Disulfide Cross-Linked Polymer Capsules:  En Route to Biodeconstructible Systems

Hydrogen-bonded multilayer thin films were constructed using poly(vinylpyrrolidone) and poly(methacrylic acid) functionalized with cysteamine. The resulting films included thiol moieties that were cross-linked to render the films stable at physiological pH. Film buildup was followed using quartz crystal microgravimetry, which was also used to demonstrate the improved stability imparted by reacting the thiol moieties to form disulfide bonds. Films without disulfide bonds were readily deconstructed at physiological pH, while those with disulfide bonds were swollen upon exposure to this pH (7) but remained intact. Addition of a common thiol-disulfide exchange reagent, dithiothreitol (DTT) at pH 7 led to disassembly of the multilayer films. The films were also prepared on colloidal substrates (as demonstrated using confocal microscopy) and were used to retain a model drug (fluorescently labeled transferrin) and release this molecule when triggered by the addition of DTT. This approach has potential for the in vivo applications of hollow capsules, as thiol-disulfide exchange leading to deconstruction of the capsules can occur with the assistance of intracellular proteins.