Diffusion-induced phase separation 3D printed scaffolds for dynamic tissue repair

Many hydrogen-bonded cross-linked hydrogels possess unique properties, but their limited processability hinders their potential applications. By incorporating a hydrogen bond dissociator (HBD) into these hydrogels, we developed injectable 3D printing inks termed diffusion-induced phase separation (DIPS) 3D printing inks. Upon extrusion into water and subsequent diffusion of HBD, these ink cure rapidly. The DIPS-printed scaffold retained most of the original hydrogel properties due to the regeneration of hydrogen bonds. Additionally, the reversible nature of hydrogen bonds provides DIPS 3D-printed scaffolds with exceptional recycling and reprinting capabilities, resulting in a reduction in the waste of valuable raw ink materials or additives. Postprocessing introduces new crosslinking methods that modulate the mechanical properties and degradation characteristics of DIPS scaffolds over a broad range. Based on its suitable mechanical properties and bioactivity, we successfully repaired and functionally reconstructed a complex defect in penile erectile tissue using the DIPS scaffold in a rabbit model. In summary, this approach is relevant for various hydrogen-bonded cross-linked hydrogels that offer mild printing conditions and enable the incorporation of bioactive agents. They can be used as scaffolds for dynamic tissue reconstruction, wearable devices, or soft robots. Herein, we present a method for creating novel extruded 3D printing inks using hydrogen-bonded cross-linked hydrogels, called DIPS 3D printing. Urea acts as a switch for the gel-sol transition of DIPS inks, enabling fast, high-fidelity 3D printing under mild conditions. The printed DIPS scaffold can be used as a tissue-engineered scaffold for dynamic organ repair.image