ABSTRACT
Nanoparticles are being used in a rapidly increasing variety of biomedical applications, including detection, imaging, and treatment of disease. These particles have controllable dimensions in the nanometer range, matching the scale of biological entities and facilitating intimate interactions with cells and molecular constituents. They exhibit
4.1 Introduction ....................................................................................................97 4.2 Theoretical Background and Underlying Physics......................................... 100
4.2.1 Effects of Alternating Magnetic Fields in Human Application ........ 100 4.2.2 Physical Mechanisms of Heat Generation ........................................ 101
4.2.2.1 Eddy Current Generation ................................................... 102 4.2.2.2 Hysteresis Loss .................................................................. 103 4.2.2.3 Relaxation Loss .................................................................. 104
4.2.3 Relaxation Time Constants ............................................................... 105 4.2.4 Power Dissipation for Superparamagnetic Nanoparticle Heating .... 107 4.2.5 Effects of Properties on Superparamagnetic Heating ...................... 109
4.3 Experimentally Characterizing SAR ............................................................ 111 4.3.1 Magnetic Nanoparticles .................................................................... 113 4.3.2 Heating Studies and Experimental Setup ......................................... 113 4.3.3 Measuring SAR ................................................................................ 114 4.3.4 Experimental Results ........................................................................ 114
4.4 Conclusion .................................................................................................... 115 Nomenclature ......................................................................................................... 117
Greek Symbols .............................................................................................. 118 References .............................................................................................................. 118
size, and shape. One of the special features of iron oxide nanoparticles is their ability to serve as colloidal mediators for heat generation in externally applied, alternating magnetic fields. This application has been termed magnetic fluid hyperthermia (MFH) and has attracted growing research interest for treatment of malignant tumors due to its potential for highly specific energy delivery through a minimally invasive (or potentially noninvasive) platform. In this method, magnetic particles delivered to tissue induce localized heating when exposed to an alternating magnetic field, leading to thermal damage concentrated to the tumor [1]. Although cancer therapy has been the overwhelming focus in development thus far, magnetically heated nanoparticles have also demonstrated promise for application in thermoresponsive drug delivery [2,3], activation of ion channels and neurons [4], remote-controlled microfluidic valves [5], and heat-initiated shape-memory alloys [6]. As a result of the well-demonstrated biocompatibility of iron oxide nanoparticles, magnetite (Fe3O4) and maghemite (Fe2O3) are the most popular materials for in vivo investigations [7].
