How to mass-produce robots at the size of a cell

Tiny robots, no bigger than one cell, could be mass-produced thanks to a new method developed by MIT researchers. Microscopic devices, which the team calls "syncells" (short for "synthetic cells"), could eventually be used to monitor conditions inside a pipeline or to search for a disease by floating in the blood. .

The key to producing such tiny devices in large quantities is a method developed by the team to control the natural fracturing process of atomic-sized fragile materials, by directing fracture lines to produce tiny pockets of predictable size and shape. These circuits contain electronic circuits and materials capable of collecting, recording and outputting data.

The new process, called "autoperforation", is described in an article published today in the journal Nature Materialsby Michael Strano, MIT professor, Pdtwei Liu, postdoc, Albert Liu, graduate student, and eight others at MIT.

The system uses a two-dimensional form of carbon called graphene, which forms the outer structure of the tiny syncellules. A layer of the material is deposited on a surface, then tiny points of a polymeric material, containing the electronic components of the devices, are deposited by a sophisticated laboratory version of an ink jet printer . Then a second layer of graphene is deposited on top.

Controlled fracturing

People think that graphene, an ultrathin but extremely resistant material, is a "floppy disk", but is actually fragile, says Strano. But instead of considering this fragility as a problem, the team understood that it could be used to their advantage.

"We discovered that you could use fragility," says Strano, professor of chemical engineering at Carbon P. Dubbs at MIT. "It's counter-intuitive.Before this work, if you've ever said that you could fracture a material to control its shape at the nanoscale, I would have been incredulous."

But the new system does just that. It controls the fracturing process so that, rather than generating random fragments of material, such as the remains of a broken window, it produces parts of uniform shape and size. "What we have discovered is that you can impose a deformation field to guide the fracture, and that you can use it for controlled manufacturing," says Strano.

When the top layer of graphene is placed on the series of polymer dots, which form round pillars, the places where the graphene drapes over the rounded edges of the pillars form lines of high stress in the material. As Albert Liu describes it, "Imagine a slowly falling web on the surface of a circular table.You can very easily visualize the developing circular deformation towards the edges of the table, which is very similar to what happens when a flat sheet of graphene bends around these printed polymer pillars ".

As a result, fractures are concentrated along these boundaries, says Strano. "And then something quite amazing happens: the graphene breaks completely, but the fracture will be guided to the periphery of the pillar." The result is a clean, round piece of graphene that seems to have been cut cleanly by a microscopic drill.

Since there are two layers of graphene, above and below the polymer pillars, the two resulting discs adhere to their edges to form something that looks like a tiny pocket for pita bread, with the polymer sealed. inside. "And the advantage here is that it's essentially a single step," as opposed to many of the complex clean-room steps that are required for other processes to try to make microscopic robotic devices, Strano says.

The researchers also showed that other two-dimensional materials, in addition to graphene, such as molybdenum disulfide and hexagonal boronitride, worked just as well.

Robots similar to cells

From a size ranging from that of a human red blood cell, to about 10 microns at a time, these tiny objects "start to look and behave like a living biological cell." In fact, under a microscope you could convince most people that this is a cell, "says Strano.

This work follows on from previous research conducted by Strano and his students on the development of syncells capable of collecting information on chemistry or other properties from their environment using sensors located at their location. surface, and store them for later recovery, for example by injecting a swarm of such particles into one end of the pipeline and recovering them to each other to obtain data on the internal conditions. Although the new syncells do not have as many capacities as the previous ones, they have been assembled individually, while this work shows a way to mass-produce such devices.

In addition to the potential uses of syncells for industrial or biomedical surveillance, the way in which tiny devices are made is in itself an innovation with great potential, according to Albert Liu. "This general procedure for using controlled fracture as a method of production can be extended to many scales of length," he says. "[It could potentially be used with] essentially all 2D materials of choice, allowing in principle future researchers to adapt these atomically thin surfaces to any desired shape for applications in other disciplines. "

According to Albert Liu, this is "one of the only means currently available to produce large-scale, self-contained integrated microelectronics" that can function as free-floating independent devices. Depending on the nature of the internal electronic components, the devices may be provided with movement, detection of various chemicals or other parameters, as well as memory storage.

There is a wide range of potential new applications for this type of robotic devices the size of a cell, says Strano, who describes many possible uses in a book that he co-authored with Shawn Walsh, an expert from Army Research Laboratories, entitled "Robotic Systems and Autonomous Platforms", published this month by Elsevier Press.

As a demonstration, the team "wrote" the letters M, I and T in a memory array within a sync, which stores information under different levels of electrical conductivity. This information can then be "read" with the help of an electrical probe, showing that the material can function as a form of electronic memory in which data can be written, read and erased at will. It can also store data without the need for energy, which can be used to collect information later. Researchers have shown that particles are stable over a period of months, even when they float in water, which is a harsh solvent for electronics, according to Strano.

"I think this opens up a new toolbox for micro and nanofabrication," he said.

Explore further:
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More information:
Pingwei Liu et al, Autoperforation of 2D materials to generate two-terminal memestive Janus particles, Nature Materials (2018). DOI: 10.1038 / s41563-018-0197-z