Polyelectrolyte multilayer capsules templated on biological cells: core oxidation influences layer chemistry

Polyelectrolyte multilayer capsules have been fabricated in aqueous media b y step-wise assembling of sodium polystyrene sulfonate (PSS) and polyallyla mine hydrochloride (PAH) on human red blood cells and melamine formaldehyde resin particles as templates, followed by removal of these templates by tw o different procedures. The melamine formaldehyde core can be dissolved in pH 1.1. The removal of the cell cores was achieved by an oxidation with sod ium hypochlorite solution (pH 12). The effect of these treatments on the ch emical composition of the capsules and of a randomly formed polyelectrolyte complex was studied. The melamin resin templated capsules have basically t he same composition as the untreated complex revealing no chemical changes induced by the acid. But about 20% of the total hollow capsules mass can be attributed to a rest of melamin resin. The treatment with NaOCl solution c hanged the chemical composition of the capsules drastically. The amino grou ps of polyallylamine were oxidized to nitriles, nitroso-, nitro-, azo- and carbonyl groups. Positive charges disappeared. Covalent bonds were formed w hich crosslink the polymer chains. Simultaneously, the amount of PSS is str ongly reduced to 10% of the original value. The stability of the capsules c an be understood as a result of crosslinking and hydrophobic interactions. The cell templated capsules are monodisperse, being replicas in size and sh ape of the template but their chemical composition is different compared wi th the initial polyelectrolyte multilayer film. The altered chemical proper ties are responsible for new physical and mechanical properties such as hig her elasticity, high chemical stability, as well as selective adsorption an d permeation for charged ions. (C) 2001 Elsevier Science B.V. All rights re served.