Pulsatile Releasing Platform of Nanocontainers Equipped with Thermally Responsive Polymeric Nanovalves

Polymer-gated reservoirs built of an ordered porous anodic aluminum oxide (AAO) platform equipped with poly(N-isopropylacrylamide) (PNIPAM) brushes grafted from the surface using atom transfer radical polymerization were fabricated and studied. The brushes of different lengths were grafted from the AAO surface with pores having diameters of 30, 50, and 80 nm, respectively. Polymer brushes served as thermally responsive valves that can immediately open and close the pores just by crossing the PNIPAM lower critical solution temperature. Calcein was used as a model fluorescent molecule to follow a release process from the platform of the gated nanocontainers. The studied systems enable the burst release of the loaded substance, followed by diffusion-controlled release that depends on the pores' diameter. These platforms are characterized by a high loading capacity in comparison to polymer films and can be loaded repeatedly. Importantly, the opening/closing of the nanocontainers is reversible, and a pulsatile release can be easily realized. Such platforms combined with highly localized heating devices can find potential applications in many systems where small controlled amounts of substances have to be released on demand, such as lab-on-a-chip, total analysis, and nano/microfluidic systems.