Magnetic Particles for Biomedical Applications

This chapter discusses applications of magnetic materials in bioengineering and medicine [1–8]. Magnetism and magnetic materials have been used for many decades in many modern medical applications, and several new applications are being developed in part because of the availability of superior electromagnets, superconducting magnets and permanent magnets [9–12]. Advances in the synthesis and characterization of magnetic particles, especially nanomagnetic particles, have also aided in the use of magnetic biomaterials [6–12]. We begin with an introduction to magnetism and magnetic materials, followed by a discussion of the characterization, synthesis techniques and applications of magnetic biomaterials [8, 9]. Magnetic materials can be applied to cell separation, immunoassay, magnetic resonance imaging (MRI), drug and gene delivery, minimally invasive surgery, radionuclide therapy, hyperthermia and artificial muscle applications [1–5, 7]. Physical properties which make magnetic materials attractive for biomedical applications are, first, that they can be manipulated by an external magnetic field – this feature is useful for separation, immunoassay and drug targeting, and second, hysteresis and other losses occur in alternating magnetic fields – this is useful in hyperthermia applications. In biology, there has been much interest in the possible use by bees and pigeons of magnetic materials as biological compasses for navigation. Some magnetotactic bacteria are known to respond to a magnetic field, they contain chains of small magnetite particles and they can navigate to the surface or bottom of the pools that they live in using these particles. These particles can be obtained by disruption of the cell wall followed by magnetic separation; the presence of the lipid layer makes these particles biocompatible and they can be readily functionalized for a variety of biomedical applications. The earliest known biomedical use of naturally occurring magnetic materials involves magnetite (Fe3O4) or lodestone which was used by the Indian surgeon Sucruta around 2,600 years ago. He wrote in the book Ayurveda that magnetite can be used to extract an iron arrow tip. Current areas in medicine to which magnetic biomaterials can be applied include molecular and cell biology, cardiology, neurosurgery, oncology and radiology.