Biomedical Engineering Reference
In-Depth Information
g
-PGA-Phe (water soluble) with
e
-PL in phosphate-buffered saline (PBS). The
formation and stability of the PIC nanoparticles was investigated by dynamic
light scattering (DLS) measurements. Monomodal anionic PIC nanoparticles were
obtained using nonstoichiometric mixing ratios. When unmodified
g
-PGA was
mixed with
e
-PL in PBS, the formation of PIC nanoparticles was observed.
However, within a few hours after the preparation, the PIC nanoparticles
dissolved in the PBS. In contrast,
g
-PGA-Phe/
e
-PL nanoparticles showed
high stability for a prolonged period of time in PBS, and over a wide range of
pH values. The stability and size of the PIC nanoparticles depended on the
g
-PGA-Phe/
e
-PL mixing ratio and the hydrophobicity of the
g
-PGA. The
improved stability of the PIC nanoparticles was attributed to the formation of
hydrophobic domains in the core of the nanoparticles. The fabrication of PIC
nanoparticles using hydrophobic interactions was very useful for the stabilization
of the nanoparticles.
3 Polymeric Nanoparticles for Antigen Delivery and Adjuvant
3.1 Preparation of Antigen-Loaded Nanoparticles
Nanoparticles containing encapsulated, surface-immobilized or surface-adsorbed
antigens are being investigated as vaccine delivery systems as alternatives to the
currently used alum, with an objective to develop better vaccine systems and
minimize the frequency of immunization. The encapsulation of antigenic proteins
or peptides into PLGA nanoparticle carrier system can be carried out through
mainly three methods: the water-in-oil-in-water (w/o/w) emulsion technique, the
phase separation method, and spray drying. The w/o/w double emulsion process is
popularly used to load proteins into nanoparticles (Fig.
10
)[
92
,
93
]. In this process,
an antigen is first dissolved in an aqueous solution, which is then emulsified in an
organic solvent to make a primary water-in-oil emulsion. This initial emulsion is
further mixed in an emulsifier-containing aqueous solution to make a w/o/w double
emulsion. The ensuing removal of the solvent leaves nano- and microparticles in
the aqueous continuous phase, making it possible to collect them by filtration or
centrifugation. However, the possible denaturation of the proteins at the oil-water
interface limits the usage of this method. It has been reported that this interface
causes conformational changes in bovine serum albumin (BSA) [
94
,
95
]. Moreover,
it has a disadvantage in that the entrapment efficiency is very low. The prevention
of protein denaturation and degradation, as well as high entrapment efficiency,
would be of particular importance in the preparation of nanoparticles containing
water-soluble drugs such as a protein. Improved protein integrity has been achieved
by the addition of stabilizers such as carrier proteins (e.g., albumin), surfactants
during the primary emulsion phase, or molecules such as trehalose and mannitol to
