Sol-gel synthesis, physicochemical characteristics and in vitro pH-responsive metformin drug release of uniformly polydopamine coated mesoporous silica nanospheres

A recent attention has been paid to the repurposing potential of metformin drug for cancer chemotherapy. Herein, pH-responsive metformin drug delivery nanocarriers were achieved using sol-gel synthesized mesoporous silica nanospheres (MSN) uniformly coated with polydopamine (PDA) shell. The PDA coating shell around the MSN surface was in situ formed through oxidative self-polymerization of dopamine monomers in an alkaline solution at room temperature. The microstructure, structural and textural characteristics of PDA@MSN were examined and compared to uncoated MSN. Furthermore, PDA coated metformin (MET) drug-loaded MSN were used to study the pH-responsive MET drug release behaviour under neutral and acidic conditions. The in vitro release test showed that the PDA coating shell not only protects MET drug leakage under normal physiological conditions (pH 7.4) but also allows for its controlled/sustained release in acidic conditions (pH 4.5 and pH 5.5) which closely mimic the intracellular acidity (pH 4.5–5.5) of endosomes/lysosomes formed around drug-loaded nanocarriers after their endocytosis by cancer cells.