Controlled and Triggered Small Molecule Release from a Confined Polymer Film

A device composed of a poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel layer sandwiched between two thin Au layers (all on a glass support) was used as a novel platform for controlled and triggered small molecule delivery. Tris (4-(dimethylamino)phenyl)methylium chloride (Crystal Violet, CV), which is positively charged, was loaded into the microgel layer of the device and released in a pH dependent fashion, at a rate that could be controlled by the thickness of the Au layer coating the microgels. Specifically, at pH 6.5 (above the pKa for AAc) the microgels were negatively charged, promoting the strong interaction between the CV and the microgels, hindering its release from the layer. At pH 3.0 the microgel's AAc groups are protonated making the microgel mostly neutral, allowing CV to be released from the microgel layer at a rate that depends on the thickness of the Au covering the microgels. Specifically, devices with thin Au overlayers on the microgel layer allow CV to be released from the device faster than devices with thick Au overlayers. The ability to tune the release rate with pH and Au layer thickness is advantageous for developing implantable devices that are capable of releasing small molecule drugs in a triggered and controlled fashion.