Light-based fabrication and 4D customization of hydrogel biomaterials.

Light has become an essential tool to make and manipulate living systems in the increasingly intertwined fields of cell biology and materials science. With the ever-expanding interdisciplinary nature of current scientific research and the ongoing hunt for orthogonal, high-precision stimuli for biomaterial synthesis and modification, light has emerged as the gold standard with its low cytotoxicity and high bioorthogonality, enabling the modulation of properties in both 3D space and time (that is, 4D). Not only can light govern when and where changes occur, dosage modulation permits control over the extent of material customization, providing a route to engineered constructs approaching the 4D complexity of native tissue. Recent technological innovations span advances in stereolithography, digital light processing, volumetric bioprinting, multiphoton lithography and grayscale fabrication. Material chemistries have matched pace with the technologies: novel photochemistries permit the building of dynamic materials with complex mechanical and biochemical functionalities, such as on-demand protein activation, rapid gel formation/degradation and immobilization/release of signalling factors. Herein, we discuss the union of rapid light-based manufacturing and photoresponsive chemistries and highlight future opportunities using photochemistry in the design and user-defined customization of hydrogel biomaterials. We anticipate that these areas will continue to evolve in tandem and be influenced by new insights from traditionally disparate disciplines (such as protein engineering and inorganic chemistry), facilitating further discoveries in cellular development and disease progression, as well as orchestrating advanced tissue construction.