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

Abstract

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.

Co-Ion Specific Effect Aided Phase Separation in Polyelectrolyte Hydrogels toward Extreme Strengthening and Toughening

“…Polyelectrolyte (PE) hydrogels are 3D cross-linked network materials composed of abundant charged groups with high water content. They are ubiquitous in nature 1,2 and have myriad applications, such as superabsorbent materials, 3 soft actuators, 4,5 biomedicine, and so forth. 6,7 Unfortunately, PE single network (PE-SN) gels are weak and brittle, which seriously limits their practical applications.…”

“…Polyelectrolyte (PE) hydrogels are 3D cross-linked network materials composed of abundant charged groups with high water content. They are ubiquitous in nature , and have myriad applications, such as superabsorbent materials, soft actuators, , biomedicine, and so forth. , Unfortunately, PE single network (PE-SN) gels are weak and brittle, which seriously limits their practical applications . Particularly, PE-SN gels with ∼90% water content exhibit fracture energy lower than 10 J/m 2 and are prone to failure at a tensile stress less than MPa and breaking strain less than 100%. , Harnessing the salt-sensitive nature of PE provides versatile means to tune their properties by simply changing the electrolyte nature.…”

Synergistic Fire Resistance of Nanobrick Wall Coated 3D Printed Photopolymer Lattices

“…Additive manufacturing (AM) has become a major focus of both academia and industry over the past decade due partially to its promise to enable the fabrication of unique geometries that are inaccessible to other forms of manufacture (e.g., machining or injection molding). , Among polymer-based forms of AM, vat photopolymerization (VP) has rapidly grown in both academic and industrial importance. − Some advantages of VP include its wide array of potential chemistries (i.e., hydrogel materials, high performance engineering plastics, and so-called “4D” materials that exhibit a response to an external stimulus). − …”

A Superabsorbent Sodium Polyacrylate Printing Resin as Actuator Material in 4D Printing

“…[15][16][17][18][19] Stimuli-responsive materials for 4D printing often use the shape memory effect or swelling in a medium as a driving force, like hydrogels in water. [2,7,14,20] While the swelling behavior of some hydrogels is solely triggered in the presence of water, [21][22][23] other materials can react to different external factors such as temperature and light (e.g., poly(N-isopropylacrylamide) called PNIPAm), [11][12][13]24,25] an electric field, [26][27][28][29] or a change in pH (polyacrylic acid). [30][31][32] It is often beneficial if the hydrogel material exhibits a strong swelling behavior-a high swelling ratio as well as the ability to expand against external pressure-to use hydrogels as actuators in 4D printed parts.…”