Abstract
In spite of all the efforts towards deciphering the silk spinning process of spiders, the underlying mechanism is yet to be fully revealed. In this research, we designed a novel approach that allowed us to quantitatively evaluate the concentration change of silk dope during the liquid-to-solid spinning process of the orb-weaver Nephila pilipes. As a prior characterization of the optimal silking conditions, we first gauged the influence of silking-rate, ranging from 1.5 to 8.0 m/min, on dragline silk diameters and silk tensile strengths obtained from the spiders. Next, to evaluate the liquid content of the silk dope, the major ampullate gland was dissected and the concentration of the sac portion was measured by thermogravimetric analysis (TGA). The solid content of the dragline fibers leaving the spinneret was investigated by calculating the ratio of collected dried silk to the weight loss of the spider recorded in situ upon spinning. As the results indicate, the tensile strength and diameter of the spun dragline fibers were 800–1100 MPa and 8–11 μm, respectively. The liquid content of silk stored in the major ampullate sac (50.0 wt%) was significantly lower than that of silk leaving the spinnerets (80.9–96.1 wt%), indicating that a liquid supplying mechanism might be involved during the spinning process. This reveals, for the first time, quantitative evidence in support of the lubricative hypothesis proposed formerly, namely that a liquid coating layer is supplemented to compensate for silking resistance during the spinning process of a spider. The spigot, at the exit of the spinneret, is speculated to serve as a valve-like controller that regulates the lubrication process along with fiber formation. Taken together, these findings provide understanding of the physiological functions in the spider spinning process and could further shed some light on the future biomimetic development of silk material fabrication.
Highlights
Studies of spider silk fibers are largely motivated by the exceptional strength, toughness, biocompatibilities, and potential medical applications of the fibers [1,2,3,4,5]
To collect the dragline silk, we pulled the silk from the spinnerets of a secured spider under a dissecting microscope taped the two threads on a rotor powered by a motor [32]
Major ampullate dragline silks of N. pilipes were collected at varied winding speeds via a programmable reeling rotor
Summary
Studies of spider silk fibers are largely motivated by the exceptional strength, toughness, biocompatibilities, and potential medical applications of the fibers [1,2,3,4,5]. In spite of significant efforts to mimic native spider silk fibers, the mechanical performance of artificially-generated fibers, spun from either recombinant or natural silk, are often far below the expectation of super-strong fibers [2,4,5,6,7,8,9,10,11,12]. Understanding the silk spinning process of spiders, the naturally born spinners, could provide an essential piece of the blueprint for the fabrication of novel artificially spun materials with superior properties. Many biomimetic spinning processes could hardly recreate the native spider silk spinning machinery inside the spider’s body, and the inferior physical properties of those resulting artificially-spun fibers are generally reported [18]. The typical ampullate gland consists of a tubular tail portion, a sac-like midpiece, and a thin looped spinning duct linking the fluid silk reservoir with the spinneret
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