4 Shaping of PEC Particles
Shaping aspects of PEC particles, especially on the nanolevel, is a relatively new
field, although early interesting experimental work addressing other aspects has
been carried out. For example, the groups of Gelman [83] and Shinoda [84]
performed early experiments on a molecular level, focusing on what one would
nowadays call the template effects of the semiflexible host PEL molecules on the
conformation of the oppositely charged guest PEL molecules (see Sect. 4.2.2).
These authors used combinations of charged homopolypeptides and oppositely
charged polysaccharides in low concentration ranges, but to our knowledge did
not observe or study colloidal aspects such as phase separation and nanoparticle
formation. Hence, neither particle size nor shape aspects were addressed. However,
due to the potential applications, these early original experiments together with
more recent results (including colloidal aspects) will be discussed further.
4.1 Spherical PEC Particles
PEC particles with a spherical shape are the most prominent and the possibility to
influence their overall particle size has been extensively described in Sect. 3.
Additional internal shaping aspects within spherical PECs can be seen in the ratio
between the more flexible hydrophilic nonstoichiometric shell and the more compact hydrophobic stoichiometric core part of PEC particles, according to a widely
claimed PEC model [85]. Such internal shaping presumably could also be
influenced by structural and media parameters. However, analytical access to the
internal structure of water-rich and therefore emulsion-like rather than suspensionlike PEC particles is limited with the present analytical techniques. More information can be obtained on the overall external shape of PEC particles.
4.2 Rod-like PECs
4.2.1 PECs of Synthetic Polyelectrolytes
In contrast to spherical PECs, studies on rod-like PECs are less known and to date
there are few reports on the influence of the PEL conformation (globular, flexible,
or stiff) on the shape (spheres, rods, disks) of the final PEC particles, which could be
used for structuring or scaffolding purposes on the nano- or microlevel of e.g.
biomaterials. An initial nice example on templating elongated nanoscopic
structures of PEC by inherently stiff PEL was given by Rabe and coworkers [86].
Complexes between stiff dendronized poly(styrene) bearing protonated
peripherical amine groups (PG4) and DNA are reported. In Fig. 21, high resolution
SFM images of PG4/DNA complexes deposited onto mica are shown.
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
225
Shaping aspects of PEC particles, especially on the nanolevel, is a relatively new
field, although early interesting experimental work addressing other aspects has
been carried out. For example, the groups of Gelman [83] and Shinoda [84]
performed early experiments on a molecular level, focusing on what one would
nowadays call the template effects of the semiflexible host PEL molecules on the
conformation of the oppositely charged guest PEL molecules (see Sect. 4.2.2).
These authors used combinations of charged homopolypeptides and oppositely
charged polysaccharides in low concentration ranges, but to our knowledge did
not observe or study colloidal aspects such as phase separation and nanoparticle
formation. Hence, neither particle size nor shape aspects were addressed. However,
due to the potential applications, these early original experiments together with
more recent results (including colloidal aspects) will be discussed further.
4.1 Spherical PEC Particles
PEC particles with a spherical shape are the most prominent and the possibility to
influence their overall particle size has been extensively described in Sect. 3.
Additional internal shaping aspects within spherical PECs can be seen in the ratio
between the more flexible hydrophilic nonstoichiometric shell and the more compact hydrophobic stoichiometric core part of PEC particles, according to a widely
claimed PEC model [85]. Such internal shaping presumably could also be
influenced by structural and media parameters. However, analytical access to the
internal structure of water-rich and therefore emulsion-like rather than suspensionlike PEC particles is limited with the present analytical techniques. More information can be obtained on the overall external shape of PEC particles.
4.2 Rod-like PECs
4.2.1 PECs of Synthetic Polyelectrolytes
In contrast to spherical PECs, studies on rod-like PECs are less known and to date
there are few reports on the influence of the PEL conformation (globular, flexible,
or stiff) on the shape (spheres, rods, disks) of the final PEC particles, which could be
used for structuring or scaffolding purposes on the nano- or microlevel of e.g.
biomaterials. An initial nice example on templating elongated nanoscopic
structures of PEC by inherently stiff PEL was given by Rabe and coworkers [86].
Complexes between stiff dendronized poly(styrene) bearing protonated
peripherical amine groups (PG4) and DNA are reported. In Fig. 21, high resolution
SFM images of PG4/DNA complexes deposited onto mica are shown.
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
225