The effect of spinning forces on spider silk properties.

A new forced silking procedure has been developed that allows measurement of the low forces involved in the silking process and, subsequently, retrieval and tensile testing of the samples spun at the measured silking forces. A strong correlation between silking force and tensile behaviour of spider silk has been established. Fibres spun at high silking force--compared with the conventional yield stress--are stiff and show stress-strain curves previously found in forcibly silked fibres. By contrast, fibres spun at low and very low silking forces are more compliant, and their tensile behaviour corresponds to that of fibres naturally spun by the spider or to fibres subjected to maximum supercontraction, respectively. It has also been found that samples retrieved from processes with significant variations in the silking force are largely variable in terms of force-displacement curves, although reproducibility improves if force is re-scaled into stress. Fibres retrieved from processes with constant silking force show similar tensile properties both in terms of force-displacement and stress-strain curves.