Investigation of thermoplastic melt flow and dimensionless groups in 3D bioplotting

We investigate the key 3D bioplotting processing parameters, including needle diameter and dispensing pressure, on the shear rates, shear stresses, pressure drops, and swell ratios of extruded miscible polycaprolactone (PCL) blends having a range of viscosities. Assuming simple capillary flow, we construct flow curves and we estimate that the shear stresses inside the needle of the bioplotter range from 2500 to 20,000 Pa and the corresponding shear rates from 2 to 25 s −1 , depending upon the viscosity of the blend. We further identify relevant dimensionless numbers that reflect the material rheological properties and processing conditions; these include the capillary number ( Ca ), Bond number ( Bo ), Weissenberg number ( Wi ), and elasticity number ( El ). At most processing conditions Ca > 1, whereas Bo