Biomedical Engineering Reference
In-Depth Information
9.4 Nanostructured biomaterials for nervous
system applications
9.4.1 Nervous system facts
Nervous system function has also been restored using nanotechnology. The
human nervous system has two components which are the central nervous
system and the peripheral nervous system. The central nervous system consists
of the brain and spinal cord and the peripheral nervous system consists of nerves
outside the brain and spinal cord. It includes both neurons and nerve fibers. The
majority of these neurons are located near the spinal cord at ganglia. Nerve
fibers extend to sensory structures, glands, blood vessels and muscles. Two
major classes of cells, neurons and glia, exist in the nervous system. Glia in the
brain is divided into three classes, oligodendrocytes, astrocytes and microglia.
They provide structural support for neurons, as well as regulate neuronal
activities [109]. The neurons of the nervous systems are interconnected into
complex arrangements and use electrochemical signals and neurotransmitters to
transmit impulses from one neuron to the next. The nervous system is probably
the most complex and mystic system in human beings. In the following section,
several common nervous system implants and medical approaches are
introduced and how nanotechnology is improving such biomaterials illustrated.
9.4.2 Neutral applications of nanotechnology
For the treatment of brain diseases, current drug delivery systems are far less
than satisfactory. The blood±brain barrier (BBB) has at least three resistances,
tight junctions, choroid plexus and cerebral capillaries, which can block most
drugs except small hydrophobic drugs. One classic example is that dopamine
(which was originally chosen to treat Parkinson's disease) cannot pass through
the BBB. Lately, nanotechnology has significantly helped drug delivery for
brain diseases. For example, iron oxide magnetic nanoparticles consisting of an
iron oxide core from several to a few hundred nanometer diameters are coated
either with organic (like poly(ethylene glycol)) or inorganic (like silicon)
materials to improve biocompatibility and drug delivery [110]. Moreover, one
benefit of magnetic nanoparticles is that they can be directed by a magnetic
force as well as via surface receptors to control drug delivery. In addition, they
are able to pass through artificial and real BBB membranes by endocytosis, due
to the small size of nanoparticles [20, 21]. In another study, such magnetic
nanoparticles were found not to trigger any inflammatory responses in both in
vitro and in vivo models [111]. In the market today, there are numerous com-
mercialized iron oxide magnetic nanoparticle products, such as SoluLink,
TurbeBeads, Bioclone, etc. There are functionalized iron oxide magnetic
nanoparticles for either drug delivery or other biomedical applications. Another
important application of magnetic nanoparticles is to enhance MRI. For iron
