3D bioprinting of complex structures by the method of freeform reversible embedding of suspended hydrogels

There has been an increasing demand for bioengineered blood vessels for use in both regenerative medicine and drug screening. However, availability of a true bioengineered vascular graft remains limited. Three-dimensional (3D) bioprinting offers a potential approach to fabricate blood vessels or vascularized tissue structures of various architectures and sizes for transplantation and regeneration. Although some studies have reported the achievement of 3D printing of large-sized blood vessels in the human body, there are still some urgent problems to be solved, such as incomplete microvascular simulation and low biocompatibility and mechanical strength of scaffold materials. Traditional vertical stacking method has some disadvantages like uneven pipe diameter and number of layers printed. An alternative solution is needed to solve these problems. In our study, we tested printability of hollow vessel-like scaffolds into the gelatin support bath using an extruded 3D printer as an alternative solution, using appropriate support bath formulation. Alginate is widely used in extrusion bioprinting of vascular tissue structures. For example, alginate can be physically crosslinked with the concomitant calcium chloride (CaCl2) solution to ensure structural fidelity of bioprinted hollow structures. In our study, a 1% alginate solution was prepared as a bioink. The aim of this study is to print vessel-like scaffolds with the aid of hydrogel using an extruded 3D printer. Using an extruded 3D printer, vessel-like scaffolds were bioprinted with alginate bioink using the FRESH method. In our study, two different support bath formulations were used, and their printability was evaluated. Swelling was observed during printing in the gelatin support bath V0. Therefore, it was decided that v1 is more suitable for printability. Flow test and tensile test results of hollow vessel-like scaffold obtained with gelatin support bath V1 were observed. The hollow vessel-like scaffold was observed to withstand the flow test for more than 3 hours.