Synergistic effects of glycerol on the hydration dynamics and rheological properties of collagen.

As a polar green solvent that stabilizes collagen, glycerol is widely used in many cosmetic and biomedical applications. Glycerol stabilizes collagen's triple helical structure by replacing the water molecules in the hydration shell, which are directly involved in maintaining collagen's structure through the inter- and intra-molecular hydrogen bonds. It is essential to understand how glycerol affects the hydration dynamics of collagen, which in turn influences its viscoelasticity. This understanding helps to optimize the ratio of glycerol needed for targeted applications. In this study, hydration dynamics studies using NMR spectroscopy revealed that the T2 relaxation times of different water fractions in collagen increase with the addition of glycerol, resulting in loosening of the collagen structure as observed from AFM of collagen fibrils. These results are complemented by Raman spectroscopy, indicating a reduction in intermediate water with increasing glycerol concentration. Molecular dynamics simulation also supports the decreased protein hydration under the influence of glycerol in the second hydration shell. Linking hydration dynamics to rheological properties shows that glycerol preserves viscoelastic characteristics, contributes to a softer structure by decreasing the elastic modulus, and enhances the thermal stability of collagen. Thus, this study emphasizes the role of glycerol in altering the hydration dynamics of collagen, which in turn influences its mechanical properties, making it significant for applications in collagen-based cosmetics and biomedical fields.