Additive manufacturing of high aspect-ratio structures with self-focusing photopolymerization

1 Photocrosslinkable polymers have been exploited to attain impressive advantages in printing freestanding, micrometer-scale, 2 mechanically compliant features. However, more integrated understanding of both the polymer photochemistry and the 3 microfabrication processes could enable new strategic design avenues, unlocking far-reaching applications of the light-based 4 modality of additive manufacturing. One promising approach for achieving high-aspect-ratio structures is to leverage the 5 phenomenon of light self-trapping during the photopolymerization process. In this review, we discuss the design of materials that 6 facilitate this optical behavior, the computational modeling and practical processing considerations to achieve high aspect-ratio 7 structures, and the range of applications that can benefit from architectures fabricated using light self-trapping—especially those 8 demanding free-standing structures and materials of stiffnesses relevant in biological applications. Coupled interactions exist 9 among material attributes, including polymer composition, and processing parameters such as light intensity. We identify strong 10 opportunities for predictive design of both the material and the process. Overall, this perspective describes the wide range of 11 existing polymers and additive manufacturing approaches, and highlights various future directions to enable constructs with new 12 complexities and functionalities through the development of next-generation photocrosslinkable materials and 13 micromanufacturing methods. 14