Surface chemistry at the nanometer scale influences insulin aggregation

We synthesized surfaces with different hydrophobicities and roughness by forming self-assembled monolayers (SAMs) of mixed amine and octyl silanes. Insulin aggregation kinetics in the presence of the above surfaces is characterized by a typical lag phase and growth rate. We show that the lag time but not the growth rate varies as a function of the amine fraction on the surface. The amount of adsorbed protein and the adsorption rate during the aggregation process also vary with the amine fraction on the surface and are maximal for equal parts of amine and octyl groups. For all surfaces, the growth phase starts for identical amounts of adsorbed insulin. The initial surface roughness determines the rate at which protein adsorption occurs and hence the time to accumulate enough protein to form aggregation nuclei. In addition, the surface chemistry and topography influence the morphology of aggregates adsorbed on the material surface and the secondary structures of final aggregates released in solution.