Due to their ability to be remotely controlled, speedy nano-robots can exhibit promising performance in major industrial applications, from cleaning up the environment to transporting pharmaceutical agents to a desired location in the body.
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Professor Daniel Schwartz and his team at the University of Colorado have discovered minuscule, self-propelled particles called 'nanoswimmers' with a diameter of 250 nm that can escape mazes 20 times faster than passive debris; the properties that are incredibly beneficial in various applications (Simpkins, 2021).
What are Nanoswimmers?
The tiny spherical particles are composed of polymer or silica with two halves, each with distinctive properties. Their unusual feature earned them their alias 'Janus particle', named after a two-faced god in Roman mythology. Although Janus particles were first introduced in 1989 (Casagrande, et al., 1989) while describing a glass particle with hydrophobic and hydrophilic faces, the nanoswimmers only came to the attention approximately two decades ago, as the research community understood their potential applications.
At that time, the lack of equipment and incompetent modeling setup limited any advancement. Now, with enough research and study on the subject, researchers believe that those nanoswimmers have a catalytic surface on one of the hemispheres that encourages chemical reactions. As a result, the entire particle takes energy from its environment and causes it to move independently, and that ability is known as self-propulsion (Bustos, 2021).
Nanoswimmers as the Nano-Robots
The most distinctive feature of these nanoswimmers is their ability to be self-propelled, which means they can transduce free energy from their surroundings and convert it into motion that helps them move in a particular direction. In 2017, scientists at the Max Planck Institute for Intelligent Systems presented the world's smallest jet propulsion system, with a tube diameter of 220 nm (Max Plank Institute for Intelligent Systems, 2017). With it, the research group announced two new approaches for constructing propulsion systems for tiny floating bodies.
First, generated by bubbles, which are oscillated by ultrasound, and second, due to enzymatic reaction that causes a current (Max Planck Institute, 2017). Typically, the passive particles, known as Brownian particles, randomly circulate in Brownian motion.
Professor Schwartz's team converted those passive Brownian particles into self-propelled nanoswimmers that can circulate through a porous maze. Due to the property of self-propulsion, these nanoswimmers conceived additional strength needed to bypass through the exit holes within the maze.
Initially, the team had difficulty observing those tiny nanoswimmers within complex interconnected areas. To overcome this, Haichao Wu, Professor Schwartz's graduate student, created a platform by using refractive index liquid in the porous medium that affected the speed of light traveling through a material. This made the maze invisible, easing tracking of 3D trajectories of the particles and creating visual representations, which enormously helped motion observation (Montalbano, 2021).
Nanoswimmers Competence in Clean-Up and Drug Delivery Applications
A current Horizon2020 project, SONOBOTS, led by a team at the ETH Zurich, has developed nano-robots showing promising development towards cancer and blood clots treatment. The team used ultrasound to guide the nano-sized robots diligently to the disease site, allowing them to deliver drugs effectively and efficiently without impacting the red blood cells.
Researchers also demonstrated the properties of the nano-robots as nanoswimmers. Here, they were visualized by guiding air bubbles trapped within a polymer shell alongside an imaging chemical (European Comission, 2019). Another interesting consideration is the self-healing property of these nanoswimmers when they are taken out of the lab to harsh real-life environments and are expected to suffer damage.
Recently, scientists at the University of California have invented 2 cm long fish-shaped robots made up of a conductive bottom layer and a hydrophobic middle layer covered with strong, magnetic microparticles. The tail contained platinum that can form oxygen bubbles during reaction with hydrogen peroxide fuel, driving robots forward through fluids (Karshalev, et al., 2021).
The robots moved around the edge of the dish filled with hydrogen peroxide fuel, and no matter how many times and where it was cut, the robots could heal themselves through a strong magnetic interaction. They can execute crucial operations with this ability, such as cleaning up the environment and delivering drugs to targeted tissues.
Future of Nano-Robots
The nanoswimmers have great potential to be the next-generation nano-robots that can positively contribute to numerous industries. In the medical field, they can facilitate targeted drug delivery and assist effective treatment while reducing the severity of damage caused by chronic diseases.
As for clean-up technology, researchers have already noticed the usefulness of nanoswimmers' motion as a positive side effect to clean the environment from unwanted contaminants as they displace themselves. Once it is clear how a more significant population of nanoswimmers' behave within defined areas, they could be an attractive option at escaping cavities inside maze-like environments to clean up soil, enhance water filtration, or even supply drugs to cells and tissues.
The self-healing strategy of nanoswimmers could help in the sustainable development of the miniaturization of the robots that opens the door to many more applications.
References and Further Reading
Bustos Mark (2021) The Janus Particle: How These Two-Faced 'Nanoswimmers' Could Improve Drug Delivery, Waste Recovery [Online] The Science Times. Available at: https://www.sciencetimes.com/articles/32010/20210630/janus-particle-two-faced-nanoswimmers-improve-drug-delivery-waste-recovery.htm (Accessed on 28 July 2021).
Casagrande C. et al. (1989) "Janus Beads": Realization and Behaviour at Water/Oil Interfaces. EPL (Europhysics Letter). 10.1209/0295-5075/9/3/011.
European Comission (2019) Acousto-Magnetic Micro/Nanorobots for Biomedical Applications [Online] European Comission- Cordis. Available at: https://cordis.europa.eu/project/id/853309 (Accessed on 28 July 2021).
Karshalev Emil. et al. (2021) Swimmers Heal on the Move Following Catastrophic Damage. Nano Letters. 10.1021/acs.nanolett.0c05061.
Max Planck Institute (2017) New drive for tiny vessels [Online] Max Planck Institute. Available at: https://www.mpg.de/11051373/microrobot-nanorobot-propulsion (Accessed on 28 July 2021).
Max Plank Institute for Intelligent Systems (2017) World's smallest jet engine invented in Stuttgart [Online] Max Plank Institute for Intelligent Systems. Available at: https://www.is.mpg.de/news/world-s-smallest-jet-engine-invented-in-stuttgart (Accessed on 28 July 2021).
Montalbano Elizabeth (2021) Want Tiny Particles That can Move Through Tight Spots? Meet the Nanoswimmers [Online] DesignNews. Available at: https://www.designnews.com/materials/want-tiny-particles-can-move-through-tight-spots-meet-nanoswimmers (Accessed on 28 July 2021).
Simpkins Kelsey (2021) Speedy nano-robots could someday clean up soil and water, deliver drugs [Online] ScienceDaily. Available at: https://www.sciencedaily.com/releases/2021/06/210629144307.htm (Accessed on 28 July 2021).