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

Polyelectrolyte multilayer capsules have been fabricated in aqueous media by step-wise assembling of sodium polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) on human red blood cells and melamine formaldehyde resin particles as templates, followed by removal of these templates by two 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 sodium hypochlorite solution (pH 12). The effect of these treatments on the chemical composition of the capsules and of a randomly formed polyelectrolyte complex was studied. The melamin resin templated capsules have basically the 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 changed the chemical composition of the capsules drastically. The amino groups of polyallylamine were oxidized to nitriles, nitroso-, nitro-, azo- and carbonyl groups. Positive charges disappeared. Covalent bonds were formed which crosslink the polymer chains. Simultaneously, the amount of PSS is strongly reduced to 10% of the original value. The stability of the capsules can be understood as a result of crosslinking and hydrophobic interactions. The cell templated capsules are monodisperse, being replicas in size and shape of the template but their chemical composition is different compared with the initial polyelectrolyte multilayer film. The altered chemical properties are responsible for new physical and mechanical properties such as higher elasticity, high chemical stability, as well as selective adsorption and permeation for charged ions.