Exploring the Structural Transformation Mechanism of Chinese and Thailand Silk Fibroin Fibers and Formic-Acid Fabricated Silk Films

Abstract

Silk fibroin (SF) is a protein polymer derived from insects, which has unique mechanical properties and tunable biodegradation rate due to its variable structures. Here, the variability of structural, thermal, and mechanical properties of two domesticated silk films (Chinese and Thailand B. Mori) regenerated from formic acid solution, as well as their original fibers, were compared and investigated using dynamic mechanical analysis (DMA) and Fourier transform infrared spectrometry (FTIR). Four relaxation events appeared clearly during the temperature region of 25 °C to 280 °C in DMA curves, and their disorder degree (fdis) and glass transition temperature (Tg) were predicted using Group Interaction Modeling (GIM). Compared with Thai (Thailand) regenerated silks, Chin (Chinese) silks possess a lower Tg, higher fdis, and better elasticity and mechanical strength. As the calcium chloride content in the initial processing solvent increases (1%–6%), the Tg of the final SF samples gradually decrease, while their fdis increase. Besides, SF with more non-crystalline structures shows high plasticity. Two α- relaxations in the glass transition region of tan δ curve were identified due to the structural transition of silk protein. These findings provide a new perspective for the design of advanced protein biomaterials with different secondary structures, and facilitate a comprehensive understanding of the structure-property relationship of various biopolymers in the future.

Influence of the Casting Concentration on the Mechanical and Optical Properties of FA/CaCl2-Derived Silk Fibroin Membranes

“…et al and Zhang et al [33,37]. While all these works have a similar sequence of process steps, they focus on different aspects of the FA/CaC 2 manufacturing chain [33][34][35][36][37] [35][36][37]. However, Zhang et al previously reported on the influence of dissolution of silk fibroin in FA/CaCl 2 on the molecular weight ratio and concluded that in comparison to common dissolution methods facilitating LiBr, CaCl 2 +EtOH, Ca(NO 3 ) 2 +MeHO or LiSCN, among others, the FA/CaCl 2 solvent rather showed decreased alterations in molecular weight [45].…”

“…The dissolution of silk fibroin using FA/CaCl 2 has been thoroughly investigated in several publications, such as Liu. et al and Zhang et al [33,37]. While all these works have a similar sequence of process steps, they focus on different aspects of the FA/CaC 2 manufacturing chain [33][34][35][36][37] [35][36][37].…”

“…The aim of this study was to evaluate the production processes and the resulting properties of casted silk fibroin membranes fabricated via formic acid (FA) and calcium chloride (CaCl 2 ) dissolution. In recent years there have been several works that have established this novel dissolving process using FA/CaCl 2 as an integral part of the regeneration process of silk fibroin [33][34][35][36][37]. Though this technique has recently evolved and is now recognized as a fast and cheap manufacturing method, it has scarcely been investigated so far.…”

Protein and Polysaccharide-Based Fiber Materials Generated from Ionic Liquids: A Review

“…In several studies [17,144], formic acid was mixed with calcium chloride to break down natural silk by disrupting the native structure and breaking down carbon-carbon and carbon-nitrogen chains. Prolonged exposure to formic acid lowered the molecular weight of the silk and affected the thermal stability of the final biopolymer, including its glass transition temperature and region.…”

“…A poor solvent will significantly affect the miscibility of protein or polysaccharide polymers and reduce the mechanical properties of the final materials [14][15][16]. In addition, many organic solvents will markedly alter the original molecular weight of protein materials such as silks [17]. Therefore, the use of ionic liquid (IL) is frequently applied for tuning the final properties of the material.…”