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Research Article
Nanotechnological
Applications of Block Copolymers in Biomedicine
Finizia Auriemma and
Claudio De Rosa
Dipartimento di
Chimica “P. Corradini”, Università di Napoli “Federico
II”, Complesso Monte Sant’ Angelo, Via Cintia, 80126
Napoli, Italy
For correspondence:
E-mail:
finizia.auriemma@unina.it or
clderosa@unina.it
Tropical
Journal of Pharmaceutical Research, February 2011;
10(1):
1-2
Block copolymers (BCP) are
comprised of at least two different, immiscible polymers
that are covalently linked. These materials evolve
spontaneously in organized structures with domains of
nanometer size. With dependence on the ratio of each
polymer, BCPs are able to form lamellae, cylinders,
spheres, or more complicated structures. They have been
demonstrated to be of broad importance in
nanotechnological applications in several different
fields, including nanostructured membranes, BCP
templates for nanoparticle synthesis, photonic crystals,
high-density information storage media and nanomedicine.
Their applicability to nanotechnology stems from the
scale of the microdomains and the convenient tunability
of size, shape, periodicity and properties afforded by
changing their molecular parameters [1].
In this Editorial, we wish
to focus on the use of BCPs in nanomedicine. One of the
most promising research fields is the use of amphiphilic
BCPs made up of at least two biocompatible and
biodegradable polymers having different water solubility
and linked by covalent bonds to prepare nano-objects for
targeted drugs and gene delivery. In aqueous media,
these amphiphlic BCPs form well-defined micelles with a
core consisting of the less soluble block(s) and a
highly swollen corona of the more soluble block(s).
Depending on the degree of swelling of the corona and
the relative composition of the copolymer, spherical and
worm- or rod-like micelles are formed as well as more
complex vesicles and compound micelles [1]. It has been
shown that encapsulation of a pharmaceutical agent
within the hydrophobic core associated with the high
water solubility of nano-sized micelle, may result in
greatly improved drug safety and efficacy with the
possibility of new therapies. In particular, the
incorporation of molecules that target specific cellular
signals on the outer surfaces of such smart nano-objects,
or the construction of nano-assemblies with copolymers
that have specific interaction with cells, is essential
for designing carrier systems with specific cellular
recognition. These systems have been explored as smart
nano-carriers for drugs, which should recognize a
biological target, e.g., inflamed tissue, and only
release the drug at this site to ensure local treatment
[1-3]. With this approach, bioactive compounds like
DNA/RNA molecules could even be transported into cells
and delivered at specific cell organelles [1-3].
BCP based nano-structures
that somehow approach natural assemblies in terms of
their complexity, functionality, and performance, have
also been designed to respond in a controlled manner to
external stimuli. Such stimulus-responsive
nanostructures, which are also referred to as “smart”,
“intelligent”, or “environmentally sensitive”
nanostructures, are systems that exhibit sharp changes
in response to physical stimuli such as heat,
ultrasound, and light, or to chemical stimuli such as
pH, ions in solution, and chemical substances [4]. In
this way, a specific drug delivery to a target tissue
and specific activation of the delivered drug within the
targeted cell, may enhance efficacy and minimize any
adverse drug effects during drug targeting [4]. A direct
extension of BCP approach for building micellar nano-object
consists in the preparation of external stimuli -
responsive nanoassemblies to be used in vivo,
loaded with magnetic resonance imaging (MRI) [5]
contrast agents or fluorescent dyes for near infrared (NIR)
imaging [6]. These systems have the potential of
facilitating the use of an external trigger and
enhancing the therapeutic effects of smart drug
carriers.
Besides drug delivery and
therapeutic nanomedicine applications, another large
area of nanomedicine research in which BCPs have
demonstrated profound impact consists in their use for
fabrication via the bottom-up approach of the basic
elements for LAB-on Chip devices that allow for the
electrophoretic routing, preconcentration, and
separation of ions and biomolecules and/or of electronic
nanodevices for molecular recognition of DNA and
plasmide [1,7]. For such applications, the ability of
BCPs is exploited to evolve spontaneously in organized
periodic nanostructures. As explained above, with
dependence on the ratio of each polymer, lamellae,
cylinders, spheres, or more complicated structures can
be formed. Typically, considering a cylindrical or
lamellar structure, nanochannels are simply formed by
selectively etching one of the components. This is the
case in which one of the components of the copolymer is
used as a structural material, another one as a
sacrificial material, while the last one determined the
surface chemistry of the channel. An alternative
approach is to use BCPs after selective etching, as a
mask to pattern a film or a substrate (block copolymer
lithography) [7].
A typical application of
long channels with sections of nanoscopic size obtained
using the BCP approach, is building innovative
nanofluidic devices for proteomics and/or genomics. The
section of these channels, indeed, are close to the
typical size of biomolecules such as DNA and proteins.
Though well established, high-throughput genotyping
techniques are now routinely used; implementation of
such nanofluidic chips have the potential advantages of
reducing the costs of applied and basic research in this
field, drastically improving the diagnostic and the
early detection of eventual predisposition to diseases,
providing better and faster separation tools to analyze
the tiny changes of proteome and track their evolution
[8,9].
In the field of molecular
recognition, effective immobilization of enzymes require
a high specific functionalized area. Use of
self-assembly of amphiphilic BCPs for nanopatterning
conductive surface with functionalized nanodomains is a
viable tool in this research area [1,2,7].
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