Ever 3D-printed an object and then changed your mind about the design? Maybe the colour was wrong, or it was too small for the intended purpose. Usually, you would be stuck with that poor design choice. Now, however, scientists at MIT have created a 3D printing method that allows them to alter a printed object.
Stereolithography is a common 3D printing technique that works by shining light onto a liquid solution of monomers - the building blocks of plastic and other materials - to form layer upon layer of solid polymers in a specific design or pattern, until the final shape is complete.
Previously, once an object had been printed these polymers were considered “dead” – they couldn’t be extended to form new polymer chains, which would alter the printed object. The new MIT method, however, allows them to add polymers that alter the material's chemical composition and mechanical properties.
Jeremiah Johnson, the Firmenich career development associate professor of Chemistry at MIT, said: “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.”
In 2013, Johnson and his colleagues demonstrated that they could use UV light to stimulate the polymers and add new features to 3D-printed materials. They experimented by using the light to break apart the polymers at certain points in a printed object, which created free radicals (extremely reactive molecules).
The free radicals would then bind to new monomers to form a solution surrounding the object and become incorporated in the original material. Unfortunately, the radicals were found to be too reactive: they were difficult to control and could be damaging to the material.
In order to find a solution to this issue, the MIT team designed new polymers that would react to light. The polymers contained chemical groups known as TTCs, that are activated when turned on by light. For instance, when blue light from an LED shines on the polymers, it attaches new monomers to the TTCs, which makes them stretch out. As the 3D-printed object is made up of these monomers, they can give the material it is made out of new properties.
“That’s the breakthrough in this paper: We really have a truly living method where we can take macroscopic materials and grow them in the way we want to,” said Johnson.
As well as changing the colour of an object, the research team found they could make materials become bigger or smaller using different temperatures by adding a specific monomer. They also fused two structures together, by shining light on the regions when they came into contact with each other. The research was published in ACS Central Science.
Though this is an important step forward in the world of 3D-printing and overcoming the limitations of the materials involved, it is not perfect. This new technique is limited by the fact it requires an oxygen-free environment. The team is now working on finding different catalysts that can be used in the presence of oxygen.
This article was originally published by WIRED UK
