Wettability-Programmable Poly(vinyl alcohol)/Glutaraldehyde Hydrogel with Triple Network for 3D-Printed Monolithic...

Conventional microfluidic chips fabricated from polydimethylsiloxane (PDMS), glass, and silicon suffer from intrinsically fixed surface wettability, tedious post-modification, and inhomogeneous wetting inside enclosed three-dimensional (3D) microchannels, which severely restrict their applications in biphasic fluid manipulation. Herein, we develop a photocurable poly(vinyl alcohol) (PVA)-based hydrogel featuring a triple synergistic network for digital light processing (DLP) 3D printing of integrated microfluidic devices. Under acidic catalysis, glutaraldehyde (GA) undergoes acetalization with PVA to form the first crosslinked network, which consumes hydrophilic hydroxyl groups and introduces hydrophobic alkyl segments. Subsequently, the hydrogel framework is co-constructed by a PVA hydrogen-bonding physical network and a UV-initiated covalent network derived from acrylamide (AAm), acrylic acid (AAc), and poly(ethylene glycol) diacrylate (PEGDA), ultimately yielding a triple-crosslinked network. By adjusting the GA loading, the water contact angle of the hydrogel can be continuously tuned from 15.42° (hydrophilic) to 111.66° (hydrophobic). Benefiting from the interpenetrating multi-network architecture, the tensile strength increases from 48.76 kPa to 118.27 kPa, and the elastic modulus increases from 14.72 to 63.84 kPa. DLP 3D printing enables the direct fabrication of monolithic microfluidic chips with smooth microchannels down to approximately 160 μm in width, without requiring any post-treatment. Fluorescence characterization confirms that the hydrophilic channels allow stable laminar flow of deionized water, while the hydrophobic channels enable low-friction transport of mineral oil. This work establishes a comprehensive strategy integrating molecular design, wettability programming, and 3D additive manufacturing, providing a scalable platform for applications in fluid transportation, biochemical detection, environmental monitoring, and wearable microfluidics.