Biocompatible tissue-engineered scaffold polymers for 3D printing and its application for 4D printing

In severe tissue destruction, not only large number of cells are destroyed, but also the extracellular matrix (ECM). The ECM is a three-dimensional (3D) network that provides essential physical scaffolds for the cellular constituents. It is necessary to fabricate a scaffold with the same geometry as the ECM of the desired tissue for the final tissue or organ to be made exactly in the shape of the natural body tissue or organ. 3D printers can print patient-specific scaffolds with complex geometric shapes and precise details due to their easy integration with imaging techniques. In addition, the combination of 3D printing with smart materials led to the emergence of 4D printing, which enables scaffolds to mimic the dynamic nature of tissues to a very large extent. This review presents the advantages of 3D and 4D printing compared to other methods of fabricating tissue engineering scaffolds and the biopolymers used in them. Furthermore, the presentation emphasizes the potential of hydrogels in the context of 4D printing scaffolds. In the following, due to the influence of the selection of process parameters on the quality and properties of the printed scaffolds, the effects of 3D and 4D printing parameters on the mechanical, morphological and biological properties of scaffolds is investigated.