Loading and Delivery Characteristics of Binary Mixed Polymer Brush‐Grafted Silica Nanoparticles

Binary mixed poly(acrylic acid) (PAA)/polystyrene (PS) brush-grafted silica nanoparticles are evaluated for loading and delivery of a hydrophobic fluorescent dye as a model drug. A previous cryo-electron tomography study of mixed PAA/PS brush-grafted silica nanoparticles shows that in N,N-dimethylformamide (DMF) PAA and PS are microphase separated laterally, while in water PS collapses to form isolated domains within the PAA matrix. Thus, loading with hydrophobic small molecules can be performed in DMF, followed by slow transfer to an aqueous buffer. Loading and release experiments with the fluorescent dye Nile Blue indicate a release half-life of approximate to 13 d. Comparison of the loading capability of mixed brush-grafted nanoparticles with varying percentages of PS indicates that a high percentage of the hydrophobic PS polymer is required in the mixed-brush layer for retention of Nile Blue. In vitro delivery experiments demonstrate that Nile Blue-loaded mixed brush-grafted nanoparticles can mediate delivery of dye to HeLa cells.