3D Printable Hydrogel with a Controlled Hierarchical Network through Aqueous PhotoATRP Using a Well-Defined Telechelic Bromide Macroinitiator

It is known that reversible-deactivation radical polymerization (RDRP) offers distinct advantages in preparing homogeneous gel network microstructures. However, flexibly regulating hydrogel network microstructures via RDRP remains a significant challenge. Herein, we fully leveraged the advantages of atom transfer radical polymerization (ATRP) in preparing well-defined polymers and uniform hydrogel networks and proposed a strategy to construct hydrogel structures with a controlled hierarchical network. This approach employs a presynthesized, well-defined telechelic bromide macroinitiator (via ATRP) to initiate the photoATRP of vinyl monomers and divinyl cross-linkers. A primary polymer network was first formed by the telechelic macroinitiator. Subsequently, the active chain-end sites initiated ATRP of small-molecule cross-linkers, thereby grafting a covalently linked secondary cross-linked network. In other words, we have embedded larger, uniformly sized pores within a smaller, homogeneous network structure. The size of these "macropores" can be tuned by adjusting the molecular weight of the macroinitiator. This hierarchical architecture endows the hydrogel with significantly altered swelling behavior and mechanical properties. Furthermore, by using carbon-dot-catalyzed aqueous photoATRP, this type of hydrogel with a controllable hierarchical structure can be fabricated via digital light processing (DLP) 3D printing technology. This work provides new insights into the regulation of the microstructure and macroscopic properties of hydrogel materials.