Silk Fibroin-Substrate Interactions at Heterogeneous Nanocomposite Interfaces

Silk fibroin adsorption at the heterogeneous hydrophobic-hydrophilic surface of graphene oxide (GO) with different degrees of oxidation is addressed experimentally and theoretically. Samples are prepared using various spin-assisted deposition conditions relevant to assembly of laminated nanocomposites from graphene-based components, and compared with silicon dioxide (SiO2) as a benchmark substrate. Secondary structure of silk backbones changes as a function of silk fibroin concentration, substrate chemical composition, and deposition dynamics are assessed and compared with molecular dynamic simulations. It is observed that protofibrils form at low concentrations while variance in the deposition speed has little effect on silk secondary structure and morphology. However, balance of nonbonded interactions between electrostatic and van der Waals contributions can lead to silk secondary structure retention on the GO surface. Molecular dynamics simulations of silk fibroin at different surfaces show that strong van der Waals interactions play a pivotal role in losing and disrupting secondary structure on graphene and SiO2 surfaces. Fine tuning silk fibroin structure on heterogeneous graphene-based surfaces paves the way toward development of biomolecular reinforcement for biopolymer-graphene laminated nanocomposites.