Lab makes 4D printing more practical

Date:
June 9, 2020
Source:
Rice University
Summary:
Soft robots and biomedical implants that reconfigure themselves upon
demand are closer to reality with a method to print shapeshifting
materials.



FULL STORY ==========================================================================
Soft robots and biomedical implants that reconfigure themselves upon
demand are closer to reality with a new way to print shapeshifting
materials.


========================================================================== Rafael Verduzco and graduate student Morgan Barnes of Rice's Brown
School of Engineering developed a method to print objects that can
be manipulated to take on alternate forms when exposed to changes in temperature, electric current or stress.

The researchers think of this as reactive 4D printing. Their work
appears in the American Chemical Society journal ACS Applied Materials
and Interfaces.

They first reported their ability to make morphing structures in a mold in 2018. But using the same chemistry for 3D printing limited structures to
shapes that sat in the same plane. That meant no bumps or other complex curvatures could be programmed as the alternate shape.

Overcoming that limitation to decouple the printing process from shaping
is a significant step toward more useful materials, Verduzco said.

"These materials, once fabricated, will change shape autonomously,"
Verduzco said. "We needed a method to control and define this shape
change. Our simple idea was to use multiple reactions in sequence to print
the material and then dictate how it would change shape. Rather than
trying to do this all in one step, our approach gives more flexibility
in controlling the initial and final shapes and also allows us to print
complex structures." The lab's challenge was to create a liquid crystal polymer "ink" that incorporates mutually exclusive sets of chemical
links between molecules. One establishes the original printed shape, and
the other can be set by physically manipulating the printed-and-dried
material. Curing the alternate form under ultraviolet light locks in
those links.

Once the two programmed forms are set, the material can then morph back
and forth when, for instance, it's heated or cooled.

The researchers had to find a polymer mix that could be printed in a
catalyst bath and still hold its original programmed shape.

"There were a lot of parameters we had to optimize -- from the solvents
and catalyst used, to degree of swelling, and ink formula -- to allow
the ink to solidify rapidly enough to print while not inhibiting the
desired final shape actuation," Barnes said.

One remaining limitation of the process is the ability to print
unsupported structures, like columns. To do so would require a solution
that gels just enough to support itself during printing, she said. Gaining
that ability will allow researchers to print far more complex combinations
of shapes.

"Future work will further optimize the printing formula and use scaffold- assisted printing techniques to create actuators that transition between
two different complex shapes," Barnes said. "This opens the door to
printing soft robotics that could swim like a jellyfish, jump like a
cricket or transport liquids like the heart."

========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Morgan Barnes, Seyed Sajadi, Shaan Parekh, Muhammad M. Rahman,
Pulickel
M. Ajayan, Rafael Verduzco. Reactive 3D Printing of Shape
Programmable Liquid Crystal Elastomer Actuators. ACS Applied
Materials & Interfaces, 2020; DOI: 10.1021/acsami.0c07331 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200609130010.htm

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