Lithography-based 3D printing of hydrogels

Additive manufacturing is an engineering tool that enables the creation of complex structures for biomedical use, such as 3D scaffolds for tissue engineering and regenerative medicine, as well as in vitro disease models for drug testing. In particular, lithography-based techniques such as digital light processing and volumetric additive manufacturing have enabled advances in the 3D processing of photoreactive resins into structured hydrogels. In this Review, we introduce light-based lithographic 3D printing methods to process hydrogels and provide a guide to lithography-based printing, from bioresin selection to the optimization of print parameters. Moreover, we highlight examples of in vitro and in vivo biomedical applications of hydrogels, for which lithography-based approaches have been leveraged, and discuss efforts to process hydrogels into heterogeneous structures with multi-scale organization. Finally, we provide a perspective on the challenges and opportunities in this field.