Single-Chain Polymer Nanoparticles for Application in Nanomedicine - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 24

with the conventional surfactant-based micelles, polymer micelles
are composed of block copolymers (having both hydrophobic and
hydrophilic parts) or triblock copolymers (with one hydrophobic
and two hydrophilic parts or one hydrophilic and two hydrophobic
parts). Although the structural “core-shell” arrangement is similar to
surfactant-based micelles, polymer micelles self-associate at much
lower concentrations (low critical micelle concentration, CMC),
typically 10 −6 -10 −7 M compared with 10 −3 -10 −4 M for surfactant-
based micelles.
A dendrimer is a polymeric nanostructure (1-10 nm) built around
a core unit. There are several branching units around the core units
in a layer-by-layer fashion which defines the growth, size and the
microenvironment within the dendrimer. Dendrons are formed after
the removal of the core units and can be divided into three areas:
the (empty) core, the interior (branching units), and the periphery
(end-groups). The empty core of dendrons can be utilized for the
entrapment of drug molecules for solubilisation, controlled release,
targeting, or protection from surrounding degrading environment.
Dendrimers off er unique properties such as uniform particle size
(especially for lower generation, i.e. up to G-3), poly-valency of
the end groups, which helps in binding to diverse receptors, and
an ability to bind a variety of targeting agents to their high density
peripheral functional groups.

2.2 Single-Chain Polymer Nanoparticles

Very recently, a new method for producing polymer nanoparticles
has emerged as a fascinating alternative to the strategies mentioned
earlier in this chapter: the intramolecular cross-linking and collapse
of single polymer chains. This elegant method allows the facile
preparation of tiny nanoparticles from 1.5 to 20 nm in diameter,
with a wide variety of chemical compositions and functionalities.
In addition, the sizes of the particles fabricated in such manner can
be tuned by (i) controlling the molecular weight of the precursor
polymer chain and (ii) the percentage of cross-linking units used
to perform the intramolecular chain-collapse. For all these reasons,
single-chain polymer nanoparticles (SCPNs) are envisaged as
promising candidates for applications in nanomedicine.
In order to control the molecular weight of the precursor
polymer chain, these need to be synthesized using polymerisation