Fig. 3: The printhead was validated with a material library developed for bone TE.

Extrusion and continuous gradient production were possible with five different materials covering a wide range of viscosities. Rheological measurements consisted of viscosity measurements at various shear rates at empirically determined printing temperatures for the materials (A). Gradient printing with the selected materials was tested by printing continuously in a single plane, while switching pressures from being applied only to one material to only the other material, and monitoring how the extruded composition changed in response (B). The top panel in B schematically shows the printing path using two different materials (shown in blue and yellow), the position along the print path where pressure was applied to one material, but not the other (denoted by the signal in the respective color), and how that changed the composition along the print path. The middle panel shows the printed gradients using the four filler-loaded materials switching with PEOT/PBT without filler. The bottom panel shows the intensity of the middle panel images along the print path plotted against the print length. The empirical knowledge of composition switching time after a signal application was used to plan the printing of a long bone defect-shaped scaffold with a polymer-only core and a HA-loaded polymer cortical region (C). The top image in C shows a long bone defect-shaped scaffold printed with PEOT/PBT alone, and the bottom image shows a similar scaffold being produced with a HA composition gradient.