Guiding Lights: Tissue Bioprinting Using Photoactivated Materials.

Photoactivated materials have found widespread use in biological and medical applications and are playing an increasingly important role in the nascent field of three-dimensional (3D) bioprinting. Light can be used as a trigger to drive the formation or the degradation of chemical bonds, leading to unprecedented spatiotemporal control over a material's chemical, physical, and biological properties. With resolution and construct size ranging from nanometers to centimeters, light-mediated biofabrication allows multicellular and multimaterial approaches. It promises to be a powerful tool to mimic the complex multiscale organization of living tissues including skin, bone, cartilage, muscle, vessels, heart, and liver, among others, with increasing organotypic functionality. With this review, we comprehensively discuss photochemical reactions, photoactivated materials, and their use in state-of-the-art deposition-based (extrusion and droplet) and vat polymerization-based (one- and two-photon) bioprinting. By offering an up-to-date view on these techniques, we identify emerging trends, focusing on both the chemistry and instrument aspects, thereby allowing the readers to select the best-suited approach. Starting with photochemical reactions and photoactivated materials, we then discuss principles, applications, and limitations of each technique. With a critical eye to the most recent achievements, the reader is guided through this exciting, emerging field, with special emphasis on cell-laden hydrogel constructs.