2.11 3D bioprinting of vascular structure
3D bioprinting was conducted on a custom-made integrated tissue and organ printing (ITOP). In brief, the printer had a X, Y, and Z stage controllers, a distributing pneumatic pressure control system for accurately dispensing several materials within a single print. The bioprinter sat in a closed chamber which control temperature and humidity. It could deposit cell-laden hydrogels together with synthetic polymers and overcome the limitations on the size, shape, and structural integrity of single hydrogel prints and create customizable tissue.
For printing our constructs, we added 5% GelMA solution into the syringe with the nozzle of 300 μm (Izumi, Japan). The flat structure and the concave structure were printed with the pressure of 100 kPa and the feedrate of 60 mm/min. We crosslinked the flat structure under UV light for 10s to increase mechanical strength, then placed it on top of concave structure, and crosslinked this integrated structure for 100s to make the two individual structures combine unitedly (Fig 3E).
For the bionic vascular structure with cells, 10×106SMCs were mixed into 5% GelMA solution, and then printed as described above. Prior to the seeding process, 50 μg/ml fibronectin (Invitrogen, USA) solution was injected into the channel to increase cell adhesion. HUVECs suspension (30×106 cell/ml) was injected into the channel, and the structures were incubated at 37℃ for 2 hours. The structures were flipped every 30 minutes to permit cell attachment on all sides, which resulted in a monolayer of HUVECs on the channel wall(Freeman et al., 2019).