Characterization of casein and poly-L-arginine multilayer films

Thin films containing casein appear to be a promising material for coatings used in the medical area to promote biomineralization. alpha- and beta-casein and poly-L-arginine multilayer films were formed by the layer-by layer technique and their thickness and mass were analyzed by ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D). (PLArg/casein) films deposited in 0.15 M NaCl exhibit fast (exponential-like) growth of the film thickness with the number of layers. The resulting films were c.a. 10 times thicker than obtained for poly-L-arginine and natural polyanions. We investigated the effect of the type of casein used for the film formation, finding that films with alpha-casein were slightly thicker than ones with beta-casein. The effect of polyethylene imine anchoring layer on the thickness and mass of adsorbed films was similar as for linear polyelectrolyte pairs. Thickness of wet films was c.a. two times larger than measured after drying that suggests their large hydration. The analysis of the mass of films during their post-treatment with the solutions of various ionic strength and pH provided the information concerning films stability. Films remain stable in the neutral and weakly basic conditions that includes HEPES buffer, which is widely used in cell culture and biomedical experiments. At the conditions of high ionic strength films swell but their swelling is reversible. Films containing caseins as polyanion appear to be more elastic and the same time more viscous than one formed with polyelectrolyte pairs. XPS elemental analysis confirmed binding of calcium ions by the casein embedded in the multilayers. (C) 2014 Elsevier Inc. All rights reserved.