Poly(acrylic acid)-Based Hydrogel Actuators Fabricated via Digital Light Projection Additive Manufacturing

Electroactive polymers that exhibit
controlled deformation under
an applied electric field, either in liquid or air, have great potential
as soft robotic actuators. However, materials for soft robotics currently
face challenges, including slow response, high actuation potential,
and a lack of underlying mechanistic understanding. Additionally,
fabrication of soft robotic actuators with complex design features
has historically been restricted by two-dimensional fabrication methods.
In this work, we investigate cross-linked poly­(acrylic acid)-based
actuators prepared utilizing digital light projection (DLP), an additive
manufacturing technique that enables fabrication of actuators with
complex geometries. A series of photopolymerizable inks are prepared
incorporating acrylic acid (monomer), trimethylolpropane trimethacrylate
(cross-linker), and phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide
(photoinitiator). Soft actuators are 3D-printed utilizing a commercial
DLP 3D printer operating under 405 nm UV light. These 3D-printed actuators
exhibit large deformation (up to 43°), high actuation speed (up
to 1.08°/s), and stable actuation performance for bending cycles
under relatively low actuation voltage (4–6 V). Factors such
as acrylic acid content, cross-linker concentration, actuator thicknesses,
and electric field strength are varied, and their impact on the 3D-printed
actuators are evaluated and discussed. Lastly, a membrane valve actuator
is fabricated, and its ability to open and close under applied potential
is demonstrated.