Bioprinting of Coaxial Multicellular Structures for a 3D Co-culture Model

With three dimensional (3D) bioprinting technology, it is feasible to fabricate various types of tissue models, in which multiple kinds of cells can be co-cultured. In this study, a novel 3D coaxial co-culture model in vitro was established by direct bioprinting. Using a four-layer coaxial nozzle, novel coaxial multicellular structures were fabricated, which contained two layers of alginate hydrogel as shell and two layers of hollow channels for cell perfusion. Sodium alginate (Na-Alg) was crosslinked by calcium cation with the contact of coaxial flows, forming a tubular coaxial structure of hydrogel. Human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs) were used for a typical vascular co-culture model. Collagen solutions loaded with HUVECs and HUVSMCs were perfused into the layers of hollow channels and gelled at 37 ℃. The forming effect was favorable with good integrity. Pertinent process parameters of the bioprinting were investigated. Mechanical properties of four-layer coaxial structures were evaluated, indicating the higher mechanical strength than monolayer hydrogel structure. Cell viability assay after cell perfusion showed that the process of cell perfusion was feasible. In 7-day culture, cells maintained a steady proliferation. The immunohistochemical expression of HUVECs and HUVSMCs was detected in the structure. Cell work showed good biological functions of this 3D coaxial co-culture model.