Hofmeister-assisted electro-fabrication of Janus gelatin hydrogels with tunable structure and biofunctionality

Natural vessel structures inspire Janus hydrogels with spatially separated functions. Here, we report a one-step electro-fabrication strategy to construct gelatin-based Janus hydrogels featuring a dense, hydrophobic inner layer and a porous, hydrophilic outer layer. Introducing sodium citrate generates a directional ion gradient under an electric field, triggering interface-directed gelation through the Hofmeister effect and enhancing anticoagulant performance. The layered architecture can be finely tuned by varying voltage, deposition time, and gelatin concentration, producing inner pores below 5 μm and outer pores of 20-120 μm. Compared with the conventional diffusion-driven soaking process that requires 24 h to form a weak hydrogel (<1 MPa), this method achieves initial gelation within 15 min and yields, after only 1.5 h of electro-fabrication, a robust network with a tensile strength of 2.31 ± 0.33 MPa and an elongation at break of 230 ± 45%. The resulting hydrogel also demonstrates sustained citrate release, excellent cytocompatibility, hemocompatibility, and intrinsic antibacterial activity. This rapid, crosslinker-free approach enables efficient fabrication of interface-engineered hydrogels with tunable properties for soft-matter and biomedical applications.