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 Delta C (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.