Jan 13, 2017 | By Benedict

Chemists at MIT have developed a 3D printing technique that allows for the alteration of a printed object’s chemical structure and the chemical joining of multiple 3D printed objects. They say the technique could greatly expand the complexity of objects that can be created with 3D printing.

3D printing is an incredibly versatile manufacturing technique, capable of creating many things from many kinds of material. But there are limitations to the technology: for one, 3D printed objects are, on the whole, unalterable. They can be post-processed, sanded down, even machined into smaller shapes, but the chemical structure of a 3D printed polymer object is, for all intents and purposes, “dead.” Excitingly, a group of chemical necromancers at MIT have developed a technique for 3D printing objects whose chemical composition can be altered even after printing. The technique also allows multiple 3D printed objects to be fused together.

Under the lead authorship of Mao Chen and Yuwei Gu, the MIT team published their findings in today’s issue of ACS Central Science. Jeremiah Johnson, the Firmenich Career Development Associate Professor of Chemistry at MIT, was senior author on the research paper, and explained to MIT staff how the new technique can be used to increase the complexity of 3D printed objects. “The idea is that you could print a material and subsequently take that material and, using light, morph the material into something else, or grow the material further,” he said.

Stereolithography, the liquid resin 3D printing technique pioneered by 3D Systems and popularized by modern companies like Formlabs, is one of the more accurate processes available to general users of 3D printing technology. A stereolithography 3D printer shines a series of bright projections onto a vat of liquid resin which cures (hardens) in response to light. Layer by layer, a solid object is formed. By taking stereolithography and combining it with a technique known as “living polymerization,” Johnson and his team have been able to create 3D printed materials whose growth can be halted and then restarted at a later point in time.

MIT's Johnson Research Group, some of whom worked on the 3D printing research

Back in 2013, the MIT researchers discovered that, by using UV light, they could break apart the polymers of 3D printed structures, creating reactive molecules called “free radicals.” The free radicals could then bind to new monomers from a solution surrounding the object, incorporating them into the original material. “The advantage there is you can turn the light on and the chains grow, and you turn the light off and they stop,” Johnson said. “In principle, you can repeat that indefinitely and they can continue growing and growing.”

Unfortunately, attempting to control the free radicals proved overly difficult, with excessive damage inflicted upon the 3D printed material. Luckily however, the MIT chemists had another trick up their sleeve: blue light from an LED. Polymers such as those used for 3D printing contain chemical groups, TTCs, which can be activated by organic catalysts that are turned on by light. When subjected to blue light from an LED, these TTCs stretch out as new monomers are attached. And since these monomers are added uniformly, they provide the material with new properties. “We really have a truly living method where we can take macroscopic materials and grow them in the way we want to,” Johnson said.

By using the LED light technique, the MIT researchers found that they could alter various attributes of 3D printed structures, including their stiffness and hydrophobicity (how much they repel or absorb water). And by adding a certain type of monomer, the chemists were also able to make materials swell or contract in response to temperature. Better still, they were able to chemically fuse two 3D printed objects by shining a light on the interconnecting regions. The researchers say that this particular process could be used to create huge, chemically stable 3D printed structures of unprecedented complexity.

One obstacle the researchers faced was keeping the environment of the experiments oxygen-free, since the organic catalyst used in the process cannot function in the presence of oxygen. The group is, however, testing other catalysts that could catalyze similar polymerizations in the presence of oxygen.

By merging the fields of polymer science and materials science, the MIT researchers have opened up several exciting opportunities for advanced 3D printing.



Posted in 3D Printing Technology



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