Harnessing precision in hydrogel architectures through reversible-deactivation radical polymerisation techniques

Hydrogels, featuring unique three-dimensional network structures and excellent compatibility with diverse biological environments, have attracted widespread interest for applications in biomedicine, drug delivery, soft robotics, tissue engineering, and bioelectronics. Hydrogels are traditionally synthesised through radical polymerisation of functional monomers, during which both chain propagation and crosslinking occur. This process forms a three-dimensional network, with a pore-like structure determined by the crosslinking density and the organisation of any template used. Traditional radical polymerisation leads to random chain propagation, limiting control over the structural features of the resulting hydrogel. Reversible-deactivation radical polymerisation (RDRP) techniques, such as reversible addition-fragmentation chain transfer (RAFT) polymerisation, atom transfer radical polymerisation (ATRP), and nitroxide-mediated polymerisation (NMP), are powerful tools for the precise synthesis of hydrogels. These methods enable molecular-level control over network architecture and ensure uniform distribution of functional groups, resulting in materials with tailored swelling behaviour, mechanical properties and functional performance. The significant progress achieved by researchers in this field has inspired us to review recent advances in the application of RDRP techniques for hydrogel synthesis, emphasising their advantages over hydrogels synthesised by conventional polymerisation methods. Additionally, we discuss the underlying design strategies for integrating functional monomers, crosslinking elements, and stimuli-responsive features into hydrogel systems. We conclude by highlighting studies that explore hydrogels with controlled architectures for applications in self-healing systems, multi-responsive materials, bioactive hydrogels and other advanced functions.