MIT engineers develop new approach to vat photopolymerization with dissolvable supports.
The combination of speed, precision and material versatility has made vat photopolymerization (VPP) one of the most prolific 3D printing technologies for additive manufacturing (AM) applications. Beyond prototyping, VPP has seen widespread use in creating customized medical implants, such as prosthetics and hearing aids, plus forming the basis for one of AM’s biggest success stories to date: dental aligners.
However, the need to print structural supports from the same material has limited VPP in both sustainability and design freedom. But that could soon change thanks to a group of engineers at MIT who have developed a new VPP process that utilizes two different wavelengths of light.
Their key innovation is a resin that responds differently to ultraviolet and visible light: the former cures the resin into a crosslinked thermoset polymer of the sort typically produced by VPP, while the latter yields a rigid but dissolvable thermoplastic. Combing the two sources together, the engineers have been able to create parts with easily removable supports that simply dissolve when immersed in food-safe solvents such as D-limonene, ethyl acetate, and even mineral oil.
Moreover, the support material is recyclable, able to be blended back into fresh resin and used to print a new set of parts with dissolvable supports. Tests of the new system, dubbed selective solubility vat photopolymerization (SSVP) yielded functional and complex structures, including gear trains and lattices.
“You can now print – in a single print – multipart, functional assemblies with moving or interlocking parts, and you can basically wash away the supports,” said MIT graduate student Nicholas Diaco in a press release. “Instead of throwing out this material, you can recycle it on site and generate a lot less waste. That’s the ultimate hope.”
Diaco and his colleagues report that they were able to synthesize their dual-wavelength resin using a mixture of two commercially available monomers, along with a third “bridging” monomer that linked the other two together under UV light.
“With all these structures, you need a lattice of supports inside and out while printing,” Diaco said. “Removing those supports normally requires careful, manual removal. This shows we can print multipart assemblies with a lot of moving parts, and detailed, personalized products like hearing aids and dental implants, in a way that’s fast and sustainable.”
“We’ll continue studying the limits of this process, and we want to develop additional resins with this wavelength-selective behavior and mechanical properties necessary for durable products,” said professor of mechanical engineering John Hart in the same release. “Along with automated part handling and closed-loop reuse of the dissolved resin, this is an exciting path to resource-efficient and cost-effective polymer 3D printing at scale.”
The research is published in the journal Advanced Materials Technologies.
