Adsorption of collagen fragments on titanium oxide surfaces:: A molecular dynamics study

The adsorption of flexible collagen I triple helices with lengths of 8 nm in aqueous solution on a partially hydroxylated rutile layer (pH = 7.4) is modelled by classical molecular dynamics simulation with trajectories of up to 5 ns lengths. The carboxyl groups of glutamic and aspartic acids form hydrogen bonds with surface protons, which result in stable contact points at 300 K, if the bond length is smaller than 2 angstrom. Lysine side chains bind to surface hydroxyl groups. In spite of rotational motion around the C-N figure axis and opening and closing of hydrogen bonds, the amino groups are immobilized at the surface at N-O distances below 4 angstrom. In all runs the proteins have few contact points to the surface even though it is perfectly planar in our simulation. We suggest that the experimentally observed increase of adsorption energy and area per molecule over time may be associated to an increase of the number of contact points, which induces spreading of the adsorbate.