Reversible controlled assembly of chitosan and dextran sulfate: a new method for nanoparticle elaboration.

Colloidal polyelectrolyte complexes (PECs) were obtained by the controlled assembly of oppositely charged dextran sulfate and chitosan, at room temperature, in water and under moderate stirring. The control over the assembly process was achieved by the slow dialysis of the sodium chloride added to the polyelectrolyte solutions prior to mixing them. This method was carried out at high polymer concentrations of 1.5 wt% and 3 wt%, with screening salt concentrations (SSC) from 2 mol L(-1) and chitosans of degree of acetylation (DA) from 39% and above. The resulting particles featured a size distribution between 350 and 580 nm, a positive surface charge (30-58 mV) and remained stable for 40 days at 37 °C. The reversibility of the controlled assembly was established by adding 2 mol L(-1) NaCl to the dispersion, the particle solubilized and then re-formed upon dialysis of the salt.