break new ground by creating a device that can be used even in non-aqueous conditions to expand its potential for use, he added.
“For instance, it should be possible to incorporate a gel electrolyte to the active material, forming a nanocomposite actuator that is reminiscent to ionic polymer metal composites actuators,” Chhowalla said. “In so doing, the range of applications of the device can be extended to dry conditions.”
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.