Biomedical Engineering Reference
In-Depth Information
terials [151]. Another interesting nanoparticle composite material was described
by Pyun and coworkers, who developed a method to form long chains of Co
nanoparticles [153]. Here, the thermal decomposition of Co
2
(CO)
8
in the presence
of a polymer mixture containing amino phosphine oxide, alkyl phosphine oxide,
amine, and/or carboxylic acid binding groups, caused the particles to self- assemble
into linear structures [153] .
In some cases, multifunctional nanoparticles have been used during polymer
synthesis (i.e., as monomeric building blocks) to form crosslinked dense networks.
As an example, when Park and coworkers used dopamine as the surface binding
group and crosslinking agent for polydimethylsiloxane [154], there was a clear
impact on the overall mechanical properties of the elastomer, with the particle
composite being almost twice as rigid and slightly harder [154].
14.3.5.3.3
Block Copolymers
Several recent reports have referred to block copo-
lymers being used for the formation of shells and the encapsulation of magnetic
nanoparticles. These types of material are advantageous because of the intrinsic
and controllable structure of the polymer blocks, this property being especially
useful for promoting particle interactions, solubility and - potentially - a uniform
shape of the core@shell nanocomposite. Kim and Taton have used block copoly-
mers to encapsulate iron oxide, CdSe@ZnS, and Au nanoparticles into multipar-
ticle composites with polyfunctionality [133]. For this, a polystyrene-polyacrylic
acid block copolymer was mixed with hydrophobic nanoparticles to form a micro-
emulsion in water, and a crosslinker then added [152, 133]. The coencapsulation
of QDs with iron oxide nanoparticles was found to cause a signifi cant reduction
in the quantum yield of the semiconductors [133]. When Gao
et al.
encapsulated
iron oxide nanoparticles with doxorubicin (an anti-cancer agent) in block copoly-
mer shells of maleimide- poly(ethylene glycol) - block - poly(
D
,
L
lactide) [155] , the
external surface was functionalized with cyclic Arg - Gly - Asp peptide ( cRGD ) to
specifi cally target
3
endothelial integrins and promote cellular uptake [155].
Subsequent doxorubicin release from the polymer was found to be increased at a
higher pH [155] .
In another example, Belfi eld and Zhang used ring-opening metathesis polym-
erization (ROMP) to form di-block copolymers for the synthesis and stabilization
of iron oxide nanoparticles [156]. The block copolymers were synthesized from
norbornene and the 2-cyanoethyl ester of norbornene carboxylic acid, with more
stable and crystalline iron oxide particles being observed when the cyano ester
block was larger than the norbornene [156]. Very recently Svergun, Bronstein and
coworkers produced magnetic iron oxide core@block copolymer shell nanoparti-
cles with a good size monodispersity [157]. These iron oxide nanoparticles were
produced via a standard high-temperature reduction route with oleic acid to yield
highly uniform magnetic nanoparticle sizes [157] . When poly(maleic anhydride - alt -
1-octadecene) was added, the hydrophobic chains of the octadecene block were
able to interpenetrate the surface-bound oleic acid ligands [157]. An analysis using
small-angle X-ray scattering (SAXS) showed that 99.9% of the polymeric shells
contained only a single nanoparticle [157] .
α
v
β
