Liquid crystal elastomers
(LCEs) have grown in popularity in recent
years as a stimuli-responsive material for soft actuators and shape
reconfigurable structures. To make these material systems electrically
responsive, they must be integrated with soft conductive materials
that match the compliance and deformability of the LCE. This study
introduces a design and manufacturing methodology for combining direct
ink write (DIW) 3D printing of soft, stretchable conductive inks with
DIW-based “4D printing” of LCE to create fully integrated,
electrically responsive, shape programmable matter. The conductive
ink is composed of a soft thermoplastic elastomer, a liquid metal
alloy (eutectic gallium indium, EGaIn), and silver flakes, exhibiting
both high stretchability and conductivity (order of 105S m–1). Empirical tuning of the LCE printing parameters
gives rise to a smooth surface (<10 μm) for patterning the
conductive ink with controlled trace dimensions. This multimaterial
printing method is used to create shape reconfigurable LCE devices
with on-demand circuit patterning that could otherwise not be easily
fabricated through traditional means, such as an LCE bending actuator
able to blink a Morse code signal and an LCE crawler with an on/off
photoresistor controller. In contrast to existing fabrication methodologies,
the inclusion of the conductive ink allows for stable power delivery
to surface mount devices and Joule heating traces in a highly dynamic
LCE system. This digital fabrication approach can be leveraged to
push LCE actuators closer to becoming functional devices, such as
shape programmable antennas and actuators with integrated sensing.