Silk fibroin layer-by-layer microcapsules for localized gene delivery

Herein, we describe the delivery of plasmid DNA (pDNA) using silk fibroin (SF) layer-by-layer assembled microcapsules. Deposition of fluorescently labeled SF onto polystyrene (PS) template particles resulted in increasing fluorescence intensity and decreasing surface charge in correlation to SF layer number. After removal of the PS core, hollow, monodisperse, and structurally stable SF microcapsules of variable size and shell thickness were obtained. Plasmid DNA encoding for enhanced green fluorescent protein (eGFP) was loaded onto 1 or 4 μm capsules, either by incorporation of pDNA within the innermost layer of the shell or by adsorption to the microcapsules surface, and in vitro pDNA release, cytotoxicty and eGFP expression were studied. Sustained pDNA release over 3 days was observed using both loading techniques, being accelerated in the presence of protease. DNA loaded SF microcapsules resulted in efficient cell transfection along with low cytotoxicity after 3 days incubation compared to treatment with pDNA/branched polyethylenimine complexes. Among the tested conditions highest transfection efficiencies were achieved using 1 μm capsules where pDNA was adsorbed to the capsule surface. Our results suggest that SF microcapsules are suitable for the localized delivery of pDNA, combining low cytotoxicity and high transfection efficiency.