The developments that aroused fresh technical interest in magnetic separations
are:
1. New methods for generating high magnetic field gradients.
2. The introduction of reasonably priced efficient and superconducting
magnets [8].
3. New developments in magnetic labeling techniques for cells and microspheres that have extended the useful range of High Gradient Magnetic
Separations (HGMSs) into many important areas of biotechnology [1].
No widely-used magnetic method has yet been developed to separate cells on
the basis of the amount of ligand bound. By combining magnetic extraction,
used as a rate process, with countercurrent extraction, it is now possible to use
magnetic separation of cells as a quantitative technique, separating on the basis
of the number of ligands bound per cell. This could be qualitative, based on the
amount of ligand bound to each kind of cell, or quantitative, based on the
amount of ligand bound to cells of the same type, some with high receptor content and some with low.
There are numerous examples of potential uses of magnetic extraction
methods. Separation of high CD4 from low CD4 binding cells from all other
cells in whole blood is a very significant procedure for the study of immune
function in leukemia, AIDS, and immunomodulation caused by environmental stresses. Research laboratories have recently used receptor number as a
dependent variable in a variety of scientific applications, such as endocrinology
[9], growth regulation [10, 11], virology [12, 13], carcinogenesis [14, 15], infectious diseases [16], neurology [17], and nutrition [18].
2.1.1
Existing Methods – Brief Summary
Magnetic separation methods can be classified into two main types. In the first
type, separand is intrinsically magnetic so that magnetic separation can take
place without any modification. There are only a few examples of such materials
in biotechnology, such as red blood cells containing high concentrations of
paramagnetic hemoglobin, magnetotactic bacteria containing small magnetite
particles within their cells, and magnetic particles used in waste water purification systems. In the second type, one or more non-magnetic components of a
mixture have to be rendered magnetic by the attachment of a magnetically
responsive entity. The newly formed complexes have magnetic properties and
can be manipulated using an external magnetic field [5].
Magnetic properties include ferromagnetism, paramagnetism, and diamagnetism, and specific materials including cells and biomolecules can exhibit
these properties [8]. The most naturally labeled cells that are separated by
HGMS are probably the magnetoactive aquatic bacteria [19]. These organisms
contain small single-domain crystals of magnetite, and the ability to be
oriented in a magnetic field remains even when the organism dies. Several
patents have already been granted in the USA and Japan describing potential
uses of these rare organisms in medical applications [1].
Multistage Magnetic and Electrophoretic Extraction of Cells, Particles and Macromolecules
145
are:
1. New methods for generating high magnetic field gradients.
2. The introduction of reasonably priced efficient and superconducting
magnets [8].
3. New developments in magnetic labeling techniques for cells and microspheres that have extended the useful range of High Gradient Magnetic
Separations (HGMSs) into many important areas of biotechnology [1].
No widely-used magnetic method has yet been developed to separate cells on
the basis of the amount of ligand bound. By combining magnetic extraction,
used as a rate process, with countercurrent extraction, it is now possible to use
magnetic separation of cells as a quantitative technique, separating on the basis
of the number of ligands bound per cell. This could be qualitative, based on the
amount of ligand bound to each kind of cell, or quantitative, based on the
amount of ligand bound to cells of the same type, some with high receptor content and some with low.
There are numerous examples of potential uses of magnetic extraction
methods. Separation of high CD4 from low CD4 binding cells from all other
cells in whole blood is a very significant procedure for the study of immune
function in leukemia, AIDS, and immunomodulation caused by environmental stresses. Research laboratories have recently used receptor number as a
dependent variable in a variety of scientific applications, such as endocrinology
[9], growth regulation [10, 11], virology [12, 13], carcinogenesis [14, 15], infectious diseases [16], neurology [17], and nutrition [18].
2.1.1
Existing Methods – Brief Summary
Magnetic separation methods can be classified into two main types. In the first
type, separand is intrinsically magnetic so that magnetic separation can take
place without any modification. There are only a few examples of such materials
in biotechnology, such as red blood cells containing high concentrations of
paramagnetic hemoglobin, magnetotactic bacteria containing small magnetite
particles within their cells, and magnetic particles used in waste water purification systems. In the second type, one or more non-magnetic components of a
mixture have to be rendered magnetic by the attachment of a magnetically
responsive entity. The newly formed complexes have magnetic properties and
can be manipulated using an external magnetic field [5].
Magnetic properties include ferromagnetism, paramagnetism, and diamagnetism, and specific materials including cells and biomolecules can exhibit
these properties [8]. The most naturally labeled cells that are separated by
HGMS are probably the magnetoactive aquatic bacteria [19]. These organisms
contain small single-domain crystals of magnetite, and the ability to be
oriented in a magnetic field remains even when the organism dies. Several
patents have already been granted in the USA and Japan describing potential
uses of these rare organisms in medical applications [1].
Multistage Magnetic and Electrophoretic Extraction of Cells, Particles and Macromolecules
145