Multiresponsive Reversible Deformation of Patterned Polyacrylamide Hydrogel Constructed by a Computer-Assisted Dispenser

Materials that can undergo shape deformation have potential applications in biomedical field, yet it has always been a challenge to pattern hydrogels and accurately program target three-dimensional (3D) shapes through a simple method. Here, we develop a facile method that permits fabrication of inhomogeneous hydrogels, which can reversibly deform from planar sheet to 3D shape in response to multistimuli, such as pH values, SLDC (solutions with lower dielectric constant), and SBF (simulated body fluid). By printing NaOH solution ink on classic PAAm hydrogel sheet, the amide side groups of PAAm hydrolyzed to acrylate. The swelling mismatch of the printed and unprinted areas generates internal stress to activate hydrogel deformation. Adjusting concentration of NaOH solution or number of times of printing, it is convenient to introduce in-plane and through-thickness gradient distribution to hydrogel sheet. The inkjet printing process is easily controlled by computer, enabling the direct printing of batched and complicated patterns. Three-dimensional structures, such as helix, tube, and surface of constant Gaussian curvature can be achieved simply.