Fig. 4. Schematic drawings of some advanced 3D printing techniques for biofabrication.

(a) Illustration of the basic 3D architecture which could be achieved by using the ITOP technique to print multiple-cell hydrogels and supporting PCL polymers. (b) The upper left represents a mandible bone reconstruction designed based on a human CT image of a mandible bony defect, the upper right image shows a photograph of the 3D printed construct after culturing it in osteogenic medium for 28 days, and the lower image depicts osteogenic differentiation of stem cells in the printed construct confirmed by Alizarin Red S staining. Adapted/reproduced with permission from Springer Nature, ref. [124] (c) Schematic illustration of designing and 3D printing of a biomimetic vascularized bone scaffold, the upper image shows the computer modeling of vascularized bone, the middle images depicts the FDM/SLA 3D bioprinting platform, while the lower image represents the microstructural design of vascularized construct. Adapted/reproduced with permission from John Wiley and Sons, ref. [121] (d) Schematics illustrating the design of 3D printer with seven-channel printhead which is in turn connected to seven cartridges that are individually regulated by programmable pneumatic valves. (e) Side view of one end of a printed microfiber showing its internal 3D structure consisting of seven individually segmented bioinks. Adapted/reproduced with permission from John Wiley and Sons, ref. [125].