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Como produzir em massa robôs do tamanho de células: Técnica do MIT pode levar a pequenas, dispositivos autoalimentados para ambientes, industrial, ou acompanhamento médico.

Tiny robots no bigger than a cell could be mass-produced using a new method developed by researchers at MIT. The microscopic devices, which the team calls “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.

This photo shows circles on a graphene sheet where the sheet is draped over an array of round posts, creating stresses that will cause these discs to separate from the sheet. The gray bar across the sheet is liquid being used to lift the discs from the surface. Imagem: Felice Frankel

The key to making such tiny devices in large quantities lies in a method the team developed for controlling 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 novel process, called “autoperforation,” is described in a paper published today in the journal Nature Materials, by MIT Professor Michael Strano, postdoc Pingwei Liu, graduate student Albert Liu, and eight others at MIT.

The system uses 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. Então, a second layer of graphene is laid on top.

Controlled fracturing

People think of graphene, an ultrathin but extremely strong material, as being “floppy,” but it is actually brittle, Strano explains. But rather than considering that brittleness a problem, the team figured out that it could be used to their advantage.

“We discovered that you can use the brittleness,” says Strano, who is the Carbon P. Dubbs Professor of Chemical Engineering at MIT. “It’s counterintuitive. Before this work, if you told me 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 shards of material, like the remains of a broken window, it produces pieces of uniform shape and size. “What we discovered is that you can impose a strain field to cause the fracture to be guided, and you can use that for controlled fabrication,” Strano says.

Quando a camada superior de grafeno é colocada sobre a matriz de pontos de polímero, que formam formas pilar redondo, os locais onde as cortinas grafeno sobre as bordas arredondadas dos pilares formam linhas de alta tensão no material. Como Albert Liu descreve, “Imaginar uma toalha de mesa caindo lentamente sobre a superfície de uma mesa circular. Pode-se muito facilmente visualizar a estirpe circular desenvolver na direcção dos bordos de mesa, e isso é muito semelhante ao que acontece quando uma folha plana de grafeno se dobra em torno destes pilares de polímeros impressos.”

Como um resultado, as fraturas se concentram direita ao longo desses limites, Strano diz. “E então algo incrível acontece: O grafeno será completamente fracturar, mas a fratura será guiado em torno da periferia do pilar.”O resultado é um puro, peça redonda de grafeno que se parece como se tivesse sido limpa cortada por um furador microscópica.

Uma vez que existem duas camadas de grafeno, above and below the polymer pillars, the two resulting disks adhere at their edges to form something like a tiny pita bread pocket, with the polymer sealed inside. “And the advantage here is that this is essentially a single step,” in contrast to many complex clean-room steps needed by other processes to try to make microscopic robotic devices, Strano diz.

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

Cell-like robots

Ranging in size from that of a human red blood cell, sobre 10 micrometers across, até aproximadamente 10 times that size, these tiny objects “start to look and behave like a living biological cell. De fato, 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," ele diz. “[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.”

Isto é, 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, chamado “Robotic Systems and Autonomous Platforms,” which is being published this month by Elsevier Press.

As a demonstration, the team “wrote” the letters M, Eu, 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, ler, 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.

“I think it opens up a whole new toolkit for micro- and nanofabrication," ele diz.

Daniel Goldman, a professor of physics at Georgia Tech, who was not involved with this work, diz, “The techniques developed by Professor Strano’s group have the potential to create microscale intelligent devices that can accomplish tasks together that no single particle can accomplish alone.”


Fonte:

http://news.mit.edu, por David L. merceeiro

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