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.
Highlights
Silk is a biopolymer with perfect biocompatibility and tunable biodegradability due to its unique protein compositions and structures [1,2,3,4,5]
Dynamic Mechanical Analysis (DMA) analysis is more sensitive than Differential Scanning Calorimetry (DSC), as short-range chain motion changes are easier to detect than heat capacity changes during the phase transitions of biopolymer materials
Our study showed that by using the Group Interaction Modeling (GIM) model, the disorder degree (f dis) of silk samples can be inferred from the cohesive energy (Ecoh), the skeletal degree of freedom (N), and the loss factor at the glass transition region
Summary
Silk is a biopolymer with perfect biocompatibility and tunable biodegradability due to its unique protein compositions and structures [1,2,3,4,5]. [15,16,17,18,19,20] Juan et al [21] investigated the effect of temperature and thermal history on the mechanical properties of native silkworm and spider dragline silks by dynamic mechanical thermal analysis (DMTA) Their results showed that the DMA storage modulus and loss tangent of silk materials depend on their different chemical and physical processing methods. 2018, 19, 3309 structure and mechanical property of these two kinds of silk fibers (Thai, Chin), and combined with SSDSC and FTIR technologies to investigate these properties and transformation mechanism of their protein films regenerated from the FA solution with a changing CaCl2 content (1%~6%). These comparative studies are important for the design of advanced silk-based materials with tunable structures and properties
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