Erodible Multilayered Films Fabricated from Degradable Polyamines: Influence of Polymer Structure and Film Architecture on Film Erosion and Controlled Release
Jingtao Zhang, Nathaniel J. Fredin, and David M. Lynn. Department of Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Drive, Madison, WI 53706
Ultrathin films that erode in physiological media and permit control over the release of anionic polyelectrolytes could play an important role in the development of localized therapies. For example, we reported recently that ultrathin multilayered polyelectrolyte films fabricated from a hydrolytically degradable polyamine can be used to localize the delivery of DNA from the surfaces of macroscopic objects. This investigation sought to characterize the influence of polymer structure on the erosion profiles of multilayered polyelectrolyte assemblies fabricated from degradable polyamines and sodium poly(styrene sulfonate) (SPS). We synthesized three structurally related poly(amino ester)s having systematic variations in both charge density and hydrophobicity. These changes in structure did not influence film thickness significantly, but polymer structure was found to play an important role in defining the rates at which multilayered assemblies fabricated from these materials eroded in physiologically relevant media. Films ca. 60 nm thick fabricated from these three polymers were incubated in PBS buffer at 37 °C to characterize film erosion and controlled release profiles. These films eroded completely and released SPS in either 48 hours (two days), 150 hours (ca. 6 days) to 370 hours (ca. 14 days), respectively, as determined by ellipsometry and UV/visible spectrophotometry. These large differences in erosion rate are consistent with a systematic increase in the hydrophobicity of these polymers as well as the relative rates at which they degrade hydrolytically. This work demonstrates that it is possible to tailor the rates at which ultrathin multilayered polyelectrolyte assemblies release incorporated anionic polyelectrolytes over a large range of time periods simply by changing the structure of the degradable polyamine used to fabricate a film. We also investigated the role of film architecture on erosion and release profiles by fabricating multilayered films composed of combinations of these different degradable polyamines. The application of this approach to the fabrication of erodible assemblies having highly tunable release profiles will be discussed. The materials and principles reported here could contribute to the design of multilayered assemblies that permit a broad range of spatial and temporal control over the release of therapeutic agents from coated surfaces.