Multi-compartment membranes for multicellular robots: Everyone needs a body

April 14, 2023

(Nanowerk News) We usually think of robots as metal objects, filled with motors and circuits. But the field of molecular robotics is starting to change that. Like the formation of complex living organisms, molecular robots derive their form and function from assembled molecules stored in a single unit, namely the body. Yet the creation of this body on a microscopic level was an engineering nightmare. Now, the Tohoku University team has come up with a simple solution. Schematic diagram of how droplets extracted from a sponge self-assemble into multicellular body structures. (Image: Richard Archer / Shin-Ichiro Nomura)

The typical image of a robot consists of a motor and circuits, encased in metal. But the field of molecular robotics, pioneered in Japan, is starting to change that.

Just like how complex living organisms are formed, molecular robots derive form and function from the molecules they are assembled with. Such robots could have important applications, such as being used to treat and diagnose diseases in vivo.

The first challenge in building a molecular robot is the most basic need of any organism: a body, which holds everything together. But manufacturing complex structures, especially at the microscopic level, has proven to be an engineering nightmare, and many limitations to what is possible today.

To solve this problem, a research team at Tohoku University has developed a simple method to create molecular robots from multi-cell-like artificial objects using molecules that can organize themselves into desired shapes.

The team, including Associate Professor Shin-ichiro Nomura and postdoctoral researcher Richard Archer of the Department of Robotics at the Graduate School of Engineering, recently reported their breakthrough in an American Chemical Society publication, Langmuir (“Scalable Synthesis of Planar Macroscopic Lipid-Based Multi-Compartmental Structures”).

“Our work demonstrates a simple self-assembly technique using phospholipids and synthetic surfactants coated with a hydrophobic silicone sponge,” said Archer.

When Nomura and his colleagues introduced water into a lipid-coated sponge, the hydrophilic and hydrophobic forces allowed the lipids and surfactants to self-assemble, allowing the water to seep through. The sponge is then placed into the oil, spontaneously forming stable, micron-sized water droplets. as water is removed from the solid support. When pipetted at the surface of the water, these droplets rapidly aggregate into larger, planar macroscopic structures, such as bricks that fit together to form a wall.

“The technique we developed can easily build centimeter-sized structures from assembling micron-sized compartments and is capable of using more than one type of droplet,” added Archer. “By using different sponges with water containing different solutes, and forming different types of droplets, the droplets can combine to form heterogeneous structures. This modular approach to assembly unleashes nearly limitless possibilities.”

Teams can also turn these objects into motion-induced controllable devices. To do so, they inserted magnetic nanoparticles into the hydrophobic walls of the multi-compartment structure. Archer says this multi-compartment approach to robot design will enable flexible, modular designs with multiple functions and can redefine the robots we envision. “Future work here will bring us closer to a new generation of robots that are assembled by molecules rather than forged in steel and using functional chemicals instead of silicon chips and motors.”

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