Disulfide-stabilized poly(methacrylic acid) capsules: Formation, cross-linking, and degradation behavior

We report the preparation of monodisperse, single-component degradable polymer capsules for potential applications in encapsulation, catalysis, and controlled drug delivery. The synthesized capsules, composed entirely of poly(metbacrylic acid) (PMA), are obtained by the sequential deposition of thiolated poly(methacrylic acid) (PMA(SH)) and poly(vinylpyrrolidone) (PVPON) onto silica particles, controlled oxidation of thiol groups into bridging disulfide linkages in the PMA(SH), removal of the silica particles, and finally, release of PVPON by altering the solution pH to disrupt hydrogen bonding between PMA(SH) and PVPON. The PMA capsules are held together solely through biodegradable disulfide linkages. We demonstrate that the capsules undergo reversible swelling in response to changes in external pH, and degrade in the presence of a physiological concentration of a natural thiol-containing peptide; glutathione. These capsules are of interest for in vivo applications, where degradation of the capsules, through cleavage of the disulfide bonds, can be facilitated by the reducing environment within cells.