Reversible gelation in hydrophobic polyelectrolyte/protein mixtures: An example of cross-links between soft and hard colloids

Measurements were conducted on the linear viscoelastic properties of hydrop hobically modified poly(sodium acrylate) reversibly cross-linked with prote ins to form gels. The native structure of proteins was not markedly affecte d upon association with the amphiphilic polyelectrolyte. Hydrophobic intera ction was shown to overcome Coulombic effects on interpolymer complexation. Because of their relative hydrophobicity, neutral papain and positively ch arged lysozyme were found to be less efficient cross-linking agents than ne gatively charged bovine serum albumin: These reversible gels exhibited simi larities with chemically cross-linked macromolecules such as a plateau modu lus at high frequency and characteristic scaling at the transition point be tween sol and gel. The sol-gel transition diagrams were determined. A semiq uantitative approach, based on scaling laws, was able to capture the essent ial rheological properties of these mixtures, namely sol-gel transition and variations of storage modulus.