  Motivated by experimentally observed biocompatibility enhancement of
nanoengineered cubic zirconia ZrO2 coatings to mesenchymal stromal cells, we
have carried out computational analysis of the initial immobilization of one of
known structural fragment of the adhesive protein (fibronectin) on the
corresponding surface. We constructed an atomistic model of the zirconia
nano-hillock of 3-fold symmetry based on AFM and TEM images. First-principle
quantum-mechanical calculations show a substantial variation of electrostatic
potential at the hillock due to the presence of surface features such as edges
and vertexes. Using an implemented Monte Carlo simulated annealing method we
found the orientation of the immobilized protein on the zirconia surface (both
flat and nanostructured) and contribution of the each amino acid residue from
the protein sequence to the adsorption energy. Accounting for the variation of
the dielectric permittivity at the protein-implant interface we use a model
distance-dependent dielectric function to describe the inter-atom electrostatic
(Coulomb) interactions in the adsorption potential. We find that the initial
immobilization of the rigid protein fragment on the nanostructured pyramidal
ZrO2 surface is achieved with magnitude of adsorption energy larger than the
one for the protein on the smooth (flat) surface. The strong attractive
electrostatic interactions are a major factor in the enhanced adsorption at
nanostructured surface that is absent in the case of adsorption on the flat
uncharged surface. We show that the best electrostatic and steric fit of the
protein to the inorganic surface corresponds to a minimum of the adsorption
energy determined by the non-covalent interactions.
