Molecular Robots Use Swarming Strategy to Transport Cargo

For the first time, researchers have shown that molecular robots can deliver cargo by utilizing a swarming strategy, realizing a transport efficiency that is five times more than that of solo robots.

Swarm robotics is a new domain, stimulated by the cooperative actions of living things, that concentrates on the creation of robots and their operation in swarms to achieve complicated tasks. A swarm is a methodical collective behavior of many individuals.

Macro-scale swarm robots have been built and used for a range of applications, like forming shapes, transporting and accumulating cargo, and constructing multifaceted structures.

A group of scientists, directed by Dr. Mousumi Akter and Associate Professor Akira Kakugo from the Faculty of Science at Hokkaido University, has been successful in engineering the world’s first functional micro-sized machines exploiting the benefits of swarming.

The study findings were reported in the journal Science Robotics. The group included Assistant Professor Daisuke Inoue, Kyushu University; Professor Henry Hess, Columbia University; Professor Hiroyuki Asanuma, Nagoya University; and Professor Akinori Kuzuya, Kansai University.

A swarm of collaborating robots has several advantages that are not found in solo robots — they can respond to risks, split a workload and even form intricate structures in response to variations in the surroundings.

Microrobots and micro- and nano-scale machines have limited practical applications because of their size; if they could cooperate in swarms, their potential uses would expand tremendously.

The team built around five million single molecular machines. These machines were made up of two biological parts: microtubules connected to DNA, which enabled them to swarm; and kinesin, which were actuators equipped to transport the microtubules.

The DNA was integrated with a light-sensitive compound known as azobenzene that worked as a sensor, enabling the control of swarming. When irradiated with visible light, variations in the azobenzene’s structure caused the DNA to develop double strands and led the microtubules to form swarms. Exposure to UV light caused the reversal of this process.

For the experiments, the cargo contained polystyrene beads of diameters ranging from micrometers to tens of micrometers. These beads were treated with azobenzene-connected DNA; thus, the cargo was loaded when irradiated with visible light and unloaded when irradiated with UV light. However, the azobenzene and DNA used in the molecular machines and the cargo were diverse, thus swarming could be regulated independently of cargo-loading.

Solo machines can load and transport polystyrene beads up to 3 μm in diameter, whereas swarms of machines could convey cargo as big as 30 μm in diameter. Moreover, a comparison of transport volume and transport distance revealed that the swarms were up to five times better at transport than the solo machines.

By showing that molecular machines can be engineered to swarm and collaborate to transport cargo with high competence, this study has paved the way for the application of microrobots in numerous fields.

In the near future, we expect to see microrobot swarms used in drug delivery, contaminant collection, molecular power generation devices, and micro-detection devices.

Akira Kakugo, Associate Professor, Faculty of Science, Hokkaido University

Different diameters of cargo loading and transport by single and swarm transporters. Scale bar: 20 µm. The diameter of the cargo (d) is mentioned on the top left of each movie. Here, the swarms could load and transport cargoes with diameters up to 20.0 µm, whereas the single transporters failed to load and transport cargoes with a diameter larger than 3.4 µm. The movie is played at 100 times the speed of the original. Video Credit: Mousumi Akter, et al. Science Robotics. April 20, 2022.

Journal Reference:

Akter, M., et al. (2022) Cooperative cargo transportation by a swarm of molecular machines. Science Robotics. doi.org/10.1126/scirobotics.abm0677.