Release of polyphenolic drugs from dynamically bonded layer-by-layer films

Layer-by-layer (LbL) assembled films have been exploited for surface-mediated drug delivery. The drugs loaded in the films were usually released via diffusion or the degradation of one of the film components. Here we demonstrate that drug release can also be achieved by exploiting the dynamic nature of hydrogen-bonded LbL films. The films were fabricated from tannic acid (TA), a model polyphenolic drug, and poly(vinyl pyrrolidone) (PVPON). The driving force for the film buildup is the hydrogen bonding between the two components, which was confirmed by Fourier transform infrared (FTIR) spectra. The film growth is linear, and the growth rate of the film decreases with increasing assembly temperature. Because of the reversible/dynamic nature of hydrogen bonding, when soaked in aqueous solutions, the PVPON/TA films disassemble gradually and thus release TA to the media. The release rate of TA increases with increasing pH and temperature but decreases with increasing ionic strength. Scanning electron microscopy (SEM) studies on the surface morphology of the film during TA release reveal that the film surface becomes smoother and then rougher again because of the dewetting of the film. The released TA can scavenge ABTS(+•) cation radicals, indicating it retains its antioxidant activity, a major biological activity of polyphenols.