Microscopic cubes trap cells with magnetic actuation

By using magnetic energy from their environment, the so-called “microbot origami” structures have the potential to be used as cell characterisation tools, fluid micromixers, and components of artificial muscles and soft biomimetic devices.

The findings, led by researchers at North Carolina State University and Duke University, are published in Science Advances.

“This research is about a topic of current interest – active particles which take energy from their environment and convert it into directional movement,” said Orlin Velev, INVISTA Professor of Chemical and Biomolecular Engineering at NC State and co-corresponding author of the paper.

To create the microbot origami, the researchers started with microscopic polymer cubes that are metallic on one side. Depending on their positioning, the cubes can be assembled in many different ways.

“Since they are magnetised and interacting, the cubes store energy,” Velev said in a statement.

Tiny particles in the shape of cubes attach together in sequences where they face in different directions to form clusters that are opened by applying a magnetic field, then closed by turning the magnetic field off.

“They close because they are releasing the stored magnetic energy,” said Velev. “Thus, you inject internal energy every time you open the microclusters and release it when they close.”

According to NC State, the researchers then gave the tiny cluster a specific task of capturing a yeast cell. The microbot formed into a boxy shape and, through its opening and closing motions, “swam” to surround the yeast cell. The researchers then turned off the magnetic field that controlled the folding of the microbot to capture the yeast cell, moved it and finally released it.

“We’ve shown here a prototype of self-folding microbot,” Velev said, “that can be used as a microtool to probe the response of specific types of cells, like cancer cells, for instance.”

“Previously reported microrobotic structures have been limited to performing simple tasks such as pushing and penetrating objects due to their rigid bodies. The ability to remotely control the dynamic reconfiguration of our microbot creates a new ‘toolbox’ for manipulating microscale objects and interacting with its microenvironment,” said Koohee Han, a Ph.D. candidate at NC State and first author of the paper.

“As the microbot folds, it can compress liquids or solids and you can use it as a tool to measure bulk mechanical properties, like stiffness,” said Wyatt Shields, a postdoctoral researcher at Duke University and NC State University who co-authored the paper. “In some ways, it is a new metrological tool for gauging elasticity at the microscopic level.”

The authors say that the design of microbot origami mimics nature. “The cube sequence programs the shapes of the folding microbots. Proteins work in the same way,” Shields said. “The sequence of amino acids in a protein will determine how it folds, just as the sequence of cubes in our microbot will determine how it folds.”

Velev said that future work will concentrate on making the particles move on their own, rather than steering them with magnetic fields.

The paper is co-authored by Nidhi Diwakar, Research Triangle Materials Research Science and Engineering Center, North Carolina; Bhuvnesh Bharti, Louisiana State University; and Gabriel P. López, University of New Mexico.