Page 75 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 2 STRUCTURAL CONTROL OF NANOPARTICLES
the new structures are sometimes required to be used as a core, embedded in the phospholipids shell.
reassembled by a self-association mechanism in order Cosurfactants with polyethylene glycol (PEG) chain
to play a subsequent role. The timings of disassembling are also embedded in the shells to hydrate the particle
and reassembling are also critical to exhibit the func- surface. When the nanoparticles thus prepared were
tions desired. For medical and pharmaceutical uses, the intravenously injected into the blood of hamsters, the
prepared nanoparticles have to be finally disassembled; surface hydration contributed to the long-circulation
then, the components have to be utilized by the body or of the particles in the blood. Since the size of the
eliminated from the body. To efficiently and safely particles was smaller than 100 nm, these particles
complete the whole process that the nanoparticles will exhibited the enhanced penetration and retention
go through, the components, the structures of particles, effect [6, 7].
layers and phases, and the bonding modes have to be The so-called quantum dot (qdot) is shown in
designed and prepared optimally. Table 2.1.1(f) [9]. The feasibility of in vivo targeting
Many kinds of fabrication process have been by using semiconductor quantum dots (qdots) was
proposed to construct nanocomposite particles for pro- explored. Qdots are small ( 10 nm) inorganic
viding desired functions. The phases and layers in nanocrystals that possess unique luminescent prop-
Fig. 2.1.1 are constructed sequentially or simultane- erties; their fluorescence emission is stable and is
ously by depositing atoms, compounds, and particles tuned by varying the particle size or composition.
physically or chemically in the gas or liquid phase: the ZnS-capped CdSe qdots coated with a lung-targeting
intrinsic association forces and external mechanical peptide accumulated in the lungs of mice after
forces can be the driving force in the structure-making intravenous (i.v.) injection, whereas two other pep-
process. In the present stage of nanotechnology, it is tides specifically directed qdots to blood vessels or
not so easy to complete the fabrication process in the lymphatic vessels in tumors. They also showed that
controlled manner. adding polyethylene glycol (PEG) to the qdot
In this section, typical examples of nanoparticles coating prevented qdots from non-selective accumu-
designed and prepared for medical and pharmaceutical lation in reticuloendothelial system (RES).
applications have been discussed (Table 2.1.1) [1]. The pharmaceutical application of nanoparticles can
be found in latex systems that have been used as coat-
ing materials in the spray-coating processes such as
2.1.2. Hollow particles fluidized bed, spouted bed, and tumbling fluidized bed
process [10]. Commercially available latexes are
Liposomes are typical hollow particles (Table 2.1.1 formed as monolithic structures from random co- or
(a–c)) [2–4]. Liposomes are small vesicles with phos- terpolymers that are designed to be used chiefly for
pholipid-bilayer shells. It is common that the cores coating such coarse particles as granules and tablets.
contain just an aqueous phase, sometimes dissolving For further and broader application of this technique,
water-soluble drugs. Hydrophobic agents can be the novel terpolymer and core–shell latexes have been
incorporated into the bilayer. Targeting agents that proposed through development of fine particle coating
specifically associate the particles with target cells technology and highly functional microcapsules, such
are put on the surface by binding phospholipids to as thermosensitive drug-releasing microcapsules using
them for anchoring to the bilayer. Liposomes enclos- sophisticated latexes with temperature-dependent
ing magnetite nanoparticles are reported for applying swelling properties.
them to hyperthermia treatment and diagnosis of An aqueous latex exhibiting a low degree of agglom-
cancer (Table 2.1.1(a)) [2].
eration, low membrane permeation, and high coating
efficiency was developed using terpoly(ethyl acrylate
2.1.3. Core–shell particles (EA)/methyl methacrylate (MMA)/2-hydroxyethyl
methacrylate (HEMA)), whose monomer molar ratio
Lipid microemulsions are aqueous dispersions of was 6:12:8 or 12:6:4 (Table 2.1.1(g)) [11]. Different
nanoparticles with liquid cores of lipid and shells of from blend latexes, the composite latexes composed of
phospholipid monolayer. When the cores are solid the low-permeable 12:6:4 polymer core and the non-
lipids, they are called “solid lipid nanoparticles” (Table adhesive 6:12:8 polymer shell with a 6:4 core–shell
2.1.1(w)). Therein, hydrophobic and amphiphilic weight ratio formed a low-permeable membrane by
agents are embedded in the cores and shells, respec- heat treatment. The composite latexes exhibited a very
tively. The surface-modifying compounds are anchored low degree of agglomeration, with the polymer yield
in the same manner as liposomes. remaining very high. These properties were still effec-
A typical lipid nanoparticle is shown in Table 2.1.1(d) tive even in the coating of cornstarch as fine as 12 m:
[5–7]. They were designed for delivering gadolinium at a 50% level of coating, the mass median diameter of
in cancer neutron capture therapy [8]. The gadolinium the product was 16 m and it contained only 3%
is chelated with diethylenetriamine pentaacetic acid agglomerates.
(DTPA) to make distearylamide (Gd-DTPA-SA). Gd- Another aqueous composite latex that suppressed the
DTPA-SA is not dissolved in water and the soybean oil electrostatic particle-adhesion in the coating process

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