  This study presents the spreading of a single filament of a yield stress
(viscoplastic) fluid extruded onto a pre-wetted solid surface. The filaments
spread laterally under surface tension forces until they reach a final
equilibrium shape when the yield stress dominates. We use a simple experimental
setup to print the filaments on a moving surface and measure their final width
using optical coherence tomography. Additionally, we present a scaling law for
the final width and determine the corresponding pre-factor using asymptotic
analysis. We then analyse the level of agreement between the theory and
experiments and discuss the possible origins of discrepancies. The process
studied here has applications in extrusion-based thermoplastic and bio-3D
printing.
