Photopolymerization in 3D Printing

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, microfluidics, 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 the 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 detail. This review also spotlights recent progress on the use of controlled living radical photo-polymerization techniques (i.e., reversible addition-fragmentation chain-transfer polymerization) in 3D printing, which will pave the way for widespread growth of new generations of 3D materials with living features and possibility for postprinting modifications.