The properties of native silk fibroin (SF) solution/gel from bombyx mori silkworms during the full fifth instar larval stage

The properties of native silk fibroin (SF) solution in the gland of silkworms during the full fifth instar larval stage were examined in an attempt to elucidate the mechanism of natural silk spinning in the silkworm. The flow and gelation behavior, birefringence phenomenon, rheological properties, specific viscosity and conformation of SF solutions from the gland of silkworms were measured by polarized light microscope, HAKKE rheometer, Ubbelohde viscometer and Solid-state 13C NMR, respectively. After comparing their properties with regenerated SF solutions from natural silk fibers, it is believed that there exists a progressive maturation process favorable to spin silk fibers with excellent properties from native SF solution and a weak bonded and highly oriented SF gel network with SF molecules partly extended in α-helix conformation is formed in the middle section of the gland of silkworms. This suggests that a biomimetic maturation process for making spinnable solution might be necessary for artificial silk fiber spinning in order to obtain improved fiber properties.