(261b) Protein-Loaded Self-Assembled Silk Fibroin Coatings for Sustained Drug Delivery from PLLA Electrospun Scaffold Surfaces

Electrospun scaffolds derived from aliphatic polyesters, including poly (L-lactic acid) (PLLA), have been regularly studied for tissue engineering applications due to their ease of processing, robust mechanical properties, and nontoxic biochemical degradation. However, practical applications of PLLA scaffolds suffer due to their lack of bioactive moieties and their hydrophobic nature, which generally do not provide beneficial cell-surface interactions. Recently, we have developed a novel approach for generating bioactive nano-thin coatings of silk fibroin, a protein derived from the cocoons of Bombyx mori silkworm. Our bottom-up approach utilizes the concurrent adsorption and self-assembly of silk fibroin, leading to extremely dense, adherent, and conformal coatings that can be grown on a variety of surfaces. We have previously shown the ability to grow these coatings on topologically complex PLLA electrospun scaffolds without requiring covalent chemistries or surface pre-treatment. Importantly, these silk fibroin nano-thin coatings led to increased efficacy of the scaffolds for neuroregenerative applications, as seen by enhanced adhesion of dorsal root ganglia as well as neurite extension. Recently we have shown the ability of these nano-thin coatings to encapsulate macromolecular payloads, such as bioactive proteins, on substrate surfaces through a non-covalent one-pot approach where the payload is co-assembled into the coating by adding it directly into the coating solution. Our one-pot coating process can incorporate proteins with various physicochemical properties and the payloads can then be released from the coatings over time in a sustained manner. Importantly, our process does not cause significant loss of enzymatic activity, as shown using lysozyme as a model payload. Because our coatings are made without reactive chemicals, this method for surface functionalization is highly compatible with biologics, which are often disrupted by conventional non-bioorthogonal grafting chemistries. Here, we furthermore demonstrate that loaded silk fibroin coatings can be grown on electrospun PLLA scaffolds. We use dye-conjugated model proteins with various physicochemical properties to investigate the loading characteristics of our co-assembly approach. Additionally, we show our ability to control the loaded protein mass by varying their concentration in the coating solution as well as coating time, which can allow for a 6-fold increase in total loaded mass. Furthermore, by using silk fibroin and payload proteins with separately detectable dyes (rhodamine and fluorescein), we elucidate fundamental mechanisms underlying co-assembly of payload proteins with silk fibroin, both in solution and at a solid surface. Specifically, we find that smaller, more hydrophobic, and less positively charged proteins co-assemble to a higher degree. Finally, we investigate the ability to incorporate biomedically relevant growth factors, including nerve growth factor, to show the practical applicability of these nano-thin silk fibroin coatings in directing a desired bioresonse for in vitro or in vivo applications. Overall this work demonstrates a facile and versatile method for engineering the surface functionality of electrospun scaffolds for drug delivery and tissue engineering applications.