The fabrication and characterization of stable core-shell superparamagnetic nanocomposites for potential application in drug delivery

Two systems of core-shell superparamagnetic nanoparticles in the size range of 45–80 nm have been fabricated by the coating of bare magnetite particles with either mesoporous silica or liposomes and the loading/release of the anti-cancer drug Mitomycin C (MMC) from their surfaces has been investigated. The magnetic cores of size ∼10 nm were produced by a co-precipitation method in aqueous solution, with the silica coating containing an unstructured network of pores of size around 6 nm carried out using a surfactant-templating approach and the liposome coating achieved by an evaporation-immersion technique of the particles in a lipid solution. Stability measurements using a scanning column magnetometry technique indicated that the lipid-coating of the particles halts the sedimentation otherwise apparent in <1 h for the bare magnetite to produce an ultra-stable system and thereby overcome one of the main barriers to potential in-vivo applications. Whilst an increase in stability was also observed in the silica-coated system, it was still unstable over a few hours and will require further investigation. Magnetization curves of the coated systems were indicative of superparamagnetic behavior whilst the in vitro loading and release of MMC resulted in two distinctly different outcomes for the two systems: (i) the silica-coated particles saturated in <4 h to a loading of around 7 μg/mg of material, releasing about 6% at a near constant rate over 48 h whilst (ii) the lipid-coated particles saturated to around only 4 μg/mg over the same time period but with a subsequent rapid release rate over the first 3 h to 27% then rising near-linearly to a value of about 45% at the 48 h mark. This gives scope for systems' to be tuned to the appropriate rate and load delivery as required by clinical need with further investigations underway.