cationically modified cyclodextrins, emphasizing colloidal stability, narrow size
distribution of the formed nanoplexes, and satisfactory DHA uptake.
Furthermore, Yuan et al. [144] introduced spherical PEC particles obtained by
complexation of the cationic graft copolymer PEI-graft-poly(N-vinylpyrrolidone)
(PEI-g-PVP) with anionic block copolymer of PVP-block-poly(2-acrylamido-2methyl-1-propanesulfonic acid) (PVP-b-PAMPS); the particle size was around
140 nm. Folic acid was entrapped in the micelle core by electrostatic attraction
and the release rate was strongly dependent on the pH of the release medium.
Another complexation technique was reported by Chuang et al. [145], who
prepared PEC particles by templating polymerization of acrylic acid in the presence
of CHT at various monomolar ratios (0.2/1.1 to 1.0/1.1). Hollow CHT/PAC
particles were formed with sizes of around 200 nm, which varied with the pH of
the medium, and zeta-potentials of around 25 mV. The release of doxycycline
(DOC) incorporated by various feeding processes was found to last for up to 8 days.
Recently, thermosensitive PEC particles were prepared by Guiying et al. [146],
who complexed the block copolymer poly(t-butyl acrylate-co-acrylic acid)-blockpoly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM] with the graft copolymer
chitosan-graft-poly(N-isopropylacrylamide) (CHT-g-PNIPAM) and entrapped DOX.
Like the complexes between terpolymer systems described by Schacher et al. [65],
these PEC particles had a multishell structure with hydrophobic PtBA in the core,
anionic PAC and cationic CHT in the middle, and PNIPAM in the outer shell
(Fig. 31a). DOX release was suppressed at neutral pH and elevated at low pH due
to electrostatic repulsion between cationic DOX and the polycation component or
reduced ion pairing between polycation and polyanion, resulting in channels enabling
DOX passage (Fig. 31b). At temperatures above the LCST, DOX release was
promoted and the authors claim that PEC/PEC aggregation was responsible.
Although such thermoinducable drug release by PEC nanoparticles had been initiated
by these authors, Lyon and coworkers [63] previously reported the uptake and release
of DOX from a related PEM. This PEM consisted of cationic PAH and an anionic
copolymer of NIPAAM and acrylic acid. A significant dependence of porosity and
thus drug retention/release on both temperature and pH was found.
5.2.3 Adhesive Films of PEC Nanoparticles for Local Drug Administration
In the previous section, release from such drug-loaded PECs was shown for PEC
particles in the volume phase and the drug delivery was intended to act systemically, i.e., the whole body should be reached by PEC particles through blood
circulation.
Recently, initial work was described by us regarding drug release from an
adhesive layer of cast PEC particles [147]. Such interfacial drug-loaded PEC
systems are closely related to drug-loaded PEM systems, which were initiated by
Chung and Rubner [148] based on dye/PEM. Both approaches, PEM and adhesive
PEC, are highly relevant for the generation of locally acting drug-eluting modification layers on biomedical devices such as stents, implants, bone substituting
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
241
distribution of the formed nanoplexes, and satisfactory DHA uptake.
Furthermore, Yuan et al. [144] introduced spherical PEC particles obtained by
complexation of the cationic graft copolymer PEI-graft-poly(N-vinylpyrrolidone)
(PEI-g-PVP) with anionic block copolymer of PVP-block-poly(2-acrylamido-2methyl-1-propanesulfonic acid) (PVP-b-PAMPS); the particle size was around
140 nm. Folic acid was entrapped in the micelle core by electrostatic attraction
and the release rate was strongly dependent on the pH of the release medium.
Another complexation technique was reported by Chuang et al. [145], who
prepared PEC particles by templating polymerization of acrylic acid in the presence
of CHT at various monomolar ratios (0.2/1.1 to 1.0/1.1). Hollow CHT/PAC
particles were formed with sizes of around 200 nm, which varied with the pH of
the medium, and zeta-potentials of around 25 mV. The release of doxycycline
(DOC) incorporated by various feeding processes was found to last for up to 8 days.
Recently, thermosensitive PEC particles were prepared by Guiying et al. [146],
who complexed the block copolymer poly(t-butyl acrylate-co-acrylic acid)-blockpoly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM] with the graft copolymer
chitosan-graft-poly(N-isopropylacrylamide) (CHT-g-PNIPAM) and entrapped DOX.
Like the complexes between terpolymer systems described by Schacher et al. [65],
these PEC particles had a multishell structure with hydrophobic PtBA in the core,
anionic PAC and cationic CHT in the middle, and PNIPAM in the outer shell
(Fig. 31a). DOX release was suppressed at neutral pH and elevated at low pH due
to electrostatic repulsion between cationic DOX and the polycation component or
reduced ion pairing between polycation and polyanion, resulting in channels enabling
DOX passage (Fig. 31b). At temperatures above the LCST, DOX release was
promoted and the authors claim that PEC/PEC aggregation was responsible.
Although such thermoinducable drug release by PEC nanoparticles had been initiated
by these authors, Lyon and coworkers [63] previously reported the uptake and release
of DOX from a related PEM. This PEM consisted of cationic PAH and an anionic
copolymer of NIPAAM and acrylic acid. A significant dependence of porosity and
thus drug retention/release on both temperature and pH was found.
5.2.3 Adhesive Films of PEC Nanoparticles for Local Drug Administration
In the previous section, release from such drug-loaded PECs was shown for PEC
particles in the volume phase and the drug delivery was intended to act systemically, i.e., the whole body should be reached by PEC particles through blood
circulation.
Recently, initial work was described by us regarding drug release from an
adhesive layer of cast PEC particles [147]. Such interfacial drug-loaded PEC
systems are closely related to drug-loaded PEM systems, which were initiated by
Chung and Rubner [148] based on dye/PEM. Both approaches, PEM and adhesive
PEC, are highly relevant for the generation of locally acting drug-eluting modification layers on biomedical devices such as stents, implants, bone substituting
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
241