Novel superparamagnetic micro-devices based on magnetised PLGA/PLA microparticles obtained by supercritical fluid emulsion and coating by carboxybetaine-functionalised chitosan allowing the tuneable release of therapeutics

When superparamagnetic nanoparticles are loaded within micro-carriers of thermosensitive and injectable biopolymers, “smart” microdevices are obtained: they respond to an external magnetic field (EMF) through the release of any co-encapsulated molecules with a remote on-off control. Creating reliable and effective fabrication technologies for the production of these smart nano/micro-devices remains a challenge. In this work Supercritical Emulsion Extraction technology (SEE) is proposed for the fabrication of microcapsules with a core of poly-lactic-co-glycolic acid (PLGA) or poly-lactic acid (PLA) covered by carboxybetaine-functionalized chitosan (f-chi) and loaded with paramagnetic nanoparticles (MAG, mean size of 6.5±3.0 nm) and water soluble fluorescein (Fluo). Fluo is co-encaspulated as a fluorescent marker for the release study. Microcarriers showed a mean size of 800±60nm with an encapsulation efficiency of up to 90%. The inversion of surface charge, after the f-chitosan coating, suggested the presence of a uniform functionalized surface available for further chemical linkage. The external chitosan layer had a thickness of 200±50nm. An excellent MAG dispersion was confirmed within the biopolymer matrix that was shown to be responsive to EMF; indeed, Fluo was released over 3 or 5 days from PLGA or f-chiPLGA microdevices into PBS medium at 37°C; whereas, remote on-off controlled release was achieved when an Alternating Magnetic Field (AMF) was applied