Some Observations on the Structure and Function of the Spinning Apparatus in the Silkworm Bombyx mori

Abstract

Silkworm silk has outstanding mechanical properties despite being spun at room temperature and from aqueous solution. Although it has been proposed that fiber formation is mainly induced by shearing and extensional flow in the spinneret, the detailed structure and function of the spinning apparatus of Bombyx mori silkworms are still not fully elucidated. In this paper we describe three aspects of the functional microanatomy of the spinning apparatus: changes in the diameter of the silk gland duct with distance along the duct, how the birefringence of the fibroin changes as it flows down the duct, and the detailed three-dimensional structure of the silk press and related structures. The existence of a double escaped nematic liquid crystal texture in the fibroin in a region of the duct is described. After this region the birefringence suddenly disappeared until the start of an internal draw down taper which commenced just before the silk press. In the internal draw down taper the birefringence increased dramatically to an asymptotic value as a thread was drawn from the fibroin gel. The structure of the silk press suggests that it acts as a restriction die whose diameter can be regulated.

Silk tape nanostructure and silk gland anatomy of trichoptera

“…This was similar to the internal drawdown taper observed in the anterior narrowing of the spider and silkworm glands. 23,37 The role of the transition site in fiber formation merits further physiological and structural investigation.…”

A microfluidic cell for studying the formation of regenerated silk by synchrotron radiation small- and wide-angle X-ray scattering

“…While the structure and function of spinning ducts in spiders 1 and silk worms 2,3 have been studied extensively, microscopic models of silk protein ͑fibroin͒ aggregation and silk fiber formation have still to be experimentally verified. 1,4,5 In-situ synchrotron radiation ͑SR͒ micro-small-angle X-ray and micro-wide-angle X-ray scattering ͑ -SAXS and -WAXS͒ experiments during forced silking of Nephila spiders 6 provide microstructural information on the nascent silk thread at the exit of the spigots.…”

Applicability of biotechnologically produced insect silks

“…Such a material in principle could challenge the animals due to the relatively high forces needed for processing. However, liquid crystal structures have been observed in silk ducts of spider and silkworm silk glands, which disappear right before the dope enters the spinneret [38,39]. These structures reduce inter-molecular friction resulting in a lower viscosity and thereby reducing the energetic effort of spinning a fibre.…”