Microstructure and mechanical properties of chitosan/casein films

Caseins are amphiphilic, disordered proteins generally existing as assembled micelles containing αs1-, αs2-, β- and κ-caseins found in bovine milk1. At pH 3 (2% acetic acid solution), the Cas self-assembled into structures that presented an average size of 320 nm and a ζ-potential of + 28 mV. The hydrodynamic radius of the Cas micelles is reported as 35 nm1, indicating that at pH 3, the micelles built larger aggregates. The isoelectric point of casein is ~ 4.7, explaining the positive ζ-potential value. Many materials have been combined with chitosan (Chi) to produce new systems with tailored properties. When combined with Chi, casein (Cas) enhances cell adhesion and proliferation, especially in epithelial cells2. In this work, Cas was incorporated to Chi and cast as films, which will be evaluated as scaffolds for fibroblasts. Chi was dissolved in 2% acetic acid solution (pH 3) to a final concentration of 10 g/L, then Cas solution was dripped to Chi solution at 1 and 10% v/v), and cast as films. Incorporating casein into the Chi films increased the film roughness from 4 nm to 100 nm (Fig. 1), and the contact angle increased from 86° to 95° (10% Cas). No leaching of Cas from the films to water was detected, indicating the favorable interaction between the Cas positively charged residues and Chi hydroxy groups.