Comparative Electrokinetic Study of Alginate-Coated Colloidal Particles

Abstract

Alginates are a family of natural polysaccharides with promising potential in biomedical applications and tissue regeneration. The design of versatile alginate-based structures or hydrogels and their stability and functionality depend on the polymer's physicochemical characteristics. The main features of alginate chains that determine their bioactive properties are the molar ratio of mannuronic and glucuronic residues (M/G ratio) and their distribution along the polymer chain (MM-, GG-, and MG blocks). The present study is focused on investigating the influence of the physicochemical characteristics of alginate (sodium salt) on the electrical properties and stability of the dispersion of polymer-coated colloidal particles. Ultrapure and well-characterized biomedical-grade alginate samples were used in the investigation. The dynamics of counterion charge near the vicinity of adsorbed polyion is studied via electrokinetic spectroscopy. The results show that the experimental values of the frequency of relaxation of the electro-optical effect are higher compared to the theoretical ones. Therefore, it was supposed that polarization of the condensed Na⁺ counterions occurs at specific distances according to the molecular structure (G-, M-, or MG-blocks). In the presence of Ca²⁺, the electro-optical behavior of the particles with adsorbed alginate molecules almost does not depend on the polymer characteristics but was affected by the presence of divalent ions in the polymer layer.

Keywords: adsorption; alginate; colloidal particles; cross-linking; electrokinetic spectroscopy.

Figure 1

Electrophoretic mobility, U_ef, of particles in the presence of different concentrations of alginates: A082 (▲), A122 (■), and A047 (●). Open symbol corresponding to the mobility of bare oxide particles.

Figure 2

Electrophoretic mobility, U_ef, of particles with adsorbed alginate layer in the presence of CaCl₂: A082 (▲), A122 (■), and A047 (●). Open symbols correspond to the particles with adsorbed alginate layer without addition of CaCl₂. The concentration of alginate in suspension is 10⁻² mg/mL. The vertical dot line indicates the interval of CaCl₂ concentrations with almost constant ionic strength of the suspensions.

Figure 3

Dependence of the registered electro-optical effect, α_kHz, (A) and electrical conductivity, χ, (B) from a suspension of particles with adsorbed alginate layer in the presence of CaCl₂: A082 (▲), A122 (■), and A047 (●). Open symbols correspond to the particles with adsorbed alginate layer without salt. The concentration of alginate in suspension is 10⁻² mg/mL. The vertical dot line indicates the interval of CaCl₂ concentrations where the ionic strength of the suspensions is almost constant. The frequency of the electric field is 1 kHz. The electric field strength is 2.3 × 10⁴ V/m.

Figure 4

Frequency dependence of the electro-optical effect, α, from a stabilized suspension of particles with adsorbed alginate layer in the presence of 2.5 × 10⁻⁵ M CaCl₂: A082 (▲), A122 (■), and A047 (●). Open symbols correspond to the particles with adsorbed alginate layer without salt. The concentration of alginate in suspension is 10⁻² mg/mL. The electric field strength is 2.3 × 10⁴ V/m. Inset: Frequency dependence of suspension of bare particles.

Figure 5

Electro-optical effect from suspensions of particles stabilized by adsorbed alginate molecules: A082 (△), A122 (□), and A047 (○). The concentration of alginate in suspension is 10⁻² mg/mL. The frequency of the electric field is 3 kHz.

Figure 6

Dependence of the electrophoretic mobility, U_ef, of β-FeOOH particles as a function of a number of adsorbed steps of chitosan/alginate film formed from A082 (▲), A122 (■), and A047 (●). Open symbol corresponding to the mobility of bare β-FeOOH particles first alginate layer (ALG1) chitosan layer (CS1) and second alginate layer (ALG2).

Figure 7

Frequency dependence of the electro-optical effect, α, from a stabilized suspension of particles with adsorbed ALG1 (○), CS1 (□), ALG2 (●), and in the presence of Ca²⁺ (▲) for a film formed from alginate A082 (A), A122 (B), and A047 (C). The concentration of polysaccharides is 10⁻² mg/mL. The electric field strength is 2.3 × 10⁴ V/m.

Figure 7

Frequency dependence of the electro-optical effect, α, from a stabilized suspension of particles with adsorbed ALG1 (○), CS1 (□), ALG2 (●), and in the presence of Ca²⁺ (▲) for a film formed from alginate A082 (A), A122 (B), and A047 (C). The concentration of polysaccharides is 10⁻² mg/mL. The electric field strength is 2.3 × 10⁴ V/m.

Figure 8

Dependence of the hydrodynamic thickness of particles with chitosan/alginate film formed from ALG-A (▲), ALG-B (■), and ALG-C (●) as a function of the adsorbed steps.

Scheme 1

Schematic chemical structure of alginate sodium salt (guluronate, G, and mannuronate, M, residues) and chitosan (acetylated, A, and deacetylated, D, monomers).

Figure 9

Representative SEM photographs of bare β-FeOOH particles (a) and particles with adsorbed alginate/chitosan film (b).