Unexpected high toughness of <i>Samia cynthia ricini</i> silk gut.

Abstract

Silk gut fibers were produced from the silkworm <i>Samia cynthia ricini</i> silk glands by the usual procedure of immersion in a mildly acidic solution and subsequent stretching. The morphology of the silk guts was assessed by scanning electron microscopy, and their microstructure was assessed by infrared spectroscopy and X-ray diffraction. It was found that both naturally spun and <i>Samia</i> silk guts share a common semicrystalline microstructure. The mechanical characterization of the silk guts revealed that these fibers show an elastomeric behavior when tested in water, and exhibit a genuine ground state to which the fiber may revert independently of its previous loading history. In spite of its large cross-sectional area compared with naturally spun silk fibers, <i>Samia</i> silk guts show values of work to fracture up to 160 MJ m^-3, much larger than those of most of their natural counterparts, and establish a new record value for this parameter in silk guts.