Magnetic Materials for Biomedical Applications

Magnetic materials are of interest for biomedical applications for the ability to remotely control magnetic particles through the use of non-invasive magnetic fields. Specific applications of magnetic materials in biomedical fields include magnetic resonance imaging, drug delivery, and hyperthermia-based cancer treatments. The most commonly used material for these applications are iron oxides, which suffer from acute toxicity and unknown fate in vivo and thereby limit their applications. An alternative approach is to substitute magnetic ions into a biocompatible and biodegradable material to impart magnetic properties. Hydroxyapatite (HA), the main inorganic component of natural bone, is widely studied as a biomaterial for its excellent biocompatibility and osteoconductivity. The crystal structure of HA is highly flexible allowing for a wide range of substitutions for tailoring material properties. Hydroxyapatite with magnetic properties may be an alternative to iron oxides for the aforementioned applications. Iron, cobalt, and manganese substituted hydroxyapatite powders were synthesized via ion exchange and characterized to verify successful substitution into the lattice structure of HA. All substitutions were successfully prepared and resulted in ion-substituted hydroxyapatite with magnetic properties. Experimental results were also in good agreement with theoretical calculations which predicted manganese substituted hydroxyapatite to have the largest magnetic moment. The synthesized magnetic hydroxyapatites are shown to be biocompatible, making them suitable for magnetic resonance imaging and drug delivery applications while providing a biodegradable and biocompatible alternative to iron oxides for these applications. Magnetic materials have also been used in tumor therapy applications. For tumor therapy applications the materials blood circulation time is desired to be as long as possible to enhance accumulation at the tumor site. Semi-flexible filomicelles have been shown to have significantly longer circulation times than rigid spheres or rods. Type I collagen, the main organic phase of bone, is a filamentous protein and semiflexible polymer that allows for mineralization within specific zones of the fiber. Through self-assembly and bio-templating we have developed a method to induce mineralization of iron oxide within collagen fibers to form a flexible and magnetic “nanoworm” for tumor therapy application