Continuously growing multi-layered hydrogel structures with seamless interlocked interface

Many natural tissues feature layered structures for multi-functionality as each layer consists of different cell types and therefore exhibits unique physicochemical properties. Creating such complex multi-layered structures in human-made soft materials is hardly achievable with common gelation methods, lacking spatiotemporal control, and thus demands a living polymerization-based controllable continuous growing process to imitate bio-tissue growth. Herein, a method, namely, ultraviolet-triggered surface catalytically initiated radical polymerization (UV-SCIRP), is demonstrated in living growth of uniform hydrogel layers at room temperature, facilitated by the in situ generation of Fe2+ ion catalysts from the surface-bound Fe3+ ions of the hydrogel substrate. Reiterative application of UV-SCIRP enables fabrication of multi-layered hydrogels with diverse components and layered features. The surface-catalyzed gelation makes the method effective in constructing complex hydrogel patterns, non-flat arbitrary-shaped hydrogel objects, and blood vessel-like intricate multi-layered hydrogel tubes. This work manifests a new route to engineer bioinspired structural hydrogels and complex soft architectures with on-demand functions.