Polymeric hollow spheres with sizes ranging from nanometer to micrometer scale are particularly functional materials owing to their potential application as drug delivery system (DDS). In order to control the encapsulation and releasing of drug molecules from the interiors under physiological conditions, smart hollow spheres, which are sensitive to temperature has been reported. For the construction of DDS, poly(N-isopropylacrylamide) (PNIPAAm), has been widely investigated due to its sharp thermosensitive phase transition at the lower critical solution temperature (LCST). However, a major problem associated with the application of this polymeric spheres is their poor mechanical stability in the highly swollen state, which leads to a highly undesired burst release of carried drug molecules.
In this study we aimed to integrate both high loading efficiency and controlled drug release into hybrid composite material composed of thermoresponsive copolymer hollow microspheres poly(N-isopropylacrylamide-co-styrene) (PNIPAAm-co-PS ) and outer graphene oxide layer. The PNIPAAm-co-PS microspheres synthesized via one-pot precipitation polymerization method show excellent size monodispersity with well-defined hollow-core structure suitable for high drug uptake. The diffusion-driven drug release is controlled by the electrostatically deposited layer of GO nanosheets, which effectively suppresses the initial burst release and enables sustained drug release in in vitro testing. Moreover, the hybrid microspheres show improved drug encapsulation by 46.4% which is attributed to the diffusion barrier properties and π-conjugated structure of GO. Our hybrid system shows advantage over reported drug-loaded PNIPAAM spheres where temperature-influenced drug release cannot be controlled or requires sophisticated drug loading approach.