Dipolar Magnetic Interactions in Mn-Doped Magnetite Nanoparticles Loaded into PLGA Nanocapsules for Nanomedicine Applications

Nanocapsules made of poly(lactic-co-glycolic acid) (PLGA) copolymer and with a different load of oleate-coated Mn-doped magnetite nanoparticles are studied for potential nanomedicine applications as nanocarriers with magnetic functionalities, in particular magnetic heating. The mean size of the PLGA nanocapsules and of the magnetic nanoparticles is around 200 and 8 nm, respectively. The aim is to study to what extent the different concentration of magnetic nanoparticles and their confinement into the PLGA nanocapsules affect their spatial arrangement and their magnetic interaction. This is crucial for making progress in the field of magnetic nanocarriers, tailoring their magnetic properties and thus optimizing their performance. The results obtained by combining structural and magnetic analyses indicate that the nanoparticles form aggregates into the PLGA nanocapsules - reaching larger dimension in the sample with the higher magnetic load - and that the dipolar interactions rule the magnetization process and the magnetic relaxing behavior, which are factors determining the magnetic heating capacity. In particular, a double role of the dipolar interactions in the magnetic heating mechanism is highlighted: they stabilize the magnetic moments of the nanoparticles against superparamagnetism and give rise to low-remanence magnetic configurations of the nanoparticle aggregates. While the first effect enhances the heating efficiency, the second one appears harmful.