Extended Release Antibacterial Layer-by-Layer Films Incorporating Linear-Dendritic Block Copolymer Micelles

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Abstract

The electrostatic layer-by-layer (LbL) assembly approach offers large potential in the area of drug delivery from thin films; however, because the processing technique is aqueous-based, there have been few strategies proposed to incorporate hydrophobic molecules into these films. Here we create an LbL film that is capable of incorporating hydrophobic drug at high loadings via encapsulation with linear-dendritic block copolymer micelles and demonstrate for the first time release times of a hydrophobic antibacterial agent over a period of several weeksa significant improvement over reports of other micelle-encapsulated thin films with release times of several minutes. The amphiphilic linear-dendritic block copolymer is composed of poly(propylene oxide) (PPO), which forms the hydrophobic core creating the compartment for hydrophobic drug encapsulation, and poly(amidoamine) (PAMAM), which forms the outer corona of the micelle. The PAMAM is polycationic, enabling LbL deposition with negatively charged poly(acrylic acid) (PAA). The stable PPO−PAMAM micelles incorporated into the LbL films encapsulated a hydrophobic bactericide, triclosan, which have loading capacities as high as 80−90%. Film thickness and UV−vis measurements confirm the formation of the LbL film and incorporation of triclosan into the film. Fluorescence measurements of PPO−PAMAM/PAA films with pyrene indicated the presence of hydrophobic domains in the film. GISAXS revealed regular spacing of approximately 10.5 nm in the direction parallel to the film substrate, which is approximately the same size as the PPO−PAMAM micelles in aqueous solution. Volume fraction measurements based on elemental analysis and TGA confirm the GISAXS data. An in vitro release study revealed long release times of triclosan on the order of weeks, and a Kirby Bauer test was performed on Staphylococcus aureus, demonstrating that the drug released was still active to inhibit the growth of bacteria.

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