Biomedical Engineering Reference
In-Depth Information
than do magnetite-producing cells. Interestingly, greigite magnetosomes in MMPs
have several morphologies within the same organism, including bullet- shaped,
cubic, and smaller more irregular particles [1]. Other uncultured greigite-produc-
ing bacteria have irregular elongated magnetosomes of approximately 60nm
length, often in more disordered double chains (Figure 11.5 h). Greigite- producing
cells analyzed using off-axial electron holography were seen to contain magneto-
somes that were elongated along the [111] axis but were irregular with respect to
crystallographic orientation, morphology, and chain organization; the result of this
was many magnetosomes which had a much reduced magnetic moment [61].
The application of magnetosomes as nanomaterials has been envisaged from a
technological standpoint only quite recently, and this has occurred almost exclu-
sively in the fi eld of biomedical applications. The reason for this is because mag-
netosomes lend themselves perfectly for use as biomedical nanomagnetic particles,
in several ways:
•
The magnetic particles are obtained directly from the cell with an inherent lipid
coating, which is ideal if the particle is to be modifi ed with bioactive compounds.
•
The strict control that a biological system offers over particle size, shape and
crystal quality allows the provision of a highly uniform geometric and crystallinity.
•
Although the particle size and shape is well conserved within each strain of
bacteria, a range of magnetosome morphologies and sizes have been observed
in various bacteria (Figure 11.5; Table 11.2), with some of these shapes being
irreproducible synthetically
in vitro
.
•
Magnetosomes have highly defi ned and distinctive magnetic properties, which
results in a very attractive range of nanomagnetic materials that may be used for
biomedical applications.
11.4.3
Magnetosome Formation
The biological machinery and mechanism of biomineralization of magnetite
within magnetosomes has been the subject of intensive research over the past 20
years, with the quantity and quality of data obtained increasing dramatically
recently with the advent of new and improved bioanalytical tools in areas such as
gene sequencing and bioinformatics. The study and understanding of this process
has derived from two investigative approaches: (i) proteomics studies, analyzing
the proteins associated with the magnetosome; and (ii) genomic studies, which
have been performed in parallel and have concentrated on gene sequence, muta-
genesis and bioinformatic comparative analysis. Both approaches have also been
complemented by physical analyses such as high- resolution transmission electron
microscopy (TEM). Although the biomineralization of magnetite has not been
completely elucidated, the information obtained via these approaches has provided
a comprehensive foundation and solid hypothetical models.
