Aims: The purpose of this work is the preparation and characterisation of bioactive ferrimagnetic biomaterials. These materials can form a stable bond to the bone and can be heated by the application of an external alternating magnetic field, so they are good candidates for non-invasive hyperthermic treatment of solid bone tumours.
Methods: The investigated materials are glass-ceramics belonging to the system SiO2-CaO-Na2O-P2O5-FeO-Fe2O3. They can be obtained by different methods, such as melting of traditional raw materials (oxides, carbonates or phosphates), thermal treatment of wet-chemistry derived precursors, or sintering. In the first two methods, different amounts of magnetite can crystallize inside the amorphous phase during cooling from the processing temperature to r.c., leading to a glass-ceramic. In the sintering method, glass powders and magnetite particles are intimately mixed and successively thermally treated, so that a composite material is obtained. A complete characterization was performed in terms of morphology and microstructure (SEM, TEM, XRD, DTA), bioactivity (soaking in SBF), magnetic properties (hysteresis loss) and calorimetric measurements (specific power loss).
Results: Depending on the synthesis process it is possible to obtain both dense and macroporous devices (glass-ceramic or composites up to some centimeters size) as well as glass-ceramic micrometric particles. The magnetite crystals inside the amorphous phase are nanometric or submicrometric, depending on the synthesis method. The glass-ceramics have a bioactive behaviour, since hydroxyapatite grows on their surface after few days of soaking in Simulated Body Fluid. The hysteresis loss and the specific power loss are compatible with the temperature required for hyperthermic treatments of neoplastic tissues.
Conclusions: Innovative magnetic biomaterials have been designed and synthesized by a careful optimization of the composition and processing parameters. Different synthesis methods can be used to prepare these biomaterials, in function of the tissue characteristics and magnetic field conditions. Due to the possibility of producing very small devices, these materials can be implanted by non-invasive surgical techniques, and since they are bio-compatible, can be let inside the body for a long period, being subjected to multiple heating cycles. Due to their bioactivity they could be proposed as an alternative for the treatment of bone tumors after surgical resection
