Protein aggregation in aqueous poly(vinyl alcohol) solutions

Proteins that have previously been self-assembled into β-sheet-containing structures in aqueous solution are incubated in aqueous poly(vinyl alcohol) (PVA) solutions of varying PVA molecular weights and therefore viscosities. Fourier transform infrared (FTIR) spectroscopy shows that the self-assembly is driven by protein–protein hydrophobic interactions that correspond to the formation of a β-sheet nanostructure, which previous results show to happen in purely aqueous solution. Unlike in aqueous solution, the self-assembly kinetics are retarded by a factor that is directly related to the PVA solution’s viscosity. Examination of dried solutions over time with scanning electron microscopy shows the formation of ‘spikes’ that organize radially into ‘pompons’. The pompons appear, maximize in number and then disappear with time. Higher-viscosity solutions allow a longer window to see the pompons before their disappearance. FTIR spectroscopy and thioflavin T staining suggest that the spikes are β-sheet-containing protein structures. Thermal analysis shows that the aggregated protein structures restrict PVA molecular motion, as demonstrated by an increase in PVA glass transition temperature and an increase in PVA crystallinity. The results show that self-assembling proteins in polymer solutions could be an interesting way to form biobased nanocomposites.