Impact of calcium chloride concentration on structure and thermal property of Thai silk fibroin films

Regenerated Thai silk fibroin films were successfully fabricated using a novel calcium chloride–formic acid solution system. Different concentrations of calcium chloride (1.0, 1.5, 2.0, 3.0, 4.0, and 6.0 mass% in formic acid) could be embedded into the silk structure, and their glass transition temperature (T_g), specific heat (C_p), and thermal stability were studied and compared by the methods including scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and step-scan DSC (SSDSC). The results showed that with the increase in the CaCl₂ content during film fabrication, the ΔC_p value of the final samples in the glass transition region gradually increased, while T_g and the thermal stability decreased, suggesting that a more non-crystalline structure formed in the sample produced with a high concentration of CaCl₂. These findings offer a new strategy for the fabrication of biocompatible silk materials with different structures, and it can be used for different silk fibroins for various biomaterial applications in the future.