Ionic strength affects lysozyme adsorption and release from SBA-15 mesoporous silica

In the present work we investigated the effect of ionic strength on the adsorption and release of a model therapeutic protein-hen egg white lysozyme (E.C.3.1.1.17)-from SBA-15 mesoporous silica. The biological function of lysozyme is the hydrolysis of polysaccharides constituting bacterial cell walls and, hence, it is a powerful antimicrobial agent. Here, lysozyme adsorption on SBA-15, carried out at different temperatures, showed that the adsorption capacity generally decreases with increasing the temperature, according to an exothermic process. The lysozyme adsorption kinetics on SBA-15 can be described through a pseudo-second order model or, alternatively, with an intraparticle diffusion model. Finally, the sustained release of lysozyme from SBA-15, carried out at 37 °C in a buffer solution at the physiological pH (7.4) and ionic strength (0.15 M NaCl), was measured both in terms of released amount of protein and released enzymatic activity. We found that the ionic strength of the immobilizing solution strongly affects lysozyme release trends. These effects are likely due to the interaction of electrolytes with both the biological and the inorganic surfaces, which results in the modulation of the forces at the basis of adsorption and release processes.