Biomedical Engineering Reference
In-Depth Information
The use of biologics, polymers, silicon materials, carbon materials, and metals
has been proposed for the preparation of innovative drug delivery devices. One of
the most promising materials in this fi eld are the
carbon-nanotubes composites
and
hybrid materials
coupling the advantages of polymers (biocompatibility and
biodegradability) with those of carbon nanotubes (cellular uptake, stability, electro-
magnetic, and magnetic behavior). The applicability of polymer-carbon nanotubes
composites in drug delivery, with particular attention to the controlled release by
composites hydrogel, is being extensively investigated in the present days [
1
].
Engineered devices at the nanometer scale are small enough to interact directly
with subcellular compartments and to probe intracellular events. The ability to
assemble and study materials with nano-scale precision leads to opportunities in
both the basic biology (e.g. testing of biological hypotheses that require nano-scale
manipulation) and development of new biological technologies (e.g. drug delivery
systems, imaging probes, or nanodevices).
Millimeter-scale and micrometer-scale controlled release systems have been
well studied, and some systems have been approved for clinical use. As we already
know. one of the major advances in recent years has been
further reduction in the
size of these systems
: it is now possible to make
polymer delivery systems
that are
nanometer in scale, can be easily injected or inhaled, and are much smaller than-and
capable of being internalized by-many types of human cells [
10
,
12
-
15
].
Examples of drug-delivery nanoparticles are:
Liposomal systems (Vesicles
with targeting poly-ethylene-glycol (PEG groups))
Solid biodegradable nanoparticles (polymer emulsions with targeting or PEG
groups on the surface)
Dendrimer-polymer conjugates (5 nm)
Polymer nanoparticles [
17
]
ECM that surrounds the cells and tissues in the body is composed of fi bers that
are typically 10 nm to 100 nm in diameter. Although there are a variety of ways of
achieving nano-scale delivery systems, including self-assembling systems based on
liposomes or micelles
, the most stable and versatile systems
are miniaturized ver-
sions of the synthetic materials
that have already been used in drug-delivery appli-
cations. Construction of such a system is usually accomplished by degradable
polymers such as
pegylated granules
(PLGA) [
15
]. These particles can be injected
in circulation, or used to release drugs, locally. The encapsulated drugs can be com-
plex, if appropriate methods of fabrication are used to assemble the nanoparticles.
For example, it is now possible to make 300 nm particles that have functional DNA
within the solid matrix.
Polymer materials have many potential uses in drug delivery, serving as
vehicles for drug distribution and release
. One usually obtains a complex mixture
of particles of different sizes and shapes, however, the methods of fabrication are
still imperfect.
Matching method of particle formation with drugs has been one
of the major challenges in this area
. Many different ways to make small particles,
especially with Nanotechnology have now been described (Fig.
10.1
).
Unfortunately,
few of these methods are compatible with most drugs
. Finding better ways to
