Assessing complex protein-solvent interactions using environment-controlled crack-growth experiments

The modulation of protein functionality, i.e. their ability to fold/unfold, by adding low molecular weight substances to the “natural” solvent water is an important issue in biochemistry. Taking advantage of the unique ability of gelatin to self assemble into elastic networks via partial renaturation of the native collagen protein, we propose to recast the issue into a fracture mechanics one. We describe a method to decipher the effect of alcohols as cosolvents on gelatin networks from the shift of fracture energy in response to an environmental shock. After suitable subtraction of the viscous dissipation we are able characterize the solvent/network interaction by the relative shift of the free energy characteristic of the crosslinked→dismanteled transition of the network associated to its fracture. Using two alcohols, methanol and glycerol, we show that our method is able to accounts for their known contrasting effects on proteins. We briefly discuss the nature of the energy of interaction. In addition we unveil an open issue regarding the origin and consequence of the poroelastic solvent flow associated to crack propagation in hydrogels.