distribution measured by DLS kept approximately constant at around 100 nm. However, the solid content was reduced to a certain extent because there was considerable
precipitation during the two centrifugation steps during the two centrifugation steps.
Furthermore, in PEC-0x and PEC-1x dispersions DLS signals at 20 nm were present,
while in PEC-2x ones they were absent, which can be explained by the removal of
primary PEC particles upon centrifugation in the sense of an accelerated Ostwald
ripening (see Sects. 3.2.3 and 3.3.2).
Other authors, e.g., Dautzenberg and Jaeger [51] and Pergushov et al. [52],
filtered the raw dispersions before SLS or DLS, respectively. Membrane syringe
filters with cutoff pores up to 450 nm were used, allowing removal of larger
aggregate particles and collection of smaller particles at a lower PDI.
3 Sizing of PEC Particles
PEC particle size can be influenced by various parameters related to preparation,
PEL structure, and the medium (pH and concentration of PEL and salt). Preparative
parameters have already been mentioned in Sect. 2.2. In this section, PEL structural
parameters (Sect. 3.1) and then media parameters (Sect. 3.2) influencing PEC
particle size will be discussed. Finally, sizing the internal structural density of
PEC systems by structural and media parameters will be outlined (Sect. 3.3). In
that frame, the pore size and the degree of compartmentation are important
observables. This is of high relevance for PEC-based pharmaceutical carrier
systems because pore size and compartmentation control the retention potential
of PEC systems towards low and high molecular weight drugs.
3.1 PEL Structural Parameters
The influence of PEL structural parameters such as weakness/strength, charge
density, molecular weight, linear or branched topology, and monomer properties
of charged copolymers on PEC particle size are reviewed.
3.1.1 Charge Density
The influence of charge density was addressed in early work of Dautzenberg and
colleagues [28] using a system of cationic and anionic copolymers of acrylamide.
They showed that for equal charge density of the PEL components, the “symplex”
particles adopt a compact structure, whereas in systems with strongly deviating
charge density of the PEL components a loose “fluctuating” structure prevails. This
finding was in line with later work of Dautzenberg and Jaeger [51] on cationic
copolymers of DADMAC and N-methylvinyl acetamide (NMVA) and anionic PSS.
The work of Mende et al. [53] on PDADMAC and degraded anionic copolymers of
acrylamide and acrylate (PAMAC) with varying charge density confirmed this
208
M. M€ uller
precipitation during the two centrifugation steps during the two centrifugation steps.
Furthermore, in PEC-0x and PEC-1x dispersions DLS signals at 20 nm were present,
while in PEC-2x ones they were absent, which can be explained by the removal of
primary PEC particles upon centrifugation in the sense of an accelerated Ostwald
ripening (see Sects. 3.2.3 and 3.3.2).
Other authors, e.g., Dautzenberg and Jaeger [51] and Pergushov et al. [52],
filtered the raw dispersions before SLS or DLS, respectively. Membrane syringe
filters with cutoff pores up to 450 nm were used, allowing removal of larger
aggregate particles and collection of smaller particles at a lower PDI.
3 Sizing of PEC Particles
PEC particle size can be influenced by various parameters related to preparation,
PEL structure, and the medium (pH and concentration of PEL and salt). Preparative
parameters have already been mentioned in Sect. 2.2. In this section, PEL structural
parameters (Sect. 3.1) and then media parameters (Sect. 3.2) influencing PEC
particle size will be discussed. Finally, sizing the internal structural density of
PEC systems by structural and media parameters will be outlined (Sect. 3.3). In
that frame, the pore size and the degree of compartmentation are important
observables. This is of high relevance for PEC-based pharmaceutical carrier
systems because pore size and compartmentation control the retention potential
of PEC systems towards low and high molecular weight drugs.
3.1 PEL Structural Parameters
The influence of PEL structural parameters such as weakness/strength, charge
density, molecular weight, linear or branched topology, and monomer properties
of charged copolymers on PEC particle size are reviewed.
3.1.1 Charge Density
The influence of charge density was addressed in early work of Dautzenberg and
colleagues [28] using a system of cationic and anionic copolymers of acrylamide.
They showed that for equal charge density of the PEL components, the “symplex”
particles adopt a compact structure, whereas in systems with strongly deviating
charge density of the PEL components a loose “fluctuating” structure prevails. This
finding was in line with later work of Dautzenberg and Jaeger [51] on cationic
copolymers of DADMAC and N-methylvinyl acetamide (NMVA) and anionic PSS.
The work of Mende et al. [53] on PDADMAC and degraded anionic copolymers of
acrylamide and acrylate (PAMAC) with varying charge density confirmed this
208
M. M€ uller