A Study of the Buffer Capacity of Polyelectrolyte Microcapsules Depending on Their Ionic Environment and Incubation Temperature

Abstract

Polyelectrolyte microcapsules (PMCs) are used in the development of new forms of drugs, coatings and diagnostic systems. Their buffer capacity, depending on the conditions of the medium, has not been practically studied, although it can affect the structure of both the capsule itself and the encapsulated agents. In this connection, we studied the buffer capacity of polyelectrolyte microcapsules of the composition (polystyrene sulfonate/polyallylamine)3 ((PSS/PAH)3) depending on the concentration and the type of salt in solution, as well as the microcapsule incubation temperature. It was found that the buffer capacity of microcapsules in the presence of mono- and di-valent salts of the same ionic strength did not differ practically. Increasing the NaCl concentration to 1 M led to an increase of buffer capacity of PMCs at pH ≥ 5, and an increase in NaCl concentration above 1 M did not change buffer capacity. The study of the buffer capacity of pre-heated PMCs showed that buffer capacity decreased with increasing incubation temperature, which was possibly due to the compaction of the PMCs and an increase in the number of compensated PAH sites. The addition of 1 M sodium chloride to heated PMCs presumably reversed the process described above, since an increase in the ionic strength of the solution led to an increase of the buffer capacity of the PMCs. The effects described above confirm the hypothesis put forward that the buffer properties of microcapsules are determined by uncompensated PAH regions in their composition.

A Study of the Buffer Capacity of Polyelectrolyte Microcapsules Depending on Their Concentration and the Number of Layers of the Polyelectrolyte Shell

“…Additionally, we found the dependence of the buffer capacity’s behavior on the PMC shell’s composition, the presence of an encapsulated protein, the magnitude of ionic strength, and the temperature of the solution. These studies demonstrated that the buffer properties of microcapsules are determined by the charged regions of PAH (uncompensated with PSS) in the composition of their shell [ 2 , 9 ]. However, as described above, the number and density of PAH charged groups (distance between nearest groups of -NH 3 + groups) also depend on the number of microcapsule shell layers and the number of microcapsules themselves.…”

“…Dubrovsky et al demonstrated the buffer capacity of polyelectrolyte microcapsules and the dependence of the behavior of the buffer capacity on the presence of an encapsulated protein [ 2 ], the ionic strength, and the temperature of the solution [ 9 ]. Additionally, these works confirmed that the buffer properties of microcapsules are determined by polyallylamine (PAH) sites uncompensated with polystyrene sulfonate in the composition of a PMC’s shell.…”

Short-Term Stability of Electrochemical Properties of Layer-by-Layer Coated Heterogeneous Ion Exchange Membranes

“…The third component was a single layer of polyamine adsorbed from the dispersion— in one case this was polyallylamine (purchased from Merck KGaA, Darmstadt, Germany; the resulting membrane is denoted as MK-40-M-PAH) and in the other case it was polyethylenimine (purchased from Merck KGaA, Darmstadt, Germany; the resulting membrane is denoted as MK-40-M-PEI). Polyallylamine is used for layer-by-layer assembly [ 39 ] as a component of new promising materials (such as thermo-responsive polymers with cleavage-induced phase transition [ 40 ] or coatings decomposing by application of electric potential [ 41 ]), including biomedical applications such as creation of nano-capsules for drug delivery [ 42 ] and food packaging [ 43 ]. Polyethylenimine is frequently used as a polymer carrier [ 44 ] and basis for loading of nanoparticles [ 45 ] or coating for medical applications [ 46 ].…”