Structure/property relationships in erodible multilayered films: influence of polycation structure on erosion profiles and the release of anionic polyelectrolytes.

We have investigated the influence of polymer structure on the erosion profiles of multilayered polyelectrolyte assemblies fabricated from sodium poly(styrene sulfonate) (SPS) and three different hydrolytically degradable polyamines. We synthesized three structurally related poly(beta-amino ester)s (polymers 1-3) 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 60 nm thick fabricated from polymer 1 and SPS eroded completely in 50 h when incubated in PBS buffer at 37 degrees C, as determined by ellipsometry. Analogous films fabricated from polymers 2 and 3 eroded and released SPS into solution over significantly longer time periods ranging from approximately 150 h (ca. 6 days) to 370 h (ca. 15 days), respectively. These differences are consistent with a systematic increase in the hydrophobicity of polymers 1-3 as well as the relative rates at which these polymers degrade hydrolytically. This work demonstrates that it is possible to tailor the rates at which thin, 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. The principles reported here may therefore 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.