Fig. 9.

Experimental validation through extrusion of native silk feedstock and pultruding silk fibres via forced reeling. a Pushing experimental validation rig: Zwick Z0.5 universal testing machine in compression mode, with hypodermic needle mount and spin tank. b Schematic representation of extrusion device seen in a. c Schematic representing the key components of the forced reeling system (custom geometry/spool and restrained silkworm) used for pultrusion experimental validation. d Take-up spool and silkworm mid-reeling experiment, with a strand of silk visible between the two. e Plotting stress against reeling speed shows an approximately linear relation between the two variables. The stress encountered during forced reeling is of the same order of magnitude (3–12 MPa) as the pressure predicted through our computational models (6–13 MPa), which supports the argument for pultrusion as the dominant spinning mechanism. f The relationship between the pressure required to extrude native silk feedstock through a non-tapering duct and its diameter is shown. Coloured lines f and filled squares g refer to the correspondingly coloured hypodermic needles used as extrusion dies. The internal diameter of each is constant over a 20 mm length, and is provided for each size. Values presented are maximum pressures attained. For lower speeds and larger diameters, the measured forces showed an initial rise to a steady plateau where the sample continued to flow through the needle, the value of which is presented in these cases. In the higher speed and/or lower diameter cases, failure during the initial rise in pressure was often experienced, and hence maximum pressure reached is presented as an indicator of minimum pressure required, though it is likely the plateau region would be higher. For clarity, only the first 2 mm of the extruded length are shown, for an overview of the entire extrusion process, see Supplementary Fig. 4. g Comparison of our experimental data with previous simulations (Kojic (2006), orange plus; Moriya (2008), yellow circles; Moriya (2009), green x; Breslauer (2009), blue triangle), our extension of Kojic’s work (blue dot-dashes), and the limiting case of our geometric explorations (pale green) (see Fig. 5) shows good agreement, with pressures of similar magnitudes to those predicted through simulation required to extrude native silk feedstock through a non-tapering duct