Liquid-Solid Co-Printing Technique Could Allow for Print-in-Place Creation of Transistors and Robots

Capable of printing incredibly complex shapes with hollow or liquid-filled areas, this technique borrows its core concept from 2D printers.

Gareth Halfacree
20 days ago3D Printing / Robotics

A trio of researchers at the University of Colorado Boulder's Department of Mechanical Engineering have showcased a multi-material 3D printing approach, dubbed liquid-solid co-printing, which they say could enable 3D printers to construct robots from scratch without post-print assembly.

"I think there’s a future where we could, for example, fabricate a complete system like a robot using this process," says Robert MacCurdy, assistant professor and senior author of the paper detailing the mixed-material solid-and-liquid printing approach, which uses non-curing liquids as both support material and working fluids.

The core concept is fairly basic, and effectively borrowed from traditional two-dimensional printers. "Color printers combine a small number of primary colors to create a rich range of images," MacCurdy explains. "The same is true with materials. If you have a printer that can use multiple kinds of materials, you can combine them in new ways and create a much broader range of mechanical properties."

Rather than mixing colors, however, the team's 3D printer, a modified Stratasys J750, mixes materials to create solids and liquids — allowing complex liquid-filled voids to be constructed in a single pass, and without the traditional post-processing such prints would require.

"We found that the surface tension of a liquid can be used to support solid material, but it is helpful to pick a liquid material that is more dense than the solid material — the same physics that allow oil to float on top of water," MacCurdy explains — having picked a standard curable polymer and a cleaning solution as the materials to mix for a practical experiment.

The result: Twisting liquid-filled voids and a network of channels mimicking those found inside human lungs. "Both structures would have been nearly impossible to make through previous approaches," MacCurdy claims. "We hope that our results will make multi-material inkjet 3D printing using liquids and solids more accessible to researchers and enthusiasts around the world."

The team says that the approach offers a "key new capability in additive manufacturing," and hopes that it could lead to print-in-place systems for fluidic circuits and hydraulic structures for everything from electrochemical transistors and lab-on-a-chip devices to fully-functional robots.

"Liquid-solid co-printing requires virtually no post-processing to remove liquid from channels (with the exception of input and output ports to purge channels) and eliminates the need for heat treatments common in the use of MJM for micro/mesofluidic channels," the researchers conclude. "Complex 3D multi-material micro/mesofluidic systems, such as the integrated one- way flap valve in this study, demonstrate the versatility of this print process."

The team's work has been published in the journal Additive Manufacturing under closed-access terms.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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