Impact of a protein addition on the microstructure and rheological properties of silica hydrogels

Silica gels are colloidal hydrogels that can be used in drug delivery techniques, and the introduction of proteins into the system would be of interest in cases where the protein is the element to be delivered. In this study repulsive colloids (silica particle) are mixed with ionic species to form a fractal gel. We then study the impact of adding a protein (bovine serum albumin (BSA)), whose overall charge is the same sign as silica, on the structural and mechanical properties of the gel. Thanks to SAXS and rheology measurements, we can deduce some micro and macro parameters such as, the interaction potential between beads, the gelation time, the elastic modulus and the critical strain of the gel and their variation with the volume fraction in BSA. The protein allows to form gels with very low ionic strength compared to the case without proteins; BSA acts as a binding agent between the silica particles. Thanks to a power-law model, hypotheses are proposed about the gel structure, to make a link between the structure and the mechanical properties.