Next-Generation Bioinks in 3D Bioprinting: Advances, Challenges, and Emerging Opportunities

3D bioprinting is an innovative technology that has advanced the field of tissue engineering and regenerative medicine by allowing the layer-by-layer deposition of cells, biomaterials, and bioactive molecules to create sophisticated biological constructs. In this context, bioinks serve as essential vehicles for creating a microenvironment that can support cell attachment, proliferation, differentiation, and maturation into tissues and organs. The current review offers a complete review of the key aspects associated with the development of 3D bioprinting bioinks, including design concepts, classification, properties, and latest trends. Several important characteristics and features of bioinks, namely, rheology, cross-linking mechanism, cell-matrix interactions, degradation process, and biofunctionalization approach, are analyzed in detail. Natural, synthetic, and hybrid bioinks with regard to printability, biocompatibility, mechanical strength, and potential for tissue regeneration are comparatively discussed. Major technologies used for bioprinting, such as inkjet printing, extrusion printing, and laser-assisted printing, are presented. Moreover, recent advances in multimaterial printing, coaxial printing, vascularization, and maturation processes in 3D bioprinting are considered. Next-generation bioinks such as nanocomposite bioinks, decellularized extracellular matrix-based bioinks, stimuli-responsive smart bioinks, 4D bioprinting materials, and artificially designed bioinks are discussed. Applications of bioprinting in skin, bone, cartilage, neural, cardiac, and tumor tissue engineering, drug screening, and personalized medicine are emphasized.