Hydrogen-Bonded Multilayers With Controllable pH-Induced Disintegration Kinetics for Controlled Release Applications From Surfaces

We report on incorporation of coordination complexes into hydrogen-bonded multilayers which was found to be an effective method to control pH-induced disintegration kinetics of hydrogen-bonded multilayers. By taking advantage of the strong metal chelating and hydrogen donating properties of Tannic Acid (TA), coordination complexes of Zr4+ and TA (Zr(IV)-TA complexes) were prepared and then self-assembled at the surface using hydrogen accepting polymers such as poly (N-vinyl caprolactam) (PVCL) or poly(N-isopropyl acrylamide) (PNIPAM). Incorporation of Zr(IV)-TA complexes into hydrogen-bonded multilayers allowed controlling kinetics of pH-induced disintegration of the films. We found that the onset of pH-triggered disintegration of the multilayers could be delayed for similar to 10h at a physiologically related pH, which may be an important feature for controlled delivery applications from surfaces. In contrast to neutral polymer/TA multilayers which dissolve rapidly above their critical pH, multilayers of Zr(IV)-TA complexes dissolved in a linear fashion in a longer period of time than that of multilayers composed solely from hydrogen bonding polymers. Multilayers of Zr(IV)-TA complexes could uptake methylene blue at a moderately acidic pH and release the dye molecules at strongly acidic conditions. This study contributes to fundamental understanding of structure-property relationship in hydrogen-bonded LbL films. Considering the interesting biological properties of TA, multilayers of Zr(IV)-TA complexes may be promising for future biomedical applications