Magnetic Nanoparticle Composites in Complex Matrices: The Role of Particle Dispersion in Providing Controlled Stimulus Response

Magnetic nanoparticles (MNPs) have potential biomedical applications as efficient mediators for AC-magnetic field hyperthermia and as contrast agents for magnetic resonance imaging (MRI) due to their strong responses to applied magnetic fields. However, several challenges are associated with the use of MNPs for in vivo biomedical applications that must be addressed to realise these technologies. The surface chemistry of MNPs must be engineered to prevent nanoparticle aggregation and reduce their rate of interaction with biomolecules. This work focuses on the development of synthetic strategies to address the longstanding challenges of maintaining the in vivo magnetic efficiency of MNPs as theragnostic agents and as magnetic components in responsive nanocomposite materials. Multicore iron oxide nanoparticles, nanoflowers (NFs), display strong magnetic responses arising from complex internal magnetic ordering. A catechol-derived grafting approach is described to strongly bind polyethylene glycol (PEG) to NFs and provide stable hydrogen-bonded hydrated layers that ensure exceptional long-term colloidal stability in buffers and media even at clinical MRI field strength and high concentration. The approach enables the first comprehensive study into the MRI (relaxivity) and hyperthermic (SAR) efficiencies of fully dispersed NFs. The predominant role of internal magnetization dynamics in providing high relaxivity and SAR that are unaffected by PEG molecular weight or corona formation in biological environments is identified. The PEGylated NF suspensions exhibited intra-tumour stability and promising retention of relaxivity in vivo due to the strongly anchored PEG layer. For magnetic-polymer nanocomposites, NF dispersion ensures that SAR is fully retained despite their immobilization in the polymer matrix. The retention of SAR in bulk polymers is exploited for further biomedical functionality by utilising their heating capabilities for triggered therapeutic drug release stimulated by increased local temperature. The polymer formulation is also shown to be suitable for two-photon polymerization and dynamic light processing printing techniques enabling high resolution 3D fabrication of magnetic composites. Finally, the magnetic polymer nanocomposites were investigated as magnetically retrievable adsorbents for the removal of micropollutants from aqueous solution. This multifunctional approach demonstrates practical synthetic methods for the preparation of nanomaterials for therapeutic, diagnostic, and environmental applications, while also contributing to the understanding of the fundamental magnetic and chemical mechanisms enabling these applications.