Energy lab's microscopic robots assemble selves, can move larger objects

Scientists at the Energy Department’s Argonne National Laboratories have developed microscopic, self-assembling robots that can manipulate other tiny objects. The experimental technology has the potential to allow researchers, and possibly industry, to build structures and devices at the microscopic scale.

The tiny robots were an offshoot of research into new types of materials by DOE physicists Alexey Snezhko and Igor Aronson. The goal of the scientists’ work is to develop structures that behave like biological systems, the two said in an interview.

Snezhko and Aronson have developed self-assembling structures one millimeter wide that can be controlled by magnetic fields, according to a posting on Argonne's website. Consisting of microscopic particles of nickel or iron, the structures are suspended in the interface between a solution of water and silicon oil. When an alternating magnetic field is activated, the particles assemble into flower-like shapes the scientists call “asters.”

Applying a second, small magnetic field allows the scientists to move the asters and to open and close the structures like tiny jaws. This allows the tiny robots to pick up, move and release objects such as glass or plastic beads.

The researchers also discovered two types of asters, which rotate or swim in opposite directions. By grouping several of these counter-rotating asters together in a circle, Snezhko and Aronson were able to use them to draw small, free-floating particles into the center of the circle and keep them there.

Manipulating very small objects is a challenge for robotics. The asters are in a size category between mechanical micromanipulators and laser-powered manipulation. Gripping and manipulating very small objects without damaging them has always been a problem with mechanical systems, Aronson said. The asters exert more force than lasers, but are more delicate than mechanical grips, which opens the potential for a variety of applications in micro-scale engineering and research.

But to get there, more must be understood about how objects assemble and function at this scale. The Argonne research has been ongoing for four years. It began with the scientists studying the interaction of molecules and surfaces and interfaces. Snezhko and Aronson’s first discovery was that in an oil and water medium, nickel and iron particles will self-assemble into long strands, or “snakes.” They then sought to scale down the size of the snakes, which led to the development of the asters.

The research is multi-purposed. Besides working with the asters, the scientists have developed algorithms and computer models to predict what happens in the interface. “We have a pretty good idea of what’s going on now,” Aronson said.

The robots represent an important stage between the mesoscale (multi-molecular) and the molecular level. The niche for microscopic robots is very diverse, Aronson said. Among the applications that the Argonne researchers have studied are activities that take place in the interface area of oily substructures, such as the zone between oil and water. In these areas, microrobots would be useful by being able to apply and remove substances without destroying the interface.

Another advantage is that the microrobots can be manufactured and controlled autonomously. It is possible to develop a computer program to control the magnetic coils that manipulate the robots.

The scientists are also studying how to provide individual particles in the asters with more functionality. One consideration is to use microscopic rod structures because parts of the rods can be assigned different functions, such as being able to recognize certain particles. The micro robots currently cannot distinguish between a glass bead and a plastic one. One of the scientists’ goals is to make the robots able to distinguish this difference.

Snezhko and Aronson are now trying to modify and control the functionality of particles when their structures change. The goal of the current work is to understand what happens and what works in these combinations. “We’re trying to find the basic principles of how to make them and what functionality they will have,” Aronson said.

Fully understanding how the micro robots operate in two-dimensional systems will allow researchers to move on to more complex, three-dimensional applications. This would open the possibility of technologies capable of building new types of electronics or other structures at the molecular level. “But in order to move there, we need to understand what happens in two dimensional systems,” Snezhko said.

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