Controlled graphene fracturing for mass production of cell sized robots

Blood Cell sized robots could be mass-produced using a new method developed by researchers at MIT.

Nature Materials – Autoperforation of 2D materials for generating two-terminal memristive Janus particles

Syncells (short for synthetic cells), might eventually be used to monitor conditions inside an oil or gas pipeline or to search out disease while floating through the bloodstream.

They have developed a way to control the natural fracturing process of atomically-thin, brittle materials, directing the fracture lines so that they produce miniscule pockets of a predictable size and shape. Embedded inside these pockets are electronic circuits and materials that can collect, record, and output data.

The process is called autoperforation.

They use a two-dimensional form of carbon called graphene, which forms the outer structure of the tiny syncells. One layer of the material is laid down on a surface, then tiny dots of a polymer material, containing the electronics for the devices, are deposited by a sophisticated laboratory version of an inkjet printer. Then, a second layer of graphene is laid on top.

Graphene is actually brittle.

The team figured out that they could use brittleness for their advantage.

They control the fracturing process so that rather than generating random shards of material, like the remains of a broken window, it produces pieces of uniform shape and size.

Cell-like robots

Ranging in size from that of a human red blood cell, about 10 micrometers across, up to about 10 times that size, these tiny objects “start to look and behave like a living biological cell. In fact, under a microscope, you could probably convince most people that it is a cell,” Strano says.

This work follows up on earlier research by Strano and his students on developing syncells that could gather information about the chemistry or other properties of their surroundings using sensors on their surface, and store the information for later retrieval, for example injecting a swarm of such particles in one end of a pipeline and retrieving them at the other to gain data about conditions inside it. While the new syncells do not yet have as many capabilities as the earlier ones, those were assembled individually, whereas this work demonstrates a way of easily mass-producing such devices.

Apart from the syncells’ potential uses for industrial or biomedical monitoring, the way the tiny devices are made is itself an innovation with great potential, according to Albert Liu. “This general procedure of using controlled fracture as a production method can be extended across many length scales,” he says. “[It could potentially be used with] essentially any 2-D materials of choice, in principle allowing future researchers to tailor these atomically thin surfaces into any desired shape or form for applications in other disciplines.”

This is, Albert Liu says, “one of the only ways available right now to produce stand-alone integrated microelectronics on a large scale” that can function as independent, free-floating devices. Depending on the nature of the electronics inside, the devices could be provided with capabilities for movement, detection of various chemicals or other parameters, and memory storage.

There are a wide range of potential new applications for such cell-sized robotic devices, says Strano, who details many such possible uses in a book he co-authored with Shawn Walsh, an expert at Army Research Laboratories, on the subject, called “Robotic Systems and Autonomous Platforms,” which is being published this month by Elsevier Press.

As a demonstration, the team “wrote” the letters M, I, and T into a memory array within a syncell, which stores the information as varying levels of electrical conductivity. This information can then be “read” using an electrical probe, showing that the material can function as a form of electronic memory into which data can be written, read, and erased at will. It can also retain the data without the need for power, allowing information to be collected at a later time. The researchers have demonstrated that the particles are stable over a period of months even when floating around in water, which is a harsh solvent for electronics, according to Strano.

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