Magnetic Nanoparticles for Biomedicine - Intracellular Delivery: Fundamentals and Applications - page 364

fluids), magnetorheological fluids, magnetic polymers, magnetic inorganic mate-
rials, magnetically modified biological structures, magnetic particles with bound
biomolecules etc. can serve as typical examples. In many cases magnetically
responsive composite materials consist of small magnetic particles (most often
formed by magnetite, maghemite or various ferrites), usually in the nanometer to
micrometer range, dispersed in a polymer, biopolymer or inorganic matrix; alter-
natively magnetic particles can be adsorbed on the outer surface of diamagnetic
particles (Safarik and Safarikova 2009b ).
Magnetic properties of such materials enable their applications in numerous
areas (Arruebo et al. 2007 ; Safarik and Safarikova 2009a ), namely:

- Magnetically responsive nano- and microparticles and other relevant materials

can be selectively separated (removed) from the complex samples using an
external magnetic field (e.g. using an appropriate magnetic separator, permanent
magnet, or electromagnet). This process is very important for bioapplications
due to the fact that absolute majority of biological materials have diamagnetic
properties which enable efficient selective separation of magnetic materials.
Magnetic particles can be targeted to the desired place and kept there using an -

external magnetic field. These properties can be used e.g. for sealing the rotating
objects or in the course of magnetic drug targeting.
Magnetic particles can generate heat when subjected to high frequency alternat-

-

ing magnetic field; this phenomenon is employed especially during magnetic
fluid hyperthermia (e.g., for cancer treatment).
Magnetic iron oxides nanoparticles generate a negative T2 contrast during mag- -

netic resonance imaging thus serving as efficient contrast agents.
Magnetorheological fluids exhibit great increase of apparent viscosity when

-

subjected to a magnetic field.
Magnetic nano- and microparticles can be used for magnetic modification of -

diamagnetic biological materials (e.g. cells or plant-derived materials), organic
polymers and inorganic materials, and for magnetic labeling of biologically
active compounds (e.g. antibodies, enzymes, aptamers etc.).

In most cases synthetic (laboratory-produced) magnetically responsive nano-
and microparticles and related structures have been developed, however, biologi-
cally produced magnetic particles (e.g., magnetosomes produced by magnetotactic
bacteria) have been successfully used for selected bioapplications (Arakaki et al.
2008 ). This short review chapter shows typical examples of biocompatible mag-
netic materials synthesis and typical examples of their biomedical applications.

2 Synthesis of Magnetic Nanoparticles

Many chemical procedures have been used to synthesize magnetic nano- and
microparticles applicable for bioapplications, such as classical coprecipitation, reac-
tions in constrained environments (e.g., microemulsions), sol-gel syntheses, sono-
chemical and microwave reactions, hydrothermal reactions, hydrolysis and thermolysis