Hydrogel based 3D printing: Bio ink for tissue engineering

Advancement in additive manufacturing has opened new avenues to serve the biomedical field, including tissue engineering. The major focus of tissue engineering is to replicate or restore the lost functions of failed organs/damaged tissues by integrating cells and biomaterials. The ease in fabrication of customized scaffolds with high precision and low material wastage are the key features of additive manufacturing over conventional methods. Recently, hydrogel materials as bio ink have shown their potential in biomedical field owing to their resemblance to extracellular matrix and biocompatibility. The application of hydrogels can be exploited for regenerative medicine, wound healing, and drug delivery. Various hydrogels find their application in tissue engineering that can be fabricated into scaffolds using a wide range of processes of additive manufacturing. However, due to the lack of structural strength, the hydrogel matrix is incorporated with different additives in order to improve overall mechanical properties. This review article gives a comprehensive overview on the use of hydrogels of different kinds, such as naturally occurring, synthetic, and composite hydrogels, as prospective bio ink materials for tissue engineering. Different sources of hydrogels, their fabrication and tissue engineering specific properties are discussed in detail. Further, the fundamental and technological challenges for additive manufacturing of hydrogel bioink material for tissue engineering are reviewed. This article will facilitate the reader with recent advancements and the current challenges in bioprinting of hydrogels for tissue engineering.