The physical basis of fabrication of amyloid-based hydrogels by lysozyme

The fabrication of amyloid-based hydrogels has attracted remarkable attention within the field of materials science and technology. These materials have a multitude of potential applications in the biomaterials field such as developing scaffolds for tissue engineering, drug delivery and hygiene products. Despite the potential new applications of these materials, the physical nature of their assembly is not well understood. In this study, we have investigated how the conformation of the amyloid precursor state (I) is formed and correlated with the assembly of amyloid-based hydrogels. A transparent hydrogel was fabricated at pH 7.4 by cooling of the temperature-induced unfolded state of hen egg white lysozyme (HEWL). The completely unfolded state (U) at the gelation concentration of HEWL was obtained around 90 °C in the presence of tris(2-carboxyethyl)phosphine (TCEP), with a TCEP/HEWL molar ratio of 4 : 1. The characterization of the hydrogel showed that it was composed of an amyloid fibril-like material. The physical nature of its assembly was examined in detail and it was found that the hydrogel formation reaction was a three-step, four-states process (U → I → F → H). We concluded that the properties of the pre-molten globule state (I) of the protein correlated only with the fibrillation process, whereas the assembly of the fibrils into an hydrogel was found to be almost independent of the I state. Thus, the study presented here provides a complete biophysical insight into the pathway of lysozyme hydrogel assembly.