Photoacoustic imaging for three-dimensional bioprinted constructs

Bioimaging is used to inspect the successful growth and functional differentiation of cells in printed biomaterials, which are ultimately finalized into functional artificial tissues capable of replacing native tissues. While optical bioimaging techniques are commonly utilized, the current trend in three-dimensional (3D) bioprinting towards replicating complex 3D microarchitectures poses a challenge for conventional optical imaging techniques in providing clear cross-sectional images due to the opaque nature of tissue. Consequently, these limitations necessitate lengthy and destructive preparation processes, which are associated with sacrificing cell viability and damaging the bioprinted material. Photoacoustic imaging (PAI) is a versatile imaging technique that extends the advantages of the optical bioimaging technique to undiscovered depths enabled by its acoustic hybridity, making itself a promising tool for non-destructive imaging of 3D bioprinted constructs. In this review, we introduce the flexible spectral contrasts provided by PAI, which are potentially applicable to 3D-bioprinted constructs, and summarize bioprinting studies that functionally implement PAI for in vitro and in vivo assessments. Finally, we provide an outlook on practical considerations for the more complete integration of these two fields, anticipating more fruitful discoveries as bioprinting advances towards more complex hierarchies.