If some magnetic materials, such as iron oxides, are small enough -
perhaps a few millionths of a millimeter across, smaller than most
viruses - they have an unusual property: their magnetization randomly
flips as the temperature changes.
By applying a magnetic field to these crystals, scientists can make
them almost as strongly magnetic as ordinary fridge magnets. It might
seem odd, but this is the strongest type of magnetism known. This
phenomenon is called superparamagnetism.
‘Superparamagnetic crystals could soon be zipping drugs around your body, taking them to diseased organs, revealed a study.’
In theory, superparamagnetic particles could be ideal for drug
delivery, as they can be directed to a tumor simply by using a magnetic
field. Their tiny size, however, has made them difficult to guide
precisely - until now.
But now a
team of Chinese researchers has found the solution, and their discovery
has opened new applications that could use these crystals to improve -
and perhaps even save - many lives.
Kezheng Chen and Ji Ma from Quingdou University of Science and
Technology, Quingdou, China have published a method of producing
superparamagnetic crystals that are much larger than any that have been
made before. They recently published their findings in Physics Letters A
"The largest superparamagnetic materials that we have been able to
make before now were clusters of nanocrystals that were together about a
thousand times smaller than these," commented Dr. Chen. "These larger
crystals are easier to control using external magnetic fields, and they
will not aggregate when those fields are removed, which will make them
much more useful in practical applications, including drug delivery."
Chen and Ma explained that the high temperature and pressure under
which the crystals form made tiny meteorite-like 'micro-particles' of
magnetite escape from their surface. This caused the unusual pock-marked
appearance of the crystal surfaces and induced a high degree of stress
and strain into the lattice of the growing crystals.
Crystals that grow under such high stresses and strains form with
irregularities and defects in their crystal lattice, and it is these
irregularities that are responsible for the unusual magnetic properties
of Chen's crystals.
Magnetite crystals of a similar size that are grown at a lower
temperature and under normal pressure are only very weakly magnetic.
This method of making larger superparamagnetic crystals paves the
way for the development of superparamagnetic bulk materials that can be
reliably controlled by moderate external magnetic forces,
revolutionizing drug delivery to tumors and other sites in the body that
need to be targeted precisely.
And this is just the beginning. Chen's crystals might, for example,
be useful in the many engineering projects that need "smart fluids" that
change their properties when a magnetic field is applied. These can
already be used to make vehicle suspension systems that automatically
adjust as road conditions change, increasing comfort and safety, and to
build more comfortable and realistic prosthetic limbs.
Now that superparamagnetism is no longer restricted to minute
particles that are difficult to handle, researchers can start exploring
in which ways this can contribute to improving our lives.