[Analysis of protective mechanism of silk protein based cryoprotectants]

Dimethyl sulfoxide (Me ₂SO) supplemented with fetal bovine serum (FBS) is a widely used cryoprotectant combination. However, high concentration of Me ₂SO is toxic to cells, and FBS presents problems related to diseases such as bovine spongiform encephalopathy and viral infections. Silk protein is a kind of natural macromolecule fiber protein with good biocompatibility and hydrophilicity. The aim of this paper is to analyze the cryoprotective mechanism of silk protein as cryoprotectant. Firstly, differential scanning calorimetry (DSC) was used to measure the thermal hysteresis activity (THA) of silk protein. The THA of 10 mg/mL sericin protein was 0.96°C, and the THA of 10% (V/V) fibroin protein was 1.15°C. Then the ice recrystallization inhibition (IRI) of silk protein-PBS solution was observed with cryomicroscope. The cold stage was set at - 7°C, after 40 minutes' incubation, the mean grain size rate (MGSR) of sericin protein and fibroin protein were 28.99% and 3.18%, respectively, which were calculated relative to phosphate buffer saline (PBS) control. It is indicated that sericin and silk fibroin have certain effects of inhibiting recrystallization of ice crystals. Finally, the structure and physicochemical properties of silk protein were analyzed by Fourier transform infrared spectroscopy (FTIR). The results showed that the content of the random coil was 75.62% and the β-sheet structure was 24.38% in the secondary of sericin protein. The content of the β-sheet structure was 56.68%, followed by random coil structure 22.38%, and α-helix 16.84% in the secondary of fibroin protein. The above analysis demonstrates the feasibility of silk fibroin as a cryoprotectant, and provides a new idea for the selection of cryoprotectants in the future.