Biomedical Engineering Reference
In-Depth Information
4
Examples of Biomedical Applications of Magnetic Particles
Magnetically responsive nano- and microparticles have many already established
and potential applications in various areas of biosciences, biotechnology and envi-
ronmental technology. Biomedicine related applications are mainly based on the
utilization of selected properties, namely magnetic separation, magnetic targeting,
heat production and MRI contrast increase.
4.1
In Vitro Application of Magnetic Particles
Magnetic separation is a very simple, fast, efficient and gentle tool for the rapid
isolation of target molecules, cell organelles and cells from complex biological
mixtures and crude samples such as blood, bone marrow, tissue homogenates,
urine, stools and other biological materials. The molecules and cells isolated by
magnetic separation are usually pure, viable and unaltered. The gentle test tube
magnetic separation is the technology of choice when there is a need for high yields
of pure and biologically active compounds and biological structures in small scale
(Šafařík and Šafaříková
1999, 2004
).
Magnetic separations have been mainly employed for the immunomagnetic
separation (IMS) of eukaryotic target cells (e.g., cancer cells, stem cells or
T-lymphocytes). The progress of this procedure has been enabled by the devel-
opment of monoclonal antibodies and the improved characterization of cells
specific antigens. It is now possible to separate many specific cell types from
mixed populations in blood, bone marrow and other sources without cell loss or
damage. By positive isolation the cells of interest are magnetically labeled by
specific particles and subsequently isolated for analysis. For some downstream
applications (e.g., mRNA or DNA isolation) the beads can remain attached to
the isolated cells. For other applications (e.g., FACS analysis) magnetic micro-
beads have to be removed from the cell surface. By negative isolation (= depletion),
unwanted cells are removed prior to analysis of the remaining population.
Primary coated Dynabeads and some other magnetic particles are ready-to-use
products for a wide variety of cell surface markers. In addition, secondary
coated magnetic particles offer an excellent possibility to make beads with the
reactivity of choice using mouse, rat, sheep or rabbit antibodies (Šafařík and
Šafaříková
1999
).
The magnetic separation procedure can be scaled up if large quantities of living
cells are required. Several commercially available devices enable to separate target
cells from larger volume of blood or cells suspensions. The CliniMACS System
(Miltenyi Biotec, Germany) is based on MACS Technology which employs MACS
MicroBeads (nano-sized superparamagnetic particles approximately 50 nm in
diameter, composed of an iron dextran matrix coupled to specific antibodies) and a
magnetic separation unit. CliniMACS permits the automated separation of cells on
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