The physicochemical properties of biopolymer-based PECs with controlled pH
and/or thermoresponsiveness were described by Glampedaki et al. [138, 139]. The
study [138] illustrates a novel combination between negatively charged pH- and
thermoresponsive microparticles of poly(isopropylacrylamide-co-acrylic acid)
(PNIAA) and positively charged chitosan chains. Morphological and physicochemical
aspects of the stimuli-responsiveness of the complexes were investigated through
scanning electron microscopy, polyelectrolyte titration, UV–vis spectroscopy, analytical centrifugation, and tensiometry. The PNIAA thermoresponsiveness kinetics was
found to be both temperature- and pH-dependent. Chitosan/PNIAA complexes
appeared more hydrophobic below LCST and more hydrophilic above LCST, compared with PNIAA alone. Their demixing behavior revealed that chitosan/PNIAA
complexes are more sensitive to pH and temperature changes than their individual
components. Finally, complexes were found to be surface-active, with their surface
activity lying between those of chitosan and PNIAA. The information obtained
about hydrophilicity/hydrophobicity aspects of the studied systems is considered
essential, as they are intended for interesting applications such as polyester surface
functionalization.
The preparation of pH- or thermoresponsive microgels of NIPAAm copolymerized
with acrylic acid, either alone or complexed with chitosan is described [138]. All
properties of the microgels are in very good correlation with those expected from the
chemical structure of the polymers used for their preparation.
A new type of a dual system using mixtures of chitosan and a thermosensitive
polymer has been described in Sect. 2.7 [47–50].
PECs also have been the focus of an expanding number of studies for their wide
use in medicine. For instance, biopolymer nanoparticles have been described as
very promising nanosized carrier materials with great potential in health care and
environmental sciences [140].
Mu ¨ller et al. [141] described PEC nanoparticles prepared by mixing solutions of
oppositely charged PEL, whose size and shape can be regulated by external and media
parameters. An improved preparation protocol for PEC nanoparticles based on consecutive centrifugations was elaborated, resulting in better reproducibility and lower
polydispersity. Experimental and simulation evidence showed that salt and PEL
concentration are sensitive parameters for size regulation of spherical PEC
nanoparticles. The authors outline certain advantages of dispersed PEC particles for
life science applications due to easy preparation, graded nanodimensions, achievable
solid content, and uptake/release properties for proteins and drugs.
The physicochemical and biological properties of DNA and small interfering
RNA (siRNA) complexes prepared from a set of maltose-, maltotriose-, or
maltoheptaose-modified hyperbranched PEIs [termed (oligo-)maltose-modified
PEIs; OM-PEIs] were investigated [142]. The authors showed that pH-dependent
charge densities of the OM-PEIs correlate with the structure and degree of grafting
and with the length of the oligomaltose. Decreased zeta-potentials of OM-PEIbased complexes and changes in the thermodynamics of DNA complex formation
are observed, while the complex sizes are largely unaffected by maltose grafting
and the presence of serum proteins.
58
G. Petzold and S. Schwarz
and/or thermoresponsiveness were described by Glampedaki et al. [138, 139]. The
study [138] illustrates a novel combination between negatively charged pH- and
thermoresponsive microparticles of poly(isopropylacrylamide-co-acrylic acid)
(PNIAA) and positively charged chitosan chains. Morphological and physicochemical
aspects of the stimuli-responsiveness of the complexes were investigated through
scanning electron microscopy, polyelectrolyte titration, UV–vis spectroscopy, analytical centrifugation, and tensiometry. The PNIAA thermoresponsiveness kinetics was
found to be both temperature- and pH-dependent. Chitosan/PNIAA complexes
appeared more hydrophobic below LCST and more hydrophilic above LCST, compared with PNIAA alone. Their demixing behavior revealed that chitosan/PNIAA
complexes are more sensitive to pH and temperature changes than their individual
components. Finally, complexes were found to be surface-active, with their surface
activity lying between those of chitosan and PNIAA. The information obtained
about hydrophilicity/hydrophobicity aspects of the studied systems is considered
essential, as they are intended for interesting applications such as polyester surface
functionalization.
The preparation of pH- or thermoresponsive microgels of NIPAAm copolymerized
with acrylic acid, either alone or complexed with chitosan is described [138]. All
properties of the microgels are in very good correlation with those expected from the
chemical structure of the polymers used for their preparation.
A new type of a dual system using mixtures of chitosan and a thermosensitive
polymer has been described in Sect. 2.7 [47–50].
PECs also have been the focus of an expanding number of studies for their wide
use in medicine. For instance, biopolymer nanoparticles have been described as
very promising nanosized carrier materials with great potential in health care and
environmental sciences [140].
Mu ¨ller et al. [141] described PEC nanoparticles prepared by mixing solutions of
oppositely charged PEL, whose size and shape can be regulated by external and media
parameters. An improved preparation protocol for PEC nanoparticles based on consecutive centrifugations was elaborated, resulting in better reproducibility and lower
polydispersity. Experimental and simulation evidence showed that salt and PEL
concentration are sensitive parameters for size regulation of spherical PEC
nanoparticles. The authors outline certain advantages of dispersed PEC particles for
life science applications due to easy preparation, graded nanodimensions, achievable
solid content, and uptake/release properties for proteins and drugs.
The physicochemical and biological properties of DNA and small interfering
RNA (siRNA) complexes prepared from a set of maltose-, maltotriose-, or
maltoheptaose-modified hyperbranched PEIs [termed (oligo-)maltose-modified
PEIs; OM-PEIs] were investigated [142]. The authors showed that pH-dependent
charge densities of the OM-PEIs correlate with the structure and degree of grafting
and with the length of the oligomaltose. Decreased zeta-potentials of OM-PEIbased complexes and changes in the thermodynamics of DNA complex formation
are observed, while the complex sizes are largely unaffected by maltose grafting
and the presence of serum proteins.
58
G. Petzold and S. Schwarz