A More-Efficient, Less-Wasteful 3D-Printing Method

Andrew Corselli

Researchers have developed a resin that turns into two different kinds of solids, depending on the type of light that shines on it: Ultraviolet light cures the resin into a highly resilient solid, while visible light turns the same resin into a solid that is easily dissolvable in certain solvents. (Image: Courtesy of the researchers; MIT News)

Hearing aids, mouth guards, dental implants, and other highly tailored structures are often products of 3D printing. These structures are typically made via vat photopolymerization — a form of 3D printing that uses patterns of light to shape and solidify a resin, one layer at a time.

The process also involves printing structural supports from the same material to hold the product in place as it’s printed. Once a product is fully formed, the supports are removed manually and typically thrown out as unusable waste.

MIT engineers have found a way to bypass this last finishing step, in a way that could significantly speed up the 3D-printing process. They developed a resin that turns into two different kinds of solids, depending on the type of light that shines on it: Ultraviolet light cures the resin into a highly resilient solid, while visible light turns the same resin into a solid that is easily dissolvable in certain solvents.

The team exposed the new resin simultaneously to patterns of UV light to form a sturdy structure, as well as patterns of visible light to form the structure’s supports. Instead of having to carefully break away the supports, they simply dipped the printed material into solution that dissolved the supports away, revealing the sturdy, UV-printed part.

The supports can dissolve in a variety of food-safe solutions, including baby oil. Interestingly, the supports could even dissolve in the main liquid ingredient of the original resin, like a cube of ice in water. This means that the material used to print structural supports could be continuously recycled: Once a printed structure’s supporting material dissolves, that mixture can be blended directly back into fresh resin and used to print the next set of parts — along with their dissolvable supports.

The researchers applied the new method to print complex structures, including functional gear trains and intricate lattices.

The researchers applied the new method to print complex structures, including functional gear trains, intricate lattices, and a dental implant. (Image: Courtesy of the researchers; MIT News)

Here is a Tech Briefs interview, edited for length and clarity, with Co-Author and Graduate Student Nicholas Diaco.

Tech Briefs: What was the biggest technical challenge you faced while developing this new resin?

Diaco: We have a system that has two separate polymer networks — two separate chemistries that react independently of one another. One is inherently dissolvable, and one's insoluble. But the problem is that when we wanted the material to not dissolve, it would still dissolve quite a bit. It would form a not very good brittle, porous structure. So, we had to try a ton of stuff.

Eventually we found that we had to add a tiny bit of one additional ingredient — kind of a bridging monomer — that formed links between these two otherwise incompatible orthogonally reactive systems to get them to stick together. That was what ended up putting it over the edge. But it took a lot of months to figure out just the exact chemical and just the exact proportions needed to get that to work perfectly.

Tech Briefs: Can you explain in simple terms how the new method works, please?

Diaco: We have one material that's a liquid, and, depending on what color of light you shine at it, it solidifies into either a solid that can be dissolved away or into a solid that is very resistant to dissolution. That allows us in a single 3D print, to create structures that either dissolve or don't dissolve away. That lets us automate the most difficult and most expensive step of 3D printing, which is removing support materials after the printing is done.

Tech Briefs: Do you have any set plans for further research, work, etc.?

Diaco: We have a ton of really exciting ones. Some of the ones that I’m allowed to talk about are:

We want to drastically improve the resolution to be on par with what's needed for dental and hearing aid applications because those are the largest uses of this technology. Invisalign, for instance, is entirely made using this.

We want to incorporate a wider variety of material properties. So, right now the material is relatively stiff and brittle, but we want to be able to create tough engineering plastics. We want to be able to create stretchy elastomers, like rubbers, to be able to serve a wide variety of other applications, and different colors as well. We want to expand the scope of materials that are possible to print with this method.

And we want to show that it's possible to have a robotic handling system that can take people totally out of the equation. You can just put in resin and on the other end of the process you get your final products without needing a lot of human intervention, which is what's needed currently. That's another big one we're interested in.

Tech Briefs: Those are all the questions I have. Is there anything else you'd like to add that I didn't touch upon?

Diaco: I think the other really important thing that we're focused on is the recycling aspect of our material. One important thing about it is that we're able to dissolve our support material; our dissolvable material is basically the main component of the resin itself. That allows us to create more resin out of the dissolved material. Because of that we're limiting the amount of material waste that happens with this process. Ordinarily, between 10 and 20 percent of your material, which is quite expensive, has to be thrown away because it’s support material, which can’t be reused. That's one of the major components of the cost of this type of 3D printing. But, because we can reuse that support material, we think that's going to be a really significant benefit both for sustainability and cost.