Encapsulation of Iron Oxide Nanoparticles into Poly(lactic acid) Micro/Nanoparticle System and Poly(lactic acid)/Polystyrene Bio-Blend Microparticle System

Magnetic iron oxide nanoparticles (IO NPs) have a wide application in biomedical engineering, catalysis, magnetic resonance imaging and so on. However, free IO NPs have several challenges such as aggregation and chemical activity, causing loss of magnetism and dispersibility. In order to protect naked IO NPs, a controllable process to encapsulate either hydrophobic or hydrophilic IO NPs into the hydrophobic biodegradable polymer micro/nanoparticles has been developed to meet various applications of magnetic nanoparticles. By applying the same experimental setup, we can generate polymer particles with different shapes and sizes, encapsulating either hydrophobic or hydrophilic NPs, by simply adjusting the water phase viscosity and the emulsion temperature. In this study, both a pure poly (lactic acid) (PLA) system and a bio-blend of poly(lactic acid)/polystyrene (PS) were employed to encapsulate hydrophobic (~5 nm) or hydrophilic (~10 nm) iron oxide nanoparticles (IO NPs). In order to encapsulate hydrophilic IO NPs, a water-in-oil-in-water (W/O/W) emulsion was formed via only one emulsion step. The transformation between hollow microparticles and solid nanospheres was realized by repeating the emulsion process between high temperature (HT) and room temperature (RT).  Hydrophobic IO NPs were encapsulated into nanospheres via an oil-in-water (O/W) emulsion or microparticles via W/O/W emulsion.