MIT never ceases to amaze with the cutting-edge projects and technologies it pioneers. The school’s latest project is impressive on a small scale: researchers have devised a method to shrink 3D printed structures down to the nanoscale. The technique uses accessible technologies and is reportedly capable of creating objects made from various materials, including metals, quantum dots and even DNA.
The innovative technique, recently published about in the journal Science, consists of printing a polymer scaffold structure using a laser, attaching other materials to the scaffold and then shrinking it. The research team says it is capable of shrinking objects down so that they are one thousandth the volume of the original.
“It’s a way of putting nearly any kind of material into a 3D pattern with nanoscale precision,” explained senior author Edward Boyden, the Y. Eva Tan Professor in Neurotechnology and an associate professor of biological engineering and of brain and cognitive sciences at MIT. The novel technique could be used to manufacturing nanoscale structures for applications in optics, medicine and robotics, among others.
A shrink ray? Not quite
Despite this simple explanation, there is more that goes into the process. Interestingly, the process is an adaptation of a previous technique developed by Professor Boyden and his students a few years ago for high-resolution imaging of brain tissue. This original technique, called expansion microscopy, involves embedding tissue into a hydrogel structure and then expanding it. This process is now widely used in biology research.
In its more recent project, the MIT team effectively reversed the expansion process, starting with large-scale objects embedded in expanded hydrogels and then shrinking them down to the nanoscale. This new process is known as “implosion fabrication.”
Honey, I shrunk the scaffold
The shrinking is achieved by using a polyacrylate-based absorbent material to construct the scaffold, which is then bathed in a solution containing fluorescein molecules that attach themselves to the scaffold when they are activated by laser light. More precisely, the fluorescein molecules are attached to specific locations within the hydrogel structure using two-photon microscopy. These molecules end up acting as anchors that can bind to other types of molecules.
“You attach the anchors where you want with light, and later you can attach whatever you want to the anchors,” Boyden explained. “It could be a quantum dot, it could be a piece of DNA, it could be a gold nanoparticle.”
Daniel Oran, the study’s lead author, added: “It’s a bit like film photography — a latent image is formed by exposing a sensitive material in a gel to light. Then, you can develop that latent image into a real image by attaching another material, silver, afterwards. In this way implosion fabrication can create all sorts of structures, including gradients, unconnected structures, and multi-material patterns.”
Once the molecules are attached to the desired locations, the whole structure can be shrunk by simply adding an acid. This acid blocks the negative charges of the polyacrylate gel, causing the material to contract because its molecules are no longer repelling each other. The shrinking process, which can result in structures one-thousandth the size of the original, is ideal for producing high-resolution, dense structures.
In its research, the MIT team successfully created objects measuring about 1 cubic millimeter with a resolution of 50 nanometers. Presently, they are also capable of achieving resolutions of about 500 nanometers if the scale of the object is slightly larger (about 1 cubic centimeter). The researchers add that the resolution of the process will be improved with further advancements.
Nanoscale optics and robotics
In terms of applications, the MIT team believes its process could be used in optics for making specialized lenses for studying the properties of light, as well as for fabricating smaller, higher quality lenses for microscopes, endoscopes or smartphone cameras. Down the line, the technique could also be used to build nanoscale electronics for robots.
“There are all kinds of things you can do with this,” Boyden concluded. “Democratizing nanofabrication could open up frontiers we can’t yet imagine. 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.”