Tech Briefs Magazine - February 2021 - 37

Manufacturing & Prototyping
4D Printing of Morphing Structures
A new method manufactures complex shapeshifters for soft robots and biomedical implants.
Rice University, Houston, Texas

oft robots and biomedical implants
that reconfigure themselves upon demand are closer to reality with a new way
to print shapeshifting materials. Researchers have 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 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.
These materials, once fabricated, will
change shape autonomously, so the
team needed a method to control and
define this shape change. The new
method uses multiple reactions in se-

quence to print the material and then
dictate how it would change shape.
Rather than trying to do this all in one
step, the approach gives more flexibility
in controlling the initial and final shapes
and also allows printing of 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. Parameters such as the
solvents and catalyst used, degree of

swelling, and ink formula had to be optimized to allow the ink to solidify rapidly
enough to print while not inhibiting the
desired final shape actuation.
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. 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, opening the door
to printing soft robotics that could swim
like a jellyfish, jump like a cricket, or
transport liquids.
Watch the process in action on Tech Briefs
TV at www.techbriefs.com/tv/4Dprinting.
For more information, contact Mike
Williams at mikewilliams@rice.edu; 713348-6728.

1
Programmed shape
TTNI

UV
Cure

tch

Stre
De-swell

Deform

Cur

Catalyst bath

3
2

The process by which 3D printing is used to make shapeshifting materials that may be useful in making soft robots or as biomedical implants. (Credit:
Verduzco Laboratory/Rice University)

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