Tunable Thermoshrinkable Hydrogels for 4D Fabrication of Cell-Seeded Channels

Fabricating hydrogel-based channels with diameters below 200 µm remains challenging in advanced in vitro modeling and tissue engineering. To address this challenge, thermoshrinkable hydrogels that undergo reversible isotropic dimensional changes with temperature are developed. A thermoresponsive polymer with methacrylate groups (PNH-MA) is synthesized from polyethylene glycol (PEG), N–isopropylacrylamide (NIPAM), and 2-hydroxyethyl acrylate (HEA), enabling photo-cross-linking and precise material tuning. PNH-MA hydrogels can shrink up to 90% in volume (50% in diameter) and remain transparent allowing cellular imaging. In a four-dimension (4D) fabrication strategy, channels seeded with proximal tubule epithelial cells are shrunk to reduce diameters. Using pin pull-out mold casting, channels of 120 and 410 µm diameters are shrunk to 65 and 200 µm, respectively. While needle injection is challenging for channels smaller than 200 µm, volumetric printing addresses this limitation. The shrinkage properties enable leak-proof perfusion, allowing cell seeding and continuous unilateral flow in channels as small as 100170 µm. PNH-MA polymers represent one of the few examples of low-viscosity resins successfully used for hydrogel volumetric printing of complex scaffolds. This study highlights the potential of PNH-MA hydrogels for scalable, high-precision tubular scaffold fabrication in advanced in vitro modeling.