Rapid Assessment of Combined Drop on Demand and Extrusion-based Bioprinting with Controlled Shear Stress and High Shape Fidelity

We present a novel combination of drop on demand (DoD) and extrusion-based bioprinting to generate high-precision patterns of cells inside large hydrogel volumes. Extrusion-based bioprinting has the great advantage of enabling a fast deposition of high viscous cell-loaded hydrogel with reasonable precision. Compromises between high shape fidelity and cell viability, as well as short process times often require many iterations of optimizing process parameters and varying compositions of the hydrogel. To limit the multitude of parameters during extrusion-based bioprinting, a method for rapid process assessment was developed. This enables to define limits for printing temperature, flow rate and nozzle size from basic rheological measurements with regard to the biological and mechanical requirements. The combination of extrusion-based bioprinting with DoD bioprinting allows for precise deposition of low viscous cell suspension and adjustable concentrations of crosslinking agent. Together, the technologies were used to print a bone replacement model by using the pre-defined process parameters. Adiposed-derived stem cells (ASC) prone to osteogenic differentiation were homogenously extruded in a cuboid structure of 10×10×5 mm. Human umbilical vein endothelial cells (HUVEC) were printed as highly dense cell suspension lines inside the extruded hydrogel to allow a potential vascularization of the structure in vivo.