Self-assembled nano-thin silk fibroin coatings for tissue engineering and drug delivery applications

Abstract

Proteins are exceptional biomaterials as they are generally biocompatible, biodegradable, and can direct specific cellular responses. However, their ability to be applied as stable and uniform surface coatings to functionalize biomedical devices is limited due to their weak adhesive and cohesive interactions. B. mori silk fibroin is a supramolecular protein that has gained a large interest in various biomedical fields, including tissue engineering and drug delivery. This protein has been shown to be biocompatible, biodegradable, and importantly, can be used to produce stable protein coatings driven by inter- and intramolecular self-assembly. However, current top-down strategies for generating these coatings are often limited by substrate chemistry, due to their weak adhesive properties, and are not applicable to topographically complex surfaces, such as tissue engineering scaffolds.This thesis will assess the ability to generate functional biomedical protein coatings though a novel bottom-up approach, which leverages the concurrent interfacial adsorption and potassium phosphate-induced supramolecular self-assembly of B. mori silk fibroin. This non-covalent coating strategy results in the formation of dense, hydrogel-like nano-thin coatings. These coatings can be grown over time without apparent surface saturation, and exhibit both adhesive and cohesive properties which results in adherent and stable surface modifications. Importantly, the coatings can be grown on substrates exhibiting a wide range of chemistries and surface hydrophobicity, showing potential as a facile universal coating process. Coatings were applied to poly(L-lactic acid) electrospun tissue engineering scaffolds to study the ability of the self- assembled coatings to functionalize complex non-planar surfaces and provide surface functionality to improve their regenerative efficacy. The coatings were shown to form homogeneously along the scaffold fiber surfaces, and improved scaffold bioactivity shown using in vitro dorsal root ganglia cell studies. Finally, the ability to generate nano-thin protein-loaded silk fibroin coatings for drug delivery applications are shown using a modular co-assembly approach. The co-assembly process is shown to be tolerant to payloads with different net charges and hydrophobicity but is limited by payload size. This co-assembly process results in extremely homogeneous incorporation of payload proteins, and 4-5x higher surface loading than physical adsorption alternatives. Importantly, the incorporated protein payloads can be released for up to 14 days while maintaining >80% activity, suggesting that co-assembled coatings could be potentially used to deliver bioactive protein payloads for in vivo or in vitro studies. Overall, this research supports the development of a facile universal coating strategy that can be applied as a bottom-up approach to functionalize biomaterial surfaces utilizing the interfacial supramolecular self-assembly of B. mori silk fibroin.