(349a) Leveraging Solution-Phase Conditions to Promote Nano-Thin Coating Formation Utilizing Silk Fibroin’s Self-Assembly Mechanism
AIChE Annual Meeting
Wednesday, November 18, 2020 - 8:00am to 9:00am
Silk fibroin is a fiber-forming protein derived from the thread of Bombyx mori silkworm cocoons. This biocompatible protein, under the influence of kosmotropic agents such as potassium phosphate, can undergo self-assembly to transform from a water-soluble protein to a robust Î²-sheet rich elastomeric material. By leveraging the concurrent non-specific adsorption and self-assembly of silk fibroin, we demonstrate the growth of adherent and smooth nano-thin silk fibroin coatings on a variety of surfaces. These coatings demonstrate the ability to functionalize topographically complex surfaces without requiring chemical derivatization or specific adhesive interactions, showing potential as a versatile surface modification for biomedical applications. Here, we examine the effects of coating solution parameters such as protein concentration, pH, time, as well as kosmotropic and chaotropic salts from the Hofmeister series, on the solution-phase assembly and interfacial adsorption behavior of silk fibroin. Coating formation, measured using quartz crystal microbalance with dissipation, shows a strong dependence on pH, salt species and concentration. These coatings display continual growth over time with no apparent saturation at low to intermediate potassium phosphate concentrations, a behavior not described by traditional protein adsorption models. Sodium chloride salt solutions did not initiate self-assembly. Moreover, while sodium chloride could increase the amount of silk fibroin adsorbed compared to silk fibroin without additional salts, continual coating growth was not observed. This result suggests that attractive protein-protein interactions are required for sustained coating growth. Since, in our system, surface adsorption occurs simultaneously with solution-phase protein assembly, and we hypothesize the two phenomena are interdependent. We therefore also investigated the solution-phase self-assembly of silk fibroin under various conditions that promoted or did not promote coating growth, including potassium phosphate concentration and pH. Our results showed that at low to intermediate potassium phosphate concentrations, where coatings grow continuously without saturation, silk fibroin formed small aggregates with narrow size distribution, whereas at high potassium phosphate concentrations, where coating growth was inhibited, silk fibroin formed large micron-scale aggregates. Thus, our findings suggest that the continuous growth of nanothin silk fibroin coatings by interfacial self-assembly requires a balance between inter-protein assembly and surface adsorption.