The ability to make materials small (nanoscale small) opens up almost endless possibilities in possible advances in medicine, robotics, optics, and more. For example, a nano-robot that can repair at the cellular level, nanomaterials that deliver chemotherapy to a cancer cell, or a nanosensor that can monitor the blood when placed under the skin. Some ideas bear resemblance to works of science fiction, or simply fiction if you are a fan of the travels of Lemuel Gulliver.
A team at the MIT Media Lab in Cambridge, MA is working to turn fiction into reality. The lab of Ed Boyden, PhD, one of the co-inventors of optogenetics, in conjunction with Adam Marblestone, PhD, a research scientist at Google DeepMind, recently published a new strategy for the fabrication of nanoscale 3D objects of virtually any shape. The article, “3D nanofabrication by volumetric deposition and controlled shrinkage of patterned scaffolds” appeared in Science in December.
“It’s a way of putting nearly any kind of material into a 3D pattern with nanoscale precision,” says Boyden. The group, led by Boyden lab research assistant Daniel Oran and graduate student Samuel Rodriques, developed a process that can directly write highly conductive, 3D silver nanostructures within an acrylic scaffold via volumetric silver deposition. The team can shrink objects embedded in expanded hydrogels to nanoscale, creating tiny 3D objects of nearly any shape—a process they call “implosion fabrication.” They can also pattern the objects with a variety of useful materials, including metals, quantum dots, and DNA.
Implosion fabrication is an extension of the team’s previously described process of expansion microscopy, where liquid is added to an incredibly absorbent polyacrylate material, commonly found in diapers. The idea for the concept, Rodriques tells GEN, came “because we previously worked on expansion microscopy” and that “conceptually, implosion fabrication is the inverse process of expansion microscopy.”
The scaffold is bathed in fluorescein, which bind when activated by lasers and act as anchors for other molecules of the researchers’ choosing. According to Boyden, “you attach the anchors where you want with light, and later you can attach whatever you want to the anchors.” He adds, “It could be a quantum dot, it could be a piece of DNA, it could be a gold nanoparticle.” Upon the addition of an acid, which blocks the negative charges in the polyacrylate gel so that they no longer repel each other, the polyacrylate is dehydrated and the entire structure shrinks to a 1000-fold reduction in volume.
The team was “surprised by how much the gels were capable of shrinking!” Rodriques notes, adding “when we set out, we imagined we would be able to shrink things by a factor of ~3 (in linear dimension or 27x in volume), but we never imagined we would be able to shrink them by a factor of 20 (in linear dimension—10,000x in volume).”
Their report of precise delivery of nanomaterials in multiple, complex patterns “enables unprecedented formation of nanomaterials of controlled geometry and high performance,” writes Timothy Long, PhD, and Christopher Williams, PhD, from Virginia Polytechnic Institute and State University (Virginia Tech), in a commentary on the significance of the work that appeared in the same issue of Science as the research paper.
The technique can be used for various diverse purposes and performed with relative ease by many scientists—one of the most exciting aspects of this work according to Rodriques. He notes that they didn’t need to work in a clean room nor did they have to use specialized deposition equipment, something that is necessary for most nanofabrication approaches. With the necessary equipment already found in many biology and materials science labs, the strategy can be easily transferred to other kinds of materials. “With a laser you can already find in many biology labs, you can scan a pattern, then deposit metals, semiconductors, or DNA, and then shrink it down,” Boyden says.
According to Rodriques, they are currently working on expanding the materials that they can use with the technology; for example, to develop methods for semiconductors. When asked about potential applications in medicine, he notes that, “if we are able to fabricate flat lenses using this technology, we could easily imagine applying it to make very high-resolution endoscopes, much smaller and with much better resolution than what is currently available. Also, the material is very similar to materials that have been used in the past to scaffold cells in space, which may have implications in the future for creating organs.”
With regard to expanding this technology further into other nanomaterials and nanosensors, Boyden notes that those applications “might be possible, but since our objects must be dehydrated to be shrunk, they would probably need further processing to work in an aqueous environment.” He adds that they have not yet made objects with moving parts, but those may be possible with further engineering. “There are all kinds of things you can do with this,” Boyden says. “Democratizing nanofabrication could open up frontiers we can’t yet imagine.” Big goals that will benefit from these diminutive tools.
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