Azobenzene-Enhanced 3D Printed Complex Hydrogels: Unlocking Light and pH Responsiveness in Polyelectrolyte-Based Networks

The progression of 3D printing technologies for hydrogels is driven by next-generation fabrication methods, which offer unprecedented precision and the ability to create sophisticated smart materials with specific, tailored properties. Yet, the research landscape concerning the formulation of 3D inks for multifunctional smart hydrogels remains in an early, exploratory phase. Herein, we introduce a printable dual-responsive hydrogel system based on polyelectrolyte complex networks, integrating azobenzene moieties for light sensitivity and polyionic components for pH responsiveness. By exploiting the reversible dynamic bonds between β-cyclodextrin (CD) and azobenzene, three unique polymer networks were synthesized, each featuring an Azo-modified polyelectrolyte and a CD-functionalized polyelectrolyte within a P(OEGMA-co-EGDEMA) framework. The design of these networks endows them with dual responsiveness to both light and pH variations. The synthesized interpenetrating polymer networks and supramolecular polymer networks were rigorously analyzed to assess their physicochemical properties, encompassing their swelling capacity, thermal behavior, mechanical properties, and reactivity to light exposure and pH variations. The pH-responsive behavior was further explored through bilayer constructs, exhibiting distinct bending responses under varying pH conditions. Additionally, UV spectroscopy highlighted the photoresponsive nature of the azobenzene-modified components and hydrogels. These complex hydrogels were successfully 3D printed using digital light processing technology into complex shapes, demonstrating their potential for advanced applications in futuristic biomimetic designs and soft robotics.