Influence Of Nanostructure On Collagen Adsorption Onto TiO₂Surface Via Molecular Dynamics Simulation

Titanium biomaterials with its elastic modulus close to bone, has been widelyused in orthopedic and cardiovascular field for its excellent mechanical andbiological properties, which is also contributed by its superficial compact titaniumoxide layer. There are lots of factors that may account for the bioactivitiy ofbiomaterials, but the surface topography is thought to be the main factor that couldaffect cell adhesion and the formation of “contanct guidance” alone. Generally,protein plays an intermediate role in cell adsorption and the “contact guidance”phenomenon, so the research on how the topographical surfaces affect the proteinadsorption will be of great inportance in realising these two phenomenons, as wellas be good for designing appropriate surface topography to improve bioactivity.As peroxinectin and scaffolding protein, collagen plays an important role inguiding cell adhesion and biomineralization. Collagen adsorbing on rutile surfacewith different nanotopography will be studied in detail using the classical moleculardynamics simulation, which should provide theoretical basis for interpreting proteinadsorption procedure at the molecular level. Rutile surfaces with steps alongdifferent crystal orientations are modeled and the procedure of water or collagenadsorption conformation on rutile with different surface steps is studied from theprospect of adsorption conformation and structural transformation of collagen. Inaddition, rough surface with common nanostructure is built and the factor that theinitial distance between rutile and collagen is studied to investigate its influence onadsorption. The effect of groove width on collagen adsorption is discussed in thisthesis. At the end of this paper, the effect of ions on collagen adsorption in solution,e.g., NaCl solution, is studied.The simulation results show that the nanostructures on rutile surface affect thecollagen adsorption mainly in the following aspects. The water near surface,especially the first layer water molecules near TiO₂surface have positive effect oncollagen adsorption. However, water away from TiO₂surface, that is, the secondlayer water or above with violent movement could hinder the adsorption of collagen.The hydrogen bond between amino acid residues in collagen also affects collagenadsorption. It will be benefical to form more stable adsorption conformation, when the hydrogen bond are formed after collagen adsorbed on TiO₂. On the contrary, thehydrogen bond may hinder side chain stretching and forming the direct bindingmode with TiO₂surface atoms. The initial distance between collagen and TiO₂affects the adsorption stability. When the distance is shorter, more residues will bindwith TiO₂surface, resulting in more stable protein conformation on TiO₂surface.The width of grooves on the TiO₂surface has great effect on collagen adsorption.The interaction energy between collagen and TiO₂could be greater than any othercondition when collagen parallels to groove initially and the groove width isidentical to the diameter of collagen. This should have positive effect on collagenadsorption. However, if collagen doesn’t parallel to grooves, the increase of groovewidth will enhance collagen adsorption. It will be appropriate for collagenadsorption with the increase of groove width. In addition, the existance of cations insolution， e.g., Na+， could play an active role in collagen adsorption. The Na+adsorbed on the TiO₂surface interacts with the negatively charged side chain of Asp,which will be responsible for the indirect binding mode between collagen and TiO₂.