Stable polydopamine capsules are prepared by the single-step deposition and self-polymerization of dopamine onto a range of colloidal silica template particles with different sizes and porosities. MTT assays reveal negligible cytotoxicity of the capsules toward cells.

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.

Over the last 15 years, the layer-by-layer (LbL) assembly technology has proven to be a versatile method for surface modification. This approach is likely to find widespread application because of its simplicity and versatility; however, the conventional use of highly charged materials with limited responsive behaviour presents some key limitations. In this tutorial review, the formation of multilayer thin films prepared through non-electrostatic interactions is reviewed. We discuss the assembly of films via a number of different methodologies, with particular emphasis on those that provide enhanced orientational control, stimuli-responsive behaviour, and improved film stability.

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(methacrylic acid) (PMA), are obtained by the sequential deposition of thiolated poly(methacrylic acid) (PMASH) and poly(vinylpyrrolidone) (PVPON) onto silica particles, controlled oxidation of thiol groups into bridging disulfide linkages in the PMASH, removal of the silica particles, and finally, release of PVPON by altering the solution pH to disrupt hydrogen bonding between PMASH 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.

Polymer films and coatings are among the popular and most successful tools to modulate surface properties of biomaterials, specifically tissue responses and fouling behavior. Over the past decade, a novel opportunity has been widely investigated, namely utility of surface coatings in surface-mediated drug delivery. In these applications, deposited polymer films act as both a coating to modulate surface properties and a reservoir for active therapeutic cargo. The field has recently accelerated beyond the proof-of-concept reports toward delivering practical solutions and established technologies for biomedical applications. This review briefly summarizes the recent successes of polymer thin films, specifically those constructed by sequential polymer deposition technique, in surface-mediated drug delivery.