Lithography-based 3D printing of hydrogels

Additive manufacturing is an engineering tool that enables the creation of complex structures for biomedical use, such as for 3D scaffolds for tissue engineering and regenerative medicine and in vitro disease models for drug testing. Lithography-based techniques (e.g., digital light processing DLP, volumetric additive manufacturing VAM) have particularly advanced in recent years for the 3D processing of photoreactive resins into structured hydrogels. The aim of this review is to introduce the various light-based lithographic 3D printing methods that are being used to process hydrogels, provide a guide to lithography-based printing from bioresin selection to the optimization of print parameters, highlight examples of in vitro and/or in vivo biomedical applications of hydrogels where lithography-based approaches have been leveraged, and discuss recent advanced efforts to process hydrogels into heterogenous structures with multi-scale organization. Finally, a perspective on the challenges and opportunities ahead in this field is provided.