Protein adsorption entropic forces

What is the driving force for protein adsorption Is the adsorption driven by overall energetic (enthalpic) interactions or does the entropic contribution prevail Do both entropic and enthalpic contributions play a major part in the adsorption process, the extent of each depending on the particular protein and surface in question An illuminating thermodynamic analysis given by Norde and Lyklema 62,66) for the adsorption of two different globular proteins (human serum albumin, HSA, and bovine pancreatic ribonuclease, RNase) on polystyrene latices will be presented. We believe this analysis has general validity. 

Several different forces may be involved in protein adsorption at the solid-liquid interface hydrogen bonding, electrostatic forces, and hydrophobic interactions. Entropic factors such as loss of water, structural deformation of the protein onto hydrophobic patches and dehydration of the protein may drive the adsorption process when there are non favourable electrostatic interactions. 

Rejection of protein adsorption to the outermost grafted surface is attributed to a steric hinderance due to the tethered chains. A grafted surface in contact with an aqueous medium, a good solvent of the chains, has been identified to have a diffuse structure [67]. Reversible deformation of tethered chains due to invasion of mobile protein molecules into the layer would lead to a repulsive force which is governed by the balance of entropic elasticity of the chains and osmotic pressure owing to the rise in the segment concentration. The overlapped repulsive force would prevent the direct contact of protein molecules with the substrate surface. 

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