The field of 3D printing is continuing its rapid development in both academic and industrial research environments. The development of 3D printing technologies has opened new implementations in rapid prototyping, tooling, dentistry, microfluidic, biomedical devices, tissue engineering, drug delivery, etc. Among different 3D printing techniques, photopolymerization-based process (such as stereolithography and digital light processing) offers flexibility over the final properties of the 3D printed materials (such as optical, chemical and mechanical properties) using versatile polymer chemistry. The strategy behind the 3D photopolymerization is based on using monomers/oligomers in liquid state (in presence of photoinitiators) that can be photopolymerized (via radical or cationic mechanism) upon exposure to light source of different wavelengths (depending on the photoinitiator system). An overview of recent evolutions in the field of photopolymerization-based 3D printing and highlights of novel 3D-printable photopolymers is provided herein. Challenges that limit the use of conventional photopolymers (i.e. initiation under UV light) together with prospective solutions such as incorporation of photosensitive initiators with red-shifted absorptions are also discussed in details. This review also spotlights recent progress on the use of controlled living radical photopolymerization techniques (i.e. reversible addition-fragmentation chain-transfer (RAFT) polymerization) in 3D printing; which will pave the way for widespread growth of new generations of 3D materials with living features and possibility for post-printing modifications.

3D printing has changed the fabrication of advanced materials as it can provide customized and on‐demand 3D networks. However, 3D printing of polymer materials with the capacity to be transformed after printing remains a great challenge for engineers, material, and polymer scientists. Radical polymerization has been conventionally used in photopolymerization‐based 3D printing, as in the broader context of crosslinked polymer networks. Although this reaction pathway has shown great promise, it offers limited control over chain growth, chain architecture, and thus the final properties of the polymer networks. More fundamentally, radical polymerization produces dead polymer chains incapable of postpolymerization transformations. Alternatively, the application of reversible deactivation radical polymerization (RDRP) to polymer networks allows the tuning of network homogeneity and more importantly, enables the production of advanced materials containing dormant reactivatable species that can be used for subsequent processes in a postsynthetic stage. Consequently, the opportunities that (photoactivated) RDRP‐based networks offer have been leveraged through the novel concepts of structurally tailored and engineered macromolecular gels, living additive manufacturing and photoexpandable/transformable‐polymer networks. Herein, the advantages of RDRP‐based networks over irreversibly formed conventional networks are discussed.

Here, for the first time, we report the 3D printing of polymeric materials via a photo-controlled reversible addition fragmentation chain transfer (photo-RAFT) polymerization process. Our 3D printing resin formulation is based on the use of trithiocarbonate (TTC) RAFT agent, which can mediate radical polymerization via direct photolysis under visible light irradiation (λ = 405 nm). Re-activation of the TTC units within the 3D printed materials enables post-printing transformation.