Influence of pH, temperature, and concentration on stabilization of aqueous hornet silk solution and fabrication of salt‐free materials

Abstract

We found that an aqueous solution of silk from cocoons produced by hornet larvae (hornet silk) can be obtained when the solution is adjusted to basic conditions of pH > 9.2. It is known that native hornet cocoons can be dissolved in concentrated aqueous solution of salts, such as lithium bromide (LiBr) and calcium chloride (CaCl2). Upon the removal of these salts from solution by dialysis, solidification, gelation, or sedimentation of hornet silk is known to occur. In the present study, under basic conditions, however, no such solidification occurred, even after salt removal. In this study, ammonia was used for alkalization of solution because it is volatilized during the casting process and pure hornet silk materials can be obtained after drying. The effects of the concentrations of hornet silk and ammonia, as well as dialysis temperature, on preventing gelation during dialysis were investigated. Dialysis conditions that limit the degradation of hornet silk by hydrolysis in alkali solution were identified. Moreover, casting conditions to prepare flexible and transparent hornet silk film from aqueous ammonia solution were optimized. Molecular structural analysis of hornet silk in aqueous ammonia solution and cast film indicated the formation of α-helix conformations.

Stabilization of Viruses by Encapsulation in Silk Proteins

“…Consequently, any practical silk protein film used to stabilize viruses cannot be folded in its characteristic “water-insoluble” native state. Film casting conditions can dramatically affect silk protein folding and the proportion of α-helix, β-sheet and disordered structures (for example, see refs and ). Because of this variability in molecular structure as a function of casting conditions, we used FTIR to investigate correlations between the molecular structure of the proteins and their ability to stabilize viruses (Figure ).…”

Conformation change of hornet silk proteins in the solid phase in response to external stimulation

“…5 The lithium bromide solution of hornet silk was poured into a bag made of a semipermeable membrane (size: 8/32; Wako Pure Chemical Industries, Osaka, Japan) and suspended in 0.1-N ammonia water. 18 The commercially available ammonia solution (Nacalai Tesque Inc., Kyoto) contains 28 w/w % ammonia, which corresponds to a concentration of 14.8 N. During dialysis, the dialysis fluid was stirred slowly and changed 4 times over a 24-hour period. The dialysis was continued until the electric conductivity of the solution no longer decreased.…”